{
  "title": "OrthoPrep FRCS Question Bank",
  "subtitle": "1575 unique single-best-answer questions across orthopaedic basic sciences and clinical sub-specialties, with full explanations.",
  "author": "Professor Mohamed A. Imam and the OrthoGlobe faculty",
  "parts": [
    {
      "title": "Bone",
      "chapters": [
        {
          "title": "Bone Structure & Composition",
          "range": "Q1-Q10",
          "questions": [
            {
              "number": 1,
              "stem": "Which component of bone provides the majority of its tensile strength?",
              "options": [
                "Hydroxyapatite crystals",
                "Proteoglycans",
                "Water",
                "Osteocalcin",
                "Type I collagen fibres"
              ],
              "answer": "E",
              "explanation": "Type I collagen fibres provide tensile strength (like steel reinforcing bars), while hydroxyapatite provides compressive strength (like concrete). Together they form a composite material. Bone's tensile strength (~130 MPa) is lower than its compressive strength (~170 MPa) because the collagen component is relatively weaker than the mineral component.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 2,
              "stem": "What percentage of bone by weight is composed of organic matrix?",
              "options": [
                "10%",
                "35%",
                "50%",
                "25%",
                "65%"
              ],
              "answer": "D",
              "explanation": "Bone composition by weight is approximately 65% mineral (hydroxyapatite), 25% organic matrix (90% of which is Type I collagen), and 10% water. By volume, organic matrix and water constitute approximately 55% and mineral 45%. The distinction between weight and volume composition is frequently tested.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 3,
              "stem": "A patient with osteopetrosis presents with a fracture. Which statement best explains the paradox of dense but brittle bones?",
              "options": [
                "Defective osteoclasts prevent normal remodelling, leaving unremodelled woven bone",
                "Increased collagen cross-linking reduces flexibility",
                "Excessive osteoblast activity produces abnormal collagen",
                "Vitamin D deficiency reduces mineral quality",
                "Increased osteocyte density weakens lacunar walls"
              ],
              "answer": "A",
              "explanation": "In osteopetrosis, defective osteoclasts cannot resorb bone normally. This prevents the normal remodelling cycle that replaces old, microdamaged bone with new lamellar bone. The result is dense but unremodelled bone that is brittle because accumulated microdamage cannot be repaired and the bone retains a disorganised structure. Dense bone ≠ strong bone — toughness requires the ability to absorb energy through microcrack deflection, which requires normal Haversian remodelling.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 4,
              "stem": "The Haversian system in cortical bone consists of concentric lamellae surrounding a central canal. What is the approximate diameter of a typical osteon?",
              "options": [
                "50 micrometres",
                "200 micrometres",
                "100 micrometres",
                "500 micrometres",
                "1000 micrometres"
              ],
              "answer": "B",
              "explanation": "A typical osteon (Haversian system) is approximately 200 micrometres (0.2 mm) in diameter, consisting of 4-20 concentric lamellae surrounding a central Haversian canal containing blood vessels, nerves, and loose connective tissue. Volkmann's canals connect adjacent Haversian canals and the periosteal/endosteal surfaces. The cement line at the periphery of each osteon acts as a barrier to crack propagation, contributing to bone's toughness.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 5,
              "stem": "Which of the following correctly describes the orientation of collagen fibres in lamellar bone?",
              "options": [
                "All fibres run parallel in the same direction",
                "Fibres are randomly oriented like woven bone",
                "Fibres alternate direction in successive lamellae (plywood-like)",
                "Fibres spiral around the central canal in one direction",
                "Fibres run perpendicular to the bone surface only"
              ],
              "answer": "C",
              "explanation": "In lamellar bone, collagen fibres are arranged in a highly organised plywood-like pattern where successive lamellae have fibres oriented in alternating directions (approximately 90° rotation between layers). This arrangement provides strength in multiple directions, unlike woven bone where fibres are randomly oriented. The alternating fibre pattern is one reason lamellar bone is mechanically superior to woven bone.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 6,
              "stem": "A bone biopsy shows wide osteoid seams with a reduced mineralisation front. What is the most likely diagnosis?",
              "options": [
                "Osteoporosis",
                "Paget's disease",
                "Osteopetrosis",
                "Osteomalacia",
                "Osteogenesis imperfecta"
              ],
              "answer": "D",
              "explanation": "Wide osteoid seams with a reduced mineralisation front are the hallmark histological features of osteomalacia (inadequate mineralisation of osteoid). In osteoporosis, osteoid is normal but there is reduced bone mass — the bone that is present is normally mineralised. Paget's disease shows a mosaic pattern of woven and lamellar bone. Osteopetrosis shows dense unremodelled bone. OI shows thin cortices with reduced but structurally abnormal collagen.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 7,
              "stem": "Frost's mechanostat theory describes bone adaptation to mechanical loading. At what strain range does bone resorption exceed formation (disuse window)?",
              "options": [
                "50-200 microstrain",
                "200-1500 microstrain",
                "0-50 microstrain",
                "1500-3000 microstrain",
                "Above 3000 microstrain"
              ],
              "answer": "C",
              "explanation": "Frost's mechanostat theory defines strain thresholds for bone adaptation: Below 50-100 microstrain (the 'minimum effective strain for remodelling'), bone is in the disuse window where resorption exceeds formation, leading to atrophy. Between 100-1500 microstrain is the adapted/physiological window. Between 1500-3000 microstrain, formation exceeds resorption (the 'minimum effective strain for modelling'). Above approximately 25,000 microstrain, fracture occurs. This concept explains disuse osteoporosis with immobilisation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 8,
              "stem": "Which type of bone forms first at a fracture site?",
              "options": [
                "Lamellar bone",
                "Cortical bone",
                "Cancellous bone",
                "Haversian bone",
                "Woven bone"
              ],
              "answer": "E",
              "explanation": "Woven bone forms first at a fracture site because it can be laid down rapidly in any direction without requiring an existing bone surface. It has randomly oriented collagen fibres and higher cellularity compared to lamellar bone. Woven bone is subsequently remodelled to lamellar bone over months through the normal remodelling cycle (see Ch 4). In adults, woven bone is pathological except at fracture sites and tendon/ligament insertions.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 9,
              "stem": "Hydroxyapatite has the chemical formula Ca10(PO4)6(OH)2. Which element substitution is most commonly responsible for increased crystal size and reduced solubility in mature bone?",
              "options": [
                "Carbonate replacing phosphate groups",
                "Fluoride replacing hydroxyl groups",
                "Magnesium replacing calcium",
                "Strontium replacing calcium",
                "Silicon replacing phosphate"
              ],
              "answer": "B",
              "explanation": "Fluoride ions can substitute for hydroxyl groups in hydroxyapatite, forming fluorapatite which has larger crystals and is less soluble (more resistant to acid dissolution — this is the basis of fluoride in dental care). In biological bone, carbonate substitution for phosphate actually reduces crystal size and increases solubility, contributing to the metabolic availability of bone mineral. Magnesium and strontium can substitute for calcium but are less common.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 10,
              "stem": "Which structure acts as a barrier to crack propagation in cortical bone, contributing to fracture toughness?",
              "options": [
                "Cement line (reversal line)",
                "Haversian canal",
                "Volkmann's canal",
                "Canaliculus",
                "Howship's lacuna"
              ],
              "answer": "A",
              "explanation": "The cement line (also called reversal line) at the periphery of each osteon acts as a barrier to crack propagation. When a microcrack encounters a cement line, it is deflected along the line rather than propagating through the osteon, absorbing energy and increasing fracture toughness. This is analogous to how fibres in a composite material arrest crack growth. The cement line is a region of relatively hypomineralised bone formed during the reversal phase of remodelling where osteoclastic resorption transitions to osteoblastic formation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Bone Cells & Remodelling",
          "range": "Q11-Q19",
          "questions": [
            {
              "number": 11,
              "stem": "Which cell type produces the majority of RANKL in adult bone?",
              "options": [
                "Osteoblasts",
                "Osteocytes",
                "Osteoclasts",
                "Macrophages",
                "Fibroblasts"
              ],
              "answer": "B",
              "explanation": "Xiong et al. (2011) demonstrated that osteocytes are the primary source of RANKL in adult bone, not osteoblasts as was previously believed. Osteocytes comprise 90-95% of all bone cells and act as the master orchestrators of remodelling through the lacuno-canalicular network.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 12,
              "stem": "The drug denosumab acts by inhibiting which molecule?",
              "options": [
                "Sclerostin",
                "RANK",
                "RANKL",
                "OPG",
                "Cathepsin K"
              ],
              "answer": "C",
              "explanation": "Denosumab is a monoclonal antibody against RANKL. By binding RANKL, it prevents RANKL from activating RANK on osteoclast precursors, thereby inhibiting osteoclast differentiation and reducing bone resorption. OPG is the endogenous decoy receptor for RANKL — denosumab essentially mimics OPG's action.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 13,
              "stem": "Which zone of the basic multicellular unit (BMU) contains active osteoclasts?",
              "options": [
                "Closing cone",
                "Reversal zone",
                "Quiescent zone",
                "Formation zone",
                "Cutting cone"
              ],
              "answer": "E",
              "explanation": "In the BMU, the cutting cone is at the leading edge and contains active osteoclasts that resorb bone in a tunnel approximately 200 micrometres in diameter. Behind them is the reversal zone where mononuclear cells prepare the resorbed surface. The closing cone follows, where osteoblasts deposit new lamellar bone. The entire cycle takes 4-6 months.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 14,
              "stem": "Sclerostin is a protein produced by osteocytes that inhibits bone formation. Which signalling pathway does it block?",
              "options": [
                "Wnt/beta-catenin pathway",
                "RANK/RANKL pathway",
                "Hedgehog pathway",
                "Notch pathway",
                "BMP pathway"
              ],
              "answer": "A",
              "explanation": "Sclerostin (encoded by the SOST gene) inhibits the Wnt/beta-catenin signalling pathway in osteoblasts, suppressing osteoblast differentiation and bone formation. Romosozumab is an anti-sclerostin antibody that blocks sclerostin, thereby disinhibiting Wnt signalling and stimulating bone formation. Loss-of-function mutations in SOST cause sclerosteosis (excessive bone formation).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 15,
              "stem": "An osteoclast is identified on histology. Which of the following is NOT a characteristic feature?",
              "options": [
                "Multinucleated giant cell",
                "Ruffled border",
                "Derived from haematopoietic stem cells",
                "Alkaline phosphatase activity",
                "Howship's lacuna"
              ],
              "answer": "D",
              "explanation": "Alkaline phosphatase is a marker of OSTEOBLAST activity, not osteoclasts. Osteoclasts are characterised by: multinucleation (4-20 nuclei), a ruffled border (for acid and enzyme secretion), a clear/sealing zone (attachment to bone surface), derivation from haematopoietic monocyte-macrophage lineage, and they sit in Howship's lacunae (resorption pits). Their key enzyme is tartrate-resistant acid phosphatase (TRAP), not alkaline phosphatase.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 16,
              "stem": "Osteoprotegerin (OPG) acts as a decoy receptor for RANKL. Which cells are the primary producers of OPG?",
              "options": [
                "Osteoclasts",
                "T-lymphocytes",
                "Macrophages",
                "Chondrocytes",
                "Osteoblasts and stromal cells"
              ],
              "answer": "E",
              "explanation": "OPG is primarily produced by osteoblasts and bone marrow stromal cells. It acts as a soluble decoy receptor that binds RANKL and prevents it from activating RANK on osteoclast precursors. Oestrogen stimulates OPG production, which is why post-menopausal oestrogen deficiency leads to increased osteoclastogenesis and accelerated bone loss.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 17,
              "stem": "Which of the following best describes the 'coupling' mechanism in bone remodelling?",
              "options": [
                "Osteoclasts directly stimulate osteoblasts via cell contact",
                "Osteocytes simultaneously activate osteoclasts and osteoblasts",
                "PTH activates both cell types equally",
                "Resorption releases growth factors (TGF-beta, BMPs, IGF) from the bone matrix that recruit osteoblasts",
                "Mechanical loading activates both formation and resorption"
              ],
              "answer": "D",
              "explanation": "Coupling refers to the process by which bone resorption is followed by bone formation at the same site. During resorption, osteoclasts release growth factors previously embedded in the mineralised matrix, including TGF-beta, BMPs, IGF-1, and PDGF. These factors recruit osteoblast precursors to the resorbed surface, initiating the formation phase. This matrix-derived coupling mechanism ensures that resorption and formation remain linked.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 18,
              "stem": "The lifespan of an osteoclast is approximately:",
              "options": [
                "2 days",
                "2 weeks",
                "2 months",
                "6 months",
                "2 years"
              ],
              "answer": "B",
              "explanation": "Osteoclasts have a short lifespan of approximately 2 weeks, after which they undergo apoptosis. This is important pharmacologically because bisphosphonates accelerate osteoclast apoptosis (via the mevalonate pathway for nitrogen-containing bisphosphonates), effectively shortening an already short lifespan. By contrast, osteoblasts live approximately 3 months and osteocytes can survive for decades, embedded within the mineralised matrix.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 19,
              "stem": "A patient with chronic kidney disease develops secondary hyperparathyroidism. Which is the PRIMARY mechanism driving increased bone resorption?",
              "options": [
                "PTH stimulation of RANKL expression by osteoblasts/osteocytes",
                "Direct PTH stimulation of osteoclast RANK receptors",
                "Reduced vitamin D causing direct osteoclast activation",
                "Metabolic acidosis dissolving hydroxyapatite",
                "Aluminium toxicity from dialysis"
              ],
              "answer": "A",
              "explanation": "PTH does NOT act directly on osteoclasts (osteoclasts lack PTH receptors). Instead, PTH binds to PTH1R receptors on osteoblasts and osteocytes, stimulating them to increase RANKL expression and decrease OPG production. The resulting increase in RANKL/OPG ratio drives osteoclast differentiation and activation via the RANK/RANKL pathway. This is why understanding the indirect mechanism of PTH action through the RANK/RANKL system is critical.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Bone Development & Growth",
          "range": "Q20-Q29",
          "questions": [
            {
              "number": 20,
              "stem": "Which growth plate zone is the weakest mechanically and the site through which Salter-Harris fractures most commonly propagate?",
              "options": [
                "Reserve zone",
                "Proliferative zone",
                "Zone of provisional calcification",
                "Hypertrophic zone",
                "Primary spongiosa"
              ],
              "answer": "C",
              "explanation": "The zone of provisional calcification is the weakest zone because the cartilage matrix has begun to calcify but has not yet been replaced by true bone. Salter-Harris Type I and II fractures propagate through this zone. The reserve (germinal) zone is important prognostically — fractures involving this zone (Types III, IV, V) carry a higher risk of growth disturbance.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 21,
              "stem": "The IHH/PTHrP negative feedback loop controls growth plate chondrocyte differentiation. Where is PTHrP produced?",
              "options": [
                "Hypertrophic chondrocytes",
                "Reserve zone chondrocytes",
                "Perichondrium/periarticular region",
                "Osteoblasts in the primary spongiosa",
                "Proliferative zone chondrocytes"
              ],
              "answer": "C",
              "explanation": "PTHrP is produced in the perichondrium/periarticular region in response to IHH signalling from prehypertrophic chondrocytes. PTHrP then acts on proliferative chondrocytes to delay their differentiation into hypertrophic chondrocytes, maintaining the proliferative zone. This creates a negative feedback loop that controls the rate of growth plate progression.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 22,
              "stem": "A Salter-Harris Type II fracture involves:",
              "options": [
                "Physis and metaphysis",
                "Physis only",
                "Physis and epiphysis",
                "Physis, epiphysis, and metaphysis",
                "Crush injury to physis"
              ],
              "answer": "A",
              "explanation": "Salter-Harris Type II involves the physis and metaphysis (a Thurston-Holland fragment of metaphysis). It is the MOST COMMON type (75%). The fracture propagates through the zone of provisional calcification then exits through the metaphysis. Prognosis is generally good because the germinal zone is intact. Type I = physis only, Type III = physis + epiphysis, Type IV = physis + epiphysis + metaphysis, Type V = crush of physis.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 23,
              "stem": "Which type of ossification forms the clavicle and skull vault?",
              "options": [
                "Endochondral ossification",
                "Intramembranous ossification",
                "Appositional growth",
                "Perichondral ossification",
                "Enchondral ossification"
              ],
              "answer": "B",
              "explanation": "Intramembranous ossification forms flat bones directly from mesenchymal tissue without a cartilage intermediate. It forms the clavicle (the FIRST bone to ossify at 5 weeks gestation) and the skull vault bones. Endochondral ossification forms most other bones through a cartilage template. The clavicle is unique in being a long bone formed by intramembranous ossification — this is why it is spared in achondroplasia (which affects endochondral ossification).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 24,
              "stem": "In distraction osteogenesis, bone forms in the distraction gap by which mechanism?",
              "options": [
                "Endochondral ossification",
                "Contact healing",
                "Enchondral ossification",
                "Intramembranous ossification",
                "Secondary bone healing"
              ],
              "answer": "D",
              "explanation": "Bone forms in the distraction gap during distraction osteogenesis primarily by intramembranous ossification — mesenchymal cells differentiate directly into osteoblasts without a cartilage intermediate. The rate is approximately 1mm/day after a latency period of 5-7 days. This is based on Ilizarov's principles: preservation of periosteal blood supply, a latency period before distraction, a rate of 1mm/day in 4 increments (0.25mm x4), and a consolidation period before frame removal.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 25,
              "stem": "Which growth plate zone contains the stem cells responsible for longitudinal growth?",
              "options": [
                "Proliferative zone",
                "Prehypertrophic zone",
                "Hypertrophic zone",
                "Zone of provisional calcification",
                "Reserve (germinal) zone"
              ],
              "answer": "E",
              "explanation": "The reserve (germinal) zone contains the stem cells that supply chondrocytes to the proliferative zone. Damage to this zone (e.g., Salter-Harris Type III or IV involving the reserve zone) carries the worst prognosis for growth disturbance. The proliferative zone contains rapidly dividing chondrocytes arranged in columns — this is where most longitudinal growth occurs through chondrocyte proliferation and matrix production.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 26,
              "stem": "The physis contributes what percentage of longitudinal growth of the femur from the DISTAL end?",
              "options": [
                "30%",
                "50%",
                "85%",
                "95%",
                "70%"
              ],
              "answer": "E",
              "explanation": "The distal femoral physis contributes approximately 70% of femoral longitudinal growth (and about 40% of total lower limb growth), making it the fastest growing physis in the body. This has important clinical implications: injuries to the distal femoral physis carry a high risk of significant limb length discrepancy. The proximal tibial physis contributes approximately 55% of tibial growth. The rule of thumb is: around the knee, most growth comes from near the knee.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 27,
              "stem": "A physeal bar is identified occupying 30% of the physeal area in a 10-year-old with 4 years of growth remaining. What is the most appropriate management?",
              "options": [
                "Observation",
                "Bar resection with fat interposition (Langenskiold)",
                "Epiphysiodesis of the affected physis",
                "Corrective osteotomy",
                "Completion of growth arrest"
              ],
              "answer": "B",
              "explanation": "The Langenskiold procedure (physeal bar resection with fat or cement interposition) is indicated when: the bar involves <50% of the physeal area AND there is >2 years of growth remaining. This patient meets both criteria (30% bar, 4 years remaining). If the bar is >50% or <2 years growth remains, options include contralateral epiphysiodesis (to equalise limb lengths), corrective osteotomy, or limb lengthening.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 28,
              "stem": "Achondroplasia is caused by a mutation in FGFR3. Which growth plate zone is primarily affected?",
              "options": [
                "Reserve zone",
                "Hypertrophic zone",
                "Zone of provisional calcification",
                "Proliferative zone",
                "Primary spongiosa"
              ],
              "answer": "D",
              "explanation": "The FGFR3 mutation in achondroplasia causes constitutive activation of the receptor, which normally acts as a NEGATIVE regulator of chondrocyte proliferation. The result is reduced proliferation in the proliferative zone of the physis, causing impaired endochondral ossification and short bones. Intramembranous ossification (skull vault, clavicle) is unaffected — this is why the skull is normal sized but the skull base (endochondral) is small, causing foramen magnum stenosis.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 29,
              "stem": "Which of the following statements about the secondary ossification centre is correct?",
              "options": [
                "It appears before the primary ossification centre",
                "It forms by intramembranous ossification",
                "It appears in the epiphysis and contributes to articular cartilage",
                "It is responsible for longitudinal growth",
                "It fuses before the primary centre at skeletal maturity"
              ],
              "answer": "C",
              "explanation": "The secondary ossification centre appears AFTER the primary centre, typically postnatally (exceptions: distal femur and proximal tibia appear in utero). It forms in the epiphysis by endochondral ossification. It does NOT contribute to longitudinal growth (that is the role of the physis/growth plate). At skeletal maturity, the physis fuses (not the secondary centre). The articular cartilage persists throughout life as a remnant of the original cartilage model.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Fracture Healing",
          "range": "Q30-Q39",
          "questions": [
            {
              "number": 30,
              "stem": "According to Perren's strain theory, what is the maximum interfragmentary strain that permits lamellar bone formation?",
              "options": [
                "2%",
                "0.5%",
                "10%",
                "17%",
                "100%"
              ],
              "answer": "A",
              "explanation": "Perren's strain theory states that tissues can only form in a fracture gap where the strain does not exceed their tolerance: lamellar bone 2%, woven bone 2%, cartilage 10%, fibrous tissue 17%, granulation tissue 100%. Absolute stability (compression plating) produces <2% strain, allowing direct primary healing. Relative stability (IM nailing, casting) produces higher strains that permit callus formation through the endochondral pathway.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 31,
              "stem": "In secondary (indirect) fracture healing, which phase involves the replacement of cartilaginous callus with woven bone?",
              "options": [
                "Haematoma formation",
                "Inflammatory phase",
                "Soft callus formation",
                "Hard callus formation (endochondral ossification)",
                "Remodelling"
              ],
              "answer": "D",
              "explanation": "Secondary healing proceeds through 5 overlapping phases: haematoma (immediate), inflammation (hours-days, macrophages key cell), soft callus (weeks 1-3, cartilaginous callus via chondrocytes), hard callus (weeks 3-12, endochondral ossification replaces cartilage with woven bone), and remodelling (months-years, woven bone replaced by lamellar bone through Haversian remodelling). The hard callus phase is essentially endochondral ossification recapitulating growth plate biology.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 32,
              "stem": "Which of the following is NOT a component of the 'diamond concept' of fracture healing?",
              "options": [
                "Osteogenic cells",
                "Osteoconductive scaffold",
                "Antibiotic prophylaxis",
                "Osteoinductive growth factors",
                "Mechanical stability"
              ],
              "answer": "C",
              "explanation": "The diamond concept (Giannoudis et al. 2007) identifies four essential elements for fracture healing: osteogenic cells (mesenchymal stem cells, osteoblasts), osteoconductive scaffold (matrix for cell attachment), osteoinductive growth factors (BMPs, TGF-beta that stimulate cell differentiation), and mechanical stability (appropriate fixation). Vascularity is sometimes added as a fifth element. Antibiotic prophylaxis is important for infection prevention but is not a component of the diamond concept.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 33,
              "stem": "Primary (direct) bone healing occurs by which mechanism?",
              "options": [
                "Contact healing and gap healing via Haversian remodelling",
                "Callus formation followed by remodelling",
                "Endochondral ossification",
                "Intramembranous ossification in the fracture gap",
                "Distraction osteogenesis"
              ],
              "answer": "A",
              "explanation": "Primary bone healing occurs with absolute stability (compression plating, lag screws). It involves contact healing (where bone ends are in direct contact, cutting cones of osteoclasts cross the fracture line followed by osteoblasts) and gap healing (in small gaps <200 micrometres, lamellar bone fills the gap directly, then remodels). There is NO callus formation. This is Haversian remodelling across the fracture site.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 34,
              "stem": "A patient with a tibial shaft fracture undergoes exchange nailing for delayed union. Which is the MOST important biological mechanism by which exchange nailing promotes healing?",
              "options": [
                "Increased mechanical stability from a larger nail",
                "Reaming debris provides osteogenic cells and growth factors",
                "Reaming deposits autologous bone graft in the canal",
                "Reaming stimulates periosteal blood supply",
                "The new nail provides better rotational control"
              ],
              "answer": "B",
              "explanation": "While all listed factors contribute, the most important biological mechanism is that reaming produces debris rich in osteogenic cells (mesenchymal stem cells from marrow), growth factors (from bone matrix), and osteoconductive material (bone graft particles). This reaming debris fills the fracture gap and provides all three biological elements of the diamond concept. The reaming process also stimulates a periosteal blood supply response and the larger nail provides improved mechanical stability.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 35,
              "stem": "In the inflammatory phase of fracture healing, which cell type is considered the KEY orchestrator?",
              "options": [
                "Neutrophils",
                "Fibroblasts",
                "Osteoblasts",
                "Platelets",
                "Macrophages"
              ],
              "answer": "E",
              "explanation": "Macrophages are the key orchestrating cell of fracture healing (as in wound healing, see Ch 28). They arrive by day 2-3, phagocytose debris, and release critical growth factors including PDGF, TGF-beta, VEGF, and BMPs that recruit mesenchymal stem cells and stimulate angiogenesis. While platelets release initial growth factors from the fracture haematoma, and neutrophils provide early bacterial killing, it is the macrophage that coordinates the transition from inflammation to repair.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 36,
              "stem": "Autologous iliac crest bone graft is considered the 'gold standard' because it provides which combination of properties?",
              "options": [
                "Osteogenic + osteoconductive + osteoinductive",
                "Osteoconductive + osteoinductive",
                "Osteogenic + osteoconductive",
                "Osteoconductive + mechanical strength",
                "Osteoinductive + mechanical strength"
              ],
              "answer": "A",
              "explanation": "Autologous iliac crest bone graft is the gold standard because it is the ONLY graft material that provides ALL THREE biological properties: osteogenic (contains living MSCs and osteoblasts), osteoconductive (provides a scaffold for cell attachment and vascular ingrowth), and osteoinductive (contains BMPs and growth factors that stimulate differentiation of MSCs into osteoblasts). Allograft is osteoconductive and weakly osteoinductive but NOT osteogenic. Demineralised bone matrix is osteoinductive + osteoconductive. Ceramics are osteoconductive only (see Ch 18).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 37,
              "stem": "A hypertrophic non-union (elephant foot appearance) of the femoral shaft is identified. What does this indicate about the biological and mechanical environment?",
              "options": [
                "Inadequate biology but adequate mechanical stability",
                "Both biology and mechanical stability are inadequate",
                "Infection is present",
                "The fracture gap exceeds the critical size defect",
                "Adequate biology but inadequate mechanical stability"
              ],
              "answer": "E",
              "explanation": "A hypertrophic non-union shows abundant callus (elephant foot or horse hoof appearance) indicating that the biological environment is adequate — cells are active and producing callus. However, the fracture has not united because the mechanical environment is inadequate (excessive motion preventing callus maturation). Treatment is MECHANICAL: improve stability (e.g., exchange nailing, compression plating). An atrophic non-union (pencil point) indicates inadequate biology requiring BIOLOGICAL treatment (bone grafting, BMP).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 38,
              "stem": "At what rate should distraction osteogenesis be performed according to Ilizarov's principles?",
              "options": [
                "0.25 mm/day",
                "1 mm/day in 4 increments",
                "0.5 mm/day",
                "2 mm/day",
                "5 mm/day"
              ],
              "answer": "B",
              "explanation": "Ilizarov established that the optimal distraction rate is 1mm/day divided into 4 increments of 0.25mm (rhythm of distraction). Faster rates risk non-union of the regenerate; slower rates risk premature consolidation. A latency period of 5-7 days after corticotomy allows initial callus formation before distraction begins. Bone forms in the distraction gap by intramembranous ossification. After the desired length is achieved, a consolidation period (typically 1 month per cm of lengthening) is required.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 39,
              "stem": "Which growth factor is MOST important for angiogenesis during fracture healing?",
              "options": [
                "BMP-2",
                "TGF-beta",
                "VEGF",
                "PDGF",
                "FGF-2"
              ],
              "answer": "C",
              "explanation": "Vascular endothelial growth factor (VEGF) is the most important angiogenic factor during fracture healing. It stimulates endothelial cell proliferation and new blood vessel formation (angiogenesis) in the fracture callus. Adequate vascularity is essential for the transition from soft callus (avascular cartilage) to hard callus (vascularised bone) through endochondral ossification. Impaired angiogenesis (e.g., from smoking, which damages VEGF signalling) is a major risk factor for non-union. BMP-2 is primarily osteoinductive; TGF-beta is multifunctional; PDGF recruits MSCs; FGF-2 stimulates fibroblast proliferation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Bone Biomechanics",
          "range": "Q40-Q49",
          "questions": [
            {
              "number": 40,
              "stem": "According to Wolff's law, what happens to bone when the mechanical strain falls below 50-100 microstrain?",
              "options": [
                "Bone mass increases",
                "Bone maintains equilibrium",
                "Woven bone forms",
                "Bone resorption exceeds formation (disuse atrophy)",
                "Fracture occurs"
              ],
              "answer": "D",
              "explanation": "Frost's mechanostat quantified Wolff's law: below 50-100 microstrain (the minimum effective strain for remodelling), the disuse window activates and resorption exceeds formation, leading to atrophy. This explains why immobilisation, bed rest, and space flight cause osteoporosis. The adapted window (100-1500 microstrain) maintains bone mass. Above 1500 microstrain, formation exceeds resorption (modelling).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 41,
              "stem": "Cortical bone is strongest in which loading mode?",
              "options": [
                "Tension",
                "Shear",
                "Torsion",
                "Bending",
                "Compression"
              ],
              "answer": "E",
              "explanation": "Carter and Spengler (1978) demonstrated that cortical bone is strongest in compression (~170 MPa), weaker in tension (~130 MPa), and weakest in shear (~65 MPa). This is because hydroxyapatite crystals (the ceramic component) are excellent at resisting compression. In bending, one surface is in tension and the other in compression — fractures initiate on the TENSION side because this is the weaker mode.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 42,
              "stem": "The area moment of inertia (I) of a long bone diaphysis is most analogous to which concept?",
              "options": [
                "The material's strength",
                "The cross-sectional geometry's resistance to bending",
                "The material's stiffness",
                "The bone's density",
                "The bone's fatigue life"
              ],
              "answer": "B",
              "explanation": "The area moment of inertia (second moment of area, I) is a purely geometric property that describes how the cross-sectional area is distributed relative to the neutral axis. A hollow tube (like a long bone diaphysis) has a much higher I than a solid rod of the same cross-sectional area because material is distributed further from the neutral axis. I determines the structure's resistance to bending and buckling — bending stiffness = E×I (Young's modulus × moment of inertia).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 43,
              "stem": "A titanium femoral stem (Young's modulus 110 GPa) is compared to a cobalt-chrome stem (230 GPa). Which statement is correct regarding stress shielding?",
              "options": [
                "Titanium causes more stress shielding because it is lighter",
                "Both cause equal stress shielding",
                "Cobalt-chrome causes more stress shielding because it is stiffer",
                "Neither causes stress shielding in cemented stems",
                "Stress shielding only occurs with uncemented stems"
              ],
              "answer": "C",
              "explanation": "Stress shielding occurs when a stiffer implant shields surrounding bone from physiological loads, causing adaptive resorption (Wolff's law). Cobalt-chrome (E=230 GPa) is approximately twice as stiff as titanium (E=110 GPa), and both are far stiffer than cortical bone (E=17-20 GPa). The stiffer the implant relative to bone, the more load it carries and the less load is transmitted to bone, causing more stress shielding. Titanium's lower modulus produces less stress shielding, which is one reason it is preferred for some implant applications.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 44,
              "stem": "A butterfly fragment on the compression side of a long bone fracture indicates which type of loading?",
              "options": [
                "Bending",
                "Axial compression",
                "Pure tension",
                "Torsion",
                "Shear"
              ],
              "answer": "A",
              "explanation": "In bending, one surface is in tension (fracture initiates here as a transverse crack) and the opposite surface is in compression. On the compression side, a wedge-shaped butterfly fragment is produced because the bone fails along oblique shear planes (bone is weakest in shear). The combination of a transverse fracture line on the tension side with a butterfly fragment on the compression side is the hallmark of a bending injury. Torsion produces a spiral fracture. Axial compression produces impaction. Pure tension produces a transverse fracture.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 45,
              "stem": "Which property of bone DECREASES most significantly with ageing, explaining why elderly fractures are often comminuted?",
              "options": [
                "Ultimate tensile strength",
                "Young's modulus (stiffness)",
                "Compressive strength",
                "Energy absorption to failure (toughness)",
                "Bone mineral density"
              ],
              "answer": "D",
              "explanation": "Burstein et al. (1976) showed that while bone strength and stiffness change modestly with age, the energy absorption to failure (toughness — the area under the stress-strain curve) decreases dramatically after age 40. This means elderly bone fractures at lower energy levels and shatters (comminutes) rather than producing clean fracture lines, because it cannot absorb and redistribute energy through plastic deformation. Reduced toughness is related to accumulation of microdamage, increased mineralisation, and collagen cross-link changes.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 46,
              "stem": "Euler's buckling equation predicts that the critical buckling load of a column is inversely proportional to the square of its length. If a femoral nail is placed in a femur with a 4cm defect, and the same nail is used in a femur with a 2cm defect, how does the risk of nail failure by buckling compare?",
              "options": [
                "Same risk in both",
                "4x higher risk with 4cm defect",
                "2x higher risk with 4cm defect",
                "8x higher risk with 4cm defect",
                "16x higher risk with 4cm defect"
              ],
              "answer": "B",
              "explanation": "Euler's formula: Critical buckling load = (pi squared × E × I) / L squared. If the unsupported length (L) doubles from 2cm to 4cm, the critical buckling load decreases by a factor of (4/2) squared = 4. Therefore, the 4cm defect has a 4x higher risk of buckling failure. This is why large bone defects pose biomechanical challenges — the unsupported length of the implant increases, dramatically reducing its resistance to buckling.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 47,
              "stem": "A viscoelastic material like bone exhibits which of the following properties?",
              "options": [
                "Constant stress-strain relationship regardless of loading rate",
                "Perfectly elastic recovery after all loads",
                "No energy dissipation during loading cycles",
                "Linear stress-strain relationship to failure",
                "Strain rate-dependent behaviour — stiffer and stronger at higher loading rates"
              ],
              "answer": "E",
              "explanation": "Bone is viscoelastic, meaning its mechanical behaviour depends on the rate of loading. At higher strain rates (e.g., high-energy trauma), bone is stiffer and stronger but also more brittle. At lower strain rates (e.g., standing), bone is less stiff but more ductile. Viscoelastic materials also exhibit creep (continued deformation under constant load), stress relaxation (decreased stress under constant strain), and hysteresis (energy dissipation during loading-unloading cycles). This strain rate dependence explains why high-energy fractures produce more comminution.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 48,
              "stem": "The bending stiffness of a structure is determined by which formula?",
              "options": [
                "Young's modulus × area moment of inertia (E × I)",
                "Stress × strain",
                "Force × distance",
                "Stress / strain",
                "Force / area"
              ],
              "answer": "A",
              "explanation": "Bending stiffness = E × I, where E is Young's modulus (material property) and I is the area moment of inertia (geometric property). This means bending stiffness can be increased either by using a stiffer material (higher E) or by changing the cross-sectional geometry to distribute material further from the neutral axis (higher I). This is why a hollow tube (bone, IM nail) is much more resistant to bending than a solid rod of the same weight — the material is distributed at a greater distance from the centre.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 49,
              "stem": "Subchondral bone sclerosis in osteoarthritis is an example of which biomechanical principle?",
              "options": [
                "Hooke's law",
                "Euler's buckling",
                "Wolff's law",
                "Pascal's principle",
                "Bernoulli's equation"
              ],
              "answer": "C",
              "explanation": "Subchondral sclerosis in OA is a direct application of Wolff's law — as articular cartilage thins and loses its shock-absorbing capacity, the underlying subchondral bone experiences increased stress. According to Wolff's law, bone responds to increased stress by depositing more bone, producing sclerosis. Similarly, osteophytes form at joint margins where new stress concentrations develop. The bone is adapting its structure to the altered mechanical environment — exactly as Wolff predicted in 1892.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Metabolic Bone Disease",
          "range": "Q50-Q59",
          "questions": [
            {
              "number": 50,
              "stem": "A DEXA scan reports a T-score of -2.8 at the lumbar spine. According to WHO criteria, this represents:",
              "options": [
                "Normal bone density",
                "Osteopenia",
                "Severe (established) osteoporosis",
                "Osteoporosis",
                "Requires additional Z-score for diagnosis"
              ],
              "answer": "D",
              "explanation": "WHO criteria (Kanis 1994): T-score above -1.0 = normal, -1.0 to -2.5 = osteopenia, below -2.5 = osteoporosis, below -2.5 WITH fragility fracture = severe/established osteoporosis. A T-score of -2.8 without a fragility fracture = osteoporosis. The T-score compares to a young adult reference population; the Z-score compares to age-matched peers and is used in premenopausal women and men under 50.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 51,
              "stem": "Bisphosphonates reduce bone resorption by which primary mechanism?",
              "options": [
                "Blocking RANKL binding to RANK",
                "Stimulating OPG production by osteoblasts",
                "Inhibiting the mevalonate pathway in osteoclasts, promoting apoptosis",
                "Directly inhibiting cathepsin K",
                "Blocking PTH receptor binding"
              ],
              "answer": "C",
              "explanation": "Nitrogen-containing bisphosphonates (alendronate, zoledronic acid) inhibit farnesyl pyrophosphate synthase in the mevalonate pathway within osteoclasts. This prevents prenylation of small GTPases (Ras, Rho, Rac) essential for osteoclast function, leading to osteoclast apoptosis. The P-C-P backbone (replacing the O in pyrophosphate P-O-P) provides high affinity for hydroxyapatite, concentrating the drug at sites of active resorption. Non-nitrogen bisphosphonates (etidronate, clodronate) are metabolised to toxic ATP analogues.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 52,
              "stem": "Which histological finding is pathognomonic of Paget's disease in the sclerotic phase?",
              "options": [
                "Wide osteoid seams",
                "Giant osteoclasts with inclusion bodies",
                "Tunnelling resorption",
                "Fibrosis of marrow spaces",
                "Mosaic pattern of cement lines"
              ],
              "answer": "E",
              "explanation": "The mosaic pattern of irregular cement lines is pathognomonic of the sclerotic (late) phase of Paget's disease, reflecting the chaotic and repeated cycles of disordered resorption and formation. Giant osteoclasts with up to 100 nuclei containing viral inclusion bodies are characteristic of the LYTIC (early) phase. In the mixed phase, both features coexist. The mosaic pattern produces structurally disorganised bone that is enlarged but mechanically weak.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 53,
              "stem": "A patient on long-term denosumab has treatment discontinued. What is the MOST significant risk?",
              "options": [
                "Osteonecrosis of the jaw",
                "Atypical femoral fracture",
                "Hypocalcaemia",
                "Rebound vertebral fractures from rapid bone loss",
                "Oesophageal irritation"
              ],
              "answer": "D",
              "explanation": "Denosumab discontinuation produces a REBOUND effect with rapid bone loss over 6-12 months, often below pre-treatment levels, and a significantly increased risk of multiple vertebral fractures. This occurs because RANKL accumulated during treatment becomes suddenly unopposed, producing a surge of osteoclastogenesis. The FDA issued a boxed warning in 2024. Patients should not stop denosumab without transitioning to an alternative antiresorptive (typically bisphosphonate). ONJ and atypical fractures are risks during treatment, not after stopping.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 54,
              "stem": "Looser zones (pseudofractures) on radiographs are characteristic of which condition?",
              "options": [
                "Osteoporosis",
                "Osteomalacia",
                "Paget's disease",
                "Osteopetrosis",
                "Hyperparathyroidism"
              ],
              "answer": "B",
              "explanation": "Looser zones are radiolucent lines perpendicular to the cortex, representing bands of unmineralised osteoid. They are pathognomonic of osteomalacia and typically occur bilaterally and symmetrically at the medial femoral neck, pubic rami, lateral scapular border, and ribs. They represent stress fractures through weakened, undermineralised bone that fail to mineralise during healing. In osteoporosis, bone is normally mineralised but reduced in mass — Looser zones do not occur.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 55,
              "stem": "In primary hyperparathyroidism, bone resorption is mediated through PTH acting on which cells?",
              "options": [
                "Osteoblasts and osteocytes (which then increase RANKL production)",
                "Osteoclasts directly (via PTH receptors on osteoclasts)",
                "Chondrocytes in the growth plate",
                "Macrophages",
                "Fibroblasts"
              ],
              "answer": "A",
              "explanation": "Osteoclasts do NOT have PTH receptors. PTH acts on osteoblasts and osteocytes via the PTH1R receptor, stimulating them to increase RANKL expression and decrease OPG production. The resulting shift in the RANKL/OPG ratio drives osteoclast differentiation and activation via the RANK/RANKL pathway (see Ch 2). This indirect mechanism is frequently tested — candidates must understand that PTH's effect on resorption is mediated THROUGH osteoblasts/osteocytes, not directly on osteoclasts.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 56,
              "stem": "Which of the following is the most serious long-term complication of Paget's disease?",
              "options": [
                "Pathological fracture",
                "Sarcomatous transformation",
                "Hearing loss",
                "High-output cardiac failure",
                "Nerve root compression"
              ],
              "answer": "B",
              "explanation": "While all listed options are recognised complications, sarcomatous transformation (Paget's sarcoma, usually osteosarcoma) is the most serious, carrying a very poor prognosis (5-year survival <10%). It occurs in <1% of Paget's patients but should be suspected if there is sudden increase in pain, swelling, or rising alkaline phosphatase in a previously stable Paget's lesion. Pathological fractures and deformity are more common but less lethal. High-output cardiac failure occurs in polyostotic disease due to increased blood flow through pagetic bone.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 57,
              "stem": "The FRAX tool integrates clinical risk factors with BMD to calculate:",
              "options": [
                "10-year probability of major osteoporotic and hip fracture",
                "Lifetime fracture risk",
                "5-year probability of any fracture",
                "Annual bone loss rate",
                "Treatment response prediction"
              ],
              "answer": "A",
              "explanation": "The FRAX tool (Kanis 2008) calculates the 10-year probability of a major osteoporotic fracture (hip, clinical spine, proximal humerus, distal forearm) and separately the 10-year probability of hip fracture. It integrates clinical risk factors (age, sex, BMI, prior fragility fracture, parental hip fracture, smoking, alcohol, glucocorticoids, RA, secondary osteoporosis) with femoral neck BMD. NICE recommends using FRAX to guide treatment decisions — patients above the intervention threshold should receive pharmacological treatment.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 58,
              "stem": "Rickets in children and osteomalacia in adults share the same underlying pathology. Which investigation finding distinguishes rickets from osteomalacia?",
              "options": [
                "Raised alkaline phosphatase",
                "Low serum calcium",
                "Low serum phosphate",
                "Raised PTH",
                "Widened growth plate on X-ray"
              ],
              "answer": "E",
              "explanation": "Both rickets and osteomalacia are caused by defective mineralisation (usually vitamin D deficiency) and share biochemical findings of raised ALP, low/normal calcium, low phosphate, and raised PTH. The distinguishing feature is that rickets additionally affects the GROWTH PLATE — widened, irregular, cupped and frayed metaphyses on X-ray (see Ch 3). This is because the zone of provisional calcification cannot mineralise. Osteomalacia in adults does not affect growth plates (closed) and instead produces Looser zones.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 59,
              "stem": "Romosozumab is a monoclonal antibody against which target?",
              "options": [
                "RANKL",
                "TNF-alpha",
                "Sclerostin",
                "PTHrP",
                "Cathepsin K"
              ],
              "answer": "C",
              "explanation": "Romosozumab is an anti-sclerostin antibody. Sclerostin is produced by osteocytes and inhibits the Wnt/beta-catenin signalling pathway in osteoblasts, suppressing bone formation. By blocking sclerostin, romosozumab disinhibits Wnt signalling, stimulating osteoblast differentiation and bone formation. It is the first bone-forming biologic agent. The FRAME trial (Cosman 2016) showed 13% increase in lumbar spine BMD at 12 months. Cardiovascular safety concerns (ARCH trial) led to contraindication in patients with recent MI or stroke.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        }
      ]
    },
    {
      "title": "Musculoskeletal Tissues",
      "chapters": [
        {
          "title": "Articular Cartilage & Synovium",
          "range": "Q60-Q69",
          "questions": [
            {
              "number": 60,
              "stem": "Which type of collagen predominates in articular cartilage?",
              "options": [
                "Type I",
                "Type III",
                "Type IV",
                "Type II",
                "Type X"
              ],
              "answer": "D",
              "explanation": "Type II collagen is the predominant collagen in articular cartilage (90-95% of total collagen), arranged in an arcade-like pattern (Benninghoff arcades) from perpendicular in the deep zone to parallel in the superficial zone. Type I collagen predominates in bone, tendon, ligament, and fibrocartilage (including meniscus and repair tissue after microfracture). Type X collagen is found in the calcified zone of cartilage and in the hypertrophic zone of the growth plate.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 61,
              "stem": "According to the biphasic model (Mow 1980), what percentage of the applied load is initially supported by the fluid phase of articular cartilage?",
              "options": [
                "10%",
                "30%",
                "50%",
                "90%",
                "70%"
              ],
              "answer": "D",
              "explanation": "The biphasic model describes cartilage as a solid phase (collagen-proteoglycan matrix) and fluid phase (water, 65-80% of wet weight). When load is applied, approximately 90% is initially supported by hydrostatic pressure in the fluid phase (fluid pressurisation). As fluid gradually exudes through the matrix (creep), load transfers to the solid phase. This mechanism protects the solid matrix from excessive stress and is the basis of cartilage's remarkable load-bearing capacity.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 62,
              "stem": "A microfracture procedure produces repair tissue composed predominantly of:",
              "options": [
                "Hyaline cartilage with Type II collagen",
                "Elastic cartilage",
                "Fibrocartilage with Type I collagen",
                "Woven bone",
                "Fibrous tissue only"
              ],
              "answer": "C",
              "explanation": "Microfracture produces fibrocartilage, not hyaline cartilage. The repair tissue is predominantly Type I collagen (like tendon and ligament) rather than Type II (native articular cartilage). This is biomechanically inferior — less resilient, lower compressive strength, and poorer wear characteristics. ACI and OATS/mosaicplasty produce repair tissue with more hyaline-like properties (Type II collagen). This distinction between fibrocartilage (Type I) and hyaline cartilage (Type II) repair is frequently tested.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 63,
              "stem": "The proteoglycan aggrecan is bound to hyaluronic acid via which link protein in articular cartilage?",
              "options": [
                "Fibronectin",
                "Decorin",
                "Biglycan",
                "COMP",
                "Link protein"
              ],
              "answer": "E",
              "explanation": "Aggrecan molecules are non-covalently bound to a central hyaluronic acid backbone via link protein to form large proteoglycan aggregates. Each aggrecan monomer has a core protein with numerous GAG side chains (chondroitin sulphate and keratan sulphate) that carry fixed negative charges. These negative charges attract water through the Donnan osmotic effect, creating the swelling pressure that gives cartilage its compressive resistance. Loss of aggrecan (by MMP degradation in OA) leads to loss of compressive resistance.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 64,
              "stem": "Which zone of articular cartilage has collagen fibres oriented PARALLEL to the articular surface?",
              "options": [
                "Superficial (tangential) zone",
                "Middle (transitional) zone",
                "Deep (radial) zone",
                "Calcified zone",
                "Tidemark"
              ],
              "answer": "A",
              "explanation": "In the superficial zone (10-20% of thickness), collagen fibres are oriented PARALLEL to the surface, providing resistance to shear forces and forming a smooth gliding surface. In the middle zone (40-60%), fibres are randomly oriented (oblique). In the deep zone (30%), fibres are oriented PERPENDICULAR to the surface (radial), anchoring into the calcified zone. This arrangement follows Benninghoff's arcade model and is optimised for the complex loading environment of the joint.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 65,
              "stem": "Articular cartilage receives its nutrition primarily through which mechanism?",
              "options": [
                "Direct blood supply from subchondral bone",
                "Diffusion from synovial fluid",
                "Lymphatic drainage",
                "Periosteal vessels",
                "Nutrient arteries"
              ],
              "answer": "B",
              "explanation": "Articular cartilage is avascular and receives nutrition by diffusion from the synovial fluid, facilitated by the pumping action of joint loading and unloading (cyclic compression drives fluid in and out of the cartilage matrix). This is why joint immobilisation is detrimental to cartilage health (reduces nutrient exchange) and why continuous passive motion (CPM) was advocated by Salter to promote cartilage nutrition and healing.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 66,
              "stem": "The tidemark in articular cartilage represents:",
              "options": [
                "The boundary between superficial and middle zones",
                "The boundary between cartilage and subchondral bone",
                "The cement line between old and new cartilage",
                "The site of collagen fibre insertion",
                "The boundary between uncalcified and calcified cartilage"
              ],
              "answer": "E",
              "explanation": "The tidemark is a basophilic line visible on histology that demarcates the boundary between the uncalcified deep zone and the calcified zone of articular cartilage. It represents the mineralisation front. Below the tidemark, the calcified zone anchors the articular cartilage to the underlying subchondral bone plate. The cement line (different from the tidemark) lies between the calcified zone and subchondral bone. Advancement of the tidemark into uncalcified cartilage (tidemark duplication) is seen in OA, reducing the functional cartilage thickness.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 67,
              "stem": "Synovial fluid viscosity is primarily determined by which molecule?",
              "options": [
                "Albumin",
                "Type II collagen",
                "Hyaluronic acid (hyaluronan)",
                "Lubricin (PRG4)",
                "Fibronectin"
              ],
              "answer": "C",
              "explanation": "Hyaluronic acid (hyaluronan) is the primary determinant of synovial fluid viscosity. It is a large, non-sulphated GAG produced by Type B synoviocytes (fibroblast-like). Normal synovial fluid is highly viscous due to high-molecular-weight hyaluronan, giving it non-Newtonian (shear-thinning) properties. In inflammatory joint disease (RA), hyaluronan is degraded by enzymes and free radicals, reducing viscosity. Lubricin (PRG4) is important for boundary lubrication at the cartilage surface but contributes less to bulk viscosity.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 68,
              "stem": "An Outerbridge Grade III chondral lesion is characterised by:",
              "options": [
                "Softening and swelling of cartilage",
                "Fissuring less than 1.3cm diameter",
                "Exposed subchondral bone",
                "Fragmentation and fissuring greater than 1.3cm diameter reaching subchondral bone",
                "Normal cartilage"
              ],
              "answer": "D",
              "explanation": "Outerbridge classification (1961): Grade I = softening and swelling, Grade II = fragmentation and fissuring in an area <1.3cm diameter, Grade III = fragmentation and fissuring >1.3cm diameter down to subchondral bone, Grade IV = erosion with exposed subchondral bone. Note that Grade III reaches subchondral bone but does NOT expose it (the calcified zone may still be intact), while Grade IV has frank bone exposure. This grading is the most commonly used arthroscopic classification of chondral damage.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 69,
              "stem": "Which cell type in the synovial membrane is primarily responsible for phagocytosis of wear debris?",
              "options": [
                "Type B synoviocytes (fibroblast-like)",
                "Type A synoviocytes (macrophage-like)",
                "Chondrocytes",
                "Mast cells",
                "T-lymphocytes"
              ],
              "answer": "B",
              "explanation": "The synovial membrane contains two main cell types: Type A synoviocytes are macrophage-like cells derived from the monocyte lineage, responsible for phagocytosis of debris (including wear particles from joint replacements — this is the first step in particle disease leading to osteolysis, see Ch 16). Type B synoviocytes are fibroblast-like cells that produce synovial fluid components including hyaluronic acid and lubricin. In RA, both types are activated — Type A cells release inflammatory cytokines while Type B cells proliferate to form the pannus tissue that destroys cartilage.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Tendons, Ligaments & Meniscus",
          "range": "Q70-Q79",
          "questions": [
            {
              "number": 70,
              "stem": "The 'toe region' of a tendon stress-strain curve represents:",
              "options": [
                "Crimped collagen fibres straightening under initial load",
                "Plastic deformation",
                "Tendon rupture",
                "Viscoelastic creep",
                "Elastic limit"
              ],
              "answer": "A",
              "explanation": "The toe region (0-2% strain) represents the straightening of crimped collagen fibres under initial load — a low-stiffness region where the tendon stretches easily. Beyond this, the linear region (2-4% strain) represents direct loading of straightened collagen fibres — higher stiffness. Microscopic failure begins at approximately 4% strain with progressive fibre rupture. Macroscopic rupture occurs at 8-10% strain. This crimped-to-straight transition is a unique biomechanical feature of collagenous tissues.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 71,
              "stem": "The meniscus increases tibiofemoral contact area by approximately:",
              "options": [
                "10%",
                "20%",
                "60%",
                "40%",
                "80%"
              ],
              "answer": "C",
              "explanation": "The menisci increase the tibiofemoral contact area by approximately 60%, transmitting 50-70% of the load in extension and up to 85% in flexion. This dramatically reduces contact stress on articular cartilage. Total meniscectomy removes this load distribution function, converting the loading pattern to high focal stresses that accelerate articular cartilage degeneration (Fairbank changes). This is the biomechanical rationale for meniscal preservation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 72,
              "stem": "Which zone of the meniscus has blood supply and therefore healing potential?",
              "options": [
                "Inner one-third (white-white zone)",
                "Outer one-third (red-red zone)",
                "Middle one-third (red-white zone)",
                "The entire meniscus is avascular",
                "The entire meniscus is vascular"
              ],
              "answer": "B",
              "explanation": "Arnoczky & Warren (1982) demonstrated that the peripheral one-third (red-red zone) receives blood supply from the perimeniscal capillary plexus arising from the joint capsule. The inner two-thirds (white-white zone) is avascular and relies on diffusion from synovial fluid. The red-white zone (middle third) has partial vascularity. Repair is most successful in the red-red zone; tears in the white-white zone are treated by partial meniscectomy.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 73,
              "stem": "The four-zone enthesis at a ligament-bone insertion consists of (in order from ligament to bone):",
              "options": [
                "Bone → fibrocartilage → mineralised fibrocartilage → ligament",
                "Ligament → mineralised fibrocartilage → fibrocartilage → bone",
                "Ligament → bone → fibrocartilage → mineralised fibrocartilage",
                "Ligament → fibrocartilage → mineralised fibrocartilage → bone",
                "Fibrocartilage → ligament → bone → mineralised fibrocartilage"
              ],
              "answer": "D",
              "explanation": "O'Brien (1992) described the four-zone enthesis: ligament (dense collagenous tissue) → fibrocartilage (unmineralised) → mineralised fibrocartilage → bone. This arrangement provides a gradual transition in stiffness from flexible ligament to rigid bone, reducing stress concentration at the interface. This normal enthesis is NOT recreated in ACL reconstruction, which is why graft-tunnel healing forms a direct insertion rather than an indirect (four-zone) insertion.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 74,
              "stem": "What is the predominant collagen type in tendon?",
              "options": [
                "Type I",
                "Type II",
                "Type III",
                "Type IV",
                "Type X"
              ],
              "answer": "A",
              "explanation": "Type I collagen comprises approximately 85-95% of tendon dry weight, arranged in a hierarchical structure: tropocollagen molecules → microfibrils → fibrils → fibres → fascicles → tendon (Cooper & Misol 1970). Type III collagen is present in small amounts in the endotenon and epitenon and increases during healing (initially comprising up to 30% of repair tissue before gradually being replaced by Type I). Type II collagen is found at fibrocartilaginous entheses where tendons wrap around bony prominences.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 75,
              "stem": "Woo et al. (1991) demonstrated that 8 weeks of immobilisation reduces ligament strength by approximately:",
              "options": [
                "10%",
                "20%",
                "40%",
                "90%",
                "60%"
              ],
              "answer": "E",
              "explanation": "Woo et al. showed that immobilisation causes rapid deterioration of ligament mechanical properties — strength decreases by approximately 60% within 8 weeks. Remobilisation restores properties but much more slowly (up to 12 months to regain baseline). This is the scientific basis for early controlled mobilisation after ligament injury and reconstruction. The mechanism involves reduced collagen synthesis, increased collagen degradation, and loss of collagen cross-linking during immobilisation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 76,
              "stem": "During ACL graft ligamentisation, the graft is at its WEAKEST at approximately:",
              "options": [
                "Immediately after implantation",
                "2-3 weeks",
                "6-8 weeks",
                "6 months",
                "1 year"
              ],
              "answer": "C",
              "explanation": "After implantation, the ACL graft undergoes ligamentisation: avascular necrosis (weeks 1-4), revascularisation with cellular repopulation (weeks 4-12), and remodelling (months 3-12+). The graft reaches its nadir of mechanical strength at approximately 6-8 weeks, when the original graft tissue has undergone necrosis but revascularisation and new collagen production are not yet mature. This biological vulnerability at 6-8 weeks is why rehabilitation protocols restrict aggressive loading during this period.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 77,
              "stem": "The predominant collagen fibre orientation in the meniscus is:",
              "options": [
                "Radial",
                "Random",
                "Vertical",
                "Circumferential (hoop)",
                "Oblique"
              ],
              "answer": "D",
              "explanation": "The predominant collagen orientation in the meniscus is CIRCUMFERENTIAL (hoop), running parallel to the peripheral edge. This converts axial compressive loads into circumferential (hoop) stresses, allowing the meniscus to resist being extruded from the joint. Radial (tie) fibres run perpendicular to the circumferential fibres and prevent longitudinal splitting. A radial tear disrupts the circumferential fibres and is more biomechanically significant than a longitudinal tear, which runs between circumferential bundles.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 78,
              "stem": "A patient develops Achilles tendinopathy. Which statement about the histopathology is correct?",
              "options": [
                "Acute inflammatory infiltrate with neutrophils predominates",
                "The condition is primarily an inflammatory tendinitis",
                "Tendon rupture always precedes tendinopathy",
                "The pathology is identical to a traumatic tendon tear",
                "Histology shows mucoid degeneration, disorganised collagen, and neovascularisation without significant inflammation"
              ],
              "answer": "E",
              "explanation": "Tendinopathy is a DEGENERATIVE condition, not primarily inflammatory — hence the term 'tendinopathy' rather than 'tendinitis'. Histology characteristically shows mucoid (myxoid) degeneration, disorganised collagen fibres, hypercellularity, neovascularisation, and ground substance accumulation WITHOUT significant inflammatory cell infiltrate. This has important treatment implications: anti-inflammatory medications (NSAIDs) may have limited benefit because inflammation is not the primary pathology. Eccentric loading exercises promote collagen remodelling and are the mainstay of treatment.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 79,
              "stem": "Which fluoroquinolone side effect directly relates to tendon basic science?",
              "options": [
                "Tendon calcification",
                "Tendon rupture from inhibition of tenocyte proliferation and collagen synthesis",
                "Tendon ossification",
                "Tendon adhesion formation",
                "Tendon hypertrophy"
              ],
              "answer": "B",
              "explanation": "Fluoroquinolone antibiotics (ciprofloxacin, levofloxacin) are associated with tendinopathy and tendon rupture, particularly the Achilles tendon. The mechanism involves direct toxicity to tenocytes: inhibition of tenocyte proliferation, reduced collagen synthesis, increased MMP expression (collagen degradation), and oxidative stress. Risk is increased in elderly patients, those on corticosteroids, and renal impairment. This is a clinically important drug-tendon interaction (see Ch 22) and explains the FDA black box warning on fluoroquinolones.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Skeletal Muscle & Peripheral Nerve",
          "range": "Q80-Q89",
          "questions": [
            {
              "number": 80,
              "stem": "According to Seddon's classification, a nerve injury with conduction block but intact axons and full recovery expected is termed:",
              "options": [
                "Neurapraxia",
                "Neurotmesis",
                "Axonotmesis",
                "Sunderland Grade III",
                "Sunderland Grade V"
              ],
              "answer": "A",
              "explanation": "Neurapraxia (Seddon 1943) is a conduction block with intact axons — the mildest form of nerve injury. There is NO Wallerian degeneration. Recovery is complete, typically within 6-12 weeks. Common causes include compression, traction, and ischaemia. NCS shows conduction block at the injury site with preserved distal responses. Axonotmesis involves axon disruption with Wallerian degeneration but intact connective tissue framework. Neurotmesis is complete nerve disruption.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 81,
              "stem": "The rate of peripheral nerve regeneration after axonotmesis is approximately:",
              "options": [
                "0.1 mm/day",
                "5 mm/day",
                "1 mm/day",
                "10 mm/day",
                "1 cm/day"
              ],
              "answer": "C",
              "explanation": "Peripheral nerve regeneration occurs at approximately 1mm/day (approximately 1 inch/month). After Wallerian degeneration of the distal segment, Schwann cells proliferate to form bands of Bungner that guide regenerating axons from the proximal stump. The regeneration rate can be used clinically to predict recovery time — e.g., a radial nerve injury in the spiral groove (14cm above elbow) should show signs of brachioradialis reinnervation in approximately 14 weeks if regeneration is occurring.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 82,
              "stem": "Which muscle fibre type is predominantly affected in Duchenne muscular dystrophy?",
              "options": [
                "Type I (slow-twitch) selectively",
                "All fibre types are affected equally",
                "Type IIA (fast oxidative) selectively",
                "Type IIB (fast glycolytic) selectively",
                "Only cardiac muscle is affected"
              ],
              "answer": "B",
              "explanation": "In DMD, the absence of dystrophin affects ALL muscle fibre types because dystrophin is essential for the structural integrity of the sarcolemma in all skeletal (and cardiac) muscle fibres. Dystrophin links the F-actin cytoskeleton to the extracellular matrix via the dystrophin-associated glycoprotein complex (DAG). Without dystrophin, the sarcolemma is mechanically unstable, leading to membrane damage with each contraction, calcium influx, and progressive fibre necrosis. The disease affects all fibre types, though the clinical pattern (proximal weakness first) reflects the loading pattern of muscles.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 83,
              "stem": "The sliding filament theory of muscle contraction states that:",
              "options": [
                "Actin and myosin filaments shorten during contraction",
                "Actin filaments slide past stationary myosin filaments",
                "Myosin filaments slide past stationary actin filaments",
                "The Z-lines expand during contraction",
                "Actin filaments slide relative to myosin filaments without either changing length"
              ],
              "answer": "E",
              "explanation": "Huxley (1954) proposed the sliding filament theory: during contraction, actin (thin) filaments slide past myosin (thick) filaments powered by ATP-dependent cross-bridge cycling, shortening the sarcomere. Crucially, NEITHER filament changes length — the sarcomere shortens because the filaments slide past each other, bringing the Z-lines closer together. The A-band (myosin length) remains constant; the I-band (actin only) and H-zone (myosin only) shorten.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 84,
              "stem": "Wallerian degeneration involves:",
              "options": [
                "Degeneration of the distal nerve segment with Schwann cell proliferation",
                "Degeneration of the proximal nerve segment",
                "Degeneration of the cell body in the dorsal root ganglion",
                "Random patchy degeneration throughout the nerve",
                "Demyelination without axonal loss"
              ],
              "answer": "A",
              "explanation": "Wallerian degeneration (Waller 1850) is the orderly degeneration of the DISTAL nerve segment after axonal transection. The distal axon and myelin sheath break down and are phagocytosed by macrophages. Schwann cells proliferate and align to form bands of Bungner, which serve as guides for regenerating axons growing from the proximal stump. This process takes approximately 2-3 weeks to complete. The proximal segment undergoes a brief retrograde degeneration of 1-2 nodes of Ranvier before regeneration begins.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 85,
              "stem": "Type I (slow-twitch) muscle fibres are characterised by:",
              "options": [
                "High glycolytic capacity, low mitochondrial density, fast contraction, white colour",
                "Low oxidative capacity, high glycolytic capacity, fatigue-resistant",
                "High power output, rapid fatigue",
                "High oxidative capacity, high mitochondrial density, slow contraction, red colour",
                "Low capillary density, low myoglobin"
              ],
              "answer": "D",
              "explanation": "Type I (slow-twitch) fibres are characterised by: high oxidative (aerobic) capacity, high mitochondrial density, high capillary density, high myoglobin content (giving red colour), slow contraction speed, and high fatigue resistance. They are recruited for sustained, low-intensity activities (posture, endurance). Type IIB fibres are the opposite: fast-twitch, glycolytic, low mitochondrial density, white, high power but rapid fatigue (sprinting). Type IIA are intermediate: fast oxidative-glycolytic.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 86,
              "stem": "Dantrolene, the treatment for malignant hyperthermia, acts by:",
              "options": [
                "Blocking acetylcholine receptors at the neuromuscular junction",
                "Blocking voltage-gated sodium channels",
                "Inhibiting myosin ATPase",
                "Enhancing SERCA pump activity",
                "Inhibiting calcium release from the sarcoplasmic reticulum via RYR1"
              ],
              "answer": "E",
              "explanation": "Dantrolene acts by directly blocking the ryanodine receptor (RYR1) on the sarcoplasmic reticulum, reducing calcium release into the sarcoplasm. In malignant hyperthermia (usually caused by RYR1 mutations), volatile anaesthetics trigger uncontrolled RYR1 opening, causing massive calcium release, sustained contraction, and hypermetabolism. Dantrolene reverses this by reducing the calcium available for contraction. It is the specific antidote and must be available wherever general anaesthesia is administered.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 87,
              "stem": "A Tinel's sign that advances distally over serial examinations indicates:",
              "options": [
                "Worsening nerve compression",
                "Neuroma formation",
                "Active nerve regeneration",
                "Complete nerve transection",
                "Chronic regional pain syndrome"
              ],
              "answer": "C",
              "explanation": "An advancing Tinel's sign (tingling produced by tapping over the nerve that moves distally over time) indicates active axonal regeneration. The advancing front of regenerating axons is sensitive to percussion. The rate of advancement (approximately 1mm/day) can be monitored to confirm regeneration is occurring and to predict when reinnervation of target muscles should occur. A STATIC Tinel's sign that does not advance may indicate neuroma formation at the injury site (failed regeneration).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 88,
              "stem": "In a lower motor neuron (LMN) lesion, which of the following clinical findings is expected?",
              "options": [
                "Spasticity and hyperreflexia",
                "Positive Babinski sign",
                "Clasp-knife rigidity",
                "Flaccid paralysis, muscle wasting, fasciculations, and areflexia",
                "Clonus"
              ],
              "answer": "D",
              "explanation": "LMN lesions produce flaccid paralysis (loss of muscle tone), muscle wasting and atrophy (denervation atrophy), fasciculations (spontaneous firing of denervated motor units), and areflexia or hyporeflexia (loss of the reflex arc). This contrasts with UMN lesions which produce spasticity, hyperreflexia, positive Babinski sign, clonus, and NO fasciculations or early wasting. The distinction between UMN and LMN signs is fundamental to neurological examination (see Ch 27 for spinal cord tracts).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 89,
              "stem": "The motor end-plate contains which type of acetylcholine receptor?",
              "options": [
                "Muscarinic M1",
                "Nicotinic (N1/Nm)",
                "Muscarinic M2",
                "Alpha-adrenergic",
                "Beta-adrenergic"
              ],
              "answer": "B",
              "explanation": "The motor end-plate (neuromuscular junction) contains nicotinic acetylcholine receptors (specifically Nm or N1 subtype). These are ligand-gated ion channels that open when ACh binds, allowing Na+ influx and K+ efflux, producing an end-plate potential. If threshold is reached, a muscle action potential is generated. Succinylcholine (depolarising block) and non-depolarising agents (e.g., rocuronium) both act at this receptor but by different mechanisms. Muscarinic receptors are found in the autonomic nervous system, not at the motor end-plate.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Intervertebral Disc & Soft Tissue Healing",
          "range": "Q90-Q98",
          "questions": [
            {
              "number": 90,
              "stem": "According to Nachemson's intradiscal pressure measurements, in which position is the disc pressure HIGHEST?",
              "options": [
                "Seated flexed forward",
                "Supine",
                "Standing erect",
                "Seated erect",
                "Prone"
              ],
              "answer": "A",
              "explanation": "Nachemson (1966) measured intradiscal pressures in vivo: supine ~25 kg, standing ~100 kg, seated erect ~140 kg, seated flexed forward ~275 kg (in a 70kg individual). Seated flexion produces the highest disc pressures because: (1) the erector spinae muscles are mechanically disadvantaged and must generate high forces, (2) the flexed posture increases the moment arm of body weight above the disc, (3) sitting eliminates the hip extensors from sharing the load. This explains why disc herniations are associated with prolonged seated flexion.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 91,
              "stem": "The nucleus pulposus of the intervertebral disc contains predominantly which collagen type?",
              "options": [
                "Type II",
                "Type I",
                "Type III",
                "Type X",
                "Type XI"
              ],
              "answer": "A",
              "explanation": "The nucleus pulposus contains predominantly Type II collagen (similar to articular cartilage), along with aggrecan, hyaluronic acid, and water (80% in youth). The annulus fibrosus contains predominantly Type I collagen (similar to tendon/ligament), arranged in concentric lamellae with fibres alternating at approximately 30 degrees to each other. This structural difference is important: the nucleus distributes load hydrostatically while the annulus resists tensile forces.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 92,
              "stem": "The intervertebral disc receives its nutrition primarily through:",
              "options": [
                "Direct blood supply from segmental arteries",
                "Lymphatic drainage",
                "Synovial fluid",
                "Periosteal vessels",
                "Diffusion through the vertebral endplate"
              ],
              "answer": "E",
              "explanation": "The intervertebral disc is the largest avascular structure in the body. Nutrition occurs primarily by diffusion through the porous central concavity of the vertebral endplate, driven by loading and unloading cycles (pump mechanism). The outer annulus may receive some direct blood supply from periannular vessels. Smoking, diabetes, and atherosclerosis impair endplate perfusion, accelerating disc degeneration (Urban & Roberts 2003). L4/5 is the largest and most avascular disc, explaining its high degeneration rate.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 93,
              "stem": "Continuous passive motion (CPM) after intra-articular surgery is based on which principle established by Salter?",
              "options": [
                "Immobilisation promotes better healing",
                "Motion accelerates inflammation",
                "CPM increases collagen degradation",
                "Motion prevents adhesion formation and enhances nutrition by diffusion",
                "CPM prevents all complications"
              ],
              "answer": "D",
              "explanation": "Salter (1989) demonstrated that CPM promotes healing of articular cartilage, tendon, and ligament by: (1) enhancing nutrition through diffusion (cycling drives fluid exchange in avascular tissues), (2) preventing adhesion formation (maintaining gliding surfaces), (3) stimulating cellular activity and collagen alignment along stress axes, and (4) preventing the detrimental effects of immobilisation on adjacent tissues (Woo 1991 showed 60% strength loss in ligaments after 8 weeks immobilisation).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 94,
              "stem": "In the annulus fibrosus, collagen fibres in successive lamellae are arranged at alternating angles of approximately:",
              "options": [
                "10 degrees",
                "45 degrees",
                "30 degrees",
                "60 degrees",
                "90 degrees"
              ],
              "answer": "C",
              "explanation": "Annulus fibrosus lamellae contain Type I collagen fibres arranged at approximately 30 degrees to the horizontal (disc plane), with successive lamellae alternating in direction. This criss-cross pattern provides resistance to both tensile and torsional forces. The arrangement is analogous to the plies of a radial tyre. The outer annulus has approximately 15-25 concentric lamellae. This alternating fibre orientation means the annulus resists loading in multiple directions, unlike a tendon whose fibres are all aligned parallel.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 95,
              "stem": "Which disc-related change occurs FIRST in the degenerative cascade?",
              "options": [
                "Annular tears",
                "Nucleus dehydration with proteoglycan loss",
                "Osteophyte formation",
                "Endplate fracture",
                "Disc space narrowing on X-ray"
              ],
              "answer": "B",
              "explanation": "The degenerative cascade begins with nucleus dehydration (Adams & Roughley 2006): proteoglycan content decreases (especially aggrecan), reducing the osmotic pressure that attracts and retains water. The nucleus becomes progressively dehydrated and fibrotic, losing its ability to distribute load hydrostatically. This shifts load to the annulus (causing annular tears) and endplates (causing endplate changes). Disc space narrowing and osteophyte formation are late radiographic findings. The important point is that the cascade STARTS with biochemical changes in the nucleus, not structural failure of the annulus.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 96,
              "stem": "The sinuvertebral nerve supplies which structures in the spine?",
              "options": [
                "The paraspinal muscles only",
                "The skin overlying the spine",
                "The facet joints only",
                "The anterior longitudinal ligament only",
                "The contents of the spinal canal including the posterior annulus, PLL, and dura"
              ],
              "answer": "E",
              "explanation": "The sinuvertebral nerve (recurrent meningeal nerve of Luschka) is a mixed nerve that re-enters the spinal canal through the intervertebral foramen. It supplies the posterior annulus fibrosus, the posterior longitudinal ligament, the ventral dura, epidural blood vessels, and periosteum of the vertebral body. Importantly, in the NORMAL disc, only the outer one-third of the annulus has nerve fibres. In the DEGENERATE disc, nerve ingrowth extends into the inner annulus and even the nucleus — this neoinnervation may contribute to discogenic pain.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 97,
              "stem": "After Achilles tendon repair, the maximum tensile strength of the healed tendon compared to the original is approximately:",
              "options": [
                "30-40%",
                "70-80%",
                "50-60%",
                "90-95%",
                "100%"
              ],
              "answer": "B",
              "explanation": "Like wound healing (see Ch 28), healed soft tissues never regain 100% of original strength. Tendon healing follows the same phases as wound healing (inflammation → proliferation → remodelling) and reaches approximately 70-80% of original tensile strength at 1 year. The repair tissue has inferior collagen organisation, reduced cross-linking, and a higher proportion of Type III collagen compared to native tendon. Adhesion formation between the tendon surface and surrounding sheath is an additional complication that limits gliding function.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 98,
              "stem": "The annulus fibrosus is thinnest in which region, explaining the direction of most disc herniations?",
              "options": [
                "Anterior",
                "Lateral",
                "Posterolateral",
                "Superior",
                "Inferior"
              ],
              "answer": "C",
              "explanation": "The posterior annulus is thinner than the anterior, and the posterolateral region is the thinnest because it receives less reinforcement from the posterior longitudinal ligament (which is narrow over the disc, broad over the vertebral body). The PLL partially blocks direct posterior (central) prolapse, deflecting nuclear material posterolaterally. This is why most disc herniations are posterolateral, compressing the traversing nerve root at that level (e.g., L4/5 posterolateral prolapse compresses the L5 root — see Ch 27).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        }
      ]
    },
    {
      "title": "Biomechanics",
      "chapters": [
        {
          "title": "Core Biomechanical Principles",
          "range": "Q99-Q108",
          "questions": [
            {
              "number": 99,
              "stem": "Young's modulus (elastic modulus) is defined as:",
              "options": [
                "Force per unit area",
                "Change in length divided by original length",
                "Energy absorbed per unit volume",
                "Stress divided by strain (in the elastic region)",
                "Strain divided by stress"
              ],
              "answer": "D",
              "explanation": "Young's modulus (E) = stress / strain in the linear elastic region of the stress-strain curve. It quantifies STIFFNESS — how much a material deforms under a given load. A higher E means a stiffer material. Cortical bone E ~ 17-20 GPa, cancellous bone ~ 0.1-2 GPa, stainless steel ~ 200 GPa, titanium ~ 110 GPa, CoCr ~ 230 GPa, PMMA ~ 2.5 GPa, UHMWPE ~ 1 GPa. The mismatch between implant and bone modulus drives stress shielding (see Ch 15).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 100,
              "stem": "The area under the stress-strain curve up to the point of fracture represents:",
              "options": [
                "Toughness (energy to failure)",
                "Stiffness",
                "Yield strength",
                "Ultimate tensile strength",
                "Resilience"
              ],
              "answer": "A",
              "explanation": "The area under the entire stress-strain curve to failure represents TOUGHNESS — the total energy absorbed per unit volume before fracture. Resilience is the area under the curve to the yield point (elastic energy absorbed). Stiffness is the slope of the linear region (Young's modulus). Yield strength is the stress at the yield point. Toughness is clinically important — it decreases with ageing (Burstein 1976, see Ch 5), explaining why elderly fractures comminute at lower energy.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 101,
              "stem": "If the diameter of an IM nail is increased from 10mm to 12mm, by approximately what factor does its bending stiffness increase?",
              "options": [
                "1.2x",
                "1.4x",
                "2.1x",
                "1.7x",
                "2.5x"
              ],
              "answer": "C",
              "explanation": "Bending stiffness is proportional to the area moment of inertia, which for a circular cross-section is proportional to r-to-the-fourth (or d-to-the-fourth). Ratio = (12/10) to the fourth = 1.2 to the fourth = 2.07, approximately 2.1x. This dramatic increase from a modest diameter change illustrates the power of the fourth-power relationship. This is why reaming (increasing nail diameter by even a few mm) substantially increases construct stiffness.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 102,
              "stem": "Which of the following correctly describes the relationship in Euler's column buckling equation?",
              "options": [
                "Critical load is proportional to length squared",
                "Critical load is inversely proportional to length",
                "Critical load is proportional to column cross-sectional area",
                "Critical load is inversely proportional to length squared",
                "Critical load is independent of material stiffness"
              ],
              "answer": "D",
              "explanation": "Euler's buckling: Pcr = (pi-squared x E x I) / L-squared. Critical buckling load is directly proportional to E (material stiffness) and I (area moment of inertia, geometry), but INVERSELY proportional to L-SQUARED (unsupported length). Doubling the unsupported length reduces the critical buckling load by a factor of 4. This explains why bone defects dramatically increase the risk of implant failure — the unsupported length of the nail/plate increases, quadratically reducing buckling resistance.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 103,
              "stem": "The stress-strain curve of a ductile material like stainless steel differs from a brittle material like ceramic in which key way?",
              "options": [
                "Ductile materials undergo significant plastic deformation before failure",
                "Ductile materials have a steeper elastic region",
                "Brittle materials have a longer plastic deformation region",
                "Brittle materials have a higher Young's modulus always",
                "Ductile materials have no yield point"
              ],
              "answer": "A",
              "explanation": "Ductile materials (stainless steel, titanium) undergo significant PLASTIC DEFORMATION before fracture — the stress-strain curve shows a long region beyond the yield point before ultimate failure. Brittle materials (ceramics, PMMA, glass) fail with little or no plastic deformation — they go directly from elastic deformation to fracture with minimal warning. This is why ceramic bearings can catastrophically fracture without prior deformation, while metal implants typically bend or fatigue before complete failure.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 104,
              "stem": "A force couple consists of:",
              "options": [
                "A single force applied at the centre of mass",
                "Two equal and opposite forces applied at the same point",
                "A force and its reaction force at a fulcrum",
                "A compressive and tensile force in the same direction",
                "Two equal and opposite forces applied at different points, creating a pure moment"
              ],
              "answer": "E",
              "explanation": "A force couple is two equal, opposite, and parallel forces applied at different points on a body. The result is a pure rotational moment (torque) with NO translational force. In orthopaedics, force couples are important in: (1) rotator cuff function (subscapularis IR vs infraspinatus/teres minor ER creating balanced rotation), (2) plate fixation (compression plate creates a force couple across the fracture), and (3) Charnley's hip biomechanics (abductor-body weight force couple at the hip).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 105,
              "stem": "The fatigue life of a material (S-N curve) shows that:",
              "options": [
                "Higher stresses always increase fatigue life",
                "Lower stresses permit more cycles before failure",
                "Fatigue occurs only in metals, not polymers or bone",
                "All materials have an infinite fatigue life below the yield stress",
                "Temperature does not affect fatigue life"
              ],
              "answer": "B",
              "explanation": "The S-N (stress vs number of cycles) curve shows that lower applied stresses permit more loading cycles before fatigue failure. Some materials (e.g., steel) have an endurance limit below which they can withstand infinite cycles. Others (e.g., titanium, aluminium, bone) have no true endurance limit and will eventually fail at any cyclic stress. Fatigue failure of implants (e.g., plate fracture at the screw hole) occurs by microcrack initiation at stress concentrators (holes, surface defects) followed by slow crack propagation through the material.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 106,
              "stem": "Stress is defined as:",
              "options": [
                "Force multiplied by distance",
                "Change in length divided by original length",
                "Energy absorbed per unit volume",
                "Force divided by area",
                "Force divided by displacement"
              ],
              "answer": "D",
              "explanation": "Stress (sigma) = Force / Area (units: Pascals = N/m-squared, or MPa = N/mm-squared). It represents the internal force distribution per unit area within a material. Types include: tensile stress (pulling apart), compressive stress (pushing together), shear stress (sliding parallel), bending stress (combined tension + compression), and torsional stress (twisting, a form of shear). Strain (epsilon) = change in length / original length (dimensionless ratio). Young's modulus = stress / strain.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 107,
              "stem": "The concept of 'stress concentration' at a screw hole in a plate means:",
              "options": [
                "Stress is evenly distributed across the plate",
                "Stress is lower at the hole than surrounding material",
                "The screw absorbs all the stress",
                "The plate becomes stiffer at the hole",
                "Local stress at the hole exceeds the average stress in the plate"
              ],
              "answer": "E",
              "explanation": "A stress concentration (or stress riser) occurs at any geometric discontinuity — holes, notches, sharp corners, threads. The local stress at the discontinuity is HIGHER than the average stress in the surrounding material. For a circular hole in a plate under tension, the stress concentration factor is approximately 3 (local stress = 3x average). This is why implant fatigue fractures typically initiate at screw holes — the local cyclic stress exceeds the fatigue strength of the material. Reducing stress concentration is a key principle in implant design (rounded holes, smooth transitions).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 108,
              "stem": "A viscoelastic material exhibits which of the following behaviours?",
              "options": [
                "Rate-dependent mechanical properties (strain rate sensitivity)",
                "Perfectly elastic recovery after all loads",
                "No energy dissipation during loading",
                "Constant stiffness regardless of loading conditions",
                "Brittle fracture without warning"
              ],
              "answer": "A",
              "explanation": "Viscoelastic materials (bone, cartilage, tendon, IVD, polymers) exhibit rate-dependent behaviour: they are stiffer and stronger at higher loading rates but more ductile at lower rates. They also show: creep (continued deformation under constant load), stress relaxation (decreasing stress under constant strain), and hysteresis (energy dissipation during loading-unloading cycles, represented by the area between the loading and unloading curves). This explains why bone behaves differently in high-energy trauma (stiff/brittle, comminution) vs slow loading (more ductile, simpler fracture patterns).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Gait Analysis",
          "range": "Q109-Q118",
          "questions": [
            {
              "number": 109,
              "stem": "The hip joint reaction force during normal single-leg stance is approximately:",
              "options": [
                "Equal to body weight",
                "3x body weight",
                "1.5x body weight",
                "5x body weight",
                "7x body weight"
              ],
              "answer": "B",
              "explanation": "Pauwels (1935) calculated the hip joint reaction force during single-leg stance as approximately 3x body weight. This is because the abductor muscles (gluteus medius/minimus) must generate approximately 2x body weight to balance the body weight moment across the hip joint (the abductor lever arm is shorter than the body weight lever arm, typically 1:2 ratio). Joint reaction force = body weight + abductor force = BW + 2BW = 3BW. During dynamic gait, peak forces reach 3-5x body weight.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 110,
              "stem": "A walking stick should be used in which hand to reduce hip joint reaction force?",
              "options": [
                "Ipsilateral (same side as affected hip)",
                "Either hand equally",
                "Contralateral (opposite side to affected hip)",
                "Both hands simultaneously",
                "A walking stick does not affect hip joint force"
              ],
              "answer": "C",
              "explanation": "A walking stick used in the CONTRALATERAL hand reduces hip joint reaction force because it creates a force on the OPPOSITE side of the body that reduces the body weight moment about the hip. The stick acts on a LONG moment arm (from the hand to the hip centre), so even a modest stick force (10-15% body weight) can reduce the joint reaction force by 30-50%. An ipsilateral stick would increase the body weight moment and is biomechanically counterproductive.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 111,
              "stem": "Which muscles are the primary power generators during terminal stance (push-off)?",
              "options": [
                "Hip flexors (iliopsoas)",
                "Ankle plantarflexors (gastrocnemius/soleus)",
                "Quadriceps",
                "Hip extensors (gluteus maximus/hamstrings)",
                "Ankle dorsiflexors (tibialis anterior)"
              ],
              "answer": "B",
              "explanation": "The ankle plantarflexors (gastrocnemius and soleus) are the primary power generators during terminal stance and pre-swing (push-off). They generate a concentric contraction producing approximately 80% of the total positive work during the gait cycle. Loss of this power source (e.g., transtibial amputation) significantly increases energy expenditure because compensatory mechanisms at the hip must replace this energy. This is why prosthetic foot design that stores and returns energy (energy-storing feet) improves gait efficiency in amputees.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 112,
              "stem": "A positive Trendelenburg sign indicates weakness of which muscle group?",
              "options": [
                "Quadriceps",
                "Hamstrings",
                "Hip flexors",
                "Ankle dorsiflexors",
                "Hip abductors (gluteus medius/minimus)"
              ],
              "answer": "E",
              "explanation": "A positive Trendelenburg sign occurs when the pelvis drops on the CONTRALATERAL (swing) side during single-leg stance on the affected side, indicating weakness of the hip ABDUCTORS (primarily gluteus medius, supplied by the superior gluteal nerve L5, see Ch 26). Causes include: superior gluteal nerve injury (e.g., Hardinge approach), L5 radiculopathy, hip OA (pain inhibition), muscular dystrophy, and post-trochanteric osteotomy. The compensatory 'Trendelenburg gait' or 'abductor lurch' involves leaning the trunk OVER the affected hip to reduce the body weight moment arm.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 113,
              "stem": "During which phase of the gait cycle does the quadriceps act eccentrically to control knee flexion?",
              "options": [
                "Loading response (foot flat)",
                "Initial contact only",
                "Midstance",
                "Terminal stance",
                "Swing phase"
              ],
              "answer": "A",
              "explanation": "During loading response (foot flat), the knee flexes approximately 15-20 degrees to absorb the impact of body weight transfer. The QUADRICEPS contracts ECCENTRICALLY (lengthening while generating force) to control this flexion and prevent the knee from buckling. This is one of the determinants of gait — knee flexion in stance reduces the vertical excursion of the centre of gravity, conserving energy. Loss of this mechanism (e.g., quadriceps weakness, stiff knee) increases energy cost and produces a characteristic gait pattern (stiff-leg gait with circumduction in swing or excessive pelvic obliquity).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 114,
              "stem": "The energy cost of walking after a transtibial amputation increases by approximately:",
              "options": [
                "10%",
                "20%",
                "65%",
                "40%",
                "100%"
              ],
              "answer": "D",
              "explanation": "Waters & Mulroy (1999) established that transtibial amputation increases the energy cost of walking by approximately 40%, with a 20% decrease in comfortable walking speed. Transfemoral amputation increases energy cost by approximately 65% with 40% speed reduction. This data is essential for understanding rehabilitation goals and prosthetic prescription. The increase is primarily due to loss of the ankle plantarflexor power generators and reduced shock absorption from loss of ankle dorsiflexion in stance.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 115,
              "stem": "The six determinants of gait described by Inman et al. function primarily to:",
              "options": [
                "Increase walking speed",
                "Maximise stride length",
                "Minimise the vertical and lateral displacement of the centre of gravity",
                "Increase hip joint reaction forces",
                "Reduce the stance phase percentage"
              ],
              "answer": "C",
              "explanation": "Inman's six determinants (pelvic rotation, pelvic tilt, knee flexion in stance, foot mechanics, knee mechanics, lateral pelvic displacement) all serve to minimise the vertical and lateral excursion of the centre of gravity during walking. A perfectly smooth path of the CoG would require zero energy for vertical displacement. Each determinant smooths the sinusoidal path of the CoG, reducing the total work required to 'lift' the body with each step. Loss of any determinant (e.g., knee flexion in stance after TKA) increases energy cost.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 116,
              "stem": "During normal gait, hip joint reaction force is highest during:",
              "options": [
                "Double support phases",
                "Swing phase",
                "Single support (midstance) phase",
                "Initial contact only",
                "Pre-swing only"
              ],
              "answer": "C",
              "explanation": "During single support (midstance and terminal stance), the entire body weight plus the abductor muscle force acts through the hip joint, producing the highest joint reaction forces (3-5x BW). During double support, body weight is shared between both limbs, reducing the force on each hip. During swing, the hip on the weight-bearing side carries the full single-support load while the swinging hip has minimal load. The peak hip joint force occurs at approximately 15% and 50% of the gait cycle (early and late single support).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 117,
              "stem": "In Trendelenburg GAIT (compensatory pattern), the patient leans their trunk:",
              "options": [
                "Away from the affected hip during stance",
                "Toward the affected hip during stance",
                "Forward during stance",
                "Backward during stance",
                "Laterally to both sides equally"
              ],
              "answer": "B",
              "explanation": "In Trendelenburg GAIT (also called 'abductor lurch'), the patient compensates for weak abductors by leaning the trunk TOWARD the affected hip during stance phase. This shifts the centre of gravity CLOSER to (or even lateral to) the hip joint centre, reducing or eliminating the body weight moment that the abductors must counterbalance. This reduces the joint reaction force but produces an abnormal, energy-inefficient gait pattern. This is DIFFERENT from a positive Trendelenburg SIGN (which is the pelvic drop on the contralateral side).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 118,
              "stem": "A patient with weak hip abductors on the left side demonstrates a compensatory trunk lean towards the left during the stance phase of the left leg. This gait pattern is called:",
              "options": [
                "Antalgic gait",
                "Trendelenburg gait",
                "Short-leg gait",
                "Steppage gait",
                "Compensated Trendelenburg (Duchenne) gait"
              ],
              "answer": "E",
              "explanation": "A compensated Trendelenburg (Duchenne) gait involves the patient leaning the trunk over the affected side during stance. This moves the centre of mass closer to the hip joint, reducing the body weight moment arm and thus reducing the force the weak abductors need to generate. An uncompensated Trendelenburg gait shows the pelvis dropping on the contralateral (swing) side without trunk lean.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Joint Biomechanics",
          "range": "Q119-Q128",
          "questions": [
            {
              "number": 119,
              "stem": "The friction coefficient of a normal synovial joint is approximately:",
              "options": [
                "0.05-0.15",
                "0.2-0.3",
                "0.5-0.7",
                "0.001-0.01",
                "1.0"
              ],
              "answer": "D",
              "explanation": "The friction coefficient of a normal synovial joint (0.001-0.01) is remarkably low — lower than any man-made bearing surface. This is achieved through multiple lubrication mechanisms working simultaneously: boundary lubrication (lubricin), fluid film lubrication (squeeze film, hydrodynamic), boosted lubrication, and weeping lubrication. By comparison, metal-on-polyethylene has a friction coefficient of 0.05-0.15, metal-on-metal ~0.2-0.3, and ceramic-on-ceramic ~0.04-0.07.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 120,
              "stem": "Charnley chose a small (22mm) femoral head because frictional torque is proportional to:",
              "options": [
                "Friction coefficient x load x head radius",
                "Head radius only",
                "Load only",
                "Head radius squared",
                "Friction coefficient only"
              ],
              "answer": "A",
              "explanation": "Frictional torque = mu x F x r (friction coefficient x normal force x head radius). Charnley recognised that for a given friction coefficient and load, a smaller head radius produces less frictional torque, which translates to less shear stress at the fixation interfaces and potentially less loosening. This was the biomechanical rationale for his 22.225mm head size, though modern practice uses 28-36mm heads because cross-linked PE has reduced the wear penalty and the stability advantage of larger heads outweighs the friction disadvantage.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 121,
              "stem": "Boundary lubrication in a synovial joint is primarily provided by:",
              "options": [
                "Hyaluronic acid",
                "Type II collagen",
                "Albumin",
                "Lubricin (PRG4)",
                "Water"
              ],
              "answer": "D",
              "explanation": "Boundary lubrication (thin molecular film adsorbed on the cartilage surface) is primarily provided by lubricin (PRG4, proteoglycan 4), which is produced by superficial zone chondrocytes and Type B synoviocytes. Boundary lubrication operates at low speeds and high loads when the fluid film is too thin to separate the surfaces. Hyaluronic acid is the primary determinant of synovial fluid VISCOSITY and contributes to fluid film lubrication, but it is lubricin that provides the boundary layer.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 122,
              "stem": "The instantaneous centre of rotation of the knee during flexion:",
              "options": [
                "Remains fixed at the centre of the femoral condyle",
                "Moves anteriorly along the tibial plateau",
                "Moves posteriorly along the tibial plateau",
                "Oscillates randomly",
                "Remains at the tibial spine throughout"
              ],
              "answer": "C",
              "explanation": "The instantaneous centre of rotation of the knee moves POSTERIORLY along the tibial plateau during flexion due to the four-bar linkage mechanism of the cruciate ligaments. This creates the combined rolling-sliding motion: in early flexion predominantly rolling, in later flexion predominantly sliding. This posterior translation of the contact point is called 'femoral rollback' and is essential for full flexion — it prevents impingement of the posterior femur on the posterior tibial plateau. TKA designs attempt to replicate this (posterior-stabilised designs use a cam-post mechanism for rollback).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 123,
              "stem": "The 'boosted' lubrication mechanism described by Walker et al. involves:",
              "options": [
                "Injection of exogenous lubricant into the joint",
                "Increased blood flow to the synovium during exercise",
                "Thermal expansion of synovial fluid",
                "Release of phospholipids from the cartilage surface",
                "Concentration of hyaluronic acid at the contact area as water is squeezed out of cartilage"
              ],
              "answer": "E",
              "explanation": "Boosted lubrication (Walker 1968) occurs when cartilage is compressed: water is squeezed OUT of the porous cartilage matrix, leaving behind concentrated hyaluronic acid (a large molecule that cannot pass through the pores). This concentrated HA provides a viscous gel lubricant at the loaded contact area. The mechanism is self-reinforcing — higher loads squeeze more water out, concentrating more HA where it is most needed. This works synergistically with weeping lubrication (fluid expression providing the lubricating film) and boundary lubrication (lubricin surface coating).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 124,
              "stem": "In a total hip replacement, which bearing combination has the LOWEST friction coefficient?",
              "options": [
                "Ceramic-on-ceramic",
                "Metal-on-polyethylene",
                "Metal-on-metal",
                "Ceramic-on-polyethylene",
                "Metal-on-PTFE"
              ],
              "answer": "A",
              "explanation": "Ceramic-on-ceramic (CoC) has the lowest friction coefficient of all arthroplasty bearing combinations (~0.04-0.07), followed by ceramic-on-polyethylene (~0.05-0.08), metal-on-polyethylene (~0.05-0.15), and metal-on-metal (~0.2-0.3). The superior wettability and surface finish of ceramic produces the lowest friction. However, ceramics are brittle and can catastrophically fracture (a rare but devastating complication). All artificial bearings have much higher friction coefficients than the natural joint (0.001-0.01), highlighting the remarkable efficiency of biological lubrication.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 125,
              "stem": "The shoulder joint achieves stability primarily through which mechanism?",
              "options": [
                "Bony congruence (deep socket)",
                "Concavity compression by the rotator cuff muscles",
                "Negative intra-articular pressure and capsulolabral restraints alone",
                "Weight of the arm providing a gravitational stabilising effect",
                "Coracoacromial arch providing a rigid superior restraint"
              ],
              "answer": "B",
              "explanation": "The shoulder (glenohumeral) joint has the greatest ROM of any joint but the least bony congruity (the glenoid covers only 25-30% of the humeral head). CONCAVITY COMPRESSION (rotator cuff muscles compressing the humeral head into the glenoid concavity) is the primary dynamic stabilisation mechanism. The labrum deepens the glenoid by approximately 50% and increases the concavity for compression. Additional stabilisers include the glenohumeral ligaments (IGHL is the primary restraint in abduction/ER), negative intra-articular pressure, and the rotator interval. The coracoacromial arch provides superior restraint mainly in massive cuff tears.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 126,
              "stem": "During knee flexion, the combination of rolling and sliding at the tibiofemoral joint serves to:",
              "options": [
                "Increase joint friction",
                "Eliminate the need for menisci",
                "Reduce the role of the cruciate ligaments",
                "Prevent the femur from rolling off the posterior tibial plateau",
                "Increase compressive load on the joint"
              ],
              "answer": "D",
              "explanation": "If the femoral condyle rolled without sliding (pure rolling), it would rapidly translate posteriorly and 'fall off' the back of the tibial plateau by approximately 40 degrees of flexion. The SLIDING component (anterior slide of the femur on the tibia) counteracts the posterior translation from rolling, keeping the femoral condyle on the tibial surface throughout full flexion. This is why the four-bar linkage of the cruciates is essential — the ACL and PCL constrain the rolling-sliding ratio to maintain joint congruency. ACL rupture disrupts this, causing abnormal anterior tibial translation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 127,
              "stem": "In the normal hip, the abductor muscles act at a mechanical disadvantage. This means:",
              "options": [
                "The abductors generate more force than body weight",
                "The abductors generate less force than body weight",
                "The abductors and body weight produce equal moments",
                "The abductor lever arm is longer than the body weight lever arm",
                "The joint reaction force equals body weight"
              ],
              "answer": "A",
              "explanation": "The abductor muscles act at a mechanical disadvantage because their lever arm (distance from GT to hip centre, approximately 5cm) is shorter than the body weight lever arm (distance from hip centre to body's midline, approximately 10cm) — a ratio of approximately 1:2. For the joint to be in equilibrium, the abductor FORCE must be approximately TWICE body weight to produce a moment equal to the body weight moment. This is why the hip joint reaction force is approximately 3x BW (body weight + 2x BW from abductors). A walking stick in the contralateral hand acts on a long moment arm, dramatically reducing the required abductor force.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 128,
              "stem": "The coefficient of friction for a metal-on-polyethylene bearing surface in a total hip replacement is approximately:",
              "options": [
                "0.001-0.01",
                "0.3-0.5",
                "0.5-0.7",
                "Greater than 1.0",
                "0.05-0.15"
              ],
              "answer": "E",
              "explanation": "Metal-on-polyethylene (MoP) has a friction coefficient of approximately 0.05-0.15 (Charnley's original bearing). This is 5-15 times higher than the natural synovial joint (0.001-0.01) but acceptably low for clinical function. The friction coefficient varies with load, speed, and lubrication (synovial fluid acts as lubricant). Modern highly cross-linked PE has reduced wear rates without significantly changing the friction coefficient. For comparison: ceramic-on-ceramic ~0.04-0.07, metal-on-metal ~0.2-0.3.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Implant Biomechanics",
          "range": "Q129-Q138",
          "questions": [
            {
              "number": 129,
              "stem": "According to Baumgaertner, the tip-apex distance (TAD) should be less than which value to minimise lag screw cut-out risk?",
              "options": [
                "10mm",
                "15mm",
                "25mm",
                "20mm",
                "30mm"
              ],
              "answer": "C",
              "explanation": "Baumgaertner et al. (1995) defined the TAD as the sum of the distances from the lag screw tip to the femoral head apex on AP and lateral views. They demonstrated that a TAD > 25mm is the single strongest predictor of lag screw cut-out in intertrochanteric fracture fixation. Maintaining TAD < 25mm reduces cut-out rates to less than 2%. This is one of the most frequently tested biomechanical principles in the FRCS examination.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 130,
              "stem": "A locking plate differs from a conventional plate in which fundamental way?",
              "options": [
                "Locking plates are made of titanium while conventional plates are stainless steel",
                "Locking screws lock into the plate at a fixed angle, providing angular stability without bone-plate friction",
                "Locking plates are thicker and stiffer",
                "Locking plates can only be used in the upper limb",
                "Locking plates do not need to be contoured to the bone surface"
              ],
              "answer": "B",
              "explanation": "The fundamental difference is that locking screws create a fixed-angle construct between screw and plate (the screw head threads into the plate hole). This provides angular stability that does NOT depend on friction between the plate and bone surface. Conventional plates rely on compression of the plate against bone (friction) for stability — if the plate is not perfectly contoured, the screws can toggle and lose purchase. Locking plates function as internal fixators, preserving periosteal blood supply because they do not require intimate bone-plate contact.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 131,
              "stem": "The working length of a plate construct is defined as:",
              "options": [
                "The total length of the plate",
                "The distance from the first to the last screw",
                "The distance between the two screws closest to the fracture on either side",
                "The unsupported length of the bone",
                "The length of the plate not covered by screws"
              ],
              "answer": "C",
              "explanation": "Working length is the distance between the two screws closest to the fracture on either side of the plate (Gautier & Sommer 2003). Plate stiffness varies with 1/L-cubed (L = working length). Doubling the working length reduces stiffness 8-fold. A SHORT working length (screws close to fracture) = RIGID construct suitable for compression/absolute stability. A LONG working length (screws far from fracture) = FLEXIBLE construct suitable for bridge plating/relative stability.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 132,
              "stem": "A lag screw achieves interfragmentary compression by which mechanism?",
              "options": [
                "The screw threads engage both cortices equally",
                "The screw is tightened until it bends",
                "The screw head pushes the plate against bone",
                "Friction between the screw and near cortex provides compression",
                "The screw threads engage only the far cortex while the screw glides through the near cortex"
              ],
              "answer": "E",
              "explanation": "A lag screw achieves compression by having threads that engage ONLY the far cortex (either through a fully threaded screw in an over-drilled near cortex, or a partially threaded screw). As the screw is tightened, the head pulls the near cortex fragment toward the far cortex fragment, compressing the fracture. The near cortex must have a glide hole (diameter equal to the outer thread diameter) to allow this sliding compression. If threads engage both cortices, the screw cannot compress — it merely holds the fragments at their existing distance.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 133,
              "stem": "The pullout strength of a screw from bone is primarily determined by:",
              "options": [
                "The screw head design",
                "The outer thread diameter and the length of screw thread purchase in bone",
                "The screw core (root) diameter",
                "The screw material",
                "The number of cortices engaged"
              ],
              "answer": "B",
              "explanation": "Pullout strength is proportional to the outer thread diameter (larger threads = more bone engaged) and the length of thread purchase in bone (more threads in bone = more resistance). The shear stress at the bone-thread interface must exceed the pullout force. In osteoporotic bone, pullout strength is reduced because the low-density cancellous bone cannot resist the shear forces. Strategies to improve pullout include: longer screws, larger diameter screws, bicortical purchase, cement augmentation, and locking plate constructs (which convert pullout forces into fixed-angle loading of the plate-screw construct).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 134,
              "stem": "An IM nail is described as a 'load-sharing' device. This means:",
              "options": [
                "The nail and bone share the load proportionally",
                "The nail bears 100% of the load",
                "The nail bears no load — it only maintains alignment",
                "The nail shares load with the plate",
                "Load sharing only occurs in non-union"
              ],
              "answer": "A",
              "explanation": "An IM nail is a load-sharing device — both the nail and the bone share the mechanical load. The proportion of load carried by each depends on their relative stiffness (E x I). In a comminuted fracture with bone defect, the nail carries more load. As callus forms and matures, the bone carries an increasing proportion of the load, gradually 'stress-protecting' the nail less. This contrasts with a plate used in compression mode, which acts as a load-BEARING device, carrying most of the load on the tension side. Load sharing promotes callus formation (secondary healing) through controlled micromotion.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 135,
              "stem": "Why does a screw hole in a plate act as a stress concentrator?",
              "options": [
                "The screw creates friction against the plate",
                "The screw head pushes against the plate edges",
                "The hole fills with fluid that transmits pressure",
                "The hole removes material, concentrating stress at the reduced cross-section",
                "Screws weaken the plate by chemical reaction"
              ],
              "answer": "D",
              "explanation": "A screw hole removes material from the plate, creating a geometric discontinuity. Stress must flow around the hole, concentrating at the reduced cross-section at the sides of the hole. For a circular hole in tension, the stress concentration factor is approximately 3 (local stress = 3x average). This is why implant fatigue fractures typically initiate at empty screw holes — the cyclic stress at the hole exceeds the material's fatigue endurance limit. This is also why it is important not to leave empty screw holes at the highest-stress region of the construct (usually at the fracture site).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 136,
              "stem": "A reverse oblique intertrochanteric fracture is best fixed with a cephalomedullary nail rather than a sliding hip screw because:",
              "options": [
                "The nail is cheaper",
                "The nail provides more rotational control",
                "The SHS cannot accommodate the fracture pattern — the fracture slides into varus rather than compression",
                "The SHS is contraindicated in all trochanteric fractures",
                "The nail allows earlier weight bearing"
              ],
              "answer": "C",
              "explanation": "The sliding hip screw works by allowing CONTROLLED COLLAPSE — the lag screw slides within the barrel, converting the applied force into compression at the fracture site. This works for standard intertrochanteric fractures where the fracture line runs from the greater to the lesser trochanter. In a reverse oblique fracture, the fracture line runs from medial-superior to lateral-inferior — the fracture geometry causes the shaft to MEDIALISE rather than compress, and the SHS mechanism cannot resist this (the screw slides but the fracture displaces into varus). A cephalomedullary nail resists medialisation of the shaft because it is an intramedullary device that acts as a buttress against lateral displacement.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 137,
              "stem": "In cemented total hip arthroplasty, cement acts as:",
              "options": [
                "An adhesive bonding metal to bone",
                "A shock absorber that reduces stress on bone",
                "A biological agent that stimulates bone growth",
                "A grout that fills the space between implant and bone, creating an interlock",
                "A barrier against infection"
              ],
              "answer": "D",
              "explanation": "PMMA bone cement is NOT an adhesive — it does not chemically bond to either metal or bone. It acts as a GROUT that fills the space between the implant and the prepared bone surface, creating a mechanical interlock. The cement interdigitates with the cancellous bone trabeculae and conforms to the implant surface, transferring load by mechanical interlock rather than chemical bonding. A good cement mantle (2-3mm uniform thickness, no voids, pressurised into cancellous bone) is essential for longevity. Cement has a modulus of approximately 2.5 GPa — between PE (1 GPa) and cortical bone (17-20 GPa).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 138,
              "stem": "Stress shielding around a femoral stem is MOST pronounced with which combination?",
              "options": [
                "Cemented, collarless, titanium stem",
                "Uncemented, press-fit, cobalt-chrome stem with proximal porous coating",
                "Uncemented, titanium stem with full porous coating",
                "Cemented, collared, stainless steel stem",
                "Short metaphyseal-only stem"
              ],
              "answer": "B",
              "explanation": "Stress shielding is greatest with: (1) STIFFER material (cobalt-chrome E=230 GPa > titanium E=110 GPa > bone E=17-20 GPa), (2) UNCEMENTED fixation (rigid bone-implant interface), (3) PROXIMAL porous coating (load transfer only proximally, bypassing diaphyseal bone), (4) LARGER stem diameter (higher area moment of inertia = stiffer construct). A cobalt-chrome uncemented stem with proximal coating transfers load from the proximal femur directly to the stem, shielding the diaphysis from load — Wolff's law causes adaptive remodelling with cortical thinning. Modern designs use shorter stems, titanium alloy, and proximal loading to minimise stress shielding.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Material Properties",
          "range": "Q139-Q141",
          "questions": [
            {
              "number": 139,
              "stem": "Fatigue failure of an orthopaedic implant occurs when:",
              "options": [
                "REPEATED CYCLIC loading below the material's yield strength accumulates microdamage over time → crack initiation → crack propagation → eventual failure (the implant breaks from accumulated microcracking, not a single overload)",
                "A single massive overload breaks the implant",
                "The implant corrodes chemically",
                "The implant is too large",
                "The surgeon applies excessive force during insertion"
              ],
              "answer": "A",
              "explanation": "Fatigue failure: repeated CYCLIC loading at stress levels BELOW the yield strength gradually accumulates MICRODAMAGE → a crack INITIATES (typically at a stress concentrator — a notch, scratch, screw hole, or surface defect) → with continued cycling, the crack PROPAGATES across the implant → eventually the remaining cross-section is insufficient to bear the load → CATASTROPHIC FAILURE (the implant breaks). This is NOT from a single overload (that would be acute fracture). Clinical examples: (1) plate fatigue fracture (if a fracture non-union subjects the plate to repeated bending cycles without bone sharing the load → the plate eventually fails). (2) Stem fracture in THA (rare with modern designs). (3) Pedicle screw breakage (if pseudarthrosis develops → cyclic loading of the screws → fatigue failure). Prevention: use implants with proven fatigue resistance (CoCr > Ti for fatigue strength), reduce stress concentrators (polished surfaces, smooth transitions), achieve fracture union (bone shares the load → reduces implant stress), and use appropriate implant size. S-N curve (stress vs. number of cycles to failure): characterises a material's fatigue behaviour.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 140,
              "stem": "Young's modulus (modulus of elasticity) represents:",
              "options": [
                "The maximum strength of a material before fracture",
                "The total energy absorbed before failure",
                "The ductility of a material",
                "The hardness of a material",
                "The STIFFNESS of a material — defined as the ratio of stress to strain in the elastic (linear) region of the stress-strain curve (higher modulus = stiffer material)"
              ],
              "answer": "E",
              "explanation": "Young's modulus (E) = stress / strain in the ELASTIC region of the stress-strain curve. It represents STIFFNESS — the resistance of a material to elastic deformation. Higher Young's modulus = STIFFER material (deforms less for a given stress). Values in orthopaedics: cortical bone ~15-20 GPa, cancellous bone ~0.1-5 GPa, titanium ~110 GPa, CoCr ~230 GPa, stainless steel ~200 GPa, PMMA cement ~2-3 GPa, UHMWPE ~1 GPa. Clinical relevance: (1) STRESS SHIELDING — implants with much higher modulus than bone (CoCr > Ti > bone) shield the bone from mechanical loading → bone resorption (Wolff's law). Titanium has lower modulus than CoCr → closer to bone → less stress shielding (one reason Ti is preferred for stems). (2) Modulus mismatch between plate and bone affects load-sharing (stiffer plate → more load through plate, less through bone). The stress-strain curve also defines: yield point (transition from elastic to plastic deformation), ultimate tensile strength (maximum stress), and failure point.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 141,
              "stem": "On a stress-strain curve, the yield point represents:",
              "options": [
                "The origin (zero stress and strain)",
                "The transition from ELASTIC (reversible) to PLASTIC (permanent) deformation — beyond this point, the material will not return to its original shape when the load is removed",
                "The point of material failure",
                "The maximum stress the material can withstand",
                "The modulus of elasticity"
              ],
              "answer": "B",
              "explanation": "The stress-strain curve key points: (1) ELASTIC REGION (linear portion): stress is proportional to strain (Hooke's law), deformation is REVERSIBLE (remove the load → material returns to original shape). The slope of this region = Young's modulus. (2) YIELD POINT: the transition from elastic to plastic behaviour — the stress at which PERMANENT (irreversible) deformation begins. Below the yield point → elastic. Above → plastic. (3) PLASTIC REGION: deformation is permanent (the material doesn't return to its original shape). (4) ULTIMATE TENSILE STRENGTH: the maximum stress the material can withstand (peak of the curve). (5) FAILURE/FRACTURE POINT: the material breaks. Clinical analogy: when a bone is loaded below its yield point → it deforms elastically and recovers. Above the yield point → permanent deformation occurs (plastic deformation of bone = microdamage/stress fracture precursors). Beyond ultimate strength → fracture. Ductile materials (metals): significant plastic deformation before failure (can bend before breaking). Brittle materials (ceramics, PMMA): minimal plastic deformation → fail suddenly (snap without warning).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Force Couples",
          "range": "Q142",
          "questions": [
            {
              "number": 142,
              "stem": "The rotator cuff muscles function as a force couple with the deltoid during shoulder abduction. The cuff's role is to:",
              "options": [
                "Generate all the abduction force alone",
                "Only externally rotate the shoulder",
                "Push the humeral head superiorly",
                "Prevent all shoulder motion",
                "Compress and stabilise the humeral head against the glenoid (concavity compression), creating a stable fulcrum that allows the deltoid to elevate the arm effectively"
              ],
              "answer": "E",
              "explanation": "The rotator cuff muscles (supraspinatus, infraspinatus, teres minor, subscapularis) act as a FORCE COUPLE with the deltoid. During abduction: the DELTOID generates the primary upward (abduction) force. However, the deltoid also has a significant SUPERIOR SHEARING component (it pulls the humeral head upward against the acromion). The rotator cuff counteracts this: the infraspinatus/teres minor (posterior cuff) and subscapularis (anterior cuff) exert a COMPRESSIVE and DEPRESSOR force on the humeral head — pulling it into the glenoid (concavity compression) and stabilising it as a fixed fulcrum. Without the cuff: the deltoid cannot elevate the arm effectively (it just shrugs the shoulder — the humeral head migrates superiorly without a stable fulcrum). This is why MASSIVE IRREPARABLE cuff tears lead to pseudoparalysis (inability to elevate despite intact deltoid) and why rTSA works — it creates a fixed fulcrum (glenosphere) that allows the deltoid alone to power elevation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Materials",
          "range": "Q143-Q147",
          "questions": [
            {
              "number": 143,
              "stem": "Trabecular metal (porous tantalum) is used in orthopaedic implants because of its:",
              "options": [
                "Extremely high porosity (~80%), excellent osteointegration, high coefficient of friction, and biocompatibility — ideal for revision arthroplasty and bone defect reconstruction",
                "Low cost and easy availability",
                "Magnetic properties useful for MRI",
                "Similarity to PMMA cement",
                "Use exclusively in paediatric implants"
              ],
              "answer": "A",
              "explanation": "Trabecular metal (porous tantalum) has a structure that mimics cancellous bone with ~80% porosity (vs ~30-50% for other porous coatings) and an average pore size of 430μm — ideal for bone ingrowth. It has the highest coefficient of friction of any orthopaedic implant material (preventing micromotion at the bone-implant interface — essential for initial stability in revision surgery where bone quality is poor). It is highly biocompatible, corrosion-resistant, and has excellent compressive strength despite its porosity. Uses: acetabular revision (augments, shells), tibial components, metaphyseal cones/sleeves for revision TKA bone defects, and tumour prosthesis reconstruction. Trade name: Trabecular Metal (Zimmer Biomet).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 144,
              "stem": "The phenomenon where a material fails under repeated cyclic loading below its yield strength is called:",
              "options": [
                "Creep",
                "Stress relaxation",
                "Stress shielding",
                "Fatigue failure",
                "Viscoelasticity"
              ],
              "answer": "D",
              "explanation": "Fatigue failure occurs when a material fractures under repeated cyclic loading at stress levels BELOW its static yield strength. Microscopic cracks initiate at stress concentration points (holes, notches, surface defects), propagate with each loading cycle, and eventually reach a critical size causing sudden failure. This is clinically relevant to: implant failure (plate/nail fracture), stress fractures in bone, and polyethylene wear in arthroplasty.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 145,
              "stem": "Cobalt-chromium alloy is commonly used in arthroplasty components because of its:",
              "options": [
                "Low cost and easy manufacturing",
                "High elasticity and flexibility",
                "High wear resistance and corrosion resistance",
                "Low density like titanium",
                "Bioabsorbable properties"
              ],
              "answer": "C",
              "explanation": "Cobalt-chromium (CoCr) alloys have excellent wear resistance, corrosion resistance, and high strength — making them ideal for bearing surfaces (femoral heads, tibial trays, femoral components in TKA). They are harder than titanium, making them more suitable for articulating surfaces. Titanium is preferred for implant bodies/stems due to its lower elastic modulus (closer to bone → less stress shielding), biocompatibility, and MRI compatibility. Stainless steel is cheaper and used for temporary implants (plates, screws).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 146,
              "stem": "Highly cross-linked polyethylene (XLPE) used in arthroplasty bearing surfaces is manufactured by:",
              "options": [
                "Heating the polyethylene without radiation",
                "Adding metal particles to the polymer",
                "Irradiating conventional UHMWPE with gamma radiation (5-10 Mrad) to create additional cross-links between polymer chains, then thermal treatment to remove free radicals",
                "Coating conventional PE with ceramic",
                "Using a different monomer"
              ],
              "answer": "C",
              "explanation": "Highly cross-linked polyethylene is manufactured by irradiating conventional UHMWPE with gamma radiation at doses of 5-10 Mrad (50-100 kGy) — significantly higher than the 2.5-4 Mrad used for sterilisation of conventional PE. The radiation creates free radicals that form cross-links between the long-chain PE molecules, dramatically reducing wear rates (5-10× lower than conventional PE). However, residual free radicals cause oxidation and embrittlement. To address this: remelting (eliminates free radicals but reduces mechanical properties) or annealing (retains more strength but doesn't eliminate all radicals). Vitamin E-infused XLPE is the newest generation — the antioxidant stabilises free radicals without the trade-offs of thermal treatment.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 147,
              "stem": "Cobalt-chromium (CoCr) alloy is commonly used in orthopaedic implants because of its:",
              "options": [
                "Low cost and easy manufacturing",
                "Biological similarity to bone",
                "Magnetic properties",
                "Excellent corrosion resistance, high wear resistance, and biocompatibility (ideal for bearing surfaces)",
                "Flexibility matching bone"
              ],
              "answer": "D",
              "explanation": "CoCr alloys have excellent corrosion resistance (passive chromium oxide layer), high hardness and wear resistance (ideal for bearing surfaces — femoral heads, tibial trays, femoral components), good fatigue strength, and acceptable biocompatibility. Disadvantages: higher modulus than titanium (more stress shielding), cobalt and chromium ion release (particularly in MoM bearings → ARMD), nickel content (allergy concern — some CoCr alloys contain ~1% nickel), and harder to machine than titanium. Titanium alloys (Ti-6Al-4V) are preferred for stems and plates because of their lower modulus (less stress shielding), excellent biocompatibility, and superior osteointegration. CoCr is preferred for BEARING surfaces; titanium for FIXATION/ingrowth surfaces.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Stress-Strain Curves",
          "range": "Q148-Q149",
          "questions": [
            {
              "number": 148,
              "stem": "On a stress-strain curve, the slope of the linear elastic region represents which property?",
              "options": [
                "Yield strength",
                "Ultimate tensile strength",
                "Toughness",
                "Ductility",
                "Young modulus (elastic modulus)"
              ],
              "answer": "E",
              "explanation": "The Young modulus (E) = stress/strain in the linear elastic region. It represents the stiffness of the material. A steeper slope = higher modulus = stiffer material. This is calculated before the yield point, in the region where the material behaves elastically and returns to its original shape upon unloading.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 149,
              "stem": "The area under the entire stress-strain curve up to the point of fracture represents:",
              "options": [
                "Toughness",
                "Stiffness",
                "Yield strength",
                "Resilience",
                "Hardness"
              ],
              "answer": "A",
              "explanation": "Toughness is the total energy absorbed per unit volume before fracture, represented by the entire area under the stress-strain curve. Resilience is the area under the curve up to the yield point only (energy absorbed in elastic deformation). A tough material can absorb significant energy before failure.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Viscoelasticity",
          "range": "Q150-Q151",
          "questions": [
            {
              "number": 150,
              "stem": "A tendon is held at a fixed length (constant strain). Over time the force required to maintain this length gradually decreases. This property is called:",
              "options": [
                "Creep",
                "Stress relaxation",
                "Hysteresis",
                "Fatigue",
                "Strain hardening"
              ],
              "answer": "B",
              "explanation": "Stress relaxation: constant strain applied, stress (force) decreases over time. Creep: constant stress applied, strain (deformation) increases over time. These are fundamental viscoelastic properties of biological tissues. Hysteresis is the energy lost between loading and unloading cycles (area between the two curves).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 151,
              "stem": "When a viscoelastic material is subjected to cyclical loading and unloading, the loading curve does not overlap the unloading curve. The energy lost as heat during each cycle is represented by:",
              "options": [
                "The slope of the curves",
                "The yield point",
                "The ultimate tensile strength",
                "The area between the loading and unloading curves",
                "The elastic modulus"
              ],
              "answer": "D",
              "explanation": "Hysteresis is the energy dissipated as heat during each loading-unloading cycle, graphically represented by the area enclosed between the loading and unloading curves. All biological tissues exhibit hysteresis. This property means that biological tissues are not perfectly elastic — some energy is lost in each deformation cycle.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Implant Materials",
          "range": "Q152-Q154",
          "questions": [
            {
              "number": 152,
              "stem": "Cobalt-chromium alloy has an elastic modulus of approximately 210 GPa. Titanium alloy (Ti-6Al-4V) has a modulus of approximately 110 GPa. Cortical bone has a modulus of approximately 17 GPa. Which material causes the MOST stress shielding when used as a femoral stem?",
              "options": [
                "Cobalt-chromium alloy",
                "Titanium alloy",
                "UHMWPE",
                "Cortical bone allograft",
                "Carbon fibre"
              ],
              "answer": "A",
              "explanation": "Stress shielding occurs when a stiff implant bears load that would normally be carried by bone, leading to bone resorption via Wolff's law. The greater the mismatch between implant modulus and bone modulus, the greater the stress shielding. CoCr (210 GPa) has the highest modulus mismatch with bone (17 GPa), so it causes the most stress shielding.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 153,
              "stem": "Stainless steel 316L used in orthopaedic implants contains which element to improve corrosion resistance?",
              "options": [
                "Copper",
                "Molybdenum",
                "Silver",
                "Calcium",
                "Aluminium"
              ],
              "answer": "B",
              "explanation": "316L stainless steel contains iron, chromium (~18%), nickel (~14%), and molybdenum (~3%). Chromium forms a passive oxide layer providing corrosion resistance. Molybdenum further enhances pitting corrosion resistance, particularly important in the chloride-rich physiological environment. The 'L' denotes low carbon content, reducing susceptibility to intergranular corrosion.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 154,
              "stem": "Which type of corrosion occurs at the junction between two different metals in a modular implant (e.g., at the head-neck taper of a hip prosthesis)?",
              "options": [
                "Pitting corrosion",
                "Crevice corrosion",
                "Galvanic corrosion",
                "Fretting corrosion",
                "Stress corrosion"
              ],
              "answer": "C",
              "explanation": "Galvanic corrosion occurs when two dissimilar metals are in contact in an electrolyte solution (body fluids). The less noble metal (lower electrode potential) preferentially corrodes. This is relevant at modular junctions (e.g., CoCr head on titanium stem taper). Fretting corrosion also occurs at tapers due to micromotion, and the two mechanisms often coexist.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            }
          ]
        },
        {
          "title": "Bone Cement",
          "range": "Q155-Q157",
          "questions": [
            {
              "number": 155,
              "stem": "Polymethylmethacrylate (PMMA) bone cement functions primarily as a:",
              "options": [
                "Adhesive bonding implant to bone",
                "Biological scaffold for bone ingrowth",
                "Ceramic coating",
                "Drug delivery system",
                "Grout filling the space between implant and bone"
              ],
              "answer": "E",
              "explanation": "PMMA acts as a grout (space filler), not an adhesive. It creates a mechanical interlock by filling the gaps between the implant and the trabecular bone. It does not chemically bond to either the implant or the bone. Pressurisation during insertion improves cement penetration into trabecular interstices, creating a stronger mechanical interdigitation (cement mantle).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 156,
              "stem": "During polymerisation of PMMA bone cement, the reaction is:",
              "options": [
                "Exothermic",
                "Endothermic",
                "Isothermal",
                "Reversible",
                "Catalysed by UV light"
              ],
              "answer": "A",
              "explanation": "PMMA polymerisation is an exothermic free-radical addition reaction. Temperatures at the cement-bone interface can reach 70–80°C, which can cause thermal necrosis of adjacent bone (bone cell death occurs above 56°C for >1 minute). Lavage with cold saline and improved cementing techniques help mitigate thermal damage. The initiator is benzoyl peroxide (powder) activated by N,N-dimethyl-p-toluidine (liquid).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 157,
              "stem": "Third-generation cementing technique includes all of the following EXCEPT:",
              "options": [
                "Vacuum mixing of cement",
                "Hand mixing of cement in an open bowl",
                "Pulsatile lavage of the canal",
                "Use of a distal cement restrictor",
                "Pressurisation with a cement gun"
              ],
              "answer": "B",
              "explanation": "Third-generation cementing includes: (1) pulsatile lavage and drying of the canal, (2) distal intramedullary cement restrictor, (3) retrograde cement insertion with a cement gun, (4) pressurisation, and (5) vacuum or centrifugal mixing to reduce porosity. Hand mixing in an open bowl is a first-generation technique that increases porosity and weakens the cement mantle.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Tribology",
          "range": "Q158-Q161",
          "questions": [
            {
              "number": 158,
              "stem": "In a native synovial joint, the primary mode of lubrication during high-load, low-velocity activities (e.g., standing) is:",
              "options": [
                "Hydrodynamic lubrication",
                "Boundary lubrication",
                "Squeeze-film lubrication",
                "Elastohydrodynamic lubrication",
                "Boosted lubrication"
              ],
              "answer": "C",
              "explanation": "Squeeze-film lubrication operates when two surfaces approach each other under load — the viscous synovial fluid is squeezed out from between the surfaces, but cannot escape instantaneously, creating a transient lubricating film. This is the dominant mechanism during high-load, low-velocity activities like standing still. Hydrodynamic lubrication operates during high-velocity motion. Boundary lubrication (lubricin) protects when the fluid film breaks down.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 159,
              "stem": "The dominant wear mechanism responsible for osteolysis following total hip arthroplasty with a metal-on-polyethylene bearing is:",
              "options": [
                "Fatigue wear",
                "Corrosive wear",
                "Erosive wear",
                "Adhesive and abrasive wear",
                "Third-body wear only"
              ],
              "answer": "D",
              "explanation": "Adhesive and abrasive wear are the primary mechanisms generating submicron polyethylene particles in metal-on-polyethylene THA. Adhesive wear occurs when asperities on the surfaces bond and tear off. Abrasive wear occurs when a harder surface (metal) scratches the softer surface (polyethylene). These submicron particles trigger the macrophage-mediated osteolytic cascade. Third-body wear (from bone/cement particles) accelerates the process but is not the dominant mechanism.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 160,
              "stem": "Cross-linked polyethylene was developed to reduce wear. The cross-linking process involves:",
              "options": [
                "Adding carbon fibres to the polymer",
                "Mixing with ceramic particles",
                "Heating above melting point only",
                "Adding antioxidants only",
                "Gamma irradiation to create cross-links between polymer chains"
              ],
              "answer": "E",
              "explanation": "Highly cross-linked polyethylene (HXLPE) is produced by exposing conventional UHMWPE to high-dose gamma or electron beam irradiation (typically 50–100 kGy), which creates cross-links between polymer chains. This dramatically reduces adhesive/abrasive wear rates (by 60–90% in simulator studies). Post-irradiation thermal treatment (remelting or annealing) reduces free radicals that cause oxidative degradation. Vitamin E can also be added as an antioxidant.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            },
            {
              "number": 161,
              "stem": "In arthroplasty tribology, 'third-body wear' refers to:",
              "options": [
                "Wear between the two articulating surfaces only",
                "Wear from corrosion products",
                "Wear caused by particles trapped between the bearing surfaces",
                "Wear from cyclic loading",
                "Wear from impingement"
              ],
              "answer": "C",
              "explanation": "Third-body wear occurs when foreign particles (cement debris, metal fragments, bone particles, broken PMMA, ceramic fragments) become trapped between the bearing surfaces and accelerate wear. The four modes of wear described by McKellop: Mode 1 = articulation between intended surfaces (normal). Mode 2 = bearing against non-bearing surface (e.g., head against rim). Mode 3 = third-body particles between bearings. Mode 4 = two non-bearing surfaces rubbing (e.g., backside wear of PE insert against metal tray).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Ceramics",
          "range": "Q162-Q163",
          "questions": [
            {
              "number": 162,
              "stem": "The main advantage of a ceramic-on-ceramic bearing couple in total hip arthroplasty compared to metal-on-polyethylene is:",
              "options": [
                "Lower dislocation rate",
                "Easier revision surgery",
                "Lower cost",
                "Greater range of head sizes",
                "Dramatically lower volumetric wear rate"
              ],
              "answer": "E",
              "explanation": "Ceramic-on-ceramic (CoC) bearings have dramatically lower volumetric wear rates compared to metal-on-polyethylene, producing fewer and biologically inert wear particles. This significantly reduces the risk of osteolysis and aseptic loosening. The main disadvantage is the risk of ceramic fracture (rare with modern 4th-generation alumina/BIOLOX delta) and audible squeaking.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 163,
              "stem": "Alumina ceramic used in joint replacements has which key mechanical property?",
              "options": [
                "High ductility",
                "High hardness and scratch resistance",
                "High tensile strength",
                "High elasticity",
                "High porosity"
              ],
              "answer": "B",
              "explanation": "Alumina (Al₂O₃) ceramic has exceptional hardness, scratch resistance, and wettability, making it an excellent bearing surface. Its hardness means it maintains a smooth surface finish, reducing adhesive/abrasive wear. However, ceramics are brittle (low fracture toughness) and can fracture catastrophically with no plastic deformation warning. Modern 4th-generation ceramics (BIOLOX delta) add zirconia to improve toughness.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Joint Reaction Force",
          "range": "Q164-Q167",
          "questions": [
            {
              "number": 164,
              "stem": "During single-leg stance, the hip joint reaction force is approximately how many times body weight?",
              "options": [
                "2.5–3 times",
                "0.5 times",
                "1 times",
                "5 times",
                "8 times"
              ],
              "answer": "A",
              "explanation": "During single-leg stance, the abductor muscles must generate force to balance the body weight acting through the centre of mass. Using a free body diagram: the body weight lever arm is approximately 3 times the abductor lever arm. Therefore, abductor force ≈ 2× body weight, and JRF ≈ body weight + abductor force ≈ 3× body weight. During running, JRF increases to 5–8× body weight.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 165,
              "stem": "A patient uses a walking stick in the CONTRALATERAL hand. This reduces the hip joint reaction force by approximately:",
              "options": [
                "10%",
                "50–60%",
                "80%",
                "25–30%",
                "It increases JRF"
              ],
              "answer": "D",
              "explanation": "A walking stick in the contralateral hand creates an additional moment arm on the opposite side of the body from the affected hip, reducing the force the abductors need to generate to maintain pelvic equilibrium. This reduces the JRF by approximately 25–30%. The stick should be used on the contralateral side and advanced with the affected leg (reciprocal gait pattern).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            },
            {
              "number": 166,
              "stem": "Increasing the femoral offset during total hip arthroplasty has which effect on hip biomechanics?",
              "options": [
                "Decreases the abductor moment arm and increases JRF",
                "Has no effect on JRF",
                "Increases leg length only",
                "Reduces stability only",
                "Increases the abductor moment arm and reduces JRF"
              ],
              "answer": "E",
              "explanation": "Increasing femoral offset lengthens the perpendicular distance from the centre of the femoral head to the abductor muscle line of action (abductor moment arm). A longer moment arm means less abductor force is needed to maintain pelvic balance during gait. Since JRF = body weight + abductor force, reducing abductor force reduces JRF. Additional benefits: increased soft tissue tension (stability) and restored abductor function.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 167,
              "stem": "Using a walking stick in the contralateral hand reduces the hip joint reaction force (JRF) by approximately:",
              "options": [
                "10%",
                "60%",
                "30%",
                "90%",
                "No effect"
              ],
              "answer": "B",
              "explanation": "Using a walking stick in the CONTRALATERAL hand reduces the hip JRF by approximately 60%. The stick acts as a lever — applying a force through the stick creates a moment about the hip that opposes the body weight moment, dramatically reducing the abductor muscle force required to stabilise the pelvis. Since JRF = body weight + abductor muscle force, reducing the abductor demand reduces the total JRF. This is why a stick must be used in the OPPOSITE hand (contralateral) — using it on the same (ipsilateral) side actually INCREASES the abductor moment arm requirement. The JRF on a normal hip during single-leg stance is approximately 2.5-3× body weight.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "AO Principles",
          "range": "Q168-Q169",
          "questions": [
            {
              "number": 168,
              "stem": "The four AO principles of fracture management are anatomical reduction, stable fixation, preservation of blood supply, and:",
              "options": [
                "Early active mobilisation",
                "Antibiotic prophylaxis",
                "Compression plating",
                "Prolonged immobilisation",
                "Bone grafting"
              ],
              "answer": "A",
              "explanation": "The four AO/ASIF principles: (1) Anatomical reduction (especially articular fractures), (2) Stable fixation (absolute or relative as appropriate), (3) Preservation of blood supply to bone and soft tissues, (4) Early active pain-free mobilisation. These principles guide all fracture treatment decisions and are foundational to orthopaedic trauma surgery.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 169,
              "stem": "The four AO principles of fracture management are:",
              "options": [
                "Rest, Ice, Compression, Elevation",
                "Debridement, antibiotics, fixation, closure",
                "Anatomical reduction, stable fixation, preservation of blood supply, early mobilisation",
                "Traction, casting, physiotherapy, follow-up",
                "Reduction, retention, rehabilitation, review"
              ],
              "answer": "C",
              "explanation": "The four AO principles: (1) Anatomical reduction of fracture fragments (particularly intra-articular fractures). (2) Stable internal fixation to meet biomechanical requirements (absolute stability for simple fractures, relative stability for comminuted). (3) Preservation of blood supply to soft tissues and bone through gentle handling and biological fixation techniques. (4) Early, safe mobilisation of the limb and patient. These principles have evolved — modern AO emphasises biological fixation (preserving blood supply) over anatomical reduction of every fragment in comminuted fractures.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Fracture Fixation",
          "range": "Q170-Q176",
          "questions": [
            {
              "number": 170,
              "stem": "A lag screw achieves interfragmentary compression by:",
              "options": [
                "Threading into both cortices equally",
                "Being inserted without pre-drilling",
                "Using a washer to distribute load",
                "Creating a gliding hole in the near cortex and a threaded hole in the far cortex",
                "Being made of a more flexible material"
              ],
              "answer": "D",
              "explanation": "A lag screw works by creating a gliding hole (larger than the screw thread outer diameter) in the near cortex and a threaded hole (drilled with the appropriate drill bit for the core diameter) in the far cortex. When tightened, the screw threads grip only the far fragment, pulling it toward the near fragment and generating interfragmentary compression. This can be achieved with a partially threaded cancellous screw or by over-drilling the near cortex for a fully threaded cortical screw.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 171,
              "stem": "Compared to a non-locked plate, a locked plate construct has which biomechanical advantage?",
              "options": [
                "Greater interfragmentary compression",
                "Greater plate-bone friction",
                "More anatomical reduction",
                "Easier removal",
                "Higher pull-out strength in osteoporotic bone"
              ],
              "answer": "E",
              "explanation": "Locked plates create a fixed-angle construct where screws lock into the plate, functioning as an internal fixator. They do not rely on plate-bone friction for stability. This provides superior pull-out strength in osteoporotic (poor quality) bone and in periarticular/metaphyseal fractures where unicortical fixation may be necessary. Conventional plates rely on friction between plate and bone (compression).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 172,
              "stem": "The working length of an intramedullary nail is defined as the distance between:",
              "options": [
                "The two most proximal screws",
                "The proximal and distal interlocking screws closest to the fracture",
                "The tip of the nail and the most distal screw",
                "The entry point and the fracture site",
                "The two ends of the nail"
              ],
              "answer": "B",
              "explanation": "The working length of an IM nail is the unsupported length between the proximal and distal interlocking screws closest to the fracture. A longer working length means more elastic deformation is distributed over a greater length, reducing stress at any one point and allowing more controlled micromotion for secondary healing. In comminuted fractures, the working length is effectively the entire distance between the closest locking bolts.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 173,
              "stem": "Tension band wiring converts a tensile force on the convex side of a fracture into compression across the entire fracture surface. This principle is best applied to which fracture?",
              "options": [
                "Comminuted femoral shaft fracture",
                "Segmental tibial fracture",
                "Distal femoral fracture",
                "Transverse olecranon fracture",
                "Spiral humeral shaft fracture"
              ],
              "answer": "D",
              "explanation": "Tension band wiring is ideally suited for transverse fractures in bones where a muscle force creates a tensile load on one side. The classic example is the olecranon: triceps pulls create tension on the posterior (convex) surface. The tension band wire converts this tensile force into compression across the fracture when the elbow flexes. Other applications: patella fractures (quadriceps pull) and greater trochanter fractures (abductor pull). It requires an intact cortex opposite the wire.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            },
            {
              "number": 174,
              "stem": "A plate applied to the tension side of a long bone fracture (e.g., lateral femur) is biomechanically advantageous because:",
              "options": [
                "It is easier to apply surgically",
                "It allows the plate to be shorter",
                "It acts as a tension band, converting tensile forces to compression",
                "It reduces the risk of infection",
                "It avoids the neurovascular structures"
              ],
              "answer": "C",
              "explanation": "Placing a plate on the tension side of the bone means the plate resists the tensile forces while the opposite (compression) cortex bears compressive load. This is biomechanically efficient because the plate converts the bending moment into compression across the fracture on the opposite cortex, similar to the tension band principle. The femoral lateral cortex is the tension side during weight-bearing.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 175,
              "stem": "A lag screw achieves interfragmentary compression by:",
              "options": [
                "Having threads only at the tip (gliding hole in near cortex, purchase in far cortex)",
                "Having threads along its entire length",
                "Being made of a softer material",
                "Using cement augmentation",
                "Being longer than the fracture gap"
              ],
              "answer": "A",
              "explanation": "A lag screw has threads only at its tip. The near cortex is over-drilled to create a gliding hole (the smooth shaft slides through without engaging). The far cortex is drilled to the core diameter and the threads engage. As the screw is tightened, the head pulls the near fragment towards the far fragment, generating interfragmentary compression. This can be achieved with a partially threaded screw (dedicated lag screw) or by over-drilling the near cortex of a fully threaded screw (lag technique). Compression is perpendicular to the fracture plane.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 176,
              "stem": "Locking plate fixation provides angular stability. This is most advantageous in:",
              "options": [
                "Young patients with excellent bone quality",
                "Simple diaphyseal fractures in healthy bone",
                "All fractures equally",
                "Periarticular fractures in osteoporotic bone",
                "Only in open fractures"
              ],
              "answer": "D",
              "explanation": "Locking plates create a fixed-angle construct between the screw heads and the plate (screws lock into threaded plate holes). This provides angular stability independent of plate-bone friction — unlike conventional plates which rely on compression against the bone surface. Locking plates are most advantageous in osteoporotic bone (where conventional screw purchase is poor), periarticular fractures (where screws may be short and purchase limited), and bridging comminuted fractures (where the plate acts as an internal splint). They function as internal external fixators.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Polymers",
          "range": "Q177-Q178",
          "questions": [
            {
              "number": 177,
              "stem": "Ultra-high molecular weight polyethylene (UHMWPE) used in joint arthroplasty has a molecular weight of approximately:",
              "options": [
                "2–6 million",
                "100,000",
                "500,000",
                "10 million",
                "50 million"
              ],
              "answer": "A",
              "explanation": "UHMWPE has a molecular weight of 2–6 million g/mol, giving it superior wear resistance, impact strength, and low friction coefficient. It is manufactured by compression moulding or ram extrusion of UHMWPE powder. Sterilisation methods (gamma irradiation in air vs. inert gas) significantly affect long-term oxidative degradation and wear.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 178,
              "stem": "Gamma irradiation of polyethylene in air causes which long-term problem?",
              "options": [
                "Increased cross-linking only",
                "Melting of the polymer",
                "Increased molecular weight",
                "Reduced sterilisation efficacy",
                "Oxidative degradation and embrittlement"
              ],
              "answer": "E",
              "explanation": "Gamma irradiation in air generates free radicals within the polyethylene. These free radicals react with oxygen over time, causing oxidative chain scission (breaking of polymer chains), which leads to degradation, embrittlement, delamination, and accelerated wear. Modern sterilisation uses gamma irradiation in an inert atmosphere (nitrogen or vacuum) or gas plasma/ethylene oxide to avoid this problem.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            }
          ]
        },
        {
          "title": "Bone Grafts",
          "range": "Q179",
          "questions": [
            {
              "number": 179,
              "stem": "A bone graft that only provides a scaffold for new bone to grow across is described as:",
              "options": [
                "Osteogenic",
                "Osteoinductive",
                "Osteoconductive",
                "Osteoprogenitive",
                "Osteolytic"
              ],
              "answer": "C",
              "explanation": "Osteoconduction means the graft provides a physical scaffold or framework upon which host bone can grow. Synthetic bone substitutes (hydroxyapatite, tricalcium phosphate) and processed allografts are primarily osteoconductive. Osteoinduction is the ability to stimulate stem cells to differentiate into osteoblasts (e.g., BMPs). Osteogenesis requires living cells that directly form new bone.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Prostheses & Orthoses",
          "range": "Q180",
          "questions": [
            {
              "number": 180,
              "stem": "An ankle-foot orthosis (AFO) is most commonly prescribed for which condition?",
              "options": [
                "Hip flexion contracture",
                "Foot drop",
                "Knee valgus deformity",
                "Hallux valgus",
                "Femoral anteversion"
              ],
              "answer": "B",
              "explanation": "An AFO is most commonly used for foot drop (weakness of ankle dorsiflexion due to peroneal nerve palsy, L5 radiculopathy, stroke, or other neurological conditions). It maintains the ankle in a neutral or slightly dorsiflexed position during swing phase, preventing the foot from dragging. Types include solid AFO, hinged AFO, and posterior leaf spring.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Theatre Design",
          "range": "Q181",
          "questions": [
            {
              "number": 181,
              "stem": "Laminar airflow in orthopaedic theatres reduces surgical site infection by:",
              "options": [
                "Sterilising all bacteria in the air",
                "Increasing theatre temperature",
                "Reducing noise levels",
                "Eliminating the need for prophylactic antibiotics",
                "Providing unidirectional filtered air flow over the surgical field"
              ],
              "answer": "E",
              "explanation": "Laminar (ultra-clean) airflow systems deliver unidirectional filtered air (through HEPA filters) vertically downward over the operative field, reducing airborne bacterial contamination. Lidwell's landmark study showed that ultra-clean air combined with body-exhaust suits significantly reduced deep infection rates in joint arthroplasty. Standard theatre air has ~10 colony-forming units/m³; laminar flow reduces this to <1 CFU/m³.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Corrosion",
          "range": "Q182-Q183",
          "questions": [
            {
              "number": 182,
              "stem": "The passive oxide layer on titanium that provides corrosion resistance is composed of:",
              "options": [
                "Titanium carbide",
                "Titanium nitride",
                "Titanium dioxide (TiO₂)",
                "Titanium sulphide",
                "Titanium phosphate"
              ],
              "answer": "C",
              "explanation": "Titanium forms a stable, self-repairing titanium dioxide (TiO₂) passive oxide layer on its surface when exposed to oxygen. This layer is only 5–10 nm thick but provides excellent corrosion resistance in physiological environments. If damaged (e.g., during surgery), it reforms spontaneously within nanoseconds (self-passivation). This biocompatibility and corrosion resistance are key reasons for titanium's widespread use in orthopaedics.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 183,
              "stem": "Galvanic corrosion in orthopaedic implants occurs when:",
              "options": [
                "A single metal is exposed to body fluids",
                "A metal is bent repeatedly",
                "A screw is overtightened",
                "Two dissimilar metals are in contact in an electrolyte solution",
                "Cement degrades around the implant"
              ],
              "answer": "D",
              "explanation": "Galvanic corrosion occurs when two dissimilar metals (e.g., stainless steel screw in a titanium plate) are in contact in an electrolyte (body fluids). The more electronegative (anodic) metal corrodes preferentially. This is why mixing metals should be avoided in orthopaedic fixation — use titanium screws with titanium plates, or stainless steel with stainless steel. Other corrosion types: crevice (in confined spaces, e.g., screw-plate junction), fretting (micromotion at interfaces), and stress corrosion (combined stress + corrosion).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Statistics",
          "range": "Q184-Q185",
          "questions": [
            {
              "number": 184,
              "stem": "The sensitivity of a diagnostic test is defined as:",
              "options": [
                "The proportion of true positives among those with disease",
                "The proportion of true negatives among those without disease",
                "The proportion of true positives among all positive results",
                "The proportion of true negatives among all negative results",
                "The overall accuracy of the test"
              ],
              "answer": "A",
              "explanation": "Sensitivity = true positives / (true positives + false negatives) = proportion of people WITH the disease who test positive. It measures the test's ability to correctly identify those with the disease. A highly sensitive test is good for 'ruling out' disease (SnNOut — Sensitive test, Negative result, rules Out). Specificity = proportion of people WITHOUT disease who test negative.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 185,
              "stem": "A Type I error in a clinical trial is:",
              "options": [
                "Failing to detect a true difference",
                "Detecting a difference when none exists (false positive)",
                "Errors in data collection",
                "Errors in randomisation",
                "Bias in patient selection"
              ],
              "answer": "B",
              "explanation": "A Type I error (alpha error) is rejecting the null hypothesis when it is actually true — finding a statistically significant difference when no real difference exists (false positive). The probability of a Type I error is set by the significance level (α), conventionally 0.05 (5%). A Type II error (beta error) is failing to reject the null hypothesis when it is false — missing a real difference (false negative). Power = 1 − β.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Stress & Strain",
          "range": "Q186",
          "questions": [
            {
              "number": 186,
              "stem": "On a stress-strain curve for cortical bone, the area under the curve up to the point of fracture represents:",
              "options": [
                "Stiffness",
                "Yield strength",
                "Ultimate tensile strength",
                "Elastic modulus",
                "Toughness (energy absorbed to failure)"
              ],
              "answer": "E",
              "explanation": "Toughness is the total energy absorbed by the material before fracture, represented by the TOTAL area under the stress-strain curve. Stiffness (Young's modulus/elastic modulus) is the slope of the linear (elastic) portion. Yield strength is the stress at which permanent (plastic) deformation begins. Ultimate tensile strength (UTS) is the maximum stress sustained. Resilience is the area under the elastic portion only.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Implants",
          "range": "Q187-Q188",
          "questions": [
            {
              "number": 187,
              "stem": "PMMA bone cement achieves fixation by:",
              "options": [
                "Chemical bonding to bone",
                "Biological ingrowth of bone into the cement",
                "Magnetic attraction to metal implants",
                "Mechanical interdigitation into cancellous bone trabeculae",
                "Suture attachment to periosteum"
              ],
              "answer": "D",
              "explanation": "PMMA (polymethylmethacrylate) bone cement achieves fixation by mechanical interdigitation — it flows into the cancellous bone trabeculae and surface irregularities, then polymerises in situ, creating a mechanical interlock. There is NO chemical bond between cement and bone or between cement and the implant. Cement acts as a grout, not a glue. Modern cementing technique (3rd generation): pulsed lavage, drying, cement restrictor, retrograde injection, pressurisation → improved cement mantle (Barrack Grade A).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 188,
              "stem": "Stress shielding around a femoral stem in THA occurs because:",
              "options": [
                "The cement is too thin",
                "The stem absorbs all load, reducing stress on surrounding bone → bone resorbs (Wolff's law)",
                "Infection weakens the bone",
                "The bearing surface produces debris",
                "The cup is malpositioned"
              ],
              "answer": "B",
              "explanation": "Stress shielding occurs when a stiff implant (particularly a large, stiff, fully coated uncemented stem) absorbs the majority of load, bypassing the surrounding bone. According to Wolff's law (bone remodels in response to mechanical load), the unloaded bone resorbs. This is seen as proximal femoral bone loss around well-fixed uncemented stems — particularly in the calcar region (Gruen zone 7). Reducing stem stiffness (shorter, tapered, proximal coating only) minimises stress shielding.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Joint Mechanics",
          "range": "Q189",
          "questions": [
            {
              "number": 189,
              "stem": "During single-leg stance, the joint reaction force (JRF) across the hip is approximately:",
              "options": [
                "2.5-3 × body weight",
                "0.5 × body weight",
                "1 × body weight",
                "5-6 × body weight",
                "10 × body weight"
              ],
              "answer": "A",
              "explanation": "During single-leg stance, the hip JRF is approximately 2.5-3× body weight. This is because the abductor muscles (gluteus medius/minimus) must generate significant force to keep the pelvis level — the lever arm of body weight about the hip centre is approximately 3× longer than the abductor lever arm (offset). By moments equilibrium: abductor force ≈ 2× body weight, and the JRF (sum of body weight + abductor force) ≈ 3× body weight. During running, JRF can reach 5-8× body weight.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Gait",
          "range": "Q190",
          "questions": [
            {
              "number": 190,
              "stem": "During normal gait, the stance phase accounts for approximately what percentage of the gait cycle?",
              "options": [
                "30%",
                "40%",
                "60%",
                "80%",
                "95%"
              ],
              "answer": "C",
              "explanation": "Normal gait cycle: stance phase ~60% (foot is in contact with the ground) and swing phase ~40% (foot is off the ground). Stance phase subdivisions: heel strike → foot flat → midstance → heel off → toe off. Swing phase: initial swing → mid-swing → terminal swing. Double support (both feet on ground) occurs at the beginning and end of stance phase — accounts for ~20% of the gait cycle. As walking speed increases, double support time decreases. In running, there is NO double support (and a float phase where neither foot is on the ground). Trendelenburg gait, antalgic gait, and other pathological gaits alter these percentages — antalgic gait shortens stance phase on the painful side.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Plate Mechanics",
          "range": "Q191-Q192",
          "questions": [
            {
              "number": 191,
              "stem": "The 'working length' of a plate is defined as the distance between:",
              "options": [
                "The two ends of the plate",
                "The plate and the bone surface",
                "The first and last screw holes",
                "The two screws closest to the fracture on either side",
                "The fracture site and the nearest joint"
              ],
              "answer": "D",
              "explanation": "The working length of a plate is the distance between the two screws nearest to the fracture (one on each side). A longer working length distributes strain over a greater distance, reducing stress concentration at any single point — this is beneficial for bridging comminuted fractures (allows micromotion for secondary healing). A shorter working length (screws close to the fracture) increases construct stiffness — desirable for absolute stability in simple fractures with lag screw fixation. Working length is a critical concept in fracture fixation biomechanics.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 192,
              "stem": "The bending stiffness of a plate is proportional to the:",
              "options": [
                "Length of the plate",
                "Thickness (height) of the plate cubed",
                "Width of the plate squared",
                "Number of screw holes",
                "Weight of the plate"
              ],
              "answer": "B",
              "explanation": "Bending stiffness (rigidity) of a plate is proportional to the elastic modulus (E) × the moment of inertia (I). For a rectangular cross-section plate: I = (width × thickness³)/12. Therefore, bending stiffness is proportional to thickness CUBED — doubling the plate thickness increases stiffness 8-fold. Width has a linear effect. This is why increasing plate thickness is far more effective than increasing width for improving stiffness. For a cylindrical nail: I = π(r⁴)/4 — stiffness proportional to the 4th power of the radius.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            }
          ]
        },
        {
          "title": "Implant Mechanics",
          "range": "Q193",
          "questions": [
            {
              "number": 193,
              "stem": "An intramedullary nail provides which type of fixation?",
              "options": [
                "Absolute stability with interfragmentary compression",
                "No mechanical support",
                "Pure tension band fixation",
                "External splinting only",
                "Relative stability as a load-sharing device"
              ],
              "answer": "E",
              "explanation": "An IM nail provides relative stability — it acts as a load-sharing (splinting) device that allows controlled micromotion at the fracture site, promoting secondary (indirect/callus) fracture healing. The nail shares the load with the bone rather than bearing it entirely (unlike a plate which can be load-bearing). Advantages: load-sharing, minimal periosteal stripping (closed technique), early weight-bearing. Reaming: increases canal diameter for a larger nail, provides autograft (reaming debris), but temporarily disrupts endosteal blood supply (recovers within weeks from periosteal supply).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Implant Design",
          "range": "Q194",
          "questions": [
            {
              "number": 194,
              "stem": "A polished tapered cemented femoral stem (e.g., Exeter/CPT) achieves fixation by:",
              "options": [
                "Bone ingrowth into the stem surface",
                "Mechanical interlock between the stem and cement via surface texture",
                "Subsidence within the cement mantle generating hoop stresses that compress the cement against the bone (taper-slip principle)",
                "Press-fit into the canal without cement",
                "Screw fixation into the femur"
              ],
              "answer": "C",
              "explanation": "Polished tapered stems (double-taper or triple-taper design) are designed to subside slightly within the cement mantle over time. As the polished tapered stem slides distally (subsides), it generates radial (hoop) compressive stresses that push the cement outward against the bone — maintaining and potentially improving fixation over time ('taper-slip' or 'force-closed' fixation). This is fundamentally different from composite-beam (shape-closed) stems (matt/textured surface, e.g., Charnley, Lubinus) which bond to the cement and rely on the stem-cement-bone construct acting as a single unit. The Exeter stem (Stryker) is the most successful polished tapered stem, with 30+ year survival data exceeding 95%. The cement mantle must be intact and well-pressurised for taper-slip to work.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            }
          ]
        }
      ]
    },
    {
      "title": "Biomaterials",
      "chapters": [
        {
          "title": "Biomaterials: Metals",
          "range": "Q195-Q204",
          "questions": [
            {
              "number": 195,
              "stem": "Which orthopaedic metal has the LOWEST Young's modulus and therefore causes the LEAST stress shielding?",
              "options": [
                "Titanium alloy (Ti-6Al-4V)",
                "Stainless steel 316L",
                "Cobalt-chrome (CoCrMo)",
                "Tantalum",
                "Nitinol"
              ],
              "answer": "A",
              "explanation": "Ti-6Al-4V has a Young's modulus of approximately 110 GPa — the lowest of the three main orthopaedic metals. Stainless steel is ~200 GPa and cobalt-chrome is ~230 GPa. Since stress shielding is proportional to the modulus mismatch between implant and bone (17-20 GPa), titanium produces the least stress shielding. This is one reason titanium is preferred for uncemented femoral stems. Tantalum (~186 GPa) and nitinol (28-83 GPa depending on phase) are less commonly used.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 196,
              "stem": "Particle disease leading to periprosthetic osteolysis is caused primarily by:",
              "options": [
                "Infection",
                "Mechanical loosening from cement failure",
                "Macrophage-mediated inflammatory response to wear debris",
                "Direct toxicity of metal ions",
                "Stress shielding"
              ],
              "answer": "C",
              "explanation": "Particle disease (Willert & Semlitsch 1977) is the biological response to wear debris (primarily submicron PE particles). Macrophages phagocytose particles, undergo frustrated phagocytosis, and release pro-inflammatory cytokines (IL-1, IL-6, TNF-alpha). These stimulate RANKL expression, driving osteoclast-mediated bone resorption via the RANK/RANKL/OPG pathway (see Ch 2). This creates progressive osteolysis and eventually mechanical loosening. It is the most common cause of long-term THA failure.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 197,
              "stem": "The 'race for the surface' theory (Gristina 1987) describes:",
              "options": [
                "Competition between host cells and bacteria to colonise an implant surface",
                "Competition between osteoblasts and osteoclasts on bone surface",
                "Competition between different metal alloys in galvanic corrosion",
                "Competition between cement and bone for implant fixation",
                "Competition between different bacterial species in biofilm"
              ],
              "answer": "A",
              "explanation": "Gristina's 'race for the surface' describes the critical competition between host tissue cells and bacteria to colonise a newly implanted surface. If host cells (osteoblasts, fibroblasts) colonise the surface first, they form a protective tissue seal. If bacteria win, they form a biofilm (glycocalyx-protected community) that resists antibiotics and immune clearance. This concept drives: surface coatings for osseointegration (HA, porous metal), antibiotic-loaded cement, perioperative antibiotics, and meticulous aseptic technique.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 198,
              "stem": "Galvanic corrosion occurs when:",
              "options": [
                "A single metal corrodes in saline",
                "A metal is subjected to cyclic loading",
                "Metal ion allergy develops",
                "Two dissimilar metals are in contact in an electrolyte",
                "The passivation layer is intact"
              ],
              "answer": "D",
              "explanation": "Galvanic corrosion occurs when two DISSIMILAR metals are in electrical contact in an electrolyte (body fluid). The more reactive (anodic) metal preferentially corrodes. This is why metals should never be mixed in the same construct (e.g., a stainless steel screw in a titanium plate). The resulting corrosion products can cause local tissue reactions and implant failure. Other corrosion types include: crevice (in stagnant areas between components), fretting (at micromotion interfaces), pitting (localised attack through passivation layer).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 199,
              "stem": "Osseointegration, as described by Branemark, refers to:",
              "options": [
                "Fibrous tissue encapsulation of the implant",
                "Direct bone-implant contact without intervening soft tissue",
                "Cement bonding to bone",
                "Metal bonding to ceramic",
                "Inflammatory tissue reaction to implant"
              ],
              "answer": "B",
              "explanation": "Branemark (1977) defined osseointegration as direct structural and functional connection between living bone and the surface of a load-bearing implant, without intervening fibrous tissue. This is the biological basis of uncemented implant fixation. Titanium achieves osseointegration because its spontaneous TiO2 oxide layer is biocompatible and allows osteoblast attachment and bone formation directly onto the surface. Surface modifications (HA coating, porous coating, grit blasting) enhance osseointegration by increasing surface area and promoting osteoblast activity.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 200,
              "stem": "The passivation layer on stainless steel implants is formed by which element?",
              "options": [
                "Iron",
                "Nickel",
                "Molybdenum",
                "Carbon",
                "Chromium"
              ],
              "answer": "E",
              "explanation": "The corrosion resistance of stainless steel depends on a thin, self-healing passivation layer of chromium oxide (Cr2O3) that forms spontaneously on the surface when chromium content exceeds approximately 12%. In 316L stainless steel (20% chromium), this oxide layer prevents further corrosion by acting as a barrier between the metal and the body fluid electrolyte. If the passivation layer is disrupted (e.g., by fretting, scratching, or oxygen-depleted crevices), localised corrosion can occur. Titanium forms a similar but more robust TiO2 passivation layer.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 201,
              "stem": "Which metal property makes titanium UNSUITABLE as an articular bearing surface?",
              "options": [
                "Low Young's modulus",
                "High biocompatibility",
                "Poor wear resistance (notch sensitivity)",
                "Excellent corrosion resistance",
                "Non-ferromagnetic nature"
              ],
              "answer": "C",
              "explanation": "Titanium has poor WEAR resistance due to its susceptibility to surface damage and notch sensitivity. The soft TiO2 oxide layer can be scratched during articulation, exposing the underlying metal to accelerated wear. Titanium produces third-body wear particles that cause metallosis and tissue damage. This is why titanium is NEVER used as an articular bearing surface. Cobalt-chrome (harder, better wear resistance) or ceramic (alumina/zirconia, hardest) are used for bearing surfaces. Titanium is ideal for bone-contact surfaces (stems, cups, plates) where osseointegration and lower stress shielding are priorities.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 202,
              "stem": "The critical particle size for macrophage activation in particle disease is:",
              "options": [
                "0.001-0.01 micrometres",
                "50-100 micrometres",
                "500-1000 micrometres",
                "0.3-10 micrometres",
                "Greater than 1mm"
              ],
              "answer": "D",
              "explanation": "The critical particle size for biological activity is 0.3-10 micrometres — this corresponds to the size range that can be phagocytosed by macrophages. Particles smaller than 0.3 micrometres may not be efficiently phagocytosed; particles larger than 10 micrometres are too big for individual macrophage uptake (though they may trigger giant cell formation). Within the critical range, smaller particles are more biologically active per unit volume because there are more of them (greater total surface area). Highly cross-linked PE produces fewer particles AND the particles are smaller, which paradoxically could be more inflammatory — but the net effect is less osteolysis because the total particle volume is dramatically reduced.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 203,
              "stem": "Cobalt-chrome alloy is used for femoral head bearing surfaces primarily because of its:",
              "options": [
                "Low cost",
                "Excellent wear resistance and surface finish",
                "Low Young's modulus",
                "Ease of contouring",
                "MRI compatibility"
              ],
              "answer": "B",
              "explanation": "CoCr is chosen for femoral head bearing surfaces because it has excellent wear resistance (hard, maintains surface finish), excellent corrosion resistance, and can be polished to a mirror finish (low surface roughness reduces PE wear). It has the highest hardness and fatigue strength of orthopaedic metals. Its disadvantages (high modulus = stress shielding, cannot be contoured, metal ion concerns in MoM) are acceptable in this application because the bearing surface requires hardness and wear resistance above all.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 204,
              "stem": "A patient with a metal-on-metal hip replacement develops a painful hip with normal inflammatory markers. What is the most likely diagnosis?",
              "options": [
                "Adverse local tissue reaction (ALVAL) to metal debris",
                "Infection",
                "Particle disease from PE wear",
                "Periprosthetic fracture",
                "Heterotopic ossification"
              ],
              "answer": "A",
              "explanation": "Adverse local tissue reaction (ALVAL) or adverse reaction to metal debris (ARMD) is a distinctive complication of MoM bearings. Metal wear particles (CoCr) generate cobalt and chromium ions that trigger a type IV hypersensitivity reaction (delayed-type, T-cell mediated) rather than the macrophage-mediated particle disease seen with PE. Clinically: painful hip, pseudotumour (fluid collection/solid mass), tissue necrosis, elevated blood metal ion levels (Co and Cr), normal CRP/ESR (distinguishes from infection). Investigation: blood metal ions, MARS MRI (Metal Artefact Reduction Sequence). This complication led to the withdrawal of large-diameter MoM bearings from widespread use.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Biomaterials: Polymers",
          "range": "Q205-Q214",
          "questions": [
            {
              "number": 205,
              "stem": "Highly cross-linked polyethylene reduces wear compared to conventional UHMWPE by approximately:",
              "options": [
                "10-20%",
                "30-40%",
                "50-60%",
                "99%",
                "80-90%"
              ],
              "answer": "E",
              "explanation": "Muratoglu et al. (2001) demonstrated that HXLPE (irradiated to 50-100 kGy) reduces wear by 80-90% in hip simulator studies compared to conventional UHMWPE. This dramatic reduction has significantly decreased the incidence of osteolysis and extended implant longevity. Clinical registry data confirms markedly lower revision rates for osteolysis with HXLPE at 10-15 year follow-up.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 206,
              "stem": "The exothermic polymerisation of PMMA bone cement reaches peak temperatures of approximately:",
              "options": [
                "37-40°C",
                "47-50°C",
                "150-200°C",
                "70-120°C",
                "300°C"
              ],
              "answer": "D",
              "explanation": "PMMA polymerisation reaches peak temperatures of 70-120°C, well above the thermal necrosis threshold of bone (47°C for 1 minute, Eriksson 1983). The zone of thermal necrosis extends approximately 0.5-2mm from the cement mantle. Lavage cooling and optimal cement mantle thickness (2-3mm) help mitigate thermal damage. Thicker cement mantles and larger volumes generate more heat.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 207,
              "stem": "Bone cement implantation syndrome (BCIS) during cemented arthroplasty is primarily caused by:",
              "options": [
                "Fat and marrow embolisation during cement pressurisation",
                "Allergic reaction to PMMA",
                "Toxic monomer entering the bloodstream",
                "Thermal damage to surrounding tissues",
                "Antibiotic toxicity from cement"
              ],
              "answer": "A",
              "explanation": "BCIS is primarily caused by fat, marrow, and cement emboli entering the venous system during pressurisation of cement into the medullary canal. This triggers a cascade of cardiovascular effects: hypotension, hypoxia, cardiac arrhythmias, and in severe cases cardiac arrest. Risk factors include: long-stem revision, simultaneous bilateral procedures, pre-existing cardiopulmonary disease, and failure to use a distal cement restrictor/vent hole. Residual MMA monomer may contribute to vasodilation and hypotension but embolism is the primary mechanism.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 208,
              "stem": "Gamma irradiation of UHMWPE in air causes long-term deterioration through:",
              "options": [
                "Bacterial contamination",
                "Loss of radioactive material",
                "Free radical-mediated oxidation and chain scission",
                "Crystallisation",
                "Dehydration"
              ],
              "answer": "C",
              "explanation": "Gamma irradiation (25-40 kGy for sterilisation) generates free radicals within the PE polymer chains. When irradiated IN AIR, these free radicals react with atmospheric oxygen over months to years, causing oxidative chain scission, embrittlement, and delamination wear (Ries 2006). Modern HXLPE is irradiated to higher doses (50-100 kGy for cross-linking) then free radicals are eliminated by remelting, annealing, or vitamin E stabilisation. Irradiation in inert atmosphere (nitrogen or vacuum) also prevents oxidation during shelf storage.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 209,
              "stem": "PMMA bone cement achieves fixation to bone by which mechanism?",
              "options": [
                "Chemical bonding to hydroxyapatite",
                "Thermal welding to cortical bone",
                "Biological osseointegration",
                "Electrostatic attraction",
                "Mechanical interlock (interdigitation with cancellous bone)"
              ],
              "answer": "E",
              "explanation": "PMMA is NOT an adhesive — it does not chemically bond to either bone or metal. It achieves fixation by MECHANICAL INTERLOCK: liquid cement is pressurised into the cancellous bone interstices, and upon hardening it creates a grout-like interdigitation with the trabecular structure. This is why adequate cement pressurisation, pulsed lavage (to remove blood/fat and open pores), and a distal cement restrictor (to allow pressurisation rather than distal escape) are essential surgical techniques. Optimal cement penetration is 3-5mm into cancellous bone.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 210,
              "stem": "Vitamin E (alpha-tocopherol) is added to modern HXLPE to:",
              "options": [
                "Increase wear resistance",
                "Scavenge free radicals without thermal processing",
                "Act as a radiopacifier",
                "Increase the melting point",
                "Improve biocompatibility"
              ],
              "answer": "B",
              "explanation": "Vitamin E (alpha-tocopherol) is a natural antioxidant that scavenges free radicals generated during irradiation-induced cross-linking. By eliminating free radicals chemically rather than thermally (remelting/annealing), vitamin E-stabilised PE maintains both the cross-linked structure (wear resistance) AND the original crystallinity (mechanical properties). Thermal treatments like remelting eliminate free radicals but also destroy crystallinity, reducing fatigue strength and fracture toughness. Vitamin E offers the best of both worlds.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 211,
              "stem": "The Young's modulus of PMMA bone cement is approximately:",
              "options": [
                "0.5 GPa",
                "17 GPa",
                "110 GPa",
                "2.5 GPa",
                "200 GPa"
              ],
              "answer": "D",
              "explanation": "PMMA has a Young's modulus of approximately 2.5 GPa — between UHMWPE (~1 GPa) and cortical bone (~17-20 GPa). This intermediate stiffness means cement provides load transfer between the stiffer metal implant and less stiff cancellous bone, acting as a grout that distributes stress. PMMA is relatively brittle and weak in tension (30-50 MPa) but reasonable in compression (80-100 MPa). It is susceptible to fatigue failure, especially in thin or deficient cement mantles.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 212,
              "stem": "Which antibiotic is MOST commonly added to bone cement for primary THA prophylaxis?",
              "options": [
                "Vancomycin",
                "Tobramycin",
                "Gentamicin",
                "Cefuroxime",
                "Flucloxacillin"
              ],
              "answer": "C",
              "explanation": "Gentamicin is the most commonly used antibiotic in commercially available antibiotic-loaded bone cement (ALBC) for primary arthroplasty prophylaxis (e.g., Palacos R+G, Simplex with tobramycin). For revision surgery or high-risk patients, higher doses and combination antibiotics (e.g., vancomycin + gentamicin) may be hand-mixed. Antibiotic-loaded cement was identified as the single most effective prophylactic factor (11-fold reduction) in the Lidwell MRC trial (see Ch 28). Key requirements: heat-stable antibiotic, powder form, broad spectrum.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 213,
              "stem": "Charnley's original PTFE acetabular bearing was abandoned because:",
              "options": [
                "It was too expensive",
                "It caused catastrophic volumetric wear with severe tissue reaction",
                "It fractured catastrophically",
                "It caused metal ion toxicity",
                "It was too difficult to manufacture"
              ],
              "answer": "B",
              "explanation": "Charnley initially used PTFE (Teflon) as the acetabular bearing (1960) but abandoned it within 3 years because it produced catastrophic volumetric wear — approximately 500 times the debris volume compared to later UHMWPE. The massive particle load caused severe foreign body giant cell reactions and osteolysis. He then switched to UHMWPE (1963, introduced by Harry Craven), which had vastly superior wear characteristics. This historical failure illustrates the importance of adequate preclinical testing and the devastating consequences of bearing surface wear.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 214,
              "stem": "In PMMA cement, barium sulphate is added to provide:",
              "options": [
                "Radiopacity for X-ray visualisation",
                "Antibiotic activity",
                "Increased mechanical strength",
                "Faster setting time",
                "Better bone adhesion"
              ],
              "answer": "A",
              "explanation": "Barium sulphate (BaSO4) or zirconium dioxide (ZrO2) is added to PMMA cement powder as a RADIOPACIFIER to allow visualisation of the cement mantle on X-rays. This is essential for assessing cement mantle quality, detecting radiolucent lines at interfaces (which may indicate loosening), and evaluating cement integrity over time. The radiopacifier particles are inert but can act as stress concentrators within the cement, slightly reducing its fatigue strength — this is why the radiopacifier content is kept to approximately 10% by weight.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Biomaterials: Ceramics",
          "range": "Q215-Q224",
          "questions": [
            {
              "number": 215,
              "stem": "The linear wear rate of a modern alumina ceramic-on-ceramic bearing is approximately:",
              "options": [
                "0.5-1 mm/year",
                "0.1-0.2 mm/year (same as conventional PE)",
                "0.05 mm/year (same as HXLPE)",
                "Zero — ceramics do not wear",
                "Less than 5 micrometres/year"
              ],
              "answer": "E",
              "explanation": "Modern alumina CoC bearings have linear wear rates of less than 5 micrometres per year (Willmann 2000), compared to 100-200 micrometres/year for conventional UHMWPE and 30-50 micrometres/year for HXLPE. This ultra-low wear means virtually no biologically active particle generation and no clinically detectable osteolysis at 20+ years. However, ceramics are NOT wear-free — they can produce stripe wear from edge loading and ceramic particles from fracture.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 216,
              "stem": "BIOLOX delta is an alumina-matrix composite. What advantage does the addition of zirconia provide?",
              "options": [
                "Lower cost",
                "Increased radiopacity",
                "Better colour matching",
                "Reduced friction coefficient",
                "Increased fracture toughness (transformation toughening)"
              ],
              "answer": "E",
              "explanation": "BIOLOX delta contains 17% zirconia dispersed in an alumina matrix. Zirconia undergoes TRANSFORMATION TOUGHENING — when a crack tip approaches a zirconia grain, the grain transforms from tetragonal to monoclinic phase with a 3-4% volume expansion. This expansion creates compressive stresses around the crack tip that resist crack propagation, increasing fracture toughness by approximately 50% compared to pure alumina. This mechanism dramatically reduces the ceramic fracture risk to 0.02-0.05%.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 217,
              "stem": "The Prozyr zirconia femoral head was recalled because of:",
              "options": [
                "Manufacturing defect",
                "Excessive cost",
                "In-vivo tetragonal-to-monoclinic phase transformation causing surface roughening",
                "Incompatibility with PE liners",
                "Nickel allergy"
              ],
              "answer": "C",
              "explanation": "Y-TZP zirconia undergoes tetragonal-to-monoclinic phase transformation when exposed to moisture (body fluids) at body temperature — a process called low-temperature degradation or ageing (De Aza 2002). This transformation causes surface roughening, microcracking, and grain pull-out, dramatically increasing wear against both PE and ceramic counterfaces. The Prozyr recall in 2001 followed a cluster of catastrophic failures from this mechanism. This is why pure zirconia is no longer used for femoral heads — instead, zirconia is used as a TOUGHENING ADDITIVE within alumina (BIOLOX delta).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 218,
              "stem": "Hydroxyapatite coating on an uncemented implant promotes fixation by:",
              "options": [
                "Chemical bonding to the metal implant",
                "Providing an osteoconductive surface that is replaced by native bone",
                "Preventing bacterial adhesion",
                "Increasing the modulus of the implant surface",
                "Providing antibiotic activity"
              ],
              "answer": "B",
              "explanation": "HA coating (Ca10(PO4)6(OH)2, 50-200 micrometre thickness) is chemically identical to the mineral phase of bone. It provides an OSTEOCONDUCTIVE surface — osteoblasts recognise HA and attach, proliferate, and form new bone directly onto the coated surface. Over time, the HA coating is gradually resorbed and replaced by native bone (biological fixation). HA coating accelerates initial osseointegration (faster bone ongrowth) compared to uncoated porous metal, which is important during the early postoperative period when the implant is most vulnerable to migration.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 219,
              "stem": "Which ceramic property explains why ceramic bearings have the lowest friction coefficient of all arthroplasty bearing couples?",
              "options": [
                "Superior wettability and surface finish",
                "Lowest hardness",
                "Highest porosity",
                "Lowest elastic modulus",
                "Highest thermal conductivity"
              ],
              "answer": "A",
              "explanation": "Ceramics have superior WETTABILITY (hydrophilic surface attracts and retains a thin fluid film) and can be polished to an extremely smooth surface finish (Ra < 0.005 micrometres). These two properties promote fluid film lubrication between the bearing surfaces, resulting in the lowest friction coefficient of any artificial bearing (~0.04-0.07). By comparison, metal surfaces are less wettable and have rougher finishes even after polishing, resulting in higher friction (MoP 0.05-0.15, MoM 0.2-0.3).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 220,
              "stem": "Calcium phosphate ceramics (TCP, HA) used as bone graft substitutes are classified as:",
              "options": [
                "Osteogenic",
                "Osteoinductive",
                "Osteogenic + osteoinductive",
                "Osteoconductive only",
                "Osteogenic + osteoconductive + osteoinductive"
              ],
              "answer": "D",
              "explanation": "Calcium phosphate ceramics (tricalcium phosphate, hydroxyapatite, biphasic calcium phosphate) are OSTEOCONDUCTIVE ONLY — they provide a scaffold for cell attachment and vascular ingrowth but do NOT contain living cells (not osteogenic) and do NOT stimulate cell differentiation (not osteoinductive). They must be combined with osteogenic cells (e.g., marrow aspirate) and/or osteoinductive factors (e.g., BMPs) to function effectively in large defects. Compare: autograft = osteogenic + osteoconductive + osteoinductive (the gold standard, see Ch 18).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 221,
              "stem": "The risk of catastrophic ceramic fracture with modern 4th-generation alumina-matrix composite (BIOLOX delta) is approximately:",
              "options": [
                "1-2%",
                "0.5-1%",
                "0.1-0.5%",
                "Less than 0.001%",
                "0.02-0.05%"
              ],
              "answer": "E",
              "explanation": "Modern 4th-generation BIOLOX delta has a fracture risk of approximately 0.02-0.05% (Hannouche 2011), a dramatic improvement from earlier pure alumina generations (up to 1-2% with 1st generation). The improvement is due to: (1) Transformation toughening from dispersed zirconia, (2) Improved manufacturing (hot isostatic pressing reducing porosity), (3) Better quality control. Despite the low risk, ceramic fracture remains a serious complication requiring thorough synovectomy to remove all fragments.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 222,
              "stem": "Alumina ceramic is characterised by which mechanical property profile?",
              "options": [
                "High stiffness, high hardness, low toughness (brittle)",
                "Low stiffness, high toughness, low hardness",
                "High stiffness, low hardness, high toughness",
                "Low stiffness, low hardness, low toughness",
                "High stiffness, high hardness, high toughness"
              ],
              "answer": "A",
              "explanation": "Alumina is characterised by very high stiffness (E ~380 GPa), very high hardness (Vickers hardness ~2000), but LOW toughness (fracture toughness ~3-4 MPa.m1/2) — making it BRITTLE. This brittleness means alumina can fail catastrophically without warning (no plastic deformation before fracture), unlike metals which deform plastically. BIOLOX delta improves toughness to ~5-6 MPa.m1/2 through transformation toughening, but it remains brittle compared to metals. This is why ceramic heads must be handled carefully intraoperatively — a nick from a metal instrument can create a stress concentrator leading to delayed fracture.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 223,
              "stem": "Stripe wear on a ceramic femoral head indicates:",
              "options": [
                "Normal wear pattern",
                "Manufacturing defect",
                "Infection",
                "Edge loading from microseparation",
                "Corrosion"
              ],
              "answer": "D",
              "explanation": "Stripe wear is a distinctive wear pattern on ceramic femoral heads caused by edge loading — the femoral head microseparates from the acetabular liner during the swing phase of gait, then re-engages the liner edge during early stance. This produces a localised stripe of accelerated wear on the head and a corresponding area on the liner rim. Edge loading is promoted by: steep cup inclination (>45°), excessive anteversion, short neck length, and insufficient head-liner offset. Stripe wear increases the risk of squeaking and theoretically increases fracture risk.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 224,
              "stem": "Tricalcium phosphate (TCP) differs from hydroxyapatite (HA) as a bone graft substitute primarily in its:",
              "options": [
                "Osteoconductive potential (TCP is not osteoconductive)",
                "Resorption rate (TCP resorbs faster than HA)",
                "Mechanical strength (TCP is much stronger)",
                "Source (TCP is naturally derived, HA is synthetic)",
                "Biocompatibility (HA is more biocompatible)"
              ],
              "answer": "B",
              "explanation": "TCP (Ca3(PO4)2) resorbs much faster than HA (Ca10(PO4)6(OH)2) in vivo — TCP is completely resorbed within 6-24 months while HA may persist for years. Both are osteoconductive and biocompatible. Biphasic calcium phosphate (BCP) combines TCP and HA in varying ratios (e.g., 60:40 HA:TCP) to achieve intermediate resorption rates tailored to the clinical need. Faster resorption (more TCP) is desired when rapid replacement by native bone is needed; slower resorption (more HA) provides longer-lasting structural support.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Bone Graft & Substitutes",
          "range": "Q225-Q234",
          "questions": [
            {
              "number": 225,
              "stem": "Autologous iliac crest bone graft is considered the gold standard because it uniquely provides:",
              "options": [
                "Osteoconductive properties only",
                "Osteoinductive + osteoconductive properties",
                "Osteogenic + osteoconductive + osteoinductive properties",
                "Osteogenic properties only",
                "Mechanical structural support"
              ],
              "answer": "C",
              "explanation": "Autologous iliac crest graft is the ONLY material providing all three biological properties: osteogenic (living MSCs and osteoblasts), osteoconductive (trabecular scaffold for cell attachment and vascular ingrowth), and osteoinductive (endogenous BMPs and growth factors that stimulate MSC differentiation). No synthetic or allograft material combines all three. This is why autograft remains the gold standard despite donor site morbidity (pain, haematoma, infection in 25-35% of cases).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 226,
              "stem": "BMP-2 on a collagen carrier (InFUSE) was shown in the BESTT trial to reduce secondary interventions in open tibial fractures by:",
              "options": [
                "10%",
                "20%",
                "44%",
                "30%",
                "75%"
              ],
              "answer": "C",
              "explanation": "The BESTT trial (Govender et al. JBJS Am 2002) demonstrated that BMP-2 on an absorbable collagen sponge carrier reduced the need for secondary intervention (including bone grafting) by 44% in Gustilo IIIA and IIIB open tibial fractures compared to standard treatment. This established BMP-2 as a viable augmentation strategy for severe open fractures. However, BMPs have significant cost and potential complications (ectopic bone, inflammation, possible carcinogenesis concerns with high doses).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 227,
              "stem": "The Masquelet induced membrane technique involves:",
              "options": [
                "Single-stage bone grafting",
                "Direct application of BMP without scaffold",
                "Free vascularised fibula transfer",
                "Two-stage procedure: cement spacer first, then graft within the induced membrane",
                "Ilizarov distraction alone"
              ],
              "answer": "D",
              "explanation": "The Masquelet technique (2010) is a two-stage procedure: Stage 1 — a PMMA cement spacer is placed in the bone defect after debridement, inducing a biological membrane over 6-8 weeks. Stage 2 — the cement is removed (preserving the membrane) and the space is filled with autologous cancellous graft. The induced membrane is rich in BMP-2, VEGF, TGF-beta, and IL-6 — it acts as a biological chamber that prevents graft resorption and provides growth factors and vascularity. The technique has become the standard for segmental bone defects of 4-25cm.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 228,
              "stem": "Demineralised bone matrix (DBM) is classified as:",
              "options": [
                "Osteogenic only",
                "Osteoinductive + osteoconductive",
                "Osteoconductive only",
                "Osteogenic + osteoinductive + osteoconductive",
                "None of the above — it is purely structural"
              ],
              "answer": "B",
              "explanation": "DBM is prepared by acid extraction of the mineral component from allograft bone, preserving the collagen matrix and endogenous growth factors (BMPs, TGF-beta). It is OSTEOINDUCTIVE (retains growth factors that stimulate MSC differentiation) and OSTEOCONDUCTIVE (collagen matrix provides scaffold). It is NOT osteogenic (no living cells survive the processing). DBM activity varies significantly between commercial preparations and even between batches, making quality inconsistent — a recognised limitation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 229,
              "stem": "A critical-size bone defect is defined as one that exceeds:",
              "options": [
                "1 cm",
                "50% of bone length",
                "Any gap with cortical discontinuity",
                "5 cm in all bones",
                "2-2.5 times the diaphyseal diameter"
              ],
              "answer": "E",
              "explanation": "A critical-size defect exceeds approximately 2-2.5 times the diaphyseal diameter (Zimmermann & Moghaddam 2011) — this is the threshold beyond which spontaneous healing will not occur regardless of fixation stability. For the tibia (diaphyseal diameter ~25mm), this is approximately 5-6cm. For the femur (diameter ~30mm), approximately 6-7.5cm. These defects require biological augmentation (graft, BMP, induced membrane, or vascularised transfer) in addition to mechanical stabilisation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 230,
              "stem": "Fresh-frozen allograft differs from freeze-dried allograft in which key way?",
              "options": [
                "Fresh-frozen retains more mechanical strength; freeze-dried is weaker and more brittle",
                "Fresh-frozen has living cells; freeze-dried does not",
                "Fresh-frozen is osteoinductive; freeze-dried is not",
                "Fresh-frozen has higher disease transmission risk",
                "There is no difference"
              ],
              "answer": "A",
              "explanation": "Fresh-frozen allograft retains more of the original mechanical properties than freeze-dried (lyophilised) allograft. Freeze-drying removes water, making the graft more brittle and reducing its mechanical strength — it requires rehydration before use. Neither contains living cells (both are processed). Both are weakly osteoinductive (residual growth factors) and osteoconductive. Fresh-frozen graft is stored at -70°C and has a slightly higher immunogenic potential but better structural integrity. Freeze-dried graft is stored at room temperature (convenient) but is limited to non-structural applications.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 231,
              "stem": "The primary donor site complication of iliac crest bone graft harvesting is:",
              "options": [
                "Femoral nerve injury",
                "Iliac wing fracture",
                "Peritoneal perforation",
                "Chronic donor site pain",
                "Deep vein thrombosis"
              ],
              "answer": "D",
              "explanation": "Chronic donor site pain is the most common complication, reported in 25-35% of patients (some studies up to 40%). Other complications include: haematoma (5-10%), superficial infection (2-5%), lateral femoral cutaneous nerve injury (causing meralgia paraesthetica, 2-10%), iliac wing fracture (rare, more common with structural graft), peritoneal perforation (rare, with inner table harvest), and abdominal wall herniation (very rare). The morbidity of iliac crest harvesting is a major driver for developing alternatives (BMPs, synthetics, allograft).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 232,
              "stem": "Which property distinguishes osteoinduction from osteoconduction?",
              "options": [
                "Osteoinduction provides a scaffold; osteoconduction stimulates cells",
                "Osteoinduction contains living cells; osteoconduction does not",
                "Osteoinduction stimulates MSC differentiation into osteoblasts; osteoconduction provides a scaffold",
                "Osteoinduction requires blood supply; osteoconduction does not",
                "They are synonymous terms"
              ],
              "answer": "C",
              "explanation": "OSTEOINDUCTION: The ability to stimulate undifferentiated mesenchymal stem cells to differentiate into osteoblasts — this is a biological SIGNAL (BMPs are the key osteoinductive molecules). OSTEOCONDUCTION: The ability to serve as a scaffold for cell attachment, migration, and vascular ingrowth — this is a physical STRUCTURE (trabecular bone, calcium phosphate ceramics). OSTEOGENESIS: The ability to form new bone from living cells within the graft. Understanding these three distinct properties is essential for selecting appropriate graft materials.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 233,
              "stem": "The reamer-irrigator-aspirator (RIA) system provides autologous graft from:",
              "options": [
                "The iliac crest",
                "The tibial metaphysis",
                "The distal radius",
                "The calcaneum",
                "The femoral canal (intramedullary reaming)"
              ],
              "answer": "E",
              "explanation": "The RIA system harvests autologous bone graft from the femoral medullary canal during intramedullary reaming. It collects the reaming debris (which contains osteogenic cells, growth factors, and osteoconductive matrix) in a filter. RIA can provide large volumes of graft (up to 40-90 cc) — significantly more than standard iliac crest harvest (~20-40 cc). RIA graft has been shown to contain viable MSCs and endogenous growth factors (BMP-2, BMP-7). The advantage over iliac crest is reduced donor site pain and larger volume; the disadvantage is risk of femoral fracture and requires a separate surgical setup.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 234,
              "stem": "Bone morphogenetic proteins (BMPs) belong to which growth factor superfamily?",
              "options": [
                "TGF-beta superfamily",
                "Fibroblast growth factor (FGF) family",
                "Platelet-derived growth factor (PDGF) family",
                "Insulin-like growth factor (IGF) family",
                "Vascular endothelial growth factor (VEGF) family"
              ],
              "answer": "A",
              "explanation": "BMPs are members of the TGF-beta superfamily. There are over 20 identified BMPs, with BMP-2 and BMP-7 (OP-1) being the most clinically relevant in orthopaedics. BMPs bind to serine-threonine kinase receptors on MSCs and activate the SMAD signalling pathway, stimulating differentiation into chondrocytes and osteoblasts (osteoinduction). Urist first described BMP activity in 1965 by demonstrating that demineralised bone matrix implanted into muscle could induce ectopic bone formation. This discovery was fundamental to the development of recombinant BMP products.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        }
      ]
    },
    {
      "title": "Pathology & Pharmacology",
      "chapters": [
        {
          "title": "Inflammation & Immune Response",
          "range": "Q235-Q244",
          "questions": [
            {
              "number": 235,
              "stem": "The 'two-hit' model in polytrauma describes:",
              "options": [
                "Two separate injuries to the same limb",
                "Initial injury primes the immune system, then a secondary insult triggers exaggerated inflammation",
                "Two different types of fracture fixation",
                "Sequential treatment of bilateral injuries",
                "Two phases of fracture healing"
              ],
              "answer": "B",
              "explanation": "The two-hit model (Pape 2010) describes how the initial injury (first hit) activates and primes the innate immune system. During the primed state (24-72 hours), a second insult (prolonged surgery, blood loss) can trigger an exaggerated systemic inflammatory response potentially leading to ARDS and MODS. This concept underpins damage control orthopaedics — temporising fixation to minimise the surgical second hit in physiologically unstable patients.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 236,
              "stem": "Which cell is the KEY orchestrator of the acute inflammatory response?",
              "options": [
                "Neutrophil",
                "T-lymphocyte",
                "B-lymphocyte",
                "Macrophage",
                "Mast cell"
              ],
              "answer": "D",
              "explanation": "The macrophage is the key orchestrating cell of inflammation (and wound/fracture healing). Macrophages: (1) phagocytose debris and pathogens, (2) present antigens to T-cells (bridging innate and adaptive immunity), (3) release cytokines (IL-1, IL-6, TNF-alpha) that recruit and activate other immune cells, (4) produce growth factors (PDGF, TGF-beta, VEGF) that initiate repair. Neutrophils arrive first (24-48 hours) but the macrophage orchestrates the overall response.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 237,
              "stem": "Adverse local tissue reaction (ALVAL) from metal-on-metal hip bearings is which type of hypersensitivity?",
              "options": [
                "Type I (immediate/IgE)",
                "Type II (cytotoxic/IgG)",
                "Type IV (delayed/T-cell mediated)",
                "Type III (immune complex)",
                "Type V (stimulatory)"
              ],
              "answer": "C",
              "explanation": "ALVAL is a Type IV (delayed-type) hypersensitivity reaction to cobalt and chromium metal ions/particles. It is T-cell mediated with NO antibody involvement, occurring 24-72 hours after exposure. Histologically shows perivascular lymphocyte infiltration (ALVAL pattern). This cannot be detected by standard IgE-based allergy tests — requires patch testing or lymphocyte transformation testing. The reaction causes tissue necrosis, pseudotumour formation, and implant loosening.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 238,
              "stem": "The complement system is activated by which three pathways?",
              "options": [
                "Intrinsic, extrinsic, and common",
                "Classical, lectin, and alternative",
                "Primary, secondary, and tertiary",
                "Innate, adaptive, and humoral",
                "Afferent, efferent, and feedback"
              ],
              "answer": "B",
              "explanation": "The complement system is activated by three pathways: (1) Classical (activated by antigen-antibody complexes — IgG/IgM), (2) Lectin/Mannose-binding (activated by mannose on bacterial surfaces), and (3) Alternative (activated by bacterial cell surfaces directly — no antibodies needed). All three converge on C3 convertase → C3a (anaphylatoxin) + C3b (opsonisation) → C5 convertase → C5a (chemotaxis, anaphylatoxin) + C5b-9 (membrane attack complex, MAC, cell lysis). Complement plays a key role in innate immunity and fracture healing.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 239,
              "stem": "In the context of polytrauma, the 'lethal triad' consists of:",
              "options": [
                "Hypothermia, acidosis, coagulopathy",
                "Hypotension, tachycardia, oliguria",
                "Hypoxia, hypercapnia, acidosis",
                "Infection, malnutrition, immobility",
                "Pain, swelling, loss of function"
              ],
              "answer": "A",
              "explanation": "The lethal triad (hypothermia, metabolic acidosis, coagulopathy) is a self-reinforcing cycle where each element worsens the others: hypothermia impairs clotting factor function, acidosis reduces factor activity, and coagulopathy causes ongoing haemorrhage leading to more hypothermia and acidosis. Recognition of the lethal triad is the trigger for damage control surgery — abbreviated procedures to stop haemorrhage and contamination, followed by ICU resuscitation before definitive fixation. Core temperature <35°C, pH <7.2, and INR >1.5 are commonly used thresholds.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 240,
              "stem": "TNF-alpha is produced primarily by:",
              "options": [
                "Osteoblasts",
                "Neutrophils",
                "Fibroblasts",
                "Mast cells",
                "Activated macrophages and T-cells"
              ],
              "answer": "E",
              "explanation": "TNF-alpha (tumour necrosis factor alpha) is a key pro-inflammatory cytokine produced primarily by activated macrophages and T-cells. It plays central roles in: acute inflammation (vasodilation, increased vascular permeability, neutrophil recruitment), fracture healing (early inflammatory phase), bone remodelling (stimulates RANKL expression → osteoclastogenesis), and RA pathogenesis (drives synovial inflammation and joint destruction — target of biological DMARDs: etanercept, adalimumab, infliximab, see Ch 22 and Ch 29).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 241,
              "stem": "Damage control orthopaedics (DCO) involves:",
              "options": [
                "Definitive fixation within 6 hours of injury",
                "Non-operative management of all fractures",
                "Temporary external fixation followed by delayed definitive fixation",
                "Immediate amputation of severely injured limbs",
                "Intramedullary nailing within 24 hours"
              ],
              "answer": "C",
              "explanation": "DCO involves temporary skeletal stabilisation (typically external fixation) during the physiologically unstable period (first 24-72 hours when the immune system is primed), followed by definitive internal fixation once the patient has been resuscitated and stabilised (typically day 5-10). The rationale is to minimise the 'second hit' of prolonged surgery during the primed state. DCO is indicated for the borderline/unstable polytrauma patient with the lethal triad. Early total care (definitive fixation within 24 hours) is preferred for physiologically stable patients.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 242,
              "stem": "Which interleukin is the primary mediator of the acute phase response (stimulating hepatic CRP production)?",
              "options": [
                "IL-6",
                "IL-1",
                "IL-2",
                "IL-4",
                "IL-10"
              ],
              "answer": "A",
              "explanation": "IL-6 is the primary stimulant of the hepatic acute phase response, driving CRP production by hepatocytes. IL-6 is produced by macrophages, fibroblasts, and T-cells. It is also the target of tocilizumab (anti-IL-6 receptor antibody used in RA, see Ch 29). CRP rises within 6 hours of an inflammatory stimulus, peaks at 48 hours, and has a half-life of 19 hours — making it the best serological marker for monitoring acute infection and treatment response. IL-1 and TNF-alpha are also important pro-inflammatory cytokines but are less specific to the acute phase response.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 243,
              "stem": "Pattern recognition receptors (PRRs) on innate immune cells recognise:",
              "options": [
                "Specific antigens on individual pathogens (like antibodies)",
                "Self-antigens on host cells",
                "MHC molecules on transplanted tissue",
                "Pathogen-associated molecular patterns (PAMPs) shared by groups of microorganisms",
                "Cytokines released by other immune cells"
              ],
              "answer": "D",
              "explanation": "PRRs (including Toll-like receptors, TLRs) are germline-encoded receptors on macrophages, dendritic cells, and neutrophils that recognise PAMPs — conserved molecular structures shared by broad groups of pathogens (e.g., LPS on Gram-negative bacteria, peptidoglycan on Gram-positive, flagellin, viral RNA). PRRs also recognise DAMPs (damage-associated molecular patterns) from injured host tissue. This is fundamentally different from adaptive immunity where T-cell receptors and antibodies recognise specific antigens with exquisite specificity. PRRs provide rapid, broad-spectrum initial defence.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 244,
              "stem": "A patient with nickel allergy develops pain after a TKA with a cobalt-chrome femoral component. Which investigation is most appropriate to assess metal hypersensitivity?",
              "options": [
                "Serum IgE levels",
                "RAST (radioallergosorbent test)",
                "Blood culture",
                "Joint aspiration for crystal analysis",
                "Patch testing or lymphocyte transformation test (LTT)"
              ],
              "answer": "E",
              "explanation": "Metal hypersensitivity is a Type IV (delayed, T-cell mediated) reaction. Standard allergy tests (IgE levels, RAST) detect Type I (IgE-mediated) reactions and will be NEGATIVE in metal sensitivity. The appropriate investigations are: (1) Patch testing — applies metal salts to the skin and observes for delayed reaction at 48-96 hours, (2) Lymphocyte transformation test (LTT) — measures T-cell proliferation in response to metal antigens in vitro. Serum metal ion levels (cobalt, chromium) assess metal exposure but not hypersensitivity. Joint aspiration rules out infection and identifies ALVAL histology.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Infection",
          "range": "Q245-Q254",
          "questions": [
            {
              "number": 245,
              "stem": "Bacterial biofilm on an implant becomes fully mature and maximally resistant to antibiotics after approximately:",
              "options": [
                "6 hours",
                "3-4 weeks",
                "24 hours",
                "1 week",
                "6 months"
              ],
              "answer": "B",
              "explanation": "Biofilm maturation occurs over approximately 3-4 weeks. During this time, the glycocalyx (polysaccharide matrix) fully develops, creating a structured community that is 100-1000 times more resistant to antibiotics than planktonic bacteria. This timeline determines the treatment strategy: early PJI (<3-4 weeks, immature biofilm) may be treated with DAIR; chronic PJI (>4 weeks, mature biofilm) requires implant removal (two-stage exchange). Some evidence suggests biofilm formation begins much earlier (hours-days), but the clinically significant resistance develops over weeks.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 246,
              "stem": "The Kocher criteria for paediatric septic arthritis include all EXCEPT:",
              "options": [
                "Temperature >38.5°C",
                "Non-weight-bearing",
                "ESR >40 mm/hr",
                "WBC >12,000",
                "CRP >20 mg/L"
              ],
              "answer": "E",
              "explanation": "The original four Kocher criteria (1999) are: temperature >38.5°C, non-weight-bearing, ESR >40, WBC >12,000. CRP was added later by Caird et al. (2006) as a fifth criterion (CRP >20), increasing the predictive value. With all 4 original criteria present, the probability of septic arthritis is 99.6%. With 3 criteria: 93%. With 2: 40%. With 1: 3%. With 0: 0.2%.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 247,
              "stem": "MRSA acquires penicillin resistance through which mechanism?",
              "options": [
                "Beta-lactamase production",
                "Altered penicillin-binding protein PBP2a encoded by mecA gene",
                "Efflux pump mechanism",
                "Altered ribosomal target",
                "Porin channel modification"
              ],
              "answer": "B",
              "explanation": "MRSA (methicillin-resistant S. aureus) acquires resistance through the mecA gene which encodes an altered penicillin-binding protein (PBP2a). PBP2a has LOW affinity for all beta-lactam antibiotics (penicillins, cephalosporins, carbapenems), rendering them ALL ineffective. This is different from beta-lactamase production (which only hydrolyses specific beta-lactams and can be overcome by enzyme inhibitors like clavulanic acid). Treatment of MRSA: glycopeptides (vancomycin, teicoplanin), linezolid (oxazolidinone), daptomycin.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 248,
              "stem": "In DAIR for acute PJI, which antibiotic has the best biofilm penetration for staphylococcal infections?",
              "options": [
                "Vancomycin",
                "Gentamicin",
                "Flucloxacillin",
                "Rifampicin",
                "Ceftriaxone"
              ],
              "answer": "D",
              "explanation": "Rifampicin has the best penetration of staphylococcal biofilm of any available antibiotic. It achieves bactericidal concentrations within the biofilm matrix. However, it should NEVER be used as monotherapy because resistance develops rapidly — always use in combination with another anti-staphylococcal agent (e.g., vancomycin, daptomycin, or flucloxacillin). Rifampicin is started after wound healing (typically 2 weeks postoperatively) to avoid wound complications. Oral bioavailability is excellent (95%), allowing oral step-down therapy.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 249,
              "stem": "Septic arthritis causes irreversible cartilage damage within approximately:",
              "options": [
                "8 hours",
                "2 hours",
                "24 hours",
                "48 hours",
                "1 week"
              ],
              "answer": "A",
              "explanation": "Irreversible cartilage damage from proteolytic enzymes released by neutrophils can occur within 8 hours of infection onset. This makes septic arthritis a SURGICAL EMERGENCY. Neutrophil-derived enzymes (collagenases, elastases, reactive oxygen species) degrade the collagen-proteoglycan matrix. Because articular cartilage is avascular with no intrinsic repair capacity (see Ch 7), this damage cannot be reversed. Early joint aspiration, urgent surgical washout, and IV antibiotics are essential to minimise cartilage destruction.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 250,
              "stem": "Quorum sensing in bacterial biofilms refers to:",
              "options": [
                "The ability to detect antibiotics",
                "Detection of host immune cells",
                "Cell-to-cell communication that coordinates bacterial behaviour",
                "Sensing of metal implant surfaces",
                "Communication between bacteria and host cells"
              ],
              "answer": "C",
              "explanation": "Quorum sensing is a cell-to-cell communication system in biofilm bacteria. Bacteria release signalling molecules (autoinducers) that accumulate as the population grows. When a threshold concentration is reached (a 'quorum'), the bacteria coordinate their behaviour — including simultaneous transformation from biofilm (sessile) to planktonic form when external conditions are favourable. This explains delayed haematogenous spread and late recurrence of infection after apparently successful treatment.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 251,
              "stem": "The gold standard treatment for chronic periprosthetic joint infection (mature biofilm) is:",
              "options": [
                "DAIR",
                "One-stage exchange",
                "Suppressive antibiotics alone",
                "Arthrodesis",
                "Two-stage exchange"
              ],
              "answer": "E",
              "explanation": "Two-stage exchange is the gold standard for chronic PJI with mature biofilm (>3-4 weeks). Stage 1: Removal of all implants + cement + thorough debridement + antibiotic-loaded cement spacer (high-dose, typically vancomycin + gentamicin). Stage 2: Reimplantation after 6-12 weeks of systemic antibiotics and normalisation of inflammatory markers (CRP, ESR). Success rates: 85-95%. One-stage exchange is gaining popularity for selected cases (known organism, adequate soft tissues, no sinus tract) with success rates approaching two-stage in experienced centres.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 252,
              "stem": "In the diagnosis of PJI, which synovial fluid marker has the highest sensitivity and specificity?",
              "options": [
                "Alpha-defensin",
                "Synovial WBC count",
                "Synovial PMN percentage",
                "Synovial CRP",
                "Gram stain"
              ],
              "answer": "A",
              "explanation": "Synovial fluid alpha-defensin has the highest combined sensitivity (97%) and specificity (97%) for PJI diagnosis. Alpha-defensin is an antimicrobial peptide released by activated neutrophils in response to infection. It is available as a lateral flow test (Synovasure) providing results in minutes, and as a laboratory ELISA. It is included in the 2018 ICM/MSIS diagnostic criteria for PJI. Synovial WBC >3,000 and PMN >80% are also useful but less specific. Gram stain has high specificity but low sensitivity (~25%).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 253,
              "stem": "The most common causative organism of prosthetic joint infection is:",
              "options": [
                "Streptococcus pyogenes",
                "Pseudomonas aeruginosa",
                "Staphylococcus aureus",
                "Coagulase-negative staphylococci (e.g., S. epidermidis)",
                "coli"
              ],
              "answer": "D",
              "explanation": "Coagulase-negative staphylococci (especially S. epidermidis) are the most common cause of PJI overall (30-40%), particularly in chronic/delayed infections. They are skin commensals with a strong propensity for biofilm formation on implant surfaces. S. aureus is the second most common (20-30%) and predominates in acute haematogenous PJI. Together, staphylococci account for 50-65% of all PJI. Culture-negative PJI accounts for 10-20% — often due to prior antibiotic exposure or fastidious organisms.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 254,
              "stem": "A patient with sickle cell disease develops osteomyelitis. While Salmonella is classically associated, which organism is actually MOST COMMON?",
              "options": [
                "Salmonella species",
                "Streptococcus pneumoniae",
                "Staphylococcus aureus",
                "Pseudomonas aeruginosa",
                "Kingella kingae"
              ],
              "answer": "C",
              "explanation": "Although Salmonella osteomyelitis is classically ASSOCIATED with sickle cell disease (due to functional asplenia and susceptibility to encapsulated organisms), Staphylococcus aureus remains the MOST COMMON causative organism overall (>50% of cases). Salmonella is the second most common (~25-30%) and is more common in SCD than in the general population, but S. aureus still predominates. This distinction is one of the most frequently tested points in the FRCS examination. Empirical antibiotic therapy should cover both organisms.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Neoplasia",
          "range": "Q255-Q264",
          "questions": [
            {
              "number": 255,
              "stem": "The single most important radiographic feature in assessing a bone lesion is:",
              "options": [
                "Periosteal reaction",
                "Zone of transition",
                "Lesion size",
                "Cortical destruction",
                "Soft tissue mass"
              ],
              "answer": "B",
              "explanation": "The zone of transition (Simon 1976) is the interface between the lesion and normal bone. A NARROW zone (well-defined, sclerotic margin) = slow-growing, likely benign (geographic pattern, Lodwick IA-IB). A WIDE zone (ill-defined, permeative/moth-eaten) = aggressive, likely malignant or aggressive benign (Lodwick IC-III). This is the most important feature because it directly reflects the biological behaviour of the lesion — growth rate and bone's ability to mount a response.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 256,
              "stem": "According to Mankin (1996), a poorly planned biopsy of a musculoskeletal tumour can lead to unnecessary amputation in approximately what percentage of cases?",
              "options": [
                "0.5%",
                "1%",
                "10%",
                "3%",
                "20%"
              ],
              "answer": "D",
              "explanation": "Mankin et al. (1996) found that errors in biopsy technique led to diagnostic errors in 12% and unnecessary amputations in 3% of cases. Errors included: wrong biopsy approach (contaminating uninvolved compartments), transverse incisions (crossing future surgical planes), inadequate tissue sampling, and biopsy performed at non-specialist centres. This landmark paper established the principle that biopsy should be performed at (or planned in consultation with) the definitive treating tumour centre.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 257,
              "stem": "In the Enneking staging system for malignant musculoskeletal tumours, Stage IIB indicates:",
              "options": [
                "High-grade, extracompartmental",
                "Low-grade, intracompartmental",
                "Low-grade, extracompartmental",
                "High-grade, intracompartmental",
                "Any grade with metastases"
              ],
              "answer": "A",
              "explanation": "Enneking staging (1980): Stage I = low grade (G1), Stage II = high grade (G2), with subdivision A (intracompartmental = confined within anatomical compartment boundaries) and B (extracompartmental = extends beyond compartment, e.g., through cortex into soft tissues). Stage III = any grade with distant metastases. Therefore IIB = high-grade, extracompartmental, no metastases. Surgical margins required: IA = wide or marginal, IB/IIA = wide, IIB = wide or radical, III = palliative.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 258,
              "stem": "Osteosarcoma most commonly arises in which location?",
              "options": [
                "Diaphysis of the femur",
                "Epiphysis of the proximal tibia",
                "Metaphysis of the distal femur",
                "Diaphysis of the humerus",
                "Pelvis"
              ],
              "answer": "C",
              "explanation": "Osteosarcoma (the most common primary malignant bone tumour in adolescents) most commonly arises in the METAPHYSIS of the distal femur (40% of cases), followed by proximal tibia (20%) and proximal humerus (10%). The predilection for metaphyseal locations around the knee reflects the high growth activity at these sites (the distal femoral and proximal tibial physes are the fastest-growing in the body). Metaphyseal bone with high turnover may be more susceptible to malignant transformation. Classic XR: mixed lytic/scite lesion with wide zone of transition, sunburst periosteal reaction, Codman triangle, and soft tissue mass.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 259,
              "stem": "Ewing sarcoma is characterised by which chromosomal translocation?",
              "options": [
                "t(9;22)",
                "t(14;18)",
                "t(8;14)",
                "t(X;18)",
                "t(11;22)"
              ],
              "answer": "E",
              "explanation": "Ewing sarcoma characteristically has the t(11;22)(q24;q12) translocation, producing the EWS-FLI1 fusion gene. This is a diagnostic marker (detected by FISH or RT-PCR) and distinguishes Ewing's from other small round blue cell tumours (lymphoma, neuroblastoma, rhabdomyosarcoma). Ewing's affects children and young adults (peak 10-15 years), most commonly in the diaphysis of long bones and pelvis. Classic XR: permeative lytic lesion with onion-skin/laminated periosteal reaction (not sunburst). Treatment: chemotherapy (vincristine, doxorubicin, cyclophosphamide + ifosfamide, etoposide) + surgery/radiotherapy.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 260,
              "stem": "In the Mirels scoring system for metastatic bone disease, prophylactic fixation is recommended for a score of:",
              "options": [
                "≥5",
                "≥8",
                "≥6",
                "≥7",
                "≥10"
              ],
              "answer": "B",
              "explanation": "Mirels (1989): Score ≥8 indicates a >33% risk of pathological fracture and prophylactic fixation is recommended. Score 7 = borderline (consider fixation based on clinical context). Score ≤6 = observation with radiotherapy. Parameters: site (UL 1, LL 2, peritrochanteric 3), pain (mild 1, moderate 2, functional 3), type (blastic 1, mixed 2, lytic 3), size (<1/3 cortex 1, 1/3-2/3 2, >2/3 3). Maximum score = 12.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 261,
              "stem": "Chondrosarcoma differs from osteosarcoma in which key treatment aspect?",
              "options": [
                "Chondrosarcoma is treated with chemotherapy alone",
                "Chondrosarcoma has a better prognosis than osteosarcoma in all grades",
                "Chondrosarcoma always metastasises to lymph nodes first",
                "Chondrosarcoma is treated with radiotherapy alone",
                "Chondrosarcoma is resistant to both chemotherapy AND radiotherapy"
              ],
              "answer": "E",
              "explanation": "Chondrosarcoma is RESISTANT to both conventional chemotherapy AND radiotherapy — surgery with wide margins is the ONLY effective treatment. This is because chondrosarcoma has a low proliferation rate (low mitotic index), poor vascularity (limiting drug delivery), and the cartilaginous matrix acts as a barrier to drug penetration. This contrasts with osteosarcoma (responds well to neoadjuvant chemotherapy: methotrexate, doxorubicin, cisplatin) and Ewing sarcoma (responds well to both chemotherapy and radiotherapy).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 262,
              "stem": "The most common primary malignant bone tumour overall (all ages) is:",
              "options": [
                "Osteosarcoma",
                "Chondrosarcoma",
                "Ewing sarcoma",
                "Myeloma",
                "Fibrosarcoma"
              ],
              "answer": "D",
              "explanation": "Myeloma (multiple myeloma/plasmacytoma) is the most common primary malignant bone tumour in adults when all ages are considered. Osteosarcoma is most common in the adolescent age group. Myeloma has a peak incidence at 60-70 years and characteristically produces multiple punched-out lytic lesions without sclerotic margin or periosteal reaction. Bone scan may be FALSE NEGATIVE in 50% because myeloma is purely lytic (no osteoblastic reaction to take up the Tc-99m tracer, see Ch 23). Metastatic carcinoma (not a primary bone tumour) is the most common malignancy found in bone overall.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 263,
              "stem": "An osteoid osteoma is characterised by which classic clinical and radiographic features?",
              "options": [
                "Night pain relieved by NSAIDs, with a radiolucent nidus less than 2cm surrounded by reactive sclerosis",
                "Painless swelling with periosteal reaction",
                "Large destructive lesion with wide zone of transition",
                "Soap-bubble expansile lesion in the epiphysis",
                "Diaphyseal medullary sclerosis"
              ],
              "answer": "A",
              "explanation": "Osteoid osteoma is a benign bone-forming tumour with the classic presentation of NIGHT PAIN (worse at night due to prostaglandin production by the nidus) that is dramatically RELIEVED BY NSAIDs (which block prostaglandin synthesis via COX inhibition). The nidus is a small radiolucent area (<2cm by definition; if >2cm it is classified as an osteoblastoma) surrounded by dense reactive cortical sclerosis. CT scan best demonstrates the nidus. Treatment: radiofrequency ablation (CT-guided) or surgical excision with en bloc removal of the nidus. The nidus must be completely removed or the lesion recurs.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 264,
              "stem": "A giant cell tumour (GCT) of bone characteristically occurs in which location?",
              "options": [
                "Diaphysis of a long bone",
                "Metaphysis in a skeletally immature patient",
                "Epiphysis/subarticular region of a long bone in a skeletally mature patient",
                "Vertebral body",
                "Pelvis"
              ],
              "answer": "C",
              "explanation": "GCT characteristically occurs in the EPIPHYSIS/subarticular region of a long bone in skeletally mature patients (20-40 years, closed physes). The most common site is around the knee (distal femur > proximal tibia). XR shows a well-defined, eccentric, expansile lytic lesion extending to the subchondral bone (subarticular location). It has a narrow zone of transition but no sclerotic margin (unlike most benign lesions). Locally aggressive (Campanacci grade 1-3) with 2-5% risk of pulmonary metastases. Treatment: extended curettage + adjuvant (phenol/hydrogen peroxide/cement) or en bloc resection for aggressive/recurrent cases. Denosumab (anti-RANKL) is used as neoadjuvant or for inoperable cases — the giant cells express RANK and are RANKL-dependent.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Pharmacology",
          "range": "Q265-Q274",
          "questions": [
            {
              "number": 265,
              "stem": "Aspirin differs from other NSAIDs in its mechanism because it:",
              "options": [
                "Is selective for COX-2",
                "Irreversibly acetylates COX enzymes",
                "Blocks the LOX pathway",
                "Is a competitive inhibitor of COX",
                "Blocks phospholipase A2"
              ],
              "answer": "B",
              "explanation": "Aspirin IRREVERSIBLY inhibits COX by acetylating a serine residue at the active site. This is permanent for the life of the cell/platelet. Because platelets are anucleate (no nucleus, cannot synthesise new COX), aspirin's antiplatelet effect lasts for the platelet's lifespan (~7-10 days). All other NSAIDs are REVERSIBLE competitive inhibitors — their effect wears off as the drug is cleared. This irreversible mechanism is why aspirin is uniquely effective as an antiplatelet agent and why it must be stopped 7 days before surgery.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 266,
              "stem": "The CRASH-2 trial demonstrated that tranexamic acid given within 3 hours of injury reduces mortality in bleeding trauma by:",
              "options": [
                "1.5%",
                "0.5%",
                "5%",
                "10%",
                "25%"
              ],
              "answer": "A",
              "explanation": "The CRASH-2 trial (Lancet 2010, >20,000 patients) showed that TXA (1g IV bolus then 1g over 8 hours) reduced all-cause mortality by 1.5% (14.5% vs 16.0%) and death from bleeding by 0.8% when given within 3 hours. Given AFTER 3 hours, TXA appeared to INCREASE mortality. TXA works by inhibiting the conversion of plasminogen to plasmin (antifibrinolytic), preventing clot breakdown. It has been adopted for routine use in hip/knee arthroplasty (IV and topical) where it reduces blood loss by 30-50% and transfusion requirements.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 267,
              "stem": "HIT Type II (heparin-induced thrombocytopenia) is caused by:",
              "options": [
                "Direct bone marrow suppression by heparin",
                "IgG antibodies against heparin-PF4 complexes causing platelet activation and thrombosis",
                "Allergic reaction to heparin preservatives",
                "Heparin overdose",
                "Heparin-induced DIC"
              ],
              "answer": "B",
              "explanation": "HIT Type II is an immune-mediated condition where IgG antibodies form against complexes of heparin and platelet factor 4 (PF4). These antibodies bind to the Fc receptors on platelets, causing platelet ACTIVATION (not destruction), leading to the paradox of THROMBOCYTOPENIA with THROMBOSIS (not bleeding). Onset: typically day 5-14 of heparin exposure (or earlier with prior exposure). Platelet count drops >50% from baseline. Treatment: STOP ALL HEPARIN immediately, start alternative anticoagulant (argatroban, fondaparinux, or DOAC). Do NOT give warfarin until platelet count recovers (risk of warfarin-induced skin necrosis).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 268,
              "stem": "Which local anaesthetic property explains why they are less effective in infected (acidic) tissues?",
              "options": [
                "Increased protein binding in infection",
                "Reduced blood flow to infected areas",
                "Bacteria degrade the anaesthetic",
                "Inflammation increases nerve threshold",
                "Ion trapping — in acidic pH, more drug is ionised and cannot cross the nerve membrane"
              ],
              "answer": "E",
              "explanation": "Local anaesthetics (LAs) are weak bases that exist in equilibrium between ionised (charged, BH+) and non-ionised (uncharged, B) forms. Only the NON-IONISED form can cross the lipid nerve membrane. In infected/inflamed tissue, the pH is lower (more acidic), shifting the equilibrium toward the IONISED form (Henderson-Hasselbalch equation). More ionised drug = less membrane penetration = REDUCED EFFICACY. This is called 'ion trapping'. Additionally, increased blood flow in inflamed tissue washes away the LA more rapidly, further reducing duration of action.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 269,
              "stem": "Methotrexate, the first-line DMARD for rheumatoid arthritis, acts by inhibiting:",
              "options": [
                "Cyclooxygenase",
                "TNF-alpha directly",
                "Xanthine oxidase",
                "Dihydrofolate reductase (DHFR)",
                "Phospholipase A2"
              ],
              "answer": "D",
              "explanation": "Methotrexate inhibits dihydrofolate reductase (DHFR), blocking the conversion of dihydrofolate to tetrahydrofolate — a cofactor essential for DNA synthesis (purine and pyrimidine synthesis). This reduces lymphocyte proliferation and suppresses the immune-mediated joint inflammation in RA. At higher doses (used in osteosarcoma chemotherapy), methotrexate directly inhibits DNA synthesis in rapidly dividing tumour cells. In RA, it is given weekly (NOT daily — daily dosing causes fatal pancytopenia) with folic acid supplementation to reduce side effects (mucositis, hepatotoxicity, myelosuppression).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 270,
              "stem": "TNF-alpha inhibitors (etanercept, adalimumab, infliximab) are indicated in RA after failure of how many conventional DMARDs?",
              "options": [
                "Immediately as first-line",
                "After 1 DMARD",
                "After 2 DMARDs",
                "After 3 DMARDs",
                "Only after all DMARDs have failed"
              ],
              "answer": "C",
              "explanation": "NICE guidelines recommend biological DMARDs (TNF-alpha inhibitors) after failure of at least 2 conventional DMARDs (typically methotrexate + sulfasalazine or leflunomide). TNF-alpha is a key pro-inflammatory cytokine produced by macrophages and T-cells that drives joint inflammation and destruction in RA. TNF inhibitors reduce inflammation rapidly and can slow or halt erosive damage in 70% of patients. They are used in combination with methotrexate for synergistic effect. Side effects include increased infection risk (especially TB reactivation — screen with CXR and interferon-gamma release assay before starting).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 271,
              "stem": "Indomethacin is used to prevent heterotopic ossification because it:",
              "options": [
                "Directly dissolves calcium deposits",
                "Inhibits osteoblast differentiation via COX-2 blockade",
                "Stimulates osteoclast activity",
                "Blocks BMP signalling",
                "Inhibits angiogenesis"
              ],
              "answer": "B",
              "explanation": "Indomethacin (a potent non-selective NSAID) prevents heterotopic ossification (HO) by inhibiting COX-2, which reduces PGE2 production. PGE2 is essential for osteoblast differentiation and proliferation — blocking it prevents the ectopic bone formation. The same mechanism that makes indomethacin effective against HO is the reason NSAIDs (especially COX-2 inhibitors) may delay fracture healing (PGE2 is also essential for callus formation). This creates a clinical dilemma: in patients at high risk of HO (e.g., after acetabular ORIF), the benefit of HO prevention may outweigh the theoretical risk of delayed fracture healing.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 272,
              "stem": "Bisphosphonates achieve their anti-resorptive effect through which intracellular mechanism in osteoclasts?",
              "options": [
                "Inhibiting farnesyl pyrophosphate synthase in the mevalonate pathway",
                "Blocking RANK receptors on osteoclast surface",
                "Blocking vitamin D receptors",
                "Inhibiting cathepsin K",
                "Activating OPG production"
              ],
              "answer": "A",
              "explanation": "Nitrogen-containing bisphosphonates (alendronate, risedronate, zoledronic acid) inhibit farnesyl pyrophosphate synthase (FPPS) in the MEVALONATE pathway within osteoclasts. This prevents prenylation of small GTPases (Ras, Rho, Rac) essential for osteoclast cytoskeleton organisation, ruffled border formation, and survival — leading to osteoclast apoptosis. The P-C-P backbone (replacing O in pyrophosphate P-O-P) provides high affinity for hydroxyapatite, concentrating the drug at bone resorption sites. Non-nitrogen bisphosphonates (etidronate, clodronate) are metabolised to toxic ATP analogues — a different mechanism.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 273,
              "stem": "A patient on rivaroxaban requires urgent hip fracture surgery. The most appropriate management is:",
              "options": [
                "Proceed immediately — rivaroxaban has no effect on bleeding",
                "Wait 5 days for full clearance",
                "Give protamine to reverse rivaroxaban",
                "Wait 24-48 hours (2 half-lives) if haemodynamically stable; use PCC if urgent",
                "Give vitamin K to reverse rivaroxaban"
              ],
              "answer": "D",
              "explanation": "Rivaroxaban is a direct Factor Xa inhibitor with a half-life of 8-12 hours. After 2 half-lives (24-48 hours), anticoagulant effect is substantially reduced and surgery can proceed. If surgery is URGENT and cannot wait: PCC (prothrombin complex concentrate) partially reverses the effect. Andexanet alfa is the specific reversal agent for Factor Xa inhibitors but availability is limited. Protamine reverses heparin/LMWH (not DOACs). Vitamin K reverses warfarin (not DOACs). For dabigatran (direct thrombin inhibitor), idarucizumab is the specific reversal agent.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 274,
              "stem": "Which anticoagulant mechanism is correct?",
              "options": [
                "Warfarin inhibits Factor Xa directly",
                "LMWH primarily inhibits Factor IIa (thrombin)",
                "Rivaroxaban inhibits vitamin K recycling",
                "Aspirin inhibits Factor VII",
                "Unfractionated heparin potentiates antithrombin III to inhibit factors IIa and Xa equally"
              ],
              "answer": "E",
              "explanation": "Unfractionated heparin (UFH) binds antithrombin III (ATIII) and potentiates its inhibition of BOTH Factor IIa (thrombin) and Factor Xa approximately equally (anti-IIa:anti-Xa ratio ~1:1). LMWH (enoxaparin, dalteparin) also potentiates ATIII but predominantly inhibits Factor Xa (anti-IIa:anti-Xa ratio ~1:2-4). Warfarin inhibits vitamin K epoxide reductase (NOT direct factor inhibition). Rivaroxaban/apixaban directly inhibit Factor Xa. Dabigatran directly inhibits Factor IIa (thrombin). Aspirin inhibits COX (platelet TXA2 production), not clotting factors.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        }
      ]
    },
    {
      "title": "Imaging & Theatre",
      "chapters": [
        {
          "title": "Imaging",
          "range": "Q275-Q284",
          "questions": [
            {
              "number": 275,
              "stem": "On MRI, T1-weighted images are best for:",
              "options": [
                "Detecting fluid and oedema",
                "Suppressing fat signal",
                "Demonstrating anatomy (fat appears bright)",
                "Detecting infection",
                "Demonstrating blood flow"
              ],
              "answer": "C",
              "explanation": "T1 images are the 'anatomy' sequence — fat appears BRIGHT (short T1 relaxation, rapid signal recovery), water/fluid appears DARK. T1 provides excellent anatomical detail and demonstrates fat-containing structures (marrow, subcutaneous fat). T2 images are the 'pathology' sequence — water/fluid appears BRIGHT (long T2 relaxation, slow signal decay), making oedema and effusions conspicuous. Mnemonic: T1 = anatomy, fat bright. T2 = water white (W-W-II = Water White on Image Two).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 276,
              "stem": "Hounsfield units on CT: bone is approximately:",
              "options": [
                "-1000 HU",
                "0 HU",
                "+40 HU",
                "+1000 HU",
                "+3000 HU"
              ],
              "answer": "D",
              "explanation": "Hounsfield scale: air = -1000 HU, fat = -100 HU, water = 0 HU, soft tissue = +40-80 HU, bone = +1000 HU (approximately). CT windowing adjusts the display range: bone window (wide window, high level) shows cortical detail; soft tissue window (narrow window, lower level) shows muscle/organ detail. Hounsfield's invention of CT (1973) revolutionised musculoskeletal imaging and earned the Nobel Prize.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 277,
              "stem": "Gadolinium contrast in MRI is CONTRAINDICATED when eGFR is below:",
              "options": [
                "30 ml/min",
                "90 ml/min",
                "60 ml/min",
                "45 ml/min",
                "15 ml/min"
              ],
              "answer": "A",
              "explanation": "Gadolinium-based MRI contrast agents are contraindicated when eGFR <30 ml/min due to the risk of nephrogenic systemic fibrosis (NSF) — a progressive, potentially fatal fibrosing condition affecting skin, joints, and internal organs. NSF was first described in 2000 and linked to gadolinium in renal impairment in 2006. Group II agents (gadobutrol, gadoteric acid) have a lower NSF risk than Group I agents. Always check renal function before gadolinium administration.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 278,
              "stem": "Bone scan (Tc-99m MDP) may be FALSE NEGATIVE in which condition?",
              "options": [
                "Osteosarcoma",
                "Paget's disease",
                "Stress fracture",
                "Osteomyelitis",
                "Myeloma"
              ],
              "answer": "E",
              "explanation": "Myeloma produces false-negative bone scans in up to 50% of cases because it is purely lytic — osteoclast-mediated destruction WITHOUT the compensatory osteoblastic response that takes up the Tc-99m MDP tracer. Bone scan detects OSTEOBLASTIC activity, not osteolytic. This is why skeletal survey (XR), low-dose whole-body CT, or PET-CT are preferred for myeloma staging. Other causes of false-negative bone scan include: purely lytic renal/thyroid metastases, avascular lesions, and very early disease.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 279,
              "stem": "STIR sequence on MRI is used to:",
              "options": [
                "Enhance bone detail",
                "Suppress FAT signal to make fluid/oedema more conspicuous",
                "Improve resolution of ligaments",
                "Demonstrate blood vessels",
                "Reduce scan time"
              ],
              "answer": "B",
              "explanation": "STIR (Short Tau Inversion Recovery) uses an inversion pulse timed to null the fat signal, making fluid and oedema much more conspicuous (bright against a dark background). It is particularly useful for detecting bone marrow oedema (stress fractures, infection, tumour infiltration) and soft tissue oedema. STIR is more reliable than fat-saturated T2 in areas of magnetic field inhomogeneity (e.g., around metal implants — though MARS sequences are specifically designed for metal artefact reduction).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 280,
              "stem": "DEXA scanning measures bone mineral density using:",
              "options": [
                "Single X-ray beam at one energy",
                "Ultrasound waves",
                "Two X-ray beams at different energies to distinguish bone from soft tissue",
                "MRI signal intensity",
                "CT Hounsfield units"
              ],
              "answer": "C",
              "explanation": "DEXA (Dual Energy X-ray Absorptiometry) uses TWO X-ray beams at different energy levels. The differential absorption of the two beams by bone mineral vs soft tissue allows mathematical separation, providing a precise measurement of areal bone mineral density (g/cm2). Results are reported as T-score (comparison to young adult peak bone mass) and Z-score (comparison to age-matched peers). T-score is used for postmenopausal women and men >50; Z-score for premenopausal women and younger men. WHO criteria: T-score >-1.0 normal, -1.0 to -2.5 osteopenia, <-2.5 osteoporosis (see Ch 6).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 281,
              "stem": "The three phases of a Tc-99m bone scan are:",
              "options": [
                "Arterial, venous, delayed",
                "Uptake, distribution, excretion",
                "Flow, blood pool, delayed (bone)",
                "Early, intermediate, late",
                "Perfusion, ventilation, metabolic"
              ],
              "answer": "C",
              "explanation": "Three-phase bone scan: (1) FLOW phase (dynamic, first 60 seconds) — shows arterial blood flow to the region, (2) BLOOD POOL phase (static, 2-5 minutes) — shows regional blood volume/hyperaemia, (3) DELAYED phase (static, 2-4 hours) — shows bone uptake of tracer (osteoblastic activity). All three phases positive in infection and fracture. Delayed phase only positive in most tumours and metabolic bone disease. Bone scan has high sensitivity but LOW specificity — a 'hot spot' requires correlation with clinical context and other imaging.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 282,
              "stem": "Which MRI sequence is used to reduce metal artefact around orthopaedic implants?",
              "options": [
                "Standard T1",
                "Standard T2",
                "STIR",
                "MARS (Metal Artefact Reduction Sequence)",
                "Gadolinium-enhanced T1"
              ],
              "answer": "D",
              "explanation": "MARS (Metal Artefact Reduction Sequence) uses modified pulse sequences (increased bandwidth, reduced echo spacing, view-angle tilting) to minimise the magnetic susceptibility artefact caused by ferromagnetic and paramagnetic implant materials. Standard MRI sequences produce large signal voids and geometric distortion around metal implants, obscuring adjacent structures. MARS allows evaluation of periprosthetic soft tissues, which is essential for diagnosing ALVAL/pseudotumour around MoM bearings, periprosthetic fractures, and soft tissue masses.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 283,
              "stem": "In a suspected stress fracture with normal X-rays, which imaging modality has the HIGHEST sensitivity?",
              "options": [
                "Repeat X-ray at 2 weeks",
                "MRI",
                "CT scan",
                "Ultrasound",
                "Bone scan"
              ],
              "answer": "B",
              "explanation": "MRI has the highest sensitivity (~98%) AND specificity (~99%) for stress fractures, detecting bone marrow oedema before a cortical fracture line is visible on any other modality. On MRI: T1 shows low signal in oedematous marrow (replaces normal bright fat), T2/STIR shows high signal (oedema). MRI also detects the fracture line itself and associated soft tissue changes. Bone scan has similar sensitivity (~98%) but lower specificity and requires a 72-hour delay for optimal sensitivity. CT is excellent for cortical detail but less sensitive for early stress reactions.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 284,
              "stem": "Proton density (PD) weighted MRI sequences are best for imaging:",
              "options": [
                "Bone marrow pathology",
                "Blood vessels",
                "Tumour enhancement",
                "Nerve roots",
                "Ligaments and menisci"
              ],
              "answer": "E",
              "explanation": "Proton density (PD) weighted sequences provide excellent contrast between structures with different proton densities, making them ideal for imaging LIGAMENTS and MENISCI (low signal = dark against intermediate signal cartilage and bright fluid). PD sequences are the workhorse of knee MRI for evaluating meniscal tears, cruciate ligaments, and articular cartilage. PD fat-saturated (PD FS) sequences combine the tissue contrast of PD with fat suppression, making fluid/oedema adjacent to ligaments and menisci more conspicuous.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Laboratory & Statistics",
          "range": "Q285-Q293",
          "questions": [
            {
              "number": 285,
              "stem": "A Type I error (alpha) in a study is:",
              "options": [
                "Rejecting the null hypothesis when it is actually true (false positive)",
                "Accepting the null hypothesis when it is actually false",
                "Selecting an inappropriate statistical test",
                "Using too small a sample size",
                "Failing to randomise properly"
              ],
              "answer": "A",
              "explanation": "Type I error (alpha, false positive) = rejecting the null hypothesis when it is actually true (concluding there IS a difference when there IS NOT). By convention, alpha is set at 0.05 (5%) — meaning we accept a 5% chance of a false positive. A P-value <0.05 means the probability of obtaining the observed result (or more extreme) by chance alone is less than 5%, if the null hypothesis were true. Type II error (beta, false negative) = accepting the null hypothesis when it is actually false. Power = 1 - beta (usually set at 80%).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 286,
              "stem": "The 68-95-99.7 rule describes:",
              "options": [
                "The percentage of studies achieving significance",
                "The probability of Type I error at different alpha levels",
                "The sensitivity of diagnostic tests at different cut-offs",
                "The percentage of data within 1, 2, and 3 standard deviations of the mean in a normal distribution",
                "The confidence intervals at different sample sizes"
              ],
              "answer": "D",
              "explanation": "In a normal (Gaussian) distribution: 68% of data falls within 1 SD of the mean, 95% within 2 SD, and 99.7% within 3 SD. This is fundamental to understanding confidence intervals: a 95% CI is approximately mean +/- 2 SE (where SE = SD/sqrt(n)). The 95% CI means that if the study were repeated 100 times, 95 of the resulting CIs would contain the true population parameter.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 287,
              "stem": "A study has a sensitivity of 95% and specificity of 90%. In a population with 1% disease prevalence, the PPV is approximately:",
              "options": [
                "1%",
                "50%",
                "9%",
                "88%",
                "95%"
              ],
              "answer": "C",
              "explanation": "With sensitivity 95%, specificity 90%, prevalence 1%: In 10,000 people: 100 have disease (prevalence 1%), 9,900 do not. True positives = 100 x 0.95 = 95. False positives = 9,900 x 0.10 = 990. PPV = 95/(95+990) = 95/1085 = ~8.8% (approximately 9%). Even with excellent test characteristics, the PPV is very low in a low-prevalence population because false positives vastly outnumber true positives. This illustrates why PPV depends critically on PREVALENCE, not just sensitivity/specificity.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 288,
              "stem": "An RCT is Level II evidence. What constitutes Level I evidence?",
              "options": [
                "Expert opinion",
                "Systematic review or meta-analysis of RCTs",
                "Case series",
                "Individual RCT",
                "Prospective cohort study"
              ],
              "answer": "B",
              "explanation": "Evidence hierarchy (Sackett 2000): Level I = Systematic review/meta-analysis of RCTs (highest quality), Level II = Individual RCT, Level III = Cohort studies (prospective/retrospective), Level IV = Case-control studies, Level V = Case series, expert opinion (lowest quality). A well-conducted systematic review pools data from multiple RCTs, increasing statistical power and providing a more precise estimate of treatment effect than any single RCT. The Cochrane Collaboration produces the gold standard systematic reviews.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 289,
              "stem": "The Kaplan-Meier method is used to analyse:",
              "options": [
                "Time-to-event (survival) data",
                "Continuous normally distributed data",
                "Categorical data",
                "Correlation between two variables",
                "Diagnostic test accuracy"
              ],
              "answer": "A",
              "explanation": "Kaplan-Meier analysis (1958) is the standard method for analysing time-to-event (survival) data — plotting the probability of 'surviving' (remaining event-free) over time. In orthopaedics, it is used for implant survival analysis (event = revision). The method handles CENSORED data (patients lost to follow-up or still event-free at study end). Results are presented as Kaplan-Meier curves with confidence intervals. Comparison between groups uses the log-rank test. NICE requires 10-year implant survival of >95% (based on registry data using Kaplan-Meier analysis).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 290,
              "stem": "Power in a study is defined as:",
              "options": [
                "The probability of Type I error",
                "The sample size divided by the effect size",
                "The P-value threshold",
                "The standard deviation of the outcome",
                "The probability of correctly rejecting a false null hypothesis (1 - beta)"
              ],
              "answer": "E",
              "explanation": "Power = 1 - beta (where beta = probability of Type II error/false negative). Power is the probability of CORRECTLY detecting a true difference when one exists. Convention is to set power at 80% (beta = 0.20) — meaning we accept a 20% chance of missing a true effect. Power depends on: (1) Sample size (larger = more power), (2) Effect size (larger difference = easier to detect), (3) Alpha level (higher alpha = more power but more false positives), (4) Variability in data (less variability = more power).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 291,
              "stem": "Which statistical test is appropriate for comparing a continuous, normally distributed outcome between two independent groups?",
              "options": [
                "Chi-squared test",
                "Mann-Whitney U test",
                "Paired t-test",
                "Unpaired (independent) t-test",
                "Fisher's exact test"
              ],
              "answer": "D",
              "explanation": "Unpaired (independent) t-test compares the means of two INDEPENDENT groups when the data is continuous and normally distributed. Paired t-test compares two related measurements (e.g., before and after in the same patients). Mann-Whitney U is the non-parametric equivalent of the unpaired t-test (used when data is NOT normally distributed or ordinal). Chi-squared and Fisher's exact tests are for categorical data (proportions). The decision tree: continuous + normal → t-test; continuous + non-normal → Mann-Whitney; categorical → chi-squared/Fisher's.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 292,
              "stem": "A funnel plot in a meta-analysis is used to assess:",
              "options": [
                "Publication bias",
                "Heterogeneity between studies",
                "Study quality",
                "Statistical significance",
                "Sample size adequacy"
              ],
              "answer": "A",
              "explanation": "A funnel plot is a scatter plot of individual study effect sizes (x-axis) against their precision/sample size (y-axis). In the absence of publication bias, the plot should be symmetrically distributed around the pooled effect estimate (shaped like an inverted funnel — large precise studies clustered near the top, small less precise studies spread wider at the bottom). ASYMMETRY suggests publication bias — typically, small studies with negative results are less likely to be published, creating a gap in one side of the funnel. Heterogeneity is assessed by the I-squared statistic, not the funnel plot.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 293,
              "stem": "'SnNOUT' means:",
              "options": [
                "A sensitive test, when positive, rules in disease",
                "A sensitive test, when NEGATIVE, rules OUT disease",
                "A specific test, when negative, rules out disease",
                "A specific test, when positive, rules out disease",
                "Sensitivity and specificity are equal"
              ],
              "answer": "B",
              "explanation": "SnNOUT: A highly Sensitive test, when Negative, rules OUT disease. If a test with 99% sensitivity is negative, you can be very confident the disease is absent (very few false negatives). SpPIN: A highly Specific test, when Positive, rules IN disease. If a test with 99% specificity is positive, you can be very confident the disease is present (very few false positives). These mnemonics help apply diagnostic test properties in clinical decision-making.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        }
      ]
    },
    {
      "title": "Applied Anatomy",
      "chapters": [
        {
          "title": "Upper Limb Anatomy",
          "range": "Q294-Q303",
          "questions": [
            {
              "number": 294,
              "stem": "The scaphoid receives 70-80% of its blood supply via which route?",
              "options": [
                "Volar branches entering the tubercle",
                "Interosseous branches from the ulnar artery",
                "Direct branches from the anterior interosseous artery",
                "Palmar arch branches entering the waist",
                "Dorsal carpal branches of the radial artery entering the dorsal ridge (retrograde supply)"
              ],
              "answer": "E",
              "explanation": "Gelberman et al. (1980) demonstrated that 70-80% of the scaphoid's blood supply comes from dorsal carpal branches of the radial artery entering the dorsal ridge, supplying the bone in a RETROGRADE (distal to proximal) direction. The remaining 20-30% enters the tubercle volarly. There are NO anastomoses between dorsal and palmar vessels. The proximal pole has the most tenuous supply — waist fractures disrupt the retrograde flow, causing AVN of the proximal pole.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 295,
              "stem": "The radial nerve lies in the spiral groove approximately how far above the lateral epicondyle?",
              "options": [
                "5 cm",
                "7 cm",
                "14 cm",
                "10 cm",
                "20 cm"
              ],
              "answer": "C",
              "explanation": "The radial nerve lies in the spiral groove of the humerus approximately 14cm above the lateral epicondyle (accompanied by the profunda brachii artery). It pierces the lateral intermuscular septum approximately 7cm above the lateral epicondyle to enter the anterior compartment. These distances are critical for safe surgical approaches to the humerus — the nerve must be identified and protected during posterior approaches to the mid-shaft.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 296,
              "stem": "The ulnar paradox describes:",
              "options": [
                "Ulnar nerve regeneration is faster than other nerves",
                "Higher ulnar lesions produce LESS clawing because FDP is also paralysed",
                "Higher ulnar lesions produce MORE clawing than lower lesions",
                "Ulnar nerve injury causes thumb weakness",
                "Ulnar nerve repairs have paradoxically good outcomes"
              ],
              "answer": "B",
              "explanation": "The ulnar paradox: a HIGHER ulnar nerve lesion (e.g., at elbow) produces LESS clawing than a LOW lesion (at wrist) because in a high lesion, FDP to the ring and little fingers is also paralysed — so the IP joints cannot flex, reducing the visible claw deformity. In a LOW lesion, FDP is intact, producing unopposed IP flexion with MCP hyperextension (from loss of lumbricals/interossei) = MORE obvious clawing. The functional deficit is actually WORSE with the higher lesion despite less visible deformity.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 297,
              "stem": "Froment's sign tests which muscle?",
              "options": [
                "First dorsal interosseous",
                "Abductor pollicis brevis",
                "Flexor pollicis longus",
                "Adductor pollicis",
                "Opponens pollicis"
              ],
              "answer": "D",
              "explanation": "Froment's sign tests ADDUCTOR POLLICIS (ulnar nerve, deep motor branch). The patient is asked to grip a piece of paper between thumb and index finger. If adductor pollicis is weak (ulnar nerve palsy), the patient compensates by flexing the thumb IP joint using FPL (median nerve, AIN branch) — this IP flexion is the positive Froment's sign. Wartenberg's sign (abducted little finger) tests the third palmar interosseous (also ulnar nerve).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 298,
              "stem": "The carpal tunnel contains how many tendons and which nerve?",
              "options": [
                "9 tendons and the median nerve",
                "7 tendons and the ulnar nerve",
                "9 tendons and the ulnar nerve",
                "11 tendons and the median nerve",
                "8 tendons and the median nerve"
              ],
              "answer": "A",
              "explanation": "The carpal tunnel contains 9 tendons (4 FDP, 4 FDS, 1 FPL) and the median nerve. The median nerve is the most superficial/palmar structure. FPL is the most radial. FDS to middle and ring fingers are palmar to FDS of index and little. Palmaris longus runs OUTSIDE the tunnel on its surface. The ulnar nerve passes through Guyon's canal (separate from the carpal tunnel), with the floor of Guyon's being the transverse carpal ligament (roof of the carpal tunnel).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 299,
              "stem": "The axillary nerve is at risk during anterior shoulder dislocation because it:",
              "options": [
                "Runs through the rotator interval",
                "Crosses the acromion superficially",
                "Passes through the quadrangular space inferior to the glenohumeral capsule",
                "Runs with the suprascapular artery",
                "Passes through the triangular interval"
              ],
              "answer": "C",
              "explanation": "The axillary nerve passes through the quadrangular space (bordered by subscapularis superiorly, teres major inferiorly, long head of triceps medially, and humeral surgical neck laterally) in close proximity to the inferior glenohumeral capsule. During anterior dislocation, the humeral head displaces anteroinferiorly, stretching or compressing the axillary nerve against the inferior capsule. Injury causes deltoid paralysis (can't abduct beyond 15°) and sensory loss over the regimental badge area. The nerve is protected during surgery by adduction and external rotation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 300,
              "stem": "The recurrent motor branch of the median nerve supplies which muscles (LOAF)?",
              "options": [
                "Lumbricals 3+4, Opponens digiti minimi, Abductor digiti minimi, Flexor digiti minimi",
                "All interossei, Adductor pollicis, All lumbricals, All hypothenar muscles",
                "Lumbricals 1-4, Opponens pollicis, All interossei, FPL",
                "Lumbricals 1+2, Opponens pollicis, Adductor pollicis, FPB",
                "Lumbricals 1+2, Opponens pollicis, Abductor pollicis brevis, Flexor pollicis brevis (superficial head)"
              ],
              "answer": "E",
              "explanation": "LOAF = Lumbricals 1+2 (radial two), Opponens pollicis, Abductor pollicis brevis (most important for opposition, most affected in CTS), and Flexor pollicis brevis (superficial head only — deep head is ulnar nerve). The recurrent motor branch has variable anatomy (Lanz 1977: extraligamentous 46%, subligamentous 31%, transligamentous 23%) — staying ulnar to the median nerve during carpal tunnel release protects all variations.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 301,
              "stem": "The suprascapular nerve passes through the suprascapular notch. Which structure runs OVER the superior transverse scapular ligament?",
              "options": [
                "Suprascapular artery",
                "Suprascapular nerve",
                "Dorsal scapular nerve",
                "Long thoracic nerve",
                "Axillary artery"
              ],
              "answer": "A",
              "explanation": "'Water (artery) under the bridge (ligament)' — the suprascapular NERVE passes UNDER the superior transverse scapular ligament through the notch, while the suprascapular ARTERY passes OVER the ligament. The nerve supplies both supraspinatus and infraspinatus. Compression in the suprascapular notch (by a ganglion from the labrum) causes wasting of BOTH muscles. Compression at the spinoglenoid notch (where the artery and nerve both pass) causes isolated infraspinatus wasting.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 302,
              "stem": "In Henry's anterior approach to the forearm (volar approach to the radius), the internervous plane is between:",
              "options": [
                "Brachioradialis (radial nerve) and flexor carpi radialis (median nerve)",
                "Pronator teres (median nerve) and brachioradialis (radial nerve)",
                "Biceps and brachialis",
                "FCU (ulnar nerve) and FDS (median nerve)",
                "Brachioradialis (radial nerve) and pronator teres, then FCR (median nerve)"
              ],
              "answer": "E",
              "explanation": "Henry's approach uses the interval between brachioradialis (radial nerve) laterally and pronator teres/FCR (median nerve) medially in the proximal forearm, then between brachioradialis and FCR distally. The plane is between the radial and median nerve territories. Structures at risk include: the superficial branch of the radial nerve (runs under brachioradialis), the radial artery (between brachioradialis and FCR), and the PIN (protected by supinating the forearm during exposure of the proximal radius — moves the PIN away from the surgical field).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 303,
              "stem": "The 6 extensor compartments of the wrist — which compartment is affected in de Quervain's tenosynovitis?",
              "options": [
                "2nd (ECRL and ECRB)",
                "3rd (EPL)",
                "1st (APL and EPB)",
                "4th (EDC and EIP)",
                "6th (ECU)"
              ],
              "answer": "C",
              "explanation": "De Quervain's tenosynovitis affects the FIRST extensor compartment, which contains APL (abductor pollicis longus) and EPB (extensor pollicis brevis). Finkelstein's test (ulnar deviation of the wrist with the thumb enclosed in a fist) stretches these tendons and reproduces pain. The 3rd compartment (EPL around Lister's tubercle) is the site of EPL rupture after distal radius fracture. The 4th compartment contains the PIN on its floor (radial side). The 5th compartment overlies the DRUJ. The 6th compartment contains ECU.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Lower Limb Anatomy",
          "range": "Q304-Q313",
          "questions": [
            {
              "number": 304,
              "stem": "The medial femoral circumflex artery (MFCA) is the dominant blood supply to the femoral head. It passes between which structures?",
              "options": [
                "Rectus femoris and vastus lateralis",
                "Gluteus medius and minimus",
                "Piriformis and obturator internus",
                "Psoas and adductor brevis/magnus",
                "Sartorius and TFL"
              ],
              "answer": "D",
              "explanation": "Gautier et al. (2000) showed the MFCA passes between psoas anteriorly and adductor brevis/magnus posteriorly, just medial to the psoas insertion on the lesser trochanter. It gives off the deep branch that ascends along the posterior femoral neck to provide the lateral epiphyseal arteries — the dominant supply to the femoral head. This anatomical course makes the MFCA vulnerable in posterior hip dislocations and displaced intracapsular NOF fractures.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 305,
              "stem": "The superior gluteal nerve runs between which muscles, and injury to it causes what clinical sign?",
              "options": [
                "Gluteus maximus and medius — Trendelenburg sign",
                "Gluteus medius and minimus — Trendelenburg sign",
                "Piriformis and gluteus medius — foot drop",
                "Gluteus minimus and obturator internus — sciatic pain",
                "Tensor fascia lata and sartorius — hip flexion weakness"
              ],
              "answer": "B",
              "explanation": "The superior gluteal nerve (L4,L5,S1) exits the pelvis ABOVE piriformis through the greater sciatic foramen and runs between GLUTEUS MEDIUS and GLUTEUS MINIMUS. It supplies both muscles (plus TFL). Injury causes abductor weakness → positive Trendelenburg sign and gait. At risk in the anterolateral (Hardinge) approach where the gluteus medius split must not extend >5cm above the greater trochanter. Also at risk from excessive retraction during any hip approach.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 306,
              "stem": "The common peroneal nerve is vulnerable at the fibular neck because it:",
              "options": [
                "Passes deep within the lateral compartment",
                "Is protected by thick muscle",
                "Passes through the interosseous membrane",
                "Is tethered to the fibular head by a ligament",
                "Wraps around the fibular neck superficially with minimal soft tissue protection"
              ],
              "answer": "E",
              "explanation": "The CPN wraps around the neck of the fibula where it is extremely superficial with minimal soft tissue coverage — only the periosteum and thin fascia separate it from the bone surface. This makes it vulnerable to: direct trauma (fibular neck fractures), compression (tight casts, leg crossing, prolonged lateral position), and traction (knee dislocation, varus injury). CPN injury produces foot drop (can't dorsiflex), loss of eversion, and sensory loss on the dorsum of the foot (except 1st web space = deep peroneal).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 307,
              "stem": "The structures behind the medial malleolus, from anterior to posterior, are (Tom Dick ANd Harry):",
              "options": [
                "Tibialis anterior, FDL, Artery/Nerve, FHL",
                "Tibialis posterior, FDL, posterior tibial Artery/tibial Nerve, FHL",
                "Tibialis posterior, FHL, Artery/Nerve, FDL",
                "FDL, Tibialis posterior, Artery/Nerve, FHL",
                "FHL, FDL, Artery/Nerve, Tibialis posterior"
              ],
              "answer": "B",
              "explanation": "Behind the medial malleolus (in the tarsal tunnel), the structures from anterior to posterior are: Tibialis Posterior (T), Flexor Digitorum Longus (D), posterior tibial Artery and tibial Nerve (AN), Flexor Hallucis Longus (H) — Tom Dick ANd Harry. This order is consistently tested. TP is the most anterior/superficial, and FHL is the most posterior. The tibial nerve divides into medial and lateral plantar nerves within or just distal to the tarsal tunnel.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 308,
              "stem": "In the posterior approach to the hip (Moore/Southern), which structures are detached from the greater trochanter?",
              "options": [
                "Gluteus medius and minimus",
                "Vastus lateralis and vastus intermedius",
                "Short external rotators (piriformis, obturator internus, gemelli)",
                "Iliopsoas and rectus femoris",
                "Gluteus maximus"
              ],
              "answer": "C",
              "explanation": "The posterior approach involves splitting gluteus maximus in line with its fibres (between superior and inferior gluteal nerve supply) and then detaching the short external rotators from the greater trochanter: piriformis, superior gemellus, obturator internus, and inferior gemellus. Quadratus femoris is often left intact. The sciatic nerve is the KEY structure at risk — it runs on the short external rotators, deep to gluteus maximus. The nerve is protected by keeping the hip in extension and placing retractors on bone (not under the rotators where the nerve lies).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 309,
              "stem": "Compartment syndrome of the leg most commonly affects which compartment FIRST?",
              "options": [
                "Superficial posterior",
                "Deep posterior",
                "Lateral",
                "Anterior",
                "All compartments equally"
              ],
              "answer": "D",
              "explanation": "The ANTERIOR compartment is most commonly and most EARLY affected in leg compartment syndrome because: (1) it has the least compliant fascial boundaries (interosseous membrane posteriorly, tibia medially, tight crural fascia laterally and anteriorly), (2) it has the smallest volume relative to its contents, and (3) the anterior tibial artery and deep peroneal nerve run through it and are vulnerable to compression. Clinical features: pain out of proportion, pain on passive toe extension (stretches anterior compartment contents), sensory loss in first web space (deep peroneal), and eventually weakness of dorsiflexion. Compartment pressure >30mmHg or within 30mmHg of diastolic = fasciotomy (Mubarak 1977).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 310,
              "stem": "The popliteal artery is the DEEPEST structure in the popliteal fossa. The order of structures from superficial to deep is:",
              "options": [
                "Nerve, vein, artery",
                "Artery, vein, nerve",
                "Nerve, artery, vein",
                "Vein, artery, nerve",
                "Artery, nerve, vein"
              ],
              "answer": "A",
              "explanation": "In the popliteal fossa, structures from SUPERFICIAL to DEEP (posterior to anterior) are: tibial NERVE (most superficial/posterior), popliteal VEIN (middle), popliteal ARTERY (deepest/most anterior — lying directly on the posterior capsule). This arrangement means the artery is closest to the knee joint and therefore most vulnerable during knee dislocation. The common peroneal nerve separates from the tibial nerve at the apex of the fossa and follows the biceps tendon laterally around the fibular neck.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 311,
              "stem": "The lateral ankle ligament complex consists of three bands. The WEAKEST and most commonly injured is:",
              "options": [
                "CFL (calcaneofibular ligament)",
                "PTFL (posterior talofibular ligament)",
                "ATFL (anterior talofibular ligament)",
                "Deltoid ligament",
                "Spring ligament"
              ],
              "answer": "C",
              "explanation": "The ATFL is the weakest of the three lateral ankle ligament bands and is the most commonly injured in ankle inversion sprains. It resists anterior translation of the talus and inversion in plantarflexion. The CFL resists inversion in neutral/dorsiflexion. The PTFL is the strongest band and is rarely injured in isolation. The deltoid (medial) ligament is the strongest ankle ligament overall. Lateral ankle sprains account for approximately 85% of all ankle sprains, with ATFL injury in virtually all cases.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 312,
              "stem": "The sciatic nerve is composed of approximately what percentage nerve tissue?",
              "options": [
                "50% nerve, 50% connective tissue",
                "80% nerve, 20% connective tissue",
                "95% nerve, 5% connective tissue",
                "Equal proportions of nerve and vascular tissue",
                "20% nerve, 80% connective tissue"
              ],
              "answer": "E",
              "explanation": "The sciatic nerve is composed of only approximately 20% nerve tissue and 80% connective tissue. This high connective tissue proportion makes surgical repair outcomes poor — bundle-to-bundle matching is difficult because the nerve fascicles are widely separated by connective tissue. This is why nerve grafting and nerve transfers are often preferred over direct repair for sciatic nerve injuries. The sciatic nerve is the largest nerve in the body.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 313,
              "stem": "The Lisfranc ligament connects which two structures?",
              "options": [
                "Calcaneum to navicular (spring ligament)",
                "Talus to calcaneum",
                "Navicular to cuboid",
                "Medial cuneiform to base of 2nd metatarsal",
                "Tibia to fibula (syndesmosis)"
              ],
              "answer": "D",
              "explanation": "The Lisfranc ligament connects the MEDIAL CUNEIFORM to the BASE OF THE 2ND METATARSAL. It is the key stabiliser of the tarsometatarsal (Lisfranc) joint complex. Disruption of this ligament (Lisfranc injury) causes instability of the midfoot and if missed, leads to progressive deformity and traumatic arthritis. It is frequently missed on initial X-rays — a fleck fracture at the base of the 2nd metatarsal (the 'fleck sign') should raise suspicion. Weightbearing XR or CT confirms the diagnosis.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Spine & Pelvis Anatomy",
          "range": "Q314-Q323",
          "questions": [
            {
              "number": 314,
              "stem": "Denis's three-column model defines spinal instability as failure of:",
              "options": [
                "Two or more columns",
                "The anterior column alone",
                "The posterior column alone",
                "Any single column",
                "All three columns"
              ],
              "answer": "A",
              "explanation": "Denis (1983) defined instability as failure of TWO or more columns. The middle column is the key to stability — if intact, the injury is generally stable. A burst fracture (middle column failure) with intact posterior column may be stable. A burst fracture with posterior ligamentous complex disruption (two-column failure) is unstable. A compression fracture (anterior column only) is stable. This model guides the surgical decision: unstable injuries typically require operative stabilisation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 315,
              "stem": "Central cord syndrome is characterised by:",
              "options": [
                "Complete paralysis below the level of injury",
                "Upper limb weakness greater than lower limb, with sacral sparing",
                "Lower limb weakness greater than upper limb",
                "Pure sensory loss without motor deficit",
                "Ipsilateral motor loss and contralateral sensory loss"
              ],
              "answer": "B",
              "explanation": "Central cord syndrome (Schneider 1954): Upper limb weakness > lower limb, with variable sensory loss and sacral sparing (preserved perianal sensation = incomplete injury). The somatotopic organisation of the corticospinal tracts (cervical fibres centrally, sacral fibres peripherally) explains this pattern — central cord damage affects the cervical fibres (upper limbs) more than the peripheral sacral fibres (lower limbs). It is the MOST COMMON incomplete SCI, typically from hyperextension in elderly patients with cervical spondylosis.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 316,
              "stem": "The artery of Adamkiewicz is the dominant segmental artery supplying the spinal cord. At which level does it most commonly arise?",
              "options": [
                "C5-C7",
                "T9-T12 (left side in 80%)",
                "T2-T5",
                "L3-L5",
                "S1-S3"
              ],
              "answer": "B",
              "explanation": "The artery of Adamkiewicz (arteria radicularis magna) most commonly arises from the left side (80%) at the T9-T12 level (range T8-L2). It is the dominant segmental artery supplying the anterior spinal artery in the lower two-thirds of the cord. Damage during thoracolumbar surgery (particularly anterior approaches) or aortic surgery can cause anterior cord syndrome — devastating paralysis with loss of motor function, pain, and temperature sensation but preserved proprioception (posterior columns supplied by separate posterior spinal arteries).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 317,
              "stem": "The posterior longitudinal ligament (PLL) is:",
              "options": [
                "Widest over the disc and narrowest over the vertebral body",
                "Uniform width throughout",
                "Only present in the cervical spine",
                "Widest over the vertebral body and narrowest over the disc",
                "The strongest spinal ligament"
              ],
              "answer": "D",
              "explanation": "The PLL is WIDE over the vertebral body and NARROW over the disc — the opposite of what might seem logical. This narrowing over the disc means the posterolateral annulus has less PLL reinforcement, explaining why most disc herniations are POSTEROLATERAL (the PLL partially blocks central herniation). The ALL is the widest and strongest spinal ligament (wide over the disc, narrow over the body — opposite pattern to PLL). The ligamentum flavum connects adjacent laminae and has the highest elastin content of any ligament.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 318,
              "stem": "In the ASIA Impairment Scale, Grade C means:",
              "options": [
                "Complete injury — no motor or sensory function below the level",
                "Sensory incomplete — sensory but no motor function preserved",
                "Motor incomplete — motor function preserved, majority of key muscles below level have strength < 3",
                "Motor incomplete — majority of key muscles below level have strength ≥ 3",
                "Normal motor and sensory function"
              ],
              "answer": "C",
              "explanation": "ASIA Impairment Scale: A = Complete (no sensory or motor below level, including S4-5). B = Sensory Incomplete (sensory preserved but no motor below level, including S4-5). C = Motor Incomplete (motor preserved below level but MAJORITY of key muscles grade <3). D = Motor Incomplete (motor preserved, MAJORITY of key muscles grade ≥3). E = Normal. The distinction between C and D is clinically important: Grade D patients are typically community ambulators while Grade C patients are often wheelchair-dependent.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 319,
              "stem": "A posterolateral disc prolapse at L4/5 will compress which nerve root?",
              "options": [
                "L5",
                "L3",
                "L4",
                "S1",
                "L4 and L5"
              ],
              "answer": "A",
              "explanation": "A posterolateral disc prolapse at L4/5 compresses the TRAVERSING L5 nerve root (which crosses the disc level before exiting at the L5/S1 foramen). The EXITING L4 root exits at the L4/5 foramen ABOVE the disc and is usually spared in a posterolateral prolapse. However, a FAR LATERAL (foraminal) prolapse at L4/5 would compress the EXITING L4 root. Rule: posterolateral prolapse compresses the TRAVERSING root (numbered one level below the disc). L5 root = dorsiflexion weakness (foot drop), great toe extension (EHL), sensation over dorsum of foot and lateral leg.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 320,
              "stem": "The ligamentum flavum has the highest content of which protein compared to other spinal ligaments?",
              "options": [
                "Type I collagen",
                "Type II collagen",
                "Fibrillin",
                "Keratin",
                "Elastin"
              ],
              "answer": "E",
              "explanation": "The ligamentum flavum has the highest elastin content (approximately 80% elastin, 20% collagen) of any ligament in the body — explaining its yellow colour ('flavum' = yellow in Latin). The high elastin content provides elastic recoil that maintains tension on the ligament throughout spinal flexion and extension, preventing it from buckling into the spinal canal during extension. In spondylotic spinal stenosis, the ligamentum flavum hypertrophies and loses elasticity, contributing to posterior canal narrowing.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 321,
              "stem": "The sacroiliac joint (SIJ) derives its stability primarily from:",
              "options": [
                "Massive ligamentous support (anterior, posterior, and interosseous sacroiliac ligaments)",
                "Bony congruence of flat joint surfaces",
                "Muscle contraction across the joint",
                "Cartilaginous fusion",
                "The pubic symphysis"
              ],
              "answer": "A",
              "explanation": "SIJ stability is predominantly LIGAMENTOUS. The posterior sacroiliac ligaments and interosseous sacroiliac ligament are among the strongest in the body. The SIJ has two parts: an anterior synovial portion (auricular surface) and a posterior ligamentous portion. The 'self-locking' mechanism occurs because the sacrum is wedge-shaped (wider superiorly) — axial load drives the sacrum into the iliac bones, and the posterior ligaments prevent it from displacing anteriorly. Disruption of these ligaments (posterior pelvic ring injury) creates instability requiring surgical fixation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 322,
              "stem": "The vertebral artery enters the transverse foramen at which cervical level?",
              "options": [
                "C1",
                "C6",
                "C2",
                "C3",
                "C7"
              ],
              "answer": "B",
              "explanation": "The vertebral artery enters the transverse foramen of C6 and ascends through the transverse foramina of C6 to C1. At C1 (atlas), it runs in a groove on the posterior arch before entering the foramen magnum. The artery is at risk during: lateral mass screw placement in the cervical spine, anterior cervical approaches below C6, and C1-C2 fixation procedures (Harms technique uses the C1 lateral mass, which is close to the vertebral artery groove). The vertebral artery anomalously enters at C5 or C7 in approximately 5% of people.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 323,
              "stem": "Cauda equina syndrome is a lower motor neuron lesion because:",
              "options": [
                "The spinal cord extends to the sacrum",
                "The nerve roots are protected by the dura",
                "The conus medullaris ends at L1/2 and below this level only nerve roots (cauda equina) exist",
                "LMN lesions are always more severe than UMN",
                "The cauda equina contains ascending sensory tracts"
              ],
              "answer": "C",
              "explanation": "The spinal cord (conus medullaris) ends at approximately L1/2 in adults. Below this level, the spinal canal contains only nerve roots (the cauda equina — 'horse's tail') suspended in CSF. These are peripheral nerves (LMN), not spinal cord (UMN). Therefore, compression of the cauda equina produces LMN signs: flaccid paralysis, areflexia, muscle wasting, and autonomic dysfunction (urinary retention, faecal incontinence, saddle anaesthesia). This is a SURGICAL EMERGENCY — decompression within 48 hours for best outcomes (some evidence suggests within 24 hours for complete CES).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        }
      ]
    },
    {
      "title": "Supplementary",
      "chapters": [
        {
          "title": "Theatre, Sterilisation & Wound Healing",
          "range": "Q324-Q333",
          "questions": [
            {
              "number": 324,
              "stem": "The Lidwell MRC trial (1982) demonstrated that antibiotic-loaded bone cement reduced deep infection by a factor of approximately:",
              "options": [
                "2-fold",
                "5-fold",
                "20-fold",
                "11-fold",
                "50-fold"
              ],
              "answer": "D",
              "explanation": "The Lidwell MRC trial demonstrated that prophylactic antibiotic-loaded bone cement provided an 11-fold reduction in deep infection rates in joint arthroplasty. The trial also showed that ultraclean air (laminar flow + body exhaust suits) reduced infection from 1.5% to 0.6%. The combination of ALBC + ultraclean air produced the lowest infection rates. This landmark trial remains the foundation of evidence for current SSI prevention practice in arthroplasty.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 325,
              "stem": "The WHO Surgical Safety Checklist consists of three phases:",
              "options": [
                "Pre-op, Intra-op, Post-op",
                "Consent, Anaesthesia, Surgery",
                "Preparation, Execution, Closure",
                "Sterile, Clean, Recovery",
                "Sign In (before anaesthesia), Time Out (before incision), Sign Out (before leaving theatre)"
              ],
              "answer": "E",
              "explanation": "The WHO Surgical Safety Checklist (Haynes et al. NEJM 2009): SIGN IN (before induction of anaesthesia — confirm patient identity, procedure, site marking, allergies, anaesthesia safety), TIME OUT (before skin incision — confirm all team members, procedure, antibiotics given, anticipated critical events, imaging displayed), SIGN OUT (before patient leaves theatre — confirm procedure performed, instrument/swab count, specimen labelling, key recovery concerns). Implementation reduced mortality by 47% and complications by 36%.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 326,
              "stem": "In the CDC wound classification, a Class III (contaminated) wound has an expected SSI rate of approximately:",
              "options": [
                "<2%",
                "5-10%",
                "15-20%",
                "30-40%",
                "50%"
              ],
              "answer": "C",
              "explanation": "CDC wound classification (Mangram 1999): Class I (Clean) <2% SSI — elective, non-traumatic, no entry into GI/GU/respiratory. Class II (Clean-contaminated) <10% — controlled entry into contaminated tract. Class III (Contaminated) 15-20% — open traumatic wound <4 hours, major break in sterile technique, gross GI spillage. Class IV (Dirty) >30% — established infection, perforated viscus, old traumatic wound. Most elective orthopaedic surgery is Class I.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 327,
              "stem": "Wound healing reaches maximum tensile strength at approximately what percentage of the original tissue strength?",
              "options": [
                "70-80%",
                "40-50%",
                "60-70%",
                "90-95%",
                "100%"
              ],
              "answer": "A",
              "explanation": "Healed wounds reach approximately 70-80% of original tissue tensile strength, typically at 1 year or later. Wound strength never returns to 100% because the repaired scar tissue has a different collagen architecture (parallel bundles rather than the basket-weave pattern of normal dermis) and fewer cross-links. At 1 week, strength is ~3%. At 3 weeks, ~20%. At 6 weeks, ~40%. At 3 months, ~60%. By 1 year, ~70-80%. This plateau explains why late wound dehiscence is rare but reinjury at the scar site may occur at lower forces than original tissue.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 328,
              "stem": "Which cell is the KEY orchestrator of wound healing (as in fracture healing)?",
              "options": [
                "Neutrophil",
                "Macrophage",
                "Fibroblast",
                "Platelet",
                "Keratinocyte"
              ],
              "answer": "B",
              "explanation": "The MACROPHAGE is the key orchestrating cell of wound healing (arriving at 48-72 hours, replacing the initial neutrophil response). It phagocytoses debris, releases growth factors (PDGF, TGF-beta, VEGF, FGFs) that recruit fibroblasts, stimulates angiogenesis, bridges innate and adaptive immunity, and coordinates the transition from inflammation to proliferation. This is the same central role macrophages play in fracture healing (see Ch 4). Depletion of macrophages severely impairs wound and fracture healing.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 329,
              "stem": "Ethylene oxide sterilisation is used for heat-sensitive items because it:",
              "options": [
                "Operates at high temperature",
                "Is faster than autoclaving",
                "Provides the cheapest sterilisation method",
                "Sterilises at low temperature (37-63°C) by alkylating microbial DNA",
                "Requires no aeration time"
              ],
              "answer": "D",
              "explanation": "Ethylene oxide (EtO) sterilises at low temperatures (37-63°C) by alkylating microbial DNA and proteins, making it suitable for heat-sensitive items (plastics, fibre-optic equipment, electrical components, powered instruments). Disadvantages: slow process (total cycle including aeration takes 12-24 hours), toxic gas (mutagenic, carcinogenic — requires thorough aeration to remove residual gas), flammable, and expensive. Autoclaving (steam at 134°C for 3 minutes or 121°C for 15 minutes) is preferred for heat-resistant items due to speed and reliability.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 330,
              "stem": "Autoclaving uses steam at what temperature and duration for standard sterilisation?",
              "options": [
                "100°C for 30 minutes",
                "160°C for 60 minutes",
                "180°C for 120 minutes",
                "90°C for 45 minutes",
                "121°C for 15 minutes or 134°C for 3 minutes"
              ],
              "answer": "E",
              "explanation": "Standard autoclaving: 121°C at 15 psi for 15 minutes OR 134°C at 30 psi for 3 minutes (porous load/flash sterilisation). The combination of high-pressure steam and temperature denatures microbial proteins and destroys all microorganisms including spores. It is the most reliable and cost-effective sterilisation method for heat-resistant instruments. The 134°C/3-minute cycle is also used for prion decontamination (CJD), though additional precautions (1M NaOH soak) are recommended for high-risk cases.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 331,
              "stem": "Type III collagen is gradually replaced by Type I collagen during which phase of wound healing?",
              "options": [
                "Haemostasis",
                "Remodelling",
                "Inflammation",
                "Proliferation",
                "All phases equally"
              ],
              "answer": "B",
              "explanation": "During the REMODELLING phase (3 weeks to 1+ year), Type III collagen (initially deposited by fibroblasts during the proliferation phase, comprising up to 30% of wound collagen) is gradually replaced by Type I collagen through simultaneous synthesis and degradation by matrix metalloproteinases (MMPs). Cross-linking progressively increases, improving tensile strength. The same collagen maturation process occurs in tendon, ligament, and fracture healing (see Ch 4, Ch 8, Ch 10). Final wound composition returns toward normal proportions (~80% Type I, 20% Type III).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 332,
              "stem": "Laminar (unidirectional) airflow in an orthopaedic theatre achieves approximately how many air changes per hour?",
              "options": [
                "10-20",
                "50-100",
                "150-200",
                "300+",
                "1000+"
              ],
              "answer": "D",
              "explanation": "Laminar (unidirectional) airflow systems achieve 300+ air changes per hour (compared to 20-25 in conventional ventilation). The air passes through HEPA filters that remove 99.97% of particles ≥0.3 micrometres, then flows vertically downward over the surgical field in a uniform unidirectional pattern, sweeping airborne contaminants away. This reduces airborne bacterial colony-forming units from ~350 CFU/m3 (conventional) to <10 CFU/m3 at the operative site. The plenum (source of positive-pressure filtered air) must be large enough to cover the entire surgical field.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 333,
              "stem": "Diathermy (electrosurgery) causes tissue damage by which mechanism?",
              "options": [
                "Direct electrical stimulation of muscles",
                "Chemical burn from electrolytic products",
                "Resistive heating of tissue as current passes through",
                "Magnetic field disruption of cellular membranes",
                "Ultrasonic vibration of tissue"
              ],
              "answer": "C",
              "explanation": "Diathermy works by passing high-frequency alternating current (300kHz-3MHz) through tissue. The tissue's RESISTANCE to current flow generates heat (Joule heating: heat = I²R). MONOPOLAR: Current passes from the active electrode through the patient to a large return plate — allows cutting (continuous, high current density = vaporisation) and coagulation (intermittent, lower density = protein denaturation). BIPOLAR: Current passes between two closely spaced prongs — more precise, less tissue damage, safer near nerves. High frequency prevents neuromuscular stimulation (which occurs at <100kHz).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Rheumatology & Crystal Arthropathies",
          "range": "Q334-Q343",
          "questions": [
            {
              "number": 334,
              "stem": "Anti-CCP antibodies are more SPECIFIC for RA than rheumatoid factor because:",
              "options": [
                "They are directed against citrullinated proteins specific to RA synovium, whereas RF is non-specific IgM against IgG",
                "They are always present in RA",
                "They are cheaper to measure",
                "They correlate better with disease activity",
                "They can be used to monitor treatment response"
              ],
              "answer": "A",
              "explanation": "Anti-CCP (anti-cyclic citrullinated peptide) antibodies target citrullinated proteins — proteins where arginine has been converted to citrulline by peptidyl arginine deiminase (PAD), a process particularly active in the inflamed RA synovium. This makes anti-CCP highly specific for RA (95% specificity vs ~80% for RF). RF (rheumatoid factor) is IgM directed against the Fc portion of IgG — it is present in many conditions (infections, other autoimmune diseases, elderly healthy individuals) making it less specific. Anti-CCP can be positive years before clinical RA onset and predicts erosive disease.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 335,
              "stem": "Monosodium urate crystals in gout are identified under polarised light as:",
              "options": [
                "Rhomboid-shaped, positively birefringent",
                "Round, non-birefringent",
                "Rod-shaped, positively birefringent",
                "Cuboid, negatively birefringent",
                "Needle-shaped, negatively birefringent (yellow when parallel to compensator)"
              ],
              "answer": "E",
              "explanation": "MSU crystals are NEEDLE-shaped and NEGATIVELY birefringent — they appear YELLOW when PARALLEL to the red compensator axis (mnemonic: 'Yellow Parallel Negative = Urate' or 'YPN'). CPPD crystals (pseudogout) are RHOMBOID-shaped and WEAKLY POSITIVELY birefringent — Blue when Parallel ('BPP = Blue Parallel Positive = CPPD/Pseudogout'). This crystal identification is one of the most commonly tested points in the FRCS examination.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 336,
              "stem": "The target serum urate level for chronic gout management is below:",
              "options": [
                "200 micromol/L",
                "300 micromol/L",
                "360 micromol/L",
                "420 micromol/L",
                "500 micromol/L"
              ],
              "answer": "B",
              "explanation": "The target serum urate is <300 micromol/L (some guidelines use <360 for non-tophaceous gout). This is below the physiological saturation point for urate crystal formation. Achieving this target promotes dissolution of existing crystal deposits and prevents new crystal formation. Allopurinol (xanthine oxidase inhibitor) is the first-line urate-lowering therapy, started at a low dose (100mg) and titrated upward. Urate-lowering therapy should NOT be started during an acute attack (can worsen symptoms) — wait at least 2 weeks.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 337,
              "stem": "HLA-B27 is associated with which group of conditions?",
              "options": [
                "Rheumatoid arthritis",
                "Gout and pseudogout",
                "Osteoarthritis",
                "SLE and scleroderma",
                "Seronegative spondyloarthropathies (ankylosing spondylitis, reactive arthritis, psoriatic arthritis)"
              ],
              "answer": "E",
              "explanation": "HLA-B27 is associated with the seronegative spondyloarthropathies: ankylosing spondylitis (>90% HLA-B27 positive), reactive arthritis (Reiter's, 70-80%), psoriatic arthritis (50-70%), and enteropathic arthritis (IBD-associated). These conditions share features: axial skeleton involvement (sacroiliitis, spondylitis), enthesitis, asymmetric oligoarthritis, and absence of RF (seronegative). RA is associated with HLA-DR4 (shared epitope). HLA-B27 testing has high sensitivity for AS but limited specificity because 8% of the general population carry HLA-B27 without disease.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 338,
              "stem": "In RA, the radiographic hallmark that distinguishes it from OA is:",
              "options": [
                "Osteophytes",
                "Subchondral sclerosis",
                "UNIFORM joint space narrowing with periarticular erosions",
                "Subchondral cysts",
                "Asymmetric joint space narrowing"
              ],
              "answer": "C",
              "explanation": "RA produces UNIFORM (concentric) joint space narrowing because the inflammatory pannus destroys the ENTIRE articular surface simultaneously. OA produces ASYMMETRIC (focal) narrowing because mechanical wear affects the loaded portion of the joint preferentially. RA also produces periarticular EROSIONS (at the 'bare areas' where synovium contacts bone directly without cartilage cover) and periarticular OSTEOPENIA (from inflammatory cytokine-driven osteoclast activation). OA produces osteophytes and subchondral sclerosis (Wolff's law response to increased stress, see Ch 5) — features NOT typical of RA.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 339,
              "stem": "Allopurinol reduces serum urate by inhibiting:",
              "options": [
                "Xanthine oxidase",
                "Phospholipase A2",
                "Cyclooxygenase",
                "HGPRT",
                "Uricase"
              ],
              "answer": "A",
              "explanation": "Allopurinol (and febuxostat) inhibit XANTHINE OXIDASE, the enzyme that converts hypoxanthine → xanthine → uric acid (the final two steps of purine metabolism). By blocking this enzyme, urate production is reduced. Allopurinol is the first-line urate-lowering therapy for chronic gout prophylaxis. Side effects include skin rash (1-2%, serious hypersensitivity syndrome with allopurinol in <0.1%), and it must be dose-adjusted in renal impairment. Febuxostat is a selective xanthine oxidase inhibitor (non-purine analogue) for allopurinol-intolerant patients.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 340,
              "stem": "Colchicine, used in acute gout, works by:",
              "options": [
                "Inhibiting xanthine oxidase",
                "Blocking COX enzymes",
                "Blocking TNF-alpha",
                "Inhibiting neutrophil microtubule polymerisation, reducing chemotaxis and phagocytosis",
                "Dissolving urate crystals"
              ],
              "answer": "D",
              "explanation": "Colchicine binds to tubulin and inhibits microtubule polymerisation in neutrophils. This impairs neutrophil chemotaxis (migration to the crystal deposition site), phagocytosis (engulfment of crystals), and degranulation (release of inflammatory mediators). It does NOT dissolve crystals or lower urate levels — it reduces the INFLAMMATORY RESPONSE to crystals. Side effects at high doses include GI toxicity (nausea, diarrhoea, vomiting) and, rarely, bone marrow suppression. Low-dose colchicine (500mcg 2-3 times daily) is better tolerated.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 341,
              "stem": "Chondrocalcinosis on X-ray (calcification of cartilage) is characteristic of:",
              "options": [
                "Gout",
                "Rheumatoid arthritis",
                "Osteoarthritis",
                "CPPD (pseudogout)",
                "Ankylosing spondylitis"
              ],
              "answer": "D",
              "explanation": "Chondrocalcinosis (calcification within articular cartilage, particularly the menisci and triangular fibrocartilage complex of the wrist) is the radiographic hallmark of CPPD crystal deposition disease (pseudogout). CPPD crystals are calcium pyrophosphate dihydrate — rhomboid-shaped and weakly positively birefringent under polarised light. Pseudogout most commonly affects the knee (60-70%), followed by wrist and shoulder. It can mimic septic arthritis (acute hot joint) — ALWAYS aspirate to exclude infection. Remember: crystals and infection can coexist.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 342,
              "stem": "The 'bamboo spine' radiographic appearance is seen in:",
              "options": [
                "Diffuse idiopathic skeletal hyperostosis (DISH)",
                "Ankylosing spondylitis",
                "Paget's disease",
                "Osteoporosis",
                "Cervical spondylosis"
              ],
              "answer": "B",
              "explanation": "Bamboo spine is the classic late radiographic finding of ankylosing spondylitis — representing flowing syndesmophytes (vertical calcification of the annulus fibrosus) bridging vertebral bodies, combined with facet joint fusion and interspinous ligament calcification, creating a continuous column that resembles bamboo. The fused spine is rigid and osteoporotic, making it vulnerable to fracture from low-energy trauma (horizontal/chalk-stick fractures through the disc space). Early AS shows sacroiliac joint widening → sclerosis → fusion (bilateral, symmetric — unlike psoriatic/reactive which is asymmetric).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 343,
              "stem": "A hot swollen joint could be septic arthritis OR crystal arthropathy. Which statement about their coexistence is correct?",
              "options": [
                "Infection and crystal arthropathy CAN coexist — always send synovial fluid for culture even if crystals are found",
                "They cannot coexist — one excludes the other",
                "Crystals in synovial fluid exclude infection",
                "Finding bacteria on Gram stain excludes crystals",
                "Crystal identification means no antibiotics are needed"
              ],
              "answer": "A",
              "explanation": "Crystal arthropathy and septic arthritis CAN coexist — the presence of crystals does NOT exclude infection. Always send synovial fluid for Gram stain, culture, and sensitivity EVEN IF crystals are identified. Septic arthritis is a surgical emergency (irreversible cartilage damage within 8 hours, see Ch 20) and missing it while attributing the hot joint to gout could be catastrophic. If there is ANY clinical doubt, treat as septic arthritis (aspiration + surgical washout + IV antibiotics) until cultures are negative at 48 hours.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Genetics, Embryology & Skeletal Dysplasias",
          "range": "Q344-Q353",
          "questions": [
            {
              "number": 344,
              "stem": "Achondroplasia results from a mutation in FGFR3. The normal function of FGFR3 in the growth plate is to:",
              "options": [
                "Stimulate chondrocyte proliferation",
                "Stimulate osteoblast differentiation",
                "NEGATIVELY regulate (inhibit) chondrocyte proliferation",
                "Promote vascular invasion of the growth plate",
                "Maintain the reserve zone stem cells"
              ],
              "answer": "C",
              "explanation": "FGFR3 normally acts as a NEGATIVE regulator of chondrocyte proliferation in the proliferative zone of the physis. The achondroplasia mutation causes constitutive (permanent) activation of FGFR3, leading to EXCESSIVE inhibition of chondrocyte proliferation and therefore reduced endochondral bone formation. Intramembranous ossification (skull vault, clavicle) is unaffected because it does not involve a cartilage intermediate or physeal chondrocyte proliferation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 345,
              "stem": "In OI Type I, the COL1A1 mutation results in:",
              "options": [
                "50% production of ABNORMAL collagen",
                "100% production of abnormal collagen",
                "Complete absence of all collagen",
                "Excessive collagen production",
                "50% production of NORMAL collagen (premature stop codon reduces quantity not quality)"
              ],
              "answer": "E",
              "explanation": "OI Type I (mildest) has a premature stop codon in the COL1A1 gene that prevents production of the alpha-1 chain from that allele. The OTHER allele produces normal collagen. Result: ONLY 50% of the normal quantity of Type I collagen is produced, but what IS produced is structurally NORMAL. This is a QUANTITATIVE defect, not qualitative. In more severe OI types (II-IV), mutations cause glycine substitutions in the alpha chain, producing STRUCTURALLY ABNORMAL collagen that disrupts the triple helix — a qualitative AND quantitative defect.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 346,
              "stem": "Hypophosphataemic rickets is notable in orthopaedics because it is:",
              "options": [
                "The only autosomal dominant metabolic condition",
                "The only autosomal recessive bone disorder",
                "The only X-linked recessive orthopaedic condition",
                "The only mitochondrial bone disorder",
                "The only X-linked DOMINANT orthopaedic condition"
              ],
              "answer": "E",
              "explanation": "Hypophosphataemic rickets (X-linked dominant) is the ONLY X-linked dominant condition in orthopaedic practice. The defective PHEX gene on the X chromosome fails to degrade FGF23, resulting in elevated FGF23 → renal phosphate wasting → rickets/osteomalacia. Inheritance: if FATHER affected → 100% daughters (he gives X to all daughters), 0% sons (he gives Y). If MOTHER affected → 50% of ALL children affected. This inheritance pattern is frequently tested.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 347,
              "stem": "The three axes of limb development and their signalling centres are:",
              "options": [
                "Proximodistal = ZPA, Anteroposterior = AER, Dorsoventral = Wnt",
                "Proximodistal = AER/Progress Zone, Anteroposterior = ZPA/SHH, Dorsoventral = Wnt-7a/Engrailed-1",
                "Proximodistal = SHH, Anteroposterior = AER, Dorsoventral = BMP",
                "All three axes controlled by the AER alone",
                "Proximodistal = Wnt, Anteroposterior = Engrailed, Dorsoventral = SHH"
              ],
              "answer": "B",
              "explanation": "The three axes: PROXIMODISTAL (shoulder→fingertip) = AER (apical ectodermal ridge) + Progress Zone, under BMP influence. ANTEROPOSTERIOR (thumb→little finger) = ZPA (zone of polarising activity) producing Sonic hedgehog (SHH), determining digit identity. DORSOVENTRAL (dorsal→volar) = Wnt-7a (dorsal) and Engrailed-1 (ventral). Limb buds appear end of week 4 (upper precedes lower by 1-2 days). Week 6 = hand paddle. Week 8 = digit separation (AER apoptosis).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 348,
              "stem": "Polydactyly is the most common congenital anomaly of the:",
              "options": [
                "Upper limb/hand",
                "Foot",
                "Spine",
                "Hip",
                "Knee"
              ],
              "answer": "A",
              "explanation": "Polydactyly is the most common congenital anomaly of the upper limb. Post-axial (ulnar side) polydactyly is more common overall and is transmitted in an autosomal dominant pattern in most cases, being most common in people of African origin. Pre-axial (radial/thumb) polydactyly is associated with syndromes. The most common long bone deficiency is fibular hemimelia.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 349,
              "stem": "Sickle cell disease is autosomal recessive. The mutation causes substitution of which amino acid?",
              "options": [
                "Glycine for alanine at position 6 of alpha-globin",
                "Proline for hydroxyproline in collagen",
                "Lysine for arginine in fibrillin",
                "Glutamic acid replaced by valine at position 6 of beta-globin",
                "Cysteine for tryptophan in dystrophin"
              ],
              "answer": "D",
              "explanation": "Sickle cell disease results from substitution of glutamic acid (Glu) by valine (Val) at position 6 of the BETA-globin chain. This single amino acid change causes haemoglobin S to polymerise under deoxygenated conditions, distorting red cells into a sickle shape. Orthopaedic manifestations: bone infarcts, AVN (femoral/humeral heads), biconcave fish vertebrae, osteomyelitis (Salmonella associated but S.aureus MORE COMMON), dactylitis, septic arthritis. Hydroxyurea increases HbF, reducing crises.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 350,
              "stem": "In Rubin's classification, achondroplasia is categorised as:",
              "options": [
                "Epiphyseal hyperplasia",
                "Epiphyseal hypoplasia",
                "Physeal hypoplasia",
                "Physeal hyperplasia",
                "Diaphyseal hypoplasia"
              ],
              "answer": "C",
              "explanation": "Rubin's classification categorises achondroplasia as PHYSEAL HYPOPLASIA — reduced activity of the growth plate (proliferative zone) due to the FGFR3 mutation. The complete Rubin's framework: Epiphysis — hyperplasia (Trevor's) / hypoplasia (SED, MED). Physis — hyperplasia (enchondromatosis/Ollier's) / hypoplasia (achondroplasia). Metaphysis — hyperplasia (HME) / hypoplasia (osteopetrosis). Diaphysis — hyperplasia (Camurati-Engelmann) / hypoplasia (OI).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 351,
              "stem": "Neurofibromatosis type 1 has complete penetrance but HIGH variable expressivity. This means:",
              "options": [
                "Everyone with the mutation develops symptoms, but severity varies widely between individuals",
                "Not everyone with the mutation develops the condition",
                "The condition skips generations",
                "Only males are affected",
                "The mutation is always inherited, never spontaneous"
              ],
              "answer": "A",
              "explanation": "COMPLETE PENETRANCE means that 100% of individuals carrying the NF1 mutation will express SOME features of the phenotype. HIGH VARIABLE EXPRESSIVITY means the severity and range of features varies enormously between individuals — some may have only cafe-au-lait spots, while others develop plexiform neurofibromas, pseudarthrosis, dystrophic scoliosis, and malignant peripheral nerve sheath tumours. NF1 gene encodes neurofibromin (tumour suppressor) on chromosome 17. 50% are new mutations.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 352,
              "stem": "DMD (Duchenne muscular dystrophy) is caused by a mutation in the gene encoding dystrophin. This is notable because:",
              "options": [
                "Dystrophin is the smallest human gene",
                "The dystrophin gene is on chromosome 21",
                "Dystrophin is only found in cardiac muscle",
                "The gene is inherited in an autosomal dominant pattern",
                "The dystrophin gene is the LARGEST known human gene"
              ],
              "answer": "E",
              "explanation": "The dystrophin gene is the LARGEST known human gene (2.2-2.4 million nucleotides, 79 exons, but only ~11,000 nucleotides code for the protein). The large size makes it susceptible to deletions (60-65% of mutations are intragenic deletions removing several exons). Dystrophin links the F-actin cytoskeleton to the extracellular matrix via the dystrophin-associated glycoprotein complex at the sarcolemma. Without dystrophin, the sarcolemma is mechanically unstable → membrane damage → calcium influx → progressive fibre necrosis. Becker's = same gene, milder (in-frame deletions produce truncated but partially functional dystrophin).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 353,
              "stem": "The Sillence classification of OI — which type has blue sclerae, is autosomal dominant, and is the MILDEST form?",
              "options": [
                "Type II",
                "Type I",
                "Type III",
                "Type IV",
                "Type V"
              ],
              "answer": "B",
              "explanation": "Sillence classification: Type I = MILDEST, BLUE sclerae, AD, hearing loss in 50% by age 40. Premature stop codon in COL1A1 → 50% production of NORMAL collagen (quantitative defect only). Type II = LETHAL perinatal, blue sclerae. Type III = most severe SURVIVABLE, WHITE sclerae, progressive deformities. Type IV = moderate, WHITE sclerae, normal hearing. Types V-VIII were added later (none have a Type I collagen mutation). Key point: OI bones are fragile but HEAL NORMALLY. Treatment: bisphosphonates (reduce fracture frequency) + IM nails (protect whole bone) + aggressive scoliosis management.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        }
      ]
    },
    {
      "title": "Trauma",
      "chapters": [
        {
          "title": "Talus",
          "range": "Q354-Q356",
          "questions": [
            {
              "number": 354,
              "stem": "The Hawkins sign on an AP ankle radiograph after a talar neck fracture is:",
              "options": [
                "A sign of AVN (bad sign)",
                "A fracture of the calcaneus",
                "A dislocation of the subtalar joint",
                "Subchondral LUCENCY (osteopaenia) of the talar dome visible at 6-8 weeks post-injury — this is a GOOD sign indicating that the talar body has an INTACT blood supply (disuse osteopaenia requires active bone resorption, which requires blood flow)",
                "Heterotopic ossification"
              ],
              "answer": "D",
              "explanation": "The Hawkins sign is a subchondral radiolucent line in the talar dome on AP ankle XR, appearing at 6-8 weeks after a talar neck fracture. It is a POSITIVE prognostic sign — indicating that the talar body has a FUNCTIONING blood supply. The logic: disuse osteopaenia (bone resorption due to non-weight-bearing) requires ACTIVE osteoclasts, which require a blood supply. If the bone is avascular (dead), it CANNOT undergo disuse osteopaenia — it remains dense/sclerotic while the surrounding living bone becomes osteopaenic (creating relative sclerosis of the dead bone — the radiographic appearance of AVN). Therefore: Hawkins sign PRESENT = blood supply intact = LOW AVN risk. Hawkins sign ABSENT at 8 weeks = talar body likely avascular = HIGH AVN risk. AVN rates by Hawkins talar neck fracture classification: Type I (undisplaced) = 0-13%, Type II (subtalar subluxation/dislocation) = 20-50%, Type III (subtalar + ankle dislocation) = 80-100%, Type IV (Type III + talonavicular dislocation) = near 100%.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 355,
              "stem": "Following a talar neck fracture that has been reduced, the Hawkins sign at 6-8 weeks is:",
              "options": [
                "Sclerosis of the talar dome indicating AVN",
                "Displacement of the fracture indicating non-union",
                "Subchondral lucency of the talar dome indicating preserved vascularity (POSITIVE prognostic sign)",
                "Collapse of the talar body",
                "Calcification around the ankle joint"
              ],
              "answer": "C",
              "explanation": "The Hawkins sign is subchondral osteopaenia/lucency seen in the talar dome on AP ankle radiograph at 6-8 weeks post-fracture. It indicates preserved blood supply — the bone is undergoing normal disuse osteoporosis, which requires an intact blood supply. Its presence is a GOOD sign (AVN is unlikely). Its ABSENCE does not confirm AVN — it means the blood supply is uncertain and continued monitoring is needed.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 356,
              "stem": "The Hawkins sign on an AP ankle radiograph taken 6-8 weeks after a talar neck fracture is:",
              "options": [
                "A sign of avascular necrosis indicating poor prognosis",
                "Sclerosis of the talar body",
                "Collapse of the articular surface",
                "Subchondral lucency (osteopaenia) in the talar dome indicating INTACT blood supply and LOW risk of AVN",
                "Displacement of the fracture"
              ],
              "answer": "D",
              "explanation": "The Hawkins sign is subchondral radiolucency (osteopaenia) in the talar dome, visible on AP ankle radiograph at 6-8 weeks post-injury. It indicates that the talar body has an INTACT blood supply — bone is being actively resorbed (which requires blood flow). This is a POSITIVE prognostic sign: AVN is unlikely if the Hawkins sign is present. ABSENCE of the Hawkins sign (with increasing sclerosis of the body) suggests AVN is developing. Talar neck fracture AVN rates (Hawkins classification): I (undisplaced) = 0-13%. II (subtalar subluxation/dislocation) = 20-50%. III (subtalar + ankle dislocation) = 83-100%. IV (+ talonavicular dislocation) = ~100%.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Patella",
          "range": "Q357",
          "questions": [
            {
              "number": 357,
              "stem": "Displaced transverse patella fractures require surgical fixation because:",
              "options": [
                "The quadriceps and patellar tendons pull the fragments apart (disrupting the extensor mechanism) — without fixation, the patient cannot perform a straight-leg raise and loses active knee extension",
                "They are always stable and heal without surgery",
                "The patella is not important for knee function",
                "They only require a sling",
                "Surgery is never needed for patella fractures"
              ],
              "answer": "A",
              "explanation": "The patella is a SESAMOID bone within the extensor mechanism of the knee (quadriceps tendon → patella → patellar tendon → tibial tubercle). A displaced transverse fracture separates the patella into proximal and distal fragments — the QUADRICEPS pulls the proximal fragment superiorly, and the patellar tendon keeps the distal fragment in place. Result: DISRUPTED extensor mechanism (the patient CANNOT actively extend the knee or perform a straight-leg raise — functionally devastating). Treatment: ORIF with tension band wiring (two parallel K-wires + figure-of-eight wire — same principle as olecranon TBW: converts the quadriceps tensile force into a compressive force across the articular surface). Alternative: cannulated screws + tension band, or plate fixation (for comminuted patterns). Undisplaced fractures (<2mm step, <3mm separation) with an INTACT extensor mechanism (patient CAN actively extend the knee and SLR) → non-operative (cylinder cast/brace in extension 4-6 weeks, then progressive ROM). Partial patellectomy: for comminuted pole fractures. Total patellectomy: last resort (significant extensor strength loss ~30%).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Femur",
          "range": "Q358-Q360",
          "questions": [
            {
              "number": 358,
              "stem": "Atypical femoral fractures (AFF) are associated with prolonged bisphosphonate use. They characteristically occur in the:",
              "options": [
                "Femoral neck (intracapsular)",
                "Subtrochanteric or diaphyseal region of the femur — transverse or short oblique fracture with lateral cortical beaking and minimal comminution, often preceded by prodromal thigh pain",
                "Distal femur condyles",
                "Femoral head only",
                "Tibial shaft"
              ],
              "answer": "B",
              "explanation": "AFFs are stress/insufficiency fractures of the subtrochanteric or femoral shaft associated with prolonged bisphosphonate use (>3-5 years). Pathophysiology: bisphosphonates suppress bone remodelling → accumulated microdamage cannot be repaired through normal remodelling → stress fracture develops in the lateral femoral cortex (the tension side under bending loads). Characteristic features (ASBMR task force criteria): (1) location: subtrochanteric or femoral shaft (between lesser trochanter and supracondylar flare), (2) TRANSVERSE or SHORT OBLIQUE fracture pattern, (3) MINIMAL or NO COMMINUTION, (4) lateral cortical BEAKING/thickening (stress reaction visible before complete fracture), (5) medial cortical SPIKE, (6) often BILATERAL (check the contralateral femur), (7) preceded by PRODROMAL thigh pain (weeks-months before fracture — the stress reaction is painful). Treatment: complete fracture → IM nail (long cephalomedullary nail — provides load-sharing fixation across the entire shaft). Incomplete fracture (lateral cortical stress reaction without complete fracture + prodromal pain) → prophylactic IM nailing (prevents completion). Prevention: drug holiday after 5 years of oral bisphosphonate (3 years for IV zoledronate) — reassess risk vs benefit.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 359,
              "stem": "Femoral shaft fractures in adults are most commonly treated with:",
              "options": [
                "Casting (insufficient for adults)",
                "External fixation in all cases",
                "Intramedullary nailing (the gold standard — provides load-sharing fixation, allows early weight-bearing, and has high union rates ~98%)",
                "Plate fixation as first choice",
                "Traction for 12 weeks"
              ],
              "answer": "C",
              "explanation": "IM nailing is the GOLD STANDARD treatment for femoral shaft fractures in adults — it provides: (1) LOAD-SHARING fixation (the nail sits within the medullary canal, sharing the load with the bone — unlike plates which are load-bearing, concentrating stress at the plate-bone interface). (2) Early WEIGHT-BEARING (most patients can be WBAT immediately or within weeks). (3) BIOLOGICAL fixation (closed nailing — no surgical exposure of the fracture site, preserving periosteal blood supply → faster healing). (4) HIGH UNION RATES (~98%). (5) Low infection rates. Technique: antegrade entry (piriformis fossa or greater trochanter tip — trochanteric entry nails increasingly used) or retrograde entry (through the intercondylar notch — useful for floating knee, ipsilateral femoral neck + shaft, obese patients). Reaming: standard (reaming provides autograft, increases blood supply to the endosteal surface, allows a larger nail → stronger construct). Plate fixation: reserved for specific indications (narrow canal, existing IM implant, ipsilateral femoral neck fracture requiring headless screws, periprosthetic fracture around TKA). External fixation: DCO in unstable polytrauma (temporary → later conversion to IM nail).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 360,
              "stem": "The most common fracture requiring hospital admission in elderly patients is:",
              "options": [
                "Distal radius fracture",
                "Tibial shaft fracture",
                "Humeral shaft fracture",
                "Ankle fracture",
                "Hip fracture (proximal femoral fracture — the most common cause of orthopaedic hospital admission in the elderly, with ~65,000-70,000 per year in the UK)"
              ],
              "answer": "E",
              "explanation": "Hip fracture (proximal femoral fracture) is the most common fracture requiring hospital admission in elderly patients and the most common reason for emergency orthopaedic admission. UK incidence: ~65,000-70,000 per year (NHFD data). Demographics: average age ~80 years, female:male ratio ~3:1. Mortality: 30-day ~6-8%, 1-year ~25-30% (hip fracture is a significant marker of frailty and mortality). Types: intracapsular (subcapital/transcervical — Garden classification, ~55%) and extracapsular (intertrochanteric/subtrochanteric — ~45%). Cost: >£2 billion per year to the NHS. NICE guidelines: surgery within 36 hours, orthogeriatric co-management, early mobilisation, falls/bone health assessment. Best Practice Tariff (BPT): financial incentive for meeting key standards (surgery <36h, orthogeriatrician <72h, physio day 1, falls/bone assessment, AMT documentation). Prevention: dual approach — falls prevention + osteoporosis treatment. The hip fracture pathway is one of the most standardised and audited pathways in UK healthcare (NHFD — National Hip Fracture Database).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Principles",
          "range": "Q361-Q374",
          "questions": [
            {
              "number": 361,
              "stem": "Compartment pressure measurement — the delta pressure (ΔP) that indicates the need for fasciotomy is:",
              "options": [
                "Absolute pressure >100 mmHg",
                "Only clinical signs matter — pressure measurement is never used",
                "Absolute pressure >10 mmHg alone",
                "ΔP ≤30 mmHg (where ΔP = diastolic blood pressure minus compartment pressure — a ΔP ≤30 mmHg indicates insufficient perfusion pressure and mandates fasciotomy)",
                "ΔP >50 mmHg"
              ],
              "answer": "D",
              "explanation": "Compartment pressure measurement assists diagnosis when clinical assessment is equivocal (unconscious patients, children, intubated/sedated patients). The DELTA PRESSURE (ΔP) is the most reliable criterion: ΔP = DIASTOLIC BP − COMPARTMENT PRESSURE. If ΔP ≤30 mmHg → the perfusion pressure driving blood through the compartment is insufficient → FASCIOTOMY indicated. Example: patient with diastolic BP 70 mmHg and compartment pressure 45 mmHg → ΔP = 70 − 45 = 25 mmHg → ΔP ≤30 → fasciotomy needed. Why ΔP is better than absolute pressure alone: an absolute threshold (e.g., >30 mmHg) doesn't account for the patient's blood pressure. A hypotensive polytrauma patient (diastolic 50 mmHg) may develop compartment syndrome at a lower compartment pressure than a hypertensive patient (diastolic 90 mmHg). The ΔP accounts for this by relating compartment pressure to perfusion pressure. Clinical diagnosis remains paramount: if the clinical picture is clear (severe pain, pain with passive stretch, tense compartment) → don't wait for pressure measurement → fasciotomy. Measurement is an adjunct, not a replacement for clinical judgement.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 362,
              "stem": "The most common complication of distal radius fractures is:",
              "options": [
                "Non-union (very rare in distal radius)",
                "CRPS (Complex Regional Pain Syndrome — previously known as reflex sympathetic dystrophy/Sudeck atrophy — characterised by disproportionate pain, swelling, skin colour/temperature changes, stiffness, and osteopaenia)",
                "Compartment syndrome",
                "Infection",
                "Nerve transection"
              ],
              "answer": "B",
              "explanation": "CRPS (Complex Regional Pain Syndrome) is the most common complication of distal radius fractures, occurring in ~5-30% of cases (depending on diagnostic criteria used). Previously called reflex sympathetic dystrophy (RSD), Sudeck atrophy, or algodystrophy. CRPS Type I: no definable nerve injury (most common after distal radius fractures). CRPS Type II (causalgia): with a definable nerve injury. Budapest criteria for diagnosis: (1) continuing pain disproportionate to the inciting event, (2) at least one symptom in ≥3 of 4 categories (sensory — hyperaesthesia/allodynia; vasomotor — temperature/colour asymmetry; sudomotor/oedema — oedema, sweating changes; motor/trophic — decreased ROM, weakness, trophic changes — hair, nail, skin). (3) No other diagnosis better explains the symptoms. Treatment: MDT approach — physiotherapy (graded motor imagery, mirror therapy, desensitisation), analgesia (neuropathic agents — gabapentin/pregabalin, amitriptyline), psychology (CBT), and vitamin C prophylaxis (500mg daily post-injury — some evidence of risk reduction). Prognosis: variable, often prolonged (months-years), can be debilitating.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 363,
              "stem": "The 'golden hour' concept in trauma refers to:",
              "options": [
                "The critical first 60 minutes after a major traumatic injury during which prompt, effective treatment can significantly improve survival and outcomes — emphasising the importance of rapid prehospital care, transport, and hospital-based resuscitation",
                "The first hour after a surgeon arrives",
                "A 60-minute surgery time limit",
                "The time it takes to read a radiograph",
                "A rest period after surgery"
              ],
              "answer": "A",
              "explanation": "The golden hour concept (attributed to R Adams Cowley, founder of the University of Maryland Shock Trauma Center): the first 60 minutes after a major traumatic injury is the critical window where rapid, effective intervention can significantly reduce mortality and morbidity. During this time: (1) haemorrhage control, (2) airway management, (3) fluid resuscitation, (4) rapid imaging and diagnosis, and (5) definitive treatment of life-threatening injuries must be initiated. The concept drives: rapid prehospital response (paramedics, HEMS — helicopter emergency medical services), 'scoop and run' vs 'stay and play' prehospital philosophy (current evidence favours rapid transport to a major trauma centre over prolonged on-scene treatment), trauma centre designation (concentrating expertise), and trauma team activation (pre-hospital notification → assembled team ready on arrival). In orthopaedics: haemorrhage from pelvic/long bone fractures can be life-threatening within the golden hour → pelvic binder, traction splints, DCO principles.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 364,
              "stem": "Tranexamic acid (TXA) in trauma should be administered within:",
              "options": [
                "24 hours of injury",
                "1 week of injury",
                "Only after surgery",
                "Only for elective procedures",
                "3 hours of injury (CRASH-2 trial demonstrated reduced mortality from haemorrhage when given within 3 hours — NO benefit and possible harm if given >3 hours)"
              ],
              "answer": "E",
              "explanation": "The CRASH-2 trial (2010, >20,000 patients) demonstrated that TXA (1g IV bolus + 1g over 8h) given within 3 HOURS of injury significantly reduced death from haemorrhage in bleeding trauma patients. Critically: TXA given AFTER 3 hours showed NO benefit and POSSIBLE HARM (increased thromboembolic events). This established the '3-hour window' as a hard time limit. TXA works by inhibiting plasminogen activation → preventing fibrinolysis → stabilising blood clots. In orthopaedics: TXA is also used routinely in elective arthroplasty (reduces blood loss by ~30%, reduces transfusion rates, without increasing VTE risk in most studies — given IV at induction or topically into the joint). TXA is now a standard component of the massive transfusion protocol in major trauma and is included in ATLS and military trauma protocols.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 365,
              "stem": "The most common fracture overall in adults is:",
              "options": [
                "Femoral neck fracture",
                "Tibial shaft fracture",
                "Distal radius fracture (the most common fracture in adults, particularly from FOOSH — fall on outstretched hand)",
                "Humeral shaft fracture",
                "Vertebral compression fracture"
              ],
              "answer": "C",
              "explanation": "The distal radius fracture is the most common fracture in adults, with a bimodal age distribution: (1) young adults (high-energy trauma — sports, RTA) and (2) postmenopausal women >50 years (low-energy FOOSH onto osteoporotic bone — fragility fracture). Colles fracture (dorsal displacement/tilt, radial shortening, dorsal comminution) is the most common pattern. Smith fracture (volar displacement — 'reverse Colles') is less common. The distal radius contributes ~80% of radial length — its physis is the most commonly injured physis in children. Treatment: undisplaced/stable → cast or removable splint. Displaced → closed reduction + cast (if acceptable alignment achieved) or ORIF (volar locking plate — DRAFFT trial showed non-superiority over K-wires, DRAFFT-2 showed non-superiority of surgery over casting). All patients >50 with a low-energy distal radius fracture should have a DEXA scan (fragility fracture → osteoporosis assessment and treatment).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 366,
              "stem": "The most common mechanism of injury causing hip fractures in the elderly is:",
              "options": [
                "Low-energy fall from standing height onto the greater trochanter (simple mechanical fall in an osteoporotic patient)",
                "High-energy RTA",
                "Sporting injury",
                "Fall from a significant height (>2 metres)",
                "Direct blow from an assault"
              ],
              "answer": "A",
              "explanation": "The overwhelming majority of hip fractures in the elderly result from LOW-ENERGY falls from standing height — a simple trip or slip causing the patient to fall directly onto the greater trochanter. In osteoporotic bone, this modest force is sufficient to fracture the proximal femur. Risk factors for falls: polypharmacy, visual impairment, cognitive impairment, muscle weakness/deconditioning, postural hypotension, environmental hazards (rugs, poor lighting), and previous falls. Hip fracture prevention requires DUAL intervention: (1) falls prevention (medication review, vision correction, strength/balance exercises, home hazard assessment) AND (2) osteoporosis treatment (DEXA scan, bisphosphonates/denosumab, calcium + vitamin D, lifestyle modification). The annual UK incidence: ~65,000-70,000 hip fractures (NHFD data). 30-day mortality: ~6-8%. 1-year mortality: ~25-30%. Hip fracture is a major public health burden and an indicator of frailty.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 367,
              "stem": "The Mangled Extremity Severity Score (MESS) is used to predict:",
              "options": [
                "Fracture healing time",
                "The likelihood of successful limb salvage vs amputation after severe open lower limb injuries (a score ≥7 has historically been used to suggest amputation rather than limb salvage)",
                "Infection risk only",
                "Time to return to sport",
                "Implant survival"
              ],
              "answer": "B",
              "explanation": "The MESS (Mangled Extremity Severity Score) predicts the need for amputation vs limb salvage in severe open lower limb injuries. Four parameters: (1) skeletal/soft tissue injury severity (1-4), (2) limb ischaemia (1-3, doubled if ischaemia time >6h), (3) shock (0-2), (4) age (0-2). Total score range: 1-14. Score ≥7: historically predicted near-100% amputation rate. Score <7: limb salvage may be successful. HOWEVER: the MESS has been criticised for being too simplistic (it doesn't account for nerve injury, which is the most important predictor of long-term functional outcome), and the LEAP study (Lower Extremity Assessment Project) showed that MESS alone should NOT be the sole determinant — some patients with MESS ≥7 had successful limb salvage, and functional outcomes of limb salvage vs amputation were SIMILAR at 2 years. Current practice: MESS is a GUIDE, not an absolute — the decision involves multidisciplinary assessment (orthopaedic, plastic, vascular), patient factors, and shared decision-making.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 368,
              "stem": "The principle of absolute stability in fracture fixation is achieved by:",
              "options": [
                "Using an intramedullary nail (that provides relative stability)",
                "Using an external fixator (relative stability)",
                "Using a cast",
                "Interfragmentary compression (lag screws, compression plates) — eliminating all motion at the fracture site → healing by primary (direct/Haversian) bone healing WITHOUT callus",
                "Applying traction"
              ],
              "answer": "D",
              "explanation": "Absolute stability = ZERO motion at the fracture site. Achieved by: INTERFRAGMENTARY COMPRESSION — (1) lag screws (compress fragments together — gliding hole in the near cortex, threaded hole in the far cortex → the screw threads pull the far fragment towards the near fragment), (2) compression plates (dynamic compression through the plate's hole geometry, or using a plate tensioner). When absolute stability is achieved: healing occurs by PRIMARY (direct/Haversian) bone healing — osteonal cutting cones remodel directly across the fracture line WITHOUT callus formation. This is appropriate for: simple fracture patterns (transverse, short oblique), intra-articular fractures (anatomical reduction required), and fractures where anatomical reduction is critical. Relative stability (some controlled motion at the fracture site — IM nails, bridge plates, external fixation) → SECONDARY healing with callus formation → appropriate for comminuted/multifragmentary fractures where anatomical reduction is impossible. The choice between absolute and relative stability depends on the fracture pattern.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 369,
              "stem": "The Gustilo-Anderson classification — which type of open fracture has the HIGHEST infection rate?",
              "options": [
                "Type I (~0-2% infection rate)",
                "Type II (~2-5%)",
                "Type IIIC (~25-50% infection rate, also the highest amputation rate due to vascular compromise + extensive soft tissue damage + contamination)",
                "Type IIIA (~5-10%)",
                "Type IIIB (~10-50%)"
              ],
              "answer": "C",
              "explanation": "Infection rates by Gustilo-Anderson type: Type I: 0-2% (low-energy, minimal contamination). Type II: 2-5% (moderate energy). Type IIIA: 5-10% (high-energy but adequate soft tissue coverage). Type IIIB: 10-50% (bone exposure, requires flap — large wound, significant contamination). Type IIIC: 25-50% (vascular injury + extensive soft tissue damage — the worst combination of compromised blood supply + contamination + tissue devitalisation). Type IIIC has the highest infection AND amputation rate because: vascular compromise means: (1) the limb is already ischaemic (tissue viability compromised), (2) systemic antibiotic delivery to the wound is impaired (no blood flow → antibiotics can't reach the tissues), (3) immune cell delivery is compromised, and (4) the extensive soft tissue damage provides ideal conditions for bacterial proliferation. The LEAP study showed that functional outcomes of limb salvage vs amputation were SIMILAR at 2 years for severe Type III injuries — shared decision-making is critical.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 370,
              "stem": "Compartment syndrome of the forearm or leg — the treatment is:",
              "options": [
                "Observation and re-assessment only",
                "Elevation alone",
                "Ice and compression",
                "Casting the limb tightly",
                "Urgent surgical fasciotomy — complete release of ALL compartments through adequate incisions within 6 hours of diagnosis (delay beyond 6 hours → muscle necrosis, Volkmann ischaemic contracture in the forearm, permanent nerve damage)"
              ],
              "answer": "E",
              "explanation": "Compartment syndrome is a surgical EMERGENCY. When intracompartmental pressure rises above the tissue perfusion pressure → muscles and nerves become ischaemic → irreversible damage begins within 6 HOURS. The ONLY treatment is URGENT FASCIOTOMY — complete surgical release of ALL compartments through adequate-length incisions. Forearm: volar fasciotomy (volar compartment — most commonly affected; curvilinear incision from proximal to the antecubital fossa across the carpal tunnel to the palm) + dorsal fasciotomy if needed. 3 compartments: volar superficial, volar deep, dorsal + mobile wad. Leg: 4 compartments must ALL be released — anterior (most commonly affected), lateral, superficial posterior, deep posterior. Two-incision technique: anterolateral (releases anterior + lateral) and posteromedial (releases superficial + deep posterior). Wounds are left OPEN (with vacuum-assisted closure or loose dressings) and closed by secondary intention or delayed primary closure/split-skin graft at 48-72 hours. Volkmann ischaemic contracture: the devastating consequence of missed forearm compartment syndrome — irreversible ischaemic muscle fibrosis → flexion contractures of the wrist and fingers.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 371,
              "stem": "The ATLS primary survey follows the sequence:",
              "options": [
                "A (Airway with C-spine control) → B (Breathing) → C (Circulation with haemorrhage control) → D (Disability/neurological status) → E (Exposure/Environment) — addressing life-threatening problems in order of lethality",
                "D-C-A-B-E",
                "E-D-C-B-A",
                "C-A-B-D-E",
                "No specific order is needed"
              ],
              "answer": "A",
              "explanation": "ATLS primary survey: A-B-C-D-E, addressing the most immediately life-threatening problems FIRST in order of lethality. A = AIRWAY with cervical spine CONTROL (clear the airway — jaw thrust, suction, adjuncts/intubation if needed, while maintaining inline c-spine immobilisation). B = BREATHING and ventilation (assess chest — look, listen, feel; identify and treat tension pneumothorax, open pneumothorax, flail chest, massive haemothorax). C = CIRCULATION with haemorrhage control (assess pulse, BP, perfusion; control external haemorrhage with pressure; establish IV access × 2 large-bore; start fluid resuscitation; identify sources of bleeding — chest, abdomen, pelvis, long bones, external/'blood on the floor'). D = DISABILITY (neurological assessment — GCS, pupils, lateralising signs, blood glucose). E = EXPOSURE + ENVIRONMENT (fully undress the patient to identify all injuries, then keep warm — prevent hypothermia with warmed blankets/fluids). Each step is addressed SEQUENTIALLY — do not move to the next letter until the current one is managed. Adjuncts: monitoring, urinary catheter, NG tube. Then: secondary survey (head-to-toe examination + history — AMPLE).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 372,
              "stem": "An avulsion fracture occurs when:",
              "options": [
                "A direct blow crushes the bone",
                "The bone is compressed axially",
                "A tendon or ligament pulls off a fragment of bone at its attachment point (the tendon/ligament is stronger than the bone at the insertion — common in children where the apophysis is weaker than the tendon)",
                "A bullet penetrates the bone",
                "The bone fractures from repeated stress"
              ],
              "answer": "C",
              "explanation": "An avulsion fracture occurs when a forceful muscle contraction or ligamentous stress PULLS a fragment of bone away at the tendon/ligament insertion point. The soft tissue (tendon/ligament) is stronger than the bone at the attachment site — so the bone fails before the soft tissue. This is particularly common in: (1) CHILDREN/ADOLESCENTS — apophyses (secondary ossification centres where tendons attach) are weaker than the mature tendons: ASIS avulsion (sartorius), AIIS (rectus femoris — sprinters), ischial tuberosity (hamstrings — hurdlers), 5th MT base (peroneus brevis), medial epicondyle (common flexor origin). (2) Elderly with osteoporotic bone (greater tuberosity avulsion of supraspinatus/infraspinatus, 5th MT base avulsion). Treatment: most avulsion fractures are treated NON-OPERATIVELY (rest, protected weight-bearing — the fragment usually heals in its new position or the remaining attachment is sufficient). Operative: if the fragment is significantly displaced (>2cm for pelvic apophyses), involves an articular surface, or the functional deficit is unacceptable.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 373,
              "stem": "The fracture classification that divides fractures into Type A (simple), Type B (wedge), and Type C (complex/comminuted) is the:",
              "options": [
                "Garden classification",
                "Neer classification",
                "Weber classification",
                "AO/OTA (Arbeitsgemeinschaft für Osteosynthesefragen / Orthopaedic Trauma Association) comprehensive fracture classification — the universal alphanumeric system for classifying all fractures by bone, segment, type, and group",
                "Gustilo-Anderson classification"
              ],
              "answer": "D",
              "explanation": "The AO/OTA classification is the universal comprehensive system for classifying ALL fractures. Structure: (1) BONE number (1=humerus, 2=radius/ulna, 3=femur, 4=tibia/fibula, 5=spine, 6=pelvis), (2) SEGMENT (1=proximal, 2=diaphysis, 3=distal), (3) TYPE: A=simple (spiral, oblique, transverse), B=wedge (spiral wedge, bending wedge, fragmented wedge), C=complex (spiral, segmental, comminuted). Each type is further divided into GROUPS (1, 2, 3) and subgroups for increasing specificity. Example: 32-A3 = femur (3), diaphyseal (2), simple type (A), transverse pattern (3). The AO system guides treatment: A-type fractures (simple) → amenable to anatomical reduction + absolute stability (lag screws + plate). C-type fractures (complex/comminuted) → biological fixation with relative stability (bridge plating, IM nail). B-type → intermediate. The system provides a common language for fracture description, research comparison, and treatment planning across institutions globally.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 374,
              "stem": "The most appropriate initial imaging investigation for a suspected fracture in the Emergency Department is:",
              "options": [
                "CT scan",
                "MRI",
                "Ultrasound",
                "Bone scan",
                "Plain radiograph (two views at right angles including the joints above and below)"
              ],
              "answer": "E",
              "explanation": "Plain radiograph remains the first-line imaging investigation for suspected fractures. The standard requirement is a MINIMUM of two views at right angles to each other (AP and lateral), including the joints above and below the suspected fracture site. This ensures that fractures are not missed due to overlap of bony structures on a single view (some fractures are only visible on one projection). Additional specific views may be needed: scaphoid views (PA in ulnar deviation + obliques), mortise view (ankle — 15° internal rotation), Zanca view (ACJ — 10° cephalad tilt), Judet views (pelvis — obturator oblique and iliac oblique for acetabulum). CT is used for complex fractures requiring operative planning (tibial plateau, pilon, acetabulum, calcaneum, cervical spine) AFTER the initial XR assessment.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Knee",
          "range": "Q375-Q377",
          "questions": [
            {
              "number": 375,
              "stem": "McMurray test for meniscal tears — a positive test is indicated by:",
              "options": [
                "Normal knee motion without symptoms",
                "A painful CLICK or CLUNK felt by the examiner during combined knee flexion, rotation, and extension — reproducing the patient's symptoms and indicating a meniscal tear being trapped and released",
                "Only visual observation of knee swelling",
                "Increased valgus laxity",
                "Anterior tibial translation"
              ],
              "answer": "B",
              "explanation": "McMurray test: patient supine, examiner holds the heel with one hand and the knee with the other (fingers on the joint line). The knee is fully flexed, then the examiner applies: (1) EXTERNAL ROTATION + VALGUS stress while EXTENDING the knee from full flexion → tests the MEDIAL meniscus (the medially compressed meniscus is trapped and clicks/clunks as it is released). (2) INTERNAL ROTATION + VARUS stress while extending → tests the LATERAL meniscus. A POSITIVE test: a palpable/audible CLICK or CLUNK felt at the joint line during the manoeuvre, associated with PAIN — reproducing the patient's mechanical symptoms. Sensitivity: ~50-70% (not highly sensitive — a negative McMurray does NOT rule out a meniscal tear). Specificity: ~70-90% (a positive test is fairly reliable). Joint line tenderness: the MOST SENSITIVE clinical sign for meniscal tears (~75-85% sensitivity). Apley's grinding test: alternative (prone, knee flexed 90°, compress + rotate — pain suggests meniscal pathology; distract + rotate — pain suggests ligamentous). MRI: gold standard imaging (~90-95% sensitivity/specificity).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 376,
              "stem": "Multiligament knee injury (knee dislocation) — the most important immediate assessment is:",
              "options": [
                "MRI of the knee",
                "Arthroscopy",
                "Physiotherapy assessment",
                "Only a clinical photograph",
                "Vascular assessment (popliteal artery injury occurs in ~5-15% of knee dislocations — an ABI <0.9 or absent distal pulses mandates urgent CT angiography or surgical exploration)"
              ],
              "answer": "E",
              "explanation": "Knee dislocation (≥3 ligaments disrupted, with or without radiographic evidence of dislocation — many reduce spontaneously before presentation) is a VASCULAR EMERGENCY. The popliteal artery is tethered at the adductor hiatus (proximally) and the soleal arch (distally) — during knee dislocation, it can be stretched, intimal-flapped, thrombosed, or transected. Vascular injury rate: ~5-15% (higher in anterior and posterior dislocations). Immediate assessment: (1) check DISTAL PULSES (dorsalis pedis + posterior tibial), (2) calculate ANKLE-BRACHIAL INDEX (ABI — ratio of ankle to brachial systolic BP): ABI <0.9 → CT ANGIOGRAPHY urgently. ABI ≥0.9 with normal pulses → serial observation (q4h pulse checks + ABI for 24-48h). Warm ischaemia time: revascularisation must occur within 6 HOURS (beyond this → amputation rate rises dramatically). Common peroneal nerve injury: ~25-30% (check foot dorsiflexion + sensation dorsal 1st web space). Ligament reconstruction: staged (typically 2-3 weeks after injury — allow soft tissue swelling to settle).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 377,
              "stem": "An acute traumatic knee effusion (haemarthrosis) in a young patient after a twisting injury most commonly indicates:",
              "options": [
                "Meniscal tear only",
                "ACL rupture (~70% of acute traumatic knee haemarthroses in young adults are due to ACL rupture)",
                "Patellar dislocation only",
                "Loose body only",
                "Synovitis"
              ],
              "answer": "B",
              "explanation": "Acute traumatic knee haemarthrosis (blood in the joint within hours of injury) in a young patient most commonly indicates ACL rupture (~70% of cases). Other causes: (1) peripheral meniscal tear with vascular disruption (~15%), (2) patellar dislocation with osteochondral fracture (~10%), (3) intra-articular fracture (tibial plateau, femoral condyle), (4) PCL rupture (less common). The classic ACL injury mechanism: non-contact pivoting/deceleration (changing direction, landing from a jump — common in football, basketball, skiing), often with an audible 'pop' followed by immediate swelling (haemarthrosis within 2-4 hours — rapid onset because the ACL is well-vascularised). Examination: positive Lachman test (~85-95% sensitivity), positive pivot shift (specific). Aspiration of a tense haemarthrosis: (1) relieves pain, (2) if FAT GLOBULES are present on the aspirated blood → indicates an intra-articular FRACTURE (fat from the bone marrow). MRI: confirms the diagnosis and identifies associated injuries (meniscal tears in ~50% of acute ACL injuries, bone bruises, collateral ligament injuries).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Fat Embolism",
          "range": "Q378-Q379",
          "questions": [
            {
              "number": 378,
              "stem": "Fat embolism syndrome (FES) typically presents 24-72 hours after long bone fracture with the classic triad of:",
              "options": [
                "Fever, jaundice, and abdominal pain",
                "Chest pain, hypertension, and bradycardia",
                "Limb swelling, erythema, and warmth",
                "Respiratory distress, neurological changes (confusion/agitation), and petechial rash (classically on the chest, axillae, and conjunctivae)",
                "Haematuria, flank pain, and fever"
              ],
              "answer": "D",
              "explanation": "Fat embolism syndrome presents 24-72 hours after long bone fractures (especially femoral shaft, bilateral fractures, or intramedullary procedures) with the classic triad: (1) respiratory distress (most common feature, occurs in 95% — bilateral pulmonary infiltrates on CXR, hypoxia, tachypnoea), (2) neurological changes (confusion, agitation, drowsiness, seizures — fat emboli to cerebral circulation), and (3) petechial rash (occurs in 50-60%, typically on the chest, axillae, conjunctivae, and oral mucosa — pathognomonic but transient, lasts <48 hours). The Gurd and Wilson criteria are used for diagnosis. Prevention: early fracture stabilisation (<24 hours) reduces FES incidence. Treatment: supportive (oxygen, ventilation if needed, fluid management). Corticosteroids: controversial, some evidence for prophylaxis in high-risk patients. FES is a clinical diagnosis — there is no definitive laboratory test.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 379,
              "stem": "Fat embolism syndrome (FES) typically presents at what time interval after long bone fractures?",
              "options": [
                "Immediately at the time of injury",
                "2–6 hours",
                "24–72 hours",
                "1–2 weeks",
                "3–4 weeks"
              ],
              "answer": "C",
              "explanation": "FES typically presents 24–72 hours after long bone fractures (particularly femoral shaft) or intramedullary procedures. The classic triad is respiratory distress (hypoxia, tachypnoea), neurological changes (confusion, agitation), and a petechial rash (typically on the chest, axillae, and conjunctivae — appears in 20–50% of cases). Gurd's criteria are used for diagnosis. Treatment is supportive (O₂, ventilation, fluids). Early fracture fixation reduces the incidence of FES.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Rhabdomyolysis",
          "range": "Q380",
          "questions": [
            {
              "number": 380,
              "stem": "Crush injury with rhabdomyolysis — the most important initial intervention to prevent acute kidney injury is:",
              "options": [
                "Aggressive intravenous crystalloid fluid resuscitation (target urine output >200-300ml/h) to dilute myoglobin and prevent tubular obstruction",
                "Immediate fasciotomy without fluid resuscitation",
                "Oral rehydration only",
                "Blood transfusion",
                "Immediate dialysis without fluid"
              ],
              "answer": "A",
              "explanation": "Rhabdomyolysis (from crush injury, compartment syndrome, prolonged immobilisation) releases myoglobin, potassium, phosphate, and CK from damaged muscle into the circulation. Myoglobin is directly nephrotoxic — it precipitates in renal tubules (particularly in acidic urine), causing acute tubular necrosis and AKI. The MOST IMPORTANT intervention is AGGRESSIVE IV crystalloid resuscitation (0.9% NaCl) to achieve a target urine output of 200-300ml/h (some guidelines suggest ≥1ml/kg/h minimum). This dilutes myoglobin concentration in the tubules and promotes its clearance. Additional measures: urinary alkalinisation with sodium bicarbonate (keeps urine pH >6.5, prevents myoglobin precipitation — controversial but commonly used), mannitol (osmotic diuresis — controversial), correct hyperkalaemia (calcium gluconate, insulin/dextrose, salbutamol), and monitor for compartment syndrome. CK >5000 IU/L: significant rhabdomyolysis risk.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "DVT/PE",
          "range": "Q381",
          "questions": [
            {
              "number": 381,
              "stem": "The Wells score is used to assess clinical probability of:",
              "options": [
                "Fracture severity",
                "Compartment syndrome",
                "Deep vein thrombosis (stratifying patients into low, moderate, and high clinical probability categories to guide further investigation)",
                "Infection risk",
                "Cardiac risk for surgery"
              ],
              "answer": "C",
              "explanation": "The Wells score is a clinical prediction tool that estimates the pre-test probability of DVT (and a separate version exists for PE). For DVT, points are assigned for: active cancer (+1), paralysis/immobilisation of lower limb (+1), recently bedridden >3 days or major surgery within 12 weeks (+1), localised tenderness along the deep venous system (+1), entire leg swollen (+1), calf swelling >3cm compared to contralateral (+1), pitting oedema (+1), collateral superficial veins (+1), previous DVT (+1), and alternative diagnosis as likely or more likely (-2). Score interpretation: ≤0 = low probability (DVT unlikely), 1-2 = moderate, ≥3 = high probability. Low probability → D-dimer (if negative, DVT excluded). Moderate/high → duplex USS. In orthopaedic patients: DVT prophylaxis is mandatory post-operatively (LMWH, DOACs, mechanical). NICE NG89 guides VTE prophylaxis for surgical patients.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "VTE Prophylaxis",
          "range": "Q382-Q383",
          "questions": [
            {
              "number": 382,
              "stem": "European guidelines on VTE prophylaxis after total hip arthroplasty recommend thromboprophylaxis for a minimum duration of:",
              "options": [
                "28-35 days (extended prophylaxis — reduces late VTE events that peak at 2-6 weeks post-operatively)",
                "5 days only",
                "10 days only",
                "24 hours only",
                "No prophylaxis recommended"
              ],
              "answer": "A",
              "explanation": "European (EFORT/ESSKA) and UK (NICE NG89) guidelines recommend EXTENDED thromboprophylaxis after THA for 28-35 days. The rationale: VTE risk remains elevated for 4-6 weeks after THA, with a second peak of symptomatic DVT/PE at 2-4 weeks post-operatively (after discharge). Options include: LMWH (enoxaparin 40mg daily SC), DOACs (rivaroxaban 10mg daily — preferred by NICE for THA/TKA), or aspirin (emerging evidence: CRISTAL trial and EPCAT-II showed aspirin non-inferior to LMWH after initial LMWH period). For TKA: minimum 14 days. For hip fracture: 28-35 days. Mechanical prophylaxis (graduated compression stockings, intermittent pneumatic compression) should be used in addition to pharmacological prophylaxis. American (AAOS) guidelines are less prescriptive about duration and more flexible on agent choice.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 383,
              "stem": "According to NICE guidelines, chemical VTE prophylaxis following elective total hip or knee arthroplasty should be continued for:",
              "options": [
                "5 days",
                "10 days for TKA, 28 days for THA",
                "14 days for both",
                "28 days for both",
                "Until the patient is fully mobile"
              ],
              "answer": "B",
              "explanation": "NICE recommends extended chemical VTE prophylaxis: 10 days for total knee arthroplasty and 28–35 days for total hip arthroplasty (reflecting the prolonged VTE risk after hip surgery). Options include LMWH, rivaroxaban, apixaban, or dabigatran. Mechanical prophylaxis (graduated compression stockings, foot pumps) should be used in addition from admission.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Neglected Injuries",
          "range": "Q384-Q389",
          "questions": [
            {
              "number": 384,
              "stem": "Neglected developmental dysplasia of the hip (DDH) presenting in a walking child (>18 months) with a dislocated hip requires:",
              "options": [
                "Pavlik harness (first-line for this age)",
                "Closed reduction alone",
                "No treatment — it resolves spontaneously",
                "Observation only until skeletal maturity",
                "Open reduction (anterior approach) with possible femoral shortening osteotomy and pelvic osteotomy (Salter/Dega/Pemberton)"
              ],
              "answer": "E",
              "explanation": "Neglected DDH in the walking child (>18 months) presents significant challenges: the femoral head is dislocated superiorly and posteriorly, the acetabulum is dysplastic (shallow), the capsule is elongated and filled with fibrofatty tissue (pulvinar), the ligamentum teres is hypertrophied, and the iliopsoas tendon constricts the capsule (hourglass constriction). Treatment: (1) Open reduction through an anterior (anterolateral/Smith-Petersen) approach — clear obstacles to reduction (pulvinar, ligamentum teres, transverse acetabular ligament, iliopsoas release). (2) Femoral shortening osteotomy — essential to reduce the pressure on the femoral head during reduction (prevents AVN by avoiding excessive force on the retinacular vessels). (3) Pelvic osteotomy (Salter innominate for <4-5yr, Dega/Pemberton for acetabular reorientation) — redirects the dysplastic acetabulum to provide coverage. The Pavlik harness is only effective before 6 months; it is contraindicated in walking-age children.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 385,
              "stem": "The Ilizarov technique (circular external fixator with distraction osteogenesis) is most commonly indicated in:",
              "options": [
                "Simple closed fractures with good alignment",
                "Acute undisplaced fractures in healthy bone",
                "Primary TKA",
                "Complex limb reconstruction: bone defects, non-unions, limb lengthening, deformity correction, and infected non-unions where internal fixation is contraindicated",
                "Routine carpal tunnel release"
              ],
              "answer": "D",
              "explanation": "The Ilizarov apparatus (circular external fixator with tensioned wires/half-pins) enables distraction osteogenesis — a biological process where gradual distraction of a corticotomy (bone cut) site at 1mm/day (0.25mm × 4 times/day) stimulates new bone formation in the distraction gap via intramembranous ossification. Indications: (1) bone defects (post-traumatic, post-infection, post-tumour resection — bone transport technique), (2) non-unions (particularly infected non-unions where internal metalwork is contraindicated), (3) limb lengthening (congenital or acquired shortening), (4) complex deformity correction (multiplanar), (5) open fracture management (particularly in contaminated environments). The technique is particularly valuable in resource-limited settings where sophisticated internal fixation may not be available. Complications: pin-site infection (~30-50%), joint contracture, premature consolidation, delayed consolidation, and patient compliance (frame worn for months).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            },
            {
              "number": 386,
              "stem": "A neglected Monteggia fracture-dislocation in a child (>4 weeks old) presents a reconstructive challenge. The key principle is:",
              "options": [
                "The radial head dislocation can be ignored",
                "Only the ulna needs treatment",
                "Only the radial head needs excision",
                "No treatment is needed",
                "Restoration of ulnar length and alignment (corrective ulnar osteotomy) is the key to achieving and maintaining radial head reduction"
              ],
              "answer": "E",
              "explanation": "In Monteggia fracture-dislocations (ulnar fracture + radial head dislocation), the radial head dislocates BECAUSE the ulna is shortened/angulated — the interosseous membrane transmits the deforming force. In acute Monteggia: reduce and fix the ulna → the radial head usually reduces concentrically. In neglected cases (>4 weeks, common in developing countries due to delayed presentation): the ulna has malunited, the radial head remains dislocated, and the annular ligament and capsule have contracted around the empty radial notch. Treatment principle: corrective ULNAR OSTEOTOMY (restore length and alignment) → this creates the mechanical conditions for radial head reduction → open reduction of radial head ± annular ligament reconstruction. Without ulnar correction, the radial head cannot be held reduced. In children: remodelling potential helps, but results deteriorate with delay. Beyond 3-5 years from injury: reconstruction becomes extremely difficult.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 387,
              "stem": "A neglected posterior hip dislocation presenting weeks after injury — the main concern preventing closed reduction is:",
              "options": [
                "Nothing — all delayed dislocations reduce easily",
                "Only cosmetic concern",
                "Low AVN risk regardless of delay",
                "Soft tissue contracture and fibrosis around the dislocated femoral head making closed reduction impossible (open reduction required), plus high AVN risk",
                "Spontaneous reduction will occur"
              ],
              "answer": "D",
              "explanation": "Neglected posterior hip dislocations (presenting >3 weeks after injury) are extremely challenging because: (1) soft tissue contractures develop around the dislocated femoral head (capsule contracts, muscles shorten, fibrosis fills the acetabulum — making closed reduction impossible), (2) AVN risk increases dramatically with delay (>48h: AVN risk increases significantly, >6h ideal for reduction), (3) sciatic nerve may be chronically stretched or compressed, (4) acetabular cartilage degenerates without the femoral head's presence. Treatment: open reduction (approach: trochanteric osteotomy for access, identify and protect the sciatic nerve, clear the acetabulum of fibrosis and debris, reduce the head). If already established AVN or >3-6 months delay with cartilage damage → THA may be the only option. In young patients: attempt open reduction even late (salvage the native joint if possible). Prevention: always reduce hip dislocations as an EMERGENCY (<6 hours).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            },
            {
              "number": 388,
              "stem": "Malunion of the distal radius with dorsal angulation (>15°) and shortening (>5mm) — the definitive corrective procedure is:",
              "options": [
                "Repeat closed reduction and casting",
                "Corrective osteotomy (opening wedge dorsal or volar approach) with bone grafting to restore radial length, inclination, and palmar tilt",
                "Acceptance of the deformity in all cases",
                "Distal radius arthroplasty",
                "Wrist fusion as the first-line treatment"
              ],
              "answer": "B",
              "explanation": "Symptomatic malunion of the distal radius with significant dorsal tilt (>15°), radial shortening (>5mm), or loss of radial inclination (>5°) causes: (1) loss of grip strength, (2) reduced wrist ROM, (3) midcarpal instability (DISI pattern), (4) altered load transmission across the wrist → post-traumatic OA, (5) DRUJ incongruity (ulnar impaction). Treatment: corrective osteotomy — the malunited bone is cut (usually through the original fracture site), the deformity is corrected to restore palmar tilt, radial length, and inclination, the resulting bone gap is filled with structural bone graft (iliac crest autograft or allograft), and the construct is stabilised with a volar locking plate. 3D planning and patient-specific guides are increasingly used. Results: significant improvement in ROM, grip strength, and pain relief in most patients.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 389,
              "stem": "Post-polio syndrome affects survivors of poliomyelitis years after initial infection. The key orthopaedic manifestations include:",
              "options": [
                "New-onset muscle weakness, fatigue, and pain in previously affected (or seemingly unaffected) muscles, often 15-40 years after the acute illness — with progressive functional decline",
                "No long-term effects",
                "Only cosmetic deformity without functional impact",
                "Complete recovery in all cases",
                "Only sensory symptoms"
              ],
              "answer": "A",
              "explanation": "Post-polio syndrome (PPS) affects 25-40% of polio survivors, typically presenting 15-40 years after the acute illness. It is characterised by: (1) NEW muscle weakness (in previously affected AND/OR previously unaffected muscles — possibly due to degeneration of enlarged motor units that compensated for the original denervation), (2) fatigue (both central and peripheral), (3) muscle and joint pain, (4) progressive functional decline (difficulty walking, falls, declining ability to perform ADLs). Orthopaedic manifestations of polio sequelae: flail limb deformities (paralytic foot drop, genu recurvatum, hip instability), leg length discrepancy, scoliosis, contractures, joint instability, and early OA (abnormal biomechanics). Treatment: orthoses (AFOs for foot drop, KAFOs for quadriceps weakness), joint stabilisation procedures (tendon transfers, arthrodesis), corrective osteotomies, and adaptive equipment. In developing countries: polio sequelae remain a significant cause of disability despite vaccination programmes.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Pelvis",
          "range": "Q390-Q396",
          "questions": [
            {
              "number": 390,
              "stem": "The Young-Burgess classification of pelvic ring injuries — the APC (anteroposterior compression) Type III injury involves:",
              "options": [
                "Pubic diastasis <2.5cm (APC-I)",
                "Pubic diastasis >2.5cm with anterior sacroiliac ligament disruption (APC-II)",
                "Complete disruption of the pelvic ring including both anterior AND posterior sacroiliac ligaments and the pelvic floor (hemipelvic instability — the 'open book' with vertical instability)",
                "Lateral compression only",
                "Vertical shear only"
              ],
              "answer": "C",
              "explanation": "Young-Burgess APC classification: APC-I = pubic symphysis diastasis <2.5cm, sacroiliac joint intact (sacrotuberous/sacrospinous ligaments intact — rotationally stable). APC-II = pubic diastasis >2.5cm, ANTERIOR sacroiliac ligaments disrupted, POSTERIOR sacroiliac ligaments INTACT (external rotation instability but vertically stable — 'open book'). APC-III = COMPLETE disruption: pubic symphysis + anterior AND posterior sacroiliac ligaments + pelvic floor ligaments (sacrotuberous, sacrospinous) → complete hemipelvic instability (rotational AND vertical instability). APC-III is haemodynamically dangerous — the pelvic volume is maximally increased (no posterior restraint → massive bleeding from venous plexus). Treatment: APC-I = conservative. APC-II = anterior fixation (symphyseal plate ± anterior SI screw). APC-III = anterior + posterior fixation (symphyseal plate + posterior SI screws/iliosacral screws).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 391,
              "stem": "Emergency management of an unstable pelvic ring fracture with haemodynamic instability — the immediate first step is:",
              "options": [
                "Application of a pelvic binder (circumferential compression to reduce pelvic volume and tamponade bleeding — applied at the level of the greater trochanters, not the iliac crests)",
                "CT scan before any treatment",
                "MRI of the pelvis",
                "Definitive ORIF in the ED",
                "Angiographic embolisation as the first step"
              ],
              "answer": "A",
              "explanation": "An unstable pelvic ring fracture (Young-Burgess APC-II/III, LC-III, VS) with haemodynamic instability is a life-threatening emergency. Haemorrhage is the primary cause of death — predominantly from the posterior venous plexus and cancellous bone (arterial bleeding accounts for only ~10-15%). The IMMEDIATE first step: APPLICATION OF A PELVIC BINDER at the level of the GREATER TROCHANTERS (not the iliac crests — the trochanters provide the fulcrum for mechanical reduction of the ring). This: (1) reduces the pelvic volume (decreases the potential space for bleeding), (2) approximates fracture surfaces (promotes tamponade), (3) stabilises the pelvis mechanically. Concurrent: ATLS resuscitation (massive transfusion protocol — 1:1:1 ratio of pRBC:FFP:platelets, TXA within 3 hours). If haemodynamically unstable DESPITE binder + resuscitation: pre-peritoneal pelvic packing (PPP) OR angiographic embolisation (for arterial bleeders identified on CT). Definitive fixation: after resuscitation (DCO principles).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 392,
              "stem": "The pelvic binder should be applied at which level?",
              "options": [
                "Iliac crests",
                "Waist level",
                "Greater trochanters",
                "Umbilicus",
                "Above the ASIS"
              ],
              "answer": "C",
              "explanation": "The pelvic binder must be applied at the level of the greater trochanters (not the iliac crests) to effectively reduce the pelvic volume and compress the fracture fragments. At this level, the binder acts as an internal rotation force on the hemipelves, closing the pelvic ring anteriorly. Applied too high (iliac crests), it may actually open the pelvis. The binder should be applied as early as possible (pre-hospital setting ideally) and should remain until definitive treatment.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 393,
              "stem": "In a rotationally unstable but vertically stable pelvic ring injury (Tile Type B), the posterior sacroiliac ligaments are:",
              "options": [
                "Completely disrupted",
                "Intact (only the anterior SI ligaments and pelvic floor are disrupted)",
                "Partially torn with vertical displacement",
                "Not relevant to classification",
                "Always associated with urological injury"
              ],
              "answer": "B",
              "explanation": "Tile B injuries are rotationally unstable but vertically stable because the posterior sacroiliac ligament complex (interosseous SI ligaments — the strongest ligaments in the body) remains intact. Only the anterior structures are disrupted: anterior SI ligaments, sacrospinous ligament (B1 open book = external rotation), or sacrotuberous ligament (B2 lateral compression). Tile C injuries have complete disruption of the posterior SI ligaments → both rotationally AND vertically unstable.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 394,
              "stem": "The Young-Burgess classification of pelvic ring injuries divides injuries by mechanism. The three main categories are:",
              "options": [
                "Anterior, posterior, and lateral",
                "Type A, B, and C",
                "Grade I, II, and III",
                "Lateral compression (LC), anteroposterior compression (APC), and vertical shear (VS)",
                "Stable, unstable, and open"
              ],
              "answer": "D",
              "explanation": "Young-Burgess classification: LC (lateral compression) = internal rotation injury (LC-I = sacral buckle + ipsilateral rami, LC-II = + crescent fracture/iliac wing, LC-III = + contralateral APC 'windswept pelvis'). APC (anteroposterior compression) = external rotation/open book (APC-I = symphysis diastasis <2.5cm, APC-II = >2.5cm + anterior SI disruption, APC-III = complete disruption = Tile C equivalent). VS (vertical shear) = axial force through hemipelvis (hemipelvis displaced superiorly). CM = combined mechanism. LC injuries are most common overall.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 395,
              "stem": "The lethal triad in trauma (hypothermia, acidosis, and coagulopathy) is significant because it:",
              "options": [
                "Has no clinical relevance",
                "Only occurs in elderly patients",
                "Is easily reversed with oral medication",
                "Only occurs in penetrating trauma",
                "Creates a self-perpetuating cycle that worsens haemorrhage and increases mortality if not aggressively interrupted"
              ],
              "answer": "E",
              "explanation": "The lethal triad (hypothermia <35°C + metabolic acidosis pH <7.25 + coagulopathy) creates a vicious cycle: hypothermia impairs clotting factor function and platelet aggregation → coagulopathy → continued haemorrhage → tissue hypoperfusion → lactic acidosis → further impairment of clotting → further hypothermia from blood loss and resuscitation with cold fluids → cycle perpetuates. Breaking this cycle is the fundamental goal of damage control resuscitation and damage control orthopaedics. Interventions: permissive hypotension (SBP 80-90 until bleeding controlled), massive transfusion protocol (1:1:1 pRBC:FFP:platelets), TXA within 3 hours, active warming (fluid warmers, forced-air warming blankets, warmed theatre), and rapid haemorrhage control (pelvic binder, tourniquet, angioembolisation, DCO with external fixation).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 396,
              "stem": "The initial emergency management of an open-book pelvic fracture with haemodynamic instability includes:",
              "options": [
                "Immediate definitive internal fixation",
                "CT scan before any intervention",
                "Application of a pelvic binder at the level of the greater trochanters to reduce pelvic volume and tamponade haemorrhage",
                "Observation without intervention",
                "Application of a binder at the iliac crest level"
              ],
              "answer": "C",
              "explanation": "A pelvic binder is applied at the level of the GREATER TROCHANTERS (not the iliac crests — placing it too high is a common error that does not effectively close the pelvic ring). The binder reduces the pelvic volume, brings the bone fragments closer together, and promotes tamponade of the venous bleeding (which accounts for ~80-90% of pelvic haemorrhage). This is a life-saving temporising measure applied in the pre-hospital or emergency department setting. If haemorrhage continues despite binder: angioembolisation (for arterial bleeding, ~10-20% of cases) or preperitoneal pelvic packing (for venous bleeding). Binder can be a commercial device (SAM pelvic sling, T-POD) or improvised (sheet wrap).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Polytrauma",
          "range": "Q397-Q406",
          "questions": [
            {
              "number": 397,
              "stem": "Damage control orthopaedics (DCO) differs from early total care (ETC) in that DCO:",
              "options": [
                "Performs definitive fixation of all fractures in the first operation regardless of patient physiological status",
                "Only applies to upper limb fractures",
                "Means no orthopaedic treatment at all",
                "Is identical to ETC",
                "Temporarily stabilises fractures (external fixation) in the physiologically unstable polytrauma patient, delaying definitive fixation until the patient is resuscitated and the lethal triad is corrected"
              ],
              "answer": "E",
              "explanation": "DCO is a staged approach for the physiologically UNSTABLE polytrauma patient (borderline or unstable — ISS >20, bilateral femoral fractures, severe chest injury, TBI, hypothermia, coagulopathy, acidosis): (1) FIRST SURGERY (DCO): temporary external fixation of long bone fractures (rapid, minimal blood loss, short anaesthetic time), thoracostomy, pelvic binder/ex-fix, haemorrhage control. (2) RESUSCITATION PHASE: ICU optimisation — correct hypothermia, acidosis, coagulopathy (break the lethal triad), restore haemodynamics. (3) DEFINITIVE SURGERY: convert ex-fix to IM nail/plate when physiologically stable (typically 5-10 days). ETC (early total care): definitive fixation of all fractures in the first operation — appropriate for the physiologically STABLE polytrauma patient. The Hannover group established the evidence for DCO vs ETC based on the 'second hit' theory (major surgery in an already compromised patient triggers a massive inflammatory response → ARDS/MOF).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 398,
              "stem": "The 'lethal triad' in trauma refers to the combination of:",
              "options": [
                "Hypoxia, hypotension, and hypothermia",
                "Hypotension, tachycardia, and confusion",
                "Acidosis, hyperkalaemia, and hypocalcaemia",
                "Hypothermia, acidosis, and coagulopathy",
                "Hypothermia, hypoglycaemia, and coagulopathy"
              ],
              "answer": "D",
              "explanation": "The lethal triad (triad of death) in trauma is hypothermia, metabolic acidosis, and coagulopathy. These three conditions form a self-perpetuating cycle: hypothermia impairs coagulation and enzyme function; acidosis further impairs clotting factor activity; ongoing haemorrhage worsens hypothermia and acidosis. Recognising and breaking this cycle is the rationale for damage control surgery.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 399,
              "stem": "The Injury Severity Score (ISS) is calculated from the Abbreviated Injury Scale (AIS) scores. A patient with an ISS ≥16 is classified as:",
              "options": [
                "Minor trauma",
                "Major/multiply injured (polytrauma)",
                "Moderate trauma",
                "Critical/non-survivable",
                "Not classifiable"
              ],
              "answer": "B",
              "explanation": "An ISS ≥16 defines polytrauma (major trauma). The ISS is calculated by taking the AIS scores of the three most severely injured body regions, squaring each, and summing them. Maximum ISS = 75. An AIS score of 6 (unsurvivable) in any region automatically gives ISS = 75. ISS correlates with mortality, ICU length of stay, and resource utilisation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 400,
              "stem": "In damage control resuscitation, the key principle is:",
              "options": [
                "Permissive hypotension with early blood product transfusion",
                "Aggressive crystalloid infusion",
                "Immediate surgical repair of all injuries",
                "Vasopressor-only management",
                "Delayed blood product administration"
              ],
              "answer": "A",
              "explanation": "Damage control resuscitation (DCR) aims to minimise the lethal triad by: (1) permissive hypotension (target SBP 80–90 mmHg, avoiding excessive crystalloid which worsens coagulopathy and hypothermia), (2) early balanced blood product transfusion (1:1:1 ratio of packed RBCs:FFP:platelets), (3) limited crystalloid use, (4) tranexamic acid within 3 hours (CRASH-2 trial). This approach has significantly improved survival in major haemorrhage.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 401,
              "stem": "The CRASH-2 trial demonstrated that which drug reduces mortality in bleeding trauma patients when given within 3 hours?",
              "options": [
                "Aspirin",
                "Recombinant Factor VIIa",
                "Desmopressin",
                "Tranexamic acid",
                "Aprotinin"
              ],
              "answer": "D",
              "explanation": "The CRASH-2 trial (2010) showed that tranexamic acid (TXA) given within 3 hours of injury significantly reduces mortality from haemorrhage in trauma patients. TXA is an antifibrinolytic that inhibits plasminogen activation, reducing clot breakdown. Given after 3 hours, it may increase mortality. Current UK trauma protocols include 1g IV TXA within 3 hours of injury.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 402,
              "stem": "During ATLS primary survey, the correct sequence is:",
              "options": [
                "Breathing, Airway, Circulation, Disability, Exposure",
                "Airway with C-spine protection, Breathing, Circulation, Disability, Exposure",
                "Circulation, Airway, Breathing, Disability, Exposure",
                "Exposure, Airway, Breathing, Circulation, Disability",
                "Airway, Circulation, Breathing, Disability, Exposure"
              ],
              "answer": "B",
              "explanation": "ATLS primary survey: A (Airway with cervical spine protection), B (Breathing and ventilation), C (Circulation with haemorrhage control), D (Disability/neurological status — GCS, pupils), E (Exposure/environment — fully undress but prevent hypothermia). Life-threatening problems are addressed as they are identified.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 403,
              "stem": "In haemorrhagic shock, the first class at which the systolic blood pressure typically begins to fall is:",
              "options": [
                "Class I",
                "Class II",
                "Class IV",
                "Blood pressure does not fall in haemorrhagic shock",
                "Class III"
              ],
              "answer": "E",
              "explanation": "Class III haemorrhagic shock (30–40% blood volume loss, 1500–2000 mL) is the first class where systolic blood pressure typically falls. Class I (<15%) and Class II (15–30%) maintain blood pressure through compensatory tachycardia and vasoconstriction. Class IV (>40%) has severe hypotension and altered consciousness.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 404,
              "stem": "The 'second hit' phenomenon in polytrauma refers to:",
              "options": [
                "A second traumatic event",
                "Rebound hypothermia after warming",
                "The physiological insult of major definitive surgery performed on an already compromised patient",
                "Secondary survey findings",
                "A second round of blood product transfusion"
              ],
              "answer": "C",
              "explanation": "The second hit phenomenon describes the additional systemic inflammatory response triggered by major surgery (e.g., prolonged IM nailing, extensive plating) performed on a patient already 'primed' by the initial trauma (first hit). This can precipitate ARDS, multi-organ dysfunction (MODS), and death. Damage control orthopaedics was developed specifically to avoid this by deferring definitive surgery until the patient is physiologically stable.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            },
            {
              "number": 405,
              "stem": "Damage control orthopaedics (DCO) involves temporary stabilisation of long bone fractures in a haemodynamically unstable polytrauma patient. The preferred method of temporary fixation is:",
              "options": [
                "External fixation",
                "Definitive IM nailing",
                "Compression plating",
                "Skeletal traction",
                "Cast immobilisation"
              ],
              "answer": "A",
              "explanation": "DCO uses external fixation as a rapid, temporary stabilisation method for long bone fractures in unstable polytrauma patients. It controls haemorrhage (particularly pelvic ring injuries), allows resuscitation, prevents the 'second hit' of prolonged definitive surgery on an already physiologically compromised patient. Once the patient is stabilised (typically 5-10 days), conversion to definitive fixation (IM nail or plate) is performed. Indications for DCO: persistent hypotension, hypothermia (<35°C), coagulopathy, acidosis (pH <7.25), bilateral femoral fractures, significant chest or head injury.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 406,
              "stem": "The ATLS primary survey follows which sequence?",
              "options": [
                "DCBAE",
                "ABCDE (Airway with cervical spine protection, Breathing, Circulation with haemorrhage control, Disability, Exposure/Environment)",
                "EDCBA",
                "CBADE",
                "No specific sequence is recommended"
              ],
              "answer": "B",
              "explanation": "The ATLS primary survey follows a strict ABCDE sequence, prioritised by the most immediately life-threatening conditions: (A) Airway maintenance with cervical spine protection — clear the airway, jaw thrust (not head tilt if c-spine injury suspected), definitive airway if needed. (B) Breathing and ventilation — assess respiratory rate, chest expansion, percussion, auscultation. Treat tension pneumothorax, open pneumothorax, flail chest immediately. (C) Circulation with haemorrhage control — IV access (2 large-bore cannulae), fluid resuscitation, direct pressure on external haemorrhage, pelvic binder, identify sources of bleeding (chest, abdomen, pelvis, long bones, external). (D) Disability — GCS, pupil response, lateralising signs, blood glucose. (E) Exposure/Environment — fully undress patient (log roll for posterior examination), prevent hypothermia (warm blankets, warmed fluids, warmed theatre). Each step is addressed IN ORDER — don't move to C until A and B are managed.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Calcaneus",
          "range": "Q407",
          "questions": [
            {
              "number": 407,
              "stem": "The Böhler angle on a lateral foot radiograph is used to assess calcaneal fractures. A normal Böhler angle is:",
              "options": [
                "0-10°",
                "50-70°",
                "80-90°",
                "20-40° (reduction below this range indicates calcaneal compression/depression, suggesting an intra-articular fracture requiring CT)",
                "Negative values are normal"
              ],
              "answer": "D",
              "explanation": "The Böhler angle is measured on a lateral foot radiograph: it is the angle formed between a line from the highest point of the anterior process to the highest point of the posterior facet, and a line from the highest point of the posterior facet to the highest point of the tuberosity. Normal: 20-40°. A DECREASED Böhler angle (< 20°) indicates loss of calcaneal height from compression of the posterior facet — strongly suggesting a displaced intra-articular calcaneal fracture. The angle helps screen for significant calcaneal fractures on XR and guides the decision for CT scanning (CT is essential for operative planning — Sanders classification). Sanders classification (based on coronal CT): Type I = undisplaced, Type II = 2 fragments, Type III = 3 fragments, Type IV = highly comminuted. Treatment: undisplaced (Sanders I) → non-operative. Displaced (Sanders II-III) → ORIF (extensile lateral approach or sinus tarsi approach). Sanders IV → primary subtalar arthrodesis or non-operative.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Scaphoid",
          "range": "Q408-Q411",
          "questions": [
            {
              "number": 408,
              "stem": "A clinically suspected scaphoid fracture with normal initial radiographs should be managed by:",
              "options": [
                "Immobilisation in a thumb spica and either early MRI (gold standard for occult fractures, sensitivity ~100%) or repeat radiographs at 10-14 days",
                "Discharge with no follow-up",
                "Full activity immediately",
                "CT scan only",
                "Surgical exploration immediately"
              ],
              "answer": "A",
              "explanation": "If clinical suspicion of a scaphoid fracture is high (anatomical snuffbox tenderness, scaphoid tubercle tenderness, pain with longitudinal compression of the thumb, and pain with radial deviation of the wrist) but initial radiographs are NORMAL: the fracture may be occult (visible only on MRI or delayed XR). Management: (1) immobilise in a THUMB SPICA (below-elbow cast or splint including the thumb to the IP joint), (2) either obtain an early MRI (gold standard — sensitivity approaching 100%, available within 24-48h in many centres, can also detect other injuries like distal radius fractures) OR (3) repeat radiographs at 10-14 days (fracture resorption at the fracture line makes it visible — but this delays diagnosis). Current best practice favours early MRI (avoids unnecessary immobilisation of the ~75% who don't actually have a fracture, reduces time off work/sport, and is cost-effective). CT is an alternative but has lower sensitivity than MRI for non-displaced fractures.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 409,
              "stem": "A patient with clinical scaphoid tenderness but normal initial radiographs should be managed with:",
              "options": [
                "Discharge with advice",
                "Immediate CT scan",
                "Immediate surgical fixation",
                "No further follow-up needed",
                "Scaphoid cast/splint and reassessment with repeat imaging at 10–14 days"
              ],
              "answer": "E",
              "explanation": "Clinical suspicion of a scaphoid fracture with normal initial radiographs warrants immobilisation in a scaphoid cast or splint and reassessment at 10–14 days with repeat radiographs or advanced imaging (MRI is gold standard for occult fractures, CT is an alternative). Up to 20% of scaphoid fractures are not visible on initial radiographs. Missing a scaphoid fracture risks non-union and AVN.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 410,
              "stem": "Non-union of the scaphoid is most likely with fractures at which location?",
              "options": [
                "Distal pole",
                "Waist",
                "Proximal pole",
                "Tuberosity",
                "Distal articular surface"
              ],
              "answer": "C",
              "explanation": "Proximal pole scaphoid fractures have the highest non-union rate because the blood supply to the scaphoid enters at the waist (dorsal branch of the radial artery) and flows retrograde to the proximal pole. A fracture at the proximal pole disrupts this retrograde supply, leading to AVN and non-union. Non-union rates: proximal pole ~30–40%, waist ~10–20%, distal pole <5%.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 411,
              "stem": "The gold standard investigation for diagnosing an occult scaphoid fracture when initial radiographs are normal is:",
              "options": [
                "Repeat radiograph at 2 weeks",
                "MRI within 24-48 hours",
                "CT scan",
                "Bone scan",
                "Ultrasound"
              ],
              "answer": "B",
              "explanation": "MRI is the gold standard for detecting occult scaphoid fractures when initial radiographs are normal. It has ~100% sensitivity and ~100% specificity within 24 hours of injury (bone marrow oedema is visible immediately). This is superior to repeat radiographs at 2 weeks (which have variable sensitivity and delay diagnosis by 2 weeks), CT (good for established fractures but may miss undisplaced fractures in acute setting), and bone scan (high sensitivity but lower specificity, radiation exposure, not always available acutely). Early MRI allows: (1) confirmed fractures to be treated appropriately (cast or screw), (2) confirmed negative MRI allows discharge from fracture clinic with no follow-up needed, reducing unnecessary immobilisation and clinic visits.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Fracture Principles",
          "range": "Q412-Q414",
          "questions": [
            {
              "number": 412,
              "stem": "A pathological fracture is defined as:",
              "options": [
                "A fracture caused by high-energy trauma to normal bone",
                "A fracture that heals normally",
                "A fracture through abnormal or diseased bone (weakened by tumour, infection, metabolic disease, or other pathology) occurring with minimal or no trauma",
                "An open fracture",
                "A stress fracture"
              ],
              "answer": "C",
              "explanation": "A pathological fracture occurs through bone that has been WEAKENED by underlying disease — it requires significantly less force than would be needed to fracture normal bone (may occur with minimal trauma such as turning in bed, or even spontaneously). Causes: (1) metastatic disease (most common cause in adults — breast, lung, prostate, kidney, thyroid), (2) primary bone tumours (osteosarcoma, Ewing), (3) myeloma, (4) metabolic bone disease (osteoporosis, Paget, hyperparathyroidism, osteomalacia), (5) infection (chronic osteomyelitis), (6) benign lesions (UBC, fibrous dysplasia, GCT, ABC, NOF). Approach: ALWAYS consider why the bone broke — if the injury mechanism is disproportionately minor for the fracture pattern, investigate for underlying pathology (full-length bone XR, bloods including Ca, PO₄, ALP, ESR, CRP, serum/urine electrophoresis, and consider staging workup if malignancy suspected).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 413,
              "stem": "The term 'comminuted fracture' means:",
              "options": [
                "An undisplaced fracture",
                "A fracture with two parts only",
                "An open fracture only",
                "A pathological fracture",
                "A fracture with THREE OR MORE fragments (multiple pieces — implies higher energy, more soft tissue damage, and often requires relative stability fixation rather than anatomical reconstruction)"
              ],
              "answer": "E",
              "explanation": "Comminuted = THREE or more fragments. The degree of comminution reflects the energy of the injury — higher energy → more fragments → more soft tissue damage → more complex management. Implications: (1) anatomical reduction of every fragment is usually IMPOSSIBLE (and attempting it → devascularises fragments → non-union). (2) RELATIVE STABILITY (bridge plating, IM nail) is preferred over absolute stability (lag screws alone) — allowing callus-mediated secondary healing. (3) The biological approach: preserve blood supply to fragments (minimise soft tissue stripping), indirect reduction techniques, length-alignment-rotation restoration without anatomical fragment reconstruction. (4) Higher complication rate: malunion, non-union, infection, compartment syndrome. Simple fracture patterns (2-part, transverse, short oblique): amenable to anatomical reduction and absolute stability (lag screw + neutralisation plate, compression plate).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 414,
              "stem": "The Arbeitsgemeinschaft für Osteosynthesefragen (AO) fracture classification uses an alphanumeric system. The number '42' refers to a fracture of the:",
              "options": [
                "Femoral diaphysis (bone 4 = femur, segment 2 = diaphysis)",
                "Proximal humerus",
                "Distal radius",
                "Proximal tibia",
                "Distal femur"
              ],
              "answer": "A",
              "explanation": "AO/OTA fracture classification: First number = bone (1=humerus, 2=radius/ulna, 3=femur... wait — in the current AO system: 1=humerus, 2=forearm, 3=femur... Actually the standard AO numbering: 3=femur, 4=tibia. Let me correct: 4=tibia in the AO system. However, traditionally in many UK references, the AO system numbers bones as: 1=humerus, 2=radius/ulna, 3=femur, 4=tibia, 5=spine, etc. Second number = segment (1=proximal, 2=diaphysis, 3=distal). Third character = fracture type (A=simple, B=wedge, C=complex). So 42 in the AO system = tibia (bone 4) diaphysis (segment 2). A 42-A fracture = simple diaphyseal tibial fracture. This system provides a universal language for fracture description across international literature.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Wrist",
          "range": "Q415-Q417",
          "questions": [
            {
              "number": 415,
              "stem": "Scapholunate dissociation (SLD) on a PA wrist radiograph shows:",
              "options": [
                "Normal carpal alignment",
                "Lunate dislocation",
                "Ulnar styloid fracture only",
                "Terry Thomas sign (widened scapholunate gap >3mm — named after the gap-toothed comedian) and cortical ring sign (rotated scaphoid appearing as a foreshortened circle)",
                "Normal scapholunate gap"
              ],
              "answer": "D",
              "explanation": "Scapholunate dissociation is the most common carpal instability pattern. The scapholunate interosseous ligament (SLIL) is disrupted → the scaphoid flexes (palmar flexion) and the lunate extends (dorsal tilt) → DISI (dorsiflexed intercalated segment instability) pattern. PA radiograph signs: (1) TERRY THOMAS sign — widened scapholunate gap >3mm (compared to <2mm normal, also called the David Letterman sign). (2) CORTICAL RING SIGN — the scaphoid rotates into flexion, appearing foreshortened with a ring-shaped cortical outline (the distal pole viewed end-on). Lateral radiograph: scapholunate angle >60° (normal 30-60°) = DISI. Treatment: acute (< 6 weeks) → arthroscopic or open ligament repair + K-wire fixation. Chronic: ligament reconstruction (3-ligament tenodesis, RASL, capsulodesis, or scapholunate axis method). End-stage (SLAC wrist — scapholunate advanced collapse → OA pattern): scaphoid excision + 4-corner fusion, or proximal row carpectomy.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 416,
              "stem": "A Colles fracture is defined as:",
              "options": [
                "Volar (anterior) displacement of the distal radius (that's a Smith fracture)",
                "An intra-articular fracture of the lunate fossa (Barton)",
                "A fracture of the radial styloid only (chauffeur/Hutchinson)",
                "Dorsal (posterior) displacement, dorsal angulation, radial shortening, and supination of the distal radius fragment — the classic 'dinner fork' deformity",
                "A fracture of the ulnar styloid only"
              ],
              "answer": "D",
              "explanation": "Colles fracture (Abraham Colles, 1814): extra-articular or minimally intra-articular fracture of the distal radius with DORSAL displacement, DORSAL angulation (loss of normal palmar tilt), RADIAL SHORTENING (impaction), and often dorsal comminution. Clinical: 'dinner fork' deformity (dorsal prominence, volar concavity when viewed from the side). Mechanism: FOOSH (fall on outstretched hand) with wrist in extension — the most common fracture mechanism. Compare: SMITH fracture = VOLAR displacement (reverse Colles — caused by fall on the back of the flexed wrist, or dashboard injury). BARTON = intra-articular fracture-subluxation (dorsal or volar lip). CHAUFFEUR/HUTCHINSON = radial styloid fracture (historically from crank-handle kickback). Die-punch = depressed lunate fossa fragment. Treatment: based on displacement, stability, and patient factors (DRAFFT evidence → K-wire or cast acceptable for many; volar locking plate for unstable/displaced/intra-articular).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 417,
              "stem": "A perilunate dislocation involves dislocation of the carpus from around the lunate. The lunate remains:",
              "options": [
                "Dislocated volarly out of the lunate fossa",
                "Dislocated dorsally",
                "In normal alignment with the radius (the rest of the carpus dislocates dorsally)",
                "Fractured and displaced",
                "Subluxed laterally"
              ],
              "answer": "C",
              "explanation": "In a perilunate dislocation, the lunate remains articulating with the radius (in or near its fossa), but the rest of the carpus (capitate and the other carpal bones) dislocates dorsally away from the lunate. This is a high-energy injury that progresses through Mayfield stages of perilunate instability (I=scapholunate disruption, II=midcarpal dislocation, III=lunotriquetral disruption, IV=lunate dislocation). A trans-scaphoid perilunate dislocation includes a scaphoid fracture. These injuries are frequently missed (~25%).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Fracture Healing",
          "range": "Q418-Q420",
          "questions": [
            {
              "number": 418,
              "stem": "Hypertrophic non-union differs from atrophic non-union in that hypertrophic non-union has:",
              "options": [
                "No biological activity (dead bone ends)",
                "Abundant callus formation (good biology/blood supply) but inadequate mechanical stability — it needs IMPROVED FIXATION rather than biological augmentation",
                "Both adequate biology and stability",
                "Only infection as the cause",
                "No treatment options"
              ],
              "answer": "B",
              "explanation": "Hypertrophic non-union: GOOD BIOLOGY (adequate blood supply, viable bone ends, abundant callus visible on XR — 'elephant foot' or 'horse hoof' appearance) but POOR MECHANICS (inadequate stability — too much motion at the fracture site prevents consolidation). Treatment: improve MECHANICAL STABILITY (revise fixation — exchange nailing with a larger nail, compression plating, or dynamisation). Biological augmentation (bone graft) is usually NOT needed (the biology is already present). Atrophic non-union: POOR BIOLOGY (avascularity, dead bone ends, no callus visible — pencil-tip appearance of bone ends on XR) ± poor mechanics. Treatment: both MECHANICAL stability (fixation) AND BIOLOGICAL augmentation (bone graft ± BMP ± reaming to provide autograft + increase blood flow). Oligotrophic non-union: intermediate — some callus but insufficient. Infected non-union: requires eradication of infection FIRST → then fixation + graft.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 419,
              "stem": "Secondary (indirect) fracture healing involves callus formation and occurs through:",
              "options": [
                "A sequence of inflammation → soft callus (cartilage/fibrocartilage via endochondral ossification) → hard callus (woven bone) → remodelling (lamellar bone)",
                "Direct osteonal (Haversian) remodelling without callus (that's primary healing)",
                "Only intramembranous ossification",
                "Cement fixation of the fracture",
                "No biological process is involved"
              ],
              "answer": "A",
              "explanation": "Secondary (indirect) fracture healing is the natural healing process for most fractures (treated non-operatively or with relative stability fixation — IM nails, bridge plates, external fixation). Four overlapping phases: (1) INFLAMMATION (0-7 days): haematoma formation, inflammatory cell recruitment (macrophages, PMNs), cytokine release (IL-1, IL-6, TNF-α, BMP), angiogenesis. (2) SOFT CALLUS (1-3 weeks): MSCs differentiate into chondrocytes → cartilage/fibrocartilage matrix forms around the fracture → ENDOCHONDRAL OSSIFICATION (cartilage template gradually replaced by woven bone — same process as growth plate bone formation). (3) HARD CALLUS (3-12 weeks): woven bone replaces the cartilage callus → the fracture gains mechanical strength. (4) REMODELLING (months-years): woven bone replaced by LAMELLAR bone (organised Haversian systems) along stress lines (Wolff's law) → the bone gradually returns to its original shape and strength. Primary (direct) healing: occurs ONLY with absolute stability (compression plating) — no callus, direct osteonal cutting cone remodelling across the fracture line (Haversian remodelling).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 420,
              "stem": "The 'diamond concept' of fracture healing describes four essential elements for successful bone union:",
              "options": [
                "Rest, ice, compression, elevation",
                "Antibiotics, debridement, fixation, coverage",
                "Diet, exercise, medication, rest",
                "Imaging, surgery, physio, follow-up",
                "Osteoconduction, osteoinduction, osteogenesis, and mechanical stability"
              ],
              "answer": "E",
              "explanation": "The diamond concept (Giannoudis, 2007) describes four essential elements for successful fracture healing, analogous to the four sides of a diamond: (1) Osteoconduction — a scaffold for new bone growth (bone graft, synthetic scaffold). (2) Osteoinduction — growth factors stimulating MSC differentiation into osteoblasts (BMPs, PDGF, TGF-β). (3) Osteogenesis — living cells capable of forming new bone (osteoblasts, osteoprogenitor cells from autograft or MSCs). (4) Mechanical stability — appropriate fixation providing the right strain environment (absolute stability for simple fractures, relative for comminuted). A deficiency in ANY element can lead to non-union. The concept guides treatment of non-unions: identify which element(s) are deficient and supplement (e.g., atrophic non-union: deficient biology → add bone graft + BMP; hypertrophic non-union: deficient stability → improve fixation).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Open Fractures",
          "range": "Q421-Q429",
          "questions": [
            {
              "number": 421,
              "stem": "The Gustilo-Anderson classification of open fractures — Type IIIB indicates:",
              "options": [
                "High-energy injury with extensive soft tissue damage, periosteal stripping, and BONE EXPOSURE requiring soft tissue coverage (flap — local or free)",
                "Low-energy wound <1cm (Type I)",
                "Wound 1-10cm without extensive soft tissue damage (Type II)",
                "Vascular injury requiring repair (Type IIIC)",
                "Closed fracture"
              ],
              "answer": "A",
              "explanation": "Gustilo-Anderson classification: Type I: wound <1cm, minimal contamination, simple fracture pattern. Type II: wound 1-10cm, moderate contamination, no extensive soft tissue damage. Type IIIA: high-energy, extensive soft tissue damage but ADEQUATE soft tissue COVERAGE of bone (can close or cover without flap). Type IIIB: high-energy, extensive soft tissue damage with BONE EXPOSURE (periosteal stripping) requiring FLAP COVERAGE (local rotational flap or free flap — the defining feature of IIIB). Type IIIC: any open fracture with a VASCULAR INJURY requiring repair (regardless of wound size — an arterial injury automatically makes it IIIC). Treatment (BOAST 4 guidelines): antibiotics within 1 hour (co-amoxiclav + gentamicin for IIIA-C), wound photo + saline-soaked dressing, joint ortho-plastic assessment within 24h, debridement within 12-24h, definitive soft tissue coverage within 72h (or 5-7 days maximum).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 422,
              "stem": "The Gustilo-Anderson classification of open fractures is formally applied at which point?",
              "options": [
                "In the ambulance at the scene",
                "On arrival in the emergency department",
                "After initial clinical assessment",
                "After definitive fixation",
                "After surgical debridement in theatre"
              ],
              "answer": "E",
              "explanation": "The Gustilo-Anderson classification is formally applied AFTER surgical debridement, not at initial presentation. The wound may appear smaller or less contaminated initially, and the true severity is only apparent after formal debridement and irrigation in theatre. Initial wound assessment should not guide definitive classification.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 423,
              "stem": "The recommended first-line antibiotic for a Gustilo Grade I or II open fracture is:",
              "options": [
                "Flucloxacillin alone",
                "Co-amoxiclav (amoxicillin/clavulanic acid)",
                "Metronidazole alone",
                "Gentamicin alone",
                "Vancomycin"
              ],
              "answer": "B",
              "explanation": "BOAST guidelines recommend co-amoxiclav as first-line antibiotic for open fractures (covers gram-positive including staphylococci and some gram-negative organisms). For penicillin-allergic patients, a cephalosporin or clindamycin is used. Gentamicin may be added for heavily contaminated or marine injuries. Antibiotics should be administered within 1 hour of presentation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 424,
              "stem": "All open fractures of the femoral shaft are classified as a minimum of which Gustilo-Anderson grade?",
              "options": [
                "Grade I",
                "Grade II",
                "Grade IIIB",
                "Grade IIIA",
                "Grade IIIC"
              ],
              "answer": "D",
              "explanation": "All open femoral shaft fractures are automatically classified as minimum Grade III, regardless of wound size, because the femur requires high-energy trauma to fracture (intrinsic bone strength necessitates high energy). With adequate soft tissue cover and no vascular injury, the grade is IIIA. Similarly, open tibial fractures with a small wound but high-energy mechanism should be graded appropriately.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 425,
              "stem": "A Gustilo Grade IIIC open fracture is defined by the presence of:",
              "options": [
                "Adequate soft tissue cover after debridement",
                "Inadequate soft tissue cover requiring flap",
                "A vascular injury requiring repair",
                "Bone loss >5 cm",
                "Bilateral open fractures"
              ],
              "answer": "C",
              "explanation": "Grade IIIC is ANY open fracture associated with an arterial injury that requires repair, regardless of the wound size or soft tissue status. The vascular injury makes this the most severe grade due to the risk of limb loss and the susceptibility of ischaemic muscle to infection. Amputation rates for IIIC injuries are significantly higher than for IIIA or IIIB.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 426,
              "stem": "On arrival in the emergency department, an open fracture wound should be managed by:",
              "options": [
                "Repeated examination by each team member",
                "Probing with a sterile instrument to assess depth",
                "Immediate wound closure with sutures",
                "Photographing the wound, then covering with saline-soaked gauze",
                "Leaving the wound open and uncovered"
              ],
              "answer": "D",
              "explanation": "BOAST guidelines state that the wound should be photographed (for documentation and to avoid repeated examinations), then covered with saline-soaked gauze and a sterile occlusive dressing. The wound should NOT be repeatedly inspected, probed, or manipulated in the ED — this risks further contamination. Formal assessment occurs in theatre during debridement.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 427,
              "stem": "The Tscherne classification grade C3 closed fracture is characterised by:",
              "options": [
                "Minimal soft tissue injury",
                "Extensive skin crush with vascular injury or established compartment syndrome",
                "Superficial abrasion",
                "Deep abrasion with impending compartment syndrome",
                "No soft tissue involvement"
              ],
              "answer": "B",
              "explanation": "Tscherne C3: extensive skin contusion or crushing, subcutaneous degloving, established compartment syndrome, or associated major vascular injury requiring repair. This represents the most severe closed soft tissue injury and significantly impacts treatment decisions and prognosis.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 428,
              "stem": "The Gustilo-Anderson classification of open fractures — Type IIIB is characterised by:",
              "options": [
                "Low-energy wound <1cm",
                "Wound 1-10cm without extensive soft tissue damage",
                "Extensive soft tissue loss with periosteal stripping requiring soft tissue reconstruction (flap coverage)",
                "Vascular injury requiring repair",
                "Clean wound with adequate bone coverage"
              ],
              "answer": "C",
              "explanation": "Gustilo-Anderson open fracture classification: Type I = clean wound <1cm, minimal contamination, simple fracture. Type II = wound 1-10cm, moderate soft tissue damage, no flaps or avulsions. Type IIIA = adequate soft tissue coverage despite extensive laceration/flap (high-energy but can be closed primarily or with SSG). Type IIIB = extensive soft tissue loss with periosteal stripping and bone exposure, requiring flap coverage (local or free flap). Type IIIC = ANY open fracture with vascular injury requiring repair (regardless of wound size). BOAST guidelines: all Type III open fractures should be managed in a major trauma centre by combined orthopaedic-plastic surgery team.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 429,
              "stem": "BOAST guidelines recommend that soft tissue coverage for Gustilo Type III open fractures should be achieved within:",
              "options": [
                "72 hours (ideally as early as possible)",
                "24 hours",
                "48 hours",
                "1 week",
                "No time limit"
              ],
              "answer": "A",
              "explanation": "BOAST 4 guidelines recommend definitive soft tissue coverage within 72 hours for Grade III open fractures. Earlier coverage (within 72h) is associated with lower infection rates, better wound healing, and better functional outcomes. For Type IIIB injuries (requiring flap coverage): this means free or local flap within 72h. The 'fix and flap' concept advocates combined orthopaedic fixation and plastic surgery soft tissue coverage in a single operative session where possible. Debridement should occur within 12-24 hours of injury (or sooner if gross contamination). The combined ortho-plastic approach in major trauma centres has significantly improved outcomes for severe open fractures.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Ankle",
          "range": "Q430-Q435",
          "questions": [
            {
              "number": 430,
              "stem": "The Weber classification of ankle fractures is based on the level of the fibular fracture relative to the:",
              "options": [
                "Tibial plafond",
                "Medial malleolus",
                "Lateral malleolus tip",
                "Calcaneus",
                "Syndesmosis (the tibiofibular syndesmotic ligaments — below, at, or above)"
              ],
              "answer": "E",
              "explanation": "Weber classification: Type A = fibular fracture BELOW the syndesmosis (infrasyndesmotic — lateral malleolus avulsion/transverse fracture at or below the joint line; syndesmosis intact, ankle mortise stable; usually treated non-operatively). Type B = fibular fracture AT the level of the syndesmosis (transsyndesmotic — oblique/spiral fracture starting at the joint line and extending proximally; syndesmosis may be partially disrupted; stability depends on whether the medial side is involved — stress XR may be needed). Type C = fibular fracture ABOVE the syndesmosis (suprasyndesmotic — syndesmosis disrupted by definition; ankle mortise unstable; requires surgical fixation to restore the syndesmosis). Corresponds to the Lauge-Hansen mechanism-based classification: A=supination-adduction, B=supination-external rotation, C=pronation-external rotation/abduction. The key clinical point: the higher the fibular fracture → the more likely the syndesmosis is disrupted → the more unstable the ankle.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 431,
              "stem": "The Lauge-Hansen classification of ankle fractures is based on:",
              "options": [
                "Only the number of fracture fragments",
                "Only the location of the fibular fracture",
                "The POSITION of the foot at the time of injury AND the DIRECTION of the deforming force (two-word descriptions: first word = foot position, second word = direction of force)",
                "Only the patient's age",
                "The surgeon's preference"
              ],
              "answer": "C",
              "explanation": "Lauge-Hansen classification describes ankle fracture patterns based on two factors: (1) the POSITION of the foot (supination or pronation) at the moment of injury, and (2) the DIRECTION of the deforming force (adduction, external rotation, or abduction). Four patterns: SER (Supination-External Rotation — MOST COMMON ~60-70%), SAD (Supination-Adduction), PER (Pronation-External Rotation), PAB (Pronation-Abduction). Each pattern produces a predictable SEQUENCE of injuries that occur in stages: SER (4 stages): Stage I = anterior tibiofibular ligament rupture, Stage II = oblique/spiral fibular fracture at the joint line (Weber B), Stage III = posterior malleolus or posterior tibiofibular ligament, Stage IV = deltoid rupture or medial malleolus fracture. The more stages involved → the more unstable the injury. The Lauge-Hansen classification guides treatment by predicting which structures are injured and helps determine stability. It correlates with but is MORE DETAILED than the Weber classification.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 432,
              "stem": "An unstable Weber B ankle fracture is determined by which finding on stress views?",
              "options": [
                "Medial clear space widening >4 mm (talar shift)",
                "Fibular shortening only",
                "Posterior malleolus fragment",
                "Anterior syndesmotic widening only",
                "Normal alignment on all views"
              ],
              "answer": "A",
              "explanation": "In a Weber B fracture, instability is determined by assessing the medial structures. Medial clear space widening >4 mm on mortise view (or on gravity/external rotation stress views) indicates deltoid ligament injury and an unstable ankle that requires operative fixation. Without medial injury, a Weber B fracture is stable and can be managed non-operatively. The medial clear space should not exceed the superior clear space between the talus and tibial plafond.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 433,
              "stem": "A Maisonneuve fracture involves a proximal fibula fracture associated with:",
              "options": [
                "An isolated medial malleolus fracture",
                "A simple lateral malleolus fracture",
                "An isolated calcaneal fracture",
                "A navicular fracture",
                "Disruption of the interosseous membrane and the ankle syndesmosis with a medial injury (deltoid rupture or medial malleolus fracture)"
              ],
              "answer": "E",
              "explanation": "The Maisonneuve fracture is a pronation-external rotation injury producing: (1) medial injury (medial malleolus fracture or deltoid ligament rupture), (2) disruption of the interosseous membrane (IOM) running up the leg, and (3) proximal fibula fracture. The ankle mortise is unstable despite the fibula fracture being remote from the ankle joint. This is why EVERY ankle injury with medial tenderness must include palpation of the proximal fibula — missing a Maisonneuve fracture leaves an unstable ankle untreated. Treatment: syndesmotic fixation (screw or suture button) ± medial malleolus ORIF. The proximal fibula fracture does NOT need fixation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 434,
              "stem": "The Weber classification of ankle fractures is based on the level of the fibular fracture relative to the:",
              "options": [
                "Medial malleolus",
                "Tibial plafond",
                "Calcaneus",
                "Ankle syndesmosis (level of the tibial plafond/joint line)",
                "Navicular"
              ],
              "answer": "D",
              "explanation": "Weber classification: Type A = fibular fracture BELOW the syndesmosis (infrasyndesmotic — usually stable, intact syndesmosis, may be associated with medial malleolus fracture from adduction mechanism). Type B = fibular fracture AT the level of the syndesmosis (transsyndesmotic — syndesmosis may or may not be disrupted, most common type ~60-70%). Type C = fibular fracture ABOVE the syndesmosis (suprasyndesmotic — syndesmosis is disrupted, unstable). The Lauge-Hansen classification (based on foot position + force direction) provides a mechanistic complement: SAD, SER, PAB, PER. Treatment: stable (Weber A, undisplaced B) → conservative (cast/boot). Unstable (displaced B with medial injury, C) → ORIF.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 435,
              "stem": "A bimalleolar ankle fracture-dislocation presents with obvious deformity. The first priority in the ED is:",
              "options": [
                "Obtain CT scan before any intervention",
                "Immediate closed reduction to restore alignment and reduce soft tissue compromise, followed by splinting and neurovascular assessment",
                "Wait for the orthopaedic registrar before touching the ankle",
                "Apply a definitive cast immediately",
                "Administer IV antibiotics for an assumed open fracture"
              ],
              "answer": "B",
              "explanation": "An ankle fracture-dislocation with obvious deformity requires IMMEDIATE closed reduction in the ED. Delay risks: skin necrosis (tented skin over the medial malleolus or lateral malleolus), neurovascular compromise (posterior tibial artery/nerve, peroneal nerve), and increased soft tissue swelling making subsequent surgery more difficult. Technique: traction, reverse the mechanism, apply a well-padded backslab. Document pre- and post-reduction neurovascular status. Obtain post-reduction radiographs. If the skin is at imminent risk of breakdown, reduction should be performed even before XR. After reduction: assess for open wound (if present → BOAST protocol), elevate, ice, plan definitive surgery (ORIF within 24h if soft tissues permit, or delay until swelling settles — 'wrinkle sign').",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Elbow",
          "range": "Q436-Q440",
          "questions": [
            {
              "number": 436,
              "stem": "The 'terrible triad' of the elbow consists of:",
              "options": [
                "Elbow dislocation + radial head fracture + coronoid fracture (all three elements contribute to severe instability and require comprehensive surgical treatment)",
                "Olecranon fracture + distal humerus fracture + ulnar nerve palsy",
                "Three elbow dislocations",
                "Lateral epicondylitis + medial epicondylitis + olecranon bursitis",
                "Elbow dislocation only"
              ],
              "answer": "A",
              "explanation": "The terrible triad of the elbow: (1) posterior ELBOW DISLOCATION + (2) RADIAL HEAD fracture + (3) CORONOID fracture. This combination creates severe instability because ALL THREE stabilisers are compromised: the coronoid (primary anterior buttress to posterior subluxation), the radial head (secondary stabiliser, particularly important as a buttress against valgus and posterior forces), and the lateral collateral ligament complex (LUCL — disrupted during dislocation). Treatment: ALL three components must be addressed surgically: (1) coronoid fixation (suture lasso or plate — even small fragments are critical for stability), (2) radial head fixation or replacement (if comminuted beyond repair — NEVER excise without replacement in the terrible triad, as this removes a critical stabiliser), (3) LUCL repair (lateral ulnar collateral ligament — reattach to the lateral epicondyle), ± (4) MCL repair (if still unstable after lateral repair), ± (5) hinged external fixator (if persistently unstable). Non-operative treatment → recurrent instability/dislocation → poor outcomes.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 437,
              "stem": "The Mason classification of radial head fractures — Type II indicates:",
              "options": [
                "Undisplaced or minimally displaced (<2mm, Type I)",
                "Displaced partial articular fracture (>2mm displacement or >30° angulation of a marginal fragment — may require ORIF if mechanical block to rotation)",
                "Comminuted fracture of the entire radial head (Type III — may require excision ± replacement)",
                "Radial head fracture with elbow dislocation (Type IV, added by Johnston)",
                "Normal radial head"
              ],
              "answer": "B",
              "explanation": "Mason classification: Type I = undisplaced or minimally displaced (<2mm) — treat non-operatively (sling, early ROM). Type II = displaced partial articular fracture (a marginal fragment >2mm displaced or >30° angulation — assess for mechanical BLOCK to forearm rotation; if blocked → ORIF with headless screws or mini-plate; if no block → may treat non-operatively with close follow-up). Type III = comminuted fracture of the ENTIRE radial head (not reconstructable — options: excision alone if no other elbow instability, or radial head REPLACEMENT if associated with MCL injury, Essex-Lopresti, or terrible triad — replacement maintains the radial column as a secondary stabiliser). Type IV (Johnston modification) = any radial head fracture associated with elbow DISLOCATION. Key: NEVER excise the radial head without replacement in the presence of ligamentous instability (MCL, IOM) or associated injuries (terrible triad, Essex-Lopresti) — loss of the radial column destabilises the elbow/forearm.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 438,
              "stem": "Distal humerus fractures in elderly patients (>70yr) with osteoporotic bone and significant comminution — when ORIF is not feasible, the treatment option is:",
              "options": [
                "Cast immobilisation (leads to stiffness and non-union)",
                "Radial head excision",
                "Only physiotherapy without any fixation",
                "Amputation",
                "Total elbow arthroplasty (TEA) — provides immediate stable fixation allowing early ROM in comminuted, unreconstructable distal humerus fractures in elderly/low-demand patients"
              ],
              "answer": "E",
              "explanation": "TEA for acute distal humerus fractures in elderly patients has gained acceptance when ORIF is not feasible — particularly for: (1) severely comminuted (AO type C3) fractures with small articular fragments that cannot be reliably reconstructed and fixed, (2) very osteoporotic bone (screws don't hold), (3) pre-existing inflammatory arthritis (RA — already compromised joint). The McKee RCT (2009) compared TEA vs ORIF for comminuted distal humerus fractures in patients >65yr and found: TEA had BETTER functional outcomes (Mayo Elbow Performance Score), lower reoperation rate, and faster recovery compared to ORIF. TEA allows IMMEDIATE ROM (no healing required — the implant provides immediate stability). Limitations: lifelong weight-lifting restriction (typically <5kg — to prevent loosening), higher complication rate in young/active patients, and limited revision options. TEA is therefore reserved for LOW-DEMAND elderly patients with unreconstructable fractures. ORIF remains the first choice whenever the fracture pattern and bone quality allow anatomical reconstruction.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 439,
              "stem": "The Essex-Lopresti injury involves a radial head fracture with:",
              "options": [
                "Ulnar shaft fracture",
                "Coronoid fracture and elbow dislocation",
                "Disruption of the interosseous membrane and DRUJ instability",
                "Olecranon fracture only",
                "Monteggia lesion"
              ],
              "answer": "C",
              "explanation": "The Essex-Lopresti lesion is a combination of comminuted radial head fracture + interosseous membrane disruption + DRUJ instability. Excision of the radial head without replacement in this injury leads to proximal migration of the radius and wrist pain/instability. Therefore, radial head replacement is MANDATORY if the head is irreparable. Always assess the DRUJ and forearm when treating radial head fractures — an Essex-Lopresti lesion can be missed.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 440,
              "stem": "Terrible triad injuries of the elbow must be repaired in a specific sequence to restore stability. The recommended order is:",
              "options": [
                "LCL first, then coronoid, then radial head",
                "Radial head first, then LCL, then coronoid",
                "LCL only — no other structures need repair",
                "Coronoid first (deepest structure), then radial head, then LCL (lateral collateral ligament complex — from deep to superficial)",
                "No specific order is recommended"
              ],
              "answer": "D",
              "explanation": "The terrible triad is repaired from deep to superficial: (1) CORONOID first — restore the anterior buttress (suture lasso through drill holes for small tip fragments, plate/screw for larger fragments). (2) RADIAL HEAD — fix (ORIF if repairable, radial head replacement if comminuted) to restore the secondary valgus stabiliser and longitudinal forearm stability. NEVER excise without replacement. (3) LCL (lateral ulnar collateral ligament) — repair back to the isometric point on the lateral epicondyle using suture anchors or drill holes. After all three repairs: assess stability through a full ROM under fluoroscopy. If still unstable: repair the MCL medially. If STILL unstable: hinged external fixator.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Shoulder",
          "range": "Q441-Q446",
          "questions": [
            {
              "number": 441,
              "stem": "Anterior shoulder dislocation (the most common direction, ~95%) typically occurs with the arm in:",
              "options": [
                "Adduction and internal rotation",
                "Full flexion only",
                "Full adduction with elbow extension",
                "Abduction, external rotation, and extension (the 'apprehension position' — forces the humeral head anteriorly against the weakest part of the capsule)",
                "The arm at the side in neutral"
              ],
              "answer": "D",
              "explanation": "Anterior shoulder dislocation accounts for ~95% of all shoulder dislocations. Mechanism: the arm is forced into ABDUCTION, EXTERNAL ROTATION, and EXTENSION — this levers the humeral head anteriorly out of the glenoid socket against the anteroinferior capsule (the weakest point). Common scenarios: fall onto an outstretched arm, tackling in rugby, seizure (bilateral posterior dislocations are classically associated with seizures and electrocution). Associated injuries: (1) Bankart lesion (anteroinferior labral tear — the 'essential lesion' of anterior instability), (2) Hill-Sachs lesion (posterosuperior humeral head compression fracture — impacted against the anterior glenoid rim during dislocation), (3) greater tuberosity fracture (~15%), (4) axillary nerve injury (most commonly injured nerve — test deltoid sensation, 'regimental badge' area). Recurrence risk: age-dependent (almost 100% in teenagers, <10% in >50 years). Treatment: closed reduction (Cunningham technique, Stimson, Kocher, Milch), sling 1-3 weeks, physiotherapy. Recurrent: Bankart repair (arthroscopic or open) or Latarjet (if bone loss >20%).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 442,
              "stem": "AC joint injuries — the Rockwood classification Type III involves:",
              "options": [
                "Complete disruption of BOTH AC AND CC (coracoclavicular) ligaments with 25-100% superior displacement of the clavicle relative to the acromion",
                "AC ligament sprain only (Type I)",
                "AC ligament disruption, CC ligaments intact (Type II)",
                "Posterior displacement of the clavicle (Type IV)",
                "Massive superior displacement >300% (Type V)"
              ],
              "answer": "A",
              "explanation": "Rockwood AC joint classification: Type I = AC ligament SPRAIN (intact, joint stable, no displacement — treat with sling, analgesia, early ROM). Type II = AC ligament DISRUPTED, CC ligaments INTACT (slight widening of AC joint but CC distance normal — non-operative). Type III = BOTH AC AND CC ligaments disrupted, CC distance increased 25-100% (clavicle displaced superiorly — the MOST CONTROVERSIAL type for treatment: non-operative works well for most patients, but some high-demand athletes/manual labourers may benefit from surgical stabilisation). Type IV = clavicle displaced POSTERIORLY (into/through the trapezius — surgical). Type V = massively displaced superiorly (CC distance increased >100-300% — surgical). Type VI = clavicle displaced INFERIORLY below the coracoid (very rare — surgical). Treatment summary: Types I-II → non-operative (>95% good outcomes). Type III → controversial (most centres initially non-operative, surgery if symptomatic at 3-6 months). Types IV-VI → surgical (various techniques: hook plate, CC suture/endobutton, TightRope, anatomical CC ligament reconstruction).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 443,
              "stem": "A 70-year-old woman presents after a fall with shoulder pain and inability to actively abduct the shoulder. Passive range of motion is full. The most likely diagnosis is:",
              "options": [
                "Frozen shoulder",
                "Acromioclavicular joint dislocation",
                "Acute rotator cuff tear",
                "Anterior shoulder dislocation",
                "Cervical radiculopathy"
              ],
              "answer": "C",
              "explanation": "Loss of active movement with preserved passive movement (pseudoparalysis) after a fall in an elderly patient strongly suggests an acute rotator cuff tear (particularly supraspinatus). In patients >40 years, shoulder dislocations are frequently associated with rotator cuff tears (~40% incidence >40 years, >80% incidence >60 years). The 'drop arm' test may be positive. MRI or ultrasound confirms the diagnosis. Acute large/massive tears in active patients should be considered for early repair (<3 weeks) before retraction and muscle degeneration occur.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 444,
              "stem": "A Segond fracture (small avulsion fracture of the lateral tibial plateau margin) is pathognomonic for:",
              "options": [
                "PCL rupture",
                "ACL rupture (lateral capsular sign — avulsion of the lateral capsular ligament from the proximal tibia)",
                "MCL rupture",
                "Meniscal tear only",
                "Patellar dislocation"
              ],
              "answer": "B",
              "explanation": "The Segond fracture is a small avulsion fracture of the lateral tibial plateau margin (also called the 'lateral capsular sign'). It represents an avulsion of the anterolateral ligament (ALL) or lateral capsular attachment from the proximal tibia and is PATHOGNOMONIC for ACL rupture — the mechanism that tears the ACL also avulses this lateral capsular attachment. It is visible on AP knee radiograph as a small sliver of bone just below the lateral joint line. When identified on XR, it should prompt urgent MRI to confirm the ACL tear and identify associated injuries (meniscal tears occur in ~75% of Segond fracture cases). The ALL (anterolateral ligament) has been increasingly recognised as an important secondary stabiliser against rotational instability (pivot shift control) — its injury (Segond fracture) explains the rotational component of ACL insufficiency.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 445,
              "stem": "The most common direction of traumatic glenohumeral dislocation is:",
              "options": [
                "Posterior",
                "Superior",
                "Inferior (luxatio erecta)",
                "Multidirectional",
                "Anterior (95-97% of all shoulder dislocations)"
              ],
              "answer": "E",
              "explanation": "Anterior shoulder dislocations account for 95-97% of all traumatic shoulder dislocations. The typical mechanism: forced abduction, external rotation, and extension (e.g., falling with the arm outstretched, tackle). The humeral head displaces anteroinferiorly (subcoracoid is the most common position). Associated injuries: Bankart lesion (anteroinferior labral tear — essential lesion for recurrent instability), Hill-Sachs lesion (posterolateral humeral head compression fracture from impact against the glenoid rim), rotator cuff tear (especially in patients >40 years), axillary nerve injury (up to 5-10%), and greater tuberosity fracture. Posterior dislocations account for 2-4% (seizures, electric shock, direct posterior force) and are frequently missed.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 446,
              "stem": "A Hill-Sachs lesion is:",
              "options": [
                "An avulsion of the anteroinferior glenoid labrum",
                "A fracture of the coracoid process",
                "A rotator cuff tear",
                "A fracture of the acromion",
                "A compression fracture of the posterolateral humeral head from impaction against the glenoid rim during anterior dislocation"
              ],
              "answer": "E",
              "explanation": "A Hill-Sachs lesion is a compression (impaction) fracture of the posterolateral aspect of the humeral head, caused by the head impacting against the anteroinferior glenoid rim during anterior shoulder dislocation. It is present in up to 65-70% of first-time anterior dislocations and nearly 100% of recurrent dislocators. A large Hill-Sachs lesion (engaging lesion — engages the glenoid rim during functional ROM in external rotation and abduction) contributes to instability and may need to be addressed surgically: remplissage (infraspinatus tenodesis into the defect to prevent engagement), bone grafting, or humeral head osteotomy. The Bankart lesion (anteroinferior labral avulsion) is the complementary injury on the glenoid side — together they are the bipolar bone loss pattern of anterior instability.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Forearm",
          "range": "Q447-Q453",
          "questions": [
            {
              "number": 447,
              "stem": "A Galeazzi fracture-dislocation consists of:",
              "options": [
                "Proximal ulna fracture + radial head dislocation (that's Monteggia)",
                "Both radius and ulna shaft fractures",
                "Radial shaft fracture + DRUJ disruption (dislocation/subluxation of the distal radio-ulnar joint)",
                "Isolated ulna shaft fracture (nightstick)",
                "Radial head fracture alone"
              ],
              "answer": "C",
              "explanation": "Galeazzi fracture-dislocation: fracture of the radial shaft (typically the distal third) + disruption of the DRUJ (distal radio-ulnar joint dislocation or subluxation). Called the 'fracture of necessity' because it ALWAYS requires ORIF — closed treatment has an unacceptable rate of DRUJ instability and malunion (~90% unsatisfactory results with non-operative treatment). Treatment: ORIF of the radial shaft fracture (3.5mm compression plate + screws) → intra-operative assessment of DRUJ stability after radius fixation. If DRUJ stable after radius fixation → immobilise in supination for 6 weeks. If DRUJ still unstable → may need DRUJ pinning or TFCC repair. Compare: MONTEGGIA = proximal ulna fracture + radial head dislocation (Bado classification). Rule: 'Galeazzi = distal = D = DRUJ' and 'Monteggia = proximal = P = Proximal radioulnar joint' — the eponymous fracture-dislocation always involves the OPPOSITE end of the forearm to the fracture.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 448,
              "stem": "Both-bone forearm fractures in adults require:",
              "options": [
                "Casting alone (insufficient for adults — high malunion rate)",
                "Only fixing the radius",
                "Only fixing the ulna",
                "ORIF of BOTH the radius AND ulna with compression plates (3.5mm) and screws — restoring anatomical length, alignment, and rotation of both bones to preserve forearm rotation",
                "External fixation of both bones"
              ],
              "answer": "D",
              "explanation": "In ADULTS, both-bone forearm fractures require ORIF of BOTH radius AND ulna — unlike children (where cast treatment can succeed due to remodelling potential). The forearm is a functional unit: the radius and ulna must maintain their anatomical relationship (precise length, bow, and rotation) to allow the 180° arc of pronation-supination. Non-operative treatment in adults → high rates of malunion and rotational loss (even 10° of malrotation can significantly reduce forearm rotation). Technique: 3.5mm dynamic compression plates (DCP) or locking compression plates (LCP) with a minimum of 6 cortices of screw fixation on each side of the fracture (3 screws above + 3 below). The radial bow must be restored (the apex of the radial bow is ~60% of the distance from the bicipital tuberosity to the distal articular surface). Approach: radius — Henry (volar, proximal) or Thompson (dorsal, distal). Ulna — direct subcutaneous approach. Post-op: early ROM (the plates provide sufficient stability for active motion).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 449,
              "stem": "Essex-Lopresti injury is a combination of:",
              "options": [
                "Only a radial head fracture",
                "Radial head fracture + interosseous membrane (IOM) disruption + DRUJ instability — a longitudinal forearm instability pattern where RADIAL HEAD EXCISION without replacement leads to proximal migration of the radius and chronic DRUJ problems",
                "Only DRUJ disruption",
                "Ulna fracture + radial head dislocation (that's Monteggia)",
                "Both bone forearm fracture"
              ],
              "answer": "B",
              "explanation": "Essex-Lopresti injury: (1) radial head fracture (usually comminuted), (2) disruption of the INTEROSSEOUS MEMBRANE (IOM — the fibrous sheet connecting the radius and ulna along their shafts), (3) DRUJ instability/disruption. This creates LONGITUDINAL FOREARM INSTABILITY — the radius can migrate PROXIMALLY relative to the ulna because both the radial head (proximal stabiliser) AND the IOM (along the shaft) are disrupted, and the DRUJ (distal stabiliser) is incompetent. CRITICAL: if the radial head is excised WITHOUT replacement in an Essex-Lopresti injury → the radius migrates proximally → chronic DRUJ pain, impaction ulnocarpal syndrome, and loss of forearm rotation. Treatment: RADIAL HEAD REPLACEMENT (NEVER excise without replacing), DRUJ stabilisation, and IOM reconstruction (emerging technique). This is why: every radial head fracture must be assessed for DRUJ tenderness and forearm stability (the Essex-Lopresti component is often MISSED acutely).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            },
            {
              "number": 450,
              "stem": "Both-bone forearm fractures in adults are treated with:",
              "options": [
                "ORIF of both radius and ulna with compression plating",
                "Cast immobilisation",
                "IM nailing of both bones",
                "External fixation",
                "Functional bracing"
              ],
              "answer": "A",
              "explanation": "Adult both-bone forearm fractures require ORIF with compression plating of both the radius and ulna. Anatomical reduction and rigid fixation are essential to restore forearm rotation (pronation/supination). The radius is approached through the Henry (anterior/volar) approach, and the ulna through a direct subcutaneous approach. 3.5mm DCP or LC-DCP plates with at least 6 cortices of fixation on each side of the fracture are standard.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 451,
              "stem": "In a forearm fracture, restoration of the radial bow is critical for which functional movement?",
              "options": [
                "Forearm pronation and supination (rotation around the ulna)",
                "Shoulder abduction",
                "Elbow flexion",
                "Wrist flexion only",
                "Finger extension only"
              ],
              "answer": "A",
              "explanation": "The radius has a lateral bow (radial bow) that is essential for forearm pronation and supination. During pronation, the radius rotates around the relatively fixed ulna — the radial bow provides the space for the radius to cross over the ulna. If the radial bow is lost (malunion with straightening of the radius), the interosseous space is reduced and pronation/supination is mechanically blocked. Studies show that loss of radial bow angulation >10° results in significant loss of forearm rotation. This is why anatomical reduction of the radial bow is critical during ORIF of forearm fractures — the plate must be contoured to restore the bow, and the radius must be reduced to full length and curvature.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 452,
              "stem": "In a Monteggia fracture-dislocation, failure to recognise the radial head dislocation leads to:",
              "options": [
                "No significant consequence",
                "Spontaneous resolution",
                "Only cosmetic deformity",
                "Chronic radial head dislocation with progressive elbow deformity, pain, and loss of function",
                "Improved elbow flexion"
              ],
              "answer": "D",
              "explanation": "Missed radial head dislocation in a Monteggia lesion leads to chronic dislocation with progressive elbow deformity (cubitus valgus), pain, restricted rotation (pronation/supination), tardy posterior interosseous nerve palsy, and secondary OA. In children, late reconstruction is possible (open reduction of radial head, ulnar osteotomy to correct alignment, annular ligament reconstruction). In adults, chronic dislocation is much harder to address — radial head excision may be needed, which compromises the elbow further. The key to prevention: always assess the radiocapitellar alignment on elbow/forearm radiographs — the radiocapitellar line must pass through the capitellum on ALL views.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 453,
              "stem": "The treatment of choice for a displaced both-bone forearm fracture in an adult is:",
              "options": [
                "Closed reduction and cast immobilisation",
                "Open reduction and internal fixation (ORIF) of BOTH bones with compression plates",
                "Fixation of the radius only and leave the ulna",
                "External fixation of both bones",
                "Intramedullary nailing of both bones"
              ],
              "answer": "B",
              "explanation": "Adult both-bone forearm fractures are treated with ORIF of BOTH the radius AND ulna using 3.5mm compression plates (LC-DCP or locking plates). This restores length, rotation, and the interosseous space — essential for pronation/supination. The radius is approached through the Henry (volar/anterior) approach and the ulna through a direct subcutaneous approach. Leaving either bone unfixed leads to malunion and loss of rotation. Closed reduction and casting has poor outcomes in adults (unlike children where remodelling can compensate). Key principle: anatomical reduction of the radius is critical to restore the radial bow (which allows pronation/supination around the ulna).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Clavicle",
          "range": "Q454-Q456",
          "questions": [
            {
              "number": 454,
              "stem": "Midshaft clavicle fractures in adults — the COTS (Canadian Orthopaedic Trauma Society) trial showed that:",
              "options": [
                "Non-operative treatment is always superior",
                "Surgery should never be offered",
                "Plate fixation of displaced midshaft clavicle fractures resulted in improved functional outcomes, lower non-union rates, and higher patient satisfaction compared to non-operative treatment at 1 year",
                "Only K-wire fixation is acceptable",
                "All clavicle fractures should be left alone"
              ],
              "answer": "C",
              "explanation": "The COTS trial (2007, Canadian RCT) compared plate fixation (3.5mm reconstruction plate or precontoured clavicle plate) vs non-operative treatment (sling) for completely displaced midshaft clavicle fractures. Key findings: (1) Plate fixation had significantly LOWER non-union rate (2% vs 14-15% non-operative). (2) Plate fixation had BETTER functional outcomes (DASH score, Constant score) at 1 year. (3) Patient satisfaction was HIGHER with surgical treatment. (4) Faster return to work/activity with surgery. This challenged the longstanding teaching that 'all clavicle fractures should be treated non-operatively' (based on historical data from Neer and Rowe with lower non-union rates — but these studies included undisplaced fractures). Current practice: undisplaced/minimally displaced → non-operative (sling + early mobilisation, ~95% union). DISPLACED (completely displaced, shortened >2cm, or with risk factors for non-union) → offer surgical fixation (plate or IM nail). Risk factors for non-union: comminution, female sex, advancing age, smoking.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 455,
              "stem": "Indications for operative fixation of a midshaft clavicle fracture include all EXCEPT:",
              "options": [
                "Shortening >2 cm",
                "Open fracture",
                "Floating shoulder",
                "Skin tenting",
                "Undisplaced fracture with no complications"
              ],
              "answer": "E",
              "explanation": "Undisplaced midshaft clavicle fractures without complications are managed non-operatively (broad arm sling, early mobilisation). Operative indications include: shortening >2cm (COTS trial), open fractures, skin tenting/impending open fracture, floating shoulder (ipsilateral clavicle + scapular neck fractures), neurovascular compromise, bilateral clavicle fractures, and polytrauma for easier mobilisation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 456,
              "stem": "The most common location for a clavicle fracture is:",
              "options": [
                "Lateral third",
                "Medial third",
                "Acromial end",
                "Middle third (approximately 80% of clavicle fractures)",
                "Sternal end"
              ],
              "answer": "D",
              "explanation": "Approximately 80% of clavicle fractures occur in the middle third. This region is biomechanically vulnerable: it is the thinnest part of the clavicle, lacks ligamentous support (unlike the lateral third which has CC and AC ligaments, and the medial third which has strong sternoclavicular ligaments), and is the transition point between the two curvatures of the clavicle. Lateral third fractures (~15%) are classified by Neer (Type I = lateral to CC ligaments/stable, Type II = medial to CC ligaments/unstable, Type III = articular surface involvement). Medial third fractures (~5%) are rare. Treatment of middle third: most are non-operative (broad arm sling). Operative indications: >2cm shortening, skin tenting, open fracture, neurovascular compromise, floating shoulder.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Hip",
          "range": "Q457",
          "questions": [
            {
              "number": 457,
              "stem": "Extracapsular hip fractures (intertrochanteric/pertrochanteric) are typically fixed with:",
              "options": [
                "Cannulated screws (those are for undisplaced intracapsular fractures)",
                "Dynamic hip screw (DHS) for stable intertrochanteric patterns, or intramedullary nail (cephalomedullary nail — e.g., PFNA, Gamma nail) for unstable or subtrochanteric patterns",
                "Hemiarthroplasty (that's for displaced intracapsular)",
                "External fixation in all cases",
                "No fixation — non-operative management"
              ],
              "answer": "B",
              "explanation": "Extracapsular hip fractures (outside the joint capsule — the blood supply to the femoral head is NOT disrupted, so AVN is not a concern → fixation rather than replacement is the treatment). STABLE intertrochanteric fractures (AO 31-A1, simple 2-part patterns with intact lateral wall): DHS (dynamic hip screw — sliding hip screw) is the gold standard. The screw slides within the barrel, allowing controlled impaction at the fracture site. UNSTABLE intertrochanteric fractures (AO 31-A2 with lateral wall comminution, A3 reverse oblique) or SUBTROCHANTERIC fractures: intramedullary nail (cephalomedullary nail — PFNA, Gamma nail, TFN). The IM nail has a biomechanical advantage in unstable patterns: shorter lever arm (load-sharing device closer to the mechanical axis), allows controlled impaction, and provides support for the comminuted lateral wall. Tip-apex distance (TAD): the most important predictor of lag screw cut-out — TAD <25mm is the target (closer to the subchondral bone of the femoral head = better fixation).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Spine",
          "range": "Q458-Q461",
          "questions": [
            {
              "number": 458,
              "stem": "Canadian C-Spine Rules — the three high-risk criteria that mandate cervical spine imaging are:",
              "options": [
                "Mild neck stiffness, age <20, and headache",
                "Only loss of consciousness",
                "Age ≥65 years, dangerous mechanism of injury (fall ≥1m/5 stairs, axial load to head, high-speed MVC/rollover/ejection, bicycle collision, motorised recreational vehicle), and/or paraesthesiae in the extremities",
                "Only neck pain",
                "Being involved in any minor incident"
              ],
              "answer": "C",
              "explanation": "The Canadian C-Spine Rules (CCR) are a clinical decision tool to determine whether cervical spine imaging is needed after trauma. THREE high-risk criteria MANDATE imaging (any one positive → radiograph/CT): (1) Age ≥65 years, (2) DANGEROUS MECHANISM (fall from ≥1m or 5 stairs, axial load to the head — e.g., diving, rugby scrum collapse, high-speed MVC >100km/h, rollover, ejection, bicycle collision, motorised recreational vehicle crash), (3) PARAESTHESIAE in the extremities (suggests cord/nerve root involvement). If NO high-risk criteria: assess for LOW-RISK factors that allow safe assessment of ROM (simple rear-end MVC, sitting in ED, ambulatory at any time, delayed onset of neck pain, no midline tenderness). If low-risk factors present → actively assess ROM (can they rotate 45° left and right?). If full active ROM → no imaging needed. CCR is more sensitive (99.4%) and specific than NEXUS for ruling out clinically significant c-spine injuries.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 459,
              "stem": "A Jefferson fracture (C1 burst fracture) involves fracture of the ring of the atlas at how many points?",
              "options": [
                "1",
                "2",
                "5",
                "No fractures — it is a ligamentous injury only",
                "2-4 (typically 4 — bilateral anterior and posterior arch fractures)"
              ],
              "answer": "E",
              "explanation": "A Jefferson fracture is a burst fracture of the C1 (atlas) ring, typically at 2-4 points (classically 4 — bilateral anterior and bilateral posterior arch fractures). It results from axial loading on the head (e.g., diving into shallow water, fall onto the top of the head). On open-mouth (odontoid/peg) view: lateral masses of C1 overhang the lateral masses of C2 (lateral mass spread). If the combined overhang of both lateral masses exceeds 6.9mm (rule of Spence), the transverse ligament is presumed ruptured → unstable injury. Stable Jefferson (transverse ligament intact): rigid collar/halo. Unstable (transverse ligament ruptured): surgical fixation (C1-C2 fusion).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 460,
              "stem": "The TLICS (Thoracolumbar Injury Classification and Severity) score guides treatment of thoracolumbar fractures. A score ≥5 indicates:",
              "options": [
                "Operative treatment recommended",
                "Non-operative treatment",
                "No treatment needed",
                "Further imaging only",
                "Physiotherapy alone"
              ],
              "answer": "A",
              "explanation": "TLICS scores three parameters: (1) Morphology: compression=1, burst=2, translational/rotational=3, distraction=4. (2) Integrity of the posterior ligamentous complex (PLC): intact=0, suspected/indeterminate=2, injured=3. (3) Neurological status: intact=0, nerve root=2, cord/conus (incomplete)=3, cord/conus (complete)=2, cauda equina=3. Total score: ≤3 = non-operative. 4 = equivocal (surgeon judgment). ≥5 = operative. The PLC integrity is the most important single factor — if the PLC is disrupted (=3 points), the total almost always reaches the operative threshold. MRI is the best investigation for assessing PLC integrity. TLICS has largely replaced the Denis three-column concept for treatment decision-making.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 461,
              "stem": "The Canadian C-spine rules: in a patient with potential cervical spine injury, clinical clearance WITHOUT imaging requires all of the following EXCEPT:",
              "options": [
                "No high-risk factors (age ≥65, dangerous mechanism, paraesthesiae)",
                "At least one low-risk factor allowing safe ROM assessment",
                "Able to actively rotate neck 45° left and right",
                "Normal GCS",
                "Patient must be pain-free in all positions"
              ],
              "answer": "E",
              "explanation": "The Canadian C-spine rules do NOT require the patient to be completely pain-free. They state: (1) No high-risk factors mandating imaging (age ≥65, dangerous mechanism — fall >1m/5 stairs, axial load, MVC >100km/h/rollover/ejection, motorised recreation, bicycle collision — and paraesthesiae in extremities). (2) At least one LOW-risk factor that allows safe assessment of ROM (simple rear-end MVC, sitting position in ED, ambulatory at any time, delayed onset neck pain, absence of midline tenderness). (3) Patient can actively rotate neck 45° LEFT AND RIGHT. If all three criteria are met → no imaging needed. If any high-risk factor present, or unable to rotate 45° → imaging required (CT). Sensitivity ~99-100% for significant cervical injury.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Humerus",
          "range": "Q462",
          "questions": [
            {
              "number": 462,
              "stem": "A Holstein-Lewis fracture is a spiral fracture of the distal third of the humeral shaft associated with:",
              "options": [
                "Axillary nerve injury",
                "Musculocutaneous nerve injury",
                "RADIAL NERVE injury (the radial nerve is tethered at the lateral intermuscular septum where it passes from the posterior to anterior compartment — a spiral fracture at this level can trap or lacerate the nerve)",
                "Median nerve injury",
                "Ulnar nerve injury"
              ],
              "answer": "C",
              "explanation": "The Holstein-Lewis fracture: a SPIRAL fracture of the DISTAL THIRD of the humeral shaft with particular risk of RADIAL NERVE injury. The radial nerve is vulnerable here because it passes through the LATERAL INTERMUSCULAR SEPTUM at approximately the junction of the middle and distal thirds of the humerus — transitioning from the posterior compartment (spiral groove) to the anterior compartment. At this point, the nerve is relatively fixed (tethered by the septum) and can be trapped, stretched, or lacerated by a displaced spiral fracture fragment. Radial nerve palsy with humeral shaft fracture: overall incidence ~11-18% (most common nerve injury associated with humeral shaft fracture). MOST (~70-90%) are NEURAPRAXIAS that recover spontaneously within 3-4 months. Management: (1) document the palsy (pre-reduction or post-reduction/post-manipulation). (2) Splint the wrist in extension (cock-up splint). (3) Observe for 3-4 months (EMG/NCS at 6 weeks baseline → repeat at 3-4 months). (4) If no recovery by 3-4 months → surgical exploration. Indications for EARLY exploration: open fracture with nerve palsy, nerve palsy developing AFTER manipulation/surgery (iatrogenic), and vascular injury requiring exploration.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Thoracolumbar Spine",
          "range": "Q463",
          "questions": [
            {
              "number": 463,
              "stem": "In the AO classification of thoracolumbar fractures, a Type B injury is characterised by:",
              "options": [
                "Compression of the anterior column",
                "Displacement/translation in any plane",
                "Transverse process fracture",
                "Distraction of the posterior or anterior tension band",
                "Spinous process avulsion only"
              ],
              "answer": "D",
              "explanation": "AO thoracolumbar: Type A = compression injuries (A0–A4). Type B = distraction injuries (posterior tension band failure in B1 bony/B2 ligamentous, or anterior tension band failure in B3). Type C = displacement/translation injuries in any plane. Severity increases A→B→C. This classification has been updated and now incorporates neurological status (N0–N4) and patient-specific modifiers.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Femoral Shaft",
          "range": "Q464-Q467",
          "questions": [
            {
              "number": 464,
              "stem": "The deforming forces on the proximal fragment of a subtrochanteric femoral fracture produce which position?",
              "options": [
                "Extension, adduction, internal rotation",
                "Flexion, abduction, external rotation",
                "Neutral alignment",
                "Extension, abduction, internal rotation",
                "Flexion, adduction, internal rotation"
              ],
              "answer": "B",
              "explanation": "In a subtrochanteric fracture, the proximal fragment is pulled into flexion (iliopsoas), abduction (gluteus medius/minimus), and external rotation (short external rotators). The distal fragment is pulled into adduction by the adductors and shortened by the hamstrings and quadriceps. Understanding these deforming forces is essential for achieving reduction during nailing — the nail entry point and starting position must accommodate the flexed/abducted proximal fragment.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 465,
              "stem": "The gold standard treatment for a displaced femoral shaft fracture in an adult is:",
              "options": [
                "Antegrade reamed intramedullary nailing",
                "Skeletal traction",
                "External fixation",
                "Compression plating",
                "Functional bracing"
              ],
              "answer": "A",
              "explanation": "Antegrade reamed IM nailing is the gold standard for adult femoral shaft fractures. It provides load-sharing fixation, high union rates (~98%), early mobilisation, and preserves the periosteal blood supply. Reaming increases the nail diameter that can be inserted, improving stability. Entry point: piriformis fossa or greater trochanter (trochanteric entry nails). Timing: within 24 hours in isolated injuries; DCO approach in polytrauma.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 466,
              "stem": "The Winquist-Hansen classification grades comminution of femoral shaft fractures. Grade III indicates:",
              "options": [
                "No comminution (simple fracture)",
                "Small butterfly fragment (<50% cortex)",
                "Large butterfly fragment (>50% cortex) — some cortical contact maintained",
                "Circumferential comminution with no cortical contact between proximal and distal fragments",
                "Segmental fracture only"
              ],
              "answer": "C",
              "explanation": "Winquist-Hansen: Grade 0 = no comminution. Grade I = small butterfly fragment (<25% cortex). Grade II = larger butterfly (25-50% cortex). Grade III = large butterfly (>50% cortex) — some cortical contact remains. Grade IV = circumferential comminution with NO cortical contact between main fragments → the nail must control length and alignment completely (no inherent stability from cortical contact). Grade III-IV fractures need special attention during nailing to avoid shortening and malrotation — static locking of the nail is mandatory.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 467,
              "stem": "A 25-year-old male sustains a closed femoral shaft fracture in an RTA. He is haemodynamically stable. The gold standard definitive treatment is:",
              "options": [
                "Reamed antegrade intramedullary nailing",
                "Skeletal traction for 12 weeks",
                "Cast bracing",
                "Compression plating",
                "External fixation as definitive treatment"
              ],
              "answer": "A",
              "explanation": "Reamed antegrade intramedullary nailing is the gold standard for adult femoral shaft fractures. Advantages: load-sharing device, allows early weight-bearing, closed technique (preserves fracture biology/periosteal blood supply), high union rates (~98-99%), low infection rates. The nail is inserted through a piriformis fossa or greater trochanter entry point and locked proximally and distally with interlocking screws. Reaming: enlarges the canal for a larger-diameter nail (increased stiffness and stability), provides autograft from the reaming debris, improves nail-bone contact. Alternatives: retrograde nailing (supracondylar/distal third fractures, ipsilateral knee pathology, pregnancy, bilateral femoral fractures, polytrauma), plating (for specific patterns or periarticular extension), external fixation (DCO in polytrauma).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Spinal Clearance",
          "range": "Q468-Q469",
          "questions": [
            {
              "number": 468,
              "stem": "The Canadian C-spine Rules state that a cervical spine can be clinically cleared without imaging if the patient meets certain criteria. Which is NOT one of these criteria?",
              "options": [
                "Alert and oriented (GCS 15)",
                "Intoxicated at the time of injury",
                "No midline tenderness",
                "Able to actively rotate the neck 45° left and right",
                "Age under 65"
              ],
              "answer": "B",
              "explanation": "The Canadian C-spine Rules require: (1) No high-risk factors (age ≥65, dangerous mechanism, paraesthesia), (2) At least one low-risk factor allowing safe assessment (simple rear-end MVC, sitting in ED, ambulatory, delayed onset neck pain, no midline tenderness), and (3) Ability to actively rotate neck 45° left and right. Intoxication is NOT a criterion that allows clearance — intoxicated patients cannot be reliably assessed clinically and require imaging.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 469,
              "stem": "In an obtunded trauma patient (GCS <15), the cervical spine cannot be clinically cleared. The investigation of choice to exclude significant cervical spine injury is:",
              "options": [
                "Plain radiographs only",
                "MRI only",
                "Flexion-extension radiographs",
                "CT cervical spine (high sensitivity for bony injury, combined with clinical assessment when the patient awakens)",
                "No investigation needed — just remove the collar"
              ],
              "answer": "D",
              "explanation": "In obtunded patients who cannot be clinically assessed, CT of the cervical spine is the investigation of choice for excluding bony cervical spine injury (sensitivity approaching 100% for significant fractures/dislocations with modern MDCT). However, CT alone cannot fully exclude ligamentous injury or unstable soft tissue damage. If the CT is normal: options include (1) maintaining the collar and reassessing when the patient is alert enough for clinical clearance, (2) MRI within 72 hours to assess ligamentous structures (disc, ligaments, spinal cord). If both CT and MRI are normal, the collar can be safely removed even in the obtunded patient. The combination of normal CT + normal MRI has ~100% NPV for significant unstable cervical spine injury.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Massive Transfusion",
          "range": "Q470",
          "questions": [
            {
              "number": 470,
              "stem": "A massive transfusion protocol (MTP) is typically activated when a trauma patient is predicted to need:",
              "options": [
                "1 unit of packed red blood cells",
                "4 units in 4 hours",
                "Any blood products",
                "Only fresh frozen plasma",
                "≥10 units of packed red blood cells in 24 hours (or ≥4 units in 1 hour)"
              ],
              "answer": "E",
              "explanation": "Massive transfusion is classically defined as replacement of ≥10 units of pRBCs in 24 hours, or ≥4 units in 1 hour. The MTP delivers blood products in a balanced ratio (1:1:1 pRBC:FFP:platelets per PROPPR trial). TXA within 3 hours (CRASH-2). Permissive hypotension (SBP 80–90 mmHg) to reduce dilutional coagulopathy. Warm all products. Monitor with TEG/ROTEM for targeted component therapy.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Floating Knee",
          "range": "Q471",
          "questions": [
            {
              "number": 471,
              "stem": "A 'floating knee' injury involves ipsilateral fractures of which two bones?",
              "options": [
                "Femur and fibula",
                "Tibia and fibula",
                "Femur and patella",
                "Tibia and calcaneus",
                "Femur and tibia"
              ],
              "answer": "E",
              "explanation": "A floating knee involves ipsilateral femoral and tibial fractures, leaving the knee joint 'floating' between two unstable segments. It is a high-energy injury with significant risk of vascular injury (popliteal artery), compartment syndrome, and associated soft tissue damage. Both fractures typically require operative fixation (usually IM nailing of both bones). Always assess the popliteal pulse and perform a thorough neurovascular examination.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Distal Humerus",
          "range": "Q472",
          "questions": [
            {
              "number": 472,
              "stem": "The terrible triad of the elbow is a posterior dislocation combined with fractures of the radial head and:",
              "options": [
                "Olecranon",
                "Lateral epicondyle",
                "Medial epicondyle",
                "Coronoid process",
                "Capitellum"
              ],
              "answer": "D",
              "explanation": "The terrible triad = posterior elbow dislocation + radial head fracture + coronoid fracture. This is highly unstable because all three primary stabilisers are compromised. Treatment requires: (1) fix or replace the radial head, (2) fix the coronoid, (3) repair the lateral ulnar collateral ligament (LUCL). Without surgical treatment, recurrent instability is almost inevitable. The LCL complex is the primary lateral stabiliser.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Olecranon",
          "range": "Q473-Q474",
          "questions": [
            {
              "number": 473,
              "stem": "Tension band wiring of an olecranon fracture converts the pull of the triceps into:",
              "options": [
                "Distraction across the fracture",
                "Compression across the articular surface",
                "Shear at the fracture site",
                "Torsion of the proximal ulna",
                "No mechanical effect"
              ],
              "answer": "B",
              "explanation": "Tension band wiring converts the tensile force of triceps pulling on the posterior olecranon into compressive force across the articular surface of the olecranon when the elbow flexes. This is the classic application of the tension band principle. Requirements: transverse fracture pattern, intact articular surface on the opposite (volar) cortex. Contraindicated in comminuted fractures (where a plate is preferred).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 474,
              "stem": "An olecranon fracture with 2mm of articular displacement in an active adult is best treated with:",
              "options": [
                "Collar and cuff sling only",
                "Below-elbow cast in extension",
                "Tension band wiring or plate fixation (ORIF)",
                "Excision of the proximal fragment",
                "Observation without treatment"
              ],
              "answer": "C",
              "explanation": "Displaced olecranon fractures (>2mm articular step or gap, or inability to extend the elbow against gravity) require operative fixation to restore the articular surface and triceps extensor mechanism. Options: (1) Tension band wiring (TBW) — two K-wires + figure-of-eight wire (converts triceps tension into articular compression during elbow flexion). Best for simple transverse fractures without comminution. (2) Plate fixation (pre-contoured locking plate) — preferred for comminuted fractures, oblique fractures, Monteggia-equivalent fracture-dislocations, and in osteoporotic bone where TBW may not hold. Excision of the proximal fragment with triceps advancement: reserved for elderly/low-demand patients with severely comminuted fractures. Non-operative: only for truly undisplaced fractures in patients who can extend against gravity.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Clinical",
          "range": "Q475",
          "questions": [
            {
              "number": 475,
              "stem": "A child presents with a painful swollen elbow after a fall. The radiograph shows a posterior fat pad sign (sail sign). This indicates:",
              "options": [
                "An intra-articular fracture (even if a fracture line is not visible — the fat pad is displaced by a haemarthrosis)",
                "Normal finding requiring no further action",
                "Soft tissue infection",
                "Ligament injury only",
                "Osteomyelitis"
              ],
              "answer": "A",
              "explanation": "The posterior fat pad sign on a lateral elbow radiograph indicates an intra-articular effusion (haemarthrosis in the setting of trauma). The posterior fat pad normally lies within the olecranon fossa and is NOT visible on a normal lateral radiograph. When an effusion (haemarthrosis) fills the joint, it displaces the posterior fat pad posteriorly and superiorly, making it visible (the 'sail sign'). In the context of trauma, a posterior fat pad sign indicates an OCCULT FRACTURE — most commonly a radial head/neck fracture in adults, or a supracondylar fracture in children. Even if NO fracture line is visible, the joint should be treated as a fracture (immobilise, follow up with repeat XR at 10-14 days to look for healing callus). An anterior fat pad can be normal (small), but an elevated anterior fat pad (large) is also abnormal.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Rehabilitation",
          "range": "Q476",
          "questions": [
            {
              "number": 476,
              "stem": "Early mobilisation after hip fracture surgery is critical. NICE recommends mobilisation:",
              "options": [
                "After 2 weeks of bed rest",
                "Only when the patient requests it",
                "After 6 weeks",
                "The day after surgery at the latest (ideally the day of surgery if medically safe)",
                "Only after radiographic confirmation of healing"
              ],
              "answer": "D",
              "explanation": "NICE guidelines recommend mobilisation the day after surgery at the latest (and ideally the same day if medically safe). Early mobilisation reduces: mortality, DVT/PE risk, chest infection, pressure sores, deconditioning, delirium, and length of hospital stay. Immediate weight-bearing as tolerated is recommended for all standard fixation and arthroplasty methods (DHS, IM nail, hemiarthroplasty, THA). The hip fracture Best Practice Tariff (BPT) incentivises: surgery within 36 hours, orthogeriatrician review within 72 hours, assessment by a physiotherapist on the day of or day after surgery, and falls and bone health assessment. The 30-day mortality for hip fractures is approximately 6-8%, and 1-year mortality is approximately 25-30% — making early comprehensive management essential.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Classification",
          "range": "Q477",
          "questions": [
            {
              "number": 477,
              "stem": "The Gustilo-Anderson classification of open fractures has how many types?",
              "options": [
                "5 (Type I, II, IIIA, IIIB, IIIC)",
                "2",
                "3",
                "7",
                "10"
              ],
              "answer": "A",
              "explanation": "The Gustilo-Anderson classification has 5 types: Type I, Type II, Type IIIA, Type IIIB, and Type IIIC. Originally described with 3 types (I, II, III), Type III was subsequently subdivided into IIIA (adequate soft tissue coverage), IIIB (soft tissue loss requiring flap), and IIIC (vascular injury requiring repair). This subclassification of Type III was essential because the outcomes and management differ dramatically between IIIA, IIIB, and IIIC. Infection rates: I = 0-2%, II = 2-5%, IIIA = 5-10%, IIIB = 10-25%, IIIC = 25-50%. The classification is applied at the time of DEFINITIVE debridement (not initial assessment — the initial assessment often underestimates the injury). Always upgrade if needed after debridement.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Emergency",
          "range": "Q478",
          "questions": [
            {
              "number": 478,
              "stem": "The single most important intervention to improve survival in a patient with a tension pneumothorax is:",
              "options": [
                "Chest X-ray first",
                "CT scan",
                "IV antibiotics",
                "Intubation",
                "Immediate needle decompression (2nd intercostal space, midclavicular line) followed by chest drain insertion — this is a CLINICAL diagnosis, do NOT delay for imaging"
              ],
              "answer": "E",
              "explanation": "Tension pneumothorax is a CLINICAL diagnosis — do NOT wait for imaging. It presents with: respiratory distress, tachycardia, hypotension, tracheal deviation AWAY from the affected side, absent breath sounds on the affected side, distended neck veins, and hyperresonance on percussion. It is immediately life-threatening: the one-way valve effect causes progressive pressure build-up in the affected hemithorax, mediastinal shift, and compression of the contralateral lung and great vessels → obstructive shock → cardiac arrest. Treatment: immediate needle decompression (14-16G cannula, 2nd intercostal space, midclavicular line, above the rib to avoid the neurovascular bundle) followed by definitive chest drain (tube thoracostomy, 5th intercostal space, anterior to mid-axillary line). This is an ATLS 'B' (Breathing) life-threatening condition addressed in the primary survey.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Tibial Plateau",
          "range": "Q479-Q483",
          "questions": [
            {
              "number": 479,
              "stem": "A Schatzker Type VI tibial plateau fracture is characterised by:",
              "options": [
                "Lateral split fracture",
                "Plateau fracture with metaphyseal-diaphyseal dissociation",
                "Lateral split-depression",
                "Pure depression",
                "Medial plateau fracture"
              ],
              "answer": "B",
              "explanation": "Schatzker VI involves a tibial plateau fracture with dissociation of the metaphysis from the diaphysis. It is the most severe pattern, typically from high-energy mechanisms, and has the worst prognosis. All plateau fractures need CT for surgical planning. Type VI often requires dual-plating (medial + lateral) or a combination of plates and external fixation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 480,
              "stem": "According to the Schatzker classification, a pure depression fracture of the lateral tibial plateau without a split component is classified as:",
              "options": [
                "Schatzker I",
                "Schatzker II",
                "Schatzker III",
                "Schatzker IV",
                "Schatzker V"
              ],
              "answer": "C",
              "explanation": "Schatzker classification: I = lateral split, II = lateral split-depression, III = pure lateral depression, IV = medial plateau, V = bicondylar, VI = plateau with metaphyseal-diaphyseal dissociation. Type III (pure depression) involves articular impaction without a cortical split. Treatment depends on degree of depression (>3–4 mm typically requires elevation and grafting).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 481,
              "stem": "In tibial plateau fractures, which meniscus is most commonly injured as an associated soft tissue injury?",
              "options": [
                "Medial meniscus",
                "Both equally",
                "Neither — meniscal injury is rare",
                "Discoid meniscus",
                "Lateral meniscus"
              ],
              "answer": "E",
              "explanation": "The lateral meniscus is most commonly injured in association with tibial plateau fractures, reflecting the predominance of lateral plateau fractures (Schatzker I–III). The lateral meniscus may be entrapped in the fracture, and MRI or arthroscopy should be considered. Ligamentous injuries (particularly ACL and MCL) are also common associations.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 482,
              "stem": "The Schatzker classification of tibial plateau fractures — Type VI is:",
              "options": [
                "Bicondylar fracture with metaphyseal-diaphyseal dissociation",
                "Lateral split fracture",
                "Lateral split-depression",
                "Pure depression of the lateral plateau",
                "Medial condyle fracture"
              ],
              "answer": "A",
              "explanation": "Schatzker classification: I = lateral split (pure wedge fracture, young patient, good bone). II = lateral split-depression (most common — split + depressed articular fragment). III = pure lateral depression (elderly, osteoporotic bone, no split). IV = medial condyle fracture (higher energy, associated with NV injury — popliteal artery and peroneal nerve). V = bicondylar (both condyles fractured). VI = bicondylar with metaphyseal-diaphyseal dissociation (the articular fragments are separated from the shaft — highest energy, most severe). CT is essential for operative planning. Articular step >2mm is an indication for reduction. Treatment: I-III → lateral plate ± bone graft under depressed fragment. IV-VI → dual plating (medial + lateral) or ring fixator.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 483,
              "stem": "A 65-year-old osteoporotic woman falls and sustains a Schatzker II tibial plateau fracture with 8mm of articular depression. Initial management should include:",
              "options": [
                "Non-operative management with early ROM",
                "CT scan for operative planning followed by ORIF with elevation of the depressed fragment and lateral plating ± bone graft",
                "Immediate above-knee amputation",
                "Aspiration of the knee joint only",
                "MRI only without operative consideration"
              ],
              "answer": "B",
              "explanation": "A Schatzker II fracture (lateral split-depression) with >2mm articular step is an indication for operative treatment. CT scanning is essential for operative planning — it delineates the fracture pattern, the degree and location of articular depression, and the presence of any medial condyle involvement not visible on XR. Treatment: open reduction (elevate the depressed articular fragment using a bone tamp through a cortical window), support the elevated fragment with bone graft or calcium phosphate cement, and stabilise with a lateral periarticular locking plate. The goal is to restore the articular surface to within 2mm of anatomical to reduce the risk of post-traumatic OA. Meniscal pathology is common (assess intra-operatively or with pre-op MRI).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Hip Dislocation",
          "range": "Q484",
          "questions": [
            {
              "number": 484,
              "stem": "The most common type of traumatic hip dislocation is:",
              "options": [
                "Anterior",
                "Central",
                "Inferior (obturator)",
                "Posterior",
                "Superior"
              ],
              "answer": "D",
              "explanation": "Posterior dislocation accounts for ~90% of traumatic hip dislocations, typically from a dashboard injury (axial force through the flexed knee pushing the femoral head posteriorly). The hip is held in flexion, adduction, and internal rotation. The sciatic nerve is at risk in 10-20% (peroneal division more commonly affected). Urgent reduction within 6 hours is critical to minimise AVN risk. CT after reduction to assess for associated posterior wall fracture and loose bodies.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Scapular Fracture",
          "range": "Q485",
          "questions": [
            {
              "number": 485,
              "stem": "Scapular body fractures are uncommon and are associated with:",
              "options": [
                "Low-energy falls",
                "Isolated injuries without other trauma",
                "High-energy trauma with associated thoracic injuries in 80-95%",
                "Osteoporotic insufficiency",
                "Pathological fractures"
              ],
              "answer": "C",
              "explanation": "Scapular body fractures require significant force (high-energy trauma) and are associated with other injuries in 80-95% of cases: rib fractures, pulmonary contusion, pneumothorax, brachial plexus injuries, vascular injuries, and ipsilateral clavicle fractures (floating shoulder). Most scapular body fractures are managed non-operatively. Glenoid and scapular neck fractures may need surgical fixation depending on displacement.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Knee Dislocation",
          "range": "Q486-Q487",
          "questions": [
            {
              "number": 486,
              "stem": "A traumatic knee dislocation mandates assessment of which vascular structure?",
              "options": [
                "Femoral artery",
                "Popliteal artery",
                "Profunda femoris artery",
                "Anterior tibial artery",
                "Posterior tibial artery"
              ],
              "answer": "B",
              "explanation": "The popliteal artery is at risk in knee dislocations due to its relatively fixed position behind the knee (tethered at the adductor hiatus proximally and the soleal arch distally). Vascular injury occurs in 20-40% of knee dislocations. Even if the knee has spontaneously reduced before arrival, a thorough vascular assessment is mandatory: clinical exam, ABI (ankle-brachial index <0.9 is abnormal), and CT angiography if any concern. Delay in diagnosis leads to amputation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            },
            {
              "number": 487,
              "stem": "A knee dislocation (multiligament injury) requires urgent assessment of which structure due to its proximity and risk of intimal injury?",
              "options": [
                "Femoral artery",
                "Saphenous vein",
                "Popliteal artery (passes directly posterior to the joint capsule, tethered proximally and distally)",
                "Profunda femoris artery",
                "Common peroneal nerve only"
              ],
              "answer": "C",
              "explanation": "The popliteal artery runs directly posterior to the knee joint capsule and is tethered proximally at the adductor hiatus and distally at the soleal arch. During knee dislocation, the artery is stretched or torn in up to 30-40% of cases (particularly anterior dislocations). Intimal injury may cause delayed thrombosis even with a palpable distal pulse initially. Therefore: ALL knee dislocations require urgent vascular assessment — CT angiography (CTA) or duplex USS regardless of pulse status. If pulse is absent: immediate vascular surgical exploration. The '6-hour rule': ischaemia time >6 hours has an amputation rate >90%. Common peroneal nerve injury also occurs in ~25-35%.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Proximal Tibia",
          "range": "Q488",
          "questions": [
            {
              "number": 488,
              "stem": "The safe zone for proximal tibial pin insertion to avoid the common peroneal nerve is:",
              "options": [
                "Directly lateral",
                "Anterolateral",
                "Directly posterior",
                "Anteromedial (between tibial tubercle and posteromedial border)",
                "Directly medial at the joint line"
              ],
              "answer": "D",
              "explanation": "Proximal tibial pins (for external fixation or skeletal traction) should be inserted from the lateral side in the anteromedial safe zone — approximately 2 cm distal to the tibial tubercle and 2 cm posterior to the anterior tibial crest (avoiding the anterior tibial artery and deep peroneal nerve anteriorly, and the common peroneal nerve laterally). The pin enters from lateral, exits anteromedially. For distal femoral pins, insert from medial to lateral to protect the femoral artery.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Proximal Femur",
          "range": "Q489-Q500",
          "questions": [
            {
              "number": 489,
              "stem": "A 78-year-old independently mobile woman with no cognitive impairment sustains a Garden IV displaced intracapsular neck of femur fracture. What is the recommended surgical treatment according to NICE guidelines?",
              "options": [
                "Cannulated screw fixation",
                "Dynamic hip screw",
                "Cemented hemiarthroplasty",
                "Conservative management",
                "Cemented total hip arthroplasty"
              ],
              "answer": "E",
              "explanation": "NICE guidelines recommend THA for displaced intracapsular NOF fractures in patients who are independently mobile, cognitively intact, and medically fit. THA provides better function, fewer reoperations, and superior quality of life compared to hemiarthroplasty in this group.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 490,
              "stem": "A dynamic hip screw (DHS) is most appropriate for which type of proximal femoral fracture?",
              "options": [
                "Stable intertrochanteric fracture (AO 31-A1)",
                "Displaced intracapsular fracture",
                "Undisplaced intracapsular fracture",
                "Subtrochanteric fracture",
                "Reverse oblique intertrochanteric fracture"
              ],
              "answer": "A",
              "explanation": "The DHS is the implant of choice for stable intertrochanteric fractures (AO 31-A1 and most A2 patterns). The sliding mechanism allows controlled collapse along the femoral neck axis. It is NOT suitable for subtrochanteric or reverse oblique fractures (where the fracture line runs in the opposite obliquity and the nail cuts out), nor for intracapsular fractures.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 491,
              "stem": "The blood supply to the femoral head is primarily from the medial femoral circumflex artery. Which branch directly supplies the weight-bearing portion of the femoral head?",
              "options": [
                "Ascending cervical branch",
                "Inferior metaphyseal artery",
                "Lateral epiphyseal artery",
                "Artery of the ligamentum teres",
                "Trochanteric anastomosis"
              ],
              "answer": "C",
              "explanation": "The lateral epiphyseal artery (a terminal branch of the deep branch of the MFCA) is the principal supply to the weight-bearing superolateral portion of the femoral head. The retinacular vessels carry this supply along the posterosuperior femoral neck. Displaced intracapsular fractures disrupt these retinacular vessels, causing AVN rates of up to 30%.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 492,
              "stem": "An 82-year-old with dementia and limited mobility sustains a displaced intracapsular NOF fracture. She uses a frame indoors. What is the most appropriate treatment?",
              "options": [
                "Cemented hemiarthroplasty",
                "Total hip arthroplasty",
                "Cannulated screw fixation",
                "Conservative management",
                "Uncemented hemiarthroplasty"
              ],
              "answer": "A",
              "explanation": "For patients with displaced intracapsular fractures who have cognitive impairment or limited pre-injury mobility, cemented hemiarthroplasty is recommended. These patients have lower functional demands and the additional complexity of THA is not justified. Cemented fixation is preferred in elderly patients (NICE) for immediate stability and reduced periprosthetic fracture risk.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 493,
              "stem": "A 55-year-old active man sustains an undisplaced (Garden I) intracapsular neck of femur fracture after a fall from a ladder. What is the most appropriate surgical treatment?",
              "options": [
                "Total hip arthroplasty",
                "Internal fixation with cannulated screws",
                "Hemiarthroplasty",
                "Dynamic hip screw",
                "Conservative management in a cast"
              ],
              "answer": "B",
              "explanation": "Undisplaced (Garden I and II) intracapsular fractures in physiologically young patients should be treated with internal fixation (typically 3 parallel cannulated screws) to preserve the native femoral head. The blood supply is more likely intact in undisplaced fractures, and union rates are approximately 90%. These patients are too young for arthroplasty as the first option.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 494,
              "stem": "NICE guidelines recommend that patients with hip fracture should undergo surgery within what time frame of admission to reduce mortality?",
              "options": [
                "6 hours",
                "12 hours",
                "24 hours",
                "36 hours",
                "48 hours"
              ],
              "answer": "D",
              "explanation": "NICE recommends surgery within 36 hours of admission (and ideally on the day of or day after admission). Delay beyond 36 hours is associated with increased 30-day mortality, pressure sores, chest infections, VTE, and length of hospital stay. Medical optimisation should not cause unnecessary delay — most patients can be safely operated within this window.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 495,
              "stem": "A tip-apex distance (TAD) of greater than 25 mm when placing a lag screw in an intertrochanteric fracture is associated with which complication?",
              "options": [
                "Infection",
                "Non-union",
                "Avascular necrosis",
                "Periprosthetic fracture",
                "Screw cut-out through the femoral head"
              ],
              "answer": "E",
              "explanation": "The tip-apex distance (TAD) is the sum of distances from the tip of the lag screw to the apex of the femoral head on AP and lateral radiographs. A TAD >25 mm is the strongest predictor of lag screw cut-out. Ideal screw placement is central-central or inferior-central in the femoral head on AP/lateral views. The TAD concept was described by Baumgaertner.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            },
            {
              "number": 496,
              "stem": "A subtrochanteric femoral fracture is best treated with which implant?",
              "options": [
                "Dynamic hip screw",
                "Cephalomedullary nail (long)",
                "Cannulated screws",
                "Short proximal femoral nail",
                "Locking plate"
              ],
              "answer": "B",
              "explanation": "Subtrochanteric fractures are high-stress injuries in cortical bone with significant deforming forces (iliopsoas flexes proximal fragment, adductors displace distal fragment medially). A long cephalomedullary nail (e.g., long gamma nail, PFNA) is the preferred implant — it provides load-sharing fixation, controls the deforming forces, and allows early weight-bearing. A DHS would fail due to excessive bending moments.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 497,
              "stem": "Atypical femoral fractures associated with long-term bisphosphonate use characteristically occur at which anatomical location?",
              "options": [
                "Femoral neck",
                "Intertrochanteric region",
                "Supracondylar region",
                "Greater trochanter",
                "Subtrochanteric region or diaphysis"
              ],
              "answer": "E",
              "explanation": "Atypical femoral fractures are stress/insufficiency fractures associated with prolonged bisphosphonate use (typically >5 years). They characteristically occur in the subtrochanteric region or femoral diaphysis. Features: transverse or short oblique fracture line, lateral cortical thickening (beaking), minimal comminution, bilateral in up to 28% of cases. Prodromal thigh pain often precedes the complete fracture.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            },
            {
              "number": 498,
              "stem": "The Garden classification of intracapsular neck of femur fractures classifies fractures into how many types?",
              "options": [
                "2",
                "3",
                "4",
                "5",
                "6"
              ],
              "answer": "C",
              "explanation": "The Garden classification divides intracapsular NOF fractures into 4 types: I = incomplete/valgus impacted (undisplaced), II = complete but undisplaced, III = complete, partially displaced (trabeculae misaligned), IV = complete, fully displaced (no continuity). In practice, the key distinction is undisplaced (I/II) vs displaced (III/IV).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 499,
              "stem": "In a patient with a displaced intracapsular NOF fracture, which complication is most significantly reduced by choosing arthroplasty over internal fixation?",
              "options": [
                "Revision surgery",
                "Infection",
                "DVT",
                "Blood loss",
                "Dislocation"
              ],
              "answer": "A",
              "explanation": "The main advantage of arthroplasty over internal fixation for displaced intracapsular fractures in elderly patients is the dramatically lower reoperation/revision rate. Internal fixation has a 30–40% failure rate in displaced fractures (non-union, AVN, screw cut-out). Arthroplasty eliminates the risk of non-union and AVN. Dislocation risk is a disadvantage of arthroplasty.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 500,
              "stem": "In an intertrochanteric fracture, the ideal position of the lag screw within the femoral head on AP and lateral radiographs is:",
              "options": [
                "Superior-anterior",
                "Inferior-posterior",
                "Superior-central",
                "Central-central or inferior-central",
                "Anterior-central"
              ],
              "answer": "D",
              "explanation": "The optimal lag screw position is central-central or inferior-central on AP and lateral views. A central or slightly inferior position on the AP view and central on the lateral provides the best mechanical support and lowest cut-out rate. Superior placement is the strongest predictor of cut-out (after TAD). Posterior placement risks posterior perforation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Pelvic Ring",
          "range": "Q501-Q508",
          "questions": [
            {
              "number": 501,
              "stem": "According to the Tile classification, a Type B1 pelvic ring injury (open book) results from which mechanism?",
              "options": [
                "Lateral compression",
                "Anteroposterior compression (external rotation)",
                "Vertical shear",
                "Axial loading",
                "Combined mechanism"
              ],
              "answer": "B",
              "explanation": "Tile B1 (open book) injuries result from anteroposterior compression (external rotation force). This disrupts the symphysis pubis anteriorly and partially tears the anterior sacroiliac ligaments, but the posterior sacroiliac ligaments remain intact. The pelvis is rotationally unstable but vertically stable because the posterior tension band (posterior SI ligaments) is preserved.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 502,
              "stem": "In the acute management of a haemodynamically unstable pelvic ring injury, what is the most appropriate immediate intervention to reduce pelvic volume and control haemorrhage?",
              "options": [
                "External fixation",
                "Open reduction internal fixation",
                "Angiographic embolisation",
                "Packing the pelvis",
                "Application of a pelvic binder"
              ],
              "answer": "E",
              "explanation": "A pelvic binder (or circumferential sheet) applied at the level of the greater trochanters is the first-line intervention for acute haemorrhage control in unstable pelvic fractures. It reduces pelvic volume, approximates fracture fragments, and tamponades venous bleeding. It should be applied in the pre-hospital setting or emergency department as part of ATLS management (BOAST guidelines).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 503,
              "stem": "The Young and Burgess classification of pelvic ring injuries includes which categories?",
              "options": [
                "Types A, B, and C",
                "Stable, rotationally unstable, completely unstable",
                "Lateral compression (LC), AP compression (APC), vertical shear (VS), combined mechanism (CM)",
                "Types I through V",
                "Anterior ring, posterior ring, combined"
              ],
              "answer": "C",
              "explanation": "The Young and Burgess classification divides pelvic ring injuries into four categories based on mechanism: LC (lateral compression, types I–III), APC (anteroposterior compression, types I–III), VS (vertical shear), and CM (combined mechanism). LC injuries are the most common. APC injuries produce the classic 'open book'. VS produces complete hemipelvic displacement.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            },
            {
              "number": 504,
              "stem": "In a lateral compression (LC) type I pelvic injury, the characteristic fracture pattern is:",
              "options": [
                "Symphysis diastasis >2.5 cm",
                "Complete posterior SI disruption with hemipelvic elevation",
                "Bilateral pubic rami fractures only",
                "Sacral compression fracture with ipsilateral pubic rami fractures",
                "Sacral fracture with contralateral pubic rami fractures"
              ],
              "answer": "D",
              "explanation": "LC-I is the most common pelvic ring injury pattern. The mechanism is a lateral force causing internal rotation of the hemipelvis. This produces an ipsilateral sacral compression (buckle) fracture posteriorly and ipsilateral pubic rami fractures anteriorly. The pelvis is rotationally stable in most cases. LC-II adds an iliac wing fracture (crescent fracture). LC-III produces a contralateral open-book pattern (windswept pelvis).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 505,
              "stem": "The posterior sacroiliac ligament complex is the strongest ligament in the body and is the key structure providing which type of pelvic stability?",
              "options": [
                "Vertical stability",
                "Rotational stability only",
                "Horizontal stability only",
                "Lateral stability only",
                "Torsional stability only"
              ],
              "answer": "A",
              "explanation": "The posterior sacroiliac ligament complex (including the interosseous sacroiliac ligaments) is the primary restraint to vertical displacement of the hemipelvis. Its disruption defines a Tile Type C injury (vertically and rotationally unstable). In Tile B injuries, the posterior SI ligaments are intact, maintaining vertical stability even though rotational stability is lost.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 506,
              "stem": "A vertical shear pelvic injury (Tile C/Young-Burgess VS) characteristically shows which radiographic finding?",
              "options": [
                "Symphysis diastasis only",
                "Bilateral pubic rami fractures only",
                "Sacral buckle fracture only",
                "Ipsilateral hemipelvic vertical displacement",
                "Widening of the sacroiliac joint only"
              ],
              "answer": "D",
              "explanation": "Vertical shear injuries produce cranial (cephalad) displacement of the hemipelvis, visible on AP pelvic radiograph as vertical migration of the affected hemipelvis relative to the contralateral side. Both anterior ring (symphysis/rami) and posterior ring (sacroiliac/sacral) disruption are present, with complete loss of both rotational and vertical stability. This is the most unstable pelvic ring injury pattern.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 507,
              "stem": "In a pelvic ring injury, which artery is the most common source of life-threatening haemorrhage?",
              "options": [
                "External iliac artery",
                "Common femoral artery",
                "Superior gluteal artery specifically",
                "Aortic bifurcation",
                "Internal iliac artery and its branches"
              ],
              "answer": "E",
              "explanation": "The internal iliac artery and its branches (particularly the superior gluteal, internal pudendal, and lateral sacral arteries) are the most common sources of arterial haemorrhage in pelvic ring injuries. However, most pelvic haemorrhage is actually venous (from the presacral and paravesical venous plexuses and cancellous bone surfaces). Arterial bleeding occurs in approximately 10–15% of cases and may require angiographic embolisation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            },
            {
              "number": 508,
              "stem": "Young and Burgess classification of pelvic ring injuries — an anterior-posterior compression (APC) Type III injury involves:",
              "options": [
                "Diastasis of the symphysis pubis <2.5 cm only",
                "Diastasis >2.5 cm with disruption of anterior SI ligaments (sacrospinous/sacrotuberous)",
                "Complete disruption of all anterior AND posterior ligamentous structures (including posterior SI ligaments) — equivalent to Tile C",
                "Lateral compression of the pubic rami",
                "Vertical shear through the SI joint"
              ],
              "answer": "C",
              "explanation": "Young-Burgess APC classification: APC-I = symphysis diastasis <2.5 cm, stretched but intact sacrospinous/sacrotuberous ligaments (stable). APC-II = symphysis >2.5 cm, ruptured sacrospinous and sacrotuberous ligaments, anterior SI ligaments disrupted, posterior SI ligaments INTACT (rotationally unstable = Tile B). APC-III = complete disruption of anterior AND posterior ligaments (both rotationally and vertically unstable = Tile C). APC-III is the 'open book' pelvis in its most severe form — hemipelvis is completely free. LC (lateral compression) types: ipsilateral rami fractures with variable posterior injury.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Acetabular Fractures",
          "range": "Q509-Q513",
          "questions": [
            {
              "number": 509,
              "stem": "According to the Judet and Letournel classification, the five elementary acetabular fracture patterns are posterior wall, posterior column, anterior wall, anterior column, and:",
              "options": [
                "Transverse",
                "Both-column",
                "T-type",
                "Posterior column + posterior wall",
                "Transverse + posterior wall"
              ],
              "answer": "A",
              "explanation": "The Judet and Letournel classification divides acetabular fractures into 5 elementary patterns (posterior wall, posterior column, anterior wall, anterior column, transverse) and 5 associated patterns (T-type, both-column, posterior column + posterior wall, transverse + posterior wall, anterior column + posterior hemitransverse). Total = 10 patterns.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 510,
              "stem": "The most common acetabular fracture pattern is:",
              "options": [
                "Anterior wall",
                "Posterior wall",
                "Anterior column",
                "Both-column",
                "Transverse"
              ],
              "answer": "B",
              "explanation": "Posterior wall fractures are the most common acetabular fracture pattern, typically resulting from a dashboard injury (axial force through the flexed knee pushing the femoral head posteriorly). They are frequently associated with posterior hip dislocation. Surgical fixation is indicated when the fragment involves >40% of the posterior wall or when the hip is unstable after reduction of the dislocation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 511,
              "stem": "On a standard AP pelvic radiograph, the six radiographic landmarks of Judet and Letournel are the iliopectineal line, ilioischial line, acetabular roof (sourcil), anterior wall, posterior wall, and:",
              "options": [
                "Obturator foramen",
                "Greater sciatic notch",
                "Teardrop (acetabular fossa)",
                "Sacroiliac joint",
                "Ischial tuberosity"
              ],
              "answer": "C",
              "explanation": "The six landmarks on the AP pelvis are: (1) iliopectineal line (anterior column), (2) ilioischial line (posterior column), (3) acetabular roof/sourcil, (4) anterior wall, (5) posterior wall, and (6) teardrop (acetabular fossa/medial wall). Disruption of each line indicates involvement of the corresponding anatomical structure. Judet oblique views (iliac and obturator) provide further information.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            },
            {
              "number": 512,
              "stem": "A posterior hip dislocation with an associated posterior wall acetabular fracture should be reduced within what time frame to minimise the risk of AVN?",
              "options": [
                "6 hours",
                "1 hour",
                "12 hours",
                "24 hours",
                "48 hours"
              ],
              "answer": "A",
              "explanation": "Posterior hip dislocations should be reduced as an emergency, ideally within 6 hours, to minimise the risk of avascular necrosis of the femoral head. The lateral epiphyseal artery is kinked or compressed by the dislocated head, and prolonged ischaemia leads to irreversible AVN. Delay beyond 6 hours significantly increases AVN risk (from ~10% to >50% in some series).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 513,
              "stem": "The Kocher-Langenbeck surgical approach to the acetabulum provides access to which structures?",
              "options": [
                "Anterior column and anterior wall",
                "Both columns",
                "Quadrilateral plate",
                "Posterior column, posterior wall, and sciatic notch",
                "Iliac wing only"
              ],
              "answer": "D",
              "explanation": "The Kocher-Langenbeck (posterior) approach provides access to the posterior column, posterior wall, and greater sciatic notch. The patient is positioned lateral or prone. The sciatic nerve must be identified and protected throughout. The piriformis and short external rotators are released or split. This approach is used for posterior wall, posterior column, and some transverse fractures.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            }
          ]
        },
        {
          "title": "Spinal Trauma",
          "range": "Q514-Q525",
          "questions": [
            {
              "number": 514,
              "stem": "According to the TLICS system (Thoracolumbar Injury Classification and Severity Score), a score of ≥5 indicates:",
              "options": [
                "Conservative management",
                "Surgical management is recommended",
                "Indeterminate — surgeon's choice",
                "Non-operative with bracing",
                "Further imaging required"
              ],
              "answer": "B",
              "explanation": "TLICS scores three parameters: injury morphology (compression=1, burst=2, translation/rotation=3, distraction=4), PLC integrity (intact=0, indeterminate=2, injured=3), and neurological status (intact=0, nerve root=2, complete cord=2, incomplete cord=3, cauda equina=3). Total ≤3 = non-operative. Score 4 = indeterminate. Score ≥5 = surgical.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 515,
              "stem": "A patient sustains a thoracolumbar burst fracture (AO Type A4). According to Denis's three-column model, which columns are involved?",
              "options": [
                "Anterior column only",
                "Middle and posterior columns",
                "All three columns",
                "Posterior column only",
                "Anterior and middle columns"
              ],
              "answer": "E",
              "explanation": "In a burst fracture, the vertebral body fails under axial compression with involvement of both the anterior column (anterior half of vertebral body and anterior longitudinal ligament) and the middle column (posterior half of vertebral body, posterior longitudinal ligament). The hallmark is retropulsion of bone fragments into the spinal canal from middle column failure. The posterior column may or may not be involved.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 516,
              "stem": "The ASIA (American Spinal Injury Association) Impairment Scale grade for a COMPLETE spinal cord injury with no sensory or motor function below the level of injury is:",
              "options": [
                "ASIA A",
                "ASIA B",
                "ASIA C",
                "ASIA D",
                "ASIA E"
              ],
              "answer": "A",
              "explanation": "ASIA A = Complete: no motor or sensory function preserved in sacral segments S4–S5. ASIA B = Incomplete: sensory but no motor function below the level, including S4–S5. ASIA C = Incomplete: motor function preserved below, more than half of key muscles grade <3. ASIA D = Incomplete: motor function preserved, at least half of key muscles grade ≥3. ASIA E = Normal.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 517,
              "stem": "A Jefferson fracture involves fractures of which vertebra?",
              "options": [
                "C2 (axis)",
                "C1 (atlas)",
                "C3",
                "C7",
                "T1"
              ],
              "answer": "B",
              "explanation": "A Jefferson fracture is a burst fracture of the C1 (atlas) ring, caused by axial loading (e.g., diving injury, fall onto vertex of head). The lateral masses of C1 are displaced laterally. It is often seen as bilateral widening of the lateral masses on the open-mouth (odontoid) view. If the total lateral mass overhang exceeds 6.9 mm (Rule of Spence), the transverse ligament is likely ruptured, making the injury unstable.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 518,
              "stem": "An odontoid (dens) fracture classified as Anderson and D'Alonzo Type II occurs at which location?",
              "options": [
                "Tip of the dens",
                "Body of C2",
                "Through the lateral mass of C1",
                "Base of C2 extending into the body",
                "Base of the dens (junction with C2 body)"
              ],
              "answer": "E",
              "explanation": "Anderson and D'Alonzo classification: Type I = avulsion of the dens tip (rare, usually stable). Type II = fracture at the base of the dens at its junction with the C2 body (most common, highest non-union rate ~10–15%). Type III = fracture extending into the body of C2 (usually heals well with immobilisation). Type II fractures are the most clinically significant due to their poor blood supply and high non-union rate.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 519,
              "stem": "A hangman's fracture is a bilateral fracture through which part of C2?",
              "options": [
                "Odontoid process",
                "Lateral masses",
                "Pars interarticularis (pedicles)",
                "Spinous process",
                "Vertebral body"
              ],
              "answer": "C",
              "explanation": "A hangman's fracture (traumatic spondylolisthesis of C2) is a bilateral fracture through the pars interarticularis of C2 caused by hyperextension and axial loading. Despite the dramatic mechanism, the spinal canal is actually widened (not narrowed), so neurological injury is uncommon. The Effendi/Levine-Edwards classification subdivides hangman's fractures into types I–III based on displacement and angulation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 520,
              "stem": "A Chance fracture (flexion-distraction injury) of the thoracolumbar spine characteristically involves failure of which column(s)?",
              "options": [
                "Anterior column in compression",
                "Posterior column in tension only",
                "Anterior column in compression, posterior in tension",
                "All three columns in distraction (tension)",
                "Middle column in compression"
              ],
              "answer": "D",
              "explanation": "A Chance fracture (seatbelt injury) is caused by flexion around an axis anterior to the spine (e.g., lap seatbelt). The spine fails in distraction (tension) through all three columns, progressing from posterior to anterior. The original Chance fracture is a purely bony injury through the vertebral body, pedicles, and spinous process. Soft tissue variants (ligamentous disruption) are less stable and more likely to need surgery.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 521,
              "stem": "In a cervical facet dislocation, a unilateral facet dislocation typically produces approximately how much anterior vertebral body translation on the lateral radiograph?",
              "options": [
                "<10%",
                "50% (one half)",
                "25% (one quarter)",
                "75% (three quarters)",
                "100% (full width)"
              ],
              "answer": "C",
              "explanation": "A unilateral facet dislocation produces approximately 25% anterior translation of the vertebral body. A bilateral facet dislocation produces approximately 50% or more translation and is associated with a much higher rate of spinal cord injury. Unilateral dislocations typically present with radiculopathy; bilateral dislocations present with cord injury.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            },
            {
              "number": 522,
              "stem": "Neurogenic shock following acute spinal cord injury presents with:",
              "options": [
                "Tachycardia and hypertension",
                "Tachycardia and hypotension",
                "Normal heart rate and hypotension",
                "Bradycardia and hypertension",
                "Bradycardia and hypotension"
              ],
              "answer": "E",
              "explanation": "Neurogenic shock results from loss of sympathetic tone below the level of spinal cord injury (typically above T6). This causes peripheral vasodilation (hypotension) and unopposed vagal tone (bradycardia). It is distinct from spinal shock (which is the transient loss of all neurological function below the injury level) and from hypovolaemic shock (which causes tachycardia).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 523,
              "stem": "In the Denis classification of sacral fractures, a Zone III fracture involves:",
              "options": [
                "The sacral ala lateral to the foramina",
                "The central sacral canal",
                "The sacral foramina",
                "The sacrococcygeal junction",
                "The sacroiliac joint only"
              ],
              "answer": "B",
              "explanation": "Denis sacral fracture zones: Zone 1 = lateral to the foramina (alar region, low neurological risk). Zone 2 = through the foramina (risk of sacral nerve root injury). Zone 3 = medial to the foramina, involving the central sacral canal (risk of cauda equina injury, bladder/bowel dysfunction). Zone 3 fractures have the highest neurological morbidity.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            },
            {
              "number": 524,
              "stem": "Cauda equina syndrome is characterised by which combination of features?",
              "options": [
                "Saddle anaesthesia, bladder dysfunction, and variable lower limb weakness",
                "Upper motor neuron signs with spasticity",
                "Bilateral radiculopathy only",
                "Unilateral foot drop only",
                "Bilateral Babinski signs with ankle clonus"
              ],
              "answer": "A",
              "explanation": "Cauda equina syndrome (CES) presents with saddle (perianal) anaesthesia, bladder dysfunction (retention or incontinence), bowel dysfunction, and variable bilateral lower limb weakness and reduced reflexes (lower motor neuron signs). It is a surgical emergency requiring urgent decompression (ideally within 48 hours of onset, though evidence suggests earlier decompression improves outcomes).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 525,
              "stem": "The most commonly injured level of the thoracolumbar spine is:",
              "options": [
                "T6–T7",
                "T8–T9",
                "L3–L4",
                "T12–L1 (thoracolumbar junction)",
                "L5–S1"
              ],
              "answer": "D",
              "explanation": "The thoracolumbar junction (T12–L1) is the most commonly injured level because it is the transition zone between the relatively rigid thoracic spine (stabilised by the rib cage) and the mobile lumbar spine. This creates a stress concentration point where deforming forces are maximal.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Tibial Shaft",
          "range": "Q526-Q533",
          "questions": [
            {
              "number": 526,
              "stem": "A closed mid-shaft transverse tibial fracture with <50% displacement and no shortening is treated non-operatively. What is the most appropriate initial immobilisation?",
              "options": [
                "Full weight-bearing immediately",
                "Above-knee plaster cast",
                "Above-knee backslab initially, then functional brace",
                "Functional brace immediately",
                "Below-knee walking cast"
              ],
              "answer": "C",
              "explanation": "Initial management of a non-operatively treated tibial shaft fracture involves an above-knee backslab (to control rotation in the acute swelling phase), followed by conversion to a functional (Sarmiento) brace at 2–4 weeks once swelling subsides. The functional brace allows knee and ankle movement while maintaining alignment. Acceptable alignment: <5° varus/valgus, <10° AP angulation, <10° rotation, <1 cm shortening.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 527,
              "stem": "The gold standard fixation for a displaced closed tibial shaft fracture in an adult is:",
              "options": [
                "Dynamic compression plate",
                "External fixation",
                "Cannulated screws",
                "Functional brace",
                "Intramedullary nail"
              ],
              "answer": "E",
              "explanation": "Intramedullary nailing is the gold standard for most displaced tibial shaft fractures in adults. It provides load-sharing fixation, allows early weight-bearing, preserves the periosteal blood supply (minimally invasive), and has high union rates. Reaming is generally preferred for closed fractures (enhances stability and union rate). Unreamed nails may be used for open fractures.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 528,
              "stem": "A tibial shaft fracture treated with an intramedullary nail achieves union via which mechanism?",
              "options": [
                "Secondary healing with callus formation",
                "Primary (direct) healing without callus",
                "Distraction osteogenesis",
                "Intramembranous ossification only",
                "Contact healing via cutting cones"
              ],
              "answer": "A",
              "explanation": "An IM nail provides relative stability, allowing controlled micromotion at the fracture site. This promotes secondary healing with callus formation through endochondral ossification. The nail acts as a load-sharing device. Primary healing (without callus) requires absolute stability, as provided by compression plating.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 529,
              "stem": "After reamed intramedullary nailing of a closed tibial shaft fracture, the patient develops increasing pain in the operated leg 6 months post-operatively with no signs of healing on radiographs. What is the most likely diagnosis?",
              "options": [
                "Infection",
                "Malunion",
                "Hardware failure",
                "Non-union",
                "Complex regional pain syndrome"
              ],
              "answer": "D",
              "explanation": "Failure to show radiographic progression of healing at 6 months with persistent pain strongly suggests non-union. Tibial shaft fractures treated with IM nailing have a non-union rate of approximately 5–10%. Risk factors include open fractures, smoking, diabetes, fracture gap, infection, and inadequate fixation. Treatment options include exchange nailing (most common first-line), dynamisation, or augmentation with bone graft.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 530,
              "stem": "In an open tibial fracture, debridement and washout should ideally be performed within what time frame?",
              "options": [
                "1 hour",
                "12 hours",
                "6 hours",
                "24 hours",
                "48 hours"
              ],
              "answer": "B",
              "explanation": "BOAST 4 (now BOAST Open Fractures) guidelines recommend formal debridement within 12 hours for severe open fractures (Gustilo IIIA/B/C) or within 24 hours for less severe injuries (Gustilo I/II). Historically, the '6-hour rule' was quoted, but evidence does not support 6 hours as a magic threshold. Antibiotic administration within 1 hour is more critical than exact debridement timing.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 531,
              "stem": "A Gustilo Grade IIIB open tibial fracture is characterised by:",
              "options": [
                "Adequate soft tissue cover after debridement",
                "Vascular injury requiring repair",
                "Wound less than 1 cm",
                "Low-energy mechanism",
                "Inadequate soft tissue cover requiring flap coverage"
              ],
              "answer": "E",
              "explanation": "Gustilo IIIB: high-energy injury with bony comminution or segmental fracture, significant soft tissue crushing/stripping/contamination, and INADEQUATE soft tissue cover after debridement — requiring flap coverage (local or free flap). This distinguishes it from IIIA (adequate cover after debridement) and IIIC (vascular injury requiring repair).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 532,
              "stem": "The Tscherne classification is used for which type of injury?",
              "options": [
                "Open fractures",
                "Closed fractures with associated soft tissue injury",
                "Ligament injuries",
                "Spinal cord injuries",
                "Burns"
              ],
              "answer": "B",
              "explanation": "The Tscherne classification grades the severity of soft tissue injury in CLOSED fractures (C0–C3). C0=negligible soft tissue injury. C1=superficial abrasion/contusion. C2=deep contaminated abrasion, direct trauma, impending compartment syndrome. C3=extensive skin contusion/crush, associated vascular injury, established compartment syndrome. This is complementary to Gustilo-Anderson (which classifies open fractures).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            },
            {
              "number": 533,
              "stem": "The most common long bone fracture in adults is:",
              "options": [
                "Femoral shaft fracture",
                "Humeral shaft fracture",
                "Tibial shaft fracture",
                "Radial shaft fracture",
                "Fibular shaft fracture"
              ],
              "answer": "C",
              "explanation": "The tibial shaft is the most commonly fractured long bone in adults. This is because the tibia has a subcutaneous anteromedial surface with minimal soft tissue coverage, making it vulnerable to direct trauma and high-energy mechanisms. It is also the most common open fracture. Risk of compartment syndrome is significant (~5-10% of tibial shaft fractures). Treatment: undisplaced/stable = functional bracing (Sarmiento tibial brace). Displaced/unstable = reamed IM nailing (gold standard for diaphyseal tibial shaft fractures). Open fractures: IM nailing (acute or delayed based on Gustilo grade) + BOAST protocol (debridement, antibiotics, coverage).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Pilon Fractures",
          "range": "Q534",
          "questions": [
            {
              "number": 534,
              "stem": "A pilon (tibial plafond) fracture differs from a typical ankle fracture in that it results from which mechanism?",
              "options": [
                "Axial loading",
                "Rotational force",
                "Inversion injury",
                "Eversion injury",
                "Direct blow"
              ],
              "answer": "A",
              "explanation": "Pilon fractures result from axial loading (e.g., fall from height, MVA with foot on brake pedal) that drives the talus into the tibial plafond. This produces articular impaction, comminution, and significant soft tissue injury. This contrasts with typical ankle fractures which result from rotational forces. The Rüedi-Allgöwer classification grades severity (I=undisplaced, II=displaced with minimal comminution, III=significant comminution).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Ankle Fractures",
          "range": "Q535-Q538",
          "questions": [
            {
              "number": 535,
              "stem": "The Weber classification categorises lateral malleolus fractures based on the level of the fibular fracture relative to which structure?",
              "options": [
                "The tibial plafond",
                "The medial malleolus",
                "The talar dome",
                "The ankle syndesmosis",
                "The lateral gutter"
              ],
              "answer": "D",
              "explanation": "Weber classification: A = below the syndesmosis (infrasyndesmotic), B = at the level of the syndesmosis, C = above the syndesmosis (suprasyndesmotic). Weber A fractures usually have an intact syndesmosis. Weber B may or may not have syndesmotic injury. Weber C always has syndesmotic disruption.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 536,
              "stem": "A Maisonneuve fracture consists of a proximal fibular fracture associated with disruption of which structures?",
              "options": [
                "The deltoid ligament only",
                "The calcaneofibular ligament",
                "The peroneal tendons",
                "The interosseous membrane and ankle syndesmosis",
                "The Achilles tendon"
              ],
              "answer": "D",
              "explanation": "A Maisonneuve fracture is a proximal fibular fracture with disruption of the interosseous membrane (from proximal to distal) and the ankle syndesmosis (AITFL/PITFL/transverse ligament). There is associated medial injury (deltoid ligament rupture or medial malleolus fracture). This is a highly unstable ankle injury despite the seemingly remote fibular fracture. Always examine the proximal fibula in any ankle injury.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 537,
              "stem": "An isolated undisplaced Weber B fibular fracture with a stable ankle mortise on stress views is best managed with:",
              "options": [
                "Non-operative management with functional bracing",
                "Immediate ORIF",
                "External fixation",
                "Syndesmotic screw fixation",
                "Arthroscopic assessment"
              ],
              "answer": "A",
              "explanation": "An isolated stable Weber B fracture (no medial tenderness, no deltoid injury, stable on stress views, and congruent mortise) can be managed non-operatively with a functional ankle brace or below-knee cast for 6 weeks. Operative fixation is reserved for unstable injuries (talar shift, medial clear space widening, syndesmotic injury, or displacement).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 538,
              "stem": "The anterior inferior tibiofibular ligament (AITFL) is the first structure injured in which Lauge-Hansen mechanism?",
              "options": [
                "Supination-adduction",
                "Pronation-abduction",
                "Pronation-dorsiflexion",
                "Pure axial loading",
                "Supination-external rotation"
              ],
              "answer": "E",
              "explanation": "In the SER (supination-external rotation) sequence, the AITFL is the first structure to fail (Stage 1), followed by the fibular fracture (Stage 2), then PITFL/posterior malleolus (Stage 3), then deltoid/medial malleolus (Stage 4). The SER mechanism is the most common ankle fracture pattern.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Calcaneal Fractures",
          "range": "Q539-Q540",
          "questions": [
            {
              "number": 539,
              "stem": "Böhler's angle is used in the assessment of calcaneal fractures. A normal Böhler's angle is approximately:",
              "options": [
                "0–10°",
                "20–40°",
                "10–15°",
                "45–60°",
                "60–80°"
              ],
              "answer": "B",
              "explanation": "Böhler's angle (tuber-joint angle) is normally 20–40°. It is measured on the lateral radiograph between a line from the highest point of the anterior process to the highest point of the posterior facet, and a line from the highest point of the posterior facet to the highest point of the tuberosity. A reduced or negative Böhler's angle indicates a displaced intra-articular calcaneal fracture with depression of the posterior facet.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 540,
              "stem": "The Sanders classification of calcaneal fractures is based on which imaging modality?",
              "options": [
                "Plain radiograph (lateral view)",
                "MRI",
                "CT scan (coronal images)",
                "Bone scan",
                "Ultrasound"
              ],
              "answer": "C",
              "explanation": "The Sanders classification uses coronal CT images at the widest point of the posterior facet. It divides fractures based on the number and location of articular fracture lines: Type I=undisplaced, Type II=2 fragments (single fracture line), Type III=3 fragments (2 lines), Type IV=4+ fragments (highly comminuted). Type IV has the worst prognosis and may be treated with primary subtalar fusion.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Foot Trauma",
          "range": "Q541-Q542",
          "questions": [
            {
              "number": 541,
              "stem": "A Lisfranc injury involves disruption at which level of the foot?",
              "options": [
                "Chopart joint (talonavicular and calcaneocuboid)",
                "Metatarsophalangeal joints",
                "Subtalar joint",
                "Tarsometatarsal joints",
                "Ankle joint"
              ],
              "answer": "D",
              "explanation": "A Lisfranc injury is a fracture-dislocation at the tarsometatarsal (TMT) joint complex. The Lisfranc ligament connects the medial cuneiform to the base of the second metatarsal. Diagnosis requires high clinical suspicion as it is frequently missed. Weight-bearing radiographs may show diastasis between the 1st and 2nd metatarsal bases. CT is more sensitive for subtle injuries.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 542,
              "stem": "A fifth metatarsal fracture at the proximal tuberosity (Zone 1) caused by an inversion injury is commonly known as:",
              "options": [
                "Jones fracture",
                "Pseudo-Jones (avulsion) fracture",
                "Dancer's fracture",
                "Stress fracture",
                "March fracture"
              ],
              "answer": "B",
              "explanation": "A Zone 1 fracture (proximal tuberosity avulsion) is commonly called a pseudo-Jones fracture. It is caused by avulsion of the peroneus brevis tendon or lateral band of the plantar fascia during inversion. It heals well with non-operative management (hard-soled shoe). A true Jones fracture is at the metaphyseal-diaphyseal junction (Zone 2) and has a higher non-union rate.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Talar Fractures",
          "range": "Q543",
          "questions": [
            {
              "number": 543,
              "stem": "In Hawkins classification of talar neck fractures, what is the approximate risk of AVN in a Type II fracture?",
              "options": [
                "0%",
                "10–20%",
                "50–75%",
                "100%",
                "20–50%"
              ],
              "answer": "E",
              "explanation": "Hawkins classification of talar neck fractures: Type I=undisplaced (AVN 0–13%), Type II=subtalar dislocation (AVN 20–50%), Type III=subtalar + ankle dislocation (AVN 70–100%), Type IV=Type III + talonavicular dislocation (AVN ~100%). The Hawkins sign (subchondral lucency in the talar dome at 6–8 weeks) indicates preserved vascularity and is a positive prognostic sign against AVN.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Soft Tissue",
          "range": "Q544-Q545",
          "questions": [
            {
              "number": 544,
              "stem": "A Morel-Lavallée lesion is a closed degloving injury most commonly found over which anatomical area?",
              "options": [
                "Greater trochanter and lateral thigh",
                "Anterior shin",
                "Dorsum of foot",
                "Anterior knee",
                "Posterior calf"
              ],
              "answer": "A",
              "explanation": "A Morel-Lavallée lesion is a closed internal degloving injury where the skin and subcutaneous fat are sheared from the underlying fascia, creating a cavity filled with haemolymph, necrotic fat, and debris. It most commonly occurs over the greater trochanter and lateral thigh, often in association with pelvic and acetabular fractures. If unrecognised, it can become infected and compromise surgical wounds.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 545,
              "stem": "In the management of a grade IIIB open tibial fracture, the soft tissue reconstruction should ideally be completed within what time frame?",
              "options": [
                "24 hours",
                "1 week",
                "72 hours (BOAST recommendation)",
                "2 weeks",
                "4 weeks"
              ],
              "answer": "C",
              "explanation": "BOAST guidelines recommend definitive soft tissue coverage (flap) within 72 hours for Grade IIIB open fractures, performed jointly by orthopaedic and plastic surgery teams ('orthoplastic' approach). Early flap coverage reduces infection rates and improves outcomes. Delay beyond 72 hours significantly increases deep infection and flap failure rates.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Compartment Syndrome",
          "range": "Q546-Q555",
          "questions": [
            {
              "number": 546,
              "stem": "The earliest and most reliable clinical sign of acute compartment syndrome is:",
              "options": [
                "Pain out of proportion to the injury, especially on passive stretch",
                "Absent distal pulses",
                "Paralysis of muscles",
                "Paraesthesia in the affected limb",
                "Pallor of the limb"
              ],
              "answer": "A",
              "explanation": "Pain out of proportion to the injury — particularly pain on passive stretch of the muscles within the affected compartment — is the earliest and most reliable clinical sign. The '5 Ps' (pain, pressure, paralysis, paraesthesia, pulselessness) are taught but pulselessness and paralysis are LATE signs indicating irreversible ischaemia. Compartment syndrome is a clinical diagnosis.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 547,
              "stem": "The delta pressure (ΔP) threshold for performing fasciotomy in compartment syndrome is:",
              "options": [
                "Absolute pressure >30 mmHg",
                "Absolute pressure >40 mmHg",
                "ΔP (diastolic BP minus compartment pressure) <30 mmHg",
                "ΔP <20 mmHg",
                "Mean arterial pressure minus compartment pressure <40 mmHg"
              ],
              "answer": "C",
              "explanation": "The delta pressure (ΔP) = diastolic blood pressure minus compartment pressure. A ΔP <30 mmHg indicates insufficient perfusion and is the accepted threshold for fasciotomy. This is more reliable than absolute compartment pressure alone because it accounts for the patient's haemodynamic status. A hypotensive patient may develop compartment syndrome at lower absolute pressures.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 548,
              "stem": "In a two-incision four-compartment fasciotomy of the leg, the medial incision is placed approximately:",
              "options": [
                "Directly over the medial border of the tibia",
                "Over the tibial crest",
                "In the midline of the calf",
                "2 cm posterior to the posteromedial border of the tibia",
                "2 cm anterior to the medial malleolus"
              ],
              "answer": "D",
              "explanation": "The medial incision is placed approximately 2 cm posterior to the posteromedial border of the tibia, allowing access to both the superficial and deep posterior compartments. The lateral incision is placed approximately 2 cm anterior to the fibular shaft to access the anterior and lateral compartments. Both incisions must be full-length from just below the knee to just above the ankle.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 549,
              "stem": "The superficial peroneal nerve is found in which compartment of the leg?",
              "options": [
                "Anterior",
                "Lateral",
                "Superficial posterior",
                "Deep posterior",
                "Subcutaneous (no compartment)"
              ],
              "answer": "B",
              "explanation": "The superficial peroneal nerve runs in the lateral compartment, supplying peroneus longus and brevis (evertors) and providing sensation to the dorsum of the foot (except the first web space, which is deep peroneal nerve territory). This is a classic exam distinction: superficial peroneal = lateral compartment, deep peroneal = anterior compartment.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 550,
              "stem": "Compartment syndrome of the forearm most commonly affects which compartment?",
              "options": [
                "Dorsal (extensor) compartment",
                "Mobile wad",
                "Thenar compartment",
                "Hypothenar compartment",
                "Volar (flexor) compartment"
              ],
              "answer": "E",
              "explanation": "The volar (flexor) compartment of the forearm is most commonly affected in compartment syndrome, often following supracondylar fractures in children or distal radius fractures. The classic late sequela of untreated volar compartment syndrome is Volkmann's ischaemic contracture (fibrosis of the deep flexor muscles leading to a claw hand deformity with flexed wrist and fingers).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 551,
              "stem": "In Volkmann's ischaemic contracture, the characteristic hand posture is:",
              "options": [
                "Extended wrist with flexed fingers",
                "Flexed wrist with extended MCP and flexed IP joints",
                "Intrinsic-plus position",
                "Ulnar claw hand",
                "Flexed wrist and flexed fingers (claw deformity) that partially correct with wrist extension"
              ],
              "answer": "E",
              "explanation": "Volkmann's contracture produces a flexed wrist with flexed MCP and IP joints due to fibrosis of the deep flexor muscles (FDP, FPL). Because the fibrosed muscles are at fixed length, passive extension of the fingers improves when the wrist is flexed (reducing tension on the flexors), and worsens when the wrist is extended. This tenodesis effect distinguishes Volkmann's from intrinsic contracture.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            },
            {
              "number": 552,
              "stem": "A patient in a plaster cast develops increasing pain. The FIRST management step should be:",
              "options": [
                "Administer stronger analgesia",
                "Elevate the limb above heart level",
                "Measure compartment pressures",
                "Split the cast (including padding) to skin along its full length",
                "Observe for 2 hours"
              ],
              "answer": "D",
              "explanation": "If compartment syndrome is suspected in a casted limb, the FIRST step is to split the cast completely (including all padding and bandages) to skin along its full length. This alone can reduce compartment pressure by 40–60%. If pain does not improve rapidly, the cast should be removed entirely. Elevation above the heart should be avoided as it may reduce arterial perfusion. If symptoms persist after cast release, formal fasciotomy is required.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 553,
              "stem": "The earliest and most reliable symptom of acute compartment syndrome is:",
              "options": [
                "Pallor",
                "Pulselessness",
                "Pain out of proportion to the injury, especially pain on passive stretch",
                "Paralysis",
                "Paraesthesia"
              ],
              "answer": "C",
              "explanation": "Pain out of proportion to the injury (particularly pain on passive stretch of the muscles within the affected compartment) is the EARLIEST and most reliable symptom of compartment syndrome. The 6 P's (pain, pressure, pain on stretch, paraesthesia, paralysis, pulselessness) represent a progression — by the time paralysis and pulselessness develop, irreversible damage has often occurred. Diagnosis is primarily clinical. Compartment pressure measurement (>30 mmHg or within 30 mmHg of diastolic pressure) confirms the diagnosis if clinical uncertainty exists.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 554,
              "stem": "The leg has four fascial compartments. The deep posterior compartment contains which of the following muscles?",
              "options": [
                "Tibialis posterior, FDL, and FHL",
                "Gastrocnemius and soleus",
                "Tibialis anterior and EHL",
                "Peroneus longus and brevis",
                "Popliteus only"
              ],
              "answer": "A",
              "explanation": "The four compartments of the leg: (1) Anterior: tibialis anterior, EHL, EDL, peroneus tertius (deep peroneal nerve, anterior tibial artery). (2) Lateral: peroneus longus and brevis (superficial peroneal nerve). (3) Superficial posterior: gastrocnemius, soleus, plantaris (sural nerve). (4) Deep posterior: tibialis posterior, FDL, FHL, popliteus (posterior tibial nerve, posterior tibial artery, peroneal artery). The anterior compartment is the most commonly affected in compartment syndrome (tightest fascial boundaries). Fasciotomy requires release of all four compartments through two incisions (anterolateral and posteromedial).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 555,
              "stem": "The earliest and most reliable clinical sign of compartment syndrome is:",
              "options": [
                "Absence of distal pulses",
                "Pain out of proportion to the injury, particularly pain on passive stretch of the affected muscles",
                "Paralysis of the affected muscles",
                "Pallor of the limb",
                "Poikilothermia (limb feels cold)"
              ],
              "answer": "B",
              "explanation": "Pain out of proportion to the injury — particularly severe pain on PASSIVE STRETCH of the muscles within the affected compartment — is the earliest and most reliable clinical sign of compartment syndrome. The '6 Ps' (Pain, Pressure, Paraesthesiae, Paralysis, Pallor, Pulselessness) are taught but are a late and unreliable sequence: by the time paralysis and pulselessness develop, irreversible damage has occurred. Loss of pulses is a very LATE sign (compartment syndrome occurs at pressures well below arterial occlusion pressure). Paraesthesiae develop earlier than motor loss. In an obtunded patient or child who cannot communicate pain: measure compartment pressures (absolute >30mmHg or delta pressure <30mmHg from diastolic = fasciotomy indicated). Delay >6-8 hours → irreversible muscle necrosis (Volkmann ischaemic contracture).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Proximal Humerus",
          "range": "Q556-Q559",
          "questions": [
            {
              "number": 556,
              "stem": "The Neer classification of proximal humeral fractures divides the proximal humerus into how many parts?",
              "options": [
                "4",
                "2",
                "3",
                "5",
                "6"
              ],
              "answer": "A",
              "explanation": "The Neer classification identifies 4 parts: (1) articular segment (head), (2) greater tuberosity, (3) lesser tuberosity, (4) shaft. A fragment is considered a 'part' if displaced >1 cm or angulated >45°. One-part fractures (undisplaced) are the most common (~80%) and are treated non-operatively. 2-part, 3-part, and 4-part fractures have increasing complexity and treatment varies from ORIF to arthroplasty.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 557,
              "stem": "The axillary nerve is most at risk in fractures of which part of the proximal humerus?",
              "options": [
                "Anatomical neck",
                "Greater tuberosity",
                "Surgical neck",
                "Lesser tuberosity",
                "Shaft"
              ],
              "answer": "C",
              "explanation": "The axillary nerve (C5, C6) passes through the quadrangular space and wraps around the surgical neck of the humerus. It is at greatest risk in surgical neck fractures and anterior shoulder dislocations. Axillary nerve injury produces weakness of deltoid (shoulder abduction) and teres minor (external rotation), with a sensory patch of numbness over the 'regimental badge area' (lateral deltoid).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 558,
              "stem": "The Neer classification of proximal humerus fractures is based on the number of displaced 'parts'. A part is considered displaced when it is separated by more than:",
              "options": [
                "1 cm or 45°",
                "2 mm or 10°",
                "3 cm or 90°",
                "Any visible fracture line",
                "5 mm or 20°"
              ],
              "answer": "E",
              "explanation": "Neer classification: a fracture 'part' is considered displaced when it is separated by >1 cm or angulated >45° from an adjacent fragment. The four potential parts are: (1) greater tuberosity, (2) lesser tuberosity, (3) articular segment (head), (4) shaft. A one-part fracture has no displaced fragments (regardless of fracture lines). Two-part: one fragment displaced. Three-part: two fragments displaced. Four-part: all fragments displaced (highest AVN risk — head loses blood supply). Most proximal humerus fractures are minimally displaced one-part fractures (~85%) treated non-operatively.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 559,
              "stem": "The nerve most at risk in proximal humerus fractures and anterior shoulder dislocations is the:",
              "options": [
                "Radial nerve",
                "Musculocutaneous nerve",
                "Suprascapular nerve",
                "Axillary nerve",
                "Long thoracic nerve"
              ],
              "answer": "D",
              "explanation": "The axillary nerve (C5, C6) is at greatest risk because it wraps around the surgical neck of the humerus in the quadrilateral space. It innervates deltoid (shoulder abduction) and teres minor (external rotation), and provides sensation to the 'regimental badge' area (lateral aspect of the upper arm over the deltoid). It is injured in up to 5-10% of proximal humerus fractures and anterior shoulder dislocations. Always test deltoid contraction and regimental badge sensation. Most axillary nerve injuries are neurapraxia and recover within 3-6 months.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Humeral Shaft",
          "range": "Q560-Q561",
          "questions": [
            {
              "number": 560,
              "stem": "A fracture of the humeral shaft at the junction of the middle and distal thirds places which nerve at greatest risk?",
              "options": [
                "Axillary nerve",
                "Radial nerve",
                "Musculocutaneous nerve",
                "Median nerve",
                "Ulnar nerve"
              ],
              "answer": "B",
              "explanation": "The radial nerve runs in the spiral (radial) groove on the posterior aspect of the humerus at the junction of the middle and distal thirds. It is the most commonly injured nerve in humeral shaft fractures (~10–15% of cases). Injury produces wrist drop (loss of wrist/finger extension) and sensory loss over the first dorsal web space. Most are neurapraxias that recover spontaneously.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 561,
              "stem": "The accepted angulation for non-operative management of an adult humeral shaft fracture in a functional brace is:",
              "options": [
                "0° only — must be anatomically reduced",
                "Up to 10° in any plane",
                "Up to 45° in any plane",
                "Up to 20° anterior angulation, 30° varus, and 15° malrotation",
                "Any angulation is acceptable"
              ],
              "answer": "D",
              "explanation": "Sarmiento's functional brace allows controlled motion at the fracture site while maintaining alignment. Accepted deformity parameters for humeral shaft fractures: up to 20° of anterior (sagittal) angulation, 30° of varus angulation, up to 15° of malrotation, and up to 3cm of shortening. These parameters produce acceptable functional and cosmetic outcomes in the majority of patients. Union rates with functional bracing: ~90-95% for closed fractures. Indications for operative fixation: unacceptable alignment beyond these thresholds, open fracture, polytrauma (for mobilisation), floating elbow, bilateral fractures, vascular injury requiring repair, and failure of conservative treatment.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Supracondylar Fracture",
          "range": "Q562",
          "questions": [
            {
              "number": 562,
              "stem": "In a Gartland Type III extension-type supracondylar fracture in a child, the brachial artery is most commonly injured by which mechanism?",
              "options": [
                "Direct laceration by fracture fragments",
                "Avulsion from the brachial plexus",
                "Compression or kinking by the displaced proximal fragment",
                "Spasm from adjacent nerve injury",
                "Tourniquet compression"
              ],
              "answer": "C",
              "explanation": "In extension-type supracondylar fractures, the distal fragment displaces posteriorly, and the sharp proximal fragment displaces anteriorly into the antecubital fossa. This anterior spike can compress, kink, or impale the brachial artery. The anterior interosseous nerve (motor branch of median nerve) is the most commonly injured nerve, followed by the radial and median nerves.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Elbow Fractures",
          "range": "Q563-Q564",
          "questions": [
            {
              "number": 563,
              "stem": "A Monteggia fracture-dislocation consists of:",
              "options": [
                "Distal radius fracture with DRUJ disruption",
                "Proximal ulna fracture with radial head dislocation",
                "Both-bone forearm fracture",
                "Radial shaft fracture with DRUJ disruption",
                "Olecranon fracture with coronoid fracture"
              ],
              "answer": "B",
              "explanation": "A Monteggia fracture-dislocation is a fracture of the proximal ulna (typically the proximal third) with dislocation of the radial head. The Bado classification divides Monteggia injuries into 4 types based on the direction of radial head dislocation. In any ulnar fracture, always assess the radial head — a Monteggia lesion can be missed if the radiocapitellar alignment is not checked on a true lateral radiograph.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 564,
              "stem": "A Mason Type II radial head fracture is characterised by:",
              "options": [
                "Undisplaced fracture",
                "Comminuted fracture of the entire head",
                "Radial head dislocation",
                "Fracture of the radial neck only",
                "Displaced fracture of part of the head (>2 mm displacement)"
              ],
              "answer": "E",
              "explanation": "Mason classification of radial head fractures: Type I = undisplaced or minimally displaced (<2 mm). Type II = displaced marginal fracture (>2 mm, involves part of the head). Type III = comminuted fracture of the entire head. Type IV (Broberg and Morrey modification) = associated elbow dislocation. Type I is treated non-operatively. Type II may need ORIF. Type III may need excision or replacement.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Clavicle Fractures",
          "range": "Q565",
          "questions": [
            {
              "number": 565,
              "stem": "The most common site of clavicle fracture is:",
              "options": [
                "Middle third",
                "Medial third",
                "Junction of medial and middle thirds",
                "Junction of middle and lateral thirds",
                "Lateral third"
              ],
              "answer": "A",
              "explanation": "Middle third clavicle fractures account for approximately 75–80% of all clavicle fractures. The middle third is the thinnest part of the bone and has no stabilising ligamentous or muscular attachments, making it the weakest point. Lateral third fractures account for ~15% and medial third ~5%. Most middle third fractures are managed non-operatively unless significantly displaced, shortened >2 cm, or in specific patient populations.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Shoulder Trauma",
          "range": "Q566-Q567",
          "questions": [
            {
              "number": 566,
              "stem": "Following an anterior shoulder dislocation, which nerve is most commonly injured?",
              "options": [
                "Suprascapular nerve",
                "Axillary nerve",
                "Musculocutaneous nerve",
                "Long thoracic nerve",
                "Radial nerve"
              ],
              "answer": "B",
              "explanation": "The axillary nerve is the most commonly injured nerve following anterior shoulder dislocation (~5–35% depending on age and studies). It wraps around the surgical neck of the humerus and passes through the quadrangular space directly inferior to the glenohumeral joint. Risk increases significantly with age (>40 years). Always test for regimental badge area sensation and deltoid power after reduction.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 567,
              "stem": "A posterior shoulder dislocation is classically associated with which mechanism?",
              "options": [
                "Fall on an outstretched hand",
                "Direct lateral force",
                "Overhead throwing injury",
                "Seizure or electrocution",
                "Axial load through the elbow"
              ],
              "answer": "D",
              "explanation": "Posterior shoulder dislocations are classically caused by seizures, electrocution, or falls with the arm in internal rotation and adduction. They are frequently missed on initial assessment (~50% missed initially). The AP radiograph may appear deceptively normal ('lightbulb sign' due to fixed internal rotation). Axillary or Velpeau views are essential for diagnosis. A reverse Hill-Sachs lesion (impaction on the anteromedial head) is pathognomonic.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Periprosthetic Fracture",
          "range": "Q568-Q569",
          "questions": [
            {
              "number": 568,
              "stem": "According to the Vancouver classification of periprosthetic femoral fractures around a hip replacement, a Type B2 fracture is characterised by:",
              "options": [
                "Fracture around a loose stem",
                "Fracture at the tip of a well-fixed stem",
                "Fracture around a loose stem with poor bone stock",
                "Fracture well below the tip of the stem",
                "Greater trochanter fracture"
              ],
              "answer": "A",
              "explanation": "Vancouver classification: A = trochanteric (AG=greater, AL=lesser). B = around or just below the stem: B1=well-fixed stem, B2=loose stem with adequate bone stock, B3=loose stem with poor bone stock. C = well below the stem tip. B2 requires revision arthroplasty (long stem). B1 can be treated with plate fixation around a stable stem. B3 needs revision with tumour-type prosthesis or allograft.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 569,
              "stem": "A Vancouver Type C periprosthetic fracture occurs:",
              "options": [
                "Around the stem tip with a well-fixed stem",
                "At the greater trochanter",
                "Well below the tip of the prosthetic stem",
                "Around a loose stem",
                "At the lesser trochanter"
              ],
              "answer": "C",
              "explanation": "Type C fractures occur well below the tip of the femoral stem, meaning the stem does not influence the fracture. They are treated as standard femoral shaft fractures (typically IM nailing or plating), as the stable prosthesis above does not need revision. The key is to ensure the nail or plate does not conflict with the prosthetic stem.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Pathological Fracture",
          "range": "Q570-Q572",
          "questions": [
            {
              "number": 570,
              "stem": "Mirels' scoring system is used to predict the risk of pathological fracture through a bony metastasis. A score of ≥9 out of 12 indicates:",
              "options": [
                "Low fracture risk — observation",
                "Moderate risk — radiotherapy only",
                "Immediate chemotherapy",
                "Bisphosphonate treatment only",
                "High fracture risk — prophylactic fixation recommended"
              ],
              "answer": "E",
              "explanation": "Mirels' score assesses 4 parameters (each scored 1–3): site (upper limb=1, lower limb=2, peritrochanteric=3), pain (mild=1, moderate=2, functional=3), type of lesion (blastic=1, mixed=2, lytic=3), and size (<1/3 cortex=1, 1/3–2/3=2, >2/3=3). Score ≥9 = high fracture risk → prophylactic fixation recommended. Score ≤7 = can consider observation/radiotherapy.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 571,
              "stem": "The most common primary tumour to metastasise to bone is:",
              "options": [
                "Lung",
                "Prostate",
                "Thyroid",
                "Breast",
                "Kidney (renal)"
              ],
              "answer": "D",
              "explanation": "Breast cancer is the most common primary tumour to metastasise to bone overall. In men, prostate is the most common. The classic mnemonic for bone metastases is 'BLT-KP': Breast, Lung, Thyroid, Kidney, Prostate. The most common sites for bony metastases are spine, pelvis, proximal femur, and ribs. Breast and prostate metastases can be lytic, blastic, or mixed.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 572,
              "stem": "A long bone with a destructive lytic lesion and a pathological fracture in a patient with known renal cell carcinoma should be managed with caution because renal metastases are characteristically:",
              "options": [
                "Radiosensitive",
                "Highly vascular",
                "Chemosensitive",
                "Slow growing",
                "Sclerotic"
              ],
              "answer": "B",
              "explanation": "Renal cell carcinoma metastases are characteristically highly vascular. Surgical fixation carries a significant risk of life-threatening haemorrhage. Pre-operative angiographic embolisation should be considered before surgical stabilisation. Thyroid metastases are similarly vascular. Renal metastases are also relatively radioresistant and chemoresistant.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Distal Radius",
          "range": "Q573-Q575",
          "questions": [
            {
              "number": 573,
              "stem": "A Colles fracture is characterised by which displacement pattern?",
              "options": [
                "Volar displacement and angulation",
                "Radial styloid fracture only",
                "Dorsal displacement and angulation",
                "Intra-articular split",
                "Dorsal rim shear fracture"
              ],
              "answer": "C",
              "explanation": "A Colles fracture is an extra-articular distal radius fracture with dorsal displacement and dorsal angulation (dinner fork deformity), typically from a fall on an outstretched hand (extended wrist). A Smith fracture is the reverse pattern (volar displacement). A Barton fracture is a shear fracture of the dorsal or volar lip (intra-articular). A chauffeur fracture is a radial styloid fracture.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 574,
              "stem": "A Colles fracture of the distal radius is characterised by:",
              "options": [
                "Dorsal displacement and angulation with radial shortening",
                "Volar displacement and angulation (Smith fracture pattern)",
                "Intra-articular fracture only",
                "Isolated ulnar styloid fracture",
                "Radial styloid fracture"
              ],
              "answer": "A",
              "explanation": "A Colles fracture is an extra-articular distal radius fracture with DORSAL displacement, dorsal angulation, and radial shortening — producing the classic 'dinner fork' deformity. Mechanism: fall on outstretched hand (FOOSH) with wrist in dorsiflexion. A Smith fracture (reverse Colles) has VOLAR displacement (fall on the back of the hand or from a direct blow). Barton fracture is an intra-articular fracture-subluxation (volar or dorsal). Chauffeur fracture is a radial styloid fracture.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 575,
              "stem": "The operative treatment of choice for an unstable distal radius fracture in an adult is:",
              "options": [
                "K-wire fixation alone",
                "External fixation as definitive treatment",
                "Cast immobilisation",
                "Intramedullary nailing",
                "Volar locking plate fixation"
              ],
              "answer": "E",
              "explanation": "Volar locking plate (VLP) fixation has become the standard of care for unstable distal radius fractures requiring operative treatment. It provides stable fixation allowing early mobilisation, maintains reduction even in osteoporotic bone (angular stability from locked screws), and can address both extra-articular and intra-articular fractures. The volar approach (modified Henry) is between FCR and radial artery. Dorsal plating risks extensor tendon irritation. K-wires alone are less stable. Ex-fix may be used in open fractures or severe comminution as a bridging device.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Forearm Fractures",
          "range": "Q576",
          "questions": [
            {
              "number": 576,
              "stem": "A Galeazzi fracture-dislocation consists of:",
              "options": [
                "Radial shaft fracture with disruption of the DRUJ",
                "Proximal ulna fracture with radial head dislocation",
                "Both-bone forearm fracture",
                "Distal ulna fracture with proximal radial dislocation",
                "Olecranon fracture with radial head dislocation"
              ],
              "answer": "A",
              "explanation": "A Galeazzi fracture is a fracture of the radial shaft (usually distal third) with disruption of the distal radioulnar joint (DRUJ). It is called 'the fracture of necessity' because it almost always requires surgical fixation (ORIF of the radius with assessment and possible fixation of the DRUJ). Diagnosis requires lateral radiograph of the wrist to assess DRUJ congruency.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Distal Femur",
          "range": "Q577",
          "questions": [
            {
              "number": 577,
              "stem": "A supracondylar femoral fracture (AO 33-A) in an adult is best treated with:",
              "options": [
                "Hip spica cast",
                "External fixation as definitive treatment",
                "Skeletal traction for 12 weeks",
                "Retrograde intramedullary nail or lateral locking plate",
                "DHS"
              ],
              "answer": "D",
              "explanation": "Supracondylar (extra-articular distal) femoral fractures are treated with either a retrograde IM nail or a lateral locking plate (LISS/LCP). The choice depends on fracture pattern, presence of articular extension, and patient factors. Retrograde nailing works well for simple extra-articular patterns. Locking plates provide angular stability and are versatile for periarticular fractures, particularly in osteoporotic bone. Both allow early mobilisation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Spine Clearance",
          "range": "Q578",
          "questions": [
            {
              "number": 578,
              "stem": "In an unconscious trauma patient, which imaging modality is used to clear the cervical spine?",
              "options": [
                "Plain radiographs only (AP, lateral, open-mouth)",
                "MRI of the cervical spine as first-line",
                "Ultrasound",
                "Flexion-extension views under fluoroscopy",
                "CT scan of the cervical spine"
              ],
              "answer": "E",
              "explanation": "CT of the cervical spine is the standard for clearing the C-spine in unconscious or obtunded trauma patients. It has near 100% sensitivity for detecting bony injuries. MRI is added if ligamentous injury is suspected (persistent neurological deficit, CT shows concerning alignment but no fracture) — typically at 24-72 hours. Plain radiographs alone are insufficient for unconscious patients (miss up to 50% of injuries detected by CT). Flexion-extension views are NEVER appropriate in unconscious patients.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Ballistics",
          "range": "Q579",
          "questions": [
            {
              "number": 579,
              "stem": "A low-velocity gunshot wound to the femoral shaft is treated as which Gustilo-Anderson grade?",
              "options": [
                "Grade II",
                "Grade IIIA",
                "Grade I (wound <1 cm)",
                "Not classified by Gustilo-Anderson",
                "Classified by the wound size alone"
              ],
              "answer": "C",
              "explanation": "Low-velocity gunshot wounds (handguns, <600 m/s muzzle velocity) typically produce a small entry wound and limited soft tissue injury. They are generally treated as Grade I open fractures — wound irrigation and debridement, prophylactic antibiotics, and definitive fracture fixation (usually IM nailing). The bullet tract is considered contaminated but the zone of injury is limited. High-velocity gunshot wounds (military rifles, >600 m/s) cause extensive tissue destruction and cavitation — treated as Grade III injuries.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            }
          ]
        },
        {
          "title": "Acetabular",
          "range": "Q580",
          "questions": [
            {
              "number": 580,
              "stem": "The ilioinguinal approach to the acetabulum provides access to which structures?",
              "options": [
                "Posterior column and posterior wall",
                "Anterior column, anterior wall, and inner pelvis",
                "Both columns simultaneously",
                "Greater sciatic notch only",
                "Posterior wall only"
              ],
              "answer": "B",
              "explanation": "The ilioinguinal approach (Letournel) provides access to the anterior column, anterior wall, quadrilateral plate (inner pelvic surface), and iliac wing. It uses three 'windows': lateral (between iliac crest and iliacus/psoas), middle (between external iliac vessels and psoas), and medial (between external iliac vessels and bladder). The femoral nerve, external iliac vessels, and spermatic cord/round ligament must be protected. The posterior column is accessed via the Kocher-Langenbeck approach.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Calcaneum",
          "range": "Q581-Q582",
          "questions": [
            {
              "number": 581,
              "stem": "The Essex-Lopresti classification of calcaneal fractures divides intra-articular fractures into:",
              "options": [
                "Anterior and posterior",
                "Medial and lateral",
                "Simple and comminuted only",
                "Tongue-type and joint depression type",
                "Open and closed"
              ],
              "answer": "D",
              "explanation": "Essex-Lopresti classifies calcaneal fractures into tongue-type (the secondary fracture line exits posteriorly through the tuberosity, creating a large posterior fragment that includes the posterior facet) and joint depression type (the secondary fracture line exits just posterior to the posterior facet, depressing the facet into the body). This classification guides surgical approach — tongue-type fractures can be reduced percutaneously with an Essex-Lopresti manoeuvre (Steinmann pin in the tuberosity fragment). The Sanders classification (CT-based) has largely superseded this for operative planning.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 582,
              "stem": "Böhler angle is measured on a lateral radiograph of the calcaneus. The normal range is:",
              "options": [
                "0-10°",
                "10-15°",
                "20-40°",
                "45-60°",
                "60-90°"
              ],
              "answer": "C",
              "explanation": "Böhler angle (tuber-joint angle) is measured on a lateral radiograph between a line from the highest point of the anterior process to the highest point of the posterior facet, and a line from the posterior facet to the top of the tuberosity. Normal: 20-40°. A reduced Böhler angle indicates a depressed calcaneal fracture. The Gissane angle (crucial angle of Gissane) is the angle formed by the downward and upward slopes of the calcaneus below the lateral process of the talus — normally 120-145°. An increased Gissane angle suggests posterior facet depression.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Periprosthetic",
          "range": "Q583",
          "questions": [
            {
              "number": 583,
              "stem": "A Vancouver Type B1 periprosthetic femoral fracture around a total hip replacement is characterised by a fracture:",
              "options": [
                "Above the stem tip with a loose stem",
                "Around a loose stem with poor bone stock",
                "Well below the stem tip",
                "At the greater trochanter only",
                "Around or just below the stem tip with a WELL-FIXED stem and adequate bone stock"
              ],
              "answer": "E",
              "explanation": "Vancouver classification of periprosthetic femoral fractures: Type A = trochanteric (AG = greater, AL = lesser). Type B1 = around/just below stem, stem WELL-FIXED, good bone stock → ORIF (plate ± cables/cerclage). Type B2 = around/just below stem, stem LOOSE, adequate bone stock → revision stem (longer uncemented). Type B3 = around/just below stem, stem LOOSE, POOR bone stock → revision with reconstruction (allograft/tumour prosthesis). Type C = well below the stem (treat as standard fracture). B1 is the key distinction — the stem is stable so it does not need revision.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Pathological",
          "range": "Q584",
          "questions": [
            {
              "number": 584,
              "stem": "The Mirels scoring system is used to predict the risk of pathological fracture through a metastatic bone lesion. A score of ≥9 indicates:",
              "options": [
                "No treatment needed",
                "Prophylactic surgical fixation is recommended",
                "Conservative management only",
                "Radiotherapy alone is sufficient",
                "Observation with repeat imaging"
              ],
              "answer": "B",
              "explanation": "Mirels scoring system evaluates 4 parameters (each scored 1-3): site (upper limb=1, lower limb=2, peritrochanteric=3), pain (mild=1, moderate=2, functional=3), lesion type (blastic=1, mixed=2, lytic=3), and size relative to cortex (<1/3=1, 1/3-2/3=2, >2/3=3). Total score 7 = low risk (<5% fracture risk, radiotherapy alone). Score 8 = borderline. Score ≥9 = high fracture risk (>33%) → prophylactic fixation recommended. This system is imperfect but widely used.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Open Fracture",
          "range": "Q585",
          "questions": [
            {
              "number": 585,
              "stem": "According to BOAST guidelines, the definitive soft tissue coverage for a Gustilo-Anderson Grade IIIB open fracture should ideally be achieved within:",
              "options": [
                "72 hours",
                "6 hours",
                "24 hours",
                "7 days",
                "No time limit"
              ],
              "answer": "A",
              "explanation": "BOAST (British Orthopaedic Association Standards for Trauma) guidelines for open fractures recommend: initial debridement within 12-24 hours (NOT necessarily within 6 hours as previously taught, unless grossly contaminated). Definitive soft tissue coverage (flap) should be achieved within 72 hours of injury (or within 72 hours of the first debridement). The combined 'orthoplastic' approach (orthopaedic surgeon + plastic surgeon working together) has improved outcomes. Grade IIIB by definition requires soft tissue coverage (flap).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "DVT",
          "range": "Q586",
          "questions": [
            {
              "number": 586,
              "stem": "The recommended pharmacological thromboprophylaxis for patients undergoing elective total hip or knee arthroplasty according to NICE guidelines is:",
              "options": [
                "Aspirin only",
                "LMWH (e.g., enoxaparin) or DOAC (e.g., rivaroxaban) for a minimum of 14 days",
                "No prophylaxis needed",
                "Warfarin started pre-operatively",
                "IV heparin for 48 hours only"
              ],
              "answer": "B",
              "explanation": "NICE recommends pharmacological thromboprophylaxis for elective THA/TKA: options include LMWH (enoxaparin), or DOACs (rivaroxaban, apixaban, dabigatran). Duration: 28-35 days for THA, 14 days for TKA (minimum). Combined with mechanical prophylaxis (graduated compression stockings, intermittent pneumatic compression). Aspirin has emerging evidence (particularly post-CRISTAL trial 2023) but is not yet universally adopted. Early mobilisation is also a key component.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Monteggia",
          "range": "Q587",
          "questions": [
            {
              "number": 587,
              "stem": "A Monteggia fracture-dislocation involves:",
              "options": [
                "Radial shaft fracture with DRUJ disruption",
                "Both-bone forearm fracture",
                "Radial head fracture with IOM disruption",
                "Olecranon fracture with elbow dislocation",
                "Ulnar shaft fracture with radial head dislocation"
              ],
              "answer": "E",
              "explanation": "A Monteggia lesion involves a proximal ulnar shaft fracture with dislocation of the radial head. The Bado classification: Type I (most common, 60%) = anterior radial head dislocation with anterior angulation of ulnar fracture. Type II = posterior radial head dislocation. Type III = lateral radial head dislocation. Type IV = both-bone fracture with anterior radial head dislocation. The key principle: the radiocapitellar line must pass through the capitellum on ALL views — if not, suspect radial head dislocation. In children, the dislocation may reduce once the ulnar fracture is anatomically reduced.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Galeazzi",
          "range": "Q588",
          "questions": [
            {
              "number": 588,
              "stem": "A Galeazzi fracture-dislocation involves:",
              "options": [
                "Ulnar shaft fracture with radial head dislocation",
                "Both-bone forearm fracture",
                "Radial shaft fracture (distal third) with DRUJ disruption",
                "Radial head fracture with olecranon fracture",
                "Ulnar coronoid fracture with elbow dislocation"
              ],
              "answer": "C",
              "explanation": "A Galeazzi fracture involves a fracture of the radial shaft (typically distal third) with disruption of the distal radioulnar joint (DRUJ). It is called 'the fracture of necessity' because it almost always requires operative fixation (ORIF of the radius) — closed treatment has an unacceptable failure rate. After plating the radius, the DRUJ is reassessed for stability. If unstable after anatomical radial reduction, the DRUJ may need pinning in supination or TFCC repair.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "NOF",
          "range": "Q589-Q591",
          "questions": [
            {
              "number": 589,
              "stem": "According to NICE guidelines, a displaced intracapsular neck of femur fracture in a fit, active patient over 65 should be treated with:",
              "options": [
                "Total hip arthroplasty",
                "Cannulated screw fixation",
                "Hemiarthroplasty",
                "DHS",
                "Conservative management"
              ],
              "answer": "A",
              "explanation": "NICE guidelines (2023 update) recommend THA for displaced intracapsular NOF fractures in patients who: (1) were able to walk independently outdoors with no more than a stick, (2) are not cognitively impaired, and (3) are medically fit for the procedure. Hemiarthroplasty is recommended for patients who are less active, have cognitive impairment, or are not fit enough for THA. Undisplaced (Garden I/II) intracapsular fractures: internal fixation (cannulated screws). Extracapsular fractures: DHS (stable) or IM nail (unstable/subtrochanteric).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 590,
              "stem": "The tip-apex distance (TAD) is used to predict screw cutout risk in DHS fixation. The recommended TAD is:",
              "options": [
                "<10 mm",
                "<15 mm",
                "<35 mm",
                "<25 mm",
                "<50 mm"
              ],
              "answer": "D",
              "explanation": "The tip-apex distance is the sum of the distances from the tip of the lag screw to the apex of the femoral head on AP and lateral radiographs (after accounting for magnification). TAD <25 mm is associated with significantly lower rates of screw cutout. TAD >25 mm has a cutout rate of ~17%. The ideal screw position is centre-centre or slightly inferior-centre on AP, and centre on lateral. Placement in the inferior half of the head on AP is protective against cutout. Anterior-superior placement is the worst position.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 591,
              "stem": "The Garden classification of intracapsular femoral neck fractures — Garden III indicates:",
              "options": [
                "Incomplete fracture (valgus impacted)",
                "Complete but undisplaced fracture",
                "Complete fracture with full displacement (trabeculae of head align with acetabulum)",
                "Complete fracture with partial displacement",
                "Pathological fracture"
              ],
              "answer": "D",
              "explanation": "Garden classification: I = incomplete (valgus impacted, trabeculae angulated into valgus). II = complete but undisplaced (trabeculae disrupted but not shifted). III = complete with partial displacement (trabeculae of the head do NOT align with the acetabulum — head is rotated/tilted but some contact remains). IV = complete with full displacement (trabeculae of the head align with the acetabular trabeculae — the head has completely separated and rotated back to its resting position in the acetabulum). Garden I-II = undisplaced → internal fixation. Garden III-IV = displaced → arthroplasty (THA or hemiarthroplasty based on patient factors).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Spinal Cord",
          "range": "Q592-Q593",
          "questions": [
            {
              "number": 592,
              "stem": "ASIA (American Spinal Injury Association) Grade C spinal cord injury means:",
              "options": [
                "Incomplete — motor function preserved below the level with most key muscles having strength <3/5",
                "Complete injury — no motor or sensory function below the level",
                "Incomplete — sensory but no motor function preserved",
                "Incomplete — motor function preserved with most key muscles ≥3/5",
                "Normal motor and sensory function"
              ],
              "answer": "A",
              "explanation": "ASIA Impairment Scale: A = Complete (no motor or sensory function in sacral segments S4-S5). B = Incomplete sensory (sensory but no motor function below level, including sacral segments). C = Incomplete motor with most key muscles below the level having strength <3/5. D = Incomplete motor with most key muscles below the level having strength ≥3/5 (functional motor preservation). E = Normal. The key distinction between A and B is sacral sparing (S4-S5 sensation, deep anal pressure, voluntary anal contraction).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 593,
              "stem": "Central cord syndrome is characterised by:",
              "options": [
                "Complete loss of motor and sensory function below the level",
                "Motor weakness greater in the lower limbs than the upper limbs",
                "Ipsilateral motor loss with contralateral sensory loss",
                "Pure sensory loss without motor involvement",
                "Motor weakness greater in the upper limbs than the lower limbs"
              ],
              "answer": "E",
              "explanation": "Central cord syndrome is the most common incomplete spinal cord injury. It results from hyperextension injury in elderly patients with pre-existing cervical spondylosis/stenosis. The central grey matter and the most medial portions of the corticospinal tracts (which carry upper limb fibres — due to the somatotopic organisation with cervical fibres medially and sacral fibres laterally) are most affected. This produces: upper limb motor weakness > lower limb weakness, variable sensory loss, and bladder dysfunction. Many patients recover walking ability but have persistent hand weakness.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Approaches",
          "range": "Q594-Q595",
          "questions": [
            {
              "number": 594,
              "stem": "The Thompson (posterior) approach to the forearm accesses the radius through which intermuscular interval?",
              "options": [
                "FCR and brachioradialis",
                "FCU and FDS",
                "ECRB and EPL (proximally) / EPL and EDC (distally)",
                "Biceps and brachialis",
                "Pronator teres and brachioradialis"
              ],
              "answer": "C",
              "explanation": "The Thompson (dorsal/posterior) approach to the proximal and middle radius uses the interval between ECRB (radial nerve) and EPL (posterior interosseous nerve/PIN) proximally, and between EPL and EDC distally. The PIN is at risk as it passes through the supinator muscle — the forearm must be kept in PRONATION to move the PIN away from the surgical field. This approach is used for proximal radius fractures and Monteggia lesions. The Henry (anterior/volar) approach uses the FCR-radial artery interval (or brachioradialis-pronator teres proximally) and is used for most forearm fractures.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 595,
              "stem": "During the Kocher approach to the elbow (for radial head fractures), the forearm should be kept in pronation to protect which nerve?",
              "options": [
                "Ulnar nerve",
                "Posterior interosseous nerve (PIN)",
                "Median nerve",
                "Musculocutaneous nerve",
                "Axillary nerve"
              ],
              "answer": "B",
              "explanation": "The Kocher approach uses the interval between anconeus (radial nerve) and ECU (PIN). The PIN wraps around the radial neck within the supinator muscle — keeping the forearm in pronation moves the PIN laterally and posteriorly, away from the surgical field. The PIN is at greatest risk during deep dissection around the radial neck and with retractor placement. PIN injury causes loss of finger and thumb MCP extension (wrist extension may be partially preserved via ECRL).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Radial Head",
          "range": "Q596",
          "questions": [
            {
              "number": 596,
              "stem": "The Mason classification of radial head fractures — Type III is:",
              "options": [
                "Comminuted fracture of the entire radial head",
                "Undisplaced or minimally displaced fracture",
                "Displaced partial head fracture (>2mm displacement, involving >30% articular surface)",
                "Radial head fracture with elbow dislocation",
                "Radial neck fracture only"
              ],
              "answer": "A",
              "explanation": "Mason classification: Type I = undisplaced or minimally displaced (<2mm) — conservative (sling, early mobilisation). Type II = displaced partial head fracture (>2mm or >30% articular surface) — ORIF if mechanical block to rotation, otherwise conservative. Type III = comminuted (entire radial head) — radial head replacement (excision only if no associated ligament/IOM injury; replacement if Essex-Lopresti or terrible triad). Johnston modified: Type IV = any radial head fracture with elbow dislocation. ALWAYS assess for Essex-Lopresti (IOM + DRUJ) and terrible triad (coronoid + LCL).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "ACJ",
          "range": "Q597",
          "questions": [
            {
              "number": 597,
              "stem": "A Rockwood Type III acromioclavicular joint (ACJ) injury involves:",
              "options": [
                "Sprain of the AC ligaments without displacement",
                "Complete rupture of AC ligaments with intact coracoclavicular (CC) ligaments",
                "Posterior displacement of the clavicle",
                "Inferior displacement of the clavicle beneath the coracoid",
                "Complete rupture of both AC and CC ligaments with 25-100% clavicle displacement (superior)"
              ],
              "answer": "E",
              "explanation": "Rockwood classification: Type I = AC ligament sprain, CC ligaments intact (no displacement). Type II = AC ligament rupture, CC ligaments sprained (mild superior displacement). Type III = both AC and CC ligaments ruptured, 25-100% superior displacement of the clavicle. Type IV = posterior displacement (through trapezius). Type V = >100% superior displacement (>100-300% CC distance increase). Type VI = inferior displacement (beneath coracoid or acromion, rare). Treatment: Types I-II = non-operative (sling). Type III = controversial (most non-operative, some athletes surgical). Types IV-VI = operative (CC ligament reconstruction/stabilisation).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Fracture Non-union",
          "range": "Q598",
          "questions": [
            {
              "number": 598,
              "stem": "A hypertrophic non-union is characterised by abundant callus ('elephant foot' or 'horse hoof' appearance) but failure to bridge. The primary cause is:",
              "options": [
                "Inadequate blood supply",
                "Mechanical instability (inadequate fixation)",
                "Infection",
                "Bone loss",
                "Radiation damage"
              ],
              "answer": "B",
              "explanation": "Hypertrophic non-union has ADEQUATE blood supply (the callus production proves biological activity) but INADEQUATE mechanical stability — the fracture moves too much for the callus to bridge and consolidate. Treatment: improve stability (exchange nailing with a larger nail, compression plating, dynamisation if the nail is statically locked). Bone graft is NOT needed (biology is intact). Atrophic non-union has POOR biology (no callus, pencil-thin bone ends) and requires BOTH improved stability AND biological augmentation (bone graft ± BMP). The Weber-Cech classification divides non-unions into viable (hypertrophic, oligotrophic) and non-viable (atrophic, necrotic, defect).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Pilon",
          "range": "Q599",
          "questions": [
            {
              "number": 599,
              "stem": "A pilon fracture of the distal tibia is caused by:",
              "options": [
                "Rotational force (same as ankle fracture)",
                "Direct lateral impact",
                "Torsional stress fracture",
                "Axial loading/compression of the tibial plafond (fall from height, MVA)",
                "Muscle avulsion"
              ],
              "answer": "D",
              "explanation": "Pilon (plafond) fractures result from axial loading of the tibial articular surface (tibial plafond) — typically from a fall from height or high-energy MVA where the talus is driven upward into the tibial plafond. This produces significant articular comminution, metaphyseal bone loss, and severe soft tissue injury (unlike rotational ankle fractures which have less energy). Rüedi-Allgöwer classification: I = undisplaced articular surface. II = displaced articular surface with minimal metaphyseal comminution. III = severe articular comminution with metaphyseal involvement. Management: staged approach — initial spanning external fixation (allow soft tissue recovery) → definitive ORIF when soft tissue permits (typically 10-21 days). Direct open approach to comminuted soft tissues risks wound breakdown.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Midfoot",
          "range": "Q600",
          "questions": [
            {
              "number": 600,
              "stem": "The fleck sign on a foot radiograph is pathognomonic for:",
              "options": [
                "Calcaneal fracture",
                "Navicular stress fracture",
                "Lisfranc injury (avulsion fracture at the base of the 2nd metatarsal from the Lisfranc ligament)",
                "Chopart joint dislocation",
                "5th metatarsal fracture"
              ],
              "answer": "C",
              "explanation": "The fleck sign is a small avulsion fracture fragment visible between the base of the 1st and 2nd metatarsals on an AP foot radiograph. It represents an avulsion of the Lisfranc ligament (which connects the medial cuneiform to the 2nd MT base) and is pathognomonic for a Lisfranc injury. Other radiographic signs: >2mm widening between 1st and 2nd MT bases, loss of alignment between the 2nd MT and middle cuneiform (on AP view) or between the 4th MT and cuboid (on oblique view). Weight-bearing radiographs are essential — non-weight-bearing films may miss subtle instability.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Paediatric",
          "range": "Q601-Q602",
          "questions": [
            {
              "number": 601,
              "stem": "The ossification centres of the paediatric elbow appear in a predictable sequence. The correct order is:",
              "options": [
                "Radial head, Capitellum, Internal epicondyle, Trochlea, Olecranon, External epicondyle",
                "Olecranon, Trochlea, Capitellum, Radial head, Internal epicondyle, External epicondyle",
                "External epicondyle, Internal epicondyle, Capitellum, Olecranon, Trochlea, Radial head",
                "All appear simultaneously at birth",
                "Capitellum, Radial head, Internal (medial) epicondyle, Trochlea, Olecranon, External (lateral) epicondyle — CRITOE"
              ],
              "answer": "E",
              "explanation": "The elbow ossification centres appear in a predictable sequence remembered by the mnemonic CRITOE: Capitellum (~1yr), Radial head (~3yr), Internal (medial) epicondyle (~5yr), Trochlea (~7yr), Olecranon (~9yr), External (lateral) epicondyle (~11yr). Approximate ages: 1-3-5-7-9-11 years. Knowing this sequence is essential for interpreting paediatric elbow radiographs — if an ossification centre appears to be present but the one that normally appears BEFORE it is absent, suspect an avulsion fracture. The classic example: the medial epicondyle (I in CRITOE) must be visible before the trochlea (T) — if the trochlea appears visible but the medial epicondyle is not in its normal position, it may be avulsed and trapped within the joint.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 602,
              "stem": "The remodelling potential of paediatric fractures is greatest in which scenario?",
              "options": [
                "Fracture in the diaphysis of a teenager",
                "Intra-articular fracture with step",
                "Fracture close to a joint in the plane of motion of that joint, in a young child",
                "Rotational deformity at any age",
                "Fracture in a non-growing bone"
              ],
              "answer": "C",
              "explanation": "Remodelling potential is greatest when: (1) the child is YOUNG (more remaining growth = more remodelling capacity), (2) the fracture is CLOSE TO A JOINT (physeal growth contributes to correction), (3) the deformity is IN THE PLANE OF MOTION of the adjacent joint (flexion/extension deformity at the elbow corrects better than varus/valgus), and (4) the bone has significant GROWTH REMAINING (proximal humerus remodels more than distal humerus because the proximal physis contributes ~80% of humeral growth). Rotational deformity does NOT remodel well at any age — this is a key exam point. Intra-articular steps do not remodel. These principles guide the acceptance criteria for paediatric fracture management.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Patella Fracture",
          "range": "Q603",
          "questions": [
            {
              "number": 603,
              "stem": "A displaced transverse patella fracture with >3 mm step or >2 mm separation is best treated with:",
              "options": [
                "Cylinder cast in extension",
                "Patellectomy as first-line",
                "Functional bracing",
                "Tension band wiring",
                "Observation only"
              ],
              "answer": "D",
              "explanation": "Displaced transverse patella fractures are treated with tension band wiring (TBW) — two parallel K-wires with a figure-of-eight cerclage wire. The tension band principle converts the pull of the quadriceps (tension force on the anterior patella) into compression across the articular surface posteriorly during knee flexion. This allows early active motion. Surgical indications: >3 mm articular step, >2 mm fragment separation, inability to perform straight leg raise (extensor mechanism disruption). Undisplaced fractures: cylindrical cast or hinged knee brace in extension for 4-6 weeks. Comminuted fractures may require partial patellectomy or cerclage wiring.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Nerve Injury",
          "range": "Q604",
          "questions": [
            {
              "number": 604,
              "stem": "A radial nerve palsy following a closed humeral shaft fracture should initially be managed by:",
              "options": [
                "Immediate surgical exploration of the nerve",
                "Observation for 3-4 months (most are neurapraxia and will recover spontaneously)",
                "Urgent tendon transfer",
                "Amputation",
                "MRI of the nerve as an emergency"
              ],
              "answer": "B",
              "explanation": "Approximately 85-90% of radial nerve palsies associated with closed humeral shaft fractures are neurapraxia (conduction block without structural axonal damage) and recover spontaneously within 3-4 months. Initial management: observation, wrist extension splint (prevents contracture), serial clinical examination, and NCS/EMG at 3-4 months if no recovery. Indications for surgical exploration: open fracture with nerve palsy, nerve palsy developing AFTER manipulation/reduction (iatrogenic entrapment), no clinical or EMG recovery by 3-4 months, and sharp/penetrating injury. If no recovery by 6 months: consider tendon transfers (PT→ECRB, FCR→EDC, PL→EPL).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Elbow Dislocation",
          "range": "Q605",
          "questions": [
            {
              "number": 605,
              "stem": "The terrible triad of the elbow consists of:",
              "options": [
                "Elbow dislocation, radial head fracture, and coronoid fracture",
                "Radial head fracture, ulnar fracture, and radial nerve palsy",
                "Monteggia lesion with olecranon fracture",
                "Supracondylar fracture, forearm fracture, and wrist fracture",
                "ACL, MCL, and medial meniscus injury"
              ],
              "answer": "A",
              "explanation": "The terrible triad of the elbow: posterior elbow dislocation + radial head fracture + coronoid fracture. It is called 'terrible' because it is inherently unstable and difficult to treat — all three stabilisers are disrupted (radial head = secondary valgus stabiliser, coronoid = anterior buttress, and LCL is always torn in the dislocation). Treatment principles: fix/replace the radial head (NEVER excise without replacement in this context), fix the coronoid (suture lasso for small fragments, plate/screws for larger), repair the LCL, and consider LUCL repair. If still unstable after all repairs: hinged external fixator. A missed or undertreated terrible triad leads to chronic instability, recurrent dislocation, and post-traumatic arthritis.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Scapula",
          "range": "Q606",
          "questions": [
            {
              "number": 606,
              "stem": "Scapula fractures are uncommon and usually result from high-energy trauma. They are importantly associated with:",
              "options": [
                "No other injuries",
                "Contralateral shoulder dislocation",
                "Ipsilateral thoracic injuries in up to 80-90% of cases (rib fractures, pulmonary contusion, pneumothorax)",
                "Isolated hand injuries",
                "Only cervical spine fractures"
              ],
              "answer": "C",
              "explanation": "Scapula fractures require significant force (~40% from MVAs, 12% from motorcycle crashes) and are associated with ipsilateral thoracic injuries in 80-90% of cases: rib fractures, pulmonary contusion, pneumothorax, haemothorax, brachial plexus injury, and subclavian/axillary vessel injury. Associated injuries to the ipsilateral clavicle create a 'floating shoulder' (double disruption of the superior shoulder suspensory complex). Most scapula body/neck fractures are treated non-operatively (sling + early ROM). Operative indications: glenoid articular fractures with >4mm step or instability, significant lateral border displacement (medialization >20mm), floating shoulder.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Essex-Lopresti",
          "range": "Q607",
          "questions": [
            {
              "number": 607,
              "stem": "An Essex-Lopresti injury involves:",
              "options": [
                "Distal radius fracture with carpal instability",
                "Ulnar shaft fracture with radial head dislocation",
                "Bilateral forearm fractures",
                "Radial head fracture with disruption of the interosseous membrane and DRUJ instability",
                "Isolated DRUJ dislocation"
              ],
              "answer": "D",
              "explanation": "The Essex-Lopresti lesion involves the triad of: (1) radial head fracture, (2) disruption of the interosseous membrane (IOM), and (3) DRUJ disruption/instability. The radius migrates proximally (loss of the radial head + IOM disruption removes the constraints to proximal migration) → DRUJ subluxation. If the radial head is excised without recognising the IOM disruption, proximal migration worsens catastrophically. Therefore: NEVER excise a radial head without checking DRUJ stability and forearm longitudinal stability. If Essex-Lopresti is suspected: radial head replacement (not excision) + DRUJ stabilisation ± IOM reconstruction. Late diagnosis is very difficult to treat.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            }
          ]
        },
        {
          "title": "Femoral Neck",
          "range": "Q608",
          "questions": [
            {
              "number": 608,
              "stem": "An undisplaced (Garden I) intracapsular femoral neck fracture in a 72-year-old active woman is best treated with:",
              "options": [
                "Internal fixation with 3 parallel cannulated screws",
                "Total hip arthroplasty",
                "Hemiarthroplasty",
                "Conservative management with bed rest",
                "External fixation"
              ],
              "answer": "A",
              "explanation": "Undisplaced intracapsular NOF fractures (Garden I and II) are treated with internal fixation regardless of age — typically with 3 parallel cannulated screws in an inverted triangle configuration. The blood supply to the femoral head is more likely to be preserved in undisplaced fractures (AVN rate ~5-10% vs 15-30% for displaced). The screws provide compression across the fracture and prevent displacement. Important: these fractures can displace if not fixed promptly — surgery within 24-36h (NICE). Post-operatively: immediate weight-bearing as tolerated (with walking aids). Follow-up: serial radiographs to monitor for AVN (may take 1-2 years to manifest) and non-union. If AVN or non-union develops → conversion to arthroplasty.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Lateral Condyle",
          "range": "Q609",
          "questions": [
            {
              "number": 609,
              "stem": "A displaced lateral condyle fracture of the humerus in a child is important because missed or inadequately treated cases can lead to:",
              "options": [
                "No significant complications",
                "Immediate radial nerve palsy only",
                "Spontaneous resolution",
                "Only cosmetic deformity",
                "Non-union, progressive cubitus valgus, and tardy ulnar nerve palsy"
              ],
              "answer": "E",
              "explanation": "Displaced lateral condyle fractures require accurate open reduction and fixation because: (1) the fracture involves the articular surface and the lateral column growth centre, (2) the fracture fragment is pulled distally and rotated by the extensor muscles (wrist extensors originate from the lateral epicondyle), (3) synovial fluid bathing the fracture inhibits healing. Inadequate treatment → non-union → progressive cubitus valgus (lateral growth arrest, continued medial growth) → tardy ulnar nerve palsy (the ulnar nerve is stretched over the medial epicondyle as valgus increases — may present years or decades later). This is the second most common paediatric elbow fracture (~17%). Milch classification: Type I (lateral to trochlear groove, Salter-Harris IV equivalent) and Type II (through trochlear groove — less stable).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Cervical Spine",
          "range": "Q610",
          "questions": [
            {
              "number": 610,
              "stem": "The most commonly injured level of the cervical spine in adults is:",
              "options": [
                "C1",
                "C2 (axis — including odontoid fractures and hangman fractures)",
                "C3",
                "C5",
                "C7"
              ],
              "answer": "B",
              "explanation": "C2 is the most commonly fractured cervical vertebra in adults, accounting for ~24% of all cervical spine fractures. This includes odontoid (dens) fractures (Anderson and D'Alonzo Type I-III), hangman fractures (bilateral pars interarticularis fractures), and miscellaneous C2 body fractures. The subaxial cervical spine: C5-C6 and C6-C7 are the most commonly injured SUBAXIAL levels (most mobile segments, most vulnerable to flexion-extension and rotational forces). C1 (Jefferson fracture) is less common than C2. In the elderly, C2 odontoid fractures are particularly common (osteoporotic bone, ground-level falls).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Imaging",
          "range": "Q611",
          "questions": [
            {
              "number": 611,
              "stem": "The Salter-Harris classification is best described on which imaging modality?",
              "options": [
                "Ultrasound",
                "CT only",
                "Plain radiograph (initial assessment), confirmed with MRI for occult injuries",
                "Bone scan",
                "PET-CT"
              ],
              "answer": "C",
              "explanation": "Plain radiographs are the initial imaging modality for paediatric physeal injuries. Types II-IV are usually visible on XR (the Thurston-Holland metaphyseal fragment in Type II is readily seen). However, Type I fractures (through the physis only) may be radiographically OCCULT — diagnosed clinically by physeal point tenderness and treated as a fracture if suspected. MRI is useful for: (1) confirming occult Type I injuries, (2) assessing the extent of Type III-IV articular involvement, (3) evaluating for physeal bar formation (growth arrest), and (4) planning treatment for complex injuries. CT can help with complex Type III-IV fractures (operative planning for articular reduction). Ultrasound is limited for physeal injuries. Bone scan and PET-CT are not first-line.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        }
      ]
    },
    {
      "title": "Basic Science",
      "chapters": [
        {
          "title": "Bone Biology",
          "range": "Q612-Q625",
          "questions": [
            {
              "number": 612,
              "stem": "Endochondral ossification differs from intramembranous ossification in that endochondral:",
              "options": [
                "Forms bone through a CARTILAGE template — mesenchymal cells first differentiate into chondrocytes that produce a hyaline cartilage model, which is then progressively replaced by bone (this is how long bones form and how fractures heal via callus)",
                "Forms bone directly from mesenchyme without a cartilage intermediate (that's intramembranous)",
                "Only occurs in the skull",
                "Does not involve any cellular activity",
                "Only occurs in adults"
              ],
              "answer": "A",
              "explanation": "Two mechanisms of bone formation: (1) ENDOCHONDRAL ossification: mesenchymal cells → chondrocytes → hyaline CARTILAGE template → the cartilage template is progressively REPLACED by bone (chondrocyte hypertrophy → matrix calcification → vascular invasion → osteoblast deposition of bone on calcified cartilage scaffold → bone replaces cartilage). This is how: long bones form (primary ossification centre in the diaphysis, secondary centres in the epiphyses), the growth plate grows (zone of proliferation → hypertrophy → calcification → ossification), and fracture CALLUS forms (secondary fracture healing — soft callus is cartilage → replaced by hard callus/woven bone). (2) INTRAMEMBRANOUS ossification: mesenchymal cells differentiate DIRECTLY into osteoblasts → bone forms directly from mesenchymal condensation WITHOUT a cartilage intermediate. This is how: flat bones form (skull, clavicle — the ONLY long bone that forms by intramembranous ossification), and DISTRACTION OSTEOGENESIS works (Ilizarov — new bone forms directly in the distraction gap).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 613,
              "stem": "The bone remodelling cycle in adult bone involves a sequence of:",
              "options": [
                "Only bone formation without any resorption",
                "ACTIVATION → RESORPTION (osteoclasts) → REVERSAL → FORMATION (osteoblasts) → QUIESCENCE — this coupled process takes approximately 3-6 months and replaces ~10% of the adult skeleton per year",
                "Random bone deposition",
                "Only resorption without formation",
                "No cellular activity in adult bone"
              ],
              "answer": "B",
              "explanation": "Adult bone is continuously remodelled through the BASIC MULTICELLULAR UNIT (BMU): (1) ACTIVATION — signalling (microdamage detection by osteocytes, hormonal signals, mechanical loading changes) recruits osteoclast precursors. (2) RESORPTION — osteoclasts resorb old or damaged bone (creating a resorption cavity/Howship lacuna in cancellous bone or a cutting cone in cortical bone — ~2-4 weeks). (3) REVERSAL — transition phase (macrophages prepare the resorbed surface, signalling molecules recruit osteoblasts — ~1-2 weeks). (4) FORMATION — osteoblasts lay down new osteoid (unmineralised bone matrix) which then mineralises to become lamellar bone (fills the resorption cavity — ~3-4 months, the longest phase). (5) QUIESCENCE — the new bone is complete, osteoblasts become osteocytes (embedded) or bone lining cells. This COUPLED process replaces ~10% of the adult skeleton per year. In osteoporosis: resorption exceeds formation → net bone loss. Anti-resorptives (bisphosphonates, denosumab): reduce the resorption phase. Anabolics (teriparatide, romosozumab): increase the formation phase.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 614,
              "stem": "Osteocytes make up approximately what percentage of all bone cells and serve as:",
              "options": [
                "1% — they are rare and functionless",
                "50% — they only produce collagen",
                "10% — they only resorb bone",
                "They don't exist in mature bone",
                "90-95% — they are the most abundant bone cell, functioning as mechanosensors that detect mechanical loading and orchestrate bone remodelling by signalling to osteoblasts and osteoclasts"
              ],
              "answer": "E",
              "explanation": "Osteocytes are the MOST ABUNDANT bone cell (~90-95% of all bone cells). They are terminally differentiated osteoblasts that have become embedded within the bone matrix they produced. They reside in LACUNAE and communicate with each other and surface cells through extensive cytoplasmic processes (CANALICULI) — forming the lacunocanalicular network (LCN). Functions: (1) MECHANOSENSORS — detect mechanical loading (fluid flow through canaliculi generates shear stress detected by osteocyte processes → transduce mechanical signals into biochemical responses). (2) Orchestrate remodelling — produce SCLEROSTIN (inhibits Wnt → suppresses bone formation — target for romosozumab), RANKL (stimulates osteoclasts), and OPG (inhibits osteoclasts). (3) Regulate phosphate metabolism (FGF23 — relevant to X-linked hypophosphataemia/rickets). (4) Detect microdamage — initiate targeted remodelling to repair microcracks. Osteocyte apoptosis (e.g., in AVN, bisphosphonate jaw osteonecrosis) → failure of mechanosensing → pathological bone.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 615,
              "stem": "The periosteum has two layers. The inner (cambium) layer is important because it contains:",
              "options": [
                "Blood vessels only",
                "Nerve fibres only",
                "Dense collagen fibres",
                "Osteoprogenitor cells and osteoblasts (essential for bone healing and growth)",
                "Fat cells"
              ],
              "answer": "D",
              "explanation": "The periosteum has two layers: the outer fibrous layer (dense connective tissue providing mechanical protection, attachment for tendons/ligaments via Sharpey fibres) and the inner cambium (osteogenic) layer (containing osteoprogenitor cells, osteoblasts, and blood vessels). The cambium layer is essential for appositional (width) growth of bone, fracture healing (periosteal callus), and bone regeneration. It is thicker and more active in children, which is why children have superior fracture healing and remodelling potential.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 616,
              "stem": "Hydroxyapatite (HA) coating on uncemented implants promotes fixation by:",
              "options": [
                "Acting as a cement substitute",
                "Increasing implant flexibility",
                "Providing a bioactive osteoconductive surface that promotes direct bone-implant bonding (osseointegration) and accelerates initial fixation",
                "Reducing implant cost",
                "Preventing all infections"
              ],
              "answer": "C",
              "explanation": "Hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) coating (~50-150μm thickness) on uncemented implants provides a bioactive, osteoconductive surface that promotes direct bonding between bone and implant (osseointegration). HA is the mineral component of bone (~65% of bone by weight), so the coating creates a biologically familiar surface for osteoblast adhesion and new bone formation. It accelerates initial fixation (important in the first weeks when the implant relies on press-fit before biological fixation occurs) and may improve long-term fixation, particularly in poor bone quality. HA resorbs over time (replaced by bone). Concerns: delamination (coating particles can cause third-body wear), thickness variation, and potential for bacterial adhesion to rough coating surfaces.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 617,
              "stem": "The basic multicellular unit (BMU) of bone remodelling follows which sequence?",
              "options": [
                "Activation → Resorption → Reversal → Formation",
                "Formation → Resorption → Reversal → Quiescence",
                "Formation → Activation → Resorption → Reversal",
                "Quiescence → Formation → Resorption → Activation",
                "Resorption → Formation → Activation → Reversal"
              ],
              "answer": "A",
              "explanation": "The BMU remodelling cycle follows the ARF sequence: Activation (osteocyte signalling recruits osteoclast precursors) → Resorption (osteoclasts resorb bone for ~3 weeks) → Reversal (transition phase, coupling signals released) → Formation (osteoblasts lay down new bone for ~3 months). The complete cycle takes approximately 4-6 months. Coupling factors (TGF-β, BMPs, IGF) released during resorption signal osteoblasts to form new bone. In osteoporosis, resorption exceeds formation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 618,
              "stem": "Endochondral ossification differs from intramembranous ossification in that endochondral:",
              "options": [
                "Occurs without any cartilage precursor",
                "Forms bone directly from mesenchyme",
                "Only occurs in flat bones",
                "Requires a cartilage template that is progressively replaced by bone",
                "Does not involve osteoblasts"
              ],
              "answer": "D",
              "explanation": "Endochondral ossification forms bone through a cartilage intermediate — a cartilage template (anlage) is first formed by chondrocytes, then progressively replaced by bone through vascular invasion, chondrocyte apoptosis, and osteoblast activity. This process forms long bones, vertebrae, pelvis, and base of skull, and is the mechanism of secondary fracture healing. Intramembranous ossification forms bone directly from mesenchymal condensation without a cartilage stage — this forms flat bones (skull, clavicle, mandible) and contributes to periosteal growth and distraction osteogenesis.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            },
            {
              "number": 619,
              "stem": "Sclerostin is a protein produced by osteocytes that inhibits bone formation. Which new osteoporosis drug targets sclerostin?",
              "options": [
                "Alendronate",
                "Romosozumab (anti-sclerostin antibody)",
                "Denosumab",
                "Teriparatide",
                "Strontium ranelate"
              ],
              "answer": "B",
              "explanation": "Romosozumab is a humanised monoclonal antibody that binds and inhibits sclerostin (produced by osteocytes). Sclerostin normally inhibits the Wnt signalling pathway, which is essential for osteoblast differentiation and bone formation. By blocking sclerostin, romosozumab has a DUAL effect: it increases bone formation AND decreases bone resorption — making it both anabolic and anti-resorptive (a unique combination). Given as monthly SC injection for 12 months, followed by transition to anti-resorptive (bisphosphonate or denosumab). Approved for severe osteoporosis with high fracture risk. Cardiovascular safety concerns limit its use in patients with recent MI or stroke.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 620,
              "stem": "Distraction osteogenesis (Ilizarov technique) forms new bone by which ossification process?",
              "options": [
                "Endochondral ossification (cartilage intermediate)",
                "No new bone is formed — only existing bone is stretched",
                "Enchondral ossification from a graft",
                "Appositional growth from periosteum only",
                "Intramembranous ossification (direct bone formation without cartilage)"
              ],
              "answer": "E",
              "explanation": "Distraction osteogenesis forms new bone by INTRAMEMBRANOUS ossification — bone forms directly from mesenchymal precursors in the distraction gap WITHOUT a cartilage intermediate. This is different from fracture healing (which typically occurs by endochondral ossification through callus). The process requires: (1) corticotomy (osteotomy preserving the periosteum and endosteal blood supply), (2) latency period (5-7 days for initial callus formation), (3) distraction phase (1mm/day in 4 divided increments — 0.25mm QDS), (4) consolidation phase (new bone matures — typically 1 month per cm of lengthening). The rate of 1mm/day is critical: too fast → fibrous non-union, too slow → premature consolidation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 621,
              "stem": "The growth plate (physis) is organised into distinct zones. Chondrocyte proliferation occurs in which zone?",
              "options": [
                "Reserve (resting) zone",
                "Hypertrophic zone",
                "Zone of provisional calcification",
                "Proliferative (columnar) zone",
                "Primary spongiosa"
              ],
              "answer": "D",
              "explanation": "The growth plate zones from epiphysis to metaphysis: (1) Reserve (resting/germinal) zone — stores chondrocytes and nutrients (supplies cells to the proliferative zone). (2) Proliferative (columnar) zone — active chondrocyte division and multiplication in longitudinal columns (responsible for longitudinal bone growth). (3) Hypertrophic zone — chondrocytes enlarge (5-10× normal size), produce Type X collagen, and begin to calcify their surrounding matrix. (4) Zone of provisional calcification — matrix calcification, chondrocyte apoptosis. (5) Primary spongiosa — vascular invasion, osteoblasts deposit bone on calcified cartilage scaffold (endochondral ossification). The hypertrophic zone is the weakest zone mechanically — Salter-Harris fractures typically propagate through here.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 622,
              "stem": "The RANK-RANKL-OPG signalling pathway is the central regulator of:",
              "options": [
                "Muscle contraction",
                "Osteoclast differentiation and bone resorption",
                "Nerve conduction",
                "Collagen synthesis",
                "Cartilage repair"
              ],
              "answer": "B",
              "explanation": "The RANK-RANKL-OPG axis is the master regulator of osteoclastogenesis. RANKL (receptor activator of NF-κB ligand) is produced by osteoblasts and stromal cells. It binds to RANK (receptor) on osteoclast precursors (monocyte-macrophage lineage), stimulating their differentiation into mature, active osteoclasts → bone resorption. OPG (osteoprotegerin) is a soluble decoy receptor also produced by osteoblasts — it binds RANKL and PREVENTS it from activating RANK → inhibiting osteoclast formation → reducing resorption. The balance between RANKL and OPG determines net bone resorption or formation. Denosumab mimics OPG (binds RANKL). GCT of bone overexpresses RANKL → denosumab effective.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 623,
              "stem": "Endochondral ossification differs from intramembranous ossification in that endochondral ossification:",
              "options": [
                "Requires a cartilage template that is subsequently replaced by bone",
                "Occurs without a cartilage template (direct bone formation from mesenchyme)",
                "Only occurs in flat bones",
                "Does not involve osteoblasts",
                "Only occurs postnatally"
              ],
              "answer": "A",
              "explanation": "Endochondral ossification: a hyaline cartilage model (template) forms first, then is progressively replaced by bone. This is the process by which most of the skeleton develops (long bones, vertebrae, pelvis, base of skull) and how growth plates function (chondrocyte proliferation → hypertrophy → calcification → vascular invasion → bone formation). Intramembranous ossification: bone forms DIRECTLY from mesenchymal condensations without a cartilage intermediate. This occurs in the flat bones of the skull (calvarium), clavicle, and mandible. Both processes involve osteoblasts forming the bone matrix. Fracture healing: secondary = endochondral (callus), primary = intramembranous (cutting cones). Distraction osteogenesis = intramembranous.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 624,
              "stem": "The periosteum has two distinct layers. The inner (cambium) layer is important because it:",
              "options": [
                "Provides only structural support",
                "Has no biological function",
                "Contains osteoprogenitor cells capable of new bone formation (essential for fracture healing and appositional bone growth)",
                "Only contains blood vessels",
                "Is identical to the outer fibrous layer"
              ],
              "answer": "C",
              "explanation": "The periosteum has two layers: (1) Outer fibrous layer — dense connective tissue providing structural attachment for tendons and ligaments (Sharpey fibres anchor it to the cortex). (2) Inner cambium (osteogenic) layer — contains osteoprogenitor cells, osteoblasts, and a rich vascular network. This layer is responsible for appositional bone growth (increasing bone diameter), fracture callus formation (the periosteal reaction seen on radiographs is new bone from the cambium layer), and bone repair. In children, the periosteum is thicker and more metabolically active than in adults — this contributes to faster fracture healing, greater remodelling potential, and the subperiosteal haematoma pattern seen in paediatric fractures.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 625,
              "stem": "The RANK-RANKL pathway is the target of denosumab. Giant cell tumour of bone (GCT) is rich in RANKL. Denosumab in GCT works by:",
              "options": [
                "Directly killing tumour cells",
                "Promoting osteoblast activity",
                "Providing a scaffold for bone growth",
                "Inhibiting angiogenesis",
                "Inhibiting RANKL → preventing osteoclast-like giant cell recruitment and activation → halting bone destruction"
              ],
              "answer": "E",
              "explanation": "GCT of bone contains two cell populations: (1) neoplastic stromal cells (the true tumour cells — express RANKL) and (2) osteoclast-like multinucleated giant cells (reactive cells recruited by RANKL signalling). Denosumab (anti-RANKL monoclonal antibody) binds RANKL → prevents activation of the giant cells → halts bone destruction and tumour growth. Indications: neoadjuvant (shrink tumour before surgery, making excision easier/less morbid), unresectable GCT (e.g., sacral, spinal), and recurrent GCT. Denosumab does NOT kill the neoplastic stromal cells — they persist, and the tumour can recur after denosumab is stopped. There is also a theoretical risk of malignant transformation to osteosarcoma (rare, requires monitoring).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Theatre",
          "range": "Q626-Q631",
          "questions": [
            {
              "number": 626,
              "stem": "Tourniquet use in limb surgery — the maximum recommended continuous application time for a pneumatic tourniquet on the upper limb is:",
              "options": [
                "2 hours (120 minutes) for the upper limb (1 hour for the forearm/hand by some guidelines) — prolonged use risks ischaemia-reperfusion injury, nerve palsy (particularly the radial nerve in the upper arm), and muscle damage",
                "30 minutes",
                "6 hours",
                "12 hours",
                "Unlimited — no time limit applies"
              ],
              "answer": "A",
              "explanation": "Tourniquet time limits: UPPER limb: recommended maximum 2 hours (120 minutes) continuously, though some guidelines suggest 1 hour for the forearm/hand. LOWER limb: maximum 2 hours (some extend to 2.5 hours for complex procedures). If longer surgery is needed: DEFLATE the tourniquet for 15-20 minutes (allows reperfusion) before reinflating. Tourniquet pressure: upper limb ~250 mmHg (or SBP + 100 mmHg), lower limb ~300 mmHg (or SBP + 150 mmHg) — sufficient to occlude arterial flow without excessive pressure. Complications: (1) nerve injury (most common — the radial nerve is particularly vulnerable in the upper arm due to compression against the humerus; tourniquet palsy presents as wrist/finger drop), (2) ischaemia-reperfusion injury (reactive hyperaemia, swelling, acidosis on deflation), (3) muscle damage (post-tourniquet syndrome — pain, swelling, weakness), (4) vascular injury (particularly in atherosclerotic vessels), (5) DVT (controversial — theoretical increased risk), (6) skin burns (chemical prep trapped under the tourniquet), (7) compartment syndrome (post-tourniquet reactive swelling + reperfusion).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 627,
              "stem": "Laminar flow in orthopaedic theatres provides:",
              "options": [
                "No benefit over conventional ventilation",
                "Complete sterilisation of all surfaces",
                "Protection against bloodborne viruses only",
                "Temperature control without air filtration",
                "Ultraclean air (≤10 CFU/m³) by delivering unidirectional, filtered air at high volume to reduce airborne bacterial contamination at the surgical site"
              ],
              "answer": "E",
              "explanation": "Laminar flow ventilation delivers unidirectional, HEPA-filtered air vertically downward (or horizontally) over the surgical field at high volume (~300 air changes/hour), creating a zone of ultraclean air (≤10 CFU/m³ — compared to ~50-150 CFU/m³ in conventional theatres). This reduces airborne bacterial contamination at the wound. It was introduced based on the landmark Charnley/Lidwell clean-air studies showing reduced deep infection rates in arthroplasty. However, recent NJR data and systematic reviews have questioned whether laminar flow actually reduces infection rates in modern practice (with prophylactic antibiotics + antibiotic cement + modern aseptic technique). Body exhaust suits (space suits) are often used in combination with laminar flow. Key points: personnel should stay WITHIN the clean zone, doors should remain closed, and movement should be minimised (disrupts laminar flow patterns).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 628,
              "stem": "Autoclaving is the standard method for sterilising orthopaedic instruments. It works by:",
              "options": [
                "Dry heat at 100°C",
                "Exposure to ethylene oxide gas only",
                "Saturated steam under pressure (typically 134°C at 2.2 bar for 3 minutes, or 121°C for 15 minutes) — kills all microorganisms including bacterial spores",
                "UV light exposure",
                "Chemical immersion in chlorhexidine"
              ],
              "answer": "C",
              "explanation": "Autoclaving (steam sterilisation) uses SATURATED STEAM under PRESSURE to achieve temperatures above 100°C (boiling point) — the high temperature and moisture denature proteins and kill ALL microorganisms including resistant bacterial spores (the most resistant life forms). Standard NHS cycles: 134°C at 2.2 bar (2 atmospheres above atmospheric) for 3 minutes (porous load/instrument cycle), or 121°C at 1 bar for 15 minutes (fluid cycle). Instruments are washed, decontaminated, inspected, packed, and then autoclaved. Biological indicators (Bacillus stearothermophilus spores) are used to verify sterilisation efficacy. Items that cannot withstand heat/moisture: sterilised by ethylene oxide (EtO) gas or hydrogen peroxide plasma (Sterrad). Prions (CJD): require special decontamination protocols (routine autoclaving may not fully inactivate prions).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 629,
              "stem": "The WHO surgical site marking should be done by:",
              "options": [
                "The nurse only",
                "The operating surgeon (or a member of the operating team with direct involvement) with the patient awake and consenting",
                "The porter",
                "The radiographer",
                "The anaesthetist only"
              ],
              "answer": "B",
              "explanation": "WHO and NICE guidelines require that the surgical site is marked by a member of the operating team who will be directly involved in the procedure — ideally the OPERATING SURGEON. The marking should be done with the patient AWAKE and ABLE TO CONFIRM the correct site. The mark should be: (1) made with an indelible skin marker, (2) clearly visible after skin preparation and draping, (3) placed at or near the incision site (not just on the limb), (4) an ARROW or the word 'YES' (some centres use the surgeon's initials). Site marking is part of the WHO Surgical Safety Checklist (Sign-in phase). Wrong-site surgery is a 'Never Event' (should never occur with proper processes). The patient should also be asked to confirm the correct side/site during the Sign-in and Time-out phases.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 630,
              "stem": "The maximum safe tourniquet time for a pneumatic tourniquet on the upper limb is generally accepted as:",
              "options": [
                "30 minutes",
                "60 minutes",
                "90 minutes",
                "120 minutes (2 hours)",
                "180 minutes"
              ],
              "answer": "D",
              "explanation": "The generally accepted maximum safe tourniquet time is 2 hours (120 minutes) for the upper limb and 2 hours for the lower limb (some authors suggest 90 minutes for the upper limb). Tourniquet pressure: upper limb = 50-100 mmHg above systolic BP (typically 200-250 mmHg). Lower limb = 100-150 mmHg above systolic (typically 300-350 mmHg). If additional time is needed, the tourniquet should be deflated for 15-20 minutes to allow reperfusion before re-inflation. Complications: nerve injury (compression neuropraxia), muscle ischaemia, rhabdomyolysis, skin burns, DVT, post-tourniquet syndrome.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 631,
              "stem": "In orthopaedic surgery, monopolar diathermy should be avoided in which situation?",
              "options": [
                "All open fractures",
                "Near metal implants (risk of thermal injury to surrounding tissue) and in patients with cardiac pacemakers",
                "All joint replacements",
                "Near a tourniquet",
                "Only in paediatric patients"
              ],
              "answer": "B",
              "explanation": "Monopolar diathermy passes current through the body from the active electrode to a return pad. It can cause: (1) burns at the return pad site if poorly applied, (2) thermal injury to tissues near metal implants (the current may concentrate around metal, causing local heating), (3) interference with cardiac pacemakers/defibrillators (can cause arrhythmias or pacemaker malfunction — bipolar diathermy is safer). Bipolar diathermy passes current only between the two tips of the forceps (no return pad needed), limiting the current path and reducing risk. For patients with pacemakers: use bipolar, have a magnet available, and have cardiology/anaesthetic awareness.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Pharmacology",
          "range": "Q632-Q652",
          "questions": [
            {
              "number": 632,
              "stem": "Local anaesthetic systemic toxicity (LAST) — the most serious cardiac manifestation is:",
              "options": [
                "Mild dizziness only",
                "Perioral tingling only (that's an early CNS warning sign)",
                "Cardiac arrest from refractory ventricular fibrillation or asystole — treated with IV LIPID EMULSION (Intralipid 20%) as the specific antidote",
                "Only localised numbness",
                "Headache"
              ],
              "answer": "C",
              "explanation": "LAST occurs when local anaesthetic (bupivacaine, lidocaine, ropivacaine) reaches toxic systemic levels (from inadvertent intravascular injection, excessive dosing, or rapid absorption). Symptoms progress: CNS toxicity FIRST (perioral tingling → metallic taste → tinnitus → dizziness → visual disturbance → tremor → seizures), then CARDIOVASCULAR toxicity (hypotension → bradycardia → arrhythmias → refractory VF/asystole → CARDIAC ARREST). Bupivacaine is the most cardiotoxic (high lipid solubility → binds avidly to cardiac sodium channels → refractory arrhythmias that are very difficult to resuscitate). Treatment of LAST: (1) STOP injection. (2) Call for help. (3) Manage airway (intubate if seizing). (4) IV LIPID EMULSION (Intralipid 20%) — the SPECIFIC ANTIDOTE: initial bolus 1.5ml/kg over 1 minute → infusion 15ml/kg/h (repeat bolus if cardiovascular instability persists). The lipid acts as a 'lipid sink' — it sequesters the lipophilic LA molecules away from cardiac sodium channels. (5) Treat seizures (benzodiazepines — AVOID propofol which is also a cardiac depressant). (6) CPR if cardiac arrest (may need prolonged resuscitation — don't give up, the lipid emulsion may take time to work).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 633,
              "stem": "Romosozumab is the newest osteoporosis treatment. It works by:",
              "options": [
                "Inhibiting sclerostin — a natural inhibitor of the Wnt signalling pathway — resulting in BOTH increased bone formation AND decreased bone resorption (dual mechanism)",
                "Inhibiting osteoclasts like bisphosphonates",
                "Providing calcium supplementation",
                "Mimicking parathyroid hormone",
                "Blocking RANKL like denosumab"
              ],
              "answer": "A",
              "explanation": "Romosozumab is a humanised monoclonal antibody that inhibits SCLEROSTIN — a glycoprotein produced by osteocytes that normally INHIBITS the Wnt signalling pathway (Wnt stimulates osteoblast differentiation and activity). By blocking sclerostin: (1) Wnt signalling is unleashed → osteoblast activity INCREASES → more bone formation, AND (2) bone resorption DECREASES (through complex coupling mechanisms). This dual mechanism (increased formation + decreased resorption) makes it the most potent bone-building agent currently available. Given as monthly SC injection for 12 months (fixed duration). After 12 months, must transition to anti-resorptive (bisphosphonate or denosumab) to maintain gains. ARCH trial: superior fracture reduction compared to alendronate. Cardiovascular safety signal: increased CV events in the ARCH trial → contraindicated in patients with recent MI or stroke within the preceding year.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 634,
              "stem": "Low molecular weight heparin (LMWH, e.g., enoxaparin) for VTE prophylaxis in orthopaedics works by:",
              "options": [
                "Inhibiting platelet aggregation (like aspirin)",
                "Dissolving existing clots (thrombolysis)",
                "Inhibiting vitamin K (like warfarin)",
                "Directly blocking thrombin (like dabigatran)",
                "Primarily inhibiting Factor Xa (anti-Xa activity) through enhancement of antithrombin III — preventing thrombin generation and clot formation"
              ],
              "answer": "E",
              "explanation": "LMWH (e.g., enoxaparin 40mg daily SC) primarily inhibits FACTOR Xa through enhancement of antithrombin III (AT-III). AT-III is a natural anticoagulant — LMWH binds to AT-III and increases its activity ~100-fold, but the shorter heparin chain length of LMWH means it preferentially catalyses anti-Xa activity (rather than anti-IIa/thrombin inhibition, which requires a longer chain — as seen with unfractionated heparin UFH). Advantages of LMWH over UFH: (1) more predictable pharmacokinetics (fixed dose, no monitoring in most cases), (2) once-daily dosing, (3) lower risk of heparin-induced thrombocytopaenia (HIT), (4) SC administration (patient can self-inject). Monitoring: anti-Xa levels (only needed in renal impairment, extremes of body weight, or pregnancy — LMWH is renally excreted). Contraindications: active bleeding, HIT, severe renal impairment (accumulation). DOACs (rivaroxaban — direct Xa inhibitor, dabigatran — direct thrombin inhibitor): oral alternatives now preferred by NICE for arthroplasty VTE prophylaxis.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 635,
              "stem": "NSAIDs (non-steroidal anti-inflammatory drugs) provide analgesia by:",
              "options": [
                "Blocking opioid receptors",
                "Enhancing GABA activity in the brain",
                "Blocking sodium channels",
                "Inhibiting cyclo-oxygenase (COX) enzymes → reducing prostaglandin synthesis → decreasing inflammation, pain, and fever",
                "Inhibiting serotonin reuptake"
              ],
              "answer": "D",
              "explanation": "NSAIDs inhibit cyclo-oxygenase (COX) enzymes, which convert arachidonic acid to prostaglandins. Prostaglandins are key mediators of inflammation, pain (sensitise nociceptors), and fever. COX-1: constitutively expressed — produces prostaglandins that protect the gastric mucosa, maintain renal blood flow, and support platelet function. COX-2: primarily induced during inflammation — produces prostaglandins that mediate pain/inflammation. Non-selective NSAIDs (ibuprofen, diclofenac, naproxen): inhibit BOTH COX-1 and COX-2 → effective analgesia but GI side effects (peptic ulceration, bleeding) and renal effects from COX-1 inhibition. COX-2 selective (celecoxib, etoricoxib): reduced GI side effects but increased cardiovascular risk (MI, stroke). In orthopaedics: NSAIDs are first-line analgesics (multimodal analgesia — reduces opioid requirement). Concerns: potential effect on fracture healing (controversial — short courses likely safe) and HO prophylaxis (indomethacin).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 636,
              "stem": "Bisphosphonates work by:",
              "options": [
                "Binding to hydroxyapatite in bone → being taken up by osteoclasts during resorption → inhibiting the mevalonate pathway (farnesyl pyrophosphate synthase) → inducing osteoclast apoptosis → reducing bone resorption",
                "Stimulating osteoblast activity (that's teriparatide)",
                "Blocking RANKL (that's denosumab)",
                "Inhibiting sclerostin (that's romosozumab)",
                "Providing calcium supplementation"
              ],
              "answer": "A",
              "explanation": "Bisphosphonates (alendronate, risedronate, zoledronic acid) have a high affinity for HYDROXYAPATITE — they bind to bone mineral surfaces and are concentrated at sites of active remodelling. During bone resorption, osteoclasts ingest the bisphosphonate-coated bone. Inside the osteoclast: nitrogen-containing bisphosphonates (all modern bisphosphonates) inhibit FARNESYL PYROPHOSPHATE SYNTHASE (FPP synthase) in the mevalonate pathway → this disrupts prenylation of signalling proteins (small GTPases: Ras, Rho, Rac) → loss of osteoclast function → osteoclast apoptosis. Result: reduced bone resorption → increased BMD → reduced fracture risk. Evidence: alendronate reduces hip fracture risk by ~40-50%, vertebral fracture by ~50%. Zoledronic acid: most potent (single annual IV infusion). Side effects: GI (oral bisphosphonates — oesophagitis), ONJ (osteonecrosis of the jaw — rare, ~1 in 10,000-100,000 for osteoporosis doses, higher with IV doses for cancer), atypical femoral fractures (subtrochanteric/diaphyseal — stress fractures from over-suppressed remodelling, risk increases with duration >5 years — 'drug holiday' consideration).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 637,
              "stem": "Denosumab works by:",
              "options": [
                "Inhibiting COX enzymes like NSAIDs",
                "Stimulating osteoblasts like teriparatide",
                "Inhibiting sclerostin like romosozumab",
                "Blocking RANKL — a monoclonal antibody that binds and neutralises RANKL, preventing osteoclast formation, function, and survival → potent anti-resorptive effect",
                "Providing calcium directly"
              ],
              "answer": "D",
              "explanation": "Denosumab is a fully human monoclonal antibody that binds and neutralises RANKL (receptor activator of NF-κB ligand). RANKL is produced by osteoblasts and osteocytes — it binds to RANK on osteoclast precursors to stimulate osteoclast differentiation, activation, and survival. By neutralising RANKL: denosumab effectively BLOCKS osteoclast formation and function → potent suppression of bone resorption → increased BMD → reduced fracture risk. Given as SC injection every 6 MONTHS (60mg). Advantages: not renally excreted (safe in CKD — unlike bisphosphonates), convenient dosing (6-monthly). Key issue: REBOUND effect — when denosumab is DISCONTINUED, there is a rapid REBOUND increase in bone resorption (osteoclast numbers surge — the 'catching up' phenomenon) → rapid bone loss → increased fracture risk (particularly multiple vertebral fractures). Therefore: denosumab must be transitioned to a bisphosphonate BEFORE or IMMEDIATELY after stopping to prevent rebound. NEVER abruptly stop denosumab without a transition plan.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 638,
              "stem": "Teriparatide (recombinant PTH 1-34) is an anabolic osteoporosis agent. It works by:",
              "options": [
                "Inhibiting osteoclasts like bisphosphonates",
                "Blocking RANKL",
                "INTERMITTENT (pulsed) administration stimulating osteoblast activity more than osteoclast activity — resulting in NET BONE FORMATION (unlike continuous PTH, which causes net resorption)",
                "Inhibiting sclerostin",
                "Providing phosphate supplementation"
              ],
              "answer": "C",
              "explanation": "Teriparatide is recombinant PTH (amino acids 1-34). The key to its anabolic effect is INTERMITTENT (pulsed) administration: daily SC injection creates a brief peak of PTH → this preferentially stimulates OSTEOBLASTS (increases osteoblast number, activity, and lifespan) MORE than osteoclasts → NET BONE FORMATION. This is fundamentally different from CONTINUOUS PTH exposure (as in primary hyperparathyroidism) — which causes sustained osteoclast activation → net bone RESORPTION. The 'anabolic window': the period where formation exceeds resorption (typically the first 12-18 months of treatment). After this, formation and resorption rebalance. Treatment: daily SC injection for a MAXIMUM of 24 months (limited duration due to theoretical osteosarcoma risk — seen in rats with lifelong high-dose treatment; not confirmed in humans, but regulatory limit applies). After stopping teriparatide: MUST transition to anti-resorptive (bisphosphonate or denosumab) to maintain the bone gains — without this, the new bone is rapidly resorbed.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 639,
              "stem": "Warfarin exerts its anticoagulant effect by inhibiting which group of clotting factors?",
              "options": [
                "Factors V and VIII",
                "Factors II, VII, IX, and X (vitamin K-dependent)",
                "Factor Xa only",
                "Factor IIa only",
                "Factors XI and XII"
              ],
              "answer": "B",
              "explanation": "Warfarin inhibits vitamin K epoxide reductase, preventing the regeneration of active vitamin K. This impairs the carboxylation and activation of the vitamin K-dependent clotting factors: II (prothrombin), VII, IX, and X, as well as the anticoagulant proteins C and S. Factor VII has the shortest half-life, so the PT/INR rises first. Protein C also has a short half-life, which is why warfarin can initially be prothrombotic (protein C depleted before full anticoagulant factors decline) — hence overlap with heparin.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 640,
              "stem": "Local anaesthetics are less effective in infected tissues because:",
              "options": [
                "Bacteria directly inactivate the anaesthetic",
                "Increased blood flow washes the anaesthetic away",
                "Nerve fibres are destroyed by infection",
                "The patient is more anxious",
                "The acidic pH of infected tissue reduces the proportion of un-ionised (active) drug"
              ],
              "answer": "E",
              "explanation": "Local anaesthetics are weak bases. In their un-ionised form, they cross the nerve membrane to reach the intracellular site of action (sodium channel). In infected tissues, the pH is lower (acidic environment). This increases the proportion of ionised (charged) drug, which cannot cross the lipid membrane. Therefore, less drug reaches the target, reducing efficacy. This is why anaesthetising infected tissues (e.g., dental abscess) is clinically difficult.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 641,
              "stem": "Clopidogrel is an antiplatelet agent that works by:",
              "options": [
                "Blocking the ADP receptor (P2Y12) on platelets, preventing ADP-mediated platelet aggregation",
                "Inhibiting COX (like aspirin)",
                "Inhibiting Factor Xa",
                "Enhancing antithrombin III",
                "Directly inhibiting thrombin"
              ],
              "answer": "A",
              "explanation": "Clopidogrel is a thienopyridine antiplatelet agent that IRREVERSIBLY blocks the P2Y12 ADP receptor on platelets, preventing ADP-mediated platelet activation and aggregation. Platelets are affected for their entire lifespan (~7-10 days). It is used for: secondary prevention of cardiovascular events (ACS, stroke, PVD), and often in combination with aspirin (dual antiplatelet therapy — DAPT) after coronary stenting. In orthopaedic practice, clopidogrel must be stopped 7 days before elective surgery to allow new platelets to replace the irreversibly inhibited ones (platelet turnover ~10% per day). Aspirin can often be continued through surgery (lower bleeding risk). Emergency surgery in patients on clopidogrel: platelet transfusion may be needed if significant bleeding.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 642,
              "stem": "The mechanism of action of denosumab in the treatment of osteoporosis is:",
              "options": [
                "Inhibits osteoblast differentiation",
                "Directly kills osteoclasts",
                "Stimulates PTH secretion",
                "Inhibits vitamin D metabolism",
                "Monoclonal antibody against RANKL, preventing osteoclast activation"
              ],
              "answer": "E",
              "explanation": "Denosumab is a fully human monoclonal antibody that binds to RANKL (receptor activator of nuclear factor kappa-B ligand), preventing it from activating RANK on osteoclast precursors. This mimics the action of the natural decoy receptor osteoprotegerin (OPG). By blocking RANKL, denosumab inhibits osteoclast formation, function, and survival, thereby reducing bone resorption and increasing bone density. Given subcutaneously every 6 months. Unlike bisphosphonates, its effect is fully reversible — stopping treatment leads to rapid bone loss.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 643,
              "stem": "Teriparatide (recombinant PTH 1-34) treats osteoporosis by which mechanism?",
              "options": [
                "Inhibiting osteoclasts",
                "Stimulating osteoblast-mediated bone formation when given intermittently",
                "Increasing calcium absorption from the gut",
                "Inhibiting RANKL",
                "Blocking vitamin D receptors"
              ],
              "answer": "B",
              "explanation": "Teriparatide is the 1-34 fragment of PTH. When administered intermittently (daily subcutaneous injection), it paradoxically stimulates osteoblast activity more than osteoclast activity, leading to NET bone FORMATION (anabolic effect). This contrasts with continuous PTH elevation (as in hyperparathyroidism), which is catabolic (net resorption). It is the only widely used anabolic bone agent. Treatment duration: maximum 24 months. Used for severe osteoporosis, failed bisphosphonate therapy, or glucocorticoid-induced osteoporosis.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 644,
              "stem": "The DOACs (direct oral anticoagulants) rivaroxaban and apixaban work by inhibiting:",
              "options": [
                "Thrombin (Factor IIa) directly",
                "Vitamin K epoxide reductase",
                "Factor Xa directly",
                "Antithrombin III",
                "Platelet aggregation"
              ],
              "answer": "C",
              "explanation": "Rivaroxaban and apixaban are direct Factor Xa inhibitors. They selectively bind to and inhibit Factor Xa (both free and prothrombinase-bound), which is the convergence point of the intrinsic and extrinsic coagulation pathways. Dabigatran is a direct thrombin (Factor IIa) inhibitor. DOACs have predictable pharmacokinetics, require no routine monitoring (unlike warfarin/INR), have fewer drug/food interactions, and rapid onset of action. Reversal: andexanet alfa for Xa inhibitors, idarucizumab for dabigatran.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 645,
              "stem": "Tranexamic acid (TXA) reduces surgical blood loss by:",
              "options": [
                "Inhibiting platelet aggregation",
                "Activating the coagulation cascade",
                "Providing exogenous clotting factors",
                "Competitively inhibiting plasminogen activation → preventing fibrinolysis (clot breakdown)",
                "Increasing haemoglobin concentration"
              ],
              "answer": "D",
              "explanation": "TXA is a synthetic lysine analogue that competitively inhibits the activation of plasminogen to plasmin, thereby preventing fibrinolysis (breakdown of fibrin clots). This stabilises clots and reduces bleeding. It is now standard practice in trauma (CRASH-2 trial: TXA within 3 hours of major trauma reduces mortality with no increase in thromboembolic events) and elective arthroplasty (reduces blood loss by 30-50%, transfusion rates, and costs). Topical TXA applied directly to the wound is also effective.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 646,
              "stem": "NSAIDs exert their anti-inflammatory and analgesic effect by inhibiting which enzyme?",
              "options": [
                "Lipoxygenase",
                "Phospholipase A2",
                "Cyclooxygenase (COX)",
                "Monoamine oxidase",
                "Xanthine oxidase"
              ],
              "answer": "C",
              "explanation": "NSAIDs inhibit cyclooxygenase (COX) enzymes, preventing the conversion of arachidonic acid to prostaglandins and thromboxanes. COX-1: constitutive (protects gastric mucosa, maintains renal blood flow, promotes platelet aggregation). COX-2: inducible (mediates inflammation, pain, fever). Non-selective NSAIDs (ibuprofen, diclofenac, naproxen) inhibit both COX-1 and COX-2 → anti-inflammatory + analgesic but risk GI ulceration and renal impairment. COX-2 selective (celecoxib): reduced GI side effects but cardiovascular risk.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 647,
              "stem": "The specific reversal agent for dabigatran (direct thrombin inhibitor) is:",
              "options": [
                "Idarucizumab (Praxbind)",
                "Vitamin K",
                "Protamine sulphate",
                "Andexanet alfa",
                "Fresh frozen plasma"
              ],
              "answer": "A",
              "explanation": "Idarucizumab (Praxbind) is a monoclonal antibody fragment that specifically binds and neutralises dabigatran within minutes. It was approved after the RE-VERSE AD trial demonstrated rapid and complete reversal. Andexanet alfa reverses Factor Xa inhibitors (rivaroxaban, apixaban). Vitamin K reverses warfarin (slow, 6-24h). Protamine reverses unfractionated heparin (partially reverses LMWH). PCC (prothrombin complex concentrate) provides rapid warfarin reversal and can be used for DOAC-related bleeding when specific reversal agents are unavailable.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 648,
              "stem": "Unfractionated heparin (UFH) exerts its anticoagulant effect by:",
              "options": [
                "Inhibiting vitamin K-dependent clotting factors",
                "Enhancing the activity of antithrombin III (which then inhibits thrombin and factor Xa)",
                "Directly inhibiting factor Xa only",
                "Inhibiting platelet aggregation via COX",
                "Promoting fibrinolysis"
              ],
              "answer": "B",
              "explanation": "Unfractionated heparin enhances the activity of antithrombin III (AT-III) approximately 1000-fold. The heparin-AT-III complex then inhibits multiple clotting factors, primarily thrombin (factor IIa) and factor Xa. LMWH (low molecular weight heparin, e.g., enoxaparin) also works via AT-III but primarily inhibits factor Xa (with less effect on thrombin). UFH is monitored by APTT (activated partial thromboplastin time). LMWH does not typically require monitoring (predictable pharmacokinetics) but anti-Xa levels can be measured if needed (renal impairment, extremes of weight). UFH reversal: protamine sulphate.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 649,
              "stem": "The reversal agent for warfarin (vitamin K antagonist) in a patient with life-threatening bleeding is:",
              "options": [
                "Protamine sulphate",
                "Idarucizumab",
                "Andexanet alfa",
                "Platelet transfusion",
                "Fresh frozen plasma (FFP) or prothrombin complex concentrate (PCC/Beriplex)"
              ],
              "answer": "E",
              "explanation": "For life-threatening warfarin-related bleeding: IV vitamin K (phytomenadione, 5-10mg — slow to act, 6-12 hours) PLUS immediate reversal with PCC (prothrombin complex concentrate/Beriplex — contains factors II, VII, IX, X — fast onset, 15-30 minutes) or FFP (if PCC unavailable — requires larger volume, slower). PCC is preferred over FFP (faster, smaller volume, more predictable). Protamine reverses heparin. Idarucizumab reverses dabigatran. Andexanet alfa reverses factor Xa inhibitors (rivaroxaban, apixaban). Always give vitamin K as well (PCC effect is temporary, vitamin K provides sustained reversal).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 650,
              "stem": "Denosumab is a monoclonal antibody used for osteoporosis that works by:",
              "options": [
                "Inhibiting osteoblast function",
                "Inhibiting sclerostin",
                "Providing exogenous vitamin D",
                "Binding to RANKL (preventing osteoclast activation and maturation)",
                "Stimulating PTH release"
              ],
              "answer": "D",
              "explanation": "Denosumab is a fully human monoclonal antibody that binds to RANKL (receptor activator of nuclear factor kappa-B ligand), preventing it from activating its receptor RANK on osteoclast precursors. This inhibits osteoclast differentiation, activation, and survival — reducing bone resorption. It mimics the natural action of OPG (osteoprotegerin, the body's endogenous RANKL decoy receptor). Given as subcutaneous injection every 6 months. Key concern: rebound effect — rapid bone loss and increased fracture risk if denosumab is stopped without transitioning to another anti-resorptive (bisphosphonate). Must transition to bisphosphonate before or immediately after stopping denosumab.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 651,
              "stem": "Teriparatide is the only currently available anabolic agent for osteoporosis that works by:",
              "options": [
                "Inhibiting osteoclasts",
                "Providing calcium supplementation",
                "Inhibiting RANKL",
                "Blocking sclerostin",
                "Intermittent PTH administration stimulating osteoblast activity and new bone formation"
              ],
              "answer": "E",
              "explanation": "Teriparatide is recombinant human PTH 1-34 (the biologically active N-terminal fragment of parathyroid hormone). When given intermittently (daily SC injection for 24 months maximum), it stimulates osteoblast activity more than osteoclast activity — resulting in NET bone formation (anabolic effect). This is paradoxical: continuous PTH elevation (as in hyperparathyroidism) causes bone RESORPTION, but intermittent pulses preferentially stimulate formation. It increases BMD more effectively than bisphosphonates, particularly in the spine. After the 24-month course, must transition to an anti-resorptive to maintain gains. Contraindications: Paget disease, unexplained raised ALP, prior skeletal radiation, bone metastases, hypercalcaemia, children (open physes).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 652,
              "stem": "Vitamin D (calcitriol/1,25-dihydroxyvitamin D3) is the active form. The final hydroxylation step converting 25-hydroxyvitamin D to the active 1,25-dihydroxyvitamin D3 occurs in the:",
              "options": [
                "Skin",
                "Liver",
                "Bone",
                "Kidney (1α-hydroxylase enzyme in the proximal tubule)",
                "Intestine"
              ],
              "answer": "D",
              "explanation": "Vitamin D metabolism: (1) Cholecalciferol (D3) is synthesised in the SKIN from 7-dehydrocholesterol under UV-B radiation (or obtained from diet). (2) It is hydroxylated in the LIVER to 25-hydroxyvitamin D (calcidiol) by 25-hydroxylase — this is the main circulating form and the level measured clinically to assess vitamin D status. (3) The final activation step occurs in the KIDNEY: 1α-hydroxylase in the proximal tubule converts 25(OH)D to 1,25-dihydroxyvitamin D3 (calcitriol) — the active hormone. Calcitriol increases intestinal calcium and phosphate absorption, promotes bone mineralisation, and supports renal calcium reabsorption. In CKD, the final hydroxylation step is impaired → deficiency of active vitamin D → hypocalcaemia → secondary hyperparathyroidism → renal osteodystrophy.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Anatomy",
          "range": "Q653-Q671",
          "questions": [
            {
              "number": 653,
              "stem": "The rotator cuff consists of four muscles. The one that is NOT part of the rotator cuff is:",
              "options": [
                "Supraspinatus",
                "TERES MAJOR (it is NOT part of the rotator cuff — it inserts on the medial lip of the bicipital groove, not on the greater or lesser tuberosity, and is innervated by the lower subscapular nerve)",
                "Infraspinatus",
                "Teres minor",
                "Subscapularis"
              ],
              "answer": "B",
              "explanation": "The four rotator cuff muscles (SITS): (1) SUPRASPINATUS (suprascapular nerve C5-C6 — initiates abduction 0-15°, inserts on the superior facet of the greater tuberosity, MOST COMMONLY torn cuff tendon). (2) INFRASPINATUS (suprascapular nerve C5-C6 — external rotation, inserts on the middle facet of the greater tuberosity). (3) TERES MINOR (axillary nerve C5-C6 — external rotation, inserts on the inferior facet of the greater tuberosity). (4) SUBSCAPULARIS (upper and lower subscapular nerves C5-C7 — internal rotation, inserts on the LESSER tuberosity — the only cuff muscle on the anterior side). TERES MAJOR is NOT part of the rotator cuff — it originates from the inferior angle of the scapula and inserts on the MEDIAL lip of the bicipital groove (alongside the latissimus dorsi). It is innervated by the lower subscapular nerve. It acts as an internal rotator, adductor, and extensor of the shoulder — functionally similar to latissimus dorsi, not the rotator cuff.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 654,
              "stem": "The common peroneal nerve (CPN) is most vulnerable to injury at the:",
              "options": [
                "Ankle joint",
                "Posterior knee",
                "Fibular NECK (the nerve winds around the neck of the fibula superficially — vulnerable to compression from casts, crossing legs, leg positioning during surgery, and direct trauma)",
                "Hip joint",
                "Inguinal ligament"
              ],
              "answer": "C",
              "explanation": "The CPN (branch of the sciatic nerve, L4-S2) is most vulnerable at the FIBULAR NECK (lateral aspect of the proximal fibula) where it winds superficially around the bone — there is minimal soft tissue protection here. Causes of CPN palsy: (1) external COMPRESSION (tight plaster cast — ALWAYS split casts and check CPN function, crossing legs, lithotomy position during surgery, compression stockings), (2) direct TRAUMA (fibular head/neck fracture, PLC knee injury — 25-30% of PLC injuries have CPN injury), (3) traction (knee dislocation, valgus osteotomy correction), (4) iatrogenic (lateral meniscal repair, proximal tibial surgery). CPN palsy causes: FOOT DROP (loss of ankle dorsiflexion — tibialis anterior, EHL, EDL), loss of foot eversion (peroneus longus/brevis), and numbness in the first dorsal web space and lateral leg. Deep peroneal nerve: motor to anterior compartment (dorsiflexion) + sensory first web space. Superficial peroneal nerve: motor to lateral compartment (eversion) + sensory dorsum of foot. Treatment: remove compressive cause, AFO (ankle-foot orthosis — prevents equinus and provides foot clearance during gait), nerve exploration if no recovery by 3 months.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 655,
              "stem": "The anatomical snuffbox is bounded by the tendons of APL and EPB (radially) and EPL (ulnarly). The most clinically important structure at its floor is the:",
              "options": [
                "Scaphoid bone (palpated here for tenderness — clinical test for scaphoid fracture) and the radial artery",
                "Ulnar nerve",
                "Median nerve",
                "Lunate bone",
                "Triquetrum"
              ],
              "answer": "A",
              "explanation": "The anatomical snuffbox (radial fossa) is a triangular depression on the radial side of the wrist, bounded by: radial border = APL and EPB tendons (1st dorsal compartment), ulnar border = EPL tendon (3rd dorsal compartment). The FLOOR contains: (1) SCAPHOID bone (palpable — tenderness here after a fall is the clinical test for suspected scaphoid fracture, 'scaphoid tenderness = fracture until proven otherwise'), (2) RADIAL ARTERY (passes through the snuffbox — palpable pulse). (3) Trapezium and radial styloid are also in the vicinity. The superficial branch of the radial nerve crosses superficially over the snuffbox (at risk during procedures in this area — including K-wire insertion for scaphoid, and radial styloid injection for de Quervain). The cephalic vein also crosses superficially.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 656,
              "stem": "The femoral triangle is bounded by the inguinal ligament superiorly, sartorius laterally, and adductor longus medially. The order of structures from lateral to medial within the triangle is:",
              "options": [
                "Vein, Artery, Nerve (VAN)",
                "Artery, Nerve, Vein",
                "Nerve, Vein, Artery",
                "Nerve, Artery, Vein (NAV — Nerve most lateral, Artery in the middle, Vein most medial, with Lymphatics even more medial)",
                "All structures are randomly arranged"
              ],
              "answer": "D",
              "explanation": "Within the femoral triangle, from LATERAL to MEDIAL: Nerve (femoral nerve), Artery (femoral artery — palpable pulse), Vein (femoral vein), with Lymphatics (deep inguinal lymph nodes and lymphatic vessels) most medially. Mnemonic: NAVL or 'NAVY' (Nerve, Artery, Vein, Y-fronts/lymphatics). This is clinically important: (1) femoral arterial puncture (cardiac catheterisation) — the artery is palpated, and the vein lies immediately MEDIAL to it. (2) Femoral nerve block — the nerve lies LATERAL to the artery. (3) The femoral nerve is at risk in the anterior approach to the hip (retraction of iliopsoas/sartorius). (4) The femoral hernia: passes through the femoral canal (the most medial compartment of the femoral sheath, medial to the vein) — bounded by: inguinal ligament (anterior), pectineal ligament/Cooper's ligament (posterior), lacunar ligament (medial), femoral vein (lateral).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 657,
              "stem": "The sciatic nerve exits the pelvis through the greater sciatic foramen, typically:",
              "options": [
                "BELOW the piriformis muscle (inferior to piriformis, passing between piriformis and the gemelli/obturator internus — this is the standard anatomical relationship in ~85-90% of people)",
                "Above the piriformis muscle",
                "Through the lesser sciatic foramen",
                "Through the obturator foramen",
                "Through the inguinal canal"
              ],
              "answer": "A",
              "explanation": "The sciatic nerve (L4-S3, the largest nerve in the body) exits the pelvis through the GREATER SCIATIC FORAMEN, passing INFERIOR to (below) the PIRIFORMIS muscle in ~85-90% of the population. In ~10-15% of people, the nerve (or one of its divisions — usually the common peroneal component) passes THROUGH the piriformis muscle belly → this variant may predispose to piriformis syndrome (sciatic nerve compression by the piriformis). The sciatic nerve then descends in the posterior thigh between the greater trochanter and the ischial tuberosity (the 'safe zone' for the posterior approach to the hip — external rotators are divided to access the hip capsule, and the sciatic nerve lies deep to the short external rotators, protected by maintaining these muscles between the retractor and the nerve). The nerve divides into the TIBIAL nerve and COMMON PERONEAL nerve, typically at the apex of the popliteal fossa (but can divide higher — even within the pelvis).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 658,
              "stem": "The lateral cutaneous nerve of the thigh (LFCN) arises from:",
              "options": [
                "L1 only",
                "S1-S2",
                "C5-C6",
                "T10-T12",
                "L2-L3 (pure sensory nerve — passes beneath or through the inguinal ligament near the ASIS, supplying sensation to the anterolateral thigh)"
              ],
              "answer": "E",
              "explanation": "The LFCN arises from the posterior divisions of L2-L3. It is a PURE SENSORY nerve (no motor function). It passes beneath (or through, in some anatomical variants) the inguinal ligament near the ASIS, then runs superficially in the thigh to supply sensation to the ANTEROLATERAL THIGH. Clinical relevance: (1) at risk during the anterior approach (DAA) to the hip (~3-15% injury rate → meralgia paraesthetica — numbness/tingling anterolateral thigh). (2) Also at risk during iliac crest bone graft harvesting (anterior approach to the iliac crest). (3) Meralgia paraesthetica (spontaneous LFCN compression): can occur without surgery — from tight clothing, obesity, pregnancy, diabetes, or idiopathic compression at the inguinal ligament. Symptoms: burning, numbness, or tingling on the anterolateral thigh. No motor loss (pure sensory). Treatment: conservative (remove compressive factors, weight loss, loose clothing) → local anaesthetic/corticosteroid injection at the inguinal ligament → surgical decompression/neurectomy (rare). Most resolve spontaneously.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 659,
              "stem": "The anterior interosseous nerve (AIN) is a pure motor branch of the median nerve. It innervates:",
              "options": [
                "Thenar muscles",
                "All forearm flexors",
                "FDP to index and middle fingers, FPL, and pronator quadratus",
                "Wrist extensors",
                "Intrinsic hand muscles"
              ],
              "answer": "C",
              "explanation": "The AIN (branch of the median nerve, arising ~5-8cm distal to the lateral epicondyle) is a PURE MOTOR nerve innervating three muscles: (1) FPL (flexor pollicis longus — thumb IP flexion), (2) FDP to the index finger (and sometimes middle finger) — DIP flexion of index, and (3) pronator quadratus (forearm pronation). The classic clinical test: ask the patient to make an 'OK sign' (pinch between thumb tip and index fingertip forming a circle). In AIN palsy: the patient cannot flex the thumb IP or index DIP → the 'OK sign' becomes a triangle (pinch with extended IP joints rather than flexed). Causes: Kiloh-Nevin syndrome (AIN neuritis), fibrous bands, deep head of pronator teres compression, fractures. There is NO sensory loss (pure motor nerve).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 660,
              "stem": "The nerve at greatest risk during a lateral malleolus fixation (posterolateral approach) is the:",
              "options": [
                "Tibial nerve",
                "Sural nerve (runs posterior to the lateral malleolus, at risk with posterior plating/lag screw insertion)",
                "Deep peroneal nerve",
                "Saphenous nerve",
                "Common peroneal nerve"
              ],
              "answer": "B",
              "explanation": "The sural nerve runs behind the lateral malleolus (between the peroneal tendons and the Achilles tendon) and is at risk during lateral malleolus fixation, particularly with posterolateral plate placement and posterior-to-anterior lag screw insertion. Injury causes numbness on the lateral border of the foot and little toe. The nerve should be identified and protected during dissection. The superficial peroneal nerve is at risk during anterolateral approaches to the ankle (crossing the anterolateral ankle ~7-10 cm above the joint). The deep peroneal nerve is at risk during anterior ankle approaches. The saphenous nerve is at risk during medial malleolus fixation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 661,
              "stem": "The dermatome of the lateral aspect of the forearm and thumb is supplied by:",
              "options": [
                "C6",
                "C5",
                "C7",
                "C8",
                "T1"
              ],
              "answer": "A",
              "explanation": "C6 dermatome: lateral forearm, thumb, and index finger (palmar and dorsal). Key myotome: wrist extensors (ECRL, ECRB), biceps. Reflex: biceps jerk and brachioradialis reflex. C6/C7 disc herniation → C7 root compression is the most common cervical radiculopathy. Dermatome testing is essential for localising nerve root lesions. Adjacent dermatomes overlap significantly, so isolated loss in one dermatome may be subtle.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 662,
              "stem": "The corticospinal (pyramidal) tract crosses to the contralateral side at which level?",
              "options": [
                "Cerebral cortex",
                "Internal capsule",
                "Medullary pyramids (pyramidal decussation at the cervicomedullary junction)",
                "C3-C4 spinal cord level",
                "Lumbar enlargement"
              ],
              "answer": "C",
              "explanation": "The corticospinal tract (primary motor pathway) originates in the motor cortex, descends through the internal capsule and cerebral peduncle, and the majority of fibres (~80-85%) cross to the contralateral side at the pyramidal decussation in the medulla oblongata (cervicomedullary junction). These crossed fibres form the lateral corticospinal tract. The remaining ~15-20% of uncrossed fibres form the anterior corticospinal tract (cross at segmental levels). This is clinically important: a unilateral brain lesion causes CONTRALATERAL motor deficit, while a unilateral spinal cord lesion below the decussation causes IPSILATERAL motor deficit.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 663,
              "stem": "The spinothalamic tract carries which sensory modalities?",
              "options": [
                "Proprioception and vibration",
                "Fine touch and two-point discrimination",
                "Motor commands",
                "Pain and temperature (and crude touch)",
                "Cerebellar coordination"
              ],
              "answer": "D",
              "explanation": "The spinothalamic tract carries pain, temperature, and crude touch. It crosses to the contralateral side within 1-2 segments of entering the spinal cord (anterior white commissure). This is clinically significant in Brown-Séquard syndrome (hemisection of the cord): ipsilateral motor loss (corticospinal tract — already crossed above) + ipsilateral proprioception/vibration loss (dorsal columns — cross in the medulla) + CONTRALATERAL pain/temperature loss (spinothalamic — crosses in the cord). The dorsal columns (fasciculus gracilis and cuneatus) carry proprioception, vibration, and fine touch — they cross at the medulla (medial lemniscus).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 664,
              "stem": "The femoral nerve (L2, L3, L4) innervates which muscle group?",
              "options": [
                "Hip adductors",
                "Quadriceps (knee extension) and iliacus (hip flexion)",
                "Hamstrings",
                "Gluteal muscles",
                "Ankle dorsiflexors"
              ],
              "answer": "B",
              "explanation": "The femoral nerve (L2-L4, posterior division of the lumbar plexus) innervates the quadriceps femoris (rectus femoris, vastus medialis, lateralis, intermedius) for knee extension, and iliacus (with psoas, forming iliopsoas) for hip flexion. It also provides the saphenous nerve (pure sensory — longest cutaneous nerve in the body), which supplies sensation to the medial leg and medial foot. The femoral nerve passes beneath the inguinal ligament, lateral to the femoral artery (NAVY: Nerve, Artery, Vein, Y-fronts = lateral to medial). It is at risk in the anterior approach to the hip and during anterior pelvic surgery.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 665,
              "stem": "The obturator nerve (L2-L4) innervates which muscle group?",
              "options": [
                "Quadriceps",
                "Hamstrings",
                "Gluteals",
                "Ankle dorsiflexors",
                "Hip adductors (adductor longus, brevis, magnus anterior, gracilis, obturator externus)"
              ],
              "answer": "E",
              "explanation": "The obturator nerve arises from the anterior divisions of L2-L4 and exits the pelvis through the obturator foramen. It innervates the hip adductor muscles (adductor longus, adductor brevis, gracilis, obturator externus, and the anterior/adductor portion of adductor magnus — the posterior/hamstring portion of adductor magnus is innervated by the sciatic nerve). It provides sensation to the medial thigh. Clinically important: obturator nerve block may be needed during TURBT (to prevent adductor spasm during resection of lateral bladder wall tumours). In orthopaedics, referred pain from the hip can follow the obturator nerve distribution to the medial thigh and knee — hip pathology can present as knee pain.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 666,
              "stem": "The ulnar nerve enters the hand through:",
              "options": [
                "Carpal tunnel",
                "Guyon canal (between the pisiform and hook of hamate)",
                "Cubital tunnel",
                "Anatomical snuffbox",
                "Triangular fibrocartilage"
              ],
              "answer": "B",
              "explanation": "The ulnar nerve enters the hand through Guyon canal (ulnar tunnel) — a fibro-osseous tunnel at the wrist between the pisiform (medially) and the hook of hamate (laterally), roofed by the pisohamate ligament and palmar carpal ligament. The ulnar artery also passes through Guyon canal. Within the canal, the ulnar nerve divides into: (1) deep motor branch (innervates all interossei, adductor pollicis, hypothenar muscles, lumbricals 3-4), and (2) superficial sensory branch (little finger and ulnar half of ring finger palmar sensation). Guyon canal compression causes ulnar tunnel syndrome — different from cubital tunnel syndrome (compression at the elbow). Causes of Guyon canal compression: ganglion cysts (most common), hook of hamate fractures (cyclists), ulnar artery thrombosis/aneurysm, and repetitive trauma (handlebar palsy in cyclists).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 667,
              "stem": "The blood supply to the menisci comes from the perimeniscal capillary plexus. What percentage of the meniscus (from the periphery) is vascular and amenable to repair?",
              "options": [
                "100% — the entire meniscus is vascular",
                "50-75%",
                "Only 5%",
                "The peripheral 10-30% (red-red zone)",
                "0% — the meniscus is entirely avascular"
              ],
              "answer": "D",
              "explanation": "The peripheral 10-30% of the meniscus receives blood supply from the perimeniscal capillary plexus (genicular arteries). This is the red-red zone — tears here have healing potential and should be repaired. The inner 70-90% is avascular (white-white zone) — nutrition from synovial fluid diffusion only, poor healing → partial meniscectomy for irreparable tears. The red-white zone (junction) has variable healing potential. Modern philosophy strongly favours meniscal preservation wherever possible — meniscectomy accelerates OA progression (Fairbank changes: joint space narrowing, osteophyte formation, flattening of the femoral condyle).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 668,
              "stem": "The interossei muscles of the hand are innervated by which nerve?",
              "options": [
                "Median nerve",
                "Radial nerve",
                "Musculocutaneous nerve",
                "Anterior interosseous nerve",
                "Ulnar nerve (deep branch)"
              ],
              "answer": "E",
              "explanation": "All interossei (4 dorsal and 3 palmar) are innervated by the deep branch of the ulnar nerve. The dorsal interossei ABDUCT the fingers (DAB = Dorsal ABduct, mnemonic) and the palmar interossei ADDUCT (PAD = Palmar ADduct). The 1st dorsal interosseous (between thumb and index) is the most commonly tested muscle for ulnar nerve function — tested by resisted index finger abduction. The ulnar nerve also innervates: adductor pollicis, hypothenar muscles (abductor digiti minimi, flexor digiti minimi, opponens digiti minimi), 3rd and 4th lumbricals, and palmaris brevis.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 669,
              "stem": "The popliteal fossa is bounded by which structures superiorly?",
              "options": [
                "Gastrocnemius medial and lateral heads",
                "Soleus and plantaris",
                "Biceps femoris (laterally) and semimembranosus/semitendinosus (medially)",
                "Popliteus and posterior capsule",
                "Adductor magnus and gracilis"
              ],
              "answer": "C",
              "explanation": "Popliteal fossa boundaries: Superior-lateral = biceps femoris. Superior-medial = semimembranosus (with semitendinosus superficial). Inferior-lateral = lateral head of gastrocnemius (and plantaris). Inferior-medial = medial head of gastrocnemius. Floor = posterior femur, oblique popliteal ligament, posterior capsule, and popliteus. Roof = skin and deep fascia. Contents: popliteal artery (deepest, against bone — at risk in knee dislocations), popliteal vein, tibial nerve, common peroneal nerve (follows biceps femoris medial border to fibular neck), short saphenous vein, lymph nodes.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 670,
              "stem": "The ligamentum flavum connects adjacent vertebral laminae and is composed predominantly of:",
              "options": [
                "Elastic tissue (elastin ~80%, collagen ~20%)",
                "Type I collagen",
                "Type II collagen",
                "Bone",
                "Fibrocartilage"
              ],
              "answer": "A",
              "explanation": "The ligamentum flavum is the most elastic ligament in the body, composed of approximately 80% elastin and 20% collagen. This high elastin content gives it a yellow colour (flavum = yellow in Latin) and allows it to stretch during flexion and recoil during extension without buckling into the spinal canal. With ageing and degeneration, the elastic tissue is replaced by collagen and the ligament hypertrophies — this contributes significantly to lumbar spinal stenosis (ligamentum flavum hypertrophy narrows the spinal canal from posteriorly). The ligamentum flavum runs from the anteroinferior surface of the lamina above to the posterosuperior surface of the lamina below.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 671,
              "stem": "The sciatic nerve divides into the tibial nerve and common peroneal nerve. The most common level of division is:",
              "options": [
                "At the hip joint",
                "At the greater sciatic foramen",
                "In the popliteal fossa (upper popliteal fossa, typically at the apex)",
                "At the ankle",
                "In the mid-thigh always"
              ],
              "answer": "C",
              "explanation": "The sciatic nerve most commonly divides into its two terminal branches — the tibial nerve and the common peroneal (fibular) nerve — in the UPPER POPLITEAL FOSSA, typically at or above the apex of the popliteal fossa (the upper third of the thigh in some descriptions). However, there is significant anatomical variation: in ~10-12% of individuals, the sciatic nerve divides within the pelvis or gluteal region (the peroneal division may pass through or above the piriformis separately). The tibial nerve continues distally in the popliteal fossa (between the heads of gastrocnemius, posterior to the popliteal vessels) to supply the posterior leg compartment and foot plantarflexors. The CPN winds around the fibular neck superficially to supply the anterior and lateral leg compartments.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Biomechanics",
          "range": "Q672-Q679",
          "questions": [
            {
              "number": 672,
              "stem": "Stress shielding around a femoral stem in THA is caused by:",
              "options": [
                "The implant bearing too much of the mechanical load (the stiffer implant preferentially carries stress, depriving the adjacent bone of its normal loading stimulus → bone resorption per Wolff's law)",
                "Excessive loading of the bone",
                "Increased bone density around the implant",
                "Infection",
                "Cement mantle failure"
              ],
              "answer": "A",
              "explanation": "Stress shielding occurs when a stiff implant (particularly a large-diameter, proximally-coated uncemented stem) carries a disproportionate amount of the mechanical load — this deprives the surrounding bone of its normal physiological stress stimulus. According to Wolff's law, bone remodels in response to the loads placed upon it: if loading decreases, bone resorbs (use it or lose it). This manifests as progressive proximal femoral bone resorption (particularly in Gruen zones 1 and 7 — the greater and lesser trochanteric regions) visible on serial radiographs. Factors increasing stress shielding: stiffer implant material (CoCr > titanium), larger stem diameter, longer porous coating (extensive coating = distal fixation → proximal stress bypass), and press-fit fixation. Factors reducing stress shielding: titanium alloy (lower modulus → less stiff), shorter stems, proximal-only coating (loads transferred proximally), and cemented fixation (cement distributes loads more evenly).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 673,
              "stem": "Wolff's law states that:",
              "options": [
                "Bone only resorbs and never forms",
                "Bone density is constant throughout life",
                "Loading has no effect on bone structure",
                "Only cortical bone responds to loading",
                "Bone remodels in response to the mechanical loads placed upon it — it becomes stronger where stressed and weaker where unstressed"
              ],
              "answer": "E",
              "explanation": "Wolff's law (Julius Wolff, 1892) states that bone adapts its structure to the mechanical demands placed upon it. Under increased loading: bone becomes stronger and denser (increased cortical thickness, trabecular realignment along stress lines). Under decreased loading: bone resorbs and weakens (disuse osteopaenia — seen in immobilisation, bed rest, spaceflight). This principle underpins: stress shielding (stiff implant reduces bone loading → resorption), fracture healing (functional loading promotes callus formation), rehabilitation (weight-bearing strengthens healing bone), and exercise prescription for osteoporosis (weight-bearing exercise increases BMD). Both cortical and trabecular bone respond to loading. The mechanostat model (Frost) refined Wolff's law: bone has a mechanical set point — loads above the threshold stimulate formation, loads below stimulate resorption.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 674,
              "stem": "Creep is a material property relevant to orthopaedics. It refers to:",
              "options": [
                "Sudden fracture under load",
                "Time-dependent progressive deformation of a material under constant load (the material slowly deforms even though the load doesn't increase)",
                "Elastic recovery after loading",
                "The material getting stronger under load",
                "Fatigue failure from cyclic loading"
              ],
              "answer": "B",
              "explanation": "Creep is the time-dependent progressive deformation (plastic deformation) of a material under a CONSTANT sustained load. Even though the applied stress doesn't change, the material slowly deforms over time. Clinical relevance: (1) UHMWPE bearing surfaces in arthroplasty undergo creep — the polyethylene slowly deforms under the sustained joint loads, contributing to penetration (the femoral head 'sinks' into the PE — bedding-in). (2) Intervertebral disc creep — sustained axial loading causes gradual height loss throughout the day (you are ~1-2cm shorter at night than in the morning). (3) Viscoelastic tissues (ligaments, tendons, cartilage) all exhibit creep behaviour. (4) Bone under sustained loading can creep (stress fractures partly result from accumulated creep damage). Creep is different from: elastic deformation (recovers immediately), plastic deformation (permanent but occurs instantly at yield), and fatigue failure (cyclic loading, not constant).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 675,
              "stem": "Viscoelastic materials exhibit time-dependent mechanical behaviour. Creep is defined as:",
              "options": [
                "Increasing stress under constant strain",
                "Sudden fracture without warning",
                "Recovery of original shape after load removal",
                "Progressive deformation (increasing strain) under constant load over time",
                "Decreased stiffness at high loading rates"
              ],
              "answer": "D",
              "explanation": "Creep is the progressive increase in strain (deformation) over time under a constant applied load/stress. It is a characteristic behaviour of viscoelastic materials — bone, cartilage, tendons, ligaments, and intervertebral discs all exhibit creep. Clinical relevance: disc height decreases during the day (creep under axial load) and recovers during sleep (we are ~1-2 cm taller in the morning). Stress relaxation is the opposite: decreasing stress over time under constant strain (e.g., ligament stretching during sustained manipulation).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 676,
              "stem": "The stress-strain curve of a material — the yield point represents:",
              "options": [
                "The point at which permanent (plastic) deformation begins — beyond this, the material will not return to its original shape",
                "The point at which the material fractures completely",
                "The point of maximum elastic deformation with full recovery",
                "The point of zero strain",
                "The point where the material melts"
              ],
              "answer": "A",
              "explanation": "The yield point on a stress-strain curve marks the transition from elastic deformation (reversible — material returns to original shape when load removed) to plastic deformation (permanent — material does not return to original shape). Below yield point: Hooke's law applies (stress proportional to strain), elastic modulus (Young's modulus) = slope of the elastic region = measure of stiffness. Beyond yield point: permanent deformation accumulates. Ultimate tensile strength (UTS): maximum stress the material can withstand. Fracture point: material fails completely. Understanding these concepts is essential for implant design and fracture mechanics.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 677,
              "stem": "Fatigue failure of an orthopaedic implant occurs when:",
              "options": [
                "The implant is loaded once beyond its ultimate strength",
                "The implant corrodes",
                "Repeated cyclic loading below the yield point eventually causes crack initiation and propagation leading to fracture",
                "The implant is too large",
                "The bone heals completely"
              ],
              "answer": "C",
              "explanation": "Fatigue failure results from repeated cyclic loading at stress levels BELOW the yield point of the material. Each loading cycle causes microscopic damage (crack initiation at stress concentrators — notches, screw holes, surface defects). With continued cycling, the crack propagates until the remaining cross-section is insufficient to bear the load → catastrophic fracture. The S-N curve (stress vs number of cycles to failure) characterises fatigue behaviour. Some materials (steel) have an endurance limit (stress below which fatigue failure never occurs). Others (titanium, aluminium) do not have a true endurance limit. Clinical examples: broken plates/screws in non-unions, IM nail fatigue failure, implant fracture after long-term use.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 678,
              "stem": "Young modulus (elastic modulus) of a material represents:",
              "options": [
                "The maximum stress before failure",
                "The total energy absorbed before fracture",
                "The amount of plastic deformation",
                "Stiffness — the ratio of stress to strain in the elastic region of the stress-strain curve",
                "The fatigue life of the material"
              ],
              "answer": "D",
              "explanation": "Young modulus (E) = stress / strain in the linear (elastic) region of the stress-strain curve. It represents STIFFNESS — a higher Young modulus means the material deforms less for a given applied stress (stiffer material). Steel E ≈ 200 GPa. Titanium E ≈ 110 GPa. Cortical bone E ≈ 17-20 GPa. PMMA cement E ≈ 2-3 GPa. UHMWPE E ≈ 1 GPa. The clinical significance: a stiffer implant (higher E) bears more load and shields the bone from stress (stress shielding → proximal bone resorption around stiff femoral stems). Titanium's lower modulus compared to stainless steel results in less stress shielding — one reason titanium is preferred for many orthopaedic implants.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 679,
              "stem": "In fracture fixation, the concept of 'strain' at the fracture site determines the type of tissue that forms. According to Perren's strain theory, what strain level promotes direct bone formation?",
              "options": [
                "100% strain",
                "10-50% strain",
                "2-10% strain (fibrocartilage)",
                "Strain has no effect on healing tissue",
                "<2% strain (direct bone healing)"
              ],
              "answer": "E",
              "explanation": "Perren's interfragmentary strain theory: the type of tissue that forms at a fracture site depends on the strain (deformation relative to the gap width). Strain = displacement/gap width. Different tissues tolerate different maximum strain levels before they fail: granulation tissue tolerates 100% strain, fibrous tissue ~10-17%, fibrocartilage ~10%, lamellar bone ~2%, and woven bone ~10%. Therefore: (1) <2% strain → direct (primary) bone healing (cutting cones cross the fracture — requires absolute stability, e.g., compression plating with lag screws). (2) 2-10% → secondary healing via callus (endochondral ossification — relative stability, e.g., IM nailing, bridging plate). (3) >10% → only fibrous tissue forms (non-union if persistent). The surgeon's choice of fixation construct determines the strain environment.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            }
          ]
        },
        {
          "title": "Metabolic Bone",
          "range": "Q680-Q685",
          "questions": [
            {
              "number": 680,
              "stem": "Paget disease of bone is characterised by disordered bone remodelling with markedly elevated:",
              "options": [
                "Serum calcium (always elevated)",
                "Alkaline phosphatase (ALP — reflects massively increased osteoblast activity during the mixed/sclerotic phases)",
                "Serum phosphate",
                "Parathyroid hormone",
                "Vitamin D"
              ],
              "answer": "B",
              "explanation": "Paget disease involves chaotic, accelerated bone remodelling in three phases: (1) Lytic phase (osteoclast-dominant — large multinucleated osteoclasts with up to 100 nuclei vs normal 3-5), (2) Mixed phase (concurrent resorption and formation), (3) Sclerotic/quiescent phase (dense, disorganised woven bone — 'mosaic' pattern on histology). ALP is MARKEDLY elevated (often 5-20× normal) — reflecting the intense osteoblast activity laying down new (but disorganised) bone. Serum calcium and phosphate are typically NORMAL (unless immobilised, when hypercalcaemia can develop). Most patients are asymptomatic (incidental finding on XR or blood test). Complications: bone pain, deformity (bowing of tibia, enlarging skull), pathological fracture (chalk-stick/transverse), deafness (temporal bone involvement), high-output cardiac failure (hypervascular bone), and sarcomatous transformation (<1% — usually osteosarcoma, aggressive, poor prognosis).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 681,
              "stem": "Osteomalacia in adults is the equivalent of rickets in children. The key distinguishing laboratory finding from osteoporosis is:",
              "options": [
                "Elevated calcium in both conditions",
                "Normal ALP in osteomalacia",
                "Low serum calcium and/or phosphate with elevated ALP in osteomalacia (defective mineralisation), whereas osteoporosis has NORMAL calcium, phosphate, and ALP (normal mineralisation of reduced bone mass)",
                "Elevated ESR in osteomalacia",
                "Low albumin in osteoporosis"
              ],
              "answer": "C",
              "explanation": "Osteomalacia = defective MINERALISATION of normal osteoid (too much unmineralised bone matrix) → soft, weak bone. Osteoporosis = normal mineralisation of REDUCED bone mass (less bone overall, but what exists is normally mineralised). This distinction is critical: Osteomalacia labs: ↓ calcium (or normal if compensated by secondary hyperPTH), ↓ phosphate, ↑ ALP (osteoblasts trying to mineralise), ↑ PTH (secondary hyperparathyroidism), ↓ 25(OH)D. Osteoporosis labs: ALL NORMAL (Ca, PO₄, ALP, PTH, vitamin D — unless a secondary cause exists). Osteomalacia XR: Looser zones (pseudofractures — bilateral, symmetric, perpendicular to cortex, pathognomonic), generalised osteopaenia, fuzzy trabecular pattern. Treatment: vitamin D + calcium supplementation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 682,
              "stem": "Primary hyperparathyroidism causes bone changes because excess PTH:",
              "options": [
                "Inhibits osteoclasts",
                "Stimulates osteoblasts without any resorption",
                "Has no effect on bone",
                "Only affects the kidneys",
                "Promotes sustained (not intermittent) osteoclast activation → bone resorption → hypercalcaemia, subperiosteal resorption, brown tumours (osteitis fibrosa cystica), and salt-and-pepper skull"
              ],
              "answer": "E",
              "explanation": "Primary hyperparathyroidism (usually a parathyroid adenoma ~85%) causes CONTINUOUS excessive PTH secretion → sustained osteoclast activation → bone resorption. This is the OPPOSITE of intermittent PTH (teriparatide) which stimulates formation. Effects: (1) hypercalcaemia (stones, bones, abdominal groans, psychic moans), (2) subperiosteal resorption (classically seen on the radial side of the middle phalanges — earliest and most specific XR sign), (3) brown tumours (osteitis fibrosa cystica — lytic lesions filled with haemosiderin-laden macrophages and osteoclast-type giant cells — NOT true tumours, they resolve with PTH normalisation), (4) salt-and-pepper skull (diffuse calvarial resorption), (5) distal clavicular resorption, (6) loss of lamina dura (teeth). Treatment: parathyroidectomy for symptomatic disease or if Ca >2.85, age <50, eGFR <60, T-score <-2.5, or vertebral fracture.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 683,
              "stem": "Osteoporosis is diagnosed by DEXA scan when the T-score is:",
              "options": [
                "≤ -2.5",
                "Between -1.0 and -2.5 (osteopaenia)",
                "≥ -1.0 (normal)",
                "≤ -3.5 only",
                "Any negative T-score"
              ],
              "answer": "A",
              "explanation": "WHO definition: T-score ≥ -1.0 = normal. T-score between -1.0 and -2.5 = osteopaenia. T-score ≤ -2.5 = osteoporosis. T-score ≤ -2.5 with a fragility fracture = severe/established osteoporosis. The T-score compares the patient's BMD to a healthy young adult reference population. The Z-score compares to age-matched peers (used in premenopausal women and men <50 years). DEXA of the hip and lumbar spine are the standard measurement sites. FRAX score (10-year fracture risk calculator) guides treatment decisions.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 684,
              "stem": "Paget disease of bone is characterised by disordered bone remodelling. The hallmark biochemical finding is:",
              "options": [
                "Elevated calcium with low phosphate",
                "Low calcium with high phosphate",
                "All markers normal",
                "Markedly elevated serum alkaline phosphatase with normal calcium and phosphate",
                "Markedly elevated PTH"
              ],
              "answer": "D",
              "explanation": "Paget disease shows markedly elevated serum ALP (reflecting intense osteoblastic activity) with NORMAL serum calcium and phosphate (the accelerated resorption and formation are coupled, maintaining mineral balance). Urinary hydroxyproline and deoxypyridinoline (markers of bone resorption) are also elevated. Calcium may be elevated if the patient is immobilised (uncoupled resorption). ALP is the most useful marker for monitoring disease activity and treatment response. Radiographic features: coarsened trabeculae, cortical thickening, bone expansion, 'picture frame' vertebra, 'cotton wool' skull.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 685,
              "stem": "In renal osteodystrophy, secondary hyperparathyroidism leads to which type of bone change?",
              "options": [
                "Purely sclerotic bone",
                "Osteitis fibrosa cystica (increased bone resorption with fibrous replacement)",
                "No bone changes",
                "Decreased PTH levels",
                "Isolated osteomalacia without other features"
              ],
              "answer": "B",
              "explanation": "In chronic kidney disease (CKD), phosphate retention and reduced 1,25-dihydroxyvitamin D₃ synthesis lead to hypocalcaemia → secondary hyperparathyroidism (elevated PTH). Persistently high PTH stimulates osteoclastic resorption → osteitis fibrosa cystica (brown tumours, subperiosteal erosions, salt-and-pepper skull, rugger jersey spine). Concurrent defective mineralisation (low vitamin D) causes osteomalacia. Renal osteodystrophy thus has components of BOTH osteitis fibrosa cystica AND osteomalacia. Radiographic features: subperiosteal erosions (radial aspect of middle phalanges — earliest and most specific sign), brown tumours, rugger jersey spine (alternating sclerotic and lucent bands).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            }
          ]
        },
        {
          "title": "Biomaterials",
          "range": "Q686-Q688",
          "questions": [
            {
              "number": 686,
              "stem": "Titanium alloy (Ti-6Al-4V) is preferred for orthopaedic implants over stainless steel because of:",
              "options": [
                "Higher stiffness (titanium is actually LESS stiff than steel)",
                "Superior biocompatibility, better corrosion resistance, lower modulus of elasticity (closer to bone — reducing stress shielding), and excellent osseointegration",
                "Lower cost in all cases",
                "Easier to manufacture",
                "No advantages — stainless steel is always better"
              ],
              "answer": "B",
              "explanation": "Titanium alloy (Ti-6Al-4V) advantages: (1) BIOCOMPATIBILITY — titanium forms a passive oxide layer (TiO₂) that is biologically inert and well-tolerated by tissues (lower allergic/inflammatory reaction rate than CoCr or stainless steel). (2) CORROSION RESISTANCE — the TiO₂ oxide layer reforms instantly if scratched (self-passivating), providing excellent corrosion resistance in the body's saline environment. (3) LOWER MODULUS OF ELASTICITY (~110 GPa vs ~200 GPa for stainless steel, vs ~230 GPa for CoCr, vs ~15-20 GPa for cortical bone) — titanium's modulus is closer to bone → less stress shielding (Wolff's law — less bone resorption around the implant). (4) OSSEOINTEGRATION — titanium surface allows direct bone-implant contact without fibrous tissue formation (why it's used for uncemented arthroplasty, dental implants, and pedicle screws). Disadvantages: lower fatigue strength than CoCr (larger stems needed), notch sensitivity, not suitable for metal-on-metal bearing surfaces (poor wear properties — galls under friction).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 687,
              "stem": "PMMA bone cement (polymethylmethacrylate) achieves fixation by:",
              "options": [
                "Chemical bonding to bone (it does NOT chemically bond)",
                "Biological osseointegration",
                "Welding to the implant",
                "Growing into the bone",
                "MECHANICAL INTERDIGITATION — the cement fills the interstices of cancellous bone under pressure, creating a strong mechanical interlock when it polymerises (not a chemical bond to bone)"
              ],
              "answer": "E",
              "explanation": "PMMA cement achieves fixation through MECHANICAL INTERDIGITATION — NOT chemical bonding. The liquid monomer (methylmethacrylate) is mixed with the powder (pre-polymerised PMMA beads + initiator/benzoyl peroxide + radiopaque agent/barium sulphate or zirconium dioxide), creating a dough that is pressurised into the prepared cancellous bone. The cement flows into the trabecular spaces and, upon polymerisation (exothermic — temperature can reach 70-80°C at the cement-bone interface), creates a MECHANICAL INTERLOCK with the cancellous bone. It is essentially a space-filling grout, not a glue. Properties: (1) exothermic reaction (can cause thermal necrosis of adjacent bone — typically a thin zone), (2) monomer toxicity (can cause hypotension — contributes to BCIS), (3) shrinkage during polymerisation (~2-5% volume), (4) creep under sustained load, (5) fatigue failure under cyclic loading. Antibiotics can be added (gentamicin, vancomycin) for prophylaxis or treatment of infection.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 688,
              "stem": "Galvanic corrosion in orthopaedic implants occurs when:",
              "options": [
                "Two DISSIMILAR metals are in contact in an electrolyte solution (body fluid) — creating an electrochemical cell where the less noble (more reactive) metal preferentially corrodes",
                "A single metal corrodes in isolation",
                "The implant is made of ceramic",
                "Only titanium is used",
                "No metal is present"
              ],
              "answer": "A",
              "explanation": "Galvanic corrosion occurs when two DISSIMILAR metals are in direct contact within an electrolyte (the body's saline environment acts as the electrolyte). The two metals form an electrochemical cell — the more reactive (anodic/less noble) metal preferentially corrodes while the less reactive (cathodic/more noble) metal is protected. This accelerates corrosion of the anodic metal beyond what would occur if it were alone. Clinical relevance: mixing stainless steel screws with titanium plates (or vice versa) creates galvanic corrosion at the interface — this is why ALL components of a construct should be the SAME metal (never mix metals). Galvanic series in orthopaedics (most noble to least): titanium > CoCr > stainless steel (316L). If titanium plate + stainless steel screw → the stainless steel screw corrodes preferentially. Other corrosion types: crevice corrosion (under screw heads, at modular junctions), fretting corrosion (micromotion at interfaces), and stress corrosion cracking (tensile stress + corrosive environment).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Pathology",
          "range": "Q689",
          "questions": [
            {
              "number": 689,
              "stem": "Osteoclasts are the cells responsible for bone resorption. They are derived from:",
              "options": [
                "Mesenchymal stem cells (osteoblast lineage)",
                "Chondrocytes",
                "Fibroblasts",
                "Haematopoietic monocyte/macrophage lineage (fusing to form large multinucleated cells that resorb bone by creating an acidic sealed compartment — the Howship lacuna)",
                "Osteocytes"
              ],
              "answer": "D",
              "explanation": "Osteoclasts are large multinucleated cells (3-20+ nuclei) derived from the HAEMATOPOIETIC monocyte/macrophage lineage (not mesenchymal — that's osteoblasts/chondrocytes). They are formed by fusion of monocyte precursors under the influence of RANKL (receptor activator of NF-κB ligand — produced by osteoblasts/osteocytes) and M-CSF. Osteoclasts resorb bone by: (1) attaching to the bone surface via integrins (creating a sealed 'ruffled border' zone), (2) acidifying the sealed compartment (H⁺ ions via proton pumps dissolve the mineral), (3) secreting proteolytic enzymes (cathepsin K, MMP-9 — digest the organic matrix). The resorption pit = HOWSHIP LACUNA. RANKL/RANK/OPG axis: RANKL (on osteoblasts) binds RANK (on osteoclast precursors) → stimulates osteoclastogenesis. OPG (osteoprotegerin — decoy receptor produced by osteoblasts) binds and neutralises RANKL → inhibits osteoclast formation. Denosumab: a monoclonal antibody against RANKL (mimics OPG) → potent anti-resorptive for osteoporosis.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Bone Graft",
          "range": "Q690",
          "questions": [
            {
              "number": 690,
              "stem": "Autologous iliac crest bone graft is considered the gold standard because it provides:",
              "options": [
                "Only osteoconduction",
                "Only osteoinduction",
                "All three properties: osteoconduction (scaffold), osteoinduction (growth factors — BMPs), and osteogenesis (living osteoblasts/MSCs) — the only graft material that provides all three",
                "Only osteogenesis",
                "None of these properties"
              ],
              "answer": "C",
              "explanation": "Bone graft biology — three key properties: (1) OSTEOCONDUCTION — the graft acts as a physical SCAFFOLD that allows new bone to grow across its surface (hydroxyapatite, calcium phosphate cements, coral, allograft bone — all provide this). (2) OSTEOINDUCTION — the graft contains GROWTH FACTORS (particularly BMPs — bone morphogenetic proteins) that stimulate mesenchymal stem cells to differentiate into osteoblasts and form new bone (DBM — demineralised bone matrix, autograft — provide this). (3) OSTEOGENESIS — the graft contains LIVING CELLS (osteoblasts, osteoprogenitor cells, MSCs) that can directly form new bone (ONLY autograft provides this — allografts are processed/sterilised, killing cells). Autologous iliac crest bone graft (ICBG) is the ONLY material that provides ALL THREE properties — this is why it remains the gold standard. Alternatives: allograft (osteoconductive ± weakly osteoinductive), DBM (osteoinductive + osteoconductive), BMPs (strongly osteoinductive), ceramics (osteoconductive only), platelet-rich plasma (growth factors but weak evidence).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Imaging",
          "range": "Q691-Q697",
          "questions": [
            {
              "number": 691,
              "stem": "On MRI, T1-weighted sequences are best for assessing:",
              "options": [
                "Oedema and fluid (those are bright on T2)",
                "Only bone tumours",
                "Only ligaments",
                "Only cartilage",
                "ANATOMY — fat appears bright (high signal), muscle appears intermediate, fluid appears dark (low signal), cortical bone appears dark"
              ],
              "answer": "E",
              "explanation": "MRI sequences — key principles: T1-weighted: best for ANATOMY. Fat = BRIGHT (high signal), muscle = intermediate grey, fluid/water = DARK (low signal), cortical bone = DARK (no mobile protons). T1 shows anatomical detail clearly — useful for: bone marrow assessment (fat-containing marrow is bright, replaced marrow from tumour/infection is dark), anatomical relationships, and post-gadolinium enhancement (enhancing tissue becomes bright on T1). T2-weighted: best for PATHOLOGY. Fluid/water = BRIGHT, fat = intermediate to bright (depending on sequence). Oedema, effusions, cysts, and most pathological processes are bright on T2 (because they contain more water). STIR (Short Tau Inversion Recovery): T2-like with FAT SUPPRESSION — fluid/oedema is bright, fat is suppressed (dark). Very sensitive for bone marrow oedema (stress fractures, AVN, tumours, infection). The mnemonic: T1 = anatomy, T2/STIR = pathology/water.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 692,
              "stem": "A bone scan (technetium-99m isotope scan) detects increased bone metabolic activity. Compared to MRI, a bone scan is:",
              "options": [
                "More specific for the cause of the abnormality",
                "HIGHLY SENSITIVE but LESS SPECIFIC than MRI — it detects areas of increased bone turnover (hot spots) but cannot determine the CAUSE (fracture, infection, tumour, arthritis, and Paget disease can all appear as hot spots)",
                "More sensitive than MRI for all conditions",
                "Only useful for infection",
                "Unable to detect any bone pathology"
              ],
              "answer": "B",
              "explanation": "Bone scan (Tc-99m MDP) is HIGHLY SENSITIVE (~95%) for detecting areas of increased bone metabolic activity — the radiopharmaceutical accumulates in areas of increased osteoblastic activity (new bone formation/remodelling). ANY condition causing increased bone turnover appears as a 'hot spot': fracture (healing), infection (osteomyelitis), tumour (primary or metastatic), arthritis, Paget disease, stress fracture, avascular necrosis (early — though established AVN may be 'cold' if the bone is dead). The limitation: bone scan is NOT SPECIFIC — it tells you SOMETHING is happening in the bone, but not WHAT. MRI is more SPECIFIC: it can differentiate between different causes (tumour shows marrow replacement, infection shows marrow oedema + soft tissue collection, fracture shows a fracture line + oedema, etc.) AND is equally or more sensitive for most conditions. However, bone scan has advantages: (1) WHOLE-BODY survey in a single study (identifies ALL areas of increased activity — useful for metastatic screening, polyostotic Paget, multifocal infection), (2) relatively inexpensive, (3) widely available. Triple-phase bone scan: adds blood flow and blood pool phases (increases specificity for infection/inflammation vs other causes).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 693,
              "stem": "On MRI, fluid (e.g., joint effusion, oedema) appears as which signal on T2-weighted images?",
              "options": [
                "Dark (low signal)",
                "Intermediate signal",
                "No signal",
                "Bright (high signal)",
                "Same as bone"
              ],
              "answer": "D",
              "explanation": "On T2-weighted MRI, fluid appears bright (high signal) because T2 weighting is sensitive to water content. This makes T2 excellent for detecting oedema, effusions, ligament tears (fluid tracking into the tear), bone marrow oedema (bone bruise), and disc degeneration. On T1-weighted images, fluid appears dark (low signal) while fat appears bright. STIR (Short Tau Inversion Recovery) sequences suppress fat signal and are very sensitive for detecting oedema.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 694,
              "stem": "A bone scan (technetium-99m MDP scintigraphy) detects:",
              "options": [
                "Areas of increased osteoblastic activity (increased bone turnover)",
                "Only infection",
                "Only tumours",
                "Soft tissue injuries only",
                "Normal bone only"
              ],
              "answer": "A",
              "explanation": "Technetium-99m MDP bone scan detects areas of increased osteoblastic activity/bone turnover. The radiopharmaceutical binds to hydroxyapatite crystals in areas of active bone formation. It is highly sensitive but NOT specific — it is positive in fractures, infection, tumours (primary and metastatic), Paget disease, arthritis, and any condition causing increased bone metabolism. A 'cold' (photopenic) area indicates absent blood supply (AVN, some aggressive tumours like myeloma that are purely lytic).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 695,
              "stem": "The radiation dose of a lumbar spine radiograph is approximately equivalent to how many chest X-rays?",
              "options": [
                "5",
                "25",
                "75",
                "150",
                "500"
              ],
              "answer": "C",
              "explanation": "A lumbar spine radiograph delivers approximately 75 times the radiation dose of a single chest X-ray. CT abdomen/pelvis is approximately 500-600 chest X-rays. A chest X-ray delivers approximately 0.02 mSv, while a lumbar spine XR is approximately 1.5 mSv. CT lumbar spine is approximately 6 mSv (~300 chest X-rays). These radiation equivalences are frequently tested.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 696,
              "stem": "On MRI, a T1-weighted image typically shows fat as:",
              "options": [
                "Dark (low signal)",
                "Invisible",
                "Bright (high signal)",
                "Green",
                "Variable depending on the pulse sequence"
              ],
              "answer": "C",
              "explanation": "On T1-weighted MRI: fat appears BRIGHT (high signal), water/fluid appears DARK (low signal). On T2-weighted MRI: both fat and water appear BRIGHT (but STIR/fat-suppressed T2 suppresses fat signal, making only water bright — ideal for detecting oedema/inflammation). This is clinically important: T1 images show anatomy clearly (fat planes delineate structures), while T2/STIR images highlight pathology (oedema, effusion, inflammation, tumour). Bone marrow (fatty) is bright on T1. AVN: the affected area is dark on T1 (loss of normal fatty marrow signal) — T1 is the most sensitive MRI sequence for detecting AVN.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 697,
              "stem": "On a plain radiograph, which sign is pathognomonic for a unicameral bone cyst (UBC) that has fractured?",
              "options": [
                "Codman triangle",
                "Sunburst periosteal reaction",
                "Onion skin periosteal reaction",
                "Bone-in-bone appearance",
                "Fallen fragment sign (a piece of cortex falls to the dependent part of the cyst)"
              ],
              "answer": "E",
              "explanation": "The fallen fragment sign is pathognomonic for a UBC that has sustained a pathological fracture. A piece of fractured cortex falls to the dependent (gravity-dependent) part of the fluid-filled cyst cavity — this can only occur in a fluid-filled cavity (not a solid tumour or ABC). UBCs are centrally located, well-defined metaphyseal lytic lesions in children (most commonly proximal humerus and proximal femur). They are classified as active (adjacent to the physis) or latent (migrated away from the physis with growth). Treatment: observation if asymptomatic. Post-fracture: immobilise (fracture may initiate healing). Persistent: aspiration + steroid injection (methylprednisolone), or curettage + bone graft.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Biology",
          "range": "Q698-Q700",
          "questions": [
            {
              "number": 698,
              "stem": "Type II collagen is the predominant collagen in:",
              "options": [
                "Hyaline articular cartilage (Type II collagen forms ~90-95% of the collagen in articular cartilage — it provides tensile strength to the cartilage matrix)",
                "Cortical bone (that's Type I)",
                "Tendons and ligaments (Type I)",
                "Skin (Type I and III)",
                "Blood vessels (Type III)"
              ],
              "answer": "A",
              "explanation": "Collagen types in musculoskeletal tissues: Type I (most abundant collagen in the body): bone, tendon, ligament, skin, dentin, annulus fibrosus. Type II: HYALINE ARTICULAR CARTILAGE (~90-95% of cartilage collagen), vitreous body, nucleus pulposus. Type III: blood vessels, skin (with Type I), uterus, early wound healing (granulation tissue — later replaced by Type I during scar maturation). Type IV: basement membranes. Type X: hypertrophic zone of the growth plate (marker of endochondral ossification — present in the zone of provisional calcification). Clinical relevance: microfracture repair tissue is predominantly Type I collagen (fibrocartilage — biomechanically inferior), while ACI/MACI aims to produce Type II (hyaline-like — biomechanically superior). Type I collagen mutations → osteogenesis imperfecta (OI — COL1A1 or COL1A2 gene mutations → brittle bones). Type II mutations → skeletal dysplasias (Stickler syndrome, achondrogenesis type II).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 699,
              "stem": "Aggrecan is the major proteoglycan in articular cartilage. Its primary function is to:",
              "options": [
                "Provide tensile strength (that's collagen)",
                "Attract and retain water through its negatively charged glycosaminoglycan (GAG) side chains — creating the swelling pressure that gives cartilage its compressive stiffness and resilience",
                "Bind bone to implants",
                "Act as a lubricant on the surface (that's lubricin/PRG4 and hyaluronic acid)",
                "Provide nothing — it is functionless"
              ],
              "answer": "B",
              "explanation": "Aggrecan is a large aggregating proteoglycan that forms the major structural proteoglycan in articular cartilage. Structure: a core protein with numerous glycosaminoglycan (GAG) side chains — predominantly CHONDROITIN SULPHATE and KERATAN SULPHATE. These GAG chains carry densely packed NEGATIVE charges (sulphate and carboxyl groups) that attract and retain WATER molecules (through osmotic pressure). Multiple aggrecan molecules bind to a hyaluronic acid backbone (via link proteins) forming massive aggregates. Function: the high density of trapped water creates SWELLING PRESSURE — this is what gives cartilage its remarkable COMPRESSIVE STIFFNESS and resilience (ability to resist and recover from compressive loads). When cartilage is loaded: water is slowly squeezed out → load is borne by the hydrated proteoglycan gel. When load is removed: water returns (drawn back by the negative charges) → cartilage recovers its shape. In OA: aggrecan is degraded by aggrecanases (ADAMTS-4 and ADAMTS-5) → loss of GAGs → loss of water content → cartilage becomes stiff, thin, and vulnerable to damage.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 700,
              "stem": "Woven bone differs from lamellar bone in that woven bone:",
              "options": [
                "Has highly organised collagen fibres in parallel lamellae (that's lamellar)",
                "Is the final mature bone structure",
                "Is only found in adults",
                "Has RANDOMLY oriented collagen fibres, is formed rapidly (fracture callus, embryonic bone, Paget disease), and is mechanically WEAKER than lamellar bone — it is eventually replaced by lamellar bone during remodelling",
                "Has the highest mechanical strength of all bone types"
              ],
              "answer": "D",
              "explanation": "Woven bone (immature/primitive bone): collagen fibres are randomly oriented (no organised lamellar structure) → mechanically WEAKER than lamellar bone. It is produced RAPIDLY when new bone is needed quickly: (1) embryonic bone formation (all bone is initially woven), (2) fracture healing (callus is initially woven bone → later remodelled to lamellar), (3) pathological conditions with rapid bone turnover (Paget disease, hyperparathyroidism, fibrous dysplasia). Woven bone is normally replaced by LAMELLAR bone through remodelling (osteoclast resorption of woven bone → osteoblast deposition of organised lamellar bone along stress lines — Wolff's law). Lamellar bone (mature bone): collagen fibres organised in parallel sheets (lamellae) arranged in concentric rings around Haversian canals (forming osteons/Haversian systems in cortical bone). This organisation gives lamellar bone its superior strength and mechanical properties. In adults: the presence of woven bone in a biopsy suggests a PATHOLOGICAL process (fracture healing, Paget, tumour, fibrous dysplasia) — normal adult bone should be lamellar.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Cartilage Repair",
          "range": "Q701",
          "questions": [
            {
              "number": 701,
              "stem": "Microfracture of an articular cartilage defect produces which type of repair tissue?",
              "options": [
                "Hyaline cartilage identical to native",
                "Woven bone",
                "Fibrous tissue only",
                "Type II collagen-rich hyaline cartilage",
                "Fibrocartilage (predominantly Type I collagen)"
              ],
              "answer": "E",
              "explanation": "Microfracture involves perforating the subchondral bone plate to allow marrow elements (MSCs, growth factors, blood) to fill the cartilage defect and form a clot. This repair tissue matures into fibrocartilage (predominantly Type I collagen) rather than true hyaline cartilage (Type II collagen). Fibrocartilage has inferior mechanical properties and durability compared to native hyaline cartilage. Despite this, microfracture provides symptomatic relief, particularly for small defects (<2 cm²) in younger patients.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Bone Metabolism",
          "range": "Q702",
          "questions": [
            {
              "number": 702,
              "stem": "Parathyroid hormone (PTH) acts on bone to:",
              "options": [
                "Inhibit osteoclast activity",
                "Promote calcium deposition in bone",
                "Stimulate osteoclast-mediated bone resorption (increasing serum calcium)",
                "Inhibit vitamin D activation",
                "Reduce serum calcium levels"
              ],
              "answer": "C",
              "explanation": "PTH is released in response to low serum calcium. It increases serum calcium through three mechanisms: (1) stimulates osteoclast-mediated bone resorption (indirectly — PTH acts on osteoblasts which then signal to osteoclasts via RANKL), (2) increases renal calcium reabsorption, (3) stimulates 1-alpha-hydroxylase in the kidney to produce active vitamin D (1,25-dihydroxyvitamin D), which increases intestinal calcium absorption. Paradoxically, intermittent low-dose PTH (teriparatide) stimulates bone FORMATION — this is exploited therapeutically in osteoporosis.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Connective Tissue",
          "range": "Q703-Q704",
          "questions": [
            {
              "number": 703,
              "stem": "The strongest ligament in the body is:",
              "options": [
                "Anterior cruciate ligament",
                "Posterior sacroiliac ligament (interosseous SI ligament)",
                "Posterior cruciate ligament",
                "Inguinal ligament",
                "Ligamentum flavum"
              ],
              "answer": "B",
              "explanation": "The posterior (interosseous) sacroiliac ligament complex is the strongest ligament in the body. It is the primary restraint to vertical displacement of the hemipelvis. Its disruption defines a Tile Type C pelvic ring injury (both rotationally and vertically unstable). The anterior SI ligaments and the sacrospinous/sacrotuberous ligaments provide additional rotational stability.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 704,
              "stem": "Proteoglycans in articular cartilage primarily resist which type of mechanical force?",
              "options": [
                "Compressive forces",
                "Tensile forces",
                "Shear forces",
                "Torsional forces",
                "Bending forces"
              ],
              "answer": "A",
              "explanation": "Proteoglycans (predominantly aggrecan) in articular cartilage are highly negatively charged molecules that attract and bind water through osmotic pressure. This water-binding capacity allows cartilage to resist compressive loads — when compressed, water is squeezed out through the collagen matrix, and when load is removed, water is drawn back in (the 'sponge effect'). Collagen (Type II) provides tensile strength. The collagen-proteoglycan interaction creates a biphasic material that resists both compression and tension.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Infection",
          "range": "Q705",
          "questions": [
            {
              "number": 705,
              "stem": "The most common organism causing septic arthritis in sexually active young adults is:",
              "options": [
                "Staphylococcus aureus",
                "Streptococcus pneumoniae",
                "Haemophilus influenzae",
                "Neisseria gonorrhoeae",
                "Escherichia coli"
              ],
              "answer": "D",
              "explanation": "Neisseria gonorrhoeae is the most common cause of septic arthritis in sexually active young adults (15–40 years). It presents as either a disseminated gonococcal infection (polyarthralgias, tenosynovitis, dermatitis) or a purulent monoarthritis. Overall across all age groups, S. aureus remains the most common organism. In neonates, Group B Streptococcus and gram-negatives are important. After joint replacement, coagulase-negative staphylococci predominate.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Muscle Physiology",
          "range": "Q706-Q707",
          "questions": [
            {
              "number": 706,
              "stem": "The sarcomere is the functional unit of skeletal muscle. The A-band consists of:",
              "options": [
                "Actin filaments only",
                "The Z-line to Z-line distance",
                "I-band region only",
                "Myosin filaments (with overlapping actin at the edges)",
                "Titin molecules only"
              ],
              "answer": "D",
              "explanation": "The A-band (Anisotropic band, appears dark on microscopy) corresponds to the length of the myosin (thick) filaments. At its edges, actin (thin) filaments overlap with myosin. The central H-zone contains myosin only (no actin overlap). During contraction, the A-band length remains CONSTANT (myosin length doesn't change) — the I-band and H-zone shorten as actin slides over myosin. The Z-line to Z-line distance defines one sarcomere.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 707,
              "stem": "The motor unit is the functional unit of the neuromuscular system. A small motor unit (e.g., in the hand intrinsics) differs from a large motor unit (e.g., in the quadriceps) in that small motor units:",
              "options": [
                "Innervate more muscle fibres per motor neuron",
                "Innervate fewer muscle fibres per motor neuron, allowing finer motor control",
                "Generate more force per unit",
                "Are only found in trunk muscles",
                "Have no clinical significance"
              ],
              "answer": "B",
              "explanation": "A motor unit consists of a single motor neuron and all the muscle fibres it innervates. Small motor units (hand intrinsics, extraocular muscles) have few muscle fibres per motor neuron (10-100) → fine, precise control. Large motor units (quadriceps, gastrocnemius) have many fibres per motor neuron (500-2000) → powerful but less precise contractions. Recruitment follows the size principle (Henneman): small motor units are recruited first (slow-twitch, fatigue-resistant, Type I fibres), then progressively larger units are recruited as more force is required (fast-twitch, Type II fibres). This orderly recruitment is fundamental to graded muscle contraction.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Embryology",
          "range": "Q708",
          "questions": [
            {
              "number": 708,
              "stem": "The apical ectodermal ridge (AER) in limb development controls growth in which axis?",
              "options": [
                "Proximodistal axis",
                "Anteroposterior axis",
                "Dorsoventral axis",
                "Rotational axis",
                "No specific axis"
              ],
              "answer": "A",
              "explanation": "The AER controls limb growth in the proximodistal axis (length). It produces FGFs (fibroblast growth factors) that maintain the underlying mesenchyme (progress zone) in a proliferative state. Removal of the AER results in truncation of the limb. The ZPA (zone of polarising activity) controls the anteroposterior axis via Sonic hedgehog (SHH). The dorsal ectoderm controls the dorsoventral axis via Wnt7a.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Nerve Injury",
          "range": "Q709-Q710",
          "questions": [
            {
              "number": 709,
              "stem": "The Seddon classification of nerve injuries includes three grades. The mildest form is:",
              "options": [
                "Neurotmesis",
                "Axonotmesis",
                "Wallerian degeneration",
                "Sunderland Grade V",
                "Neurapraxia"
              ],
              "answer": "E",
              "explanation": "Seddon classification: Neurapraxia (mildest) = conduction block without structural damage to the axon. The myelin sheath is temporarily disrupted but the axon remains intact. Full recovery occurs within hours to 12 weeks without surgical intervention. Axonotmesis = axon disrupted but endoneurium intact — Wallerian degeneration occurs distally, but regeneration follows the intact endoneurial tube (~1 mm/day). Good recovery expected. Neurotmesis = complete nerve disruption (axon + endoneurium + perineurium ± epineurium) — requires surgical repair, prognosis guarded.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 710,
              "stem": "Wallerian degeneration occurs distal to a nerve injury. What happens to the distal nerve segment?",
              "options": [
                "It remains completely normal",
                "The distal segment regenerates independently",
                "The axon and myelin degenerate distally while Schwann cells proliferate to form bands of Büngner for regeneration",
                "The nerve becomes calcified",
                "Motor function is preserved but sensation is lost"
              ],
              "answer": "C",
              "explanation": "After axonotmesis or neurotmesis, Wallerian degeneration occurs in the DISTAL segment: the axon and myelin sheath break down within 48-96 hours, macrophages clear the debris, and Schwann cells proliferate to form columns called bands of Büngner. These bands provide a scaffold for regenerating axons from the proximal stump. Regeneration occurs at approximately 1 mm/day (1 inch/month). The Tinel sign (tingling on percussion) advances distally along the nerve as regeneration progresses — its advancing front indicates the leading edge of regeneration.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Wound Healing",
          "range": "Q711-Q712",
          "questions": [
            {
              "number": 711,
              "stem": "The three phases of wound healing in chronological order are:",
              "options": [
                "Proliferative, inflammatory, remodelling",
                "Inflammatory, proliferative, remodelling (maturation)",
                "Remodelling, inflammatory, proliferative",
                "Proliferative, remodelling, inflammatory",
                "Haemostasis only — no other phases"
              ],
              "answer": "B",
              "explanation": "Wound healing phases: (1) Inflammatory phase (days 0-5): haemostasis (platelet plug, fibrin clot), vasodilation, neutrophil then macrophage infiltration (macrophages are the MOST important cell in wound healing — they orchestrate the transition to proliferative phase). (2) Proliferative phase (days 5-21): fibroblasts produce collagen (initially Type III), angiogenesis, granulation tissue formation, wound contraction (myofibroblasts), epithelialisation. (3) Remodelling/maturation phase (3 weeks to 1-2 years): Type III collagen replaced by Type I, collagen cross-linking, wound strength increases (maximum ~80% of original at 12 weeks — never reaches 100%).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 712,
              "stem": "The maximum tensile strength a healed wound achieves compared to unwounded tissue is approximately:",
              "options": [
                "80%",
                "20%",
                "40%",
                "60%",
                "100%"
              ],
              "answer": "A",
              "explanation": "A healed wound reaches a maximum of approximately 80% of the original tensile strength of unwounded tissue by 12 weeks. It NEVER reaches 100%. This is because the collagen in scar tissue is less organised than the original tissue — the collagen fibres are aligned along lines of stress but lack the complex weave of normal tissue. Wound strength at 1 week is only ~3% (held together by fibrin and granulation tissue). At 3 weeks: ~20%. At 6 weeks: ~60%. At 12 weeks: ~80% (plateau).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Bone Grafts",
          "range": "Q713-Q714",
          "questions": [
            {
              "number": 713,
              "stem": "Autologous cancellous bone graft (e.g., from the iliac crest) possesses which three biological properties?",
              "options": [
                "Only osteoconduction",
                "Only osteoinduction",
                "Only osteogenesis",
                "None of the above",
                "Osteoconduction, osteoinduction, and osteogenesis"
              ],
              "answer": "E",
              "explanation": "Autologous cancellous bone graft has all three properties: (1) Osteoconduction — provides a scaffold for new bone to grow along/into. (2) Osteoinduction — contains growth factors (BMPs, TGF-β) that stimulate mesenchymal stem cell differentiation into osteoblasts. (3) Osteogenesis — contains living cells (osteoblasts, osteoprogenitor cells) that directly form new bone. Autograft is the gold standard bone graft. Allograft (cadaveric bone) has osteoconductive and some osteoinductive properties but NO osteogenesis (cells are dead). Synthetic grafts (calcium phosphate, hydroxyapatite) are osteoconductive only.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 714,
              "stem": "The most common donor site for autologous bone graft in orthopaedics is:",
              "options": [
                "Distal radius",
                "Greater trochanter",
                "Fibula (vascularised)",
                "Anterior iliac crest",
                "Rib"
              ],
              "answer": "D",
              "explanation": "The anterior iliac crest is the most common donor site for cancellous bone graft. It provides abundant cancellous bone with high osteogenic potential. Donor site morbidity includes: pain (most common complaint, ~25-30%), haematoma, infection, lateral femoral cutaneous nerve injury (meralgia paraesthetica), iliac wing fracture, hernia through the donor site, and cosmetic deformity. The posterior iliac crest provides more bone volume with potentially less pain. Vascularised fibula graft is used for large segmental defects (>6 cm).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Sterilisation",
          "range": "Q715",
          "questions": [
            {
              "number": 715,
              "stem": "The most commonly used method of sterilising orthopaedic implants is:",
              "options": [
                "Ethylene oxide gas",
                "Gamma irradiation",
                "Autoclaving (steam sterilisation)",
                "Chemical (glutaraldehyde)",
                "Ultraviolet light"
              ],
              "answer": "C",
              "explanation": "Steam sterilisation (autoclaving) at 134°C for 3 minutes (or 121°C for 15 minutes) is the most common method for sterilising reusable orthopaedic instruments and implants. It is reliable, rapid, and non-toxic (no chemical residues). Ethylene oxide gas is used for heat-sensitive items (plastics, powered instruments) but requires long aeration times. Gamma irradiation is used for single-use disposable items (UHMWPE, sutures, dressings) during manufacturing. Prions (CJD) are NOT reliably destroyed by standard autoclaving — require higher temperatures or NaOH treatment.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Fracture Healing",
          "range": "Q716-Q717",
          "questions": [
            {
              "number": 716,
              "stem": "Secondary (indirect) fracture healing occurs through callus formation and proceeds through four stages. The correct sequence is:",
              "options": [
                "Soft callus → inflammation → remodelling → hard callus",
                "Remodelling → hard callus → soft callus → inflammation",
                "Hard callus → soft callus → inflammation → remodelling",
                "Inflammation → soft callus → hard callus → remodelling",
                "Inflammation → hard callus → soft callus → remodelling"
              ],
              "answer": "D",
              "explanation": "Secondary (indirect/endochondral) fracture healing: (1) Inflammation (haematoma formation, inflammatory cell infiltration, days 0-7). (2) Soft callus (fibroblasts and chondrocytes produce fibrocartilaginous callus, endochondral ossification begins, weeks 2-3). (3) Hard callus (woven bone replaces soft callus via endochondral ossification, weeks 3-12). (4) Remodelling (woven bone replaced by lamellar bone along lines of stress — Wolff's law, months to years). This is the healing pattern seen with IM nailing, external fixation, and cast treatment (relative stability). Primary (direct/cortical) healing occurs with absolute stability (compression plating) — direct osteonal cutting cones cross the fracture without callus.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 717,
              "stem": "Which of the following factors is most likely to impair fracture healing?",
              "options": [
                "Good blood supply to the fracture site",
                "Rigid internal fixation with compression",
                "Young patient age",
                "Adequate nutrition",
                "Smoking"
              ],
              "answer": "E",
              "explanation": "Smoking is one of the most significant modifiable risk factors for impaired fracture healing and non-union. Nicotine causes vasoconstriction (reducing blood supply to the fracture), inhibits osteoblast proliferation and differentiation, impairs angiogenesis, and reduces oxygen delivery (carbon monoxide in cigarette smoke displaces oxygen from haemoglobin). Smokers have 2-6× higher non-union rates compared to non-smokers. Other factors impairing healing: NSAIDs, diabetes, infection, inadequate fixation, periosteal stripping, malnutrition, and bisphosphonates (controversial).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Crystal Arthropathy",
          "range": "Q718-Q719",
          "questions": [
            {
              "number": 718,
              "stem": "Gout is caused by deposition of which crystal in joints?",
              "options": [
                "Monosodium urate (MSU)",
                "Calcium pyrophosphate dihydrate (CPPD)",
                "Calcium hydroxyapatite",
                "Cholesterol crystals",
                "Calcium oxalate"
              ],
              "answer": "A",
              "explanation": "Gout is caused by deposition of monosodium urate (MSU) crystals in joints and soft tissues due to hyperuricaemia. Under polarised light microscopy, MSU crystals are needle-shaped and negatively birefringent (yellow when parallel to the polariser axis). The 1st MTP joint (podagra) is the most commonly affected joint. CPPD crystals cause pseudogout — they are rhomboid-shaped and weakly positively birefringent (blue when parallel). Hydroxyapatite causes calcific tendinitis and Milwaukee shoulder. Crystal identification on aspirate is the gold standard for diagnosis.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 719,
              "stem": "Under compensated polarised light microscopy, CPPD crystals (pseudogout) appear as:",
              "options": [
                "Needle-shaped and negatively birefringent",
                "Rhomboid-shaped and weakly positively birefringent",
                "Round and non-birefringent",
                "Hexagonal and strongly birefringent",
                "Invisible under polarised light"
              ],
              "answer": "B",
              "explanation": "CPPD crystals are rhomboid (or rod-shaped) and weakly positively birefringent — they appear BLUE when aligned parallel to the axis of the compensator. MSU crystals (gout) are needle-shaped and negatively birefringent — they appear YELLOW when parallel. Mnemonic: 'Yellow Parallel = Gout = Negative birefringence' or 'PBS = Pseudogout Blue, Slow (positive)'. CPPD deposition causes chondrocalcinosis (calcification of cartilage visible on radiograph, particularly the menisci, TFCC, and symphysis pubis).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Collagen",
          "range": "Q720",
          "questions": [
            {
              "number": 720,
              "stem": "The most abundant collagen type in the human body is:",
              "options": [
                "Type II",
                "Type III",
                "Type I",
                "Type IV",
                "Type X"
              ],
              "answer": "C",
              "explanation": "Type I collagen is the most abundant collagen in the body (~90% of all collagen). Distribution: bone (90% of organic matrix), skin, tendon, ligament, meniscus, cornea, dentin, and fascia. Type II: hyaline cartilage (articular cartilage, nucleus pulposus). Type III: healing tissue (granulation tissue, early wound healing, blood vessels — later replaced by Type I). Type IV: basement membranes. Type X: hypertrophic zone of the growth plate (endochondral ossification).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Bone Structure",
          "range": "Q721-Q722",
          "questions": [
            {
              "number": 721,
              "stem": "The haversian system (osteon) is the structural unit of cortical bone. The central haversian canal contains:",
              "options": [
                "Osteocytes only",
                "Fat and marrow cells",
                "Collagen fibres only",
                "Blood vessels and nerves",
                "Hydroxyapatite crystals"
              ],
              "answer": "D",
              "explanation": "The haversian canal is the central channel of each osteon, containing 1-2 blood vessels (arteriole and venule) and nerve fibres. Concentric lamellae of bone surround the canal, with osteocytes residing in lacunae between lamellae. Osteocytes communicate via canaliculi (thin channels connecting lacunae). Volkmann canals are perpendicular channels connecting adjacent haversian canals and the periosteal/endosteal surfaces, providing blood supply connections. Osteons are arranged along lines of stress (Wolff's law).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 722,
              "stem": "Woven bone differs from lamellar bone in that woven bone:",
              "options": [
                "Has organised collagen fibres along lines of stress",
                "Is mechanically stronger than lamellar bone",
                "Has randomly orientated collagen fibres, is formed rapidly, and is weaker than lamellar bone",
                "Is only found in adults",
                "Contains no osteocytes"
              ],
              "answer": "C",
              "explanation": "Woven bone has randomly orientated collagen fibres, is formed rapidly (fracture callus, embryonic bone development, tumour bone), and is mechanically weaker than lamellar bone. Lamellar bone has highly organised collagen fibres arranged in sheets (lamellae) along stress lines, is formed slowly by appositional growth, and is mechanically stronger. All normal adult bone is lamellar. Woven bone in adults is ALWAYS pathological — it indicates rapid bone formation (fracture healing, infection, tumour, Paget disease). During fracture healing, woven bone is eventually remodelled to lamellar bone.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Growth Factors",
          "range": "Q723",
          "questions": [
            {
              "number": 723,
              "stem": "Bone morphogenetic proteins (BMPs) are members of which growth factor superfamily?",
              "options": [
                "Fibroblast growth factor (FGF) family",
                "Transforming growth factor-beta (TGF-β) superfamily",
                "Vascular endothelial growth factor (VEGF) family",
                "Insulin-like growth factor (IGF) family",
                "Platelet-derived growth factor (PDGF) family"
              ],
              "answer": "B",
              "explanation": "BMPs are members of the TGF-β superfamily. They are the most potent osteoinductive factors known — they can induce differentiation of mesenchymal stem cells into osteoblasts and chondrocytes, driving new bone formation even in ectopic sites. BMP-2 and BMP-7 (OP-1) have been used clinically for non-unions, spinal fusion, and open tibial fractures. Urist first demonstrated the osteoinductive properties of demineralised bone matrix (containing BMPs) in 1965. Concerns: cost, ectopic bone formation, cancer risk (theoretical), and swelling (especially cervical spine).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Tissue Healing",
          "range": "Q724",
          "questions": [
            {
              "number": 724,
              "stem": "Tendon healing differs from bone healing in that tendons heal primarily by:",
              "options": [
                "Endochondral ossification",
                "Complete regeneration with identical original tissue",
                "Callus formation like bone",
                "Immediate full-strength repair",
                "Formation of scar tissue (predominantly Type III then Type I collagen) rather than regeneration of original tissue"
              ],
              "answer": "E",
              "explanation": "Tendons heal by forming scar tissue — the repair tissue is predominantly Type III collagen initially (weaker, disorganised), which is gradually replaced by Type I collagen during remodelling. However, the repaired tendon NEVER fully regains the organisation and mechanical properties of the original tendon. Healing occurs via intrinsic (tenocytes within the tendon) and extrinsic (cells from the surrounding sheath and synovium) mechanisms. Controlled early motion after repair promotes intrinsic healing and reduces adhesion formation. Bone, in contrast, can heal with regeneration of original tissue (unique among musculoskeletal tissues).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Rehabilitation",
          "range": "Q725",
          "questions": [
            {
              "number": 725,
              "stem": "The MRC (Medical Research Council) scale for muscle power grades voluntary muscle contraction from 0 to 5. Grade 3 indicates:",
              "options": [
                "Movement against gravity (but not against resistance)",
                "No muscle contraction",
                "Flicker of contraction only",
                "Movement possible only with gravity eliminated",
                "Movement against some resistance"
              ],
              "answer": "A",
              "explanation": "MRC muscle power scale: Grade 0 = no contraction. Grade 1 = flicker/trace contraction (palpable but no joint movement). Grade 2 = active movement with gravity eliminated (movement possible only in the horizontal plane). Grade 3 = active movement AGAINST gravity (can lift limb against gravity but not against additional resistance). Grade 4 = movement against gravity AND some resistance (but weaker than normal). Grade 5 = normal power. Grade 3 is the critical threshold: it differentiates functional from non-functional muscle (grade ≥3 = useful function for tendon transfer donors).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Physiology",
          "range": "Q726-Q730",
          "questions": [
            {
              "number": 726,
              "stem": "The oxygen dissociation curve shifts to the RIGHT (decreased haemoglobin affinity for oxygen, releasing more O₂ to tissues) with:",
              "options": [
                "Decreased temperature and decreased CO₂",
                "Increased pH (alkalosis)",
                "Increased temperature, increased CO₂, increased 2,3-DPG, and decreased pH (the Bohr effect)",
                "Carbon monoxide exposure",
                "Hypothermia"
              ],
              "answer": "C",
              "explanation": "A RIGHT shift of the oxygen dissociation curve means haemoglobin releases oxygen more readily to tissues (lower O₂ affinity). This occurs with: increased temperature (fever, exercise), increased CO₂ (metabolically active tissues), increased 2,3-DPG (chronic hypoxia, altitude), and decreased pH/acidosis (Bohr effect — active muscles produce CO₂ and lactic acid → H⁺ ions decrease Hb-O₂ affinity → more O₂ released to working tissues). A LEFT shift (increased Hb-O₂ affinity, oxygen held tighter) occurs with the opposite: decreased temperature, decreased CO₂, decreased 2,3-DPG, increased pH, carbon monoxide, and fetal haemoglobin. Clinically relevant: massive transfusion with stored blood (low 2,3-DPG) shifts the curve LEFT → impaired O₂ delivery to tissues.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 727,
              "stem": "The Phalen test for carpal tunnel syndrome involves:",
              "options": [
                "Tapping over the median nerve at the wrist (Tinel sign)",
                "Resisted wrist extension",
                "Passive finger extension",
                "Holding the wrists in maximum flexion for 60 seconds — reproduction of paraesthesiae in the median nerve distribution is positive",
                "Grip strength testing"
              ],
              "answer": "D",
              "explanation": "Phalen test: both wrists held in maximum FLEXION (prayer position reversed, or pushing dorsum of hands together) for 60 seconds. A positive test reproduces or exacerbates paraesthesiae in the median nerve distribution (thumb, index, middle, and radial half of ring finger). Sensitivity ~70-80%. The REVERSE Phalen (wrists in maximum extension) is an alternative. Tinel sign: tapping over the carpal tunnel at the wrist crease reproduces tingling distally in the median distribution — sensitivity ~60%. Durkan test: direct compression over the carpal tunnel for 30 seconds — most sensitive clinical test (~87%). Clinical diagnosis supported by: night symptoms (waking with numbness, shaking hands to relieve), thenar wasting (late), weak APB. NCS/EMG confirms and quantifies severity.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 728,
              "stem": "After tourniquet release, the initial physiological response in the reperfused limb includes:",
              "options": [
                "Reactive hyperaemia with transient hypotension, release of anaerobic metabolites (lactate, potassium, myoglobin), and possible arrhythmias",
                "Vasoconstriction and hypertension",
                "No physiological changes",
                "Immediate cooling of the limb",
                "Increased bone density"
              ],
              "answer": "A",
              "explanation": "Tourniquet release causes ischaemia-reperfusion injury: (1) reactive hyperaemia (vasodilation in the ischaemic limb → blood pools in the limb → transient systemic hypotension), (2) washout of anaerobic metabolites accumulated during ischaemia (lactate → metabolic acidosis, potassium → hyperkalaemia → cardiac arrhythmias, myoglobin → renal injury), (3) oxygen free radical generation (reperfusion injury to tissues). Bilateral simultaneous tourniquet release is particularly dangerous — should be done sequentially with a 15-20 minute interval. The anaesthetist should be warned before release. In prolonged ischaemia (>2 hours), there is a greater metabolic load on release.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 729,
              "stem": "A patient develops perioral tingling, Chvostek sign (facial twitch on tapping facial nerve), and Trousseau sign (carpopedal spasm with BP cuff inflation) post-thyroidectomy. The most likely electrolyte abnormality is:",
              "options": [
                "Hyperkalaemia",
                "Hyponatraemia",
                "Hypermagnesaemia",
                "Hypophosphataemia",
                "Hypocalcaemia (from inadvertent parathyroid removal or devascularisation)"
              ],
              "answer": "E",
              "explanation": "Post-thyroidectomy hypocalcaemia results from inadvertent damage to or removal of the parathyroid glands (hypoparathyroidism) → reduced PTH → decreased serum calcium. Chvostek sign (facial muscle twitch on tapping the facial nerve anterior to the ear) and Trousseau sign (carpopedal spasm induced by inflating a BP cuff above systolic for 3 minutes — the most specific sign) are classic clinical indicators of hypocalcaemia. Other features: paraesthesiae (circumoral, fingertips), muscle cramps, laryngospasm (dangerous), prolonged QT interval, seizures. In orthopaedics, hypocalcaemia is also seen post-massive transfusion (citrate chelation), post-parathyroidectomy, and in renal osteodystrophy.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 730,
              "stem": "Bone remodelling occurs throughout life via the basic multicellular unit (BMU). The sequence of activity within a BMU is:",
              "options": [
                "Formation → resorption → reversal → quiescence",
                "Activation → resorption → reversal → formation → quiescence (ARF cycle)",
                "Quiescence → formation → resorption → activation",
                "Formation only — no resorption occurs in adults",
                "Random activity with no specific sequence"
              ],
              "answer": "B",
              "explanation": "The bone remodelling cycle (BMU cycle) follows a specific sequence: (1) ACTIVATION: osteocytes detect mechanical strain or microdamage → signal to lining cells on the bone surface → attract osteoclast precursors. (2) RESORPTION: osteoclasts resorb bone (creating a resorption pit/Howship lacuna), lasting ~2-4 weeks. (3) REVERSAL: mononuclear cells prepare the resorbed surface for new bone formation (cement line deposition). (4) FORMATION: osteoblasts deposit new osteoid which mineralises over ~3-4 months. (5) QUIESCENCE: osteoblasts become lining cells or osteocytes (trapped in new bone). The full cycle takes ~4-6 months. In osteoporosis, resorption exceeds formation (uncoupled remodelling — the osteoclast phase is longer/deeper than the osteoblast phase can replace).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Theatre Safety",
          "range": "Q731-Q733",
          "questions": [
            {
              "number": 731,
              "stem": "The most common nerve injury from patient positioning during surgery under general anaesthesia is:",
              "options": [
                "Sciatic nerve",
                "Femoral nerve",
                "Axillary nerve",
                "Brachial plexus",
                "Common peroneal nerve (from lateral decubitus or lithotomy position)"
              ],
              "answer": "E",
              "explanation": "The common peroneal nerve (CPN) is the most commonly injured nerve from positioning because it wraps around the fibular neck superficially with minimal soft tissue protection. Compression against the lateral leg support (in lithotomy), padded leg rests, or the operating table edge (in lateral decubitus) can cause neurapraxia → foot drop. Prevention: adequate padding over the fibular neck, avoiding prolonged compression, and careful positioning checks. The ulnar nerve at the elbow (cubital tunnel) is the most commonly injured nerve in the UPPER limb from positioning. Brachial plexus injury occurs from excessive arm abduction (>90°) or shoulder extension.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 732,
              "stem": "Diathermy in orthopaedic surgery — bipolar diathermy differs from monopolar in that bipolar:",
              "options": [
                "Requires a patient return electrode (grounding pad)",
                "Has current flowing only between the two tips of the forceps (no grounding pad needed, less tissue damage)",
                "Is used exclusively for cutting",
                "Cannot coagulate blood vessels",
                "Is more dangerous than monopolar"
              ],
              "answer": "B",
              "explanation": "Bipolar diathermy: current flows only between the two tips of the bipolar forceps — no patient return electrode (grounding pad) is needed. This limits the thermal effect to the tissue between the tips, reducing collateral tissue damage. It is safer near metal implants, pacemakers, and neurovascular structures. Monopolar diathermy: current flows from the active electrode through the patient to a grounding pad — the current path through the body can cause burns at the grounding pad site or thermal injury to structures in the path. Monopolar should NOT be used near metal implants (current channelling → thermal necrosis) or pacemakers (interference).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 733,
              "stem": "The WHO Surgical Safety Checklist 'sign-out' phase occurs:",
              "options": [
                "Before the patient leaves the operating room",
                "Before induction of anaesthesia",
                "Before skin incision",
                "After the patient is in recovery",
                "The following day"
              ],
              "answer": "A",
              "explanation": "The WHO Sign-out occurs before the patient leaves the operating room. It includes: confirmation of the procedure performed, instrument/needle/swab counts completed and correct, specimen labelling confirmed, any equipment problems documented, key concerns for recovery and post-operative management discussed. This final check ensures nothing is left behind and that the post-operative plan is communicated to the recovery team. The three phases: Sign-in (before anaesthesia), Time-out (before incision), Sign-out (before leaving theatre).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Blood Transfusion",
          "range": "Q734",
          "questions": [
            {
              "number": 734,
              "stem": "An acute haemolytic transfusion reaction is most commonly caused by:",
              "options": [
                "Bacterial contamination of stored blood",
                "Febrile non-haemolytic reaction",
                "ABO-incompatible blood transfusion (clerical error/misidentification)",
                "Allergic reaction to plasma proteins",
                "Transfusion-related acute lung injury (TRALI)"
              ],
              "answer": "C",
              "explanation": "Acute haemolytic transfusion reaction (AHTR) is caused by ABO-incompatible blood transfusion — almost always due to clerical error (wrong blood given to the wrong patient). It is the most serious and potentially fatal transfusion reaction. Anti-A and anti-B antibodies (IgM, naturally occurring) cause rapid intravascular haemolysis → DIC, renal failure, and cardiovascular collapse. Symptoms: fever, rigors, back/flank pain, hypotension, haemoglobinuria, and DIC within minutes of starting transfusion. Management: STOP transfusion immediately, supportive care (IV fluids, vasopressors), send samples for repeat crossmatch and DAT (direct antiglobulin/Coombs test).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Electrolytes",
          "range": "Q735-Q736",
          "questions": [
            {
              "number": 735,
              "stem": "Massive blood transfusion can cause hypocalcaemia because stored blood contains:",
              "options": [
                "Excess calcium",
                "Phosphate that binds calcium",
                "Potassium that displaces calcium",
                "Citrate anticoagulant (which chelates ionised calcium)",
                "No preservatives"
              ],
              "answer": "D",
              "explanation": "Stored blood contains citrate as an anticoagulant. Citrate chelates ionised calcium, and in massive transfusion (≥10 units pRBCs/24h), the citrate load overwhelms the liver's ability to metabolise it, causing clinically significant hypocalcaemia. Symptoms: perioral tingling, muscle cramps, tetany, prolonged QT interval, and potentially cardiac arrest. Treatment: IV calcium gluconate (10ml 10% solution) or calcium chloride (faster but risks tissue necrosis if extravasated). Monitor ionised calcium during massive transfusion. Other complications: hyperkalaemia (potassium leaks from stored RBCs), hypothermia, dilutional coagulopathy.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 736,
              "stem": "Hyperkalaemia is a life-threatening complication of which condition commonly seen in orthopaedic trauma?",
              "options": [
                "Simple fracture of the radius",
                "Isolated soft tissue contusion",
                "Tendon rupture",
                "Compartment syndrome and crush injury (rhabdomyolysis)",
                "Joint effusion"
              ],
              "answer": "D",
              "explanation": "Rhabdomyolysis from crush injury or compartment syndrome releases intracellular contents into the bloodstream: potassium (hyperkalaemia → cardiac arrhythmias), myoglobin (myoglobinuria → acute kidney injury), phosphate (hyperphosphataemia → secondary hypocalcaemia), and creatine kinase (CK — massively elevated, diagnostic marker). Hyperkalaemia is the most immediately life-threatening complication. ECG changes: peaked T waves → widened QRS → sine wave → cardiac arrest. Treatment: (1) cardiac protection (IV calcium gluconate), (2) shift K⁺ intracellularly (insulin + glucose, salbutamol nebuliser), (3) remove K⁺ (calcium resonium, haemodialysis if severe). Aggressive IV fluid resuscitation to maintain urine output >200 ml/h prevents renal failure.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "NCS",
          "range": "Q737",
          "questions": [
            {
              "number": 737,
              "stem": "Nerve conduction studies (NCS) can differentiate neurapraxia from axonotmesis by demonstrating that in neurapraxia:",
              "options": [
                "There is no conduction across or distal to the lesion at any time",
                "Conduction velocity is increased",
                "Conduction is preserved distal to the lesion (Wallerian degeneration has NOT occurred) but blocked across the lesion site",
                "There is complete loss of all nerve function permanently",
                "Motor and sensory responses are absent distally from the outset"
              ],
              "answer": "C",
              "explanation": "In neurapraxia, the axon is structurally intact — there is a conduction block AT the lesion site but distal conduction is normal (because Wallerian degeneration has NOT occurred). NCS performed distal to the lesion shows normal motor and sensory responses. In axonotmesis/neurotmesis, Wallerian degeneration occurs distally within 48-96 hours, so NCS distal to the lesion shows absent or reduced responses after this period. This distinction is clinically important: neurapraxia recovers fully (weeks to 3 months), axonotmesis recovers slowly (~1mm/day), neurotmesis may not recover without surgery.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "BCIS",
          "range": "Q738",
          "questions": [
            {
              "number": 738,
              "stem": "Bone cement implantation syndrome (BCIS) during cemented hip arthroplasty is characterised by:",
              "options": [
                "Hypoxia, hypotension, and/or loss of consciousness occurring around the time of cement insertion, prosthesis insertion, or joint reduction",
                "Hypertension and bradycardia",
                "Delayed wound healing only",
                "Fever at 48 hours post-operatively",
                "Isolated tachycardia without other features"
              ],
              "answer": "A",
              "explanation": "BCIS presents with the triad of hypoxia, hypotension, and/or unexpected loss of consciousness occurring at predictable times: cement insertion, prosthesis insertion, or joint reduction. It is caused by embolisation of marrow contents (fat, marrow, air, cement monomer, thromboplastins) into the venous circulation and pulmonary vasculature, causing a cardiovascular and inflammatory response. Donaldson grading: Grade 1 = moderate hypoxia (SpO₂ <94%) OR hypotension (systolic BP fall >20%). Grade 2 = severe hypoxia (SpO₂ <88%) OR hypotension (BP fall >40%) OR loss of consciousness. Grade 3 = cardiovascular collapse requiring CPR. Risk factors: pathological fracture, intertrochanteric fracture, high ASA grade, pre-existing cardiopulmonary disease.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Fat Embolism",
          "range": "Q739",
          "questions": [
            {
              "number": 739,
              "stem": "Fat embolism syndrome (FES) classically presents with the triad of:",
              "options": [
                "Fever, jaundice, and hepatomegaly",
                "Respiratory distress, neurological changes (confusion), and petechial rash",
                "Chest pain, haemoptysis, and leg swelling",
                "Headache, neck stiffness, and photophobia",
                "Abdominal pain, vomiting, and diarrhoea"
              ],
              "answer": "B",
              "explanation": "The Gurd and Wilson criteria define FES by the classic triad: (1) respiratory distress (hypoxia, tachypnoea, bilateral infiltrates — resembling ARDS, most common feature), (2) neurological changes (confusion, drowsiness, seizures — cerebral fat emboli), (3) petechial rash (non-thrombocytopenic, typically axillary folds, conjunctivae, and neck — pathognomonic when present but only in ~50%). FES occurs 24-72 hours after long bone fractures (especially femoral shaft) or after reaming/IM nailing. Pathogenesis: fat globules from medullary canal enter venous circulation → pulmonary embolisation → inflammatory response → ARDS. Treatment: supportive (oxygen, ventilation, fluids). Prevention: early fracture stabilisation (reduces but does not eliminate risk).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Cement",
          "range": "Q740",
          "questions": [
            {
              "number": 740,
              "stem": "PMMA bone cement reaches its maximum compressive strength after polymerisation. Its main weakness is resistance to:",
              "options": [
                "Compression",
                "Static loading",
                "Uniform pressure",
                "No weakness — it is equally strong in all directions",
                "Tension and shear (poor tensile strength)"
              ],
              "answer": "E",
              "explanation": "PMMA (polymethylmethacrylate) bone cement has good compressive strength (~80-100 MPa, comparable to cancellous bone) but poor tensile and shear strength (~30-50 MPa). This means it is vulnerable to failure under tension and shear loading. In THA, the cement mantle is loaded primarily in compression (ideal) but areas of tension or shear (e.g., at the stem-cement or cement-bone interface during torsion) are vulnerable to cracking and failure. Vacuum mixing reduces porosity (micro-voids act as stress concentrators) and improves fatigue resistance. Third-generation cementing technique optimises the cement mantle to maximise compressive loading.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Brachial Plexus",
          "range": "Q741-Q742",
          "questions": [
            {
              "number": 741,
              "stem": "Erb-Duchenne palsy (upper brachial plexus injury, C5-C6) presents with the arm in which classic position?",
              "options": [
                "Arm adducted, internally rotated, elbow extended, forearm pronated, wrist flexed ('waiter's tip' position)",
                "Arm abducted and externally rotated",
                "Claw hand deformity",
                "Wrist drop only",
                "Isolated finger weakness"
              ],
              "answer": "A",
              "explanation": "Erb-Duchenne palsy (C5-C6 upper trunk injury) produces the 'waiter's tip' position: shoulder adducted (loss of deltoid C5, supraspinatus C5), internally rotated (loss of infraspinatus C5-C6, teres minor C5-C6), elbow extended (loss of biceps C5-C6, brachialis C5-C6), forearm pronated (loss of biceps supination and supinator C6), and wrist flexed (loss of ECRL/ECRB C6 wrist extension). Causes: birth injury (shoulder dystocia), motorcycle accidents (head forced away from shoulder), and falls. In neonates, most recover spontaneously (neurapraxia) within 3-6 months. If no biceps recovery by 3-6 months → surgical exploration (neurolysis, nerve graft, nerve transfer).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 742,
              "stem": "Klumpke palsy (lower brachial plexus injury, C8-T1) affects the hand and may be associated with:",
              "options": [
                "Deltoid weakness",
                "Claw hand deformity with possible Horner syndrome (ptosis, miosis, anhidrosis) if T1 sympathetics are involved",
                "Wrist drop",
                "Foot drop",
                "Shoulder dislocation"
              ],
              "answer": "B",
              "explanation": "Klumpke palsy (C8-T1, lower trunk) affects the intrinsic hand muscles (interossei, lumbricals 3-4, hypothenar, thenar) causing a claw hand deformity (hyperextension at MCPs from unopposed EDC, flexion at IPJs from unopposed FDP). It may be associated with Horner syndrome if the T1 sympathetic fibres are involved (ipsilateral ptosis, miosis/small pupil, anhidrosis/loss of sweating, enophthalmos). Causes: birth injury (arm traction in breech delivery), grabbing an object during a fall (traction on C8-T1 roots), and Pancoast tumour (lung apex tumour invading lower trunk). Much rarer than Erb palsy in obstetric cases.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Nerve",
          "range": "Q743",
          "questions": [
            {
              "number": 743,
              "stem": "Long thoracic nerve injury causes which clinical finding?",
              "options": [
                "Deltoid paralysis",
                "Wrist drop",
                "Claw hand",
                "Foot drop",
                "Winging of the scapula (loss of serratus anterior)"
              ],
              "answer": "E",
              "explanation": "The long thoracic nerve (C5-C7, 'nerve of Bell') innervates serratus anterior, which protracts the scapula and holds its medial border flat against the chest wall. Injury causes MEDIAL winging of the scapula — the medial border lifts off the thorax when the patient pushes against a wall or attempts forward flexion. Causes: surgical injury (axillary node dissection, thoracotomy, first rib resection), trauma (blunt shoulder trauma), viral neuritis (Parsonage-Turner syndrome), and repetitive overhead activity. Spinal accessory nerve injury (trapezius paralysis) causes LATERAL winging (different pattern). Most long thoracic nerve palsies recover spontaneously (6-24 months). If no recovery: pectoralis major transfer (Eden-Lange, or Iceton modification).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Cartilage",
          "range": "Q744-Q746",
          "questions": [
            {
              "number": 744,
              "stem": "Articular cartilage is avascular and anueral. Its nutrition is primarily derived from:",
              "options": [
                "Blood vessels within the cartilage matrix",
                "Direct arterial supply from the bone",
                "Lymphatic drainage",
                "Synovial fluid diffusion (enhanced by joint loading and unloading cycles)",
                "Venous drainage"
              ],
              "answer": "D",
              "explanation": "Articular cartilage is avascular, anueral, and alymphatic — it has no direct blood supply, nerve supply, or lymphatic drainage. Nutrition is derived almost entirely from synovial fluid by diffusion, enhanced by the 'sponge effect' of cyclical joint loading and unloading (compression squeezes fluid out, decompression draws nutrient-rich synovial fluid in). This is why immobilisation is detrimental to cartilage health (no pump mechanism) and why early motion after injury/surgery is beneficial. Cartilage matrix: Type II collagen (~50% dry weight) + proteoglycans (aggrecan — traps water, provides compressive stiffness) + water (~70-80%). Chondrocytes produce and maintain the matrix.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 745,
              "stem": "Proteoglycans in articular cartilage are primarily responsible for:",
              "options": [
                "Providing tensile strength",
                "Attaching cartilage to bone",
                "Resisting compressive loads (by attracting and retaining water through osmotic pressure)",
                "Providing elasticity only",
                "Vascular supply to cartilage"
              ],
              "answer": "C",
              "explanation": "Proteoglycans (predominantly aggrecan) are large molecules consisting of a core protein with glycosaminoglycan (GAG) side chains (chondroitin sulphate, keratan sulphate). The negatively charged GAGs attract water through osmotic pressure (Donnan osmotic effect), creating a swelling pressure that gives cartilage its resistance to compressive loads. When compressed, water is squeezed out; when load is removed, water is drawn back in (sponge-like behaviour). Type II collagen provides the tensile framework that constrains this swelling pressure. The balance between proteoglycan swelling pressure and collagen tensile restraint gives cartilage its unique biphasic mechanical properties.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 746,
              "stem": "The tidemark in articular cartilage represents:",
              "options": [
                "The surface of the cartilage",
                "The junction between the calcified and uncalcified cartilage zones",
                "The deepest layer of bone",
                "The area of highest cellularity",
                "The blood vessel entry point"
              ],
              "answer": "B",
              "explanation": "The tidemark is a basophilic line visible on histological sections that represents the junction between the uncalcified (deep/radial zone) and calcified cartilage zones. It acts as a mechanical transition zone — converting shear stress to compressive stress at the bone-cartilage interface. The calcified cartilage anchors the articular cartilage to the underlying subchondral bone plate. With ageing and osteoarthritis, the tidemark advances (the calcified zone thickens at the expense of the uncalcified cartilage — 'tidemark advancement'), reducing the effective cartilage thickness and its shock-absorbing capacity. Tidemark duplication on histology is a feature of OA.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        }
      ]
    },
    {
      "title": "Lower Limb",
      "chapters": [
        {
          "title": "Arthroplasty",
          "range": "Q747-Q778",
          "questions": [
            {
              "number": 747,
              "stem": "Dual mobility cups in THA are specifically designed to reduce the risk of:",
              "options": [
                "DISLOCATION — the design uses a small inner bearing (femoral head articulating within a mobile PE liner) plus a large outer bearing (the PE liner articulating within the metal acetabular shell), providing a very large effective head diameter and maximum range of motion before impingement",
                "Infection",
                "Bearing wear",
                "Loosening directly",
                "Periprosthetic fracture"
              ],
              "answer": "A",
              "explanation": "Dual mobility cups (first introduced in France by Bousquet, 1974) have TWO articulations: (1) INNER bearing: a standard femoral head (22-28mm) articulates within a mobile PE liner (the head captures into the liner via a snap-fit). (2) OUTER bearing: the PE liner articulates within a polished metal acetabular shell (the liner acts as a very large 'head' — effectively giving a 40-50mm+ head diameter). The large effective head diameter provides: (1) MAXIMUM range of motion before impingement occurs (the neck contacts the PE liner at a much greater arc than a fixed liner), (2) a very HIGH 'jump distance' (the head must translate further to dislocate → dislocation rates <0.5-1%). Indications: high dislocation risk patients (previous dislocation, revision THA, cognitive impairment, neuromuscular disease, spastic patients, elderly with poor compliance to precautions, tumour reconstruction). Concern: intraprosthetic dislocation (the head can dissociate from the mobile liner — rare, ~0.5-2%). NJR data shows excellent outcomes and very low dislocation rates with dual mobility.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 748,
              "stem": "The most common complication of TKA in the first year post-operatively is:",
              "options": [
                "Deep infection",
                "Loosening",
                "Periprosthetic fracture",
                "Instability",
                "STIFFNESS (arthrofibrosis — failure to achieve adequate ROM, particularly if <90° flexion, which limits functional activities like stair climbing and rising from a chair)"
              ],
              "answer": "E",
              "explanation": "Stiffness/arthrofibrosis is the most common complication of TKA in the first year. Defined: failure to achieve functional ROM (typically <90° flexion is considered stiff — normal target post-TKA is 0-120°+ flexion). Causes: (1) excessive scar tissue/fibrosis within the joint and periarticular soft tissues, (2) pre-operative stiffness (the best predictor of post-operative ROM is pre-operative ROM), (3) inadequate post-operative rehabilitation (insufficient physiotherapy/patient compliance), (4) component malposition (overstuffed joint — PE too thick, femoral component too anterior), (5) infection (low-grade infection can present as stiffness), (6) CRPS. Treatment: (1) aggressive physiotherapy (early intervention), (2) manipulation under anaesthesia (MUA — best results if performed within 6-12 weeks of surgery, before scar tissue matures), (3) arthroscopic or open lysis of adhesions (if MUA fails), (4) revision TKA (if component malposition identified). Prevention: pre-operative ROM optimisation, intra-operative gap balancing, aggressive early post-operative physiotherapy (day of surgery mobilisation), adequate analgesia (facilitates participation in rehab).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 749,
              "stem": "Bone cement implantation syndrome (BCIS) occurs during cemented arthroplasty and is characterised by:",
              "options": [
                "Only minor discomfort",
                "Isolated fever without haemodynamic compromise",
                "Mild tachycardia only",
                "Hypotension, hypoxia, and/or loss of consciousness occurring during cementation, prosthesis insertion, or joint reduction — potentially fatal",
                "Delayed wound infection"
              ],
              "answer": "D",
              "explanation": "BCIS is a potentially fatal intra-operative event characterised by hypotension, hypoxia, and/or unexpected loss of consciousness occurring during or shortly after cementation, prosthesis insertion, joint reduction, or tourniquet deflation. It is most commonly associated with cemented hip arthroplasty for femoral neck fracture (elderly, ASA 3-4, pre-existing cardiopulmonary disease). Donaldson classification: Grade 1 = SpO₂ <94% or SBP drop >20%. Grade 2 = SpO₂ <88% or SBP drop >40% or unexpected LOC. Grade 3 = cardiovascular collapse requiring CPR. Mechanism: pressurisation of cement forces fat, marrow contents, air, and monomers into the venous system → embolic shower to the pulmonary vasculature → vasoconstriction + right heart failure. Risk factors: long-stem cemented implants, revision surgery, reaming, pre-existing cardiopulmonary disease, elderly. Prevention: medullary lavage + suction before cementation, retrograde cement insertion, venting (cement restrictor + vent hole), avoiding excessive pressurisation, adequate hydration.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 750,
              "stem": "The CRISTAL trial (2024) on VTE prophylaxis after arthroplasty demonstrated that:",
              "options": [
                "Aspirin is inferior to all other agents",
                "Warfarin is superior to LMWH",
                "Aspirin was non-inferior to rivaroxaban for VTE prevention after hip and knee arthroplasty (when used after an initial period of LMWH)",
                "No prophylaxis is needed",
                "Only mechanical prophylaxis is effective"
              ],
              "answer": "C",
              "explanation": "The CRISTAL trial (2024, Australian multicentre RCT) randomised patients undergoing THA or TKA to aspirin 100mg daily vs rivaroxaban 10mg daily (both starting after an initial 5 days of LMWH). It found aspirin was NON-INFERIOR to rivaroxaban for the prevention of symptomatic VTE, with no significant difference in bleeding complications. This trial supports the growing body of evidence (alongside EPCAT-II and other trials) that aspirin may be an acceptable, cheaper, and more accessible alternative to DOACs/LMWH for extended VTE prophylaxis after arthroplasty in standard-risk patients. However: aspirin may not be sufficient for HIGH-RISK patients (previous VTE, thrombophilia, cancer, prolonged immobility), where more potent agents remain indicated.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 751,
              "stem": "The Vancouver classification of periprosthetic femoral fractures around THA — Type B2 indicates:",
              "options": [
                "Fracture around or just below a WELL-FIXED stem (Type B1)",
                "Fracture well below the tip of the stem (Type C)",
                "Trochanteric fracture (Type A)",
                "Fracture around or just below a LOOSE stem with adequate bone stock (requires revision to long stem)",
                "Fracture above the stem"
              ],
              "answer": "D",
              "explanation": "Vancouver classification: Type A = trochanteric fractures (AG = greater trochanter, AL = lesser trochanter — usually non-operative or cerclage). Type B = fractures around or just below the stem: B1 = stem WELL-FIXED + adequate bone → ORIF (plate/cerclage — don't revise a well-fixed stem). B2 = stem LOOSE + adequate bone stock → REVISION to a long uncemented stem (diaphyseal fixation distally, bypasses the fracture). B3 = stem LOOSE + POOR bone stock → complex revision (tumour prosthesis, impaction grafting + cemented long stem, or strut allograft). Type C = fracture well below the tip of the stem (independent of the implant) → treat as a standard distal femoral fracture (plate fixation). The critical clinical distinction is B1 vs B2: intra-operative assessment of stem stability determines whether to fix around (B1) or revise (B2).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 752,
              "stem": "Metal-on-metal (MoM) hip bearings have fallen out of favour due to:",
              "options": [
                "Adverse reactions to metal debris (ARMD) — including pseudotumours, metallosis, soft tissue necrosis, and elevated cobalt/chromium ion levels causing systemic toxicity",
                "Superior wear characteristics",
                "Lower cost than other bearings",
                "No specific problems identified",
                "Better long-term outcomes than CoC"
              ],
              "answer": "A",
              "explanation": "MoM bearings (CoCr-on-CoCr) were initially attractive due to low volumetric wear and the ability to use large-diameter heads (reducing dislocation risk). However, they generate nanoscale metallic wear particles and ions (cobalt, chromium) → local tissue reactions (ARMD): pseudotumours (solid or cystic inflammatory masses), metallosis (black tissue staining with macrophage infiltration), soft tissue necrosis, osteolysis, and early loosening. Systemic effects: elevated serum cobalt and chromium levels → potential cardiotoxicity, neurotoxicity, thyroid dysfunction, and theoretical carcinogenesis risk. The ASR hip resurfacing (DePuy) was recalled in 2010 due to high failure rates — identified through NJR data. Current practice: MoM is no longer used for new implants. Patients with existing MoM implants require lifelong monitoring (annual metal ion levels, USS/MRI for ARMD if symptoms or elevated ions).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 753,
              "stem": "In TKA, the tibial component is typically aligned with:",
              "options": [
                "Maximum valgus to match the anatomical axis",
                "No specific alignment targets",
                "3-5° of posterior slope (to facilitate flexion and posterior rollback) and neutral rotational alignment (typically referenced to the medial 1/3 of the tibial tubercle or Akagi line)",
                "Maximum internal rotation",
                "Anterior slope"
              ],
              "answer": "C",
              "explanation": "The tibial component in TKA is aligned with: (1) CORONAL PLANE: perpendicular to the mechanical axis of the tibia (neutral — neither varus nor valgus). (2) SAGITTAL PLANE: 3-5° of posterior slope (matches the natural posterior inclination of the tibial plateau — this facilitates knee flexion by allowing posterior rollback of the femur on the tibia, and accommodates the PCL in CR designs). Excessive posterior slope (>7°) risks PCL over-tension (CR) or instability in flexion. Insufficient slope impairs flexion. (3) ROTATIONAL ALIGNMENT: the tibial component is externally rotated relative to the tibial shaft, typically referenced to the medial 1/3 of the tibial tubercle, the Akagi line (from the PCL attachment to the medial 1/3 of the tibial tubercle), or the posterior condylar axis. Malrotation (internal rotation) → patellar tracking problems, anterior knee pain, and flexion instability.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 754,
              "stem": "Robotics and navigation in TKA primarily aim to improve:",
              "options": [
                "Surgical speed",
                "Patient compliance with physiotherapy",
                "Implant cost",
                "Infection rates directly",
                "Component positioning accuracy and reproducibility (reducing outliers in alignment, particularly in malalignment-related complications)"
              ],
              "answer": "E",
              "explanation": "Robotic-assisted and navigation-guided TKA systems aim to improve the ACCURACY and REPRODUCIBILITY of component positioning, reducing outlier implants (those placed outside the acceptable alignment range). Studies show: (1) robotics/navigation significantly reduce the percentage of components placed outside ±3° of the planned alignment (from ~20-30% with conventional techniques to <5% with robotics). (2) This may translate to improved long-term implant survival (malalignment is associated with accelerated wear, loosening, and instability). However: current evidence on patient-reported outcomes is mixed — large RCTs have not consistently shown clinically significant improvements in pain/function scores compared to conventional surgery (likely because most conventionally placed TKAs function well). The technology improves PRECISION but the clinical benefit for the average patient is still being established. Costs: higher upfront (robotic systems, disposables, OR time), potentially offset by reduced revision rates long-term.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            },
            {
              "number": 755,
              "stem": "Third-generation cementing technique in THA includes all of the following EXCEPT:",
              "options": [
                "Pulse lavage of the femoral canal (removes blood/debris for better cement interdigitation)",
                "Finger-packing cement without any canal preparation",
                "Use of a cement restrictor (plug to prevent cement migrating distally into the diaphysis)",
                "Retrograde cement injection with a cement gun",
                "Pressurisation of cement with a proximal seal"
              ],
              "answer": "B",
              "explanation": "Third-generation cementing technique maximises the quality and durability of the cement mantle: (1) PULSE LAVAGE — high-pressure irrigation of the femoral canal to remove blood, fat, and debris (creates clean cancellous bone for optimal cement interdigitation → stronger cement-bone interface). (2) CANAL DRYING — brush + suction to dry the canal after lavage. (3) CEMENT RESTRICTOR (intramedullary plug) — placed ~2cm beyond the planned stem tip to prevent cement migrating distally and to allow pressurisation. (4) RETROGRADE CEMENT INJECTION — cement gun delivers cement from the plug upwards (retrograde), filling the canal from distal to proximal without trapping air. (5) PRESSURISATION — a proximal femoral seal is applied and cement is pressurised to force it into the cancellous interstices (improves interdigitation). (6) VACUUM MIXING — reduces cement porosity (air bubbles = stress concentrators for fatigue failure). FINGER-PACKING without canal preparation is the FIRST-generation technique — associated with poorer cement mantles, higher loosening rates, and shorter implant survival.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 756,
              "stem": "Wear particle-induced osteolysis around joint replacements is mediated by:",
              "options": [
                "Direct toxic effect of the implant metal",
                "Infection only",
                "Normal bone remodelling",
                "Macrophage activation by wear particles → release of pro-inflammatory cytokines (TNF-α, IL-1, IL-6) → osteoclast activation via RANKL → periprosthetic bone resorption → loosening",
                "Excessive exercise"
              ],
              "answer": "D",
              "explanation": "Wear particle-induced osteolysis is the primary biological mechanism of ASEPTIC LOOSENING — the most common long-term failure mode of joint replacements. Mechanism: (1) wear particles (polyethylene, metal, ceramic, or cement) are generated at the bearing surfaces and modular junctions. (2) Particles are phagocytosed by MACROPHAGES. (3) Activated macrophages release pro-inflammatory cytokines: TNF-α, IL-1, IL-6, PGE2. (4) These cytokines stimulate OSTEOCLASTS (via RANKL upregulation) → periprosthetic bone resorption. (5) Progressive osteolysis → implant loosening → pain/failure → revision. The critical particle size for macrophage activation: 0.1-10μm (submicron particles are most biologically active). Reducing wear: XLPE (5-10× lower wear than conventional PE), ceramic-on-ceramic (lowest wear), improving manufacturing/sterilisation. Monitoring: serial XR for progressive radiolucent lines around implants.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 757,
              "stem": "Unicompartmental knee arthroplasty (UKA) is indicated for isolated medial compartment OA. The classic Oxford criteria for UKA include all EXCEPT:",
              "options": [
                "Intact ACL",
                "Correctable varus deformity",
                "Full-thickness cartilage loss in the affected compartment",
                "Age-appropriate activity level",
                "Inflammatory arthritis (this is a CONTRAINDICATION — inflammatory arthritis affects all compartments and is systemic)"
              ],
              "answer": "E",
              "explanation": "The Oxford criteria for medial UKA (Oxford Partial Knee): (1) INTACT ACL (ACL deficiency → abnormal kinematics → UKA failure). (2) Correctable varus deformity (fixed varus >15° or fixed flexion contracture >15° are contraindications). (3) Full-thickness cartilage loss in the medial compartment (bone-on-bone — ensures the UKA addresses the true pathology). (4) Intact lateral compartment (preserved lateral cartilage — if lateral compartment involved, needs TKA). (5) Functionally intact MCL. Contraindications: inflammatory arthritis (RA — systemic, affects all compartments → TKA), ACL deficiency, significant lateral compartment involvement, fixed varus >15° or fixed flexion >15°, previous high tibial osteotomy (relative). UKA advantages over TKA: faster recovery, more natural knee kinematics, bone-preserving, less blood loss. 10-year survival: 93-97% (Oxford). NJR data: UKA has slightly higher revision rate than TKA but this may reflect easier revision threshold (revision of UKA → primary TKA, which has good outcomes).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 758,
              "stem": "Highly cross-linked polyethylene (XLPE) in joint arthroplasty has reduced volumetric wear by:",
              "options": [
                "No reduction compared to conventional PE",
                "5-10 times compared to conventional ultra-high molecular weight polyethylene (UHMWPE) — by increasing cross-links between polymer chains through radiation and thermal treatment",
                "Only 2%",
                "It has increased wear compared to conventional PE",
                "100 times"
              ],
              "answer": "B",
              "explanation": "XLPE has dramatically reduced the wear problem in arthroplasty. Manufacturing: UHMWPE is irradiated with gamma or electron beam radiation (typically 5-10 Mrad, vs ~2.5 Mrad for sterilisation of conventional PE) → this creates cross-links between polymer chains → the resulting material has significantly improved wear resistance. Volumetric wear reduction: 5-10× lower than conventional PE in simulator studies and clinical follow-up (linear wear rate ~0.01-0.05mm/yr for XLPE vs ~0.1-0.2mm/yr for conventional PE). However: increased cross-linking reduces: (1) fatigue strength (cross-links reduce molecular mobility → more brittle), (2) fracture toughness (risk of fracture in thin PE — concern with small acetabular cups and knee PE inserts), and (3) oxidation resistance (free radicals from irradiation → must be quenched by thermal treatment or vitamin E doping). Generations: 1st-gen XLPE (remelted — reduced oxidation but lower mechanical properties), 2nd-gen (annealed or vitamin E-infused — better balance of wear resistance + mechanical properties).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 759,
              "stem": "Ceramic-on-ceramic (CoC) bearings in THA have the lowest wear rate but the most concerning complication is:",
              "options": [
                "Ceramic fracture (catastrophic failure — reported in ~0.02-0.2% of cases, more common with earlier generations, requires complete synovectomy and component revision)",
                "High infection rate",
                "No complications at all",
                "Excessive osteolysis",
                "Metal ion release"
              ],
              "answer": "A",
              "explanation": "CoC bearings (alumina or alumina matrix composite — AMC/BIOLOX delta) produce the LOWEST volumetric wear of all bearing couples (<0.001mm/yr linear wear). However, ceramic-specific complications exist: (1) CERAMIC FRACTURE (~0.02-0.2% — catastrophic, requires urgent revision, complete synovectomy to remove ALL ceramic fragments which act as abrasive third-body wear particles, and revision to another ceramic or metal head — never revise to PE bearing after ceramic fracture as retained ceramic particles destroy the PE). (2) SQUEAKING (~1-10% — audible noise during motion, usually benign but occasionally severe enough to warrant revision; associated with edge-loading, microseparation, and component malposition). (3) STRIPE WEAR (from edge-loading due to microseparation during the swing phase — can accelerate wear in localised areas). 4th-generation ceramics (AMC/BIOLOX delta): much lower fracture risk than earlier generations (added zirconia toughening and strontium aluminate platelets). CoC is increasingly popular for young, active patients seeking maximum longevity.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 760,
              "stem": "The ODEP (Orthopaedic Data Evaluation Panel) rating of an implant indicates:",
              "options": [
                "The surgeon's skill level",
                "The cost of the implant",
                "The evidence base for the implant's long-term performance (rated by benchmark survival data from registries and published studies — used by NICE to guide implant selection)",
                "The patient's satisfaction",
                "The hospital's infection rate"
              ],
              "answer": "C",
              "explanation": "ODEP provides an independent assessment of orthopaedic implant performance based on published evidence. Rating system: implants are rated by years of follow-up data and quality of evidence. For example: ODEP 10A = ≥10 years of follow-up data at the highest evidence level (A). ODEP 7A = 7 years of data at level A. NICE recommends that implants used in the NHS should have an ODEP rating of 10A (or equivalent NJR data showing ≥95% survival at 10 years). Implants without adequate ODEP rating may still be used but should be entered into the Beyond Compliance registry (close monitoring). The system protects patients by ensuring that only implants with proven long-term track records are widely used — preventing adoption of novel designs without adequate evidence (recalls like the ASR MoM hip demonstrated the danger of adopting unproven implants). The NJR provides complementary real-world data on implant performance across the NHS.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 761,
              "stem": "The most common reason for revision TKA is:",
              "options": [
                "Bearing surface wear",
                "Infection",
                "Periprosthetic fracture",
                "Aseptic loosening (historically most common, though recent registry data shows infection becoming the leading cause of early revision in some registries)",
                "Instability"
              ],
              "answer": "D",
              "explanation": "Historically, ASEPTIC LOOSENING has been the most common reason for revision TKA overall. However, recent NJR and AJRR data show that INFECTION (PJI) has become the leading cause of EARLY revision (within the first 2 years), while aseptic loosening remains dominant for late revisions. Other common revision causes: instability (flexion/extension gap imbalance, PCL dysfunction), polyethylene wear, periprosthetic fracture, pain/stiffness, extensor mechanism failure, and component malposition. The changing pattern reflects: improved PE wear resistance (XLPE → less wear-related loosening), improved alignment techniques (navigation/robotics → fewer malpositoned implants), but persistent infection challenge (biofilm on implants, increasing antibiotic resistance, more immunocompromised patients). Overall: when all time points are combined, aseptic loosening remains the most common cause (though infection is catching up and dominates in the early period).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 762,
              "stem": "Cemented vs uncemented THA — cemented femoral stems are specifically recommended by NICE for:",
              "options": [
                "Young active patients only",
                "All patients without exception",
                "Patients with femoral neck fractures (elderly) — cemented stems have lower peri-operative periprosthetic fracture rates and possibly lower mortality compared to uncemented stems in this population",
                "Only revision surgery",
                "Patients under 50 only"
              ],
              "answer": "C",
              "explanation": "NICE guidelines recommend CEMENTED femoral stems for hip fracture patients (elderly) based on evidence that: (1) cemented stems have LOWER peri-operative periprosthetic fracture rates (~1% vs ~4-7% for uncemented press-fit stems in osteoporotic elderly bone). (2) Some evidence suggests lower early MORTALITY with cemented vs uncemented in the elderly fracture population (possibly because periprosthetic fractures and the resultant revision surgery carry significant mortality in frail elderly patients). (3) Better immediate fixation in osteoporotic bone (press-fit uncemented stems may not achieve adequate initial stability in soft cancellous bone). The COUNTERARGUMENT for uncemented: BCIS risk with cementing (particularly in elderly fracture patients — high ASA grade, cardiopulmonary disease). Balance: modern third-generation cementing techniques + adequate resuscitation + anaesthetic vigilance reduce BCIS risk. NICE: cemented is the default for fracture patients unless specific contraindications exist. For ELECTIVE THA in younger patients: uncemented is commonly used (relies on biological fixation/osseointegration — better long-term fixation potential in good bone).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 763,
              "stem": "The most common bearing couple used in THA in the UK (based on NJR data) is:",
              "options": [
                "Metal-on-metal (no longer used)",
                "Metal head on highly cross-linked polyethylene (MoXLPE — the most commonly used bearing combination, providing low wear with a proven track record and wide availability)",
                "Ceramic-on-ceramic",
                "Ceramic-on-metal",
                "Metal-on-conventional polyethylene"
              ],
              "answer": "B",
              "explanation": "Metal (CoCr) head on highly cross-linked polyethylene (XLPE) is the most commonly used bearing couple in the UK (and globally), based on NJR data. Advantages: (1) LOW WEAR (XLPE reduces wear by 5-10× compared to conventional PE), (2) PROVEN track record (decades of experience with metal-on-PE, improved further by cross-linking), (3) WIDE AVAILABILITY of head sizes (28mm-44mm — larger heads reduce dislocation risk), (4) FORGIVING of slight component malposition (PE accommodates edge-loading better than ceramic), (5) COST-EFFECTIVE. Disadvantages: PE wear (though dramatically reduced with XLPE), PE fracture risk (thin liners, small cups), and long-term osteolysis potential (though rare with XLPE). Alternative: CoC (lowest wear but fracture/squeaking risk), CoxLPE (ceramic head on PE — may have slightly lower wear than MoXLPE due to smoother ceramic surface and better wettability). MoM: no longer used (ARMD). Conventional PE: largely replaced by XLPE.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 764,
              "stem": "The Gruen zones for the femoral component in THA divide the periprosthetic femur into how many zones on AP and lateral radiographs?",
              "options": [
                "7 zones on the AP radiograph (zones 1-7 — zone 1 is the greater trochanter region laterally, zone 7 is the medial calcar region, and zones 8-14 on the lateral view for a total of 14)",
                "3 zones",
                "5 zones",
                "10 zones",
                "2 zones"
              ],
              "answer": "A",
              "explanation": "Gruen zones: the periprosthetic femur is divided into 7 zones on the AP radiograph and 7 zones on the lateral radiograph (14 total). AP view: Zone 1 = greater trochanter (lateral proximal), Zone 2 = lateral proximal stem, Zone 3 = lateral distal stem, Zone 4 = stem tip, Zone 5 = medial distal stem, Zone 6 = medial proximal stem (calcar), Zone 7 = lesser trochanter/medial calcar (medial proximal). Radiolucent lines (RLLs) in these zones indicate: loosening (progressive RLLs), osteolysis (expansile lysis), stress shielding (cortical thinning — zones 1 and 7), or normal cement mantle interface (stable, non-progressive, <2mm). Stress shielding: most prominent in zones 1 and 7 (proximal femur — the stiff stem bypasses load to the diaphysis). Subsidence: measured in zone 4 (stem tip moves distally). DeLee-Charnley zones: the corresponding zones for the ACETABULAR component (3 zones on the AP view — zone I = superolateral, zone II = superomedial, zone III = inferomedial).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 765,
              "stem": "The DeLee-Charnley zones for the acetabular component in THA — Zone I is:",
              "options": [
                "Inferomedial (that's Zone III)",
                "Superomedial (that's Zone II)",
                "At the dome only",
                "Behind the cup",
                "Superolateral (the most loaded zone — where cup loosening often begins, and where wear-related osteolysis is most commonly observed)"
              ],
              "answer": "E",
              "explanation": "DeLee-Charnley zones divide the acetabular component interface into 3 zones on the AP pelvis radiograph: Zone I = SUPEROLATERAL (the primary weight-bearing zone — subjected to the highest compressive forces during gait). Zone II = SUPEROMEDIAL (dome region). Zone III = INFEROMEDIAL (teardrop/inferior region). Radiolucent lines (RLLs) in acetabular zones: Zone I RLLs are most concerning for loosening (the zone under greatest load — mechanical failure typically begins here). Progressive RLLs in all 3 zones → cup loosening. Osteolysis from PE wear particles: often begins in Zone I (highest contact pressure → most wear occurs at the superolateral cup-head interface → particles track along the interface). Cemented cup: RLLs may be at the cement-bone interface. Uncemented cup: RLLs at the bone-implant interface. Stable fibrous fixation (cemented): non-progressive RLL <2mm in all zones (Hodgkinson classification). Cup migration: measured on serial AP XRs (change in cup centre position relative to fixed pelvic landmarks).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 766,
              "stem": "The Lewinnek 'safe zone' for acetabular cup positioning in THA specifies:",
              "options": [
                "Any position is acceptable",
                "Only inclination matters",
                "Only anteversion matters",
                "Inclination 40° ± 10° (range 30-50°) and anteversion 15° ± 10° (range 5-25°) — positioning the cup within these ranges is associated with lower dislocation rates",
                "Exact values with no tolerance"
              ],
              "answer": "D",
              "explanation": "Lewinnek safe zone (1978): defined the optimal acetabular cup position as INCLINATION (abduction angle) 40° ± 10° (range 30-50°) and ANTEVERSION 15° ± 10° (range 5-25°). Cups positioned WITHIN these ranges have significantly lower dislocation rates than those positioned outside. However: recent studies have challenged the absolute reliability of the Lewinnek safe zone — some dislocations occur even with 'well-positioned' cups, and some stable hips have cups outside the safe zone. This suggests that cup position alone doesn't determine stability — other factors contribute: femoral anteversion (combined anteversion concept: cup + stem anteversion should total ~25-40°), head size (larger = more stable), soft tissue tension (offset restoration), surgical approach (posterior → posterior capsulorrhaphy essential), and patient factors (BMI, cognitive status, compliance). Navigation/robotics: improve accuracy of cup placement within the safe zone. Despite limitations, the Lewinnek safe zone remains the most widely used reference standard.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 767,
              "stem": "Periprosthetic joint infection (PJI) is diagnosed using a combination of criteria. Which of the following is MOST suggestive of PJI?",
              "options": [
                "Normal CRP and ESR",
                "Dry tap on aspiration",
                "Only mild post-operative pain",
                "Normal radiographs",
                "Synovial fluid WCC >3,000 cells/µL AND synovial fluid PMN% >80% (from joint aspiration — these thresholds are the MSIS/ICM criteria for PJI of a hip or knee)"
              ],
              "answer": "E",
              "explanation": "PJI diagnosis uses the MSIS (Musculoskeletal Infection Society) / ICM (International Consensus Meeting) criteria — a combination of major and minor criteria. MAJOR criteria (either one = PJI confirmed): (1) two positive periprosthetic cultures with the SAME organism, (2) sinus tract communicating with the joint. MINOR criteria (scoring system): elevated serum CRP (>10mg/L), elevated ESR (>30mm/hr), elevated synovial fluid WCC (>3,000 cells/µL for chronic, >10,000 for acute), elevated synovial PMN% (>80%), positive alpha-defensin (most accurate synovial marker — ~97% sensitivity/specificity), elevated synovial CRP, single positive culture. Synovial fluid analysis: the MOST USEFUL investigation — aspirate the joint under sterile conditions. WCC >3,000 with >80% PMNs strongly suggests PJI. Alpha-defensin: the single most accurate synovial marker (can be performed as a lateral flow test in the OR). Normal CRP/ESR doesn't exclude low-grade PJI (Cutibacterium acnes infections may have normal inflammatory markers). Radiographs: often normal in early PJI.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 768,
              "stem": "The most common reason for THA in the UK is:",
              "options": [
                "Rheumatoid arthritis",
                "Primary osteoarthritis (accounts for ~90% of primary THA procedures)",
                "Avascular necrosis",
                "Femoral neck fracture",
                "Ankylosing spondylitis"
              ],
              "answer": "B",
              "explanation": "Primary osteoarthritis accounts for approximately 90% of primary THA procedures recorded in the NJR. Other indications: femoral neck fracture (~5%), AVN, RA, DDH, and other inflammatory/developmental conditions. The decision for THA is based on: (1) pain unresponsive to adequate conservative management, (2) functional limitation affecting quality of life, (3) radiographic evidence of OA. NICE: THA should be offered when conservative management has failed and pain/function significantly impact daily life. 10-year survival of primary THA in the NJR: ~95-97%.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 769,
              "stem": "The concept of enhanced recovery after surgery (ERAS) in arthroplasty aims to:",
              "options": [
                "Prolong hospital stay for maximum monitoring",
                "Eliminate all surgical risks",
                "Reduce perioperative stress response, optimise pain management, enable early mobilisation, and shorten length of stay while maintaining safety and outcomes",
                "Delay rehabilitation until 6 weeks post-operatively",
                "Only apply to young healthy patients"
              ],
              "answer": "C",
              "explanation": "ERAS (Enhanced Recovery After Surgery) is a multimodal perioperative care pathway that reduces physiological stress, improves recovery, and shortens hospital stay. Key components: (1) Pre-operative: patient education and expectation management, optimisation (HbA1c, nutrition, smoking cessation, anaemia correction), carbohydrate loading, avoid prolonged fasting. (2) Intra-operative: minimally invasive/muscle-sparing approaches where appropriate, spinal anaesthesia (reduced blood loss, better post-op analgesia), TXA, local infiltration analgesia (LIA), normothermia. (3) Post-operative: multimodal analgesia (avoiding excessive opioids — NSAIDs, paracetamol, gabapentinoids, LIA), early mobilisation (day of surgery), early oral intake, early catheter removal, DVT prophylaxis, discharge criteria-based (not day-based). Many centres now achieve same-day or next-day discharge for primary THA/TKA. ERAS applies to ALL suitable patients, not just young/healthy.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 770,
              "stem": "The most common reason for revision of total knee arthroplasty in the first 2 years is:",
              "options": [
                "Instability or malalignment",
                "Aseptic loosening",
                "Polyethylene wear",
                "Infection",
                "Periprosthetic fracture"
              ],
              "answer": "A",
              "explanation": "In the early post-operative period (<2 years), the most common reasons for TKA revision are instability, malalignment, and infection. NJR data shows instability/malalignment as the leading cause of early revision. In the longer term (>5 years), aseptic loosening and polyethylene wear become more prevalent. Instability can result from component malrotation, incorrect sizing, ligament imbalance, or inadequate constraint. Understanding the failure mode timeline guides investigation and management of the painful TKA.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 771,
              "stem": "The most important factor in long-term THA survival is:",
              "options": [
                "Patient age",
                "Surgeon volume/experience and component positioning",
                "Implant cost",
                "Hospital size",
                "Time of day the surgery is performed"
              ],
              "answer": "B",
              "explanation": "Surgeon volume and experience (including proper component positioning) is the most important modifiable factor in long-term THA survival. NJR data consistently shows that surgeons and centres performing higher volumes of arthroplasty have lower revision rates. Proper component positioning (cup inclination, anteversion, combined anteversion, leg length restoration, offset) reduces dislocation, wear, and loosening. The implant itself matters (ODEP-rated implants with proven track records should be used), but even the best implant positioned poorly will fail. Patient factors (age, BMI, activity level, comorbidities) also influence outcomes but are less modifiable.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 772,
              "stem": "ODEP (Orthopaedic Data Evaluation Panel) rates prosthetic implants. An ODEP rating of 10A means:",
              "options": [
                "The implant has been on the market for 10 years but no data exists",
                "The implant failed in 10% of cases",
                "Only 10 patients have received the implant",
                "The implant is experimental",
                "The implant has ≥10 years of data showing ≥90% survivorship at 10 years (benchmark standard)"
              ],
              "answer": "E",
              "explanation": "ODEP was established to independently assess the performance of orthopaedic implants using published evidence and NJR data. The rating system: number = years of data available, letter = evidence quality (A = best evidence, meeting benchmark of ≥90% survival at stated time point; B = acceptable evidence, approaching benchmark; * = pre-entry or insufficient data). A 10A rating means ≥10 years of data demonstrating ≥90% survivorship — this is the benchmark that NICE recommends all implants should achieve before widespread adoption. Surgeons should preferentially use ODEP 10A-rated implants. Using non-ODEP-rated or poorly rated implants could be considered a deviation from best practice and has medicolegal implications.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 773,
              "stem": "Periprosthetic fractures around THA are increasingly common. The incidence is highest with:",
              "options": [
                "Uncemented press-fit stems (higher intra-operative fracture rate during insertion, particularly in Dorr Type C/osteoporotic bone)",
                "Cemented polished tapered stems",
                "Cemented matte-finish stems",
                "Short stems",
                "Resurfacing implants"
              ],
              "answer": "A",
              "explanation": "Uncemented press-fit stems have a higher rate of intra-operative periprosthetic fracture (particularly during broaching and stem insertion) compared to cemented stems. This is because press-fit fixation requires an interference fit — the canal is under-reamed and the stem is impacted into slightly undersized bone, generating hoop stresses that can split the femur (particularly in osteoporotic bone, Dorr Type C, or stiff/narrow canals). The risk is higher in: elderly osteoporotic patients, revision surgery (cortical defects), and during the learning curve for new implant systems. Prevention: careful broaching technique, fluoroscopic monitoring, appropriate stem sizing, consider cementing in poor bone (Dorr C). Post-operative periprosthetic fractures (Vancouver classification) are more common around well-fixed uncemented stems than cemented stems, likely reflecting the initial patient selection (uncemented in younger patients with higher activity levels).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 774,
              "stem": "The most commonly performed arthroplasty procedure in the UK (per NJR) is:",
              "options": [
                "Total shoulder arthroplasty",
                "Total hip arthroplasty",
                "Ankle replacement",
                "Total knee arthroplasty (highest volume of any joint replacement)",
                "Elbow replacement"
              ],
              "answer": "D",
              "explanation": "Total knee arthroplasty is the highest-volume joint replacement procedure in the UK, with over 100,000 procedures recorded annually in the NJR. THA is the second most common (~90,000-100,000/year). The NJR covers hip, knee, shoulder, elbow, and ankle replacements. 10-year survival: TKA ~95-97%, THA ~95-97%. Both have excellent outcomes when appropriately indicated. The demand for both procedures is increasing due to an ageing population and rising obesity rates. The NJR provides essential outcomes data for quality assurance, implant surveillance, and benchmarking.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 775,
              "stem": "Aseptic loosening of a cemented femoral stem in THA is best diagnosed radiographically by:",
              "options": [
                "Normal radiographic appearance",
                "Heterotopic ossification around the hip",
                "Progressive radiolucent lines at the cement-bone interface (especially in Gruen zones 1 and 7) with component migration",
                "Sclerotic lines without migration",
                "Increased bone density around the stem"
              ],
              "answer": "C",
              "explanation": "Progressive radiolucent lines (>2mm) at the cement-bone interface, particularly in Gruen zones 1 (lateral proximal) and 7 (medial proximal/calcar), are the hallmark radiographic features of aseptic loosening. Component migration (subsidence, varus tilting), cement fracture, and pedestal formation at the tip of the stem are additional signs. Serial radiographs showing progressive changes are more diagnostic than a single film. The distinction from infection requires bloods (ESR, CRP) and joint aspiration — radiographic appearances of aseptic loosening and septic loosening can be identical.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 776,
              "stem": "The Dorr classification of proximal femoral morphology is used in THA planning. Dorr Type C (stovepipe) indicates:",
              "options": [
                "A normal champagne-flute femur with good cortical thickness",
                "A severely widened canal with thin cortices and poor metaphyseal-diaphyseal taper (stovepipe shape)",
                "A moderately widened canal with some cortical thinning",
                "A fracture of the proximal femur",
                "A previously operated femur"
              ],
              "answer": "B",
              "explanation": "Dorr classification: Type A = normal champagne-flute shape with thick cortices and good metaphyseal-diaphyseal flare (ideal for uncemented press-fit stems). Type B = intermediate — moderate cortical thinning and canal widening (suitable for either cemented or uncemented). Type C = stovepipe femur — severely widened medullary canal, very thin cortices, minimal metaphyseal-diaphyseal taper (poor for uncemented fixation due to inadequate bony contact — cemented fixation preferred). Dorr type affects stem choice: Type A → excellent uncemented fixation. Type B → either cemented or uncemented. Type C → cemented fixation (or extensively porous-coated uncemented with diaphyseal fixation). The canal flare index (CFI) can be measured to objectively classify Dorr type.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 777,
              "stem": "The crossover sign on an AP pelvis radiograph indicates:",
              "options": [
                "Femoral neck fracture",
                "Acetabular anteversion",
                "Acetabular retroversion (pincer-type FAI morphology)",
                "Pelvic fracture",
                "DDH"
              ],
              "answer": "C",
              "explanation": "The crossover sign (figure-of-eight sign) on a true AP pelvis radiograph indicates acetabular retroversion — the anterior wall of the acetabulum crosses over the posterior wall on the XR projection. In a normally anteverted acetabulum, the anterior wall line lies medial to the posterior wall line throughout. When the anterior wall crosses lateral to the posterior wall superiorly, it indicates the superior portion of the acetabulum is retroverted. Acetabular retroversion is a component of PINCER-type FAI (anterior overcoverage → impingement of the femoral head-neck junction against the retroverted anterior rim during flexion and internal rotation). Other signs of retroversion: posterior wall sign (posterior wall medial to centre of femoral head), ischial spine sign (ischial spine projects into the pelvis = retroverted).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 778,
              "stem": "The most commonly used bearing surface for the femoral component in TKA is:",
              "options": [
                "Ceramic",
                "UHMWPE",
                "Titanium",
                "Stainless steel",
                "Cobalt-chromium alloy"
              ],
              "answer": "E",
              "explanation": "The femoral component in TKA is most commonly made of cobalt-chromium (CoCr) alloy due to its excellent wear resistance, hardness, corrosion resistance, and ability to be highly polished (low surface roughness reduces PE wear). It articulates against a tibial polyethylene insert (UHMWPE or XLPE). Some newer designs use oxidised zirconium (Oxinium — ceramic surface on a metal substrate) to reduce PE wear further. Titanium is NOT used for the femoral condylar surface because it is too soft and has poor wear characteristics (scratches easily → accelerates PE wear). Titanium IS used for the tibial baseplate (good for osteointegration in uncemented designs) and for some femoral stems.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Hip",
          "range": "Q779-Q813",
          "questions": [
            {
              "number": 779,
              "stem": "The Smith-Petersen (anterior) approach to the hip utilises the internervous plane between:",
              "options": [
                "Gluteus medius and gluteus minimus",
                "Quadriceps and hamstrings",
                "Adductor longus and sartorius",
                "Sartorius (femoral nerve) and tensor fasciae latae (superior gluteal nerve) — a true internervous plane where neither muscle is denervated by the dissection",
                "Piriformis and gluteus medius"
              ],
              "answer": "D",
              "explanation": "The Smith-Petersen (anterior/anterolateral) approach — the internervous plane is between SARTORIUS (innervated by the FEMORAL nerve) laterally and TENSOR FASCIAE LATAE (innervated by the SUPERIOR GLUTEAL nerve) medially. Because these two muscles are supplied by DIFFERENT nerves, the dissection between them does not denervate either muscle — this is a TRUE internervous plane. This is the approach used for the direct anterior approach (DAA) to the hip — modified for THA with a specialised table or leg positioner. Deep to this interval: the rectus femoris (reflected head) is retracted or released, and the anterior hip capsule is exposed. The approach is INTERmuscular (between muscles, no muscles are cut) AND INTERnervous (between nerve territories) — making it the least invasive approach theoretically. The LFCN (L2-L3, pure sensory) crosses the surgical field and is at risk (~3-15% injury).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 780,
              "stem": "The Trendelenburg test is positive when:",
              "options": [
                "The pelvis DROPS on the unsupported (contralateral) side when the patient stands on the affected leg — indicating weakness of the hip abductors (gluteus medius/minimus) on the STANCE side",
                "The pelvis rises on the unsupported side (that's NEGATIVE — normal)",
                "The patient can walk normally",
                "The patient has no hip pain",
                "Both sides are level"
              ],
              "answer": "A",
              "explanation": "The Trendelenburg test: the patient stands on ONE LEG. Normal (NEGATIVE test): the pelvis RISES on the unsupported side — the hip abductors (gluteus medius and minimus) on the stance side contract and tilt the pelvis upward on the opposite side. POSITIVE test: the pelvis DROPS on the unsupported (contralateral) side — indicating that the hip abductors on the STANCE leg are INSUFFICIENT to stabilise the pelvis. The pathology is on the STANCE side (the leg the patient is standing on), NOT the side that drops. Causes of a positive Trendelenburg: (1) hip abductor weakness (gluteus medius tear/atrophy, superior gluteal nerve injury — e.g., after lateral approach THA), (2) hip joint pathology (OA, DDH — pain inhibits abductor function, shortened lever arm), (3) coxa vara (reduced abductor lever arm — the GT is relatively lower), (4) after hip arthroplasty with insufficient offset restoration (reduced abductor tension). The patient MUST be observed from BEHIND and must stand on each leg for at least 30 seconds.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 781,
              "stem": "The Hardinge (direct lateral/transgluteal) approach to the hip — the nerve at greatest risk is the:",
              "options": [
                "Sciatic nerve",
                "Femoral nerve",
                "Obturator nerve",
                "Superior gluteal nerve (must not extend the gluteus medius split more than 5cm above the greater trochanter tip)",
                "LFCN"
              ],
              "answer": "D",
              "explanation": "The Hardinge (direct lateral/transgluteal) approach splits the gluteus medius and minimus in line with their fibres, then detaches the anterior portion from the greater trochanter to expose the hip capsule. The SUPERIOR GLUTEAL NERVE (L4-S1) runs within the gluteus medius on its deep surface, approximately 5cm above the tip of the greater trochanter. If the gluteus medius split extends >5cm proximal to the GT tip, the nerve is at risk of injury → denervation of the gluteus medius and minimus → Trendelenburg gait (abductor weakness). The '5cm rule' is essential: never split gluteus medius more than 5cm above the GT tip. Other risks of the lateral approach: abductor weakness (even without nerve injury, from detachment), heterotopic ossification, and Trendelenburg limp (most common complication compared to posterior approach).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 782,
              "stem": "The Garden classification of intracapsular femoral neck fractures — Garden III indicates:",
              "options": [
                "Incomplete/impacted fracture (valgus impacted)",
                "Complete but undisplaced fracture",
                "Complete fracture with FULL displacement (trabeculae of femoral head align with acetabular trabeculae due to free rotation)",
                "An extracapsular fracture",
                "Complete fracture with PARTIAL displacement (trabeculae of the femoral head do not align with those of the acetabulum)"
              ],
              "answer": "E",
              "explanation": "Garden classification (AP radiograph): Garden I = incomplete/impacted fracture (valgus impacted — the inferior cortex is intact, trabeculae angulated into valgus). Garden II = complete but undisplaced fracture (fracture through both cortices but fragments not displaced — trabeculae align). Garden III = complete with PARTIAL displacement (the fragments have shifted but some trabecular alignment remains — the femoral head trabeculae do NOT align with the acetabular trabeculae). Garden IV = complete with FULL displacement (the femoral head is free to rotate within the acetabulum — paradoxically, the head trabeculae may ALIGN with the acetabular trabeculae because the head has rotated to its resting position). Clinical simplification: Garden I-II = undisplaced → internal fixation (cannulated screws). Garden III-IV = displaced → arthroplasty (THA if fit/active/cognitively intact; hemiarthroplasty if less active/cognitive impairment). Surgery within 36 hours (NICE).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 783,
              "stem": "The Tokuhashi scoring system is used to predict prognosis and guide treatment decisions for:",
              "options": [
                "Primary hip OA",
                "Perthes disease",
                "Spinal metastases (predicts survival and guides whether palliative, excisional, or no surgery is appropriate)",
                "ACL reconstruction timing",
                "Fracture healing prediction"
              ],
              "answer": "C",
              "explanation": "The Tokuhashi scoring system predicts life expectancy in patients with spinal metastases and guides surgical decision-making. Six parameters (scored 0-5 each, total 0-15): (1) general condition (KPS), (2) number of extraspinal bone metastases, (3) number of vertebral body metastases, (4) major organ metastases, (5) primary tumour site (thyroid/breast/prostate = better prognosis; lung/liver = worst), (6) neurological status (palsy). Score interpretation: 0-8 = poor prognosis (<6 months survival) → palliative treatment (pain management, radiation, limited surgery only for impending paralysis). 9-11 = moderate prognosis (6-12 months) → palliative surgery (decompression ± stabilisation). 12-15 = good prognosis (>12 months) → excisional surgery may be appropriate. The primary tumour site is the SINGLE most important prognostic factor for spinal metastases. Always consider: Frankel/ASIA grade, SINS (Spinal Instability Neoplastic Score) for instability assessment.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 784,
              "stem": "Avascular necrosis (AVN) of the femoral head — the most common identifiable risk factor is:",
              "options": [
                "Corticosteroid use (the most common non-traumatic cause — dose-dependent risk, even short courses of high-dose steroids increase risk)",
                "Trauma (femoral neck fracture/hip dislocation)",
                "Excessive exercise",
                "High calcium diet",
                "Vitamin D excess"
              ],
              "answer": "A",
              "explanation": "Corticosteroid use is the MOST COMMON identifiable risk factor for non-traumatic (atraumatic) AVN of the femoral head. The risk is DOSE-DEPENDENT — higher cumulative doses increase risk significantly, but even short courses of high-dose steroids (e.g., for COVID-19 treatment, organ transplant immunosuppression, SLE flares) can trigger AVN. Mechanism: corticosteroids cause fat cell hypertrophy in the bone marrow → increased intraosseous pressure → venous outflow obstruction → ischaemia → osteocyte death. Other risk factors: alcohol excess (second most common), sickle cell disease, SLE (disease itself + steroids), organ transplantation (steroids), HIV/antiretrovirals, Gaucher disease, radiation, caisson disease (decompression sickness in divers). Trauma: femoral neck fractures and hip dislocations disrupt the MFCA retinacular vessels directly. Bilateral involvement: common (~50-80% develop contralateral AVN within 2 years — screen the opposite hip with MRI).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 785,
              "stem": "The lateral approach (Hardinge/transgluteal) to the hip has a lower dislocation rate than the posterior approach primarily because:",
              "options": [
                "It has better cosmesis",
                "The anterior hip capsule and posterior structures (short external rotators, posterior capsule) are preserved — the most common dislocation direction (posterior) is protected",
                "It uses a smaller incision",
                "It avoids all nerves",
                "It is a faster procedure"
              ],
              "answer": "B",
              "explanation": "The lateral (Hardinge/transgluteal) approach preserves the posterior capsule and short external rotator muscles (piriformis, obturator internus, gemelli, quadratus femoris) — these are the structures that resist posterior dislocation (the most common direction of THA dislocation). In the posterior approach, these structures are divided to access the hip → higher posterior dislocation risk (unless the posterior capsule and rotators are repaired — posterior capsulorrhaphy + short ER repair reduces the dislocation rate to near-lateral approach levels). The anterior (DAA) approach has the LOWEST dislocation rate of all (preserves both anterior AND posterior structures). Trade-offs: lateral approach risks abductor weakness (gluteus medius split → Trendelenburg), posterior approach has higher dislocation but preserves abductors, anterior preserves everything but has a learning curve and LFCN risk.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 786,
              "stem": "The Trendelenburg gait (compensated) is characterised by:",
              "options": [
                "The pelvis dropping on the affected side",
                "Running with a normal gait pattern",
                "Walking with no visible abnormality",
                "The patient leaning their trunk TOWARDS the affected hip during stance phase (to reduce the abductor moment demand by shifting the centre of gravity closer to the hip fulcrum)",
                "Dragging the affected foot"
              ],
              "answer": "D",
              "explanation": "Compensated Trendelenburg gait: the patient leans their trunk TOWARDS the affected (weak abductor) side during the stance phase of gait. This shift moves the body's centre of gravity closer to (or directly over) the affected hip joint, reducing the moment arm of body weight about the hip → reducing the force the weakened abductors must generate to stabilise the pelvis. This is energetically inefficient but prevents the pelvis from dropping. UNcompensated Trendelenburg: the pelvis drops on the OPPOSITE (contralateral/sound) side during stance on the affected limb — the abductors are too weak to stabilise the pelvis AND the patient doesn't (or can't) lean to compensate. Bilateral Trendelenburg: waddling gait (bilateral abductor weakness — seen in bilateral DDH, muscular dystrophies, bilateral hip OA). Causes: superior gluteal nerve injury, gluteus medius tear/weakness, hip OA (pain inhibition), post-THA, DDH, polio.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 787,
              "stem": "The anterior approach to the hip (direct anterior approach/DAA, Smith-Petersen) — the nerve most at risk is the:",
              "options": [
                "Sciatic nerve (posterior approach)",
                "Lateral femoral cutaneous nerve (LFCN — a pure sensory nerve that runs near or through the surgical field, causing numbness on the anterolateral thigh in ~3-15% of cases)",
                "Superior gluteal nerve (lateral approach)",
                "Femoral nerve",
                "Obturator nerve"
              ],
              "answer": "B",
              "explanation": "The DAA (direct anterior approach) utilises the internervous plane between the sartorius (femoral nerve) and tensor fasciae latae (superior gluteal nerve). The LFCN (lateral femoral cutaneous nerve of the thigh — pure SENSORY, L2-L3) is the nerve most at risk — it runs from lateral to the ASIS, crossing the inguinal ligament and passing near or through the surgical corridor. Injury rate: ~3-15% (causing numbness/paraesthesia on the anterolateral thigh — 'meralgia paraesthetica'). This is usually well-tolerated by patients as it is purely sensory (no motor loss). DAA advantages: lowest dislocation rate (preserves both anterior and posterior structures), faster early recovery, muscle-sparing (internervous interval). DAA disadvantages: LFCN injury, learning curve, wound complications (wound over skin crease), femoral fracture risk (particularly during femoral preparation — the femoral exposure is more challenging than posterior approach), and limited extensibility for complex cases.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 788,
              "stem": "Dislocation after THA — the most common direction of dislocation is:",
              "options": [
                "Anterior (less common overall)",
                "Superior",
                "Posterior (accounts for ~65-75% of THA dislocations, particularly with the posterior surgical approach — the hip dislocates posteriorly with flexion, adduction, and internal rotation)",
                "Inferior",
                "Lateral"
              ],
              "answer": "C",
              "explanation": "Posterior dislocation is the most common direction after THA (~65-75% of all dislocations). Mechanism: flexion + adduction + internal rotation (bending forward to pick something up, sitting on a low chair, crossing legs, getting out of a car). Risk factors: posterior surgical approach (divides posterior capsule and short ERs — the primary restraints to posterior dislocation), component malposition (cup retroversion, excessive anteversion of the stem), reduced head:neck ratio, soft tissue laxity, neuromuscular conditions, cognitive impairment, and prior revision surgery. Posterior precautions: avoid flexion >90°, avoid adduction (crossing legs), avoid IR — for 6-12 weeks post-op (allowing posterior soft tissue healing). Anterior dislocation (~25-35%): occurs with extension + ER (getting up from a chair with the foot planted). More common after anterior/anterolateral approaches (if anterior capsule is resected). Dual-mobility cups: increasingly used in high-risk patients (provides greater arc of motion before impingement → lower dislocation rate).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 789,
              "stem": "The blood supply to the femoral head in adults is primarily from the:",
              "options": [
                "Foveal artery (ligamentum teres — contributes only ~10-20% in adults)",
                "Obturator artery directly",
                "Inferior gluteal artery",
                "Profunda femoris directly without branches",
                "Medial femoral circumflex artery (MFCA — via the lateral epiphyseal/retinacular vessels ascending along the femoral neck under the capsule)"
              ],
              "answer": "E",
              "explanation": "The MFCA (branch of the profunda femoris) provides the PRIMARY blood supply to the adult femoral head (~80%). The critical vessels are the LATERAL EPIPHYSEAL (retinacular) arteries — branches of the MFCA that ascend along the femoral neck beneath the synovial reflection (retinaculum of Weitbrecht) to enter the femoral head at the head-neck junction. These vessels are VULNERABLE during: (1) intracapsular femoral neck fractures (disrupted by displacement → AVN — why displaced NOF fractures in adults are treated with arthroplasty rather than fixation), (2) posterior hip dislocation (MFCA courses posteriorly → at risk during dislocation → reduce urgently <6h to minimize AVN risk), (3) posterior surgical approach (careful dissection to preserve the MFCA branches). The foveal artery (via the ligamentum teres, from the obturator artery) contributes only ~10-20% in adults (important in children but diminishes with age). The lateral femoral circumflex artery contributes minimally to the femoral head in adults.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 790,
              "stem": "The posterior approach to the hip — the nerve most at risk is the:",
              "options": [
                "Sciatic nerve (runs beneath the short external rotators that are divided during the approach — protected by keeping the hip in extension and external rotation during deep dissection)",
                "Femoral nerve (anterior)",
                "Superior gluteal nerve (lateral — >5cm above GT)",
                "LFCN (anterior/DAA)",
                "Obturator nerve"
              ],
              "answer": "A",
              "explanation": "The posterior approach (Moore/Southern approach) divides the short external rotators (piriformis, gemelli, obturator internus) to access the posterior hip capsule. The SCIATIC NERVE lies immediately deep to these muscles (between the ischial tuberosity and greater trochanter). Protection: (1) keep the hip in FLEXION (relaxes the nerve) during retraction, (2) identify and protect the nerve during deep dissection, (3) avoid excessive retraction. Sciatic nerve injury rate: ~1% (lower with careful technique). If injured: footdrop (CPN component — most vulnerable), and loss of knee flexion + ankle plantar flexion (tibial component). The posterior approach requires POSTERIOR CAPSULORRHAPHY + short external rotator repair at closure to reduce posterior dislocation risk (without repair: 3-5% dislocation, with repair: ~1-2% — similar to lateral approach). Posterior approach advantages: excellent femoral exposure (easier implant insertion, better for revision), preserves abductors (no Trendelenburg), extensile.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 791,
              "stem": "The Pauwels classification of femoral neck fractures is based on:",
              "options": [
                "The angle of the fracture line relative to the horizontal — higher angles (Type III, >70°) have greater SHEAR forces across the fracture → higher non-union and AVN risk",
                "Patient age",
                "Fracture displacement",
                "The number of fracture fragments",
                "Blood supply assessment"
              ],
              "answer": "A",
              "explanation": "Pauwels classification (measured on AP hip XR): the angle between the fracture line and the HORIZONTAL. Type I: <30° (nearly horizontal) — predominantly COMPRESSIVE forces across the fracture → best biomechanical environment for healing → lowest non-union rate. Type II: 30-50° — intermediate (mixed compression and shear). Type III: >50-70° (nearly vertical) — predominantly SHEAR forces across the fracture → shear disrupts fracture healing (fragments slide past each other rather than compressing together) → HIGHEST non-union and AVN risk. Clinical implication: Pauwels Type III fractures (high shear angle) may benefit from VALGUS osteotomy to convert the shear force into a more compressive force (realigns the fracture to a more horizontal orientation — Marti osteotomy, predominantly in young patients with NOF fractures where preservation of the native femoral head is the goal). In practice, the Garden classification (displacement) is more commonly used than Pauwels for clinical decision-making in the elderly, but Pauwels is biomechanically important and often examined.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 792,
              "stem": "A Trendelenburg test is positive when the pelvis drops on which side?",
              "options": [
                "The stance (affected) side",
                "Both sides equally",
                "Neither side — the pelvis rises instead",
                "The swing (contralateral/unsupported) side",
                "The posterior side"
              ],
              "answer": "D",
              "explanation": "A positive Trendelenburg test occurs when the patient stands on the affected leg and the pelvis drops on the CONTRALATERAL (swing) side. This indicates weak hip abductors (gluteus medius and minimus) on the stance side — they cannot support the pelvis against gravity. Causes: superior gluteal nerve injury, hip joint pathology (OA, DDH, post-THA), proximal femoral pathology (NOF non-union, trochanteric fracture), myopathy. A compensated Trendelenburg (Duchenne gait) involves trunk lean over the affected side to reduce the abductor demand.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 793,
              "stem": "The blood supply to the femoral head in adults is primarily from:",
              "options": [
                "The obturator artery via the ligamentum teres",
                "The superior and inferior gluteal arteries",
                "The medial and lateral femoral circumflex arteries (particularly the retinacular vessels from the MFCA)",
                "The profunda femoris artery directly",
                "The femoral artery directly"
              ],
              "answer": "C",
              "explanation": "The adult femoral head blood supply is primarily from the retinacular vessels, which are terminal branches of the medial femoral circumflex artery (MFCA). The MFCA is a branch of the profunda femoris (usually). The retinacular vessels run along the femoral neck beneath the synovium and enter the head at the capsular reflection. The lateral femoral circumflex artery (LFCA) contributes less. The ligamentum teres artery (from the obturator) provides minimal blood supply in adults (significant only in children). This explains the high AVN risk with displaced neck fractures.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 794,
              "stem": "The safe position for hip arthroscopy portals avoids injury to which nerve laterally?",
              "options": [
                "Femoral nerve",
                "Lateral femoral cutaneous nerve",
                "Obturator nerve",
                "Sciatic nerve",
                "Superior gluteal nerve"
              ],
              "answer": "B",
              "explanation": "The lateral femoral cutaneous nerve (LFCN/lateral cutaneous nerve of the thigh) is at risk during hip arthroscopy portal placement, particularly the anterolateral portal. The LFCN passes under or through the inguinal ligament near the ASIS and runs over the sartorius before branching. Its course is variable, making it vulnerable. Injury causes meralgia paraesthetica (numbness/burning over the anterolateral thigh). The femoral nerve is at risk with far anterior portals. The sciatic nerve is at risk with posterior portals.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 795,
              "stem": "Spontaneous osteonecrosis of the knee (SONK) most commonly affects which condyle?",
              "options": [
                "Lateral femoral condyle",
                "Lateral tibial plateau",
                "Patella",
                "Trochlea",
                "Medial femoral condyle (weight-bearing surface)"
              ],
              "answer": "E",
              "explanation": "SONK most commonly affects the weight-bearing surface of the medial femoral condyle (approximately 90% of cases). It typically presents in elderly women (>55 years) with sudden onset of severe knee pain, often without preceding trauma. MRI shows a subchondral lesion with surrounding bone marrow oedema. It is now believed to be a subchondral insufficiency fracture rather than true avascular necrosis. Treatment: non-operative (protected weight-bearing, analgesics) for small lesions. UKA or TKA for large lesions with secondary OA.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 796,
              "stem": "Avascular necrosis of the femoral head is most commonly classified using the Ficat and Arlet staging system. Ficat Stage III shows:",
              "options": [
                "Normal radiographs",
                "Sclerosis or cystic changes without collapse",
                "Crescent sign (subchondral collapse) with flattening of the femoral head",
                "Secondary osteoarthritis with joint space narrowing",
                "MRI changes only"
              ],
              "answer": "C",
              "explanation": "Ficat and Arlet classification of femoral head AVN: Stage 0 = asymptomatic, normal imaging (pre-clinical). Stage I = symptomatic, normal XR, MRI positive (bone marrow oedema). Stage II = sclerotic or cystic changes on XR without collapse (MRI shows double-line sign). Stage III = crescent sign (subchondral fracture/collapse) with flattening of the femoral head but preserved joint space. Stage IV = secondary OA with joint space narrowing and acetabular changes. Treatment: Stage I-II = core decompression ± bone graft ± BMP. Stage III = consider osteotomy (young) or arthroplasty. Stage IV = THA.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 797,
              "stem": "The Crowe classification is used to classify which condition in the context of THA planning?",
              "options": [
                "Aseptic loosening",
                "Periprosthetic fracture",
                "Femoral head AVN",
                "Paget disease of the hip",
                "Developmental dysplasia of the hip (DDH) with progressive subluxation/dislocation"
              ],
              "answer": "E",
              "explanation": "The Crowe classification grades DDH in adults for THA planning: Type I = <50% subluxation (proximal migration <10% of pelvic height). Type II = 50-75% subluxation (10-15% migration). Type III = 75-100% subluxation (15-20% migration). Type IV = >100% subluxation/complete dislocation (>20% migration — false acetabulum/neo-acetabulum). Higher Crowe types have: more leg length discrepancy, more muscular contracture, altered anatomy (short femur, narrow canal, high-riding GT), and require complex reconstruction (subtrochanteric shortening osteotomy for type III-IV, specialised implants).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 798,
              "stem": "In Perthes disease, the most common age of onset is:",
              "options": [
                "4-8 years (peak around 5-7 years)",
                "0-2 years",
                "12-15 years",
                "18-25 years",
                "Over 40 years"
              ],
              "answer": "A",
              "explanation": "Perthes disease (Legg-Calvé-Perthes) typically presents between 4-8 years of age, with a peak around 5-7 years. Boys are affected 4-5× more often than girls (but girls tend to have worse outcomes). It is bilateral in 10-15% of cases (usually sequential, not simultaneous). Aetiology: idiopathic AVN of the femoral head epiphysis — likely multifactorial (vascular interruption, coagulation abnormalities, genetic susceptibility). Presentation: painless limp initially, then hip/groin/thigh/knee pain (referred), restricted abduction and internal rotation. Exclude DDH in younger age group and SUFE in older age group. Bone age is typically delayed by 1-2 years in Perthes patients.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 799,
              "stem": "The Trendelenburg test is positive when the pelvis drops on the unsupported (contralateral) side during single-leg stance on the affected limb. This indicates weakness of the:",
              "options": [
                "Quadriceps",
                "Hip flexors (iliopsoas)",
                "Hamstrings",
                "Hip abductors (gluteus medius, primarily innervated by the superior gluteal nerve L4-S1)",
                "Ankle dorsiflexors"
              ],
              "answer": "D",
              "explanation": "A positive Trendelenburg test indicates hip abductor weakness on the STANDING limb side. The hip abductors (primarily gluteus medius, innervated by the superior gluteal nerve L4-S1) are responsible for stabilising the pelvis during single-leg stance. When they are weak or insufficient, the pelvis tilts/drops on the OPPOSITE (contralateral) side because the abductors cannot counterbalance the weight of the unsupported body. Causes: superior gluteal nerve injury, gluteus medius tear/tendinopathy, hip OA (pain inhibition), post-THA abductor damage (lateral approach or trochanteric non-union), DDH (shortened abductor lever arm), polio, L5 radiculopathy.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 800,
              "stem": "The Thomas test assesses for:",
              "options": [
                "ACL integrity",
                "Hip flexor tightness (fixed flexion deformity of the hip)",
                "Ankle dorsiflexion",
                "Shoulder impingement",
                "Carpal tunnel syndrome"
              ],
              "answer": "B",
              "explanation": "The Thomas test assesses for fixed flexion deformity (FFD) of the hip. Technique: patient supine, flex the contralateral hip fully to the chest (this flattens the lumbar lordosis and eliminates pelvic tilt compensation). If the tested (opposite) hip lifts off the bed, a fixed flexion contracture is present — measure the angle between the thigh and the bed surface. FFD is commonly seen in: hip OA (capsular contracture), hip flexor tightness (iliopsoas, rectus femoris, TFL, sartorius), post-surgical contracture, and neurological conditions (CP, stroke). In hip OA, FFD is an important clinical finding — it indicates advanced disease and can contribute to back pain (compensatory lumbar hyperlordosis). Measuring and documenting FFD is essential in pre-operative THA assessment.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 801,
              "stem": "Extracapsular neck of femur fractures (intertrochanteric) are best fixed with:",
              "options": [
                "Cannulated screws",
                "THA",
                "External fixation",
                "Cast bracing",
                "DHS (dynamic hip screw) for stable patterns, or cephalomedullary (IM) nail for unstable/subtrochanteric extension patterns"
              ],
              "answer": "E",
              "explanation": "Extracapsular (intertrochanteric) NOF fractures are treated with internal fixation (not arthroplasty) because the blood supply to the femoral head is preserved (the fracture is outside the capsule). DHS: gold standard for stable intertrochanteric fractures (AO 31-A1, A2.1) — allows controlled impaction along the axis of the femoral neck during weight-bearing. Cephalomedullary (IM) nail (e.g., PFNA, Gamma nail): preferred for unstable patterns (reverse oblique, subtrochanteric extension, lateral wall incompetence, AO 31-A3) — the nail provides a shorter lever arm and load-sharing advantage. The choice between DHS and IM nail depends on fracture stability and pattern. NICE recommends an IM nail for subtrochanteric and reverse oblique fractures. Surgery within 36 hours (NICE).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 802,
              "stem": "The lateral approach (Hardinge/transgluteal) to the hip divides which muscle?",
              "options": [
                "Gluteus maximus",
                "Piriformis",
                "Gluteus medius (anterior third detached from greater trochanter)",
                "Sartorius",
                "Tensor fasciae latae"
              ],
              "answer": "C",
              "explanation": "The Hardinge (direct lateral/transgluteal) approach splits gluteus medius longitudinally and detaches its anterior third from the greater trochanter (along with the underlying gluteus minimus and vastus lateralis). This provides excellent acetabular exposure with a low dislocation rate. The main disadvantage is the risk of denervation of the anterior gluteus medius/minimus if the dissection extends >5 cm proximal to the greater trochanter tip (the superior gluteal nerve enters the muscles ~5 cm above the GT). Abductor dysfunction (Trendelenburg limp) can occur if the repair fails or the nerve is damaged.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 803,
              "stem": "The acetabular labrum serves which primary function?",
              "options": [
                "Weight-bearing load transmission",
                "Creates a suction seal (vacuum effect) that enhances hip stability and distributes hydrostatic fluid pressure across the cartilage",
                "Muscle attachment for hip flexors",
                "Provides the primary blood supply to the femoral head",
                "Ossification centre for the acetabulum"
              ],
              "answer": "B",
              "explanation": "The acetabular labrum is a fibrocartilaginous ring attached to the acetabular rim that deepens the acetabulum by 21% (increasing coverage of the femoral head) and creates a suction seal/vacuum effect. This seal: (1) enhances hip joint stability (resists distraction forces), (2) distributes hydrostatic fluid pressure evenly across the articular cartilage (protecting against point loading), and (3) restricts fluid flow out of the joint (maintaining intra-articular fluid pressure for cartilage nutrition and joint lubrication). Labral tears (from FAI, trauma, dysplasia) disrupt this seal → increased cartilage contact stress → accelerated OA. Labral repair is preferred over debridement to restore the seal.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 804,
              "stem": "Avascular necrosis (AVN) of the femoral head is most commonly associated with which risk factors?",
              "options": [
                "Exercise and good nutrition",
                "Vegetarian diet",
                "Excessive calcium intake",
                "Corticosteroid use and alcohol excess (together account for >80% of non-traumatic cases)",
                "Regular weight-bearing exercise"
              ],
              "answer": "D",
              "explanation": "The two most significant risk factors for non-traumatic AVN of the femoral head are: (1) corticosteroid use (most common, >40% of non-traumatic cases — dose and duration dependent, mechanism: fat cell hypertrophy in marrow → increased intraosseous pressure → vascular compromise) and (2) alcohol excess (~20-40% — direct toxic effect on osteocytes + fat emboli). Together they account for >80% of non-traumatic AVN. Other associations: SLE, sickle cell disease, Gaucher disease, radiation, hyperlipidaemia, smoking, HIV, organ transplant, caisson disease (decompression). Ficat/ARCO staging guides management. MRI is the gold standard for early detection (marrow oedema, band pattern).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 805,
              "stem": "The Paprosky classification is used to classify bone defects in:",
              "options": [
                "Revision total hip arthroplasty (acetabular and femoral bone loss)",
                "Primary THA",
                "Primary TKA",
                "Tibial plateau fractures",
                "Pelvic fractures"
              ],
              "answer": "A",
              "explanation": "The Paprosky classification grades bone defects encountered during revision THA. Acetabular: Type I = supportive rim, minimal lysis. Type IIA = superior dome intact, <2cm superior migration. Type IIB = superior dome deficient, >2cm migration. Type IIC = medial wall lysis (Kohler line crossed). Type IIIA = >2cm migration with 10 o'clock to 2 o'clock support. Type IIIB = >2cm migration with <10 o'clock to 2 o'clock support (pelvic discontinuity risk). Femoral: Type I = minimal metaphyseal damage. Type II = absent calcar, extensive metaphyseal loss. Type IIIA = >4cm of intact diaphyseal bone for scratch fit. Type IIIB = <4cm of diaphyseal bone. Type IV = widened diaphysis (stovepipe femur). Treatment escalates with defect severity: uncemented cup + augments → jumbo cup → cage → custom triflange → cup-cage construct.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 806,
              "stem": "Femoroacetabular impingement (FAI) — cam morphology involves:",
              "options": [
                "Overcoverage of the femoral head by the acetabulum (deep socket)",
                "Ligamentum teres hypertrophy",
                "An aspherical femoral head-neck junction that abuts against the acetabulum during motion, damaging the labrum and cartilage",
                "Femoral neck fracture",
                "Isolated labral tear without bony abnormality"
              ],
              "answer": "C",
              "explanation": "FAI involves abnormal contact between the femoral head-neck junction and the acetabulum during hip motion. Two morphological types: CAM = aspherical femoral head-neck junction (loss of normal concavity/offset) — during hip flexion and internal rotation, the aspherical bump impacts against the anterosuperior acetabular rim, causing outside-in damage to the labrum and adjacent cartilage. PINCER = acetabular overcoverage (deep/retroverted socket or a prominent rim) — the rim contacts the femoral neck, causing labral damage by a nutcracker mechanism, then contre-coup damage to the posteroinferior cartilage. Most cases are MIXED (cam + pincer). Treatment: activity modification, physiotherapy → hip arthroscopy (cam resection/osteoplasty + labral repair ± rim trimming for pincer).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 807,
              "stem": "The posterior approach to the hip (Moore/Southern) carries the highest risk of injury to which nerve?",
              "options": [
                "Femoral nerve",
                "Obturator nerve",
                "Superior gluteal nerve",
                "Lateral femoral cutaneous nerve",
                "Sciatic nerve"
              ],
              "answer": "E",
              "explanation": "The posterior approach carries the highest risk of sciatic nerve injury (~1% in primary THA, higher in revision). The sciatic nerve lies posterior to the hip, passing below piriformis, deep to the short external rotators, and posterior to quadratus femoris. During the posterior approach, these structures are divided — excessive retraction posteriorly risks stretching or directly injuring the sciatic nerve. Prevention: keep the hip flexed and knee flexed (relaxes the nerve), gentle retraction, identify and protect the nerve, avoid excessive limb lengthening (>2-4cm stretches the nerve). The posterior approach also has a higher dislocation rate than anterior or lateral approaches unless the posterior capsule and short external rotators are repaired.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 808,
              "stem": "The blood supply to the adult femoral head is primarily from:",
              "options": [
                "Medial femoral circumflex artery (MFCA) via the retinacular vessels",
                "Obturator artery via the ligamentum teres",
                "Inferior gluteal artery",
                "Lateral femoral circumflex artery",
                "Profunda femoris directly"
              ],
              "answer": "A",
              "explanation": "The MFCA (a branch of the profunda femoris) provides the dominant blood supply to the adult femoral head via the lateral epiphyseal (retinacular) vessels that run along the femoral neck beneath the synovial reflection. The LFCA supplies the anterior femoral head and contributes to the extracapsular arterial ring. The ligamentum teres artery (branch of the obturator artery) provides a small contribution but is insufficient alone to maintain femoral head viability. This is why intracapsular femoral neck fractures have a high AVN risk (retinacular vessels from MFCA are disrupted) while extracapsular fractures do not. In children, the blood supply pattern differs (transphyseal vessels exist in young children).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 809,
              "stem": "Leg length discrepancy after THA is the most common cause of litigation in hip arthroplasty. The most important intra-operative method to assess leg length is:",
              "options": [
                "Measuring from the ASIS to the medial malleolus only pre-operatively",
                "Using a ruler to measure the wound",
                "Post-operative CT scan only",
                "Intra-operative assessment using anatomical landmarks, shuck test, and templating (± intra-operative XR or navigation)",
                "Patient self-assessment after waking from anaesthesia"
              ],
              "answer": "D",
              "explanation": "Leg length assessment during THA requires multiple methods: (1) pre-operative templating (XR with magnification marker to plan component sizes and predicted leg length change), (2) intra-operative reference points (mark the relationship between a fixed point on the pelvis/greater trochanter and a fixed point on the femur before dislocation — then reproduce after trial reduction), (3) shuck test (assess soft tissue tension and stability after trial reduction), (4) comparison of knee levels in supine position, (5) ± intra-operative fluoroscopy or computer navigation. No single method is perfectly reliable — combining multiple techniques minimises error. Acceptable LLD: <10mm is generally tolerated. >20mm causes significant symptoms and is a common cause of litigation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 810,
              "stem": "The Lewinnek safe zone for acetabular cup positioning in THA specifies:",
              "options": [
                "Cup inclination 30° ± 5°, anteversion 5° ± 5°",
                "Cup inclination 40° ± 10°, anteversion 15° ± 10°",
                "Cup inclination 60° ± 10°, anteversion 30° ± 10°",
                "Cup inclination 90°, anteversion 0°",
                "No specific values — any position is acceptable"
              ],
              "answer": "B",
              "explanation": "Lewinnek safe zone: cup inclination (abduction angle) 40° ± 10° (i.e., 30-50°) and cup anteversion 15° ± 10° (i.e., 5-25°). Components positioned within these ranges have significantly lower dislocation rates. However, recent evidence suggests that the Lewinnek safe zone alone is insufficient — up to 60% of dislocations occur with cups positioned WITHIN the safe zone. This has led to the concept of combined anteversion (cup AV + stem AV = 25-50°) and spinopelvic alignment (patients with stiff/fused lumbar spines are unable to tilt their pelvis with posture changes → cup position must compensate). Modern THA planning increasingly incorporates patient-specific spinopelvic analysis.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 811,
              "stem": "The direct anterior approach (DAA) to the hip uses the intermuscular interval between:",
              "options": [
                "Gluteus medius and piriformis",
                "Adductor longus and gracilis",
                "Biceps femoris and semitendinosus",
                "Gluteus maximus and iliotibial band",
                "Sartorius/rectus femoris (superficial) and tensor fasciae latae/gluteus medius (deep) — the Smith-Petersen interval"
              ],
              "answer": "E",
              "explanation": "The DAA uses the Smith-Petersen interval: between sartorius and rectus femoris (femoral nerve) medially, and TFL and gluteus medius (superior gluteal nerve) laterally. This is a TRUE intermuscular/internervous plane — no muscles are detached or split (unlike posterior or lateral approaches). Advantages: lower dislocation rate (anterior capsule and posterior structures preserved), faster recovery (muscle-sparing), allows supine positioning (easier intra-operative imaging, leg length assessment). Disadvantages: learning curve, LFCN injury (meralgia paraesthetica ~1-10%), wound complications (skin crease), limited exposure for complex cases (revisions, obese patients), risk of femoral fracture during broaching.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 812,
              "stem": "Trochanteric bursitis (greater trochanteric pain syndrome — GTPS) is now understood to be most commonly caused by:",
              "options": [
                "Isolated bursitis (fluid-filled bursa)",
                "Hip joint osteoarthritis",
                "Lumbar disc herniation",
                "Gluteus medius/minimus tendinopathy and tears (rather than pure bursitis)",
                "Femoral neck fracture"
              ],
              "answer": "D",
              "explanation": "Greater trochanteric pain syndrome (GTPS), formerly called trochanteric bursitis, is now recognised as being predominantly caused by gluteus medius and/or minimus tendinopathy and tears rather than isolated bursitis (MRI studies show that most patients with GTPS have tendinopathy with or without tearing, while isolated bursitis is uncommon). The gluteus medius/minimus insert onto the greater trochanter (analogous to the rotator cuff at the shoulder — hence 'rotator cuff of the hip'). Presents with lateral hip pain, worse lying on the affected side at night, tenderness directly over the GT, and pain with resisted hip abduction. Treatment: activity modification, physiotherapy (targeted gluteal strengthening exercises — best evidence), corticosteroid injection (temporary relief), and rarely surgical repair of tears (for refractory cases with MRI-confirmed tears).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 813,
              "stem": "Posterior dislocation of the hip (the most common direction, ~90%) typically occurs with the hip in which position at the time of impact?",
              "options": [
                "Flexion, adduction, and internal rotation (dashboard mechanism — knee hits dashboard with hip flexed)",
                "Extension, abduction, and external rotation",
                "Full extension only",
                "Abduction and external rotation",
                "Neutral position"
              ],
              "answer": "A",
              "explanation": "Posterior hip dislocations account for ~90% of traumatic hip dislocations and typically result from a dashboard mechanism: the knee strikes the dashboard in an RTA while the hip is FLEXED, ADDUCTED, and INTERNALLY ROTATED. The femoral head is driven posteriorly out of the acetabulum. The patient presents with the leg shortened, adducted, and internally rotated (locked). Sciatic nerve injury occurs in ~10-20% (peroneal division more commonly affected). Associated injuries: posterior wall acetabular fracture (up to 50% — CT after reduction), femoral head fracture (Pipkin classification). Reduction within 6 hours is critical to minimise AVN risk (~10% if reduced <6h, up to 40% if >6h). Reduction technique: Bigelow manoeuvre (longitudinal traction with hip flexed, then gradual abduction and ER).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Knee",
          "range": "Q814-Q858",
          "questions": [
            {
              "number": 814,
              "stem": "The posterior cruciate ligament (PCL) is tested clinically by the:",
              "options": [
                "Lachman test (that's ACL)",
                "Posterior drawer test (the examiner pushes the tibia POSTERIORLY at 90° flexion — increased posterior translation compared to the contralateral side indicates PCL insufficiency)",
                "Pivot shift test (that's ACL)",
                "Valgus stress test (that's MCL)",
                "McMurray test (that's meniscus)"
              ],
              "answer": "B",
              "explanation": "The POSTERIOR DRAWER test: patient supine, hip flexed 45°, knee flexed 90°, foot flat on the bed. The examiner sits on the patient's foot (to stabilise) and pushes the proximal tibia POSTERIORLY. Increased posterior translation compared to the other side = positive = PCL insufficiency. Grading: Grade I = <5mm (tibial plateau still anterior to the femoral condyles), Grade II = 5-10mm (plateau flush with condyles), Grade III = >10mm (plateau falls posterior to condyles — severe, suggests combined PLC injury). The POSTERIOR SAG test (Godfrey): patient supine, both hips and knees flexed to 90° → look at the tibial profile from the side. In PCL injury, the affected tibia sags posteriorly (loss of normal anterior tibial prominence). Important: in PCL-deficient knees, the starting position for the anterior drawer is already posteriorly subluxed — so an 'anterior drawer' may simply be reducing the posterior sag back to neutral (false positive for ACL — always compare to the contralateral side and assess the starting position).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 815,
              "stem": "The MCL (medial collateral ligament) of the knee is tested by:",
              "options": [
                "Anterior drawer test",
                "Lachman test",
                "VALGUS stress test (applying an abduction force at the knee with the leg in slight flexion ~20-30° — increased medial joint opening compared to the contralateral side indicates MCL injury)",
                "Posterior drawer test",
                "Dial test"
              ],
              "answer": "C",
              "explanation": "The VALGUS STRESS test: the examiner stabilises the femur with one hand and applies a VALGUS (abduction) force to the leg at the ankle/distal tibia with the other hand. Testing at: (1) 0° (full extension): tests the MCL + posterior capsule + cruciates (all are taut). Opening at 0° = SEVERE injury (MCL + at least one cruciate or posterior capsule). (2) 20-30° flexion: ISOLATES the MCL (the posterior capsule relaxes in slight flexion, the cruciates are less taut → the MCL becomes the primary medial restraint). Opening at 30° but NOT at 0° = isolated MCL injury. Grading: Grade I = 0-5mm opening (ligament sprain, no significant laxity, fibres intact). Grade II = 5-10mm opening (partial tear, clear laxity but firm endpoint). Grade III = >10mm opening (complete tear, no endpoint). Treatment: Grade I-II → non-operative (hinged knee brace, physiotherapy, functional rehabilitation — the MCL has good healing potential due to its extracapsular location and blood supply). Grade III isolated → non-operative initially (most heal) or surgery if combined with cruciate injury. Combined MCL + ACL: brace MCL → reconstruct ACL once MCL healed (6-8 weeks).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 816,
              "stem": "The normal alignment of the lower limb in the coronal plane is in slight:",
              "options": [
                "Varus (bowleg — that's abnormal in adults)",
                "Perfectly straight with zero angle",
                "Recurvatum",
                "VALGUS — the normal anatomical alignment of the lower limb has a slight valgus angle at the knee (~5-7° between the femoral anatomical axis and the tibial mechanical axis, with the mechanical axis passing just medial to the knee centre)",
                "Maximum flexion"
              ],
              "answer": "D",
              "explanation": "The normal lower limb alignment is in slight VALGUS. The femoral shaft is oblique (angled from the hip laterally to the knee medially — ~5-7° from vertical), while the tibial shaft is roughly vertical. This creates a normal physiological valgus angle at the knee (the 'Q-angle' or anatomical tibiofemoral angle ~5-7°). The mechanical axis (femoral head centre → ankle centre) passes just MEDIAL to the knee centre (through the medial tibial intercondylar eminence — within the medial compartment by ~4-8mm, creating ~1.2° mechanical valgus). Pathological alignment: VARUS (bowleg) → excessive medial compartment loading → medial OA. VALGUS (knock-knee) → excessive lateral compartment loading → lateral OA. Neutral mechanical alignment (line through knee centre) is the traditional target for TKA — achieved by making the femoral cut at ~5-7° valgus to the anatomical femoral axis (perpendicular to the mechanical axis).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 817,
              "stem": "The triad of O'Donoghue (classically described as the 'unhappy triad' of the knee) consists of injuries to the:",
              "options": [
                "PCL, LCL, and lateral meniscus",
                "ACL, LCL, and lateral meniscus only",
                "ACL, MCL, and medial meniscus (original description — now recognised that the lateral meniscus is more commonly injured with ACL tears)",
                "Both cruciate ligaments and the MCL",
                "Patellar tendon, MCL, and medial meniscus"
              ],
              "answer": "C",
              "explanation": "O'Donoghue's 'unhappy triad' was originally described as: ACL tear + MCL tear + medial meniscus tear — resulting from a valgus + external rotation force to the knee (common in contact sports). However, subsequent MRI studies have shown that the LATERAL meniscus is actually MORE commonly injured in association with acute ACL tears than the medial meniscus (the lateral compartment sustains the contrecoup bone bruise and lateral meniscal tear during the pivot-shift mechanism). The original triad remains an important teaching concept, but clinicians should be aware that the lateral meniscus is often the affected meniscus. Combined ACL + MCL injuries: manage the MCL non-operatively (hinged brace 6 weeks) → then ACL reconstruction once MCL healed and ROM restored (typically 6-8 weeks).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 818,
              "stem": "Constrained or hinged TKA implants are used when:",
              "options": [
                "In all primary TKA procedures",
                "Significant bone loss, ligamentous incompetence, or severe deformity prevents use of standard primary implants (massive instability that cannot be balanced with standard CR or PS components)",
                "Only in young patients",
                "For isolated medial compartment OA",
                "Only for post-traumatic arthritis"
              ],
              "answer": "B",
              "explanation": "Constrained or hinged TKA implants provide intrinsic mechanical stability that compensates for absent or deficient ligaments and bone. Indications: (1) revision TKA with significant bone loss (the constrained mechanism substitutes for lost bone and ligament support), (2) collateral ligament incompetence (MCL or LCL deficiency that cannot be corrected by soft tissue balancing alone), (3) massive coronal/sagittal deformity (>20-30° varus/valgus that cannot be balanced with standard releases), (4) supracondylar/periarticular fractures above TKA, (5) tumour reconstruction (distal femoral replacement). Hierarchy: CR → PS → varus-valgus constrained (VVC) → rotating hinge → fixed hinge. Use the LEAST constrained implant that provides adequate stability — excessive constraint transfers stress to the bone-implant interface, increasing loosening risk.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 819,
              "stem": "The mechanical axis of the lower limb runs from the:",
              "options": [
                "Femoral head centre to the ankle joint centre (normally passing through or just medial to the centre of the knee)",
                "Greater trochanter to the ankle joint centre",
                "ASIS to the medial malleolus",
                "Iliac crest to the 5th metatarsal",
                "Ischial tuberosity to the heel"
              ],
              "answer": "A",
              "explanation": "The mechanical axis of the lower limb is a straight line from the centre of the femoral head to the centre of the ankle joint. Normally, this line passes through or just MEDIAL to the centre of the knee (within the medial intercondylar eminence — in slight anatomical valgus ~1.2°). VARUS malalignment: the mechanical axis passes MEDIAL to the knee centre (increased medial compartment loading → medial OA). VALGUS malalignment: the mechanical axis passes LATERAL to the knee centre (increased lateral compartment loading → lateral OA). The ANATOMICAL axis of the femur follows the femoral shaft — it makes an angle of ~5-7° with the mechanical axis (the anatomical axis is not straight because the femur is oblique). In TKA planning: the goal of mechanical alignment is to restore the mechanical axis to neutral (line through knee centre) — the femoral cut is made at ~5-7° valgus to the anatomical axis to achieve this.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 820,
              "stem": "Extensor mechanism rupture — a quadriceps tendon rupture typically occurs in patients:",
              "options": [
                "Under 20 years old",
                "Only in elite athletes under 30",
                "Only in females",
                "Equally at all ages without risk factors",
                "Over 40 years old (typically 40-60 years, above the patella, associated with degenerative tendinopathy, diabetes, renal failure, fluoroquinolone use, and steroid injections)"
              ],
              "answer": "E",
              "explanation": "Quadriceps tendon rupture typically occurs in patients >40 years (peak 40-60) and involves a degenerate tendon that fails under sudden eccentric loading (e.g., stumbling, missing a step). Risk factors: degenerative tendinopathy (age), diabetes mellitus, chronic renal failure (renal osteodystrophy weakens the tendon-bone interface), fluoroquinolone antibiotics, systemic corticosteroid use, and local steroid injections. The rupture usually occurs at the tendon-bone junction (osteotendinous junction — within 2cm of the superior pole of the patella). Compare: patellar tendon rupture occurs in YOUNGER patients (<40 years, typically athletes) — below the patella at the inferior pole. Clinical: unable to straight-leg raise, palpable gap above the patella (quad) or below (patellar tendon), high-riding or low-riding patella. Treatment: BOTH require surgical repair (end-to-end repair through drill holes in the patella, heavy non-absorbable suture, ± augmentation).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 821,
              "stem": "The blood supply to the ACL is primarily from the:",
              "options": [
                "Popliteal artery via the middle genicular artery (which penetrates the posterior capsule to supply the cruciate ligaments)",
                "Anterior tibial artery",
                "Femoral artery directly",
                "Obturator artery",
                "Peroneal artery"
              ],
              "answer": "A",
              "explanation": "The ACL receives its blood supply primarily from the MIDDLE GENICULAR ARTERY (a branch of the popliteal artery that penetrates the posterior joint capsule and enters the intercondylar notch to supply both cruciate ligaments via a periligamentous synovial envelope). The inferior genicular arteries also contribute. The ACL has a relatively poor blood supply compared to extra-articular ligaments (like the MCL) — this is one reason why the ACL has limited healing capacity after rupture (combined with the hostile intra-articular synovial fluid environment which lyses blood clots and prevents organised scar formation). This poor healing capacity is why ACL injuries are treated with RECONSTRUCTION (using a graft) rather than primary REPAIR in most cases. Recent interest in primary ACL repair has re-emerged (BEAR implant — bridge-enhanced ACL repair), but reconstruction remains the gold standard.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 822,
              "stem": "Baker's cyst (popliteal cyst) is most commonly associated with:",
              "options": [
                "Normal knees without any intra-articular pathology",
                "Intra-articular knee pathology (meniscal tears, OA, inflammatory arthritis — the cyst communicates with the joint through a valvular mechanism between the semimembranosus and medial gastrocnemius)",
                "Isolated lateral ligament injury",
                "Patellar tendinopathy",
                "Quadriceps tendon rupture"
              ],
              "answer": "B",
              "explanation": "A Baker's cyst (popliteal cyst) is a fluid-filled cyst in the popliteal fossa that communicates with the knee joint through a valvular opening between the semimembranosus tendon and the medial head of gastrocnemius. In ADULTS: it is almost always SECONDARY to intra-articular pathology (meniscal tears, OA, RA, chondral damage, loose bodies) — the joint effusion is forced posteriorly through the valvular communication during knee flexion, filling the cyst. The one-way valve mechanism prevents fluid returning to the joint. Treatment: address the underlying intra-articular pathology (the cyst will resolve when the effusion resolves). Isolated cyst excision without treating the underlying cause → high recurrence rate. In CHILDREN: Baker's cysts are usually PRIMARY (idiopathic, no intra-articular pathology) and typically resolve spontaneously — observation is the treatment. Complications: cyst rupture (mimics DVT — 'pseudo-thrombophlebitis'), compression of popliteal vessels/tibial nerve (rare).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 823,
              "stem": "The dial test at the knee assesses injury to the:",
              "options": [
                "ACL",
                "MCL",
                "Patellar tendon",
                "Posterolateral corner (increased external rotation of the tibia at 30° flexion = PLC; increased at BOTH 30° and 90° = PLC + PCL combined injury)",
                "Medial meniscus"
              ],
              "answer": "D",
              "explanation": "The dial test assesses the posterolateral corner (PLC) of the knee. Technique: patient prone or supine, externally rotate both feet at 30° and then 90° knee flexion — compare the degree of external rotation side-to-side. An asymmetric increase of ≥10° of external rotation is positive. Interpretation: increased ER at 30° ONLY = ISOLATED PLC injury (the PCL is intact and acts as a secondary restraint at 90° — preventing further ER). Increased ER at BOTH 30° AND 90° = COMBINED PLC + PCL injury (the PCL is also disrupted, removing the secondary restraint at 90°). This distinction is clinically critical: isolated PLC injuries have a better prognosis than combined PLC + PCL injuries (the latter typically requires multiligament reconstruction).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 824,
              "stem": "The most reliable clinical test for ACL rupture is the:",
              "options": [
                "McMurray test (meniscus)",
                "Valgus stress test (MCL)",
                "Lachman test (anterior tibial translation with the knee in 20-30° flexion — sensitivity ~85-95%, the most reliable clinical test for ACL integrity)",
                "Posterior drawer test (PCL)",
                "Dial test (PLC)"
              ],
              "answer": "C",
              "explanation": "The Lachman test is the MOST RELIABLE clinical test for ACL rupture (sensitivity 85-95%, specificity 94%). Technique: the knee is flexed to 20-30°, the examiner stabilises the femur with one hand and applies an ANTERIOR translating force to the proximal tibia with the other. A positive test: increased anterior tibial translation compared to the contralateral side AND a SOFT endpoint (mushy/absent endpoint vs firm endpoint in an intact ACL). Why 20-30° flexion: this position relaxes the secondary restraints (hamstrings, MCL, joint capsule) that can mask ACL laxity at 90° flexion (where the anterior drawer is performed — making the anterior drawer less sensitive, ~60-70%). Pivot shift test: the most SPECIFIC test for ACL rupture (reproduces the actual subluxation event — the tibia subluxes anterolaterally in extension and reduces with a 'clunk' at 20-30° flexion). It is harder to perform (guarding, pain) and less sensitive in the clinic but highly specific.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 825,
              "stem": "The Ottawa Knee Rules — radiographs are only required if one or more of the following criteria are met. Which is NOT an Ottawa Knee Rule criterion?",
              "options": [
                "Age ≥55 years",
                "Isolated tenderness of the patella (no other bony tenderness)",
                "Tenderness at the head of the fibula",
                "Inability to flex the knee to 90°",
                "Pain during passive external rotation of the ankle (this is an Ottawa ANKLE rule, not a knee rule)"
              ],
              "answer": "E",
              "explanation": "Ottawa Knee Rules (to determine whether XR is needed after acute knee injury): XR indicated if ANY of: (1) Age ≥55 years. (2) Isolated PATELLAR tenderness (no other bony tenderness). (3) Tenderness at the HEAD OF THE FIBULA. (4) Inability to FLEX to 90°. (5) Inability to WEIGHT-BEAR immediately after injury AND in the ED (4 steps — regardless of limping). If NONE of these criteria are met → XR is NOT needed (high sensitivity for fracture — rules out significant fractures safely). The rules reduce unnecessary knee radiographs by ~25-30% without missing clinically significant fractures. Passive ER of the ankle is part of the Ottawa ANKLE rules (assessing the proximal fibula/syndesmosis for a Maisonneuve fracture) — it is NOT part of the knee rules.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 826,
              "stem": "The PCL (posterior cruciate ligament) is the primary restraint to:",
              "options": [
                "Anterior tibial translation (that's ACL)",
                "Valgus stress",
                "Varus stress",
                "External rotation",
                "Posterior tibial translation (the PCL prevents the tibia from sliding posteriorly on the femur — tested by the posterior drawer test at 90° flexion)"
              ],
              "answer": "E",
              "explanation": "The PCL is the primary restraint to POSTERIOR tibial translation — it prevents the tibia from sliding backwards on the femur. It is the STRONGEST ligament in the knee (roughly twice the strength of the ACL). Testing: POSTERIOR DRAWER test at 90° flexion (push the tibia posteriorly — compare to the contralateral side). The posterior SAG sign (Godfrey test): with the patient supine, both hips and knees flexed to 90° → look at the tibial profile from the side — in PCL injury, the affected tibia sags posteriorly (the tibial tubercle prominence is lost). PCL injury mechanism: dashboard injury (posterior force on the proximal tibia with the knee flexed — car accident), fall onto the flexed knee with the foot plantarflexed. Isolated PCL injuries: many are treated NON-OPERATIVELY (quadriceps strengthening — the quadriceps pulls the tibia anteriorly, functionally compensating for PCL deficiency). Surgery: for Grade III PCL injuries (>10mm posterior translation), combined PCL + PLC injuries, or symptomatic chronic PCL deficiency (posterior laxity causing pain/instability with stairs/deceleration).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 827,
              "stem": "High tibial osteotomy (HTO) for medial compartment OA of the knee is indicated in:",
              "options": [
                "Elderly patients with tricompartmental OA",
                "All patients with any knee OA",
                "Only patients who have already had a TKA",
                "Young active patients with isolated MEDIAL compartment OA, varus malalignment, intact ACL and lateral compartment, and good ROM — the osteotomy corrects the varus to offload the medial compartment",
                "Patients with inflammatory arthritis"
              ],
              "answer": "D",
              "explanation": "HTO (typically medial opening wedge — fixed with a locking plate + bone graft/substitute) corrects varus malalignment by transferring load from the damaged MEDIAL compartment to the preserved LATERAL compartment. The mechanical axis is corrected from varus to slight valgus (Fujisawa point — 62% of the tibial plateau width from medial, i.e., slightly lateral to the centre → transfers load to the healthy lateral compartment). Ideal candidate: young (<60-65yr), active, isolated medial compartment OA (lateral compartment and patellofemoral must be preserved), correctable varus malalignment, good ROM (>90° flexion, <10° flexion contracture), intact ACL, BMI <30-35. HTO delays or avoids the need for TKA by 7-10+ years (73-95% survival at 10 years in well-selected patients). Contraindications: lateral compartment OA, inflammatory arthritis, significant ligamentous instability (unless addressed concurrently), severe ROM restriction, overcorrection risks. If HTO eventually fails → conversion to TKA (results of TKA after prior HTO are slightly inferior to primary TKA but still good).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 828,
              "stem": "The lateral meniscus covers approximately what percentage of the lateral tibial plateau surface?",
              "options": [
                "30%",
                "50%",
                "70-80% (the lateral meniscus covers a significantly larger proportion of the lateral plateau compared to the medial meniscus covering ~50% of the medial plateau — making lateral meniscal loss more devastating biomechanically)",
                "100%",
                "10%"
              ],
              "answer": "C",
              "explanation": "The lateral meniscus covers approximately 70-80% of the lateral tibial plateau articular surface, while the medial meniscus covers approximately 50% of the medial plateau. This difference means: lateral meniscectomy causes GREATER increase in contact pressure than medial meniscectomy (removing a greater proportion of the load-bearing surface). The lateral meniscus is also more MOBILE than the medial (less firmly attached to the capsule — the popliteal hiatus creates a gap in the posterolateral capsular attachment, allowing the lateral meniscus to move ~10mm during flexion/extension vs ~5mm for the medial). Despite covering more surface, the lateral meniscus is LESS commonly torn than the medial (because its mobility protects it from entrapment). Meniscal function: load transmission (50-70% of the load in the knee passes through the menisci), shock absorption, stability, proprioception, joint nutrition, and joint congruity. Total meniscectomy increases contact pressures by 200-300%.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 829,
              "stem": "The anterior cruciate ligament (ACL) prevents:",
              "options": [
                "Posterior tibial translation (that's PCL)",
                "Anterior tibial translation AND rotational instability (the ACL is the primary restraint to anterior tibial translation, providing ~85% of the restraining force, and a secondary restraint to internal rotation)",
                "Valgus stress (that's MCL)",
                "Varus stress (that's LCL)",
                "Extension of the knee"
              ],
              "answer": "B",
              "explanation": "The ACL is the PRIMARY restraint to ANTERIOR tibial translation (~85% of the total restraining force against anterior drawer). It runs from the posterior aspect of the lateral femoral condyle (in the intercondylar notch) to the anterior intercondylar area of the tibial plateau. Two bundles: (1) anteromedial (AM) bundle — taut in flexion (tested by Lachman at 20-30°), (2) posterolateral (PL) bundle — taut in extension (contributes to rotational control). The ACL also provides secondary restraint to: (1) internal tibial rotation, (2) varus/valgus angulation. The PIVOT SHIFT test demonstrates the combined anterior translation + rotational instability that characterises the ACL-deficient knee — the tibia subluxes anterolaterally in extension and reduces with a clunk at 20-30° flexion. ACL deficiency → functional instability (giving way with pivoting activities) → progressive meniscal and cartilage damage if untreated → early OA.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 830,
              "stem": "The McMurray test for meniscal tears is performed by:",
              "options": [
                "Flexing the knee fully, then extending while applying rotational stress and varus/valgus — a palpable click or pain at the joint line suggests a meniscal tear",
                "Applying valgus stress with the knee in extension",
                "Performing an anterior drawer at 90° flexion",
                "Measuring knee circumference",
                "Passively hyperextending the knee"
              ],
              "answer": "A",
              "explanation": "McMurray test: with the patient supine, flex the knee fully, then apply external rotation + valgus force while slowly extending the knee (tests the MEDIAL meniscus — stresses the posterior horn). A palpable/audible click or pain at the medial joint line is positive. For the LATERAL meniscus: apply internal rotation + varus force during extension. The click represents the femoral condyle riding over a torn meniscal fragment. Sensitivity: ~60-70% (varies by tear location — better for posterior horn tears). Apley grind test: prone, knee flexed 90°, compress + rotate the tibia → pain = meniscal (vs distract + rotate → pain = ligament). Joint line tenderness: most sensitive but least specific sign of meniscal pathology. MRI: >90% accuracy for meniscal tears.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 831,
              "stem": "The most common meniscal tear pattern in the elderly with degenerative knees is:",
              "options": [
                "Bucket-handle tear",
                "Horizontal (cleavage) tear",
                "Radial tear at the free edge",
                "Vertical longitudinal tear",
                "Discoid meniscus tear"
              ],
              "answer": "B",
              "explanation": "Horizontal (cleavage) tears are the most common meniscal tear pattern in elderly patients with degenerative knees. They split the meniscus into upper and lower leaves along a horizontal plane, typically in the posterior horn of the medial meniscus. They result from degenerative wear rather than acute trauma. Most are asymptomatic and found incidentally on MRI (up to 60% of asymptomatic knees >50 years have meniscal tears on MRI). Symptomatic degenerative meniscal tears in the setting of OA: evidence (FIDELITY meta-analysis, ESCAPE trial) shows arthroscopic partial meniscectomy provides NO additional benefit over physiotherapy for degenerative tears with OA. Treatment: physiotherapy + weight management. Bucket-handle tears and radial tears are more common in younger patients with acute injuries.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 832,
              "stem": "The Insall-Salvati ratio measures:",
              "options": [
                "Patellar height (ratio of patellar tendon length to patellar length on lateral knee XR in 30° flexion)",
                "Femoral anteversion",
                "Acetabular coverage",
                "Tibial slope",
                "Mechanical axis"
              ],
              "answer": "A",
              "explanation": "The Insall-Salvati ratio measures patellar height on a lateral knee radiograph (taken in 30° flexion). Ratio = patellar tendon length / patellar length. Normal: 0.8-1.2. Patella alta (high-riding patella): ratio >1.2 — associated with patellar instability, recurrent dislocation, and anterior knee pain. Patella baja (low-riding/infera): ratio <0.8 — associated with post-operative stiffness (after TKA or tibial tubercle osteotomy), infrapatellar contracture syndrome, and decreased ROM. The Caton-Deschamps ratio is an alternative (AT/AP): distance from inferior articular surface of patella to anterosuperior tibial plateau / patellar articular surface length. Normal: 0.6-1.2. Patella alta: >1.2.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 833,
              "stem": "The medial collateral ligament (MCL) of the knee is tested by applying which stress?",
              "options": [
                "Varus stress at 30° flexion",
                "Anterior drawer force",
                "Valgus stress at 30° flexion",
                "Posterior drawer force",
                "Lachman manoeuvre"
              ],
              "answer": "C",
              "explanation": "The MCL is tested by applying a valgus (abduction) stress to the knee, primarily at 30° of flexion (where the posterior capsule is relaxed, isolating the MCL as the primary restraint). Laxity at 30° with a firm endpoint suggests Grade I-II MCL injury. Laxity in full extension suggests a more severe injury involving the MCL AND posterior capsule/cruciate ligaments. The MCL has good healing potential (unlike the ACL) and most isolated injuries are managed non-operatively with hinged knee brace.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 834,
              "stem": "Osteochondritis dissecans (OCD) of the knee in a skeletally immature patient with an intact articular surface is best treated with:",
              "options": [
                "Immediate surgical excision of the fragment",
                "Arthroscopic retrograde drilling of the lesion",
                "Open reduction and internal fixation",
                "Total knee arthroplasty",
                "Conservative management with activity modification and monitoring"
              ],
              "answer": "E",
              "explanation": "In skeletally immature patients, stable OCD lesions with an intact articular surface have significant healing potential. Conservative management (activity modification, protected weight-bearing, avoidance of impact sports) for 3-6 months is the first-line treatment. If healing does not occur, drilling (anterograde or retrograde) can stimulate a healing response. Unstable or displaced lesions require surgical fixation (bioabsorbable pins, Herbert screws). Excision is a last resort as it creates an articular defect requiring cartilage restoration.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 835,
              "stem": "In TKA, the 'gap balancing' technique aims to create:",
              "options": [
                "A trapezoidal flexion gap and rectangular extension gap",
                "A tight flexion gap and loose extension gap",
                "No gap at all — bone-to-bone contact",
                "Equal rectangular gaps in both flexion and extension",
                "Different gaps on medial and lateral sides"
              ],
              "answer": "D",
              "explanation": "Gap balancing aims to create equal, rectangular gaps in both flexion and extension. A balanced TKA has: (1) equal medial and lateral gaps (rectangular, not trapezoidal), and (2) equal flexion and extension gaps. Flexion gap is determined by: femoral component rotation and size, posterior condylar resection, and PCL tension. Extension gap is determined by: distal femoral resection, posterior capsule tension, and MCL/LCL balance. Mismatch creates instability: tight in flexion = too large femoral component or insufficient posterior condylar resection; tight in extension = insufficient distal femoral resection.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 836,
              "stem": "The popliteal hiatus in the posterolateral meniscus allows passage of which structure?",
              "options": [
                "Anterior cruciate ligament",
                "Medial meniscal attachment",
                "Lateral collateral ligament",
                "Popliteus tendon",
                "Posterior tibial artery"
              ],
              "answer": "D",
              "explanation": "The popliteus tendon passes through the popliteal hiatus — a gap in the posterior horn attachment of the lateral meniscus to the tibial plateau. This is a normal anatomical structure. The popliteus stabilises the posterolateral corner, unlocks the knee from full extension (by internally rotating the tibia), and acts as a dynamic lateral meniscal stabiliser. The lateral meniscus also lacks a coronary ligament attachment in this region, giving it greater mobility than the medial meniscus (lateral meniscus moves ~11mm during flexion vs ~5mm for medial). This is why discoid meniscus tears and Wrisberg variants occur laterally.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 837,
              "stem": "A Baker cyst (popliteal cyst) is a distension of which bursa?",
              "options": [
                "Suprapatellar bursa",
                "Semimembranosus-medial head of gastrocnemius bursa",
                "Prepatellar bursa",
                "Pes anserinus bursa",
                "Infrapatellar bursa"
              ],
              "answer": "B",
              "explanation": "A Baker cyst (popliteal cyst) is a distension of the semimembranosus-medial head of gastrocnemius bursa, located in the posteromedial aspect of the popliteal fossa. It communicates with the knee joint through a valvular mechanism — synovial fluid flows from the knee into the bursa during flexion but cannot return. In adults, Baker cysts are usually secondary to intra-articular pathology (meniscal tear, OA, RA, loose bodies). In children, they are usually primary (no intra-articular pathology) and resolve spontaneously. Complications: rupture (mimics DVT — pseudothrombophlebitis), compartment syndrome (rare).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 838,
              "stem": "The unhappy triad of O'Donoghue involves the ACL, MCL, and medial meniscus. The most common mechanism producing this injury is:",
              "options": [
                "Valgus force combined with external rotation (e.g., football tackle from lateral side)",
                "Hyperextension injury",
                "Direct anterior blow to the tibia",
                "Pure varus force",
                "Axial compression"
              ],
              "answer": "A",
              "explanation": "The valgus + external rotation mechanism (typically from a lateral tackle in football, or a planted foot with rotational force) stresses the MCL (valgus), ACL (rotational force), and medial meniscus (trapped between the rotating condyle and tibial plateau). This classic mechanism produces the unhappy triad. The MCL is the primary restraint to valgus stress. Once the MCL fails, the ACL is loaded next, and the meniscus is damaged by the resulting abnormal joint kinematics. Modern evidence suggests the lateral meniscus may be more commonly injured than medial in acute ACL ruptures, but the classic teaching remains ACL + MCL + medial meniscus.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 839,
              "stem": "Prepatellar bursitis ('housemaid's knee') is caused by:",
              "options": [
                "Infection of the knee joint",
                "ACL rupture",
                "Patellar fracture",
                "Meniscal tear",
                "Repeated kneeling causing inflammation of the prepatellar bursa"
              ],
              "answer": "E",
              "explanation": "Prepatellar bursitis results from repeated kneeling (cleaners, carpet layers, plumbers, gardeners), causing friction and inflammation of the prepatellar bursa (between the skin and the anterior surface of the patella). It presents as a localised fluctuant swelling over the patella with preserved knee ROM (unlike a joint effusion which restricts movement). Distinguish from: septic bursitis (red, hot, tender, ± cellulitis → aspirate), gout/pseudogout (crystal arthropathy), and knee joint effusion (intra-articular — ballotable patella, restricted ROM).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 840,
              "stem": "The physiological valgus alignment of the knee (mechanical axis passing slightly medial to the knee centre) means the normal weight-bearing axis creates approximately what percentage of load through the medial compartment?",
              "options": [
                "30%",
                "50%",
                "60-70%",
                "90%",
                "100%"
              ],
              "answer": "C",
              "explanation": "Approximately 60-70% of the knee load passes through the medial compartment during normal gait because the mechanical axis (line from hip centre to ankle centre) passes slightly medial to the knee centre. This asymmetric loading explains why medial compartment OA is far more common than lateral. Any increase in varus alignment (e.g., from medial meniscectomy, tibial plateau fracture malunion) further increases medial loading. An HTO aims to shift the load to the lateral compartment (Fujisawa point, 62% from medial edge). TKA aims to restore neutral mechanical alignment.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 841,
              "stem": "The TT-TG distance (tibial tuberosity to trochlear groove) is measured on CT or MRI to assess patellar instability. A distance greater than which value is considered pathological?",
              "options": [
                "10 mm",
                "15 mm",
                "30 mm",
                "40 mm",
                "20 mm"
              ],
              "answer": "E",
              "explanation": "The TT-TG distance measures the lateral offset of the tibial tuberosity relative to the deepest point of the trochlear groove on axial CT or MRI. Normal: <15mm on CT (<20mm on MRI due to cartilage). A TT-TG >20mm on CT is considered pathological and associated with patellar instability/maltracking. Values >20mm may warrant tibial tubercle medialisation (Elmslie-Trillat procedure or Fulkerson osteotomy) as part of the surgical management of recurrent patellar dislocation — in addition to MPFL reconstruction. Other factors: trochlear dysplasia (Dejour classification), patella alta (Caton-Deschamps/Insall-Salvati ratio), and MPFL integrity.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            },
            {
              "number": 842,
              "stem": "The gold standard investigation for confirming an ACL tear is:",
              "options": [
                "Plain radiograph",
                "MRI of the knee",
                "CT scan",
                "Bone scan",
                "Diagnostic arthroscopy"
              ],
              "answer": "B",
              "explanation": "MRI is the gold standard non-invasive investigation for diagnosing ACL tears, with sensitivity and specificity both exceeding 95%. MRI shows: ACL discontinuity (complete tear — high signal replacing the normal low-signal ligament on PD/T2 sequences), associated injuries (meniscal tears in ~50% of ACL ruptures, chondral damage, bone bruise pattern — lateral femoral condyle + posterolateral tibial plateau bruising is pathognomonic for ACL injury mechanism), MCL sprains, and posterolateral corner injuries. While arthroscopy is the definitive confirmation, MRI has largely replaced diagnostic arthroscopy for ACL assessment. Clinical examination (Lachman test) by an experienced clinician is highly accurate and may be sufficient in clear-cut cases — MRI confirms and identifies associated pathology.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 843,
              "stem": "Valgus stress testing of the knee at 30° flexion primarily assesses the integrity of the:",
              "options": [
                "ACL",
                "PCL",
                "LCL",
                "MCL (medial collateral ligament)",
                "Popliteus"
              ],
              "answer": "D",
              "explanation": "Valgus stress testing at 30° of knee flexion isolates the MCL as the primary restraint to valgus opening. At 30° flexion, the posterior capsule and cruciates are relaxed — any valgus opening is attributable to MCL insufficiency. Testing at FULL EXTENSION (0°) with valgus stress: if opening occurs, this indicates BOTH MCL AND posterior capsule/cruciate involvement (more severe injury — a combined ligament injury). MCL grading: Grade I = pain but no laxity (sprain). Grade II = opening with a definite endpoint (partial tear). Grade III = opening with no endpoint (complete tear). The MCL heals well non-operatively due to its extracapsular position and good blood supply — treatment is typically a hinged knee brace for 6 weeks with physiotherapy.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 844,
              "stem": "Multiligament knee injury with knee dislocation — what percentage of injuries have a spontaneous reduction before presentation, making the dislocation appear 'reduced' on initial radiographs?",
              "options": [
                "0%",
                "10%",
                "Up to 50% (spontaneous reduction is common — must maintain high clinical suspicion)",
                "80%",
                "100%"
              ],
              "answer": "C",
              "explanation": "Up to 50% of knee dislocations spontaneously reduce before the patient reaches the ED, making the injury appear less severe on initial radiographs (the knee looks 'relocated' on XR). This is dangerous because the vascular injury (popliteal artery — 30-40% of dislocations) may still be present despite apparent reduction. Clinical clues: gross instability on examination (multiligament laxity), massive effusion/haemarthrosis, skin dimpling, and mechanism of injury (high-energy or low-energy in obese patients). ALWAYS perform vascular assessment (CTA or duplex USS) if multiligament knee injury is suspected, even if the knee appears reduced. The ABI (ankle-brachial index) <0.9 is an indication for angiography. Delayed vascular injury (intimal tear → thrombosis hours to days later) can occur with initially normal pulses.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 845,
              "stem": "The pivot shift test for ACL deficiency is the most specific clinical test because it:",
              "options": [
                "Recreates the actual functional instability pattern (anterolateral rotatory subluxation → reduction of the tibia as the knee flexes past ~30°)",
                "Tests PCL function",
                "Measures valgus laxity",
                "Tests medial stability only",
                "Is always easy to perform"
              ],
              "answer": "A",
              "explanation": "The pivot shift test is pathognomonic for ACL deficiency. It reproduces the functional instability (giving way) that patients experience during activity. Technique: with the knee in extension, apply a valgus stress and internal rotation to the tibia while gently flexing the knee. In an ACL-deficient knee, the lateral tibial plateau subluxes anteriorly (anterolateral rotatory subluxation) — as the knee passes ~30° flexion, the ITB transitions from an extensor to a flexor, pulling the tibia back into reduction with a palpable 'clunk'. The positive test reproduces the patient's feeling of giving way. It is the MOST SPECIFIC test (~98%) but has lower sensitivity (~35% in conscious patients — hamstring guarding inhibits the test). It is most reliable under anaesthesia.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 846,
              "stem": "The most commonly injured knee ligament overall is the:",
              "options": [
                "Posterior cruciate ligament",
                "Lateral collateral ligament",
                "Medial collateral ligament",
                "Anterior cruciate ligament",
                "Popliteofibular ligament"
              ],
              "answer": "C",
              "explanation": "The medial collateral ligament (MCL) is the most commonly injured knee ligament overall. It is injured by valgus stress (force from the lateral side pushing the knee into valgus). Most isolated MCL injuries are managed non-operatively with a hinged knee brace — the MCL has excellent healing potential due to its extracapsular position and good blood supply. This contrasts with the ACL which has poor healing potential (intra-articular, bathed in synovial fluid which inhibits clot formation). The ACL is the most commonly surgically reconstructed knee ligament because it does not heal spontaneously.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 847,
              "stem": "The dial test (tibial external rotation test) at 30° flexion assesses which structure?",
              "options": [
                "Posterolateral corner (PLC) integrity",
                "ACL integrity",
                "PCL integrity",
                "Medial collateral ligament",
                "Patellar tracking"
              ],
              "answer": "A",
              "explanation": "The dial test measures the amount of tibial external rotation relative to the femur at 30° and 90° of knee flexion, comparing to the contralateral side. Increased external rotation (≥10° more than contralateral) at 30° ONLY = isolated posterolateral corner (PLC) injury (LCL, popliteus, popliteofibular ligament). Increased external rotation at BOTH 30° and 90° = combined PLC + PCL injury. PLC injuries are frequently missed and MUST be identified before ACL/PCL reconstruction — failure to address an associated PLC injury leads to graft failure.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 848,
              "stem": "The meniscus receives its blood supply from the:",
              "options": [
                "Central region (white-white zone) — well vascularised throughout",
                "Synovial fluid only",
                "Tibial plateau subchondral vessels",
                "Femoral condyle vessels",
                "Peripheral third from the perimeniscal capillary plexus (red-red zone), with decreasing vascularity centrally"
              ],
              "answer": "E",
              "explanation": "The meniscus is vascularised from the peripheral perimeniscal capillary plexus (branches of the medial/lateral genicular arteries). The peripheral 10-30% is the RED-RED zone (vascular, good healing potential → amenable to repair). The middle zone is the RED-WHITE zone (some vascularity, variable healing). The central/inner zone is the WHITE-WHITE zone (avascular, nutrition from synovial fluid diffusion, poor healing → partial meniscectomy if torn). This vascular anatomy guides surgical decision-making: tears in the red-red zone can be repaired (suture), while tears in the white-white zone are usually excised. Meniscal preservation is now prioritised because meniscectomy accelerates OA.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 849,
              "stem": "In ACL reconstruction, the two most commonly used autograft options are:",
              "options": [
                "Iliotibial band and quadriceps tendon",
                "Bone-patellar tendon-bone (BPTB) and hamstring tendon (semitendinosus ± gracilis)",
                "Achilles tendon and plantaris",
                "Peroneus longus and brevis",
                "Tibialis anterior and FHL"
              ],
              "answer": "B",
              "explanation": "The two most commonly used autografts for ACL reconstruction are: (1) BPTB (bone-patellar tendon-bone) — bone blocks allow bone-to-bone healing in tunnels, excellent fixation strength; disadvantages: anterior knee pain, kneeling pain, patellar fracture risk. (2) Hamstring tendon (semitendinosus ± gracilis, folded to create a 4-strand graft) — less donor site morbidity, no anterior knee pain; disadvantages: slightly slower graft incorporation (soft tissue-to-bone healing), potential hamstring weakness. Both have excellent outcomes with >90% satisfaction. Choice depends on patient factors, surgeon preference, and activity demands. Quadriceps tendon is increasingly used as a third option.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 850,
              "stem": "In TKA, the most common cause of failure at ANY time point across the NJR dataset is:",
              "options": [
                "Polyethylene wear",
                "Infection",
                "Pain without identifiable cause",
                "Aseptic loosening",
                "Instability"
              ],
              "answer": "D",
              "explanation": "Across all time points combined, aseptic loosening is the most common cause of TKA revision in the NJR. However, the timing matters: early failure (<2 years) is dominated by instability/malalignment and infection. Medium-term (2-5 years) sees infection and loosening. Late failure (>5 years) is predominantly aseptic loosening and polyethylene wear. Understanding the temporal pattern is key to investigating the painful TKA: early pain → think instability, infection, malrotation. Late pain → think loosening, wear, late infection.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 851,
              "stem": "The most common indication for primary total knee arthroplasty is:",
              "options": [
                "Rheumatoid arthritis",
                "Primary osteoarthritis",
                "Post-traumatic arthritis",
                "Gout",
                "Avascular necrosis"
              ],
              "answer": "B",
              "explanation": "Primary osteoarthritis is by far the most common indication for TKA, accounting for >95% of primary TKA procedures in the NJR. The decision to offer TKA is based on: (1) symptoms (pain, stiffness, functional limitation) unresponsive to adequate non-operative management, (2) impact on quality of life, (3) radiographic evidence of OA (though clinical-radiographic discordance is common). NICE states that TKA should not be withheld based on age, radiographic grade alone, or BMI alone. RA, post-traumatic OA, and other inflammatory arthropathies account for the remaining <5%.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 852,
              "stem": "In ACL reconstruction, the recommended femoral tunnel position on the lateral condyle (viewed arthroscopically) is:",
              "options": [
                "Anterior and superior (12 o'clock position)",
                "At the centre of the lateral condyle",
                "High posterior (11 o'clock)",
                "At the tibial insertion",
                "Low on the lateral wall (between 1-2 o'clock position for a right knee) — anatomical footprint"
              ],
              "answer": "E",
              "explanation": "Modern ACL reconstruction aims for anatomical femoral tunnel placement at the centre of the native ACL footprint on the lateral femoral condyle — this corresponds to a low lateral wall position, approximately 1:30 (right knee) or 10:30 (left knee) on the clock face. The historical technique placed the tunnel at the 11 o'clock (right knee) or 1 o'clock (left knee) — the 'isometric point' — which provided good anteroposterior stability but did not restore rotational stability. Anatomical placement (lower on the wall) better restores both AP and rotational stability, reducing the positive pivot shift. Tibial tunnel: aimed at the centre of the tibial footprint, posterior to the anterior horn of the lateral meniscus.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 853,
              "stem": "PCL injury is best assessed clinically using the:",
              "options": [
                "Posterior drawer test (tibia sags posteriorly relative to the femur at 90° flexion)",
                "Anterior drawer test",
                "Lachman test",
                "Pivot shift test",
                "Valgus stress test"
              ],
              "answer": "A",
              "explanation": "The posterior drawer test is the most sensitive clinical test for PCL injury. With the patient supine, hip flexed 45° and knee flexed 90°: observe for posterior tibial sag (gravity causes the tibia to sublux posteriorly if the PCL is disrupted — this is the MOST IMPORTANT sign to look for before testing). Then apply a posteriorly directed force to the proximal tibia — increased posterior translation compared to the contralateral side confirms PCL insufficiency. Grade I: 1-5mm posterior translation (partial tear). Grade II: 5-10mm (complete tear, tibia sags to the level of the femoral condyles). Grade III: >10mm (combined PCL + posterolateral corner injury). The quadriceps active test (contraction of the quadriceps reduces the posteriorly subluxed tibia forward) also confirms PCL injury.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 854,
              "stem": "The anterior approach to the knee for TKA most commonly uses which interval?",
              "options": [
                "Lateral parapatellar approach",
                "Subvastus approach",
                "Trivector approach",
                "Medial parapatellar approach (through the medial retinaculum and VMO, with patellar eversion)",
                "Posterior approach"
              ],
              "answer": "D",
              "explanation": "The standard medial parapatellar approach is the most commonly used approach for TKA worldwide. It involves a midline skin incision, then a capsular incision through the medial retinaculum and along the medial border of the patella, extending through the quadriceps tendon proximally and along the medial border of the patellar tendon distally. The patella is then everted or subluxed laterally to expose the joint. Advantages: extensile (can extend proximally or distally), excellent exposure of all three compartments, and familiar to most surgeons. Subvastus (Southern approach) and midvastus approaches are alternatives that avoid dividing the VMO (potentially better early patellar tracking and less post-operative pain) but provide more limited exposure.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 855,
              "stem": "Osteochondritis dissecans (OCD) of the knee most commonly affects which location?",
              "options": [
                "Lateral tibial plateau",
                "Medial tibial plateau",
                "Lateral aspect of the medial femoral condyle (most common site)",
                "Patella",
                "Trochlea"
              ],
              "answer": "C",
              "explanation": "OCD of the knee most commonly involves the lateral aspect of the medial femoral condyle (~70-85% of cases), adjacent to the intercondylar notch. Other locations: lateral femoral condyle (~15%), patella, and trochlea (uncommon). It is an acquired disorder of subchondral bone and overlying articular cartilage, likely from repetitive microtrauma (vascular insufficiency theory). Juvenile OCD (open physes, <20 years): better prognosis — many heal with activity modification and protected weight-bearing. Adult OCD (closed physes): poorer prognosis, more likely to progress to fragment detachment. Treatment: stable lesions → non-operative (protected WB, activity modification 3-6 months). Unstable or detached lesions → fixation (bioabsorbable pins/screws) or fragment excision + microfracture/grafting.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 856,
              "stem": "The anterior drawer test at the knee assesses the integrity of the:",
              "options": [
                "PCL",
                "MCL",
                "LCL",
                "Popliteus",
                "ACL (but is less sensitive than the Lachman test)"
              ],
              "answer": "E",
              "explanation": "The anterior drawer test assesses the ACL by applying an anteriorly directed force to the proximal tibia with the knee flexed to 90° and the foot stabilised. Increased anterior translation compared to the contralateral side suggests ACL insufficiency. However, the anterior drawer test has a sensitivity of only ~60-70% for ACL rupture (false negatives common due to hamstring guarding, meniscal blocking, or effusion). The Lachman test (performed at 20-30° flexion) is MORE SENSITIVE (~85-95%) because: (1) the hamstrings are more relaxed at 20-30°, (2) there is less meniscal blocking, and (3) the iliotibial band is less of a secondary restraint. The pivot shift test is the most specific test for ACL deficiency (pathognomonic) but is difficult to perform in the conscious anxious patient.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 857,
              "stem": "The PCL is the primary restraint to posterior tibial translation. It is most commonly injured by which mechanism?",
              "options": [
                "Valgus force",
                "Varus force",
                "Hyperflexion with internal rotation",
                "Dashboard injury (direct posterior force to the proximal tibia with the knee flexed at 90°)",
                "Lateral blow to the knee"
              ],
              "answer": "D",
              "explanation": "The PCL is the strongest intra-articular knee ligament and the primary restraint to posterior tibial translation. The most common injury mechanism is a 'dashboard injury' — in an RTA, the knee impacts the dashboard with the knee flexed at 90°, applying a direct posterior force to the proximal tibia. Other mechanisms: fall onto a flexed knee (sporting), hyperflexion. The PCL is injured in up to 38% of knee injuries in MVAs. Isolated PCL injuries can often be managed non-operatively (aggressive quadriceps rehabilitation — strong quads provide an anterior pull on the tibia that counteracts the posterior sag). Combined PCL + posterolateral corner (PLC) injuries are unstable and usually require surgical reconstruction.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 858,
              "stem": "The commonest injury pattern in knee ligament injuries presenting to the Emergency Department is:",
              "options": [
                "Isolated PCL tear",
                "Isolated ACL tear",
                "Combined ACL + PCL + MCL + LCL",
                "Isolated MCL tear (most common knee ligament injury overall, but many don't present to ED)",
                "ACL tear combined with meniscal injury"
              ],
              "answer": "B",
              "explanation": "The isolated ACL tear is the most common ligament injury presenting to the Emergency Department. While isolated MCL tears are the most common knee ligament injury OVERALL, many are managed by GPs or self-resolve and don't necessarily present to ED. ACL tears, particularly those occurring during sport, typically present acutely with a haemarthrosis (a tense knee effusion within 2-4 hours of injury is an ACL tear until proven otherwise — ~70% of acute haemarthroses are ACL tears). Other causes of acute haemarthrosis: osteochondral fracture, peripheral meniscal tear, patellar dislocation. Examination: Lachman test (most sensitive), anterior drawer, pivot shift (most specific). MRI confirms diagnosis and assesses associated injuries.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Deformity",
          "range": "Q859",
          "questions": [
            {
              "number": 859,
              "stem": "Guided growth using a tension band plate (8-plate) for angular deformity correction in children works by:",
              "options": [
                "Compressing the physis equally on both sides",
                "Permanently fusing the growth plate",
                "Temporarily retarding growth on ONE side of the physis (the convex side) while allowing continued growth on the opposite side, gradually correcting the angular deformity",
                "Lengthening the bone",
                "Removing bone to correct the angle"
              ],
              "answer": "C",
              "explanation": "Guided growth (hemiepiphysiodesis) using a tension band plate (8-plate, Stevens technique) is a minimally invasive method for correcting angular limb deformities in growing children. The plate is placed on the CONVEX side of the deformity across the physis (e.g., lateral side for genu valgum, medial side for genu varum). It temporarily TETHERS growth on that side while the opposite side continues growing normally → gradual angular correction. When the deformity is corrected (monitored with serial standing radiographs), the plate is REMOVED → normal growth resumes symmetrically. Advantages: minimally invasive (small incision, 2 screws), reversible, lower complication rate than osteotomy, avoids cast. Timing: must have sufficient growth remaining (Risser 0-1 or open triradiate cartilage). Not effective after growth plate closure.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "TKA",
          "range": "Q860-Q864",
          "questions": [
            {
              "number": 860,
              "stem": "The most important factor determining long-term TKA survival (implant longevity) is:",
              "options": [
                "Correct mechanical alignment and balanced soft tissues (the combination of accurate component positioning and well-balanced flexion/extension gaps)",
                "Patient age",
                "Implant brand exclusively",
                "Tourniquet use",
                "Type of anaesthesia"
              ],
              "answer": "A",
              "explanation": "Long-term TKA survival depends primarily on: (1) CORRECT ALIGNMENT — mechanical axis restored to within ±3° of neutral (though kinematic alignment is an emerging alternative philosophy), appropriate rotation of both femoral and tibial components, correct joint line restoration. (2) BALANCED SOFT TISSUES — equal and symmetric flexion and extension gaps (rectangular gaps, not trapezoidal), appropriate soft tissue releases for deformity correction, and balanced medial-lateral ligament tension. Malalignment → abnormal loading → accelerated PE wear → osteolysis → loosening. Imbalance → instability → pain → early revision. Patient factors (BMI, activity level, age) and implant factors (design, bearing surface, fixation method) also contribute, but the surgeon's ability to achieve correct alignment and balance is the single most important modifiable factor. This is why navigation and robotics are being developed — to improve alignment accuracy.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 861,
              "stem": "The medial parapatellar arthrotomy is the most commonly used approach for TKA. Which structure is at risk if the retinacular incision extends too far distally?",
              "options": [
                "Patellar tendon",
                "Medial collateral ligament",
                "Infrapatellar branch of the saphenous nerve",
                "Common peroneal nerve",
                "Popliteal artery"
              ],
              "answer": "A",
              "explanation": "During a medial parapatellar arthrotomy, the incision curves around the medial border of the patellar tendon and extends distally along the medial tibial border. If the tibial periosteal dissection extends too far distally or laterally, the superficial MCL insertion (on the medial tibia, approximately 6cm below the joint line) can be damaged. The patellar tendon is at risk of avulsion if the tibial insertion is compromised. The infrapatellar branch of the saphenous nerve is routinely divided, causing lateral knee numbness.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 862,
              "stem": "Valgus deformity in TKA is more technically challenging than varus because:",
              "options": [
                "The bone is always softer",
                "The patella is always dislocated",
                "The lateral collateral ligament is typically contracted and must be selectively released",
                "The PCL is always intact",
                "The tibial plateau is always fractured"
              ],
              "answer": "C",
              "explanation": "Valgus knee deformity is more challenging because: (1) the lateral structures (LCL, popliteus, ITB, posterolateral capsule) are typically contracted and need selective release, (2) the medial structures are stretched/attenuated (MCL may be deficient), (3) the lateral femoral condyle is often hypoplastic, (4) external rotation of the tibia may be present, and (5) the peroneal nerve is at higher risk during correction (tethered laterally). The sequence of lateral release is debated but generally follows: ITB (pie-crusting or release from Gerdy tubercle) → posterolateral capsule → popliteus → LCL. The MCL must be protected. More constrained implants (CCK) may be needed if the MCL is incompetent.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 863,
              "stem": "The most important determinant of patient satisfaction after TKA is:",
              "options": [
                "Radiographic alignment",
                "Implant brand",
                "Length of hospital stay",
                "Type of anaesthesia",
                "Meeting pre-operative expectations (patients with realistic expectations report higher satisfaction)"
              ],
              "answer": "E",
              "explanation": "Patient expectations are the strongest predictor of satisfaction after TKA. Studies consistently show that patients whose pre-operative expectations are met (or exceeded) report significantly higher satisfaction scores, regardless of the objective clinical outcome. Approximately 80-85% of TKA patients report high satisfaction, but ~15-20% have some degree of residual dissatisfaction — often those with unrealistic expectations (expecting complete pain relief, return to high-impact sport, or unlimited function). Pre-operative counselling should address: expected pain trajectory (may take 6-12 months for full recovery), likely functional outcome (improved but not normal), realistic activity modifications, and potential complications. The surgeon's role in expectation management is critical — it is arguably more important than implant selection or surgical technique for determining satisfaction.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 864,
              "stem": "In total knee arthroplasty, the most common cause of persistent unexplained pain in the absence of identifiable pathology is:",
              "options": [
                "Aseptic loosening",
                "Infection (must always be excluded first)",
                "Component malpositioning",
                "Unknown/idiopathic (no identifiable cause in up to 20% of painful TKAs)",
                "Referred pain from the hip"
              ],
              "answer": "B",
              "explanation": "Infection must ALWAYS be excluded first in a painful TKA — it is the most important diagnosis not to miss because it changes management entirely (revision rather than observation). Even when initial bloods and aspirate appear normal, subclinical infection can be present. Approximately 1 in 300 painful TKAs has unexplained pain with no identifiable cause despite thorough investigation. However, the examiner expects you to emphasise that infection must be excluded before labelling pain as idiopathic. Investigation: ESR, CRP, aspiration (WCC, PMN%, culture, alpha-defensin), CT rotation study, bone scan.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "FAI",
          "range": "Q865",
          "questions": [
            {
              "number": 865,
              "stem": "Cam-type femoroacetabular impingement (FAI) is caused by an abnormality of which structure?",
              "options": [
                "Acetabular rim (over-coverage)",
                "Labrum only",
                "Ligamentum teres",
                "Femoral head-neck junction (aspherical bump)",
                "Capsular thickening"
              ],
              "answer": "D",
              "explanation": "Cam-type FAI is caused by an aspherical femoral head-neck junction (a bony bump on the anterolateral head-neck junction). During flexion and internal rotation, this bump engages the acetabular rim, causing shear damage to the labrum and articular cartilage (cartilage damage starts at the chondrolabral junction). Pincer-type FAI is caused by acetabular over-coverage (focal — e.g., acetabular retroversion, or global — e.g., coxa profunda). Combined cam + pincer is the most common pattern.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Knee OA",
          "range": "Q866-Q867",
          "questions": [
            {
              "number": 866,
              "stem": "The most commonly affected compartment in primary knee osteoarthritis is:",
              "options": [
                "Lateral compartment",
                "Patellofemoral compartment",
                "Medial compartment",
                "All three equally",
                "Posterior compartment"
              ],
              "answer": "C",
              "explanation": "The medial compartment is the most commonly affected in primary (idiopathic) knee OA. This is because the medial compartment bears approximately 60–70% of the knee load during gait (the mechanical axis normally passes slightly medial to the knee centre). Progressive medial cartilage loss leads to varus deformity. The lateral compartment is more commonly affected in post-traumatic OA or lateral meniscectomy.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 867,
              "stem": "A high tibial osteotomy (HTO) for medial compartment knee OA is most suitable for:",
              "options": [
                "A young active patient with isolated medial compartment OA, a correctable varus deformity, and good range of motion",
                "An elderly sedentary patient with tricompartmental OA",
                "Any patient with knee OA regardless of alignment",
                "A patient with ligament deficiency and bone loss",
                "A patient with patellofemoral OA only"
              ],
              "answer": "A",
              "explanation": "HTO (typically medial opening wedge) is indicated for young, active patients with isolated medial compartment OA and a varus malalignment. Ideal candidate: age <60 (relative), BMI <30, isolated medial compartment disease (intact lateral compartment and patellofemoral joint), correctable varus deformity, flexion >90° with <10° flexion contracture, non-smoker, and willing to comply with protected weight-bearing. The osteotomy corrects the mechanical axis from varus to slight valgus (Fujisawa point: weight-bearing line passes through 62% of the tibial width from medial → slight overcorrection into the lateral compartment). This unloads the damaged medial compartment and delays the need for TKA by 10-15 years.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "ACL Reconstruction",
          "range": "Q868",
          "questions": [
            {
              "number": 868,
              "stem": "The most commonly used autograft for ACL reconstruction is:",
              "options": [
                "Achilles tendon",
                "Patellar tendon (bone-patellar tendon-bone, BPTB)",
                "Quadriceps tendon",
                "Hamstring tendons (semitendinosus ± gracilis)",
                "Peroneus longus tendon"
              ],
              "answer": "D",
              "explanation": "Hamstring tendons (semitendinosus ± gracilis) are the most commonly used autograft for ACL reconstruction globally. BPTB autograft is also widely used and considered by many to be the gold standard for high-demand athletes (stronger initial fixation with bone-to-bone healing, faster return to sport, but higher anterior knee pain and kneeling pain). Quadriceps tendon autograft is increasingly popular. Allografts are used in revision or multi-ligament reconstruction.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Meniscal Injury",
          "range": "Q869",
          "questions": [
            {
              "number": 869,
              "stem": "A discoid lateral meniscus is a congenital variant that is most commonly classified using which system?",
              "options": [
                "Outerbridge classification",
                "Watanabe classification",
                "Palmer classification",
                "Sanders classification",
                "Schatzker classification"
              ],
              "answer": "B",
              "explanation": "The Watanabe classification divides discoid lateral menisci into three types: Type I (complete — covers the entire lateral tibial plateau), Type II (incomplete — covers most but not all of the plateau), and Type III (Wrisberg variant — lacks posterior capsular attachment, making it unstable and prone to snapping). Type III presents with a 'snapping knee' in childhood. Treatment depends on symptoms: asymptomatic = observe; symptomatic = arthroscopic saucerisation (partial excision to reshape the meniscus) ± repair.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "THA Approach",
          "range": "Q870-Q871",
          "questions": [
            {
              "number": 870,
              "stem": "The direct anterior approach (DAA) to the hip uses which intermuscular interval?",
              "options": [
                "Gluteus medius and piriformis",
                "Gluteus medius and gluteus maximus",
                "Vastus lateralis and gluteus medius",
                "Adductor longus and pectineus",
                "Sartorius/rectus femoris and tensor fasciae latae (TFL)"
              ],
              "answer": "E",
              "explanation": "The DAA (Hueter interval/Smith-Petersen approach) uses the intermuscular plane between sartorius/rectus femoris (femoral nerve) and tensor fasciae latae (superior gluteal nerve). This is a truly internervous plane. It is a muscle-sparing approach — no muscles are detached from bone. Advantages: lower dislocation rate, faster early recovery. Disadvantages: steep learning curve, risk to lateral femoral cutaneous nerve (LFCN), wound complications in obese patients, challenging femoral exposure.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 871,
              "stem": "In the posterior approach to the hip, which muscles are divided?",
              "options": [
                "Piriformis and short external rotators",
                "Gluteus medius and minimus",
                "Tensor fasciae latae and sartorius",
                "Quadratus femoris only",
                "No muscles are divided"
              ],
              "answer": "A",
              "explanation": "The posterior (Moore/Southern) approach divides piriformis, obturator internus, gemelli (short external rotators), and the posterior capsule. The sciatic nerve lies posterior to the short external rotators and must be protected. The gluteus maximus is split in line with its fibres (not divided). Repair of the posterior capsule and short external rotators reduces dislocation rate from ~4-5% to ~1%. The posterior approach provides excellent acetabular and femoral exposure.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "THA",
          "range": "Q872-Q882",
          "questions": [
            {
              "number": 872,
              "stem": "Ceramic head fracture in THA — if a ceramic head fractures, revision MUST NOT use:",
              "options": [
                "Another ceramic head",
                "A ceramic head on a new trunnion",
                "A polyethylene liner",
                "A constrained liner",
                "A metal (CoCr) head (retained ceramic fragments would cause catastrophic third-body wear against a metal head)"
              ],
              "answer": "E",
              "explanation": "After ceramic head fracture, ALL ceramic debris must be removed from the joint (meticulous washout — ceramic particles are extremely hard and abrasive). The revision MUST use another CERAMIC head — NEVER a metal (CoCr) head. If a metal head were used, any retained microscopic ceramic fragments would cause catastrophic third-body wear against the metal surface, leading to rapid failure and massive metallosis. The trunnion should also be replaced if damaged (adapter sleeve or stem revision). Ceramic-on-PE or ceramic-on-ceramic articulation is acceptable for revision after ceramic fracture. This is a frequently tested exam point: 'after ceramic fracture → ceramic head only, NEVER metal'.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 873,
              "stem": "Leg length discrepancy following THA is most commonly caused by:",
              "options": [
                "Incorrect femoral head size",
                "Incorrect acetabular cup version",
                "Altered femoral offset and/or neck length of the femoral component",
                "Wear of the bearing surface",
                "Heterotopic ossification"
              ],
              "answer": "C",
              "explanation": "LLD after THA is most commonly caused by inaccurate restoration of femoral offset and neck length (component-related factors). Over-lengthening is usually from using a longer neck length or placing the cup too high/medially. Pre-operative templating, intraoperative assessment (shuck test, drop kick test, leg length measurement), and image guidance help minimise LLD. A discrepancy of <1 cm is generally well tolerated. LLD is the most common reason for litigation after THA in the UK.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 874,
              "stem": "Third-generation cementing technique for THA includes all EXCEPT:",
              "options": [
                "Pulsed lavage of the femoral canal",
                "Use of a cement restrictor",
                "Retrograde cement injection with a cement gun",
                "Finger packing of cement without canal preparation",
                "Pressurisation of cement"
              ],
              "answer": "D",
              "explanation": "Third-generation cementing: (1) pulsed lavage and brush cleaning of the canal (remove marrow/debris), (2) drying of the canal, (3) cement restrictor at the appropriate level, (4) retrograde injection of vacuum-mixed cement using a cement gun, (5) sustained pressurisation of cement, (6) centraliser on the stem. This produces a uniform cement mantle (Barrack Grade A = complete 'white-out' with no radiolucencies). Finger packing without preparation is a 1st-generation technique with much poorer outcomes.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 875,
              "stem": "The most common complication of total hip arthroplasty overall is:",
              "options": [
                "DVT/PE",
                "Dislocation",
                "Leg length discrepancy",
                "Periprosthetic fracture",
                "Infection"
              ],
              "answer": "B",
              "explanation": "Thromboembolic disease (DVT/PE) is the most common complication of THA overall when considering all complications including subclinical DVT. Without prophylaxis, DVT rates approach 40-60% and PE rates 1-3%. With modern prophylaxis (LMWH/DOAC + mechanical + early mobilisation), clinical DVT rates are 1-2% and fatal PE <0.1%. Among surgical complications specifically, dislocation (2-5% without precautions) and leg length discrepancy are the most common. Dislocation is the most common reason for early revision. Infection occurs in 0.5-2% of primary THA.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 876,
              "stem": "Combined anteversion (sum of cup anteversion + stem anteversion) in THA should ideally be in the range of:",
              "options": [
                "0-10°",
                "10-20°",
                "60-80°",
                "25-50°",
                "90-100°"
              ],
              "answer": "D",
              "explanation": "Combined anteversion (cup + stem) of 25-50° is the target range for minimising dislocation risk. The concept recognises that cup and stem positions are interdependent — excessive anteversion of one can be compensated by reduced anteversion of the other. If the cup is at 15° anteversion and the stem at 15° anteversion, combined = 30° (within range). This concept supplements the Lewinnek safe zone (which only addresses cup position). Ranawat's combined anteversion formula: cup anteversion + stem anteversion = 25-50° (target ~35°). Some surgeons use stem-first technique, adjusting cup position to achieve optimal combined anteversion.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 877,
              "stem": "Spinopelvic alignment is increasingly recognised as important in THA planning. A patient with a stiff (fused or ankylosed) lumbar spine has increased dislocation risk because:",
              "options": [
                "Their pelvis cannot tilt to accommodate posture changes (sitting/standing), so the functional cup position changes less → the hip relies entirely on the cup position for stability in all postures",
                "They have better hip mobility than normal",
                "Spine stiffness protects the hip",
                "There is no relationship between spine and hip",
                "They always have posterior dislocation only"
              ],
              "answer": "A",
              "explanation": "In a normal spine-hip relationship, the pelvis tilts (anteverts in standing, retroverts in sitting) to accommodate postural changes — this effectively changes the functional orientation of the acetabular cup between positions. A patient with a stiff/fused lumbar spine CANNOT tilt their pelvis → the cup position is FIXED regardless of posture. If the cup is positioned for an average pelvis tilt, it may be in a 'safe zone' for standing but functionally retroverted in sitting (risk of posterior dislocation) or vice versa. These patients need patient-specific cup positioning based on pre-operative lateral sitting and standing radiographs (assess pelvic tilt change). The Lewinnek safe zone alone is INSUFFICIENT for these patients — spinopelvic analysis is required.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            },
            {
              "number": 878,
              "stem": "Cement-in-cement revision of the femoral stem is a technique used when:",
              "options": [
                "All revision procedures",
                "The existing cement mantle is intact, well-fixed to bone (Barrack A or B), and the reason for revision is NOT stem loosening — new cement and a new stem can be placed within the retained old cement mantle",
                "The cement mantle is completely disrupted",
                "Only in primary THA",
                "The patient has a metal allergy"
              ],
              "answer": "B",
              "explanation": "Cement-in-cement revision is a bone-conserving technique used when the existing femoral cement mantle is well-fixed to the bone (Barrack Grade A or B — no or minimal radiolucent lines) but the stem needs to be changed for reasons other than loosening (e.g., recurrent dislocation requiring a different head-neck geometry, stem fracture with intact mantle, conversion from hemiarthroplasty to THA). The old stem is removed from within the intact cement mantle (by splitting/extracting), the canal within the old cement is prepared, and a new polished tapered stem is cemented within the retained old mantle using fresh cement. Advantages: preserves femoral bone stock (no need to remove well-fixed cement — which risks cortical perforation, fracture, and bone loss), shorter operation, less blood loss. Requirements: old mantle must be intact and well-fixed.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 879,
              "stem": "The most important factor in preventing dislocation after THA is:",
              "options": [
                "Patient compliance with hip precautions",
                "Using the largest possible head size",
                "Correct component positioning (cup inclination and anteversion within safe zones)",
                "Choice of bearing surface",
                "Patient BMI"
              ],
              "answer": "C",
              "explanation": "Correct component positioning is the most important modifiable surgical factor in preventing dislocation. The Lewinnek safe zone (cup inclination 40° ± 10°, anteversion 15° ± 10°) and combined anteversion concept (25-50°) guide positioning. Components positioned outside these zones have significantly higher dislocation rates. Larger head sizes (36mm vs 28mm) reduce dislocation risk by increasing the jump distance and ROM before impingement — but they don't compensate for malpositioning. Patient factors (cognitive impairment, non-compliance, neuromuscular disease) contribute but are less modifiable. Posterior approach has higher dislocation rate if posterior capsule/rotators are not repaired.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 880,
              "stem": "Bone cement in THA undergoes an exothermic polymerisation reaction. The peak temperature reached at the cement-bone interface is approximately:",
              "options": [
                "37°C (body temperature)",
                "50°C",
                "120°C",
                "200°C",
                "70-80°C (risk of thermal necrosis above 56°C at the bone-cement interface)"
              ],
              "answer": "E",
              "explanation": "During PMMA polymerisation, the exothermic reaction generates temperatures of 70-80°C within the cement mass. At the cement-bone interface, the temperature is lower (due to heat dissipation into bone and blood flow) but can still exceed 56°C — the threshold for thermal necrosis of osteocytes and bone proteins. This thermal necrosis creates a zone of dead bone at the interface. Modern cementing techniques (pulse lavage, thin cement mantle, pressurisation) and newer cement formulations aim to minimise peak temperatures. The exothermic reaction also contributes to monomer toxicity (MMA vapour released during mixing — need ventilation in theatre) and can contribute to BCIS when combined with pressurisation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 881,
              "stem": "Ceramic-on-ceramic bearing surfaces in THA have the lowest wear rate but carry the specific risk of:",
              "options": [
                "Metal ion release",
                "Polyethylene osteolysis",
                "No specific risks",
                "Catastrophic ceramic fracture (requiring urgent revision) and audible squeaking",
                "Cement reaction"
              ],
              "answer": "D",
              "explanation": "Ceramic-on-ceramic (CoC) bearings produce the lowest volumetric wear of any bearing combination (<0.1mm³/year vs ~40mm³/year for conventional MoP). They are bioinert (no metal ions, no PE particles) and have excellent wettability. However, specific risks include: (1) Ceramic fracture — catastrophic fracture of the femoral head or liner (~0.01-0.02%), requiring urgent revision with complete joint washout and removal of all ceramic fragments (ceramic debris is extremely abrasive — all fragments must be removed). A ceramic-on-metal articulation must NOT be used after ceramic fracture (third-body wear from retained ceramic particles would be catastrophic). (2) Audible squeaking (1-10%) — caused by stripe wear, microseparation, or edge loading. Usually benign but can be socially bothersome. (3) Liner chipping during insertion if not perfectly seated.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 882,
              "stem": "The concept of femoral offset in THA is important because restoring or increasing offset:",
              "options": [
                "Has no effect on hip biomechanics",
                "Only affects cosmetic appearance",
                "Increases wear rate",
                "Causes nerve injury in all cases",
                "Increases the abductor lever arm, reduces the JRF, improves stability, and restores soft tissue tension"
              ],
              "answer": "E",
              "explanation": "Femoral offset is the perpendicular distance from the centre of the femoral head to the long axis of the femur. Restoring or slightly increasing offset: (1) increases the abductor (gluteus medius) lever arm → reduces the force required by the abductors to stabilise the pelvis → reduces joint reaction force (JRF) → reduces wear. (2) Increases soft tissue tension → improves stability (reduces dislocation risk). (3) Avoids impingement (greater offset moves the GT laterally, preventing impingement against the pelvis). (4) Helps restore leg length. High-offset stems and lateralised cups are available to optimise offset. Insufficient offset → Trendelenburg gait, impingement, instability, increased JRF and wear. Excessive offset → increased bending moment on the stem (fatigue risk), lateral thigh pain.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            }
          ]
        },
        {
          "title": "ACL",
          "range": "Q883",
          "questions": [
            {
              "number": 883,
              "stem": "The ACL is the primary restraint to anterior tibial translation. At what degree of knee flexion is the Lachman test performed?",
              "options": [
                "0° (full extension)",
                "45° flexion",
                "20-30° flexion",
                "90° flexion",
                "Full flexion"
              ],
              "answer": "C",
              "explanation": "The Lachman test is performed at 20-30° of knee flexion. At this angle, the secondary restraints (menisci, collateral ligaments, posterior capsule) are most relaxed, isolating the ACL as the primary restraint to anterior tibial translation. This makes Lachman the most sensitive clinical test for ACL rupture (85-95% sensitivity). The anterior drawer test at 90° is less sensitive because the hamstrings act as secondary restraints and the posterior horn of the medial meniscus provides a block.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "PCL",
          "range": "Q884",
          "questions": [
            {
              "number": 884,
              "stem": "The posterior drawer test is positive in PCL injury. The test is performed with the knee at:",
              "options": [
                "20-30° flexion",
                "90° flexion",
                "45° flexion",
                "Full extension",
                "Full flexion"
              ],
              "answer": "B",
              "explanation": "The posterior drawer test is performed at 90° knee flexion with the foot flat on the bed. The examiner pushes the proximal tibia posteriorly. Excessive posterior translation indicates PCL injury. It is important to first assess the resting position — in PCL-deficient knees, the tibia sags posteriorly at 90° (posterior sag sign/gravity-assisted posterior drawer), which can mimic a positive anterior drawer (pseudo-Lachman). Always compare the tibial step-off with the contralateral knee.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Meniscus",
          "range": "Q885",
          "questions": [
            {
              "number": 885,
              "stem": "McMurray test is used to diagnose which knee pathology?",
              "options": [
                "Meniscal tear",
                "ACL tear",
                "PCL tear",
                "Patellofemoral syndrome",
                "Loose body"
              ],
              "answer": "A",
              "explanation": "McMurray test: patient supine, knee fully flexed. The examiner rotates the tibia (external rotation for medial meniscus, internal rotation for lateral) while extending the knee. A palpable click or pain along the joint line suggests a meniscal tear. Apley grind test is an alternative: patient prone, knee flexed 90°, axial compression + rotation = meniscus (positive if painful); axial distraction + rotation = ligament (positive if painful).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Hip Arthroplasty",
          "range": "Q886-Q895",
          "questions": [
            {
              "number": 886,
              "stem": "The Lewinnek safe zone for acetabular cup placement in THA describes an inclination angle of:",
              "options": [
                "15° ± 10° and anteversion 5° ± 5°",
                "30° ± 10° and anteversion 15° ± 10°",
                "50° ± 10° and anteversion 25° ± 10°",
                "40° ± 10° and anteversion 15° ± 10°",
                "45° and anteversion 20°"
              ],
              "answer": "D",
              "explanation": "The Lewinnek safe zone for acetabular cup placement is 40° ± 10° inclination (30°–50°) and 15° ± 10° anteversion (5°–25°). Placement within this zone is associated with a lower dislocation rate. However, it is now recognised that cup position alone does not guarantee stability — the combined anteversion of the cup and stem, soft tissue tension, and spinopelvic mobility also influence stability.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 887,
              "stem": "The Charnley low-friction arthroplasty concept was based on which key principle?",
              "options": [
                "Use of a large femoral head to maximise range of motion",
                "Use of metal-on-metal bearing surfaces",
                "Use of a small femoral head (22.25 mm) with a UHMWPE acetabular component to reduce frictional torque",
                "Use of uncemented press-fit components",
                "Use of ceramic bearings"
              ],
              "answer": "C",
              "explanation": "Sir John Charnley's low-friction arthroplasty (1962) used a small femoral head (22.25 mm) articulating with a thick UHMWPE acetabular cup, cemented with PMMA. The principle was that frictional torque at the bearing surface is proportional to the head radius — a smaller head generates less frictional torque, reducing the forces transmitted to the cement-bone interface and thereby reducing loosening. This concept revolutionised hip arthroplasty.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 888,
              "stem": "In cemented THA, the Barrack classification is used to grade the quality of the:",
              "options": [
                "Acetabular cup position",
                "Bearing surface wear",
                "Bone stock quality",
                "Surgical approach",
                "Femoral cement mantle"
              ],
              "answer": "E",
              "explanation": "The Barrack classification grades the quality of the femoral cement mantle on AP radiograph: Grade A = complete white-out (complete filling, no radiolucencies), Grade B = slight radiolucency at the cement-bone interface, Grade C = radiolucencies involving >50% of the cement-bone interface or defect in the cement mantle, Grade D = radiolucencies around the entire cement-bone interface or missing cement mantle. Grade A has the best long-term outcomes.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 889,
              "stem": "Gruen zones are used to describe the location of radiolucency or osteolysis around which component of a THA?",
              "options": [
                "Acetabular cup",
                "Femoral stem",
                "Patellar component",
                "Tibial tray",
                "Humeral stem"
              ],
              "answer": "B",
              "explanation": "Gruen described 7 zones around the femoral stem on AP radiograph (zones 1–7) and 7 on the lateral (zones 8–14). Zone 1 = lateral proximal (greater trochanter), Zone 7 = medial proximal (calcar). These zones are used to describe the pattern and location of radiolucencies, osteolysis, and bone remodelling. DeLee and Charnley zones (I–III) are used for the acetabular component.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 890,
              "stem": "The most common cause of long-term failure of cemented total hip arthroplasty is:",
              "options": [
                "Aseptic loosening",
                "Infection",
                "Dislocation",
                "Periprosthetic fracture",
                "Ceramic fracture"
              ],
              "answer": "A",
              "explanation": "Aseptic loosening is the most common cause of long-term failure and revision in cemented THA. It is primarily driven by the biological response to wear debris (particularly polyethylene particles), which activate macrophages → cytokine release → osteoclast activation (via RANKL) → periprosthetic osteolysis → progressive loosening. Improving wear characteristics (cross-linked PE, ceramic bearings) reduces this cascade.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 891,
              "stem": "The surgical approach most commonly associated with a higher risk of dislocation following primary THA is:",
              "options": [
                "Anterior (Smith-Petersen)",
                "Posterior (Moore/Southern)",
                "Anterolateral (Watson-Jones)",
                "Lateral (Hardinge)",
                "Direct anterior (Hueter)"
              ],
              "answer": "B",
              "explanation": "The posterior (Moore/Southern) approach is historically associated with the highest dislocation rate (2–5% without posterior soft tissue repair vs ~1% with other approaches). This is because it divides the posterior capsule and short external rotators, which are important posterior stabilisers. Meticulous capsular and short rotator repair significantly reduces dislocation risk. The anterior and anterolateral approaches have lower dislocation rates.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 892,
              "stem": "Which nerve is most at risk during the direct lateral (Hardinge) approach to the hip?",
              "options": [
                "Sciatic nerve",
                "Femoral nerve",
                "Superior gluteal nerve",
                "Obturator nerve",
                "Lateral cutaneous nerve of the thigh"
              ],
              "answer": "C",
              "explanation": "The direct lateral (Hardinge/transgluteal) approach splits gluteus medius and vastus lateralis, detaching the anterior portion of gluteus medius from the greater trochanter. The superior gluteal nerve enters gluteus medius approximately 5 cm above the tip of the greater trochanter. Excessive proximal dissection risks injuring this nerve, causing gluteus medius and minimus denervation and a Trendelenburg gait.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 893,
              "stem": "Uncemented femoral stems in THA achieve fixation by which mechanism?",
              "options": [
                "Chemical bonding to bone",
                "PMMA cement interdigitation",
                "Suture fixation to the periosteum",
                "Expansion of the stem after insertion",
                "Press-fit and biological bone ingrowth/ongrowth"
              ],
              "answer": "E",
              "explanation": "Uncemented stems achieve initial fixation by press-fit (interference fit into the prepared femoral canal) and long-term fixation by biological bone ingrowth (bone grows into porous surface) or ongrowth (bone grows onto the surface coating, e.g., hydroxyapatite or plasma-sprayed titanium). The pore size optimal for bone ingrowth is 50–300 μm. Micromotion must be <150 μm for bone ingrowth to occur; >150 μm leads to fibrous tissue formation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 894,
              "stem": "The Paprosky classification of femoral bone defects in revision THA Type IIIB is characterised by:",
              "options": [
                "Minimal bone loss with intact metaphysis",
                "Extensive metaphyseal damage with >4 cm of intact diaphyseal cortex",
                "Periprosthetic fracture only",
                "Extensive metaphyseal damage with <4 cm of intact diaphyseal cortex (non-supportive isthmus)",
                "Intact canal with cortical thinning"
              ],
              "answer": "D",
              "explanation": "Paprosky femoral classification: Type I = minimal bone loss, intact metaphyseal bone. Type II = extensive metaphyseal cancellous bone loss with intact diaphysis. Type IIIA = extensive metaphyseal loss but >4 cm of intact diaphyseal cortex (supportive isthmus — can use extensively coated stem). Type IIIB = <4 cm of intact diaphysis (non-supportive isthmus — needs modular tapered stem or proximal femoral replacement). Type IV = extensive loss of both metaphyseal and diaphyseal bone (proximal femoral replacement or allograft-prosthesis composite).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            },
            {
              "number": 895,
              "stem": "Cemented femoral stems are recommended over uncemented stems in elderly patients with hip fractures primarily because:",
              "options": [
                "They allow immediate full weight-bearing with lower periprosthetic fracture risk",
                "They are cheaper",
                "They have better long-term survival in all patients",
                "They are easier to insert",
                "They do not require antibiotic prophylaxis"
              ],
              "answer": "A",
              "explanation": "In elderly patients (particularly with osteoporotic bone), cemented stems provide immediate stable fixation without relying on bone ingrowth. This allows immediate full weight-bearing with a lower risk of intraoperative and early postoperative periprosthetic fracture compared to press-fit uncemented stems. NICE guidelines recommend cemented stems for hip fracture patients. Bone cement implantation syndrome (BCIS) is a recognised risk but is minimised with modern technique.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Bearing Surfaces",
          "range": "Q896-Q902",
          "questions": [
            {
              "number": 896,
              "stem": "Which bearing couple in THA produces the lowest volumetric wear rate?",
              "options": [
                "Metal-on-conventional polyethylene",
                "Metal-on-cross-linked polyethylene",
                "Ceramic-on-ceramic",
                "Metal-on-metal",
                "Ceramic-on-cross-linked polyethylene"
              ],
              "answer": "C",
              "explanation": "Ceramic-on-ceramic (CoC) bearings produce the lowest volumetric wear rate of all bearing combinations. The wear particles are biologically inert (alumina). This dramatically reduces osteolysis risk. Disadvantages include risk of ceramic fracture (rare with modern delta ceramics), squeaking (1–10%), limited revision options, and higher cost. Ceramic-on-XLPE is an increasingly popular alternative with very low wear and no fracture risk.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 897,
              "stem": "Metal-on-metal hip arthroplasty has been largely abandoned due to the risk of adverse reactions to metal debris (ARMD). Which metal ions are primarily responsible?",
              "options": [
                "Titanium and aluminium",
                "Cobalt and chromium",
                "Iron and nickel",
                "Molybdenum and vanadium",
                "Stainless steel components"
              ],
              "answer": "B",
              "explanation": "MoM bearings produce cobalt and chromium ions from wear at the bearing surface and, in modular components, from corrosion at the taper junction (trunnionosis). These metal ions cause a spectrum of adverse reactions (ARMD) including pseudotumour (inflammatory mass), ALVAL (aseptic lymphocyte-dominated vasculitis-associated lesion), metallosis, soft tissue necrosis, and osteolysis. Monitoring with serum cobalt/chromium levels and MARS-MRI is recommended for patients with MoM implants.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 898,
              "stem": "Cross-linked polyethylene was developed to reduce wear in THA. How is cross-linking achieved?",
              "options": [
                "Adding ceramic particles",
                "Mixing with bone cement",
                "Heating to melting point only",
                "Chemical cross-linking with formaldehyde",
                "High-dose gamma irradiation"
              ],
              "answer": "E",
              "explanation": "Cross-linked polyethylene (XLPE/HXLPE) is produced by exposing conventional UHMWPE to high-dose gamma or electron beam irradiation (50–100 kGy). This creates cross-links between polymer chains, dramatically reducing adhesive/abrasive wear (60–90% reduction). Post-irradiation thermal treatment (remelting or annealing) eliminates free radicals that would cause oxidative degradation. Vitamin E can also be added as an antioxidant.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 899,
              "stem": "The main disadvantage of ceramic bearing surfaces compared to polyethylene is:",
              "options": [
                "Risk of catastrophic fracture",
                "Higher wear rate",
                "Higher cost of polyethylene",
                "Increased dislocation risk",
                "Greater stress shielding"
              ],
              "answer": "A",
              "explanation": "Ceramic materials are inherently brittle with low fracture toughness, meaning they can fracture catastrophically without plastic deformation warning. Although modern 4th-generation alumina matrix composites (BIOLOX delta) have significantly reduced fracture risk (<0.01%), it remains a concern. Other disadvantages include squeaking (1–10%), revision complexity (ceramic debris in tissues), and the need to avoid malpositioning (edge loading increases risk).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            },
            {
              "number": 900,
              "stem": "In a metal-on-polyethylene THA, the biological response to polyethylene wear particles is primarily mediated by which cell?",
              "options": [
                "Osteoblasts",
                "Osteocytes",
                "T-lymphocytes",
                "Macrophages",
                "Neutrophils"
              ],
              "answer": "D",
              "explanation": "Submicron polyethylene particles (<10 μm, most biologically active at 0.2–0.8 μm) are phagocytosed by macrophages. Activated macrophages release pro-inflammatory cytokines (TNF-α, IL-1β, IL-6, PGE₂) which stimulate osteoclast differentiation and activation via the RANK/RANKL pathway. This macrophage-mediated osteolytic cascade leads to progressive periprosthetic bone loss and ultimately aseptic loosening.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 901,
              "stem": "Increasing the femoral head size in THA from 28 mm to 36 mm has which primary biomechanical advantage?",
              "options": [
                "Reduced frictional torque",
                "Lower dislocation rate due to increased jump distance",
                "Increased range of motion before impingement",
                "Reduced volumetric wear",
                "All of the above"
              ],
              "answer": "B",
              "explanation": "A larger femoral head increases the 'jump distance' (the distance the head must travel before it escapes the cup), which directly reduces dislocation risk. It also increases the head-neck ratio, allowing greater range of motion before neck-liner impingement. However, larger heads increase frictional torque and volumetric wear (though linear wear may be similar or reduced). The net benefit is significantly reduced dislocation rate.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 902,
              "stem": "The most commonly used bearing combination in primary THA in the UK (per NJR) is:",
              "options": [
                "Metal-on-metal",
                "Ceramic-on-ceramic",
                "Metal-on-highly cross-linked polyethylene (MoXLPE)",
                "Ceramic-on-highly cross-linked polyethylene (CoXLPE)",
                "Metal-on-conventional polyethylene"
              ],
              "answer": "D",
              "explanation": "Ceramic-on-highly cross-linked polyethylene (CoXLPE) has become the most commonly used bearing combination for primary THA in the UK (NJR data). It combines the advantages of: (1) ceramic head (harder, smoother, lower friction, bioinert, no metal ion release) and (2) highly cross-linked PE (dramatically reduced wear rate compared to conventional PE — irradiation cross-links the long-chain molecules). Metal-on-metal (MoM) has been largely abandoned due to adverse reactions to metal debris (ARMD). Ceramic-on-ceramic has excellent wear properties but risk of squeaking and catastrophic ceramic fracture. Metal-on-conventional PE is being replaced by cross-linked PE.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "THA Complications",
          "range": "Q903-Q906",
          "questions": [
            {
              "number": 903,
              "stem": "The most common direction of dislocation following primary THA performed via a posterior approach is:",
              "options": [
                "Anterior",
                "Superior",
                "Posterior",
                "Inferior",
                "Central (protrusio)"
              ],
              "answer": "C",
              "explanation": "Posterior dislocation is the most common direction following a posterior approach, as the posterior capsule and short external rotators have been divided. The at-risk position is flexion, adduction, and internal rotation. Following an anterior approach, anterior dislocation is more common (extension, external rotation, adduction). Overall, posterior dislocation accounts for ~70% of all THA dislocations.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 904,
              "stem": "Bone cement implantation syndrome (BCIS) during cemented THA is characterised by:",
              "options": [
                "Fever and local wound infection",
                "Delayed wound healing",
                "Fat embolism syndrome occurring days later",
                "Allergic reaction to metal implant",
                "Hypoxia, hypotension, and loss of consciousness occurring during cement/prosthesis insertion"
              ],
              "answer": "E",
              "explanation": "BCIS is a clinical syndrome characterised by hypoxia, hypotension, altered consciousness, and potentially cardiac arrest occurring during or shortly after cementation and pressurisation/stem insertion. It is caused by embolisation of fat, marrow, cement monomer, and air into the venous system and pulmonary vasculature. Risk factors include: cemented femoral component, pre-existing cardiopulmonary disease, and pathological fractures. Prevention: good lavage, venting the canal, and anaesthetic vigilance.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 905,
              "stem": "A patient presents with a painful THA 18 months after surgery. ESR and CRP are elevated. Joint aspiration yields turbid fluid with a white cell count of 12,000/μL. The most likely diagnosis is:",
              "options": [
                "Periprosthetic joint infection",
                "Aseptic loosening",
                "Crystal arthropathy",
                "Metallosis",
                "Normal post-operative finding"
              ],
              "answer": "A",
              "explanation": "Elevated inflammatory markers (ESR/CRP) combined with a joint aspirate showing elevated WCC (>3,000/μL for hip) with turbid fluid strongly suggests periprosthetic joint infection (PJI). The MSIS/ICM criteria for PJI include: major criteria (sinus tract communicating with prosthesis, or 2 positive cultures of the same organism) and minor criteria (elevated ESR/CRP, elevated synovial WCC, elevated synovial PMN%, positive alpha-defensin, single positive culture).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 906,
              "stem": "In the management of chronic periprosthetic joint infection (>4 weeks or sinus tract present), the gold standard treatment is:",
              "options": [
                "Single-stage revision",
                "Long-term suppressive antibiotics only",
                "Arthroscopic washout",
                "DAIR (debridement, antibiotics, and implant retention)",
                "Two-stage revision with antibiotic cement spacer"
              ],
              "answer": "E",
              "explanation": "Two-stage revision is considered the gold standard for chronic PJI. Stage 1: removal of all implants and cement, thorough debridement, insertion of an antibiotic-impregnated cement spacer, and 6 weeks of targeted IV antibiotics. Stage 2: reimplantation of new prosthesis after a 2-week antibiotic holiday and negative inflammatory markers/cultures. Success rates: 85–95%. DAIR is reserved for acute PJI (<4 weeks, well-fixed implant, known susceptible organism). Single-stage is gaining evidence but not yet the universal standard for chronic PJI.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            }
          ]
        },
        {
          "title": "Knee Arthroplasty",
          "range": "Q907-Q914",
          "questions": [
            {
              "number": 907,
              "stem": "The mechanical axis of the lower limb runs from the centre of the femoral head to:",
              "options": [
                "The centre of the ankle joint",
                "The tibial tubercle",
                "The centre of the knee",
                "The lateral malleolus",
                "The first metatarsal head"
              ],
              "answer": "A",
              "explanation": "The mechanical axis of the lower limb is a straight line from the centre of the femoral head to the centre of the ankle joint. In a normally aligned limb, this line passes through or just medial to the centre of the knee joint. In TKA, the goal is to restore the mechanical axis so that it passes through the centre of the knee. The anatomical axis of the femur has approximately 5–7° of valgus relative to the mechanical axis.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 908,
              "stem": "In TKA, the femoral component is typically placed in how many degrees of external rotation relative to the posterior condylar axis to create a balanced flexion gap?",
              "options": [
                "0° (neutral)",
                "5° external rotation",
                "10° external rotation",
                "3° external rotation",
                "3° internal rotation"
              ],
              "answer": "D",
              "explanation": "The femoral component is typically externally rotated approximately 3° relative to the posterior condylar axis (PCA). This aligns the component roughly parallel to the transepicondylar axis (TEA) and perpendicular to Whiteside's line (AP axis of the trochlea). This external rotation creates a balanced rectangular flexion gap and optimises patellar tracking by avoiding internal rotation of the femoral component.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 909,
              "stem": "The most common complication following TKA that affects patient satisfaction is:",
              "options": [
                "Infection",
                "Anterior knee pain / patellofemoral problems",
                "Aseptic loosening",
                "Periprosthetic fracture",
                "DVT"
              ],
              "answer": "B",
              "explanation": "Anterior knee pain and patellofemoral problems (maltracking, patellar clunk, patellar instability) are the most common complications affecting patient satisfaction after TKA. They may relate to component malrotation (particularly internal rotation of the femoral or tibial component), lateral retinacular tightness, overstuffing the patellofemoral joint, or failure to resurface the patella in the presence of patellofemoral arthritis.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 910,
              "stem": "A unicompartmental knee arthroplasty (UKA) is contraindicated in the presence of:",
              "options": [
                "Isolated medial compartment osteoarthritis",
                "Full-thickness cartilage loss medially",
                "ACL deficiency",
                "Correctable varus deformity",
                "Body mass index of 30"
              ],
              "answer": "C",
              "explanation": "ACL deficiency is a contraindication for mobile-bearing UKA (e.g., Oxford UKA) because the ACL is essential for normal kinematics and bearing stability. Without a functioning ACL, the bearing may dislocate. Other contraindications include: inflammatory arthritis, lateral or patellofemoral compartment disease, fixed flexion deformity >15°, and fixed varus/valgus >15°. Obesity (BMI >30) is a relative but not absolute contraindication.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 911,
              "stem": "In TKA, the tibial component is typically aligned perpendicular to the:",
              "options": [
                "Anatomical axis of the tibia",
                "Transepicondylar axis",
                "Mechanical axis of the tibia",
                "Posterior condylar axis",
                "Whiteside's line"
              ],
              "answer": "C",
              "explanation": "The tibial cut in TKA is made perpendicular to the mechanical axis of the tibia (which is essentially the anatomical axis of the tibia, as they nearly coincide — unlike the femur). This is typically 0° varus/valgus relative to the tibial shaft on the coronal plane. A posterior slope of 3–7° is usually incorporated to facilitate flexion and match the native tibial slope.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 912,
              "stem": "Internal rotation of the tibial component in TKA leads to which clinical problem?",
              "options": [
                "Improved patellar tracking",
                "Lateral patellar subluxation and anterior knee pain",
                "Increased flexion range",
                "Excessive valgus alignment",
                "Improved collateral ligament balance"
              ],
              "answer": "B",
              "explanation": "Internal rotation of the tibial component shifts the tibial tubercle relatively laterally, increasing the effective Q-angle and causing lateral patellar tracking and subluxation. This is one of the most common causes of anterior knee pain after TKA. Combined internal rotation of both the femoral and tibial components has an additive effect and is particularly detrimental. CT rotation studies are used to assess malrotation in painful TKA.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            },
            {
              "number": 913,
              "stem": "The posterior cruciate ligament (PCL) is sacrificed in which type of TKA design?",
              "options": [
                "Cruciate-retaining (CR)",
                "Unicompartmental (UKA)",
                "Hinged (rotating)",
                "Patellofemoral arthroplasty",
                "Posterior-stabilised (PS)"
              ],
              "answer": "E",
              "explanation": "In a posterior-stabilised (PS) TKA, the PCL is sacrificed and a tibial post and femoral cam mechanism substitutes for its function, providing anteroposterior stability and facilitating femoral rollback in flexion. In a cruciate-retaining (CR) design, the PCL is preserved and assists rollback. PS designs may achieve slightly greater flexion but have a higher risk of post-cam impingement and polyethylene wear at the post.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 914,
              "stem": "The constraint hierarchy in knee arthroplasty from least to most constrained is:",
              "options": [
                "UKA → CR-TKA → PS-TKA → CCK/VVC → Hinged",
                "PS-TKA → CR-TKA → Hinged → UKA → CCK",
                "Hinged → PS-TKA → CR-TKA → UKA → CCK",
                "CR-TKA → UKA → CCK → Hinged → PS-TKA",
                "All TKA designs have equal constraint"
              ],
              "answer": "A",
              "explanation": "Constraint hierarchy (least to most): UKA (minimal constraint, retains all ligaments) → CR-TKA (retains PCL) → PS-TKA (sacrifices PCL, cam-post mechanism) → CCK/VVC (constrained condylar, varus-valgus constraint — for ligament deficiency/instability) → Rotating hinged (most constrained — for massive bone loss, ligament deficiency, tumour reconstruction). Using the minimum constraint necessary preserves bone stock and reduces loosening risk. Higher constraint → greater force transfer to implant-bone interface → higher loosening risk.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Knee Ligaments",
          "range": "Q915-Q920",
          "questions": [
            {
              "number": 915,
              "stem": "The anterior cruciate ligament (ACL) originates from the posterolateral aspect of the intercondylar notch and inserts into which area of the tibia?",
              "options": [
                "Posterior tibial plateau",
                "Lateral tibial eminence",
                "Medial tibial plateau",
                "Anterior intercondylar area",
                "Tibial tuberosity"
              ],
              "answer": "D",
              "explanation": "The ACL originates from the posterolateral aspect of the intercondylar notch of the femur (medial surface of the lateral femoral condyle) and inserts into the anterior intercondylar area of the tibia, just anterior and lateral to the anterior tibial spine. It has two functional bundles: anteromedial (tight in flexion) and posterolateral (tight in extension). The ACL is the primary restraint to anterior tibial translation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 916,
              "stem": "The most specific clinical test for ACL rupture is:",
              "options": [
                "Pivot shift test",
                "Anterior drawer test",
                "Lachman test",
                "McMurray test",
                "Valgus stress test"
              ],
              "answer": "A",
              "explanation": "The pivot shift test is the most specific test for ACL rupture (specificity ~98%) and best correlates with functional instability. It reproduces the giving-way phenomenon by demonstrating anterolateral rotatory subluxation of the tibia in extension followed by reduction in flexion. The Lachman test is the most sensitive test (~85–95%) for ACL rupture. The anterior drawer test has lower sensitivity and specificity.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 917,
              "stem": "The PCL is the primary restraint to:",
              "options": [
                "Anterior tibial translation",
                "Valgus angulation",
                "Varus angulation",
                "External rotation",
                "Posterior tibial translation"
              ],
              "answer": "E",
              "explanation": "The PCL is the primary restraint to posterior tibial translation (posterior drawer). It originates from the anterolateral surface of the medial femoral condyle (intercondylar notch) and inserts on the posterior tibial fossa. It has two bundles: anterolateral (larger, tight in flexion) and posteromedial (tight in extension). PCL injuries commonly result from a dashboard injury (direct posterior force on the proximal tibia with the knee flexed).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 918,
              "stem": "The menisci transmit approximately what percentage of load across the knee joint?",
              "options": [
                "10–20%",
                "50–70%",
                "30–40%",
                "80–90%",
                "100%"
              ],
              "answer": "B",
              "explanation": "The menisci transmit 50–70% of the load across the knee joint (up to 85–90% in flexion). They function as shock absorbers, stabilisers, and load distributors, converting axial compressive forces into circumferential hoop stresses. Total meniscectomy increases contact stress by 200–300% and is strongly associated with accelerated osteoarthritis. This is why meniscal preservation (repair over resection) is now the standard where possible.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 919,
              "stem": "A meniscal tear in the peripheral vascularised zone (red-red zone) is best managed by:",
              "options": [
                "Observation and physiotherapy",
                "Partial meniscectomy",
                "Total meniscectomy",
                "Meniscal repair",
                "Meniscal transplant"
              ],
              "answer": "D",
              "explanation": "Tears in the peripheral (red-red) zone have the best healing potential due to good blood supply. Meniscal repair is the treatment of choice in this zone, particularly in young active patients. The goal is always to preserve as much meniscal tissue as possible to maintain the load-distributing function and prevent accelerated OA. Inside-out suture repair is the gold standard, though all-inside devices are increasingly used.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 920,
              "stem": "The posterolateral corner (PLC) of the knee is primarily responsible for resisting which force?",
              "options": [
                "Anterior tibial translation",
                "Posterior tibial translation",
                "Varus angulation and external rotation",
                "Valgus angulation and internal rotation",
                "Flexion"
              ],
              "answer": "C",
              "explanation": "The posterolateral corner structures (including the lateral collateral ligament, popliteus tendon, popliteofibular ligament, and arcuate ligament complex) are the primary restraints to varus angulation and external rotation of the tibia. PLC injuries are frequently missed and are commonly associated with ACL or PCL injuries. Failure to address a PLC injury during cruciate reconstruction leads to graft failure.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "DDH",
          "range": "Q921-Q925",
          "questions": [
            {
              "number": 921,
              "stem": "The Ortolani test in a neonate with DDH detects:",
              "options": [
                "A dislocatable hip (hip comes out of joint)",
                "A reducible hip (dislocated hip reduces back into the acetabulum)",
                "Acetabular dysplasia",
                "Avascular necrosis",
                "Leg length discrepancy"
              ],
              "answer": "B",
              "explanation": "The Ortolani test is a test of reduction: a dislocated hip that can be reduced back into the acetabulum with gentle abduction and anterior pressure on the greater trochanter. It produces a palpable 'clunk' as the femoral head reduces. The Barlow test is the opposite — it tests for a dislocatable hip (the hip can be pushed out of the acetabulum with posterior pressure during adduction). Both tests become negative by 2–3 months as soft tissues tighten.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 922,
              "stem": "The Graf classification of infant hip ultrasound in DDH uses the alpha angle to assess acetabular morphology. A normal (Graf Type I) hip has an alpha angle of:",
              "options": [
                "<43°",
                "43°–49°",
                "50°–59°",
                "≥60°",
                "≥90°"
              ],
              "answer": "D",
              "explanation": "The Graf classification uses ultrasound to assess the bony (alpha angle) and cartilaginous (beta angle) acetabular coverage. Type I (normal): alpha ≥60°. Type IIa: alpha 50–59° (physiologically immature, <3 months — may normalise). Type IIb: alpha 50–59° (>3 months — needs treatment). Type III: alpha <43° (subluxated). Type IV: dislocated (femoral head completely displaced). Alpha angle is the angle between the bony roof (iliac line) and the acetabular roof line.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 923,
              "stem": "A Pavlik harness is the first-line treatment for DDH in infants up to approximately what age?",
              "options": [
                "6 months",
                "1 month",
                "3 months",
                "12 months",
                "18 months"
              ],
              "answer": "A",
              "explanation": "The Pavlik harness is the first-line treatment for DDH in infants up to approximately 6 months of age. It maintains the hip in flexion (100–110°) and controlled abduction, allowing gradual reduction of the femoral head into the acetabulum. Success rates are approximately 90% for Graf Type III and ~70% for Type IV. If no reduction is achieved within 3 weeks, the harness should be discontinued (risk of AVN from forced abduction). Beyond 6 months, closed or open reduction under anaesthesia is typically required.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 924,
              "stem": "After closed reduction of DDH in an infant, the hip is immobilised in which position?",
              "options": [
                "Full extension and adduction",
                "90° flexion with neutral abduction",
                "Full abduction and internal rotation",
                "Extension and external rotation",
                "The human position (flexion, abduction, and mild external rotation)"
              ],
              "answer": "E",
              "explanation": "After closed reduction (performed under GA with arthrogram confirmation), the hip is immobilised in the 'human position' — approximately 100° flexion, 40–50° abduction, and mild external rotation — in a hip spica cast. Extreme abduction ('frog position') must be avoided as it increases the risk of AVN by compressing the lateral epiphyseal artery against the acetabular rim. The spica is typically maintained for 12 weeks.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 925,
              "stem": "The most feared complication of treatment for DDH is:",
              "options": [
                "Re-dislocation",
                "Leg length discrepancy",
                "Avascular necrosis of the femoral head",
                "Residual acetabular dysplasia",
                "Infection"
              ],
              "answer": "C",
              "explanation": "Avascular necrosis (AVN) of the femoral head is the most feared complication of DDH treatment, as it can lead to permanent deformity of the femoral head, premature growth plate closure, limb shortening, and early-onset osteoarthritis. AVN risk is related to: excessive/forced abduction (compresses the lateral epiphyseal artery), extreme positions, delays in treatment, and iatrogenic factors. The Bucholz-Ogden classification grades AVN severity in DDH.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            }
          ]
        },
        {
          "title": "SUFE",
          "range": "Q926-Q928",
          "questions": [
            {
              "number": 926,
              "stem": "The hallmark clinical finding in slipped upper femoral epiphysis (SUFE) is:",
              "options": [
                "Obligatory external rotation on passive flexion of the hip",
                "Increased internal rotation of the hip",
                "Trendelenburg sign",
                "Leg lengthening",
                "Fixed abduction deformity"
              ],
              "answer": "A",
              "explanation": "The pathognomonic clinical finding in SUFE is obligatory external rotation of the hip on passive flexion. As the hip is flexed, it automatically externally rotates because the posteriorly and inferiorly slipped epiphysis creates a cam effect. Internal rotation is restricted. The patient also has a shortened, externally rotated leg and an antalgic gait.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 927,
              "stem": "The treatment for an acute unstable SUFE is:",
              "options": [
                "Bed rest and traction for 6 weeks",
                "Closed reduction and percutaneous pinning",
                "Proximal femoral osteotomy",
                "Urgent in situ single screw fixation without reduction",
                "Hip spica cast"
              ],
              "answer": "D",
              "explanation": "An acute unstable SUFE (unable to weight-bear, Loder classification) is treated urgently with gentle closed reduction (to reduce AVN risk from the displaced position) followed by percutaneous single screw fixation. The reduction must be gentle — forceful manipulation significantly increases AVN risk. A stable SUFE (able to weight-bear) is treated with in situ single screw fixation without reduction attempt. AVN is the most devastating complication (~10% in unstable, <1% in stable).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 928,
              "stem": "SUFE is most common in which demographic?",
              "options": [
                "Girls aged 5–7",
                "Girls aged 15–18",
                "Boys aged 10–15",
                "Boys aged 5–7",
                "Adults over 30"
              ],
              "answer": "C",
              "explanation": "SUFE typically affects adolescents during the pubertal growth spurt. Boys are more commonly affected than girls (2–3:1 ratio), typically between ages 10–15 (boys) and 8–13 (girls). Risk factors include obesity (most important modifiable factor), male sex, African-Caribbean ethnicity, endocrine disorders (hypothyroidism, growth hormone deficiency, renal osteodystrophy), and rapid growth. Bilateral slips occur in 20–40% of cases.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Perthes Disease",
          "range": "Q929-Q931",
          "questions": [
            {
              "number": 929,
              "stem": "Perthes disease (Legg-Calvé-Perthes) is avascular necrosis of the femoral head occurring in which age group?",
              "options": [
                "Neonates",
                "Children aged 4–8",
                "Adolescents aged 13–16",
                "Young adults aged 20–30",
                "Elderly >65"
              ],
              "answer": "B",
              "explanation": "Perthes disease is idiopathic avascular necrosis of the femoral head in children, typically aged 4–8 years. Boys are affected 4–5 times more commonly than girls, but girls tend to have a worse prognosis. It is bilateral in 10–15% of cases. The disease progresses through four stages: initial/necrosis → fragmentation → reossification → remodelling. The outcome depends on the age of onset, the extent of epiphyseal involvement, and the maintenance of femoral head containment within the acetabulum.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 930,
              "stem": "The Herring lateral pillar classification of Perthes disease is based on the height of the lateral pillar during which stage?",
              "options": [
                "Initial (necrosis) stage",
                "Reossification stage",
                "Remodelling stage",
                "Healed stage",
                "Fragmentation stage"
              ],
              "answer": "E",
              "explanation": "The Herring lateral pillar classification is assessed during the fragmentation stage (when the epiphysis is maximally fragmented and the prognostic picture is clearest). Group A: lateral pillar full height (good prognosis). Group B: lateral pillar >50% height maintained (intermediate prognosis). Group C: lateral pillar <50% height (poor prognosis). A B/C border group was later added. The classification predicts outcome and guides treatment decisions.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 931,
              "stem": "Which of the following is the most important prognostic factor in Perthes disease?",
              "options": [
                "Sex of the child",
                "Duration of symptoms",
                "Bilateral involvement",
                "Age at onset",
                "Family history"
              ],
              "answer": "D",
              "explanation": "Age at onset is the single most important prognostic factor. Children who develop Perthes before age 6 have the best prognosis because they have the greatest remaining growth potential for remodelling of the femoral head. Older children (>8 years) with greater epiphyseal involvement (Herring C or Catterall IV) have a worse prognosis and are more likely to develop an aspherical femoral head, coxa magna, and early OA.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Osteoarthritis",
          "range": "Q932-Q933",
          "questions": [
            {
              "number": 932,
              "stem": "The cardinal radiographic features of osteoarthritis are:",
              "options": [
                "Joint space narrowing, subchondral sclerosis, osteophytes, subchondral cysts",
                "Juxta-articular osteoporosis, marginal erosions, uniform joint space loss",
                "Periosteal reaction, soft tissue swelling, destruction",
                "Cortical thickening, mixed lytic/sclerotic areas, bone expansion",
                "Generalised osteopenia with vertebral compression fractures"
              ],
              "answer": "A",
              "explanation": "The four cardinal radiographic features of OA are: (1) joint space narrowing (asymmetric, in weight-bearing areas), (2) subchondral sclerosis (increased bone density beneath damaged cartilage), (3) osteophytes (new bone formation at joint margins), and (4) subchondral cysts (fluid-filled cavities in subchondral bone). These contrast with RA features (juxta-articular osteoporosis, marginal erosions, uniform joint space narrowing).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 933,
              "stem": "The Kellgren-Lawrence grading system for OA severity classifies which grade as 'definite osteophytes with possible joint space narrowing'?",
              "options": [
                "Grade 0",
                "Grade 1",
                "Grade 2",
                "Grade 3",
                "Grade 4"
              ],
              "answer": "C",
              "explanation": "Kellgren-Lawrence grading: Grade 0 = normal. Grade 1 = doubtful (possible osteophytes, no definite narrowing). Grade 2 = minimal (definite osteophytes, possible joint space narrowing). Grade 3 = moderate (moderate osteophytes, definite narrowing, possible deformity). Grade 4 = severe (large osteophytes, marked narrowing, severe sclerosis, definite deformity). This system is widely used in research and clinical practice for OA classification.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Osteotomy",
          "range": "Q934",
          "questions": [
            {
              "number": 934,
              "stem": "A high tibial osteotomy (HTO) for medial compartment knee OA aims to correct the mechanical axis to pass through which part of the tibial plateau?",
              "options": [
                "Medial compartment",
                "Centre of the knee",
                "Tibial tuberosity",
                "Lateral tibial spine",
                "Lateral compartment (Fujisawa point at 62% from medial edge)"
              ],
              "answer": "E",
              "explanation": "The Fujisawa point is the target for correction in valgus-producing HTO for medial compartment OA. It is located at approximately 62% of the width of the tibial plateau measured from the medial edge (i.e., slightly lateral to the centre of the knee). This overcorrection into slight valgus unloads the medial compartment and transfers weight to the healthier lateral compartment. Under-correction to neutral is associated with early failure.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Osteochondral",
          "range": "Q935",
          "questions": [
            {
              "number": 935,
              "stem": "The most common location for an osteochondral lesion (osteochondritis dissecans) in the knee is:",
              "options": [
                "Lateral facet of the patella",
                "Lateral aspect of the medial femoral condyle",
                "Medial tibial plateau",
                "Medial aspect of the lateral femoral condyle",
                "Trochlear groove"
              ],
              "answer": "B",
              "explanation": "The lateral aspect (non-weight-bearing portion) of the medial femoral condyle is the most common location for osteochondritis dissecans (OCD) in the knee (~70% of cases). It is thought to be related to impingement from the tibial spine or lateral meniscus. OCD in the lateral femoral condyle or patella is less common but carries a worse prognosis. Treatment ranges from drilling (stable, intact articular surface) to fixation or grafting (unstable fragment).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Patellofemoral",
          "range": "Q936",
          "questions": [
            {
              "number": 936,
              "stem": "An increased Q-angle predisposes to which patellofemoral disorder?",
              "options": [
                "Lateral patellar subluxation/dislocation",
                "Patellar tendinopathy",
                "Medial plica syndrome",
                "Bipartite patella symptoms",
                "Osgood-Schlatter disease"
              ],
              "answer": "A",
              "explanation": "The Q-angle (quadriceps angle) is measured from the ASIS to the centre of the patella to the tibial tuberosity. Normal is approximately 13–15° (men) and 15–18° (women). An increased Q-angle increases the lateral vector on the patella during quadriceps contraction, predisposing to lateral patellar tracking, subluxation, and dislocation. Factors increasing Q-angle: femoral anteversion, genu valgum, lateral tibial tubercle, pes planus.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Revision THA",
          "range": "Q937",
          "questions": [
            {
              "number": 937,
              "stem": "The Paprosky classification of acetabular bone defects in revision THA — Type III involves:",
              "options": [
                "Intact rim with contained cavitary defect",
                "Distorted hemisphere with intact columns",
                "Severe bone loss with non-supportive columns — IIIA (Kohler line intact) or IIIB (Kohler line disrupted/pelvic discontinuity)",
                "Normal acetabulum",
                "Isolated superior cavitary defect"
              ],
              "answer": "C",
              "explanation": "Paprosky acetabular classification: Type I = supportive rim, minimal bone loss (standard uncemented cup). Type II = distorted hemisphere but intact columns (IIA = superior migration, IIB = superior-lateral, IIC = medial wall deficient — jumbo cup or augments). Type III = severe segmental/cavitary loss, non-supportive columns. IIIA = Kohler line intact (some columns remain — cage/antiprotrusio ring + cemented cup, or trabecular metal augments). IIIB = Kohler line disrupted → pelvic discontinuity (cage with column plating, custom triflange, or cup-cage construct).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            }
          ]
        },
        {
          "title": "Sports",
          "range": "Q938-Q940",
          "questions": [
            {
              "number": 938,
              "stem": "The unhappy triad (O'Donoghue triad) of the knee involves injury to which three structures?",
              "options": [
                "ACL, MCL, and lateral meniscus",
                "ACL, MCL, and medial meniscus",
                "PCL, LCL, and lateral meniscus",
                "ACL, LCL, and medial meniscus",
                "PCL, MCL, and medial meniscus"
              ],
              "answer": "B",
              "explanation": "The classic O'Donoghue (unhappy) triad involves ACL tear + MCL tear + medial meniscus tear. It results from a valgus force with external rotation (e.g., football tackle). However, more recent evidence suggests the lateral meniscus is actually torn more frequently than the medial meniscus in acute ACL injuries (the original description by O'Donoghue was based on open surgical findings). Exam questions typically use the classic triad (ACL + MCL + medial meniscus).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 939,
              "stem": "The most common mechanism of ACL injury is:",
              "options": [
                "Direct contact (tackle) to the knee",
                "Hyperflexion injury",
                "Direct posterior force to the tibia",
                "Non-contact pivoting/deceleration with the knee near extension",
                "Hyperextension with external rotation"
              ],
              "answer": "D",
              "explanation": "Approximately 70% of ACL injuries occur via a non-contact mechanism: sudden deceleration, change of direction (pivoting/cutting), or landing from a jump with the knee near full extension and the foot planted. The classic position of vulnerability: knee in slight flexion (10-30°), valgus angulation, and internal rotation of the femur on a fixed tibia. Contact mechanisms (tackles) account for ~30%. Female athletes have a 2-8× higher ACL injury rate than males in the same sports (hormonal, anatomical, and neuromuscular factors).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 940,
              "stem": "The Ottawa ankle rules help determine when radiographs are needed after an ankle injury. An ankle X-ray is required if there is:",
              "options": [
                "Any ankle swelling",
                "Pain anywhere around the ankle",
                "Bruising alone",
                "Patient request only",
                "Bony tenderness at the posterior edge or tip of the lateral malleolus, OR inability to weight-bear 4 steps immediately or in ED"
              ],
              "answer": "E",
              "explanation": "Ottawa ankle rules: ankle radiographs are indicated if there is: (1) bone tenderness at the posterior edge or tip of EITHER malleolus (distal 6cm), OR (2) inability to weight-bear for 4 steps both immediately after injury AND in the ED. Ottawa foot rules: foot radiographs if: tenderness at the base of the 5th metatarsal, navicular, or inability to weight-bear 4 steps. These rules have ~98-100% sensitivity for significant fractures and reduce unnecessary radiographs by ~30-40%.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Revision TKA",
          "range": "Q941",
          "questions": [
            {
              "number": 941,
              "stem": "The Anderson Orthopaedic Research Institute (AORI) classification is used to classify bone defects in:",
              "options": [
                "Primary THA",
                "Primary TKA",
                "Ankle fractures",
                "Hip fractures",
                "Revision total knee arthroplasty"
              ],
              "answer": "E",
              "explanation": "The AORI classification grades bone defects in revision TKA separately for the femur and tibia: Type 1 = intact metaphyseal bone with minor defects (standard revision components). Type 2 = damaged metaphyseal bone: 2A (one condyle/plateau) or 2B (both condyles/plateaux) — may need augments, stems. Type 3 = deficient metaphyseal bone with compromised ligament attachments — requires structural allograft, sleeves, cones, or hinged prosthesis. This classification guides the choice of revision implant constraint and augmentation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "TKA Design",
          "range": "Q942",
          "questions": [
            {
              "number": 942,
              "stem": "In a cruciate-retaining (CR) TKA, the femoral component design differs from a posterior-stabilised (PS) TKA in that the CR femoral component:",
              "options": [
                "Does NOT have a box cut — the intercondylar area is preserved to accommodate the retained PCL",
                "Has a cam-post mechanism",
                "Has a box cut in the distal femur to accommodate a cam",
                "Is always a hinged design",
                "Requires sacrifice of both cruciate ligaments"
              ],
              "answer": "A",
              "explanation": "In a CR TKA, both the PCL is retained and the intercondylar notch area of the distal femur is preserved (no box cut) — the PCL sits in this space and provides posterior stability and assists femoral rollback during flexion. In a PS TKA, the PCL is sacrificed and a box is cut in the distal femur to accommodate the cam mechanism of the femoral component, which engages a post on the tibial polyethylene insert to substitute for the PCL function (prevents posterior subluxation of the tibia and facilitates rollback). The box cut in PS designs removes additional bone stock — a disadvantage in revision situations.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            }
          ]
        },
        {
          "title": "OA",
          "range": "Q943",
          "questions": [
            {
              "number": 943,
              "stem": "The Kellgren-Lawrence grading system for osteoarthritis on plain radiographs — Grade III is:",
              "options": [
                "Normal (no OA features)",
                "Doubtful narrowing with possible osteophytes",
                "Definite osteophytes with possible joint space narrowing",
                "Moderate osteophytes with definite joint space narrowing and possible subchondral sclerosis",
                "Large osteophytes with marked narrowing, sclerosis, and possible deformity"
              ],
              "answer": "D",
              "explanation": "Kellgren-Lawrence (KL) grading: Grade 0 = normal. Grade 1 = doubtful (possible osteophytes). Grade 2 = minimal (definite osteophytes, possible narrowing). Grade 3 = moderate (moderate osteophytes, definite narrowing, some sclerosis, possible deformity). Grade 4 = severe (large osteophytes, marked narrowing, severe sclerosis, definite deformity, possible bone-on-bone). KL grading is the most widely used OA radiographic classification and is used in research, NJR data, and clinical practice. Important: clinical severity does not always correlate with radiographic grade — some patients with KL Grade IV are minimally symptomatic and vice versa.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Hip Anatomy",
          "range": "Q944",
          "questions": [
            {
              "number": 944,
              "stem": "The sciatic nerve exits the pelvis through the greater sciatic foramen. Its position relative to the piriformis muscle is:",
              "options": [
                "Above piriformis",
                "Through the substance of piriformis in all cases",
                "Below (inferior to) the piriformis muscle",
                "Medial to piriformis",
                "Anterior to piriformis"
              ],
              "answer": "C",
              "explanation": "The sciatic nerve exits the pelvis through the greater sciatic foramen BELOW (inferior to) the piriformis muscle in ~85% of people. Anatomical variations exist: in ~10-15%, the peroneal division passes through or above the piriformis. The sciatic nerve then descends in the posterior thigh between the greater trochanter and ischial tuberosity, deep to gluteus maximus. It is at risk during the posterior approach to the hip (short external rotator muscles are divided — piriformis may be tagged and used as a landmark). Hip dislocation (posterior) stretches the nerve. Sciatic nerve palsy occurs in ~1% of primary THA via the posterior approach.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "UKA",
          "range": "Q945",
          "questions": [
            {
              "number": 945,
              "stem": "The ideal candidate for unicompartmental knee arthroplasty (UKA) has which combination of features?",
              "options": [
                "Tricompartmental OA with significant deformity",
                "Isolated medial (or lateral) compartment OA with intact ACL, correctable deformity, and intact opposite compartment",
                "Inflammatory arthritis with bilateral disease",
                "Severe bone loss requiring stems and augments",
                "Patellofemoral OA with lateral compartment disease"
              ],
              "answer": "B",
              "explanation": "UKA (medial or lateral) is indicated for isolated single-compartment OA with: (1) intact ACL (essential for UKA kinematics — ACL deficiency is a contraindication), (2) intact opposite compartment and patellofemoral joint (no full-thickness cartilage loss), (3) correctable varus/valgus deformity (passively correctable to neutral — fixed deformity >10-15° is a contraindication), (4) flexion >110°, flexion contracture <5°. Oxford UKA is the most commonly implanted mobile-bearing UKA. Advantages over TKA: faster recovery, more natural kinematics, bone preservation, lower perioperative risk. Disadvantages: higher revision rate (NJR: ~10-year survival 90% UKA vs 96% TKA), risk of bearing dislocation (mobile), and progression of disease in other compartments.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        }
      ]
    },
    {
      "title": "Statistics & Evidence",
      "chapters": [
        {
          "title": "Statistics",
          "range": "Q946-Q983",
          "questions": [
            {
              "number": 946,
              "stem": "Kaplan-Meier survival analysis is used in orthopaedics to:",
              "options": [
                "Estimate the probability of an event (e.g., implant REVISION) occurring over time — accounting for patients who are CENSORED (lost to follow-up or haven't yet reached the event) — producing a survival curve showing cumulative survival at each time point",
                "Calculate the mean value of a dataset",
                "Measure the range of a dataset",
                "Calculate the standard deviation",
                "Perform a power calculation"
              ],
              "answer": "A",
              "explanation": "Kaplan-Meier (KM) survival analysis estimates the probability of 'surviving' (not having an event — e.g., not having a revision) at each time point. It handles CENSORED data — patients who are lost to follow-up, die from unrelated causes, or haven't yet reached the endpoint are 'censored' at their last known time point (they contribute data UP TO that point, then exit the analysis). This is critical because: in arthroplasty registries (NJR, AOANJRR), patients have varying follow-up lengths (some 10 years, some 2 years) — KM allows all to contribute proportionally. The output: a SURVIVAL CURVE (step function that decreases over time as events occur). The 10-year survival: the estimated percentage still 'surviving' at 10 years (e.g., NJR reports TKA 10-year survival ~95-97%). 95% confidence intervals around the curve indicate precision. Reporting: ALWAYS include the number at risk at each time point (survival estimates become unreliable when few patients remain). The log-rank test: compares KM curves between groups (e.g., comparing survival of two different implants).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 947,
              "stem": "Prevalence and incidence are measures of disease frequency. Prevalence measures:",
              "options": [
                "Only new cases of disease in a time period (that's incidence)",
                "The cure rate",
                "The mortality rate",
                "The TOTAL number of existing cases (both old and new) in a population at a given point in time or period — it is a proportion, not a rate",
                "The surgical complication rate"
              ],
              "answer": "D",
              "explanation": "PREVALENCE: the proportion of a population that HAS a disease at a specific point in time (point prevalence) or during a specific period (period prevalence). It includes BOTH old (pre-existing) and new cases. It is a SNAPSHOT of disease burden. Example: the prevalence of knee OA in adults >65yr is ~30% (30% of over-65s have knee OA at any given time). INCIDENCE: the number of NEW cases that develop in a population over a defined TIME PERIOD. It is a RATE (cases per person-time at risk). Example: the incidence of hip fracture in women >65yr is approximately 10 per 1,000 per year (10 new fractures occur per 1,000 women per year). Relationship: prevalence = incidence × duration. Chronic diseases (OA, diabetes) have HIGH prevalence relative to incidence (cases accumulate because the disease persists). Acute diseases (fractures, infections) have lower prevalence (they resolve or are treated). Prevalence is useful for: healthcare planning (how many people currently need treatment). Incidence is useful for: understanding risk factors and aetiology.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 948,
              "stem": "A Type I error (alpha error) in statistical testing is:",
              "options": [
                "Failing to detect a real difference (missing a true effect)",
                "A calculation error in the study",
                "Incorrectly REJECTING the null hypothesis when it is actually TRUE (concluding there IS a difference when there really ISN'T one — a false positive)",
                "An error in data collection",
                "An error in patient selection"
              ],
              "answer": "C",
              "explanation": "Type I error (alpha error, false positive): rejecting the null hypothesis when it is actually true — concluding there IS a significant difference/effect when in reality there ISN'T one. The probability of making a Type I error is set by the significance level (alpha, α) — conventionally 0.05 (5%). This means we accept a 5% risk of a false positive result. Type II error (beta error, false negative): FAILING to reject the null hypothesis when it is actually false — concluding there is NO significant difference when in reality there IS one (missing a real effect). The probability of Type II error is β, and POWER = 1 - β (typically set at 0.80 or 80%, meaning 20% chance of missing a true effect). Increasing sample size reduces BOTH Type I and Type II errors. Multiple comparisons increase Type I error risk (Bonferroni correction adjusts for this).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 949,
              "stem": "Statistical power of a study is defined as:",
              "options": [
                "The probability of making a Type I error",
                "The probability of correctly REJECTING the null hypothesis when it IS false (detecting a true effect when one exists) — typically set at 80% (0.80)",
                "The sample size divided by the p-value",
                "The confidence interval width",
                "The effect size alone"
              ],
              "answer": "B",
              "explanation": "Power = 1 - β (where β is the probability of a Type II error/false negative). A power of 80% means there is an 80% probability of detecting a true difference/effect if one actually exists (and a 20% chance of missing it). Power is determined by: (1) SAMPLE SIZE (larger n → more power — the most important modifiable factor), (2) EFFECT SIZE (larger true difference → easier to detect → more power), (3) SIGNIFICANCE LEVEL (higher alpha → more power but more false positives — trade-off), and (4) VARIABILITY (lower SD → more power). Power calculations should be performed BEFORE a study begins (a priori) to determine the required sample size. An underpowered study (insufficient sample size) may fail to detect a real effect → Type II error → a false negative conclusion that the treatment doesn't work.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 950,
              "stem": "The chi-squared test is used to:",
              "options": [
                "Compare means between two groups",
                "Assess correlation between continuous variables",
                "Measure the spread of continuous data",
                "Calculate regression coefficients",
                "Compare observed vs expected frequencies in CATEGORICAL data (testing whether there is a significant association between two categorical variables)"
              ],
              "answer": "E",
              "explanation": "The chi-squared (χ²) test compares observed frequencies with expected frequencies in categorical (nominal) data to determine whether there is a statistically significant association between two categorical variables. Example: is there a significant association between fracture type (open vs closed) and infection (yes vs no)? The data is arranged in a contingency table (2×2 or larger). If the expected count in any cell is <5, use FISHER'S EXACT test instead (chi-squared is unreliable with small expected frequencies). Chi-squared does NOT: compare means (use t-test), assess correlation between continuous variables (use Pearson/Spearman), or calculate regression. McNemar's test: chi-squared variant for PAIRED categorical data (before/after in the same patients). Yates correction: adjustment for continuity in 2×2 tables.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 951,
              "stem": "Sensitivity of a diagnostic test is defined as:",
              "options": [
                "The proportion of patients WITHOUT the disease who test NEGATIVE (that's specificity)",
                "The proportion of patients WITH the disease who correctly test POSITIVE (true positive rate — a highly sensitive test 'rules out' disease when negative: SnNOut)",
                "The proportion of all positive tests that are true positives (that's PPV)",
                "The total number of tests performed",
                "The false positive rate"
              ],
              "answer": "B",
              "explanation": "Sensitivity = TP / (TP + FN) = the proportion of patients who HAVE the disease and are correctly identified by the test (true positive rate). A test with HIGH sensitivity has few FALSE NEGATIVES — it rarely misses the disease. Therefore: a NEGATIVE result on a highly SENSITIVE test effectively RULES OUT the disease (SnNOut — Sensitivity, Negative result, rules Out). Example: MRI for scaphoid fracture has ~100% sensitivity — if MRI is negative, the patient almost certainly doesn't have a fracture. Specificity = TN / (TN + FP) = the proportion of patients WITHOUT the disease who correctly test negative. High specificity = few false positives. A POSITIVE result on a highly SPECIFIC test RULES IN the disease (SpPIn — Specificity, Positive result, rules In). Example: corner/bucket-handle metaphyseal fractures have ~100% specificity for NAI — if present, NAI is virtually certain.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 952,
              "stem": "The number needed to treat (NNT) represents:",
              "options": [
                "The total sample size of the study",
                "The p-value converted to a number",
                "The cost of treatment per patient",
                "The number of patients who need to be treated with the intervention for ONE additional patient to benefit compared to the control (calculated as 1/ARR — absolute risk reduction)",
                "The number of side effects"
              ],
              "answer": "D",
              "explanation": "NNT = 1 / ARR (absolute risk reduction). ARR = control event rate (CER) minus experimental event rate (EER). Example: if a drug reduces fracture risk from 10% (control) to 5% (treatment), ARR = 10% - 5% = 5% = 0.05, NNT = 1/0.05 = 20. This means: 20 patients need to be treated for 1 additional patient to benefit (avoid a fracture). The LOWER the NNT → the MORE effective the treatment (NNT of 1 = every patient benefits, which is virtually never achieved). NNH (number needed to harm) = 1/ARI (absolute risk increase) — the number treated for one additional patient to experience a specific adverse event. NNT is clinically meaningful because it translates statistical results into practical terms that patients and clinicians can understand. Always consider NNT alongside NNH: if NNT=20 for benefit but NNH=10 for a serious side effect → the treatment causes more harm than benefit.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 953,
              "stem": "A 95% confidence interval (CI) means:",
              "options": [
                "The study is 95% accurate",
                "The treatment works 95% of the time",
                "5% of patients will be harmed",
                "The result is definitely correct",
                "95% probability that the true value lies within the interval (common misconception — this is the frequentist interpretation approximation used clinically)"
              ],
              "answer": "E",
              "explanation": "A 95% CI provides a range of values within which we are '95% confident' the true population parameter lies. Strictly (frequentist interpretation): if we repeated the study 100 times, 95 of those intervals would contain the true value. Practically: it gives a plausible range for the true effect. Clinical interpretation: (1) if the 95% CI for a treatment effect CROSSES the null value (0 for a mean difference, or 1 for a relative risk/odds ratio) → the result is NOT statistically significant at p=0.05. (2) A NARROW CI = precise estimate (large sample, low variability). (3) A WIDE CI = imprecise estimate (small sample, high variability). Example: RR 0.5 (95% CI 0.3-0.8) → the CI doesn't cross 1 → statistically significant (the treatment reduces risk). RR 0.5 (95% CI 0.2-1.3) → the CI CROSSES 1 → NOT statistically significant. CIs provide MORE information than p-values alone — they show the direction, magnitude, and precision of the effect.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 954,
              "stem": "The odds ratio (OR) differs from the relative risk (RR) in that the OR:",
              "options": [
                "Can only be used in RCTs",
                "Is identical to RR in all circumstances",
                "Is the ratio of the odds of an event occurring in the exposed vs unexposed group — it approximates the RR when the event is RARE (<10%), but OVERESTIMATES the effect when the event is common",
                "Is always smaller than the RR",
                "Cannot be used in case-control studies (actually, OR is the ONLY measure usable in case-control)"
              ],
              "answer": "C",
              "explanation": "OR = (odds of event in exposed) / (odds of event in unexposed). RR = (risk of event in exposed) / (risk of event in unexposed). Key distinction: RR can only be calculated in prospective studies (cohort studies, RCTs) where you know the TRUE INCIDENCE. OR can be calculated in BOTH prospective AND retrospective (case-control) studies — in case-control studies, you cannot calculate RR (because you start with outcomes, not exposures), so OR is the only option. When the event is RARE (<10% incidence): OR ≈ RR (they are numerically very similar). When the event is COMMON (>10%): OR OVERESTIMATES the RR (the OR exaggerates the apparent effect size). This is important clinically: a reported OR of 2.0 for a common event (~30% incidence) corresponds to an actual RR of only ~1.5. Logistic regression produces ORs (not RRs). Meta-analyses of case-control studies report ORs. Meta-analyses of RCTs may report RRs or ORs.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 955,
              "stem": "The positive predictive value (PPV) of a test is most affected by:",
              "options": [
                "Disease prevalence in the tested population",
                "Sensitivity of the test",
                "Specificity of the test",
                "Sample size",
                "Test reliability"
              ],
              "answer": "A",
              "explanation": "PPV (probability that a person with a positive test truly has the disease) is heavily influenced by disease prevalence. In a low-prevalence population, even a highly sensitive and specific test will have many false positives relative to true positives, giving a low PPV. In a high-prevalence population, PPV improves dramatically. This is why screening tests work best in high-risk populations and why confirmatory tests are needed after positive screening results.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 956,
              "stem": "The standard deviation (SD) measures:",
              "options": [
                "The central tendency of the data",
                "The correlation between two variables",
                "The sample size",
                "The significance of the result",
                "The spread (dispersion) of data points around the mean"
              ],
              "answer": "E",
              "explanation": "Standard deviation measures the SPREAD or DISPERSION of data points around the mean. A larger SD means the data is more spread out (more variability); a smaller SD means the data is clustered closely around the mean (less variability). SD = √variance. In a normal distribution: 68% of values fall within ±1 SD, 95% within ±2 SD, 99.7% within ±3 SD. Standard ERROR (SE) is different: SE = SD/√n — it measures the precision of the sample mean as an estimate of the population mean (how much the sample mean is likely to vary from study to study). Larger samples → smaller SE → more precise estimate. SD describes the data spread; SE describes the precision of the mean estimate.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 957,
              "stem": "Specificity is the ability of a test to correctly identify those WITHOUT the disease. A test with 99% specificity means:",
              "options": [
                "99% of people WITH the disease test positive",
                "The test is 99% accurate overall",
                "99% of positive results are true positives",
                "99% of people WITHOUT the disease test negative (only 1% false positives)",
                "The test has 99% sensitivity"
              ],
              "answer": "D",
              "explanation": "Specificity = TN/(TN+FP). A test with 99% specificity correctly identifies 99% of people who do NOT have the disease — only 1% of truly healthy individuals will have a false positive result. High specificity is important for CONFIRMATORY tests (you want to be confident that a positive result truly means disease is present — SPin: high Specificity rules IN disease). The trade-off: very high specificity often comes at the cost of lower sensitivity (more false negatives). PPV is affected by prevalence: in a low-prevalence population, even a highly specific test can have many false positives relative to true positives. This is why the combination of sensitivity AND specificity (and the clinical context) must be considered together.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 958,
              "stem": "In an intention-to-treat (ITT) analysis, patients are analysed:",
              "options": [
                "Only if they completed the study",
                "In the group to which they were originally randomised, regardless of compliance or crossover",
                "Only if they complied with the assigned treatment",
                "Only if they had a good outcome",
                "After excluding protocol violations"
              ],
              "answer": "B",
              "explanation": "ITT analysis analyses patients in the group to which they were originally randomised, regardless of whether they completed treatment, complied with the protocol, crossed over to the other group, or dropped out. This preserves the benefit of randomisation (balanced baseline characteristics) and reflects real-world effectiveness. Per-protocol analysis (only including compliant patients) may introduce bias but shows efficacy. ITT tends to produce more conservative (smaller) treatment effects.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 959,
              "stem": "A p-value of 0.03 in a clinical trial means:",
              "options": [
                "There is a 3% chance the treatment works",
                "The treatment is 97% effective",
                "There is a 3% probability that the observed difference occurred by chance alone (assuming the null hypothesis is true)",
                "There is a 97% chance the null hypothesis is false",
                "The effect size is 3%"
              ],
              "answer": "C",
              "explanation": "The p-value is the probability of obtaining results at least as extreme as those observed, assuming the null hypothesis is true. A p-value of 0.03 means there is a 3% probability that the observed difference occurred by chance. If p < 0.05 (the conventional threshold), the result is considered statistically significant and the null hypothesis is rejected. However, statistical significance does not equal clinical significance — a small but statistically significant difference may not be clinically meaningful.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 960,
              "stem": "Power in a clinical trial refers to:",
              "options": [
                "The probability of detecting a true difference when one exists (1 minus beta)",
                "The probability of a Type I error",
                "The sample size required",
                "The effect size observed",
                "The probability of finding no difference"
              ],
              "answer": "A",
              "explanation": "Power = 1 − β (where β is the probability of a Type II error/false negative). It represents the probability of correctly rejecting the null hypothesis when it is false — i.e., detecting a true treatment effect when one exists. Conventional power is set at 0.80 (80%), meaning there is a 20% chance of missing a true effect. Power is increased by: larger sample size, larger effect size, higher alpha level, and reduced variability.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 961,
              "stem": "In a Kaplan-Meier survival analysis, the vertical drops on the curve represent:",
              "options": [
                "Events (e.g., implant failures, deaths)",
                "Patients lost to follow-up",
                "Patients entering the study",
                "Confidence intervals",
                "Standard deviations"
              ],
              "answer": "A",
              "explanation": "In a Kaplan-Meier curve, vertical drops represent events (failures, deaths, or whatever endpoint is being measured). Small tick marks on the curve represent censored observations (patients lost to follow-up or still alive/surviving at the end of the study without having the event). The curve shows the probability of survival over time. It is the standard method for reporting implant survival in arthroplasty registries.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 962,
              "stem": "A 95% confidence interval for a treatment effect that crosses zero (for mean differences) or crosses 1.0 (for odds ratios) indicates:",
              "options": [
                "The result is statistically significant",
                "The study is underpowered",
                "The treatment is harmful",
                "The treatment is definitely effective",
                "The result is NOT statistically significant at the 5% level"
              ],
              "answer": "E",
              "explanation": "If a 95% confidence interval crosses the null value (0 for mean differences, 1.0 for odds ratios/relative risks), the result is NOT statistically significant at the p=0.05 level. This means we cannot exclude the possibility that the true effect is zero (no difference). A CI that does NOT cross the null value indicates statistical significance. Wider CIs suggest greater uncertainty (often from small sample sizes). CIs provide more information than p-values alone because they show both the direction and magnitude of the effect with precision.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 963,
              "stem": "A Type I error in a clinical trial means:",
              "options": [
                "Failing to detect a true difference (false negative)",
                "Underpowered study design",
                "Incorrectly rejecting the null hypothesis when it is true (false positive)",
                "Selection bias",
                "Measurement error"
              ],
              "answer": "C",
              "explanation": "Type I error (alpha error) = rejecting the null hypothesis when it is actually true = false positive (concluding there IS a treatment effect when there is NOT one). The probability of a Type I error is set by the significance level (alpha, conventionally 0.05 or 5%). Type II error (beta error) = failing to reject the null hypothesis when it is false = false negative (missing a true treatment effect). Power = 1 - beta = probability of correctly detecting a true effect (conventionally 0.80 or 80%). Type I error is considered more serious in most contexts.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 964,
              "stem": "The Cox proportional hazards model is used in orthopaedic research primarily to:",
              "options": [
                "Calculate mean values",
                "Compare two proportions",
                "Calculate sample size",
                "Analyse time-to-event data adjusting for multiple covariates (e.g., implant survival with patient factors)",
                "Assess inter-observer reliability"
              ],
              "answer": "D",
              "explanation": "The Cox proportional hazards model is a regression analysis used for time-to-event (survival) data. It estimates hazard ratios (HRs) for covariates while accounting for censoring (patients lost to follow-up). In orthopaedics, it is commonly used to analyse implant survival while adjusting for patient factors (age, sex, BMI, diagnosis, fixation type). HR >1 = increased risk. HR <1 = decreased risk. HR = 1 = no effect. It assumes proportional hazards (the ratio of hazards is constant over time).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 965,
              "stem": "The kappa statistic measures:",
              "options": [
                "Treatment effect size",
                "Inter-observer agreement (reliability) beyond chance",
                "Sample size adequacy",
                "Sensitivity of a diagnostic test",
                "Mortality rate"
              ],
              "answer": "B",
              "explanation": "The kappa (κ) statistic measures the level of agreement between two or more observers (or the same observer on two occasions) beyond what would be expected by chance alone. κ = 0 = agreement equal to chance. κ = 1 = perfect agreement. κ < 0 = less than chance agreement. Interpretation: <0.20 = poor, 0.21-0.40 = fair, 0.41-0.60 = moderate, 0.61-0.80 = substantial, 0.81-1.00 = almost perfect (Landis and Koch). Kappa is commonly used to assess the reliability of classification systems (e.g., Neer proximal humerus, Garden NOF) and imaging interpretation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 966,
              "stem": "A correlation coefficient (Pearson r) of +0.95 between two variables indicates:",
              "options": [
                "No relationship",
                "A weak positive relationship",
                "A strong negative relationship",
                "A strong positive linear relationship",
                "A causal relationship"
              ],
              "answer": "D",
              "explanation": "Pearson correlation coefficient (r) ranges from -1 to +1. r = +1 = perfect positive correlation. r = -1 = perfect negative correlation. r = 0 = no linear correlation. |r| >0.8 = strong. |r| 0.5-0.8 = moderate. |r| <0.5 = weak. An r of +0.95 indicates a STRONG POSITIVE linear relationship. IMPORTANT: correlation does NOT imply causation — two variables may be strongly correlated but one does not necessarily cause the other (confounding variables, reverse causation, or coincidence may explain the association). Only RCTs can establish causation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 967,
              "stem": "The chi-squared test is used to compare:",
              "options": [
                "Two means from normally distributed data",
                "Proportions or frequencies between categorical variables",
                "Medians from non-parametric data",
                "Survival curves",
                "Correlation between continuous variables"
              ],
              "answer": "B",
              "explanation": "The chi-squared (χ²) test compares observed vs expected frequencies in categorical (qualitative) data to determine whether there is a significant association between two categorical variables. Example: comparing infection rates (yes/no) between two surgical techniques. Requirements: adequate sample size (expected frequency ≥5 in each cell). Fisher exact test: used when sample sizes are small (expected frequencies <5). T-test: compares means (parametric). Mann-Whitney: compares medians (non-parametric). Log-rank: compares survival curves.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 968,
              "stem": "The Mann-Whitney U test is the non-parametric equivalent of which parametric test?",
              "options": [
                "Independent samples t-test",
                "Paired t-test",
                "ANOVA",
                "Chi-squared test",
                "Pearson correlation"
              ],
              "answer": "A",
              "explanation": "The Mann-Whitney U test compares two independent groups of non-normally distributed (non-parametric) data — it is the non-parametric equivalent of the independent samples t-test. It compares medians (or more precisely, ranks) rather than means. Parametric tests (t-test, ANOVA, Pearson) assume normally distributed data. Non-parametric equivalents: Wilcoxon signed-rank = paired t-test equivalent. Kruskal-Wallis = one-way ANOVA equivalent. Spearman rank = Pearson correlation equivalent.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 969,
              "stem": "If a new drug reduces the fracture rate from 20% (control) to 12% (treatment), the relative risk reduction (RRR) is:",
              "options": [
                "8%",
                "20%",
                "40%",
                "60%",
                "80%"
              ],
              "answer": "C",
              "explanation": "ARR (absolute risk reduction) = CER - EER = 20% - 12% = 8%. RRR (relative risk reduction) = ARR / CER = 8% / 20% = 0.40 = 40%. NNT = 1/ARR = 1/0.08 = 12.5 ≈ 13 patients. Relative risk (RR) = EER/CER = 12%/20% = 0.60. RRR = 1 - RR = 1 - 0.60 = 0.40 = 40%. RRR sounds more impressive than ARR (40% vs 8%) — pharmaceutical companies often report RRR. Always ask for the ARR and NNT for clinical relevance.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 970,
              "stem": "In a standard normal (Gaussian) distribution, approximately what percentage of values fall within 2 standard deviations of the mean?",
              "options": [
                "50%",
                "68%",
                "85%",
                "99.7%",
                "95%"
              ],
              "answer": "E",
              "explanation": "In a normal (Gaussian) distribution: approximately 68% of values fall within ±1 standard deviation (SD) of the mean. 95% within ±2 SD. 99.7% within ±3 SD (the 68-95-99.7 rule or empirical rule). This is fundamental to understanding confidence intervals (a 95% CI corresponds to approximately ±2 SD) and hypothesis testing. If data is normally distributed, these percentages are predictable. Standard deviation measures the spread of data around the mean — a larger SD indicates greater variability.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 971,
              "stem": "The Kaplan-Meier survival curve is used in orthopaedics to:",
              "options": [
                "Compare means between two groups",
                "Calculate correlation coefficients",
                "Estimate and display the probability of an event (e.g., implant revision) occurring over time, accounting for censored data",
                "Determine sample size",
                "Assess inter-observer reliability"
              ],
              "answer": "C",
              "explanation": "The Kaplan-Meier method estimates the survival function — the probability of surviving (or of an implant surviving without revision) beyond a given time point. It handles CENSORED data (patients lost to follow-up, or patients who haven't yet reached the endpoint — they contribute data up to their last known follow-up point). The curve shows a step function that decreases each time an event (revision, death) occurs. The NJR uses Kaplan-Meier curves to display implant survival over time. The log-rank test compares two or more Kaplan-Meier curves to determine if there is a statistically significant difference in survival between groups. The Cox proportional hazards model extends this by adjusting for multiple covariates (age, sex, BMI, diagnosis).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 972,
              "stem": "A forest plot is used to display the results of:",
              "options": [
                "A single case report",
                "A meta-analysis (graphically showing the individual study results and the pooled estimate from multiple studies)",
                "A single RCT",
                "A qualitative study",
                "A cost-effectiveness analysis"
              ],
              "answer": "B",
              "explanation": "A forest plot is the standard graphical display for the results of a meta-analysis. Each horizontal line represents an individual study's result (point estimate ± 95% confidence interval). The size of the square (point estimate) represents the study's weight in the analysis (larger studies have bigger squares). The diamond at the bottom represents the pooled (overall) estimate from all studies combined. A vertical line of no effect (OR/RR = 1, or mean difference = 0) allows visual assessment of whether individual studies or the pooled estimate cross the line (statistically significant if the CI does not cross the line). The I² statistic measures heterogeneity between studies (I² >50% = significant heterogeneity → results should be interpreted cautiously).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 973,
              "stem": "The Wilcoxon signed-rank test is the non-parametric equivalent of the:",
              "options": [
                "Independent t-test",
                "ANOVA",
                "Chi-squared test",
                "Log-rank test",
                "Paired t-test (used for comparing two related/paired measurements when data is not normally distributed)"
              ],
              "answer": "E",
              "explanation": "The Wilcoxon signed-rank test is the non-parametric equivalent of the PAIRED t-test. It is used to compare two related/paired measurements (e.g., pre-operative vs post-operative scores in the same patients) when the data is not normally distributed or is ordinal. The paired t-test requires normally distributed data; Wilcoxon does not. Similarly: Mann-Whitney U = non-parametric equivalent of the INDEPENDENT t-test (two unrelated groups). Kruskal-Wallis = non-parametric equivalent of one-way ANOVA (≥3 groups). Friedman test = non-parametric equivalent of repeated-measures ANOVA. Choosing the correct statistical test is a frequently examined topic.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 974,
              "stem": "In evidence-based medicine, the 'number needed to harm' (NNH) is calculated as:",
              "options": [
                "Sensitivity × specificity",
                "Odds ratio × relative risk",
                "p-value × sample size",
                "1 / absolute risk increase (ARI)",
                "NNT × prevalence"
              ],
              "answer": "D",
              "explanation": "NNH = 1 / ARI (absolute risk increase). ARI = experimental event rate - control event rate (when the experimental treatment causes MORE harm). NNH tells you how many patients need to be treated with the intervention to cause one additional adverse outcome compared to the control. Example: if a new NSAID causes GI bleeding in 5% of patients vs 2% in the control group, ARI = 3% = 0.03, NNH = 1/0.03 = 33 — treating 33 patients causes one additional GI bleed. Higher NNH = safer treatment. NNH should always be considered alongside NNT to evaluate the benefit-risk balance. A treatment with NNT = 20 (need to treat 20 to prevent one event) and NNH = 100 (need to treat 100 to cause one harm) has a favourable risk-benefit ratio.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 975,
              "stem": "An ANOVA (Analysis of Variance) test is used to compare:",
              "options": [
                "Means from THREE or more independent groups (parametric data)",
                "Two means from independent groups",
                "Two proportions",
                "Survival curves",
                "Correlation between two variables"
              ],
              "answer": "A",
              "explanation": "ANOVA (one-way analysis of variance) is used to compare means from three or more independent groups when the data is normally distributed (parametric). It tests whether at least one group mean is significantly different from the others. If ANOVA is significant, post-hoc tests (e.g., Tukey, Bonferroni) determine which specific groups differ. Two groups: t-test. Three or more groups: ANOVA. Non-parametric equivalent of ANOVA: Kruskal-Wallis test (for non-normally distributed data or ordinal data with ≥3 groups). Repeated measures ANOVA: for comparing the same group at ≥3 time points.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 976,
              "stem": "Sensitivity is the ability of a test to correctly identify those WITH the disease (true positive rate). If a test has 95% sensitivity, it means:",
              "options": [
                "95% of all test results are positive",
                "95% of people WITH the disease will test POSITIVE (5% will be false negatives)",
                "95% of people WITHOUT the disease will test negative",
                "The test is 95% accurate overall",
                "95% of positive results are true positives"
              ],
              "answer": "B",
              "explanation": "Sensitivity = true positives / (true positives + false negatives) = TP/(TP+FN). A test with 95% sensitivity will correctly identify 95% of people who actually have the disease — only 5% of truly diseased individuals will be missed (false negatives). High sensitivity is important for screening tests (you don't want to miss disease). Specificity = TN/(TN+FP) — the ability to correctly identify those WITHOUT disease. High specificity is important for confirmatory tests (you don't want false positives). A useful mnemonic: SPin (high Specificity → rules IN disease) and SNout (high Sensitivity → rules OUT disease).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 977,
              "stem": "Number needed to treat (NNT) is calculated as:",
              "options": [
                "Relative risk × prevalence",
                "Sensitivity × specificity",
                "Odds ratio squared",
                "p-value divided by sample size",
                "1 / absolute risk reduction (ARR)"
              ],
              "answer": "E",
              "explanation": "NNT = 1 / ARR (absolute risk reduction). ARR = control event rate (CER) - experimental event rate (EER). NNT tells you how many patients need to be treated with the intervention to prevent one additional bad outcome compared to the control. Example: if a drug reduces fracture risk from 10% to 5%, ARR = 5% = 0.05, NNT = 1/0.05 = 20 — you need to treat 20 patients to prevent 1 fracture. Lower NNT = more effective treatment. NNT is more clinically meaningful than relative risk reduction (RRR) because it accounts for the baseline risk. NNH (number needed to harm) = 1 / absolute risk increase (ARI).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 978,
              "stem": "The odds ratio (OR) is the primary measure of association in which study design?",
              "options": [
                "Case-control study",
                "Randomised controlled trial",
                "Cohort study",
                "Cross-sectional study",
                "Ecological study"
              ],
              "answer": "A",
              "explanation": "The odds ratio (OR) is the primary measure of association in case-control studies because you cannot calculate incidence rates (and therefore relative risk) directly from case-control data (participants are selected based on outcome, not exposure). OR = (odds of exposure in cases) / (odds of exposure in controls) = (a×d)/(b×c) from the 2×2 table. OR >1 = positive association. OR <1 = negative (protective). OR = 1 = no association. In rare diseases, the OR approximates the RR (relative risk). RR is used in cohort studies and RCTs where incidence rates can be calculated directly. HR (hazard ratio) is used in time-to-event/survival analysis.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 979,
              "stem": "Positive predictive value (PPV) is defined as:",
              "options": [
                "The probability that a person with a negative test truly does not have the disease",
                "The same as sensitivity",
                "The same as specificity",
                "The probability that a person with a positive test truly has the disease = TP/(TP+FP)",
                "The proportion of all tests that are positive"
              ],
              "answer": "D",
              "explanation": "PPV = TP/(TP+FP) — the proportion of people with a positive test result who actually have the disease. It answers the clinical question: 'If my patient tests positive, what is the probability they actually have the condition?' NPV = TN/(TN+FN) — 'If my patient tests negative, what is the probability they truly don't have it?' CRITICAL: PPV and NPV are affected by disease PREVALENCE. Higher prevalence → higher PPV (more true positives in the positive results). Lower prevalence → lower PPV (more false positives). This is why screening tests work best in high-prevalence populations. Sensitivity and specificity are NOT affected by prevalence.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 980,
              "stem": "A p-value of 0.03 means:",
              "options": [
                "There is a 3% chance the treatment works",
                "There is a 97% chance the null hypothesis is true",
                "If the null hypothesis were true, there is a 3% probability of obtaining a result at least as extreme as the one observed",
                "The treatment effect size is 3%",
                "The study has 3% power"
              ],
              "answer": "C",
              "explanation": "The p-value is the probability of obtaining the observed result (or a more extreme result) IF the null hypothesis were true. A p-value of 0.03 means: 'Assuming there is no real difference (null hypothesis is true), there is a 3% chance of seeing a result this extreme by chance alone.' If p < alpha (conventionally 0.05), the result is considered statistically significant — we reject the null hypothesis. IMPORTANT: the p-value does NOT tell you the probability that the treatment works, the probability the null hypothesis is true/false, or the size of the treatment effect. Statistical significance ≠ clinical significance — a tiny, clinically irrelevant difference can be statistically significant with a large enough sample size.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 981,
              "stem": "The number needed to treat (NNT) of 20 means:",
              "options": [
                "20 patients will be cured",
                "The treatment works 20% of the time",
                "20 patients need to be treated with the intervention to prevent ONE additional adverse outcome compared to the control",
                "The treatment has a 20% complication rate",
                "The study involved 20 patients"
              ],
              "answer": "C",
              "explanation": "NNT = 20 means you need to treat 20 patients with the intervention (rather than the control/placebo) to prevent one additional adverse outcome. The lower the NNT, the more effective the treatment. NNT = 1 would be a perfect treatment (every patient benefits). NNT = 1/ARR. Example: if a drug reduces hip fracture risk from 10% to 5%, ARR = 5% = 0.05, NNT = 1/0.05 = 20. This means treating 20 patients prevents 1 hip fracture. NNT is the most clinically useful measure of treatment effect because it contextualises the benefit in absolute terms (unlike relative risk reduction which can be misleadingly large with small baseline risks).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 982,
              "stem": "A confidence interval (CI) of 95% for a mean difference of 5mm with a CI of 2-8mm means:",
              "options": [
                "There is a 95% chance the true value is exactly 5mm",
                "The result is not statistically significant",
                "The treatment has exactly 5mm benefit in all patients",
                "The study has 95% power",
                "If the study were repeated many times, 95% of the calculated CIs would contain the true population value"
              ],
              "answer": "E",
              "explanation": "A 95% CI means: if the study were repeated many times with different samples from the same population, 95% of the calculated CIs would contain the true population value. The CI of 2-8mm means we are 95% confident the true mean difference lies between 2mm and 8mm. Since the CI does NOT cross zero, the result IS statistically significant at the 5% level (p <0.05). CI interpretation: (1) if the CI does not include the null value (0 for differences, 1 for ratios) → statistically significant, (2) the WIDTH of the CI indicates PRECISION (narrow = precise, wide = imprecise), (3) the CI provides more information than the p-value alone because it shows the range of plausible effect sizes.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 983,
              "stem": "The relative risk (RR) is calculated in cohort studies. An RR of 2.0 means:",
              "options": [
                "The treatment is twice as effective",
                "The exposed group has twice the risk of developing the outcome compared to the unexposed group",
                "There is no difference between groups",
                "The treatment reduces risk by 50%",
                "The study has a 2% error rate"
              ],
              "answer": "B",
              "explanation": "Relative risk (RR) = incidence in exposed group / incidence in unexposed group. RR = 2.0 means the exposed group has TWICE the risk of developing the outcome compared to the unexposed group. RR = 1.0 = no difference in risk. RR > 1.0 = increased risk in exposed group. RR < 1.0 = decreased risk (protective exposure). RR of 0.5 = exposed group has HALF the risk (50% risk reduction = protective). RR is calculated from cohort studies and RCTs (where incidence can be measured). For case-control studies, use the odds ratio (OR) instead (cannot calculate incidence from case-control design). Relative risk reduction (RRR) = 1 - RR = proportion by which the intervention reduces the event rate compared to control.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Governance",
          "range": "Q984-Q999",
          "questions": [
            {
              "number": 984,
              "stem": "The GMC's four domains of Good Medical Practice that guide doctors' professional conduct are:",
              "options": [
                "Only clinical knowledge matters",
                "Only surgical technique",
                "Only research output",
                "Knowledge, Skills and Performance; Safety and Quality; Communication, Partnership and Teamwork; Maintaining Trust — these domains encompass all aspects of professional practice that the GMC assesses",
                "Only patient satisfaction scores"
              ],
              "answer": "D",
              "explanation": "The GMC's Good Medical Practice (updated 2024) defines the professional standards expected of all doctors registered in the UK. FOUR DOMAINS: (1) KNOWLEDGE, SKILLS AND PERFORMANCE — maintain competence, practice within your scope, keep up to date (CPD), teach and train effectively. (2) SAFETY AND QUALITY — take action if patient safety is at risk, contribute to quality improvement, respond to risks and report incidents, apply evidence-based practice. (3) COMMUNICATION, PARTNERSHIP AND TEAMWORK — communicate effectively, work collaboratively with colleagues, treat patients as partners, obtain informed consent (Montgomery), share information appropriately. (4) MAINTAINING TRUST — be honest and open (Duty of Candour), act with integrity, maintain professional boundaries, don't abuse your professional position. These domains underpin: annual APPRAISAL (all doctors discuss their practice against these domains with an appraiser), REVALIDATION (every 5 years — demonstration to the GMC that you remain fit to practise), and FITNESS TO PRACTISE investigations (when concerns are raised about a doctor).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 985,
              "stem": "Informed consent in the UK requires that the patient:",
              "options": [
                "Has CAPACITY to make the decision, receives adequate INFORMATION about the procedure (including material risks — Montgomery standard), and gives consent VOLUNTARILY without coercion — all three elements must be present",
                "Only signs a form without any discussion",
                "Is told nothing about the procedure",
                "Only agrees verbally without documentation",
                "Is forced to accept the surgeon's recommendation"
              ],
              "answer": "A",
              "explanation": "Valid informed consent requires THREE elements: (1) CAPACITY — the patient has the mental capacity to understand, retain, weigh, and communicate the decision (MCA 2005 — decision-specific, time-specific, presumed unless assessed otherwise). (2) INFORMATION — adequate information is provided: the nature and purpose of the procedure, material risks (Montgomery standard — what a reasonable patient would want to know AND what this particular patient would consider significant), benefits, alternatives (including doing nothing), and expected outcomes. The discussion should be a DIALOGUE (not a one-way lecture). (3) VOLUNTARINESS — consent is given freely, without coercion, undue influence, or pressure from healthcare professionals, family, or others. The patient must feel free to decline. Documentation: the consent form is a RECORD of the discussion (it is not consent itself — the form is evidence, not the consent). The discussion should be documented in the clinical notes (what was discussed, questions asked, patient's understanding). Consent can be withdrawn at ANY time. Emergency treatment without explicit consent: permissible if life-saving and the patient lacks capacity (best interests under MCA).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 986,
              "stem": "Clinical audit differs from research in that audit:",
              "options": [
                "Measures current practice against established standards and implements changes to improve care (a quality improvement cycle, not hypothesis-testing)",
                "Generates new knowledge (that's research)",
                "Requires ethics committee approval in all cases",
                "Is the same as research",
                "Only involves laboratory experiments"
              ],
              "answer": "A",
              "explanation": "Clinical audit is a quality improvement process that measures current clinical practice against defined STANDARDS (guidelines, protocols, best practice) → identifies gaps → implements changes → re-audits to confirm improvement (the AUDIT CYCLE: set standards → collect data → compare performance → implement changes → re-audit). It is fundamentally different from research: RESEARCH generates NEW knowledge (asks 'what should we do?'), while AUDIT measures whether we are DOING what we should already be doing (asks 'are we following best practice?'). Audit does NOT usually require ethics committee approval (it is service evaluation using existing standards, not experimental). It is a mandatory component of clinical governance, annual appraisal, and GMC revalidation. Types: standards-based audit (commonest), significant event audit, peer review, criterion-based audit.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 987,
              "stem": "Never Events in NHS surgery — which of the following is classified as a Never Event?",
              "options": [
                "A surgical site infection (complication, not a Never Event)",
                "Wrong-site surgery (operating on the wrong side, wrong level, or wrong patient — an entirely preventable error with correct safety processes)",
                "Delayed discharge",
                "Post-operative pain",
                "Normal wound healing"
              ],
              "answer": "B",
              "explanation": "Never Events are serious, largely preventable patient safety incidents that should NOT occur if available preventive measures have been properly implemented. In surgery, the key Never Events include: (1) wrong-site surgery (wrong side, wrong level, wrong patient), (2) wrong implant/prosthesis, (3) retained foreign object post-procedure (swab, instrument), (4) wrong route administration of medication. These are NOT complications of surgery (complications like SSI, DVT, or pain can occur despite correct processes). Never Events indicate a SYSTEMS FAILURE — the prevention processes (WHO Surgical Safety Checklist, site marking, time-out, count procedures) were not followed correctly. Reporting: mandatory (via NRLS/Learn from Patient Safety Events — LFPSE). Investigation: thorough root cause analysis (RCA). Duty of Candour applies: the patient must be informed.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 988,
              "stem": "The Bolam test (Bolam v Friern Hospital Management Committee, 1957) established that:",
              "options": [
                "A doctor must always follow the latest research regardless of established practice",
                "Patients must always accept the doctor's recommendation",
                "A doctor is not negligent if they act in accordance with a practice accepted as proper by a RESPONSIBLE BODY of medical opinion (even if other doctors disagree — the 'doctor-centred' standard)",
                "Only the most senior doctor can make decisions",
                "All medical decisions must be made by committee"
              ],
              "answer": "C",
              "explanation": "The Bolam test (1957) established the standard for medical negligence in UK law: a doctor is NOT negligent if they act in accordance with a practice accepted as proper by a RESPONSIBLE BODY of medical practitioners skilled in that particular art — even if another body of opinion would take a different view. This is a 'doctor-centred' standard — the court assesses whether ANY responsible group of doctors would support the action taken. The Bolitho addendum (1997) modified this: the responsible body of opinion must also be LOGICAL and defensible (the court can reject expert opinion if it is not logically supportable). Important: Bolam still applies to treatment/diagnosis decisions. For CONSENT, Montgomery (2015) replaced Bolam with a patient-centred standard (the test is now what a reasonable PATIENT would want to know, not what a reasonable doctor would disclose).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 989,
              "stem": "The NJR (National Joint Registry) is the UK's implant registry. Its primary purpose is:",
              "options": [
                "To advertise implants",
                "Only to record patient demographics",
                "To determine surgeon salaries",
                "To replace clinical trials",
                "To monitor the performance of joint replacement implants and identify poorly performing implants early (post-market surveillance — enabling early detection of higher-than-expected revision rates)"
              ],
              "answer": "E",
              "explanation": "The NJR (established 2003) collects data on ALL hip, knee, shoulder, elbow, and ankle joint replacements performed in England, Wales, Northern Ireland, and the Isle of Man. Primary purpose: POST-MARKET SURVEILLANCE — monitoring real-world implant performance to identify poorly performing implants EARLY (before widespread harm occurs). The ASR MoM hip recall (2010) was partly driven by NJR data showing higher-than-expected revision rates. The NJR provides: (1) implant-specific revision rates (compared to benchmarks), (2) surgeon and unit-level outcomes, (3) outlier identification (implants or units with higher-than-expected revision rates receive ODEP/NJR alerts), (4) national outcome data for service planning and quality improvement. Patients can access their own NJR record. Similar registries exist worldwide: AOANJRR (Australia — the most mature, established 1999), SHAR (Sweden). Registry data has been instrumental in improving arthroplasty outcomes globally.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 990,
              "stem": "The CQC (Care Quality Commission) is the independent regulator of health and social care in England. Its role includes:",
              "options": [
                "Only managing hospital finances",
                "Only performing surgical procedures",
                "Only training medical students",
                "Inspecting, rating, and regulating healthcare providers to ensure they meet fundamental standards of quality and safety",
                "Only researching new treatments"
              ],
              "answer": "D",
              "explanation": "The CQC is the independent regulator of health and adult social care in England. It: (1) registers healthcare providers (hospitals, GP practices, care homes, dental practices), (2) inspects services against fundamental standards (safe, effective, caring, responsive, well-led), (3) rates services (Outstanding, Good, Requires Improvement, Inadequate), (4) takes enforcement action against providers failing to meet standards (warning notices, conditions, suspension, prosecution), and (5) publishes inspection reports publicly (transparency). Following the Francis Report, the CQC's powers were strengthened. The hospital ratings are publicly available and inform patient choice. CQC inspections include assessment of clinical governance, patient safety, staffing, and leadership. The equivalent in Scotland is Healthcare Improvement Scotland (HIS), and in Wales is Healthcare Inspectorate Wales (HIW).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 991,
              "stem": "The Bolam test (1957) established which legal standard in medical practice?",
              "options": [
                "Consent must be informed at all times",
                "All complications must be disclosed",
                "Patient autonomy overrides medical advice",
                "Clinical guidelines are legally binding",
                "A doctor is not negligent if they acted in accordance with a responsible body of medical opinion (standard of care)"
              ],
              "answer": "E",
              "explanation": "The Bolam test (Bolam v Friern Hospital Management Committee, 1957) established that a doctor is not guilty of negligence if they acted in accordance with a practice accepted as proper by a responsible body of medical practitioners skilled in that particular field — even if other doctors would have acted differently. This 'doctor-centred' test has been partially superseded for CONSENT by the Montgomery ruling (2015, patient-centred standard) but remains relevant for TREATMENT decisions. The Bolitho amendment (1998) added that the body of opinion must be capable of withstanding logical analysis.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 992,
              "stem": "Clinical governance is defined as a framework through which NHS organisations are accountable for:",
              "options": [
                "Continuously improving the quality of their services and safeguarding high standards of care",
                "Financial management only",
                "Staff recruitment only",
                "Research output only",
                "Building maintenance"
              ],
              "answer": "A",
              "explanation": "Clinical governance (defined by Scally and Donaldson, 1998) is 'a framework through which NHS organisations are accountable for continuously improving the quality of their services and safeguarding high standards of care by creating an environment in which excellence in clinical care will flourish.' The seven pillars of clinical governance: (1) clinical effectiveness, (2) risk management, (3) patient experience, (4) communication, (5) resource effectiveness, (6) strategic effectiveness, (7) learning effectiveness. Key components include: audit, education/training, clinical effectiveness, risk management, research, information management, patient involvement, and staffing.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 993,
              "stem": "Significant Event Analysis (SEA) in NHS clinical governance involves:",
              "options": [
                "Ignoring adverse events",
                "A structured reflective analysis of a significant clinical event (positive or negative) to identify learning points and implement changes to improve future practice",
                "Only recording events for legal purposes",
                "Publishing all events in journals",
                "Punishing the individuals involved"
              ],
              "answer": "B",
              "explanation": "Significant Event Analysis (SEA), also called Significant Event Audit, is a structured process of reflective learning from significant clinical events — both positive (excellent care, innovative approaches) and negative (complications, near-misses, adverse outcomes). The process: (1) identify the event, (2) gather information (who, what, when, where), (3) hold a team meeting to discuss the event openly (blame-free culture), (4) identify what went well and what could be improved, (5) agree on action points and implement changes, (6) follow up to ensure changes are embedded. SEA is distinct from root cause analysis (RCA — more formal, used for serious incidents) and morbidity and mortality (M&M) meetings (regular departmental review of complications). All contribute to a learning culture within clinical governance. SEA is a mandatory component of medical appraisal/revalidation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 994,
              "stem": "Informed consent for surgery in the UK must include discussion of:",
              "options": [
                "Only the benefits of surgery",
                "Only what the surgeon thinks is important",
                "Only the most common complication",
                "Material risks, benefits, alternatives (including non-operative management), and the option of no treatment — in accordance with the Montgomery ruling",
                "Nothing — verbal agreement is sufficient"
              ],
              "answer": "D",
              "explanation": "Post-Montgomery (2015), informed consent requires discussion of: (1) the nature of the proposed procedure, (2) MATERIAL RISKS (risks a reasonable patient would want to know about, AND risks this particular patient would want to know about), (3) expected BENEFITS, (4) ALTERNATIVE treatments (including different surgical options and non-operative management), and (5) the option of NO treatment and its consequences. The consent process should be a dialogue (not just signing a form), documented in the medical notes, and ideally given in advance of the day of surgery to allow time for reflection. Consent forms are EVIDENCE of the process but are not themselves the consent — consent is the PROCESS of informing and agreeing. Patients can withdraw consent at any time. Emergency situations: treat in the patient's best interests under the doctrine of necessity if consent cannot be obtained.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 995,
              "stem": "The Gillick competence principle applies to:",
              "options": [
                "Adults over 65 with dementia",
                "All patients regardless of age",
                "Children under 16 who demonstrate sufficient understanding and intelligence to consent to treatment without parental consent",
                "Only patients with learning disabilities",
                "Unconscious patients in emergency situations"
              ],
              "answer": "C",
              "explanation": "Gillick competence (from Gillick v West Norfolk, 1986) established that children under 16 who demonstrate sufficient understanding and intelligence to fully understand the proposed treatment can give valid consent WITHOUT parental consent. The assessment is decision-specific — a child may be Gillick competent for one decision but not another. However, if a Gillick-competent child REFUSES treatment that is in their best interests, a person with parental responsibility or the court CAN override the refusal (unlike adults with capacity, whose refusal must be respected). Fraser guidelines specifically relate to contraceptive advice for under-16s.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 996,
              "stem": "Clinical governance encompasses which broad areas?",
              "options": [
                "Only financial management",
                "A framework including clinical effectiveness, audit, risk management, education/training, patient experience, information management, and staffing — ensuring quality improvement in healthcare delivery",
                "Only risk management",
                "Only staff training",
                "Only infection control"
              ],
              "answer": "B",
              "explanation": "Clinical governance is the system through which NHS organisations are accountable for continuously improving the quality of their services and safeguarding high standards of care. Key pillars include: (1) clinical effectiveness (evidence-based practice, guidelines), (2) clinical audit, (3) risk management (incident reporting, root cause analysis), (4) education and training (CPD, appraisal, revalidation), (5) patient and public involvement (patient experience, complaints), (6) information management (data quality, confidentiality), (7) staffing and staff management. It was introduced following the Bristol heart scandal (1998) and further strengthened after the Francis Inquiry (Mid Staffordshire, 2013).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 997,
              "stem": "The purpose of the National Joint Registry (NJR) is to:",
              "options": [
                "Replace clinical audit entirely",
                "Only track surgeon performance",
                "Only record patient demographics",
                "Regulate pharmaceutical companies",
                "Monitor outcomes of joint replacement surgery across the UK (hip, knee, shoulder, elbow, ankle), identify poorly performing implants, and improve patient safety"
              ],
              "answer": "E",
              "explanation": "The NJR collects data on all joint replacement procedures performed in England, Wales, Northern Ireland, and the Isle of Man (Scotland has the Scottish Arthroplasty Project). Its purposes: (1) monitor outcomes (revision rates, survival) for implants and procedures, (2) identify outlier implants with higher than expected failure rates (e.g., NJR flagged ASR hip resurfacing leading to global recall), (3) benchmark individual surgeon and hospital performance, (4) inform patients and surgeons to support shared decision-making, and (5) provide data for research and service improvement. The NJR has been instrumental in identifying problematic implants (MoM hips, poorly performing stems/cups) before they cause widespread harm. ODEP (Orthopaedic Data Evaluation Panel) rates implants based on NJR data — ≥10A rating = ≥90% survival at 10 years.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 998,
              "stem": "Revalidation by the GMC requires UK doctors to demonstrate fitness to practise through:",
              "options": [
                "Passing an exam every year",
                "No ongoing requirements after initial registration",
                "Annual appraisal (usually 5 appraisals over a 5-year cycle) covering supporting information demonstrating continuing fitness to practise",
                "Only attending one conference per year",
                "Completing one audit in their lifetime"
              ],
              "answer": "C",
              "explanation": "GMC revalidation requires all licensed UK doctors to demonstrate their fitness to practise through annual appraisal and a 5-yearly revalidation cycle. The supporting information typically includes: (1) CPD (continuing professional development — educational activities), (2) quality improvement (audit, quality improvement projects), (3) significant events (reflection on cases/incidents), (4) colleague and patient feedback (multi-source feedback/360° appraisal), (5) review of complaints and compliments, (6) demonstration of working within Good Medical Practice framework. The Responsible Officer (typically the medical director) makes a recommendation to the GMC about whether the doctor should be revalidated. Failure to engage with revalidation can lead to loss of licence to practise.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 999,
              "stem": "The Francis Report (2013) into failures at Mid Staffordshire NHS Foundation Trust led to which major change in NHS practice?",
              "options": [
                "Introduction of the statutory Duty of Candour, strengthened clinical governance, increased nursing ratios, and focus on patient safety culture",
                "No changes were implemented",
                "Only changes to surgical technique",
                "Reduction in hospital beds",
                "Only financial restructuring"
              ],
              "answer": "A",
              "explanation": "The Francis Report (Robert Francis QC, 2013) investigated the catastrophic failings at Mid Staffordshire NHS Foundation Trust (2005-2009), where patients suffered appalling care resulting in an estimated 400-1200 excess deaths. Key findings: culture of tolerating poor standards, bullying, target-driven management prioritising finances over patients, failure to listen to patient complaints, and inadequate regulatory oversight. Major changes implemented: (1) Statutory Duty of Candour (Regulation 20 — mandatory disclosure of patient safety incidents), (2) strengthened CQC regulation, (3) Fit and Proper Person Test for NHS directors, (4) emphasis on compassionate care and patient safety culture, (5) increased nursing staffing ratios, (6) NHS values and principles ('patients first and foremost'). It fundamentally reshaped NHS governance and safety culture.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Landmark Trials",
          "range": "Q1000-Q1008",
          "questions": [
            {
              "number": 1000,
              "stem": "The PROFHER trial on proximal humerus fractures demonstrated that:",
              "options": [
                "All proximal humerus fractures should be operated on",
                "Intramedullary nailing is the gold standard for all proximal humerus fractures",
                "Only reverse shoulder arthroplasty should be used",
                "Surgical treatment (plating or hemiarthroplasty) was NOT superior to non-operative treatment for displaced proximal humerus fractures in patients ≥65 years",
                "Fractures always heal without intervention"
              ],
              "answer": "D",
              "explanation": "The PROFHER trial (2015, UK multicentre pragmatic RCT) randomised patients aged ≥65 years with displaced proximal humerus fractures involving the surgical neck to surgical treatment (either ORIF with locking plate or hemiarthroplasty — surgeon's choice) vs non-operative treatment (sling immobilisation followed by physiotherapy). Key finding: there was NO clinically relevant difference in patient-reported outcomes (Oxford Shoulder Score) at 6 months, 12 months, or 2 years between surgical and non-operative groups. This challenged the prevailing practice of routinely operating on displaced proximal humerus fractures in the elderly. The trial influenced practice: increased non-operative management of these fractures, particularly in lower-demand elderly patients. Limitations: did not include highly comminuted 4-part fractures or fracture-dislocations (most severe patterns).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1001,
              "stem": "The DRAFFT trial (2014) on distal radius fractures demonstrated that:",
              "options": [
                "K-wire fixation is inferior to volar locking plate in all outcomes",
                "Only casting is acceptable",
                "External fixation is the gold standard",
                "Distal radius fractures always need ORIF",
                "Volar locking plate fixation was NOT superior to K-wire fixation for dorsally displaced distal radius fractures in adults at 12 months (despite being more expensive)"
              ],
              "answer": "E",
              "explanation": "The DRAFFT trial (2014, UK multicentre RCT) compared volar locking plate fixation vs percutaneous K-wire fixation for dorsally displaced distal radius fractures in adults. Key finding: there was NO significant difference in the primary outcome (Patient-Rated Wrist Evaluation, PRWE) at 12 months. Volar locking plate was significantly MORE EXPENSIVE. The DRAFFT-2 trial (2022) subsequently compared surgical fixation (plate or K-wire) vs cast immobilisation alone for the same fractures — finding no significant difference in patient-reported outcomes at 12 months. These trials have significantly changed practice: more conservative management of distal radius fractures, and K-wires preferred over expensive locking plates when surgery is indicated. The combined DRAFFT evidence supports a more non-operative approach for many dorsally displaced distal radius fractures.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1002,
              "stem": "The HEALTH trial (2020) on displaced femoral neck fractures showed that:",
              "options": [
                "Hemiarthroplasty is always superior to THA",
                "THA resulted in a lower secondary procedure rate at 24 months compared to hemiarthroplasty for displaced femoral neck fractures in patients ≥50 years (supporting THA for fit/active patients)",
                "DHS is the best treatment for all NOF fractures",
                "No surgery is needed for displaced NOF fractures",
                "External fixation is preferred"
              ],
              "answer": "B",
              "explanation": "The HEALTH trial (2020, international multicentre RCT, >1,400 patients) compared THA vs hemiarthroplasty for displaced femoral neck fractures in patients ≥50 years. Key findings: (1) THA had a significantly LOWER secondary procedure rate (reoperation) at 24 months compared to hemiarthroplasty (5.8% vs 8.8% — THA reduced the need for revision/reoperation by ~34%). (2) Functional outcomes (WOMAC) were similar at 24 months (no significant difference in overall function/pain). (3) THA had a higher dislocation rate but fewer acetabular erosions/revisions. Interpretation: THA is preferred for ACTIVE, COGNITIVELY INTACT patients with displaced intracapsular NOF fractures (lower reoperation rate justifies the slightly higher dislocation risk). Hemiarthroplasty remains appropriate for patients with reduced mobility, cognitive impairment, or limited life expectancy (simpler surgery, shorter operating time).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1003,
              "stem": "The SPORT trial (Spine Patient Outcomes Research Trial) on lumbar disc herniation demonstrated that:",
              "options": [
                "Both surgical discectomy and non-operative treatment improved symptoms over 2 years, but surgery provided faster and greater improvement in pain and function — though the difference narrowed over time",
                "Surgery is always superior to non-operative treatment with no exceptions",
                "Non-operative treatment is always superior",
                "Surgery made all patients worse",
                "There is no treatment for disc herniation"
              ],
              "answer": "A",
              "explanation": "The SPORT trial (2006, US multicentre, largest RCT for lumbar disc herniation) compared surgical discectomy vs non-operative treatment (physiotherapy, education, epidural injections as needed). Key findings: (1) BOTH groups improved significantly over 2 years (important — many disc herniations improve without surgery). (2) The surgical group had FASTER and GREATER improvement in pain and function (particularly in the first 3-6 months). (3) The difference NARROWED over time (at 4 years, both groups had similar outcomes — suggesting natural history of disc resorption plays a major role). (4) Significant crossover: ~40% of the non-operative group crossed to surgery, and ~40% of the surgical group didn't have surgery (making ITT analysis difficult — as-treated analysis showed larger surgical benefit). Implication: surgery is beneficial for faster symptom relief but many patients improve without it. Surgery is indicated for: failed adequate conservative treatment (6-12 weeks), progressive neurological deficit, or cauda equina syndrome.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1004,
              "stem": "The NICE Hip Fracture guideline (CG124/NG228) — which statement best summarises the key recommendations?",
              "options": [
                "No specific recommendations exist",
                "Only surgical timing is addressed",
                "Surgery within 36 hours, orthogeriatric co-management, early mobilisation (day after surgery), falls and bone health assessment, and multidisciplinary rehabilitation — with specific guidance on fixation method based on fracture type and patient factors",
                "Only fixation type is recommended",
                "Only rehabilitation is covered"
              ],
              "answer": "C",
              "explanation": "The NICE hip fracture guideline provides comprehensive, evidence-based recommendations across the entire patient pathway: (1) TIMING: surgery within 36 hours of admission (not arrival — but as early as possible). (2) ANAESTHESIA: spinal preferred over GA (lower mortality evidence). (3) FIXATION: intracapsular undisplaced → cannulated screws. Intracapsular displaced → THA (for fit/active/cognitively intact) or hemiarthroplasty (for less active/cognitive impairment). Extracapsular stable → DHS. Extracapsular unstable/subtrochanteric → IM nail. (4) CEMENTED stems: preferred for arthroplasty (lower peri-operative fracture risk, lower mortality vs uncemented in elderly). (5) ORTHOGERIATRIC co-management: from admission throughout the hospital stay. (6) MOBILISATION: day after surgery (ideally day of surgery). (7) FALLS ASSESSMENT + BONE HEALTH: DEXA not needed (fracture = osteoporosis → treat). (8) MULTIDISCIPLINARY REHABILITATION. (9) BPT (Best Practice Tariff): financial incentive for meeting key standards. The guideline has significantly reduced hip fracture mortality and improved outcomes across the NHS.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1005,
              "stem": "The PROFHER trial (PROximal Fracture of the Humerus: Evaluation by Randomisation) concluded that:",
              "options": [
                "All proximal humerus fractures should be operated on",
                "Surgical fixation is superior to non-operative management for displaced proximal humerus fractures",
                "Only 4-part fractures need surgery",
                "Non-operative management produced similar functional outcomes to surgical fixation for displaced proximal humerus fractures in adults",
                "Reverse TSA is the gold standard for all proximal humerus fractures"
              ],
              "answer": "D",
              "explanation": "The PROFHER trial (2015, UK multicentre RCT) found no significant difference in patient-reported functional outcomes between surgical treatment (ORIF or hemiarthroplasty) and non-operative management (sling and physiotherapy) for displaced proximal humerus fractures in adults at 2 years. This landmark study changed practice — many more proximal humerus fractures are now managed non-operatively. However, the trial has been criticised for: including a heterogeneous fracture population, not separately analysing 4-part fractures, and potential underpowering for subgroup analysis.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1006,
              "stem": "The DRAFFT trial (Distal Radius Acute Fracture Fixation Trial) compared:",
              "options": [
                "Cast treatment vs external fixation",
                "Intramedullary nailing vs plating",
                "Conservative vs operative for hip fractures",
                "Aspirin vs LMWH for thromboprophylaxis",
                "K-wire fixation vs volar locking plate fixation for distal radius fractures"
              ],
              "answer": "E",
              "explanation": "The DRAFFT trial (2014, UK multicentre RCT) compared K-wire fixation vs volar locking plate (VLP) fixation for unstable distal radius fractures. The main finding: no significant difference in patient-reported functional outcomes (PRWE score) at 12 months between the two groups. VLP provided better radiographic parameters but this did not translate to better clinical outcomes. VLP was more expensive. This challenged the widespread adoption of VLP as the default fixation method. DRAFFT-2 extended follow-up confirmed similar outcomes at 5 years.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1007,
              "stem": "The COTS (Canadian Orthopaedic Trauma Society) trial on clavicle fractures showed that:",
              "options": [
                "Operative fixation (plating) of displaced midshaft clavicle fractures resulted in improved functional outcomes, lower non-union rates, and higher patient satisfaction compared to non-operative treatment",
                "All clavicle fractures should be treated non-operatively",
                "Operative and non-operative treatment had identical outcomes",
                "Clavicle fractures never need follow-up",
                "K-wire fixation is superior to plating"
              ],
              "answer": "A",
              "explanation": "The COTS trial (2007, Canadian multicentre RCT) compared primary plate fixation vs non-operative treatment (sling) for completely displaced midshaft clavicle fractures. Key findings: the operative group had significantly better shoulder function (DASH scores), lower non-union rates (2% vs 15%), lower malunion/symptomatic malunion rates, and higher patient satisfaction at 1 year. This challenged the traditional teaching that 'all clavicle fractures should be treated non-operatively' and increased the rate of operative fixation for displaced midshaft fractures. However, not ALL displaced clavicle fractures need surgery — operative indications: >2cm shortening, skin tenting, open fracture, floating shoulder, neurovascular compromise, polytrauma, and patient preference (athletes, manual workers).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1008,
              "stem": "The CRISTAL trial (2023) provided evidence that for VTE prophylaxis after hip and knee arthroplasty:",
              "options": [
                "LMWH is far superior to aspirin",
                "Aspirin (100mg daily) was non-inferior to LMWH (enoxaparin) for VTE prophylaxis",
                "No VTE prophylaxis is needed",
                "Warfarin is the best option",
                "Mechanical prophylaxis alone is sufficient"
              ],
              "answer": "B",
              "explanation": "The CRISTAL trial (2023, Australian multicentre RCT) demonstrated that low-dose aspirin (100mg daily for 35 days after THA, 14 days after TKA) was non-inferior to enoxaparin for VTE prophylaxis following hip and knee arthroplasty. This has significant implications: aspirin is cheaper, oral (better patient compliance), and has fewer bleeding complications than LMWH. NICE has not yet fully adopted aspirin as equivalent to LMWH but it is increasingly accepted, particularly alongside mechanical prophylaxis and early mobilisation. The trial supports aspirin as a valid alternative, not necessarily as the only option.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Research Methods",
          "range": "Q1009-Q1016",
          "questions": [
            {
              "number": 1009,
              "stem": "Blinding in an RCT — a 'double-blind' study means:",
              "options": [
                "Only the surgeon is blinded",
                "Only the patient is blinded",
                "BOTH the patient AND the outcome assessor are blinded to the treatment allocation (ideally the treating clinician too, though impossible in surgical trials where the surgeon knows the procedure)",
                "Nobody is blinded",
                "Only the statistician is blinded"
              ],
              "answer": "C",
              "explanation": "Double-blinding means BOTH the patient AND the outcome assessor (the person measuring the results) do not know which treatment group the patient is in. In pharmaceutical trials: the patient, clinician, and assessor can all be blinded (using identical-looking placebo pills). In SURGICAL trials: the operating surgeon CANNOT be blinded (they know what procedure they performed — this is an inherent limitation of surgical RCTs). However, the patient can be blinded (same wound, same dressing — sham surgery controls, though ethically controversial), and the outcome assessor SHOULD always be blinded (independent assessor who doesn't know the group allocation). Blinding reduces: performance bias (clinician treats groups differently) and detection bias (assessor interprets outcomes differently). Unblinded studies overestimate treatment effects by ~17%.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1010,
              "stem": "The PICO framework for formulating a clinical research question stands for:",
              "options": [
                "Patient, Intervention, Cost, Outcome",
                "Problem, Investigation, Conclusion, Opinion",
                "Practice, Imaging, Classification, Operation",
                "Patient/Population, Intervention, Comparison, Outcome",
                "Pathology, Incidence, Comorbidity, Observation"
              ],
              "answer": "D",
              "explanation": "PICO is the standard framework for formulating a focused, answerable clinical research question: P = Patient or Population (who are you studying? — e.g., adults >65 with displaced intracapsular femoral neck fracture). I = Intervention (what treatment/exposure are you investigating? — e.g., total hip arthroplasty). C = Comparison (what are you comparing against? — e.g., hemiarthroplasty). O = Outcome (what are you measuring? — e.g., functional outcome at 12 months, mortality, revision rate). A well-structured PICO question is essential for: (1) designing a study, (2) performing a literature search (each PICO element becomes a search term), (3) critically appraising evidence, and (4) formulating clinical guidelines. Example: 'In elderly patients with displaced intracapsular NOF fracture (P), does THA (I) compared to hemiarthroplasty (C) result in better functional outcomes at 1 year (O)?'",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1011,
              "stem": "Selection bias in a clinical study occurs when:",
              "options": [
                "The participants selected for the study are NOT representative of the target population, or there are systematic differences between comparison groups at baseline",
                "Random chance produces a significant result",
                "The outcome assessor is not blinded",
                "The study has a large sample size",
                "The p-value is exactly 0.05"
              ],
              "answer": "A",
              "explanation": "Selection bias occurs when the participants enrolled in a study do not accurately represent the target population, or when there are systematic differences between comparison groups at baseline. This can distort results and limit generalisability. Types of selection bias: (1) Sampling bias — the recruitment method systematically excludes certain groups (e.g., studying hospital patients only for a condition that is mostly managed in primary care). (2) Volunteer bias — participants who volunteer may differ from those who don't (healthier, more motivated). (3) Attrition bias — differential loss to follow-up between groups (those lost may differ systematically from those retained). (4) Berkson bias — hospitalised patients may have different disease associations than the general population. Prevention: randomisation (in RCTs — distributes known and unknown confounders equally), clear inclusion/exclusion criteria, adequate follow-up, and ITT analysis (for attrition). Selection bias is particularly problematic in observational studies.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1012,
              "stem": "The level of evidence hierarchy — which study design provides the highest level of evidence?",
              "options": [
                "Expert opinion (Level V)",
                "Systematic review and meta-analysis of RCTs (Level I — the highest level of evidence)",
                "Case series (Level IV)",
                "Retrospective cohort (Level III)",
                "Prospective RCT (Level I-II)"
              ],
              "answer": "B",
              "explanation": "The evidence hierarchy (highest to lowest): Level I: systematic reviews and meta-analyses of high-quality RCTs (strongest evidence — synthesise multiple RCTs, large combined sample size, reduced random error). Individual high-quality RCTs with narrow CI are also Level I. Level II: lesser-quality RCTs (significant crossover, losses to follow-up), prospective comparative studies. Level III: case-control studies, retrospective comparative studies. Level IV: case series (no comparison group). Level V: expert opinion, case reports, bench research. Systematic reviews are at the TOP because they: (1) comprehensively identify ALL relevant studies, (2) assess quality/bias of included studies, (3) quantitatively combine results (meta-analysis — increased statistical power), (4) provide the most reliable estimate of treatment effect. However: a systematic review is only as good as the included studies (systematic review of poor RCTs = poor evidence). PRISMA guidelines: standardised reporting for systematic reviews.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1013,
              "stem": "Intention-to-treat (ITT) analysis in an RCT means:",
              "options": [
                "Only analysing patients who completed treatment as planned (that's per-protocol)",
                "Excluding patients who crossed over to the other group",
                "Only analysing patients with perfect compliance",
                "Analysing only the last 50% of enrolled patients",
                "Analysing ALL patients in the groups to which they were ORIGINALLY RANDOMISED, regardless of whether they completed, switched, or dropped out of treatment"
              ],
              "answer": "E",
              "explanation": "ITT analysis: every patient is analysed in the group to which they were ORIGINALLY RANDOMISED — regardless of: (1) whether they actually RECEIVED the allocated treatment, (2) whether they COMPLETED the treatment, (3) whether they CROSSED OVER to the other group, (4) whether they were LOST to follow-up (their last known data is included). Why ITT is important: it PRESERVES THE RANDOMISATION (the whole point of randomisation is to balance known and unknown confounders — if you start excluding patients, you break this balance and introduce selection bias). ITT gives a CONSERVATIVE estimate (tends to underestimate the treatment effect — because non-compliant patients dilute the result). Per-protocol (PP) analysis: only includes patients who COMPLETED treatment as planned — gives the 'best-case' estimate but is prone to bias (those who complete treatment may differ systematically from those who don't). CONSORT: recommends ITT as the PRIMARY analysis, with PP as a secondary/sensitivity analysis.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1014,
              "stem": "A systematic review differs from a narrative review in that a systematic review:",
              "options": [
                "Is based on the author's personal opinion and selected literature",
                "Does not require literature searching",
                "Is always shorter than a narrative review",
                "Uses a pre-defined, reproducible search strategy, explicit inclusion/exclusion criteria, and systematic data extraction and synthesis",
                "Cannot include randomised controlled trials"
              ],
              "answer": "D",
              "explanation": "A systematic review uses a rigorous, pre-defined methodology: (1) focused research question (PICO format), (2) comprehensive and reproducible literature search strategy (multiple databases), (3) explicit inclusion/exclusion criteria, (4) quality assessment of included studies (risk of bias), (5) systematic data extraction, and (6) synthesis of results (narrative or quantitative/meta-analysis). A narrative review is based on the author's selected reading and interpretation — it is susceptible to selection bias and is less reproducible. Systematic reviews with meta-analysis provide the highest level of evidence (Level I). PRISMA guidelines standardise reporting of systematic reviews.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1015,
              "stem": "PICO stands for:",
              "options": [
                "Prognosis, Indication, Cost, Observation",
                "Placebo, Intention, Control, Observation",
                "Patient, Intervention, Comparison, Outcome",
                "Patient, Investigation, Criteria, Outcome",
                "Prevalence, Incidence, Cost, Odds"
              ],
              "answer": "C",
              "explanation": "PICO is the framework for formulating a clinical research question: P = Patient/Population/Problem (who?). I = Intervention (what treatment/exposure?). C = Comparison/Control (compared to what?). O = Outcome (what result is measured?). Example: 'In patients with displaced intracapsular NOF fractures (P), does THA (I) compared with hemiarthroplasty (C) improve functional outcomes at 1 year (O)?' A well-constructed PICO question guides the systematic review search strategy, study design, and outcome selection. It is the foundation of evidence-based medicine.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1016,
              "stem": "Confounding in a clinical study occurs when:",
              "options": [
                "The sample size is too large",
                "The study is blinded",
                "A third variable is associated with BOTH the exposure AND the outcome, distorting the true relationship between them",
                "Random chance produces a significant result",
                "The questionnaire is too short"
              ],
              "answer": "C",
              "explanation": "A confounding variable is associated with both the exposure (risk factor) and the outcome (disease) and can distort the apparent relationship between them if not controlled for. Example: if studying whether alcohol causes osteoporosis, SMOKING could be a confounder (it is associated with both alcohol use and osteoporosis, and could explain some of the apparent relationship). Methods to control confounding: (1) Randomisation (in RCTs — distributes both known and unknown confounders equally), (2) Restriction (limit study population), (3) Matching (match cases and controls on potential confounders), (4) Stratification (analyse subgroups separately), (5) Multivariable analysis (regression models adjusting for confounders). Randomisation is the ONLY method that controls for UNKNOWN confounders.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Ethics",
          "range": "Q1017-Q1020",
          "questions": [
            {
              "number": 1017,
              "stem": "Gillick competence in UK law applies to children under 16 and states that:",
              "options": [
                "Children under 16 can never consent to medical treatment",
                "Only parents can ever consent for children",
                "Children must always wait until age 18",
                "A child under 16 who demonstrates sufficient understanding and intelligence to fully comprehend the proposed treatment can consent to it WITHOUT parental permission",
                "Gillick only applies to surgical procedures"
              ],
              "answer": "D",
              "explanation": "Gillick competence (from Gillick v West Norfolk and Wisbech AHA, 1986) established that children under 16 can consent to medical treatment IF they demonstrate SUFFICIENT UNDERSTANDING AND INTELLIGENCE to fully comprehend the proposed treatment, its risks, benefits, and alternatives. The assessment is DECISION-SPECIFIC — a child may be Gillick competent for one decision (e.g., a simple procedure) but not for another (e.g., complex surgery). Key points: (1) Gillick competence allows a child to CONSENT (say yes) but they CANNOT refuse treatment that is in their best interests if parents and doctors agree it is needed (Fraser guidelines — the law is asymmetric). (2) The assessing clinician documents their assessment of competence. (3) In orthopaedics: relevant for adolescent patients consenting to procedures (e.g., 14-year-old consenting to ACL reconstruction). For patients aged 16-17: presumed competent under the Family Law Reform Act 1969 (same rights as adults to consent, but refusal can still be overridden by parents/courts).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1018,
              "stem": "The Mental Capacity Act 2005 (England and Wales) — a patient is assumed to HAVE capacity unless:",
              "options": [
                "They are over 65",
                "They have any medical condition",
                "They disagree with the doctor's recommendation",
                "They have a learning disability (this alone does not mean they lack capacity)",
                "It is established on the balance of probabilities that they lack capacity to make the specific decision (capacity is assessed for each decision individually)"
              ],
              "answer": "E",
              "explanation": "The Mental Capacity Act 2005 establishes five key principles: (1) PRESUMPTION OF CAPACITY — every adult is assumed to have capacity unless proven otherwise. (2) Individuals must be given ALL PRACTICABLE HELP to make their own decision before being assessed as lacking capacity. (3) An UNWISE decision does not equal lack of capacity (a patient can make decisions others disagree with). (4) Decisions made on behalf of those lacking capacity must be in their BEST INTERESTS. (5) The LEAST RESTRICTIVE option must be chosen. Capacity assessment (2-stage test): Stage 1 — does the person have an impairment or disturbance of mind/brain function? Stage 2 — does this impairment prevent them from making the specific decision? (Can they: understand the information, retain it, use/weigh it, communicate their decision?) Capacity is DECISION-SPECIFIC and TIME-SPECIFIC — a patient may have capacity for some decisions but not others, and capacity can fluctuate.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1019,
              "stem": "The Duty of Candour (statutory, Regulation 20 of the Health and Social Care Act 2014) requires healthcare providers to:",
              "options": [
                "Inform patients (or their families) when a patient safety incident has resulted in moderate or severe harm or death — including a sincere apology (which is NOT an admission of liability), a factual account of what happened, and support going forward",
                "Only inform patients of positive outcomes",
                "Hide all adverse events from patients",
                "Only report to the GMC without informing the patient",
                "Wait for the patient to discover the error themselves"
              ],
              "answer": "A",
              "explanation": "The statutory Duty of Candour (introduced following the Francis Report recommendations) requires healthcare organisations to: (1) NOTIFY the patient (or their representative/family) as soon as reasonably practicable after becoming aware of a notifiable patient safety incident. (2) Provide a truthful ACCOUNT of all the facts known at that time. (3) Offer a sincere APOLOGY — importantly, an apology is NOT an admission of legal liability (this is enshrined in law to encourage openness). (4) Provide SUPPORT to the patient. (5) Provide a written FOLLOW-UP notification. A 'notifiable safety incident': one that results in moderate harm, severe harm, or death. The professional duty of candour (GMC/NMC): applies to ALL patient safety incidents regardless of severity — every healthcare professional has a personal duty to be open and honest with patients. Failure to comply: CQC can take enforcement action against the organisation; GMC can take action against individual practitioners.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1020,
              "stem": "The Montgomery ruling (2015) on informed consent established that:",
              "options": [
                "Bolam test applies to consent (doctor-centred)",
                "Doctors must disclose all risks that a REASONABLE PATIENT would consider significant, AND any risk that THIS PARTICULAR patient would consider significant given their individual circumstances — a patient-centred standard replacing Bolam for consent",
                "Only surgical risks need disclosure",
                "Written consent is never required",
                "The doctor decides what to disclose without patient input"
              ],
              "answer": "B",
              "explanation": "Montgomery v Lanarkshire Health Board (2015, UK Supreme Court) fundamentally changed the consent standard in the UK from a DOCTOR-CENTRED test (Bolam — 'what would a reasonable doctor disclose?') to a PATIENT-CENTRED test: the doctor must disclose: (1) all MATERIAL risks — those that a REASONABLE PATIENT in the patient's position would consider significant, AND (2) any risk that THIS particular patient would consider significant given their specific circumstances, values, and concerns. This means: the disclosure requirement varies by patient. A professional musician consenting to hand surgery needs different information than a retired patient (the risk of finger stiffness is material to the musician but may not be to the retiree). The ruling also established that alternative treatments must be discussed. Montgomery does NOT require disclosure of every conceivable risk — only MATERIAL ones. Bolam STILL applies to diagnosis and treatment decisions — Montgomery only replaced Bolam for CONSENT.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Forest Plot",
          "range": "Q1021",
          "questions": [
            {
              "number": 1021,
              "stem": "On a forest plot in a meta-analysis, if the confidence interval of a study crosses the line of no effect (1.0 for odds ratios), this means:",
              "options": [
                "The study shows a statistically significant result",
                "The study is biased",
                "The study should be excluded from the analysis",
                "The study result is NOT statistically significant",
                "The meta-analysis is invalid"
              ],
              "answer": "D",
              "explanation": "In a forest plot, each study is represented by a square (proportional to study weight) and a horizontal line (95% confidence interval). If the CI crosses the line of no effect (1.0 for OR/RR, or 0 for mean difference), the result is NOT statistically significant (i.e., we cannot exclude the possibility that the true effect is zero/null). The diamond at the bottom represents the pooled (combined) estimate — if it crosses the line of no effect, the overall meta-analysis result is not significant.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Bias",
          "range": "Q1022",
          "questions": [
            {
              "number": 1022,
              "stem": "Selection bias in a clinical trial can be minimised by:",
              "options": [
                "Blinding the patients only",
                "Using a large sample size only",
                "Adequate randomisation and allocation concealment",
                "Performing intention-to-treat analysis",
                "Using validated outcome measures"
              ],
              "answer": "C",
              "explanation": "Selection bias occurs when the groups being compared are systematically different at baseline. It is minimised by proper randomisation (allocating participants randomly to groups) and allocation concealment (ensuring the person enrolling participants does not know which group is next — e.g., sealed opaque envelopes, telephone randomisation). Blinding reduces performance and detection bias. ITT analysis reduces attrition bias. Large sample size reduces random error but not systematic bias.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Survival Analysis",
          "range": "Q1023",
          "questions": [
            {
              "number": 1023,
              "stem": "The NICE benchmark for hip and knee implant survival is:",
              "options": [
                "70% at 5 years",
                "90% at 10 years",
                "80% at 5 years",
                "95% at 10 years",
                "100% at 5 years"
              ],
              "answer": "B",
              "explanation": "NICE guidance (ODEP benchmarking) states that hip and knee implants should demonstrate ≥90% survivorship at 10 years (or projected to achieve this based on available data). Implants that do not meet this benchmark should not routinely be used. The National Joint Registry (NJR) monitors UK implant performance. This benchmark has driven out poorly performing implants and standardised arthroplasty practice. Some high-performing implants achieve >95% at 15-20 years.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Study Design",
          "range": "Q1024-Q1030",
          "questions": [
            {
              "number": 1024,
              "stem": "The highest level of evidence in the evidence hierarchy is:",
              "options": [
                "Systematic review and meta-analysis of RCTs",
                "Expert opinion",
                "Case series",
                "Cohort study",
                "Randomised controlled trial"
              ],
              "answer": "A",
              "explanation": "The evidence hierarchy (highest to lowest): Level I = systematic review/meta-analysis of RCTs, or individual high-quality RCT. Level II = lesser-quality RCT, prospective cohort study. Level III = case-control study, retrospective cohort. Level IV = case series. Level V = expert opinion, case reports. Systematic reviews synthesise multiple RCTs using rigorous methodology, providing the strongest evidence for clinical decision-making.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1025,
              "stem": "In a case-control study, the measure of association used is:",
              "options": [
                "Relative risk",
                "Absolute risk reduction",
                "Number needed to treat",
                "Hazard ratio",
                "Odds ratio"
              ],
              "answer": "E",
              "explanation": "Case-control studies compare patients WITH the disease (cases) to those WITHOUT (controls) and look backward to assess exposure. They calculate the odds ratio (OR) because the true incidence (and therefore relative risk) cannot be calculated from a case-control design (cases are selected based on outcome, not randomly sampled from a population). Cohort studies follow exposed and unexposed groups forward and can calculate relative risk (RR). RCTs also use RR (or hazard ratio for time-to-event data).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1026,
              "stem": "The SPORT trial (Spine Patient Outcomes Research Trial) provided important evidence for the surgical management of:",
              "options": [
                "Cervical myelopathy",
                "Adolescent idiopathic scoliosis",
                "Thoracolumbar burst fractures",
                "Spinal cord injury",
                "Lumbar disc herniation, spinal stenosis, and degenerative spondylolisthesis"
              ],
              "answer": "E",
              "explanation": "The SPORT trial was a landmark multicentre prospective study comparing surgical vs non-operative treatment for three common lumbar spine conditions: (1) lumbar disc herniation (discectomy vs non-operative — surgery provided faster improvement but similar long-term outcomes by 4-8 years), (2) spinal stenosis (decompressive surgery provided significant sustained benefit over non-operative treatment), (3) degenerative spondylolisthesis (decompression + fusion superior to non-operative treatment at 4 years). It included both randomised and observational cohorts due to high crossover rates in the randomised arms.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1027,
              "stem": "A cross-sectional study is also known as a prevalence study. It measures:",
              "options": [
                "Exposure and outcome at a SINGLE POINT IN TIME (snapshot) in a defined population",
                "Incidence of disease over time",
                "Treatment effect in a controlled setting",
                "Long-term survival",
                "Only genetic factors"
              ],
              "answer": "A",
              "explanation": "A cross-sectional study measures both exposure and outcome at a SINGLE POINT IN TIME (snapshot study) in a defined population. It can determine PREVALENCE (proportion of the population with the condition at that moment) but CANNOT determine INCIDENCE (new cases over time) or establish CAUSATION (because exposure and outcome are measured simultaneously — temporal relationship cannot be established). It can identify ASSOCIATIONS (correlations between exposure and outcome). Advantages: quick, inexpensive, can study multiple outcomes. Disadvantages: cannot establish causation (no temporality), susceptible to prevalence bias (only captures survivors/chronic cases, misses those who died or recovered). Example: a survey of 1000 orthopaedic patients measuring current BMI and current knee OA status → can show association but not causation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1028,
              "stem": "A cohort study follows a group of people over time to determine whether an exposure leads to an outcome. A prospective cohort is considered what level of evidence?",
              "options": [
                "Level I",
                "Level II",
                "Level III (prognostic study Level II)",
                "Level IV",
                "Level V"
              ],
              "answer": "C",
              "explanation": "Prospective cohort studies are generally Level II-III evidence (depending on the specific classification system used and the clinical question). For treatment questions: Level II evidence comes from individual RCTs or prospective cohorts with dramatic effect. For prognosis questions: prospective cohort studies are Level II. Advantages of cohort studies: can establish temporal relationship (exposure precedes outcome), calculate incidence and relative risk, study multiple outcomes from one exposure. Disadvantages: expensive, time-consuming, loss to follow-up, cannot prove causation (confounding). Retrospective cohort studies are lower quality than prospective.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1029,
              "stem": "Intention-to-treat (ITT) analysis in an RCT means:",
              "options": [
                "Only patients who completed the study are analysed (per-protocol)",
                "Only patients who had side effects are analysed",
                "Analysis is performed only at the treating centre",
                "All patients are analysed in the group to which they were RANDOMISED, regardless of whether they completed the treatment or crossed over",
                "Patients who withdrew are excluded"
              ],
              "answer": "D",
              "explanation": "ITT analysis includes ALL randomised patients in their originally assigned group, regardless of whether they completed the treatment, were non-compliant, or crossed over to the other treatment group. This preserves the benefits of randomisation (equal distribution of known and unknown confounders between groups) and reflects real-world practice (not all patients comply with treatment). It provides a CONSERVATIVE estimate of treatment effect (tends to dilute the difference between groups because of crossovers and non-compliance). Per-protocol analysis: only includes patients who completed the study as prescribed (may overestimate treatment effect but reflects the true biological effect of the treatment). Both should ideally be reported.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1030,
              "stem": "A case-control study works by:",
              "options": [
                "Randomly assigning patients to treatment or control groups",
                "Selecting patients WITH the outcome (cases) and WITHOUT the outcome (controls), then looking BACKWARDS to assess exposure",
                "Following a group forward in time to see who develops the outcome",
                "Describing a series of patients with the same condition",
                "Treating all patients and comparing before/after"
              ],
              "answer": "B",
              "explanation": "A case-control study is an observational study that starts with the OUTCOME (disease present = cases, disease absent = controls) and looks BACKWARDS in time to assess prior exposure to a risk factor. It is particularly useful for: (1) rare diseases (where cohort studies would need enormous sample sizes), (2) diseases with long latency periods, and (3) generating hypotheses. Advantages: relatively quick, inexpensive, good for rare diseases. Disadvantages: susceptible to recall bias (cases may remember exposures differently from controls), selection bias (choosing appropriate controls is critical), cannot calculate incidence or relative risk directly (uses odds ratios instead). Example: do patients with osteosarcoma (cases) have higher prior radiation exposure than controls?",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Sensitivity & Specificity",
          "range": "Q1031",
          "questions": [
            {
              "number": 1031,
              "stem": "A test with high specificity is best used for:",
              "options": [
                "Screening a population",
                "Ruling out disease",
                "Ruling in (confirming) disease",
                "Predicting prognosis",
                "Determining treatment response"
              ],
              "answer": "C",
              "explanation": "A highly specific test has few false positives — when it is positive, you can be confident the disease is present (SpPIn: Specific test, Positive result, rules In). A highly sensitive test has few false negatives — when it is negative, you can be confident the disease is absent (SnNOut: Sensitive test, Negative result, rules Out). Screening tests need high sensitivity (catch all cases). Confirmatory tests need high specificity (avoid false positives).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Ethics & Consent",
          "range": "Q1032-Q1033",
          "questions": [
            {
              "number": 1032,
              "stem": "For valid informed consent, a patient must have:",
              "options": [
                "A medical degree",
                "Written consent only — verbal is never sufficient",
                "Consent from a family member",
                "Agreement from two independent doctors",
                "Capacity, be given adequate information, and consent voluntarily without coercion"
              ],
              "answer": "E",
              "explanation": "Valid informed consent requires three elements: (1) Capacity — the patient can understand, retain, weigh, and communicate their decision (assessed using the Mental Capacity Act 2005 principles). (2) Information — adequate explanation of the procedure, risks, benefits, alternatives, and consequences of not treating (Montgomery ruling 2015: what a reasonable patient would want to know). (3) Voluntariness — consent given freely without coercion or undue influence. Written consent is evidence of the process but verbal consent can be legally valid for minor procedures.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1033,
              "stem": "According to the Montgomery ruling (2015), what standard should be used for risk disclosure during consent?",
              "options": [
                "The Bolam standard (what a reasonable body of doctors would disclose)",
                "What a reasonable patient in the patient's position would want to know",
                "What the treating surgeon considers important",
                "Only risks with >10% probability",
                "Whatever the hospital protocol states"
              ],
              "answer": "B",
              "explanation": "The Montgomery v Lanarkshire Health Board ruling (2015) established that doctors must disclose risks that a reasonable person in the patient's position would want to know, and any risks that the specific patient would consider significant. This replaced the Bolam test (what a reasonable body of doctors would do) for consent. It places the patient at the centre of the consent process and requires doctors to engage in dialogue, not just provide information.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Theatre & Safety",
          "range": "Q1034",
          "questions": [
            {
              "number": 1034,
              "stem": "The WHO Surgical Safety Checklist includes three phases. The 'time-out' phase occurs:",
              "options": [
                "Before the patient enters the operating theatre",
                "Before induction of anaesthesia",
                "After the operation is completed",
                "Immediately before skin incision",
                "During wound closure"
              ],
              "answer": "D",
              "explanation": "The WHO Surgical Safety Checklist has three phases: (1) Sign-in — before induction of anaesthesia (patient identity, site marking, consent, allergies, anticipated blood loss, airway assessment). (2) Time-out — immediately before skin incision (all team members introduce themselves, confirm patient/procedure/site, anticipated critical events, antibiotic prophylaxis given, essential imaging displayed). (3) Sign-out — before the patient leaves the operating room (instrument/swab/needle counts, specimen labelling, equipment concerns, key postoperative plans).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Audit",
          "range": "Q1035-Q1036",
          "questions": [
            {
              "number": 1035,
              "stem": "The key difference between audit and research is:",
              "options": [
                "Audit measures current practice against a defined standard, research generates new knowledge",
                "Audit requires ethical approval, research does not",
                "Research measures against a standard, audit does not",
                "Audit is always prospective, research is always retrospective",
                "There is no difference"
              ],
              "answer": "A",
              "explanation": "Audit measures current practice against a defined standard (e.g., NICE guideline, BOAST standard) to identify gaps and improve care. It is a cyclical process: set standard → measure practice → compare → implement change → re-audit. Research generates new knowledge that may change practice. Audit does not require ethical approval (it is service evaluation). Research typically requires ethics committee approval and may involve randomisation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1036,
              "stem": "The clinical audit cycle consists of which sequential steps?",
              "options": [
                "Research → publish → teach",
                "Identify topic → set standards → collect data → compare with standards → implement change → re-audit (close the loop)",
                "Observe → hypothesis → experiment → conclusion",
                "Design → randomise → analyse → publish",
                "Plan → do → study → act"
              ],
              "answer": "B",
              "explanation": "The clinical audit cycle: (1) Identify topic/problem. (2) Set standards/criteria against which to measure (evidence-based, e.g., NICE guidelines, BOAST standards). (3) Collect data (measure current practice). (4) Compare practice against the standard (analyse results). (5) Implement change (where practice falls short of the standard). (6) Re-audit (collect data again after implementing change to demonstrate improvement — 'closing the loop'). Closing the loop (re-auditing) is the ESSENTIAL step that distinguishes a completed audit from a simple data collection exercise. Audit is NOT research — it measures practice against established standards; research establishes new standards.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Clinical Trials",
          "range": "Q1037",
          "questions": [
            {
              "number": 1037,
              "stem": "External validity of a clinical trial refers to:",
              "options": [
                "Whether the trial results can be reproduced in the same population",
                "The statistical power of the study",
                "The internal consistency of the data",
                "The blinding method used",
                "Whether the trial results can be generalised to other populations and settings"
              ],
              "answer": "E",
              "explanation": "External validity (generalisability) refers to whether the trial results can be applied to populations, settings, and conditions beyond the specific study population. A trial with strict inclusion criteria may have high internal validity (accurate within the study) but low external validity (results may not apply to broader clinical practice). For example, an RCT excluding elderly patients with comorbidities may not be applicable to the typical hip fracture population.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "NJR",
          "range": "Q1038",
          "questions": [
            {
              "number": 1038,
              "stem": "The National Joint Registry (NJR) collects data on joint replacements performed in:",
              "options": [
                "USA only",
                "Scotland only",
                "England, Wales, Northern Ireland, the Isle of Man, and Guernsey",
                "Australia",
                "Worldwide"
              ],
              "answer": "C",
              "explanation": "The NJR records data on all hip, knee, ankle, elbow, and shoulder replacements performed in England, Wales, Northern Ireland, the Isle of Man, and Guernsey. Scotland has its own registry (Scottish Arthroplasty Project). The NJR is one of the largest joint registries in the world and provides invaluable data on implant survivorship, revision rates, and outcomes. Annual reports guide implant selection and identify poorly performing implants. Data is used to support the ODEP/NICE benchmarking system.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Consent",
          "range": "Q1039-Q1040",
          "questions": [
            {
              "number": 1039,
              "stem": "Under the Mental Capacity Act 2005, capacity is assumed unless proven otherwise. To have capacity, a patient must be able to:",
              "options": [
                "Understand, retain, weigh (use/balance), and communicate their decision",
                "Sign a consent form",
                "Agree with the doctor's recommendation",
                "Have a family member present",
                "Read the consent form in full"
              ],
              "answer": "A",
              "explanation": "The Mental Capacity Act 2005 (England and Wales) establishes four criteria for capacity: (1) Understand the relevant information, (2) Retain it long enough to make a decision, (3) Use or weigh (balance) the information as part of the decision-making process, (4) Communicate the decision (by any means). Capacity is: decision-specific, time-specific, and ASSUMED unless proven otherwise. A patient with capacity can make an unwise decision — the right to refuse treatment exists even if the decision seems against their best interests.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1040,
              "stem": "The Montgomery ruling (2015) established that when obtaining informed consent, a doctor must:",
              "options": [
                "Tell the patient only what the doctor thinks they need to know",
                "Only disclose risks if the patient specifically asks",
                "Not discuss any risks to avoid causing anxiety",
                "Inform the patient of material risks that a reasonable person in the patient's position would want to know (patient-centred standard)",
                "Follow the Bolam standard for consent"
              ],
              "answer": "D",
              "explanation": "The Montgomery ruling (Montgomery v Lanarkshire Health Board, 2015, UK Supreme Court) replaced the Bolam test (doctor-centred) for consent with a PATIENT-CENTRED standard. A doctor must: (1) take reasonable care to ensure the patient is aware of any MATERIAL RISKS involved in the proposed treatment, and (2) any REASONABLE ALTERNATIVE TREATMENTS. A material risk is one that a reasonable person in the patient's position would attach significance to, OR one that the doctor knows or should reasonably know this particular patient would attach significance to. This is a significant shift — the test is no longer 'what would a reasonable doctor disclose?' but 'what would a reasonable patient want to know?'",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Research Ethics",
          "range": "Q1041",
          "questions": [
            {
              "number": 1041,
              "stem": "The Declaration of Helsinki (1964, revised) established ethical principles for:",
              "options": [
                "Medical research involving human subjects",
                "Surgical consent only",
                "Pharmaceutical pricing",
                "Hospital governance",
                "Medical device regulation"
              ],
              "answer": "A",
              "explanation": "The Declaration of Helsinki (World Medical Association, 1964, most recently revised 2013) establishes ethical principles for medical research involving human subjects. Key principles: (1) informed consent from all participants, (2) research must be approved by an independent ethics committee, (3) participant welfare takes priority over research interests, (4) vulnerable populations need additional safeguards, (5) participants can withdraw at any time, (6) results must be published (both positive and negative), (7) placebo use must be justified when proven treatments exist.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Duty of Candour",
          "range": "Q1042",
          "questions": [
            {
              "number": 1042,
              "stem": "The statutory Duty of Candour requires healthcare providers to:",
              "options": [
                "Only disclose errors if the patient asks",
                "Inform patients promptly when a notifiable patient safety incident has occurred, offer an apology, and provide a follow-up in writing",
                "Cover up mistakes to protect reputation",
                "Report only to the CQC, not the patient",
                "Wait until litigation before disclosing"
              ],
              "answer": "B",
              "explanation": "The statutory Duty of Candour (Health and Social Care Act 2008, Regulation 20) requires healthcare providers to: (1) tell the patient (or their representative) when a notifiable patient safety incident has occurred, (2) apologise (apology is NOT an admission of liability), (3) provide truthful information about what happened, (4) provide a written follow-up/account. It applies to moderate harm, severe harm, and death. Introduced following the Francis Inquiry (Mid Staffordshire NHS Foundation Trust). Failure to comply is a criminal offence for NHS organisations.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Trial Design",
          "range": "Q1043-Q1044",
          "questions": [
            {
              "number": 1043,
              "stem": "Blinding in a randomised controlled trial is performed to reduce:",
              "options": [
                "Selection bias",
                "Attrition bias",
                "Performance bias and detection (observer) bias",
                "Recall bias",
                "Confounding"
              ],
              "answer": "C",
              "explanation": "Blinding (masking) reduces performance bias (clinicians treating groups differently if they know which treatment is given) and detection/observer bias (assessors measuring outcomes differently based on knowledge of allocation). Single-blind: patients blinded. Double-blind: patients AND clinicians/assessors blinded. Triple-blind: patients, clinicians, AND data analysts blinded. Randomisation reduces selection bias. ITT analysis reduces attrition bias. Blinding + randomisation together are the strongest methods for minimising bias in RCTs.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1044,
              "stem": "A non-inferiority trial is designed to show that:",
              "options": [
                "A new treatment is superior to the standard treatment",
                "There is no difference between treatments (equivalence)",
                "The treatment has no effect",
                "The placebo is better than the treatment",
                "A new treatment is no worse than the standard treatment by more than a pre-defined margin"
              ],
              "answer": "E",
              "explanation": "A non-inferiority trial aims to demonstrate that a new treatment is NOT meaningfully WORSE than the existing standard treatment (within a pre-defined non-inferiority margin, Δ). This is used when the new treatment has other advantages (e.g., fewer side effects, lower cost, easier administration) that justify its use even if it is not superior. For example: showing that aspirin is non-inferior to LMWH for VTE prophylaxis after arthroplasty (CRISTAL trial) — aspirin is cheaper and easier (oral vs injection). The non-inferiority margin must be clinically justified and pre-specified. Different from superiority trials (new > old) and equivalence trials (new = old within margins).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Levels of Evidence",
          "range": "Q1045",
          "questions": [
            {
              "number": 1045,
              "stem": "The highest level of evidence for treatment decisions is:",
              "options": [
                "Expert opinion (Level V)",
                "Case series (Level IV)",
                "Case-control study (Level III)",
                "Systematic review with meta-analysis of RCTs (Level I)",
                "Randomised controlled trial (Level II)"
              ],
              "answer": "D",
              "explanation": "The evidence hierarchy (Oxford Centre for Evidence-Based Medicine): Level I = systematic review with meta-analysis of homogeneous RCTs (highest). Level II = individual RCT (with narrow CI). Level III = cohort study, case-control study. Level IV = case series. Level V = expert opinion, mechanism-based reasoning. This hierarchy guides clinical decision-making — higher-level evidence carries more weight. However, not all questions can be answered by RCTs (ethical constraints, rare conditions), and well-designed observational studies can provide valuable evidence. Critical appraisal skills are needed to evaluate the quality within each level.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Outcome Measures",
          "range": "Q1046",
          "questions": [
            {
              "number": 1046,
              "stem": "Patient-Reported Outcome Measures (PROMs) differ from clinician-assessed outcomes in that PROMs:",
              "options": [
                "Are completed by the surgeon",
                "Measure only radiographic parameters",
                "Have no role in modern orthopaedic practice",
                "Are questionnaires completed by the PATIENT measuring their perception of health, pain, and function",
                "Only measure mortality"
              ],
              "answer": "D",
              "explanation": "PROMs are standardised questionnaires completed by PATIENTS to measure their own perception of health status, pain, function, and quality of life. They capture the patient perspective, which may differ from clinician-assessed measures. Common orthopaedic PROMs: Oxford Hip Score (OHS) and Oxford Knee Score (OKS) — 12-item questionnaires scored 0-48 (48 = best), used by the NHS for mandatory pre- and post-operative assessment of all hip and knee arthroplasties. EQ-5D — generic health-related quality of life measure (5 dimensions: mobility, self-care, usual activities, pain/discomfort, anxiety/depression). PRWE — Patient-Rated Wrist Evaluation. DASH — Disabilities of the Arm, Shoulder, and Hand. PROMs are now mandatory in the NHS for arthroplasty and are used by the NJR to benchmark outcomes.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        }
      ]
    },
    {
      "title": "Hand & Wrist",
      "chapters": [
        {
          "title": "Tendon",
          "range": "Q1047-Q1055",
          "questions": [
            {
              "number": 1047,
              "stem": "Leddy-Packer classification is used for flexor digitorum profundus (FDP) avulsions ('jersey finger'). Type I (the most severe) involves:",
              "options": [
                "FDP retraction into the PALM (no bony fragment — the vincula are ruptured, blood supply is disrupted, and the tendon end retracts maximally) — requires URGENT surgical repair within 7-10 days before the tendon shortens irreversibly",
                "FDP retraction only to the PIP level",
                "FDP retraction to the palm with bony fragment",
                "FDP retraction with a large bony fragment held at the DIP (least severe)",
                "No tendon injury"
              ],
              "answer": "A",
              "explanation": "Jersey finger: FDP avulsion from its insertion on the distal phalanx — typically the ring finger (weakest FDP insertion — anatomically, the ring finger DIP is the first to fail during a forceful grip, like grabbing a rugby jersey). Leddy-Packer classification: Type I = tendon retracts into the PALM (worst — both vincula ruptured, blood supply disrupted, tendon shortens rapidly → URGENT repair within 7-10 days — after this, the tendon becomes fibrotic and shortened, making repair impossible without grafting). Type II = tendon retracts to PIP level (held by intact vinculum longum — can be repaired up to 3-6 months). Type III = large bony fragment avulses and catches at the A4 pulley level (DIP level — tendon doesn't retract far, bone block prevents retraction → can be repaired later, but still preferably within 2-3 weeks). Type IV (Smith modification) = bony fragment + tendon avulsion from the fragment (complex). Clinical: ring finger DIP cannot flex (FDP test: hold PIP extended → ask patient to flex DIP → cannot flex = FDP avulsion). Treatment: ALL types require surgical repair (tendon reattachment to the distal phalanx — suture anchor or pull-through button technique).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1048,
              "stem": "Trigger finger (stenosing tenosynovitis) is caused by:",
              "options": [
                "Rupture of the extensor tendon",
                "Fracture of the metacarpal",
                "Thickening of the A1 pulley causing mechanical impingement of the flexor tendon nodule during gliding, resulting in catching, locking, and triggering",
                "Nerve compression",
                "Joint dislocation"
              ],
              "answer": "C",
              "explanation": "Trigger finger results from a SIZE MISMATCH between the flexor tendon (which develops a nodular thickening from repetitive microtrauma/inflammation) and the A1 PULLEY (the first pulley at the MCP joint level, which becomes thickened and stenotic). As the thickened tendon nodule passes through the narrowed A1 pulley: it catches → locks in flexion → then releases with a painful snap/trigger. Grading (Quinnell): Grade I = uneven movement without locking. Grade II = actively correctable locking. Grade III = passively correctable locking (can't unlock actively). Grade IV = fixed flexion (locked, can't be unlocked). Treatment: splinting (MCP extension night splint), corticosteroid injection INTO the tendon sheath at the A1 pulley (~60-90% success with 1-2 injections), and surgical A1 pulley release (open or percutaneous — nearly 100% success). Risk factors: diabetes (up to 10% develop trigger finger), RA, hypothyroidism, repetitive gripping. In children: trigger THUMB is most common (congenital — Notta's node, not the same pathology as adult trigger finger).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1049,
              "stem": "Mallet finger is caused by disruption of the terminal extensor tendon at its insertion on the distal phalanx. The characteristic deformity is:",
              "options": [
                "DIP hyperextension",
                "DIP FLEXION (the DIP joint droops into flexion because the terminal extensor tendon can no longer extend it — the FDP remains unopposed)",
                "PIP flexion",
                "MCP hyperextension",
                "Wrist drop"
              ],
              "answer": "B",
              "explanation": "Mallet finger: disruption of the TERMINAL EXTENSOR TENDON at its insertion on the dorsal base of the distal phalanx. Result: the DIP joint DROPS INTO FLEXION (cannot actively extend the DIP). May be: (1) tendinous mallet (tendon rupture without fracture — most common, from forced flexion against an actively extending finger, e.g., ball striking the fingertip), or (2) bony mallet (avulsion fracture of the dorsal base of the distal phalanx with or without the tendon). Treatment: MOST mallet fingers (tendinous and small bony fragments) are treated NON-OPERATIVELY — Stack splint (or equivalent) holding the DIP in EXTENSION (or slight hyperextension) continuously for 6-8 weeks, then 2 weeks of night splinting. The PIP joint must be LEFT FREE (don't splint it — allowing PIP flexion exercises prevents stiffness). If the splint is removed (even once) → the 6-week clock RESETS. Operative: for bony mallet with >30% articular surface involvement AND volar subluxation of the distal phalanx (unstable joint) — K-wire extension block technique or ORIF.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1050,
              "stem": "Lateral epicondylitis (tennis elbow) primarily involves the origin of:",
              "options": [
                "FCR at the medial epicondyle (that's medial epicondylitis)",
                "Triceps",
                "Biceps",
                "Supinator",
                "ECRB (extensor carpi radialis brevis) at the lateral epicondyle — the most commonly affected tendon in lateral epicondylitis"
              ],
              "answer": "E",
              "explanation": "Lateral epicondylitis primarily involves the ECRB (extensor carpi radialis brevis) origin at the lateral epicondyle. Like medial epicondylitis, it is a TENDINOPATHY (angiofibroblastic degeneration — Nirschl classification) rather than true inflammation. It is the most common cause of lateral elbow pain (~7× more common than medial epicondylitis). Mechanism: repetitive wrist extension and gripping → microtears at the ECRB origin → failed healing → angiofibroblastic degeneration. The ECRB is uniquely vulnerable: it directly abuts the lateral edge of the capitellum during elbow extension → mechanical abrasion contributes to degeneration. Treatment: 90% resolve with conservative management within 12-18 months. Conservative: activity modification, eccentric wrist extension exercises (Tyler twist), counterforce brace (tennis elbow strap — reduces strain on the ECRB origin), corticosteroid injection (provides short-term relief but WORSE long-term outcomes than physiotherapy — Coombes 2013 RCT). Surgery (~5-10%): open or arthroscopic debridement of degenerate ECRB tissue (Nirschl procedure).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1051,
              "stem": "The six dorsal extensor compartments of the wrist contain tendons organised in a specific order. The third compartment contains:",
              "options": [
                "APL and EPB",
                "ECRL and ECRB",
                "EDC and EIP",
                "EPL",
                "EDM"
              ],
              "answer": "D",
              "explanation": "The six dorsal extensor compartments (lateral to medial): 1st = APL, EPB (de Quervain). 2nd = ECRL, ECRB. 3rd = EPL (wraps around Lister tubercle). 4th = EDC, EIP. 5th = EDM. 6th = ECU. Mnemonic: '2, 2, 1, 2, 1, 1' (number of tendons per compartment). The EPL in the 3rd compartment wraps around Lister tubercle on the dorsal radius — this is clinically important because: (1) it can rupture after distal radius fracture (attritional rupture over the tubercle), and (2) it is a landmark for dorsal wrist surgery.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1052,
              "stem": "After flexor tendon repair in Zone II, the gold standard post-operative rehabilitation protocol involves:",
              "options": [
                "Rigid immobilisation in a cast for 6 weeks",
                "Immediate unrestricted use",
                "No splinting — free movement from day 1",
                "Delayed mobilisation starting at 6 weeks",
                "Early active mobilisation with controlled exercises within a dorsal blocking splint"
              ],
              "answer": "E",
              "explanation": "Early active mobilisation (EAM) protocols within a dorsal blocking splint (wrist in slight flexion, MCPs in flexion, IPs free) are now the gold standard after Zone II flexor tendon repair. Place-and-hold exercises, gentle active flexion within the splint, and progressive strengthening from 6 weeks produce the best outcomes — reducing adhesion formation while protecting the repair. The splint is worn for approximately 4-6 weeks. The Belfast protocol and Sheffield regime are well-known examples. Prerequisite: a strong repair (≥4-strand core suture + epitendinous) that can withstand the forces of early motion.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1053,
              "stem": "Jersey finger is an avulsion of the FDP tendon from the distal phalanx. Which finger is most commonly affected?",
              "options": [
                "Index finger",
                "Middle finger",
                "Ring finger (most commonly affected, ~75%)",
                "Little finger",
                "Thumb"
              ],
              "answer": "C",
              "explanation": "Jersey finger is a closed avulsion of the FDP tendon from its insertion on the volar base of the distal phalanx. The ring finger is affected in ~75% of cases because: (1) the ring finger FDP has the least independent excursion (it is tethered by connections to adjacent FDP tendons), and (2) during forced extension against a flexed grip (e.g., grabbing a jersey), the ring finger FDP is the last to release and takes the maximum force. Leddy and Packer classification: Type I = tendon retracts into the palm (vincular blood supply disrupted — urgent repair within 7-10 days). Type II = tendon retracts to PIP level (vincula intact, held by vinculum brevis — can repair within weeks). Type III = bony avulsion (large fragment caught at A4 pulley — repair when convenient). Examination: inability to flex the DIP joint against resistance (FDP function lost). The finger assumes an extended posture at the DIP relative to the other flexed fingers.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1054,
              "stem": "In rheumatoid arthritis, rupture of the flexor pollicis longus (FPL) tendon over a scaphoid spur is called:",
              "options": [
                "Mannerfelt lesion",
                "Vaughan-Jackson lesion",
                "Linburg-Comstock anomaly",
                "Jersey finger",
                "Trigger thumb"
              ],
              "answer": "A",
              "explanation": "The Mannerfelt lesion is attritional rupture of the FPL tendon over a bony spur on the volar aspect of the scaphoid (scaphotrapezial osteophyte) in rheumatoid arthritis. The patient loses active IP joint flexion of the thumb. It is the flexor tendon equivalent of the Vaughan-Jackson lesion (extensor tendons rupturing over the eroded distal ulna). Treatment: FPL reconstruction (tendon graft or FDS ring finger transfer) + excision of the bony spur to prevent recurrence. Both Mannerfelt and Vaughan-Jackson lesions highlight the importance of early rheumatoid hand assessment and prophylactic procedures (synovectomy, bony spur excision) before tendon rupture occurs.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1055,
              "stem": "A mallet finger injury is caused by disruption of the terminal extensor tendon (or bony avulsion) at the DIP joint. The initial treatment for a closed mallet finger is:",
              "options": [
                "Immediate surgical repair",
                "Continuous DIP extension splinting for 6-8 weeks (Stack/Zimmer splint)",
                "PIP joint splinting only",
                "Buddy strapping",
                "No treatment needed — it resolves spontaneously"
              ],
              "answer": "B",
              "explanation": "Closed mallet finger (Zone I extensor tendon injury) is treated with continuous DIP extension splinting (hyperextension or neutral) for 6-8 weeks, 24 hours a day. The PIP joint is left free. If the DIP is allowed to flex even once during the splinting period, the 6-8 week clock restarts. Night splinting continues for an additional 2-4 weeks after full-time splinting. Success rate with compliant splinting: ~80-85%. Surgical indications: bony mallet with >30% articular involvement and volar subluxation of the distal phalanx (requires K-wire fixation), or open mallet injury. Non-bony mallet in children may have a Salter-Harris I-III injury at the distal phalanx physis — splint similarly.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Nerve",
          "range": "Q1056-Q1062",
          "questions": [
            {
              "number": 1056,
              "stem": "Wartenberg syndrome is compression of the:",
              "options": [
                "Median nerve at the wrist",
                "Ulnar nerve at the elbow",
                "Superficial branch of the radial nerve (pure sensory) at the wrist/forearm, causing pain and numbness on the dorsoradial hand",
                "Posterior interosseous nerve",
                "Musculocutaneous nerve"
              ],
              "answer": "C",
              "explanation": "Wartenberg syndrome is compression of the superficial branch of the radial nerve (SBRN) — a PURE SENSORY nerve. It is compressed where it emerges between the brachioradialis and ECRL tendons in the distal forearm (~9cm proximal to the radial styloid). Symptoms: burning pain, numbness, and tingling on the dorsoradial aspect of the hand (dorsal first web space, dorsal thumb and index finger). Often confused with de Quervain tenosynovitis (both cause radial-sided wrist pain). Differentiating: Wartenberg has sensory disturbance (numbness/tingling — de Quervain does not). Finkelstein test: positive in de Quervain, may reproduce symptoms in Wartenberg (nerve stretched). Tinel sign: positive over the SBRN in Wartenberg. Treatment: activity modification, splinting, nerve decompression if persistent.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1057,
              "stem": "Carpal tunnel syndrome — the nerve compressed within the carpal tunnel is the:",
              "options": [
                "Median nerve (compressed beneath the transverse carpal ligament/flexor retinaculum — causing numbness in the thumb, index, middle, and radial half of the ring finger, plus thenar weakness)",
                "Ulnar nerve (compressed at Guyon's canal)",
                "Radial nerve",
                "Musculocutaneous nerve",
                "Posterior interosseous nerve"
              ],
              "answer": "A",
              "explanation": "The MEDIAN NERVE is compressed within the carpal tunnel — a rigid fibro-osseous tunnel bounded by the carpal bones (floor and walls) and the transverse carpal ligament/flexor retinaculum (roof). Contents of the carpal tunnel: median nerve + 4 FDS tendons + 4 FDP tendons + FPL tendon (9 tendons + 1 nerve). Symptoms: numbness/tingling in the MEDIAN nerve distribution (thumb, index, middle, and RADIAL half of ring finger — NOT the little finger, which is ulnar nerve territory), nocturnal symptoms (waking with numbness → shaking the hand relieves it — 'flick sign'), and thenar weakness (late — APB wasting, weak opposition). Clinical tests: Phalen (forced wrist flexion 60 seconds → reproduces symptoms), Tinel (tapping over the carpal tunnel → tingling in median distribution), Durkan (direct compression). Treatment: night splint (wrist in neutral), corticosteroid injection, carpal tunnel release (open or endoscopic — division of the transverse carpal ligament). NCS/EMG: confirms diagnosis (median nerve motor and sensory conduction delay across the wrist).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1058,
              "stem": "Ulnar nerve compression at the elbow (cubital tunnel syndrome) — the most common site of compression is:",
              "options": [
                "Guyon's canal (wrist)",
                "The arcade of Struthers",
                "The carpal tunnel",
                "The spiral groove of the humerus",
                "The cubital tunnel (behind the medial epicondyle, beneath the Osborne ligament/arcuate ligament — the nerve is superficial and vulnerable to compression and traction)"
              ],
              "answer": "E",
              "explanation": "The cubital tunnel is formed by the medial epicondyle (floor), the olecranon (lateral wall), and the Osborne ligament/arcuate ligament (roof — fibrous band between the two heads of FCU). The ulnar nerve is superficial here (only covered by skin and subcutaneous tissue — you can feel it as the 'funny bone') and is vulnerable to: (1) COMPRESSION (leaning on the elbow, tight cast/splint, Osborne ligament thickening), (2) TRACTION (cubitus valgus stretches the nerve with each elbow flexion cycle — tardy ulnar nerve palsy from lateral condyle non-union), (3) SUBLUXATION (the nerve may snap over the medial epicondyle during flexion in ~16% of the population). Symptoms: numbness/tingling in the ring (ulnar half) and little finger, weakness of intrinsics (interossei, lumbricals 3-4, hypothenar muscles, adductor pollicis), and eventually claw hand deformity (MCP hyperextension + IP flexion of ring and little fingers — 'ulnar claw' or 'hand of benediction' at rest). Froment sign: compensatory FPL activation (thumb IPJ flexion) when attempting key pinch — indicates adductor pollicis weakness.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1059,
              "stem": "A high radial nerve palsy (above the spiral groove) causes loss of wrist extension, finger MCP extension, and thumb extension. The clinical presentation is:",
              "options": [
                "Claw hand",
                "Wrist drop (with loss of finger and thumb extension at MCPs)",
                "Ape hand",
                "Foot drop",
                "Bishop's hand"
              ],
              "answer": "B",
              "explanation": "High radial nerve palsy (e.g., humeral shaft fracture at spiral groove, 'Saturday night palsy' from arm compression) causes wrist drop — the hand hangs limply in flexion because all wrist extensors (ECRL, ECRB, ECU), finger extensors (EDC, EDM, EIP), thumb extensors (EPL, EPB), and the supinator are paralysed. Sensation is lost on the dorsal first web space (superficial branch of radial nerve). Key point: finger flexion GRIP appears weak with wrist drop, but this is due to loss of the tenodesis effect — if you passively extend the wrist, grip strength returns (the flexor tendons are intact). Tendon transfers if no recovery: PT→ECRB (wrist extension), FCR→EDC (finger extension), PL→EPL (thumb extension).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1060,
              "stem": "The motor branch of the median nerve in the hand (recurrent motor branch) supplies which muscles?",
              "options": [
                "All interossei",
                "Hypothenar muscles",
                "Lumbricals to ring and little fingers",
                "Thenar muscles: abductor pollicis brevis, opponens pollicis, and superficial head of flexor pollicis brevis",
                "Adductor pollicis"
              ],
              "answer": "D",
              "explanation": "The recurrent motor branch of the median nerve supplies the thenar muscles: abductor pollicis brevis (APB), opponens pollicis, and the superficial head of flexor pollicis brevis. APB is the most important muscle to test for median nerve function in the hand (resisted palmar abduction of the thumb perpendicular to the palm). Damage to the recurrent branch (e.g., during carpal tunnel release) causes thenar wasting and loss of opposition — 'ape hand' deformity.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1061,
              "stem": "Froment sign is positive in ulnar nerve palsy. It demonstrates:",
              "options": [
                "Weakness of the APB (thenar)",
                "Weakness of adductor pollicis — the patient compensates by flexing the thumb IP joint (using FPL, median nerve) during key pinch",
                "Weakness of wrist extension",
                "Weakness of finger extension",
                "Weakness of shoulder abduction"
              ],
              "answer": "B",
              "explanation": "Froment sign tests adductor pollicis (ulnar nerve) weakness. Ask the patient to grip a piece of paper between the thumb and index finger using key (lateral) pinch. With ulnar nerve palsy: the adductor pollicis is weak, so the patient compensates by flexing the thumb IP joint (using FPL — innervated by the AIN branch of the median nerve) to maintain grip. A positive Froment sign = thumb IP flexion during pinch = weak adductor pollicis = ulnar nerve dysfunction. Jeanne sign: MCP hyperextension of the thumb during the same test (loss of 1st palmar interosseous and adductor contribution to MCP flexion — further compensation). Both are clinical signs of ulnar nerve palsy at any level.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1062,
              "stem": "Carpal tunnel syndrome — the motor branch most at risk is the recurrent motor branch of the median nerve, which innervates:",
              "options": [
                "Hypothenar muscles",
                "Interossei",
                "Wrist extensors",
                "Finger extensors",
                "Thenar muscles (APB, opponens pollicis, FPB superficial head) — the 'LOAF' muscles"
              ],
              "answer": "E",
              "explanation": "The recurrent motor branch of the median nerve is the most important structure at risk during carpal tunnel release. It innervates three thenar muscles: APB (abductor pollicis brevis — the most clinically important, tested by resisted palmar abduction of the thumb perpendicular to the palm), opponens pollicis, and the superficial head of FPB. The median nerve 'LOAF' muscles include: Lumbricals 1-2, Opponens pollicis, APB, and FPB (superficial head). The recurrent motor branch has variable anatomy: most commonly branches from the lateral aspect of the median nerve after exiting the carpal tunnel (extraligamentous — 46%). Variants: subligamentous (31%) and transligamentous (23%). Injury during carpal tunnel release → irreversible loss of thenar opposition and pinch strength.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Flexor Tendon",
          "range": "Q1063",
          "questions": [
            {
              "number": 1063,
              "stem": "Flexor tendon injuries in Zone II ('no man's land') are the most challenging to repair because:",
              "options": [
                "The tendons are absent in this zone",
                "Only FDP is present",
                "No blood supply exists",
                "Both FDS and FDP run together within the fibro-osseous flexor sheath beneath the pulley system — repair must restore gliding between two tendons in a tight space while preserving the critical A2 and A4 pulleys",
                "The tendons are purely sensory"
              ],
              "answer": "D",
              "explanation": "Zone II extends from the distal palmar crease to the FDS insertion on the middle phalanx — the area where BOTH FDS and FDP run together within the tight fibro-osseous flexor tendon sheath, surrounded by the pulley system (A1-A5, C1-C3). The challenge: (1) two tendons must glide independently within a confined space, (2) repair must be strong enough for early active motion protocols (prevents adhesion formation) but without excessive bulk that would block gliding, (3) the A2 and A4 pulleys MUST be preserved (cutting them causes bowstringing), (4) the vincular blood supply is limited (nutrition partly relies on synovial fluid diffusion). Modern repair: 4-6 strand core suture (Kessler modified, cruciate, Adelaide — higher strand count = stronger repair → allows early active motion) + running epitendinous suture (smooths the repair surface for better gliding). Post-op: early active motion protocol (Belfast/Manchester regime) — reduces adhesion formation but requires compliant patient and hand therapy supervision.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Extensor Tendon",
          "range": "Q1064",
          "questions": [
            {
              "number": 1064,
              "stem": "Boutonnière deformity results from disruption of the central slip of the extensor tendon at the PIP joint level. The characteristic deformity is:",
              "options": [
                "DIP flexion + PIP extension",
                "MCP hyperextension only",
                "PIP flexion + DIP hyperextension (the lateral bands sublux volarly, becoming PIP flexors and DIP hyperextensors)",
                "Wrist drop",
                "Swan-neck deformity"
              ],
              "answer": "C",
              "explanation": "Boutonnière deformity: the central slip of the extensor tendon is disrupted at the PIP joint → the PIP joint 'buttonholes' through the extensor mechanism (boutonnière = buttonhole in French). The lateral bands then sublux VOLARLY (below the PIP joint axis) → they become PIP FLEXORS (rather than extensors) and DIP HYPEREXTENSORS (because their tension is redirected distally). Result: PIP flexion + DIP hyperextension. This is the OPPOSITE of swan-neck deformity (PIP hyperextension + DIP flexion — caused by intrinsic tightness, mallet finger, or volar plate laxity). Acute closed boutonnière: splint the PIP in extension for 6 weeks (DIP must be left FREE to move — flexion exercises of the DIP help dorsalise the lateral bands back over the PIP axis). Chronic/fixed: much harder to treat (may need surgical reconstruction — lateral band mobilisation, central slip reconstruction).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Replantation",
          "range": "Q1065-Q1067",
          "questions": [
            {
              "number": 1065,
              "stem": "In digital replantation, the absolute indication for attempting replantation regardless of other factors is:",
              "options": [
                "Thumb amputation (the thumb provides ~50% of hand function — always attempt replantation regardless of level, mechanism, or patient factors)",
                "Single finger distal to FDS insertion in a manual labourer",
                "Severely crushed single finger",
                "Amputated fingertip in an elderly patient",
                "Ring avulsion injury"
              ],
              "answer": "A",
              "explanation": "The THUMB provides ~40-50% of overall hand function (opposition, pinch, grip) — its loss is devastating and cannot be compensated by the other digits. Therefore: thumb amputation is an ABSOLUTE indication for replantation, regardless of the level of amputation, mechanism, or patient factors. Other strong indications: (1) multiple digit amputations, (2) hand/wrist level amputations, (3) any amputation in a child (excellent regenerative capacity), (4) single digit amputation DISTAL to the FDS insertion in certain patients (children, musicians, patients who request it). Contraindications for replantation: (1) severe crush/avulsion with extensive zone of injury, (2) multilevel injury, (3) prolonged warm ischaemia time (>12h for digits, >6h for major limbs), (4) significant medical comorbidities making prolonged surgery dangerous, (5) single finger proximal to FDS insertion (functional outcome often worse than amputation — stiff finger impairs hand function). Cold ischaemia time: digits can tolerate up to 12-24h if properly cooled (wrap in saline-moistened gauze → sealed bag → ice water).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            },
            {
              "number": 1066,
              "stem": "The correct method of transporting an amputated digit for replantation is:",
              "options": [
                "Directly on ice",
                "In warm saline",
                "In formalin for preservation",
                "Dry gauze in a sterile container at room temperature",
                "Wrapped in saline-moistened gauze, placed in a sealed bag, then placed on ice"
              ],
              "answer": "E",
              "explanation": "The amputated part should be: (1) wrapped in saline-moistened gauze, (2) placed in a sealed plastic bag, (3) the bag placed on ice (in an ice-water mixture, not directly on ice). Direct contact with ice causes frostbite and tissue damage. The amputated part should NOT be placed in water, formalin, or on dry ice. Cool ischaemia time tolerance: digits up to 12 hours warm / 24 hours cold. Major limbs: 6 hours warm / 12 hours cold.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1067,
              "stem": "Which of the following is an absolute indication for digital replantation?",
              "options": [
                "Thumb amputation at any level",
                "Single finger proximal to FDS insertion in an adult",
                "Severely crushed single finger",
                "Ring avulsion injury (Urbaniak Class III)",
                "Single finger in an elderly patient with comorbidities"
              ],
              "answer": "A",
              "explanation": "The thumb is an absolute indication for replantation at any level because it contributes 40–50% of hand function and its loss cannot be adequately compensated. Other strong indications: multiple digits, paediatric amputations (children have excellent regeneration), hand through wrist level, and any digit in selected patients. Single finger proximal to FDS insertion has poor outcomes. Crushed/avulsed segments and Class III ring avulsions are relative contraindications.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Infection",
          "range": "Q1068-Q1069",
          "questions": [
            {
              "number": 1068,
              "stem": "Kanavel signs for flexor tendon sheath infection (pyogenic flexor tenosynovitis) include all EXCEPT:",
              "options": [
                "Fusiform (sausage-shaped) swelling of the entire finger",
                "Dorsal hand swelling only without finger involvement (this is NOT a Kanavel sign — it may indicate dorsal hand space infection or cellulitis)",
                "Flexed posture of the finger at rest",
                "Tenderness along the flexor tendon sheath",
                "Pain with passive extension of the finger"
              ],
              "answer": "B",
              "explanation": "Kanavel signs (4 cardinal signs of flexor tendon sheath infection): (1) FUSIFORM swelling — uniform sausage-shaped swelling of the entire finger (not localised to one area). (2) FLEXED POSTURE — the finger is held in slight flexion at all joints (protective position — extending the finger increases pressure within the infected sheath). (3) TENDERNESS along the entire FLEXOR TENDON SHEATH (palpation along the volar finger from proximal to distal produces tenderness along the whole sheath — not just at one point). (4) Pain with PASSIVE EXTENSION (stretching the infected sheath reproduces severe pain — the most sensitive and specific sign). ALL FOUR Kanavel signs together are highly diagnostic. Even ONE sign (particularly passive extension pain) should raise clinical suspicion. Treatment: URGENT surgical drainage (within 24 hours — delayed treatment → tendon necrosis, adhesions, finger amputation). Technique: open or catheter irrigation of the sheath. IV antibiotics. Staphylococcus aureus: most common organism.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1069,
              "stem": "A felon (pulp space infection) is an abscess of the:",
              "options": [
                "Flexor tendon sheath",
                "Web space between fingers",
                "Distal pulp space of the fingertip",
                "Nail fold",
                "Midpalmar space"
              ],
              "answer": "C",
              "explanation": "A felon is a closed-space infection of the distal pulp of the fingertip. The pulp is divided into compartments by fibrous septa connecting the skin to the distal phalanx — these create closed compartments where pressure builds rapidly, potentially causing vascular compromise and osteomyelitis of the distal phalanx. Treatment: incision and drainage (unilateral longitudinal incision avoiding the pincer area/pulp tip). Do NOT use the 'fish-mouth' or 'hockey-stick' incisions which can damage the digital nerves and create an unstable, insensate fingertip.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Avascular Necrosis",
          "range": "Q1070",
          "questions": [
            {
              "number": 1070,
              "stem": "Kienbock disease is avascular necrosis of the:",
              "options": [
                "Scaphoid",
                "Capitate",
                "Triquetrum",
                "Lunate (the central carpal bone, which has a retrograde blood supply making it vulnerable to AVN)",
                "Pisiform"
              ],
              "answer": "D",
              "explanation": "Kienbock disease is AVN of the LUNATE — the central carpal bone that articulates with the radius, scaphoid, capitate, and triquetrum. The lunate has a variable and often precarious blood supply (some lunates have only a single dorsal or palmar vascular pedicle — these are most vulnerable). Risk factors: ulnar negative variance (short ulna relative to the radius — increases load through the lunate against the radius), repetitive trauma, and single-vessel supply pattern. Lichtman classification: Stage I (normal XR, MRI shows AVN), Stage II (sclerotic lunate on XR), Stage IIIA (lunate fragmentation/collapse + NO carpal collapse), Stage IIIB (lunate collapse + carpal collapse/proximal migration of capitate), Stage IV (generalised carpal OA). Treatment: I-II → immobilisation, or radial shortening osteotomy/ulnar lengthening (if ulnar negative variance — equalises load). IIIA → radial shortening or vascularised bone graft (4+5 ECA pedicled graft from distal radius). IIIB → proximal row carpectomy or limited carpal fusion. IV → total wrist arthrodesis.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Dupuytren",
          "range": "Q1071-Q1075",
          "questions": [
            {
              "number": 1071,
              "stem": "Dupuytren disease — the pathological tissue responsible for contracture is:",
              "options": [
                "The flexor tendons themselves",
                "The extensor tendons",
                "The skin only",
                "The palmar FASCIA (myofibroblasts within the palmar and digital fascia proliferate and contract, forming cords that progressively flex the MCP and PIP joints)",
                "The bones of the hand"
              ],
              "answer": "D",
              "explanation": "Dupuytren disease is a fibroproliferative disorder of the PALMAR FASCIA — myofibroblasts (fibroblasts expressing α-smooth muscle actin) proliferate within the palmar and digital fascial bands, forming NODULES (early) and CORDS (later). The cords progressively contract, pulling the MCP and PIP joints into fixed flexion. It does NOT involve the flexor tendons (which remain normal beneath the contracted fascia). Commonly affected: ring finger (most common), little finger. Risk factors (diathesis): male, >50yr, Northern European, family history, diabetes, epilepsy (phenytoin), alcohol, smoking, manual labour (controversial). Garrod pads (knuckle pads), Peyronie disease, and Ledderhose disease (plantar fascia) — associated fibromatoses. Treatment: observation (if not functionally limiting). Needle aponeurotomy (percutaneous division of cord — office procedure, high recurrence ~60%). Collagenase injection (enzymatic fasciotomy — clostridial collagenase injected into the cord, hand manipulated next day to rupture it). Fasciectomy (surgical excision of diseased fascia — lowest recurrence ~20-30%, most invasive). Hueston tabletop test: if the palm cannot be placed flat on the table → indicates contracture >30° MCP, consider intervention.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1072,
              "stem": "In Dupuytren disease, the pathological tissue that causes finger contracture is called:",
              "options": [
                "A tendon",
                "A ligament",
                "A cord",
                "A nodule only",
                "A ganglion"
              ],
              "answer": "C",
              "explanation": "Dupuytren disease involves pathological thickening of the palmar fascia. The process begins with nodules (proliferative fibroblasts/myofibroblasts) which progress to cords (mature collagen bands). The cords contract over time, drawing the fingers into flexion. The most commonly affected finger is the ring finger, followed by the little finger. The cord is distinct from the normal palmar fascia structures (Cleland and Grayson ligaments, natatory ligaments, spiral band).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1073,
              "stem": "The spiral cord in Dupuytren disease displaces which important structure?",
              "options": [
                "Digital neurovascular bundle",
                "Flexor tendons",
                "Extensor tendons",
                "Lumbrical muscles",
                "A1 pulley"
              ],
              "answer": "A",
              "explanation": "The spiral cord forms from four anatomical structures: pretendinous band, spiral band, lateral digital sheet, and Grayson ligament. As it contracts, it displaces the neurovascular bundle centrally and superficially, placing it at significant risk during surgery. The surgeon must always identify and protect the neurovascular bundle when performing fasciectomy. The spiral cord is the most dangerous cord because of this displacement pattern.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1074,
              "stem": "Dupuytren disease involves pathological thickening and contracture of which structure?",
              "options": [
                "Flexor tendons",
                "Palmar fascia (palmar aponeurosis)",
                "Extensor tendons",
                "Volar plate",
                "Skin only"
              ],
              "answer": "B",
              "explanation": "Dupuytren disease is a fibroproliferative disorder of the palmar fascia (palmar aponeurosis). Myofibroblasts cause progressive contracture of the fascial bands, leading to fixed flexion contracture of the MCP and PIP joints. The ring finger is most commonly affected, followed by the little finger. Risk factors: Northern European descent (Viking disease), male, age >50, family history, diabetes, epilepsy (phenytoin), alcohol, smoking. The disease does NOT involve the flexor tendons themselves — the tendons function normally beneath the contracted fascia. Treatment: observation (early), collagenase injection (Xiapex), needle aponeurotomy, or surgical fasciectomy (limited or dermofasciectomy for recurrent disease).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1075,
              "stem": "In Dupuytren disease, the spiral cord is clinically important because it:",
              "options": [
                "Improves hand function",
                "Has no clinical significance",
                "Only affects the thumb",
                "Is always visible on ultrasound",
                "Displaces the neurovascular bundle centrally and superficially, putting it at risk during surgery"
              ],
              "answer": "E",
              "explanation": "The spiral cord in Dupuytren disease is formed from four pathological structures: the pretendinous band (becomes pretendinous cord), the spiral band, the lateral digital sheet, and the Grayson ligament. As the spiral cord contracts, it displaces the neurovascular bundle from its normal lateral position to a more CENTRAL and SUPERFICIAL location. This puts the digital nerve and artery at significant risk of injury during fasciectomy — especially at the level of the proximal phalanx where the displacement is greatest. The surgeon must identify and protect the neurovascular bundles at all stages of dissection. Cleland ligaments (dorsal to the NV bundle) are NOT involved in Dupuytren disease and serve as a useful landmark — the NV bundle lies palmar to Cleland ligaments.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "TFCC",
          "range": "Q1076",
          "questions": [
            {
              "number": 1076,
              "stem": "The TFCC (triangular fibrocartilage complex) is the primary stabiliser of the:",
              "options": [
                "Radiocarpal joint",
                "DRUJ (distal radio-ulnar joint) — the TFCC connects the distal radius to the ulna and provides stability during forearm rotation",
                "MCP joints",
                "Scapholunate joint",
                "CMC joint of the thumb"
              ],
              "answer": "B",
              "explanation": "The TFCC is a complex of fibrocartilage and ligaments on the ulnar side of the wrist that stabilises the DRUJ, cushions the ulnocarpal articulation, and allows smooth forearm rotation. Components: (1) articular disc (triangular fibrocartilage proper — load-bearing), (2) dorsal and palmar radio-ulnar ligaments (primary DRUJ stabilisers), (3) ulnolunate and ulnotriquetral ligaments, (4) meniscus homologue, (5) ECU subsheath. Palmer classification: Class I = traumatic tears (IA=central perforation, IB=ulnar avulsion — most important clinically, best healing potential with repair). Class II = degenerative. TFCC tears cause: ulnar-sided wrist pain (most common cause), clicking, weakness of grip, DRUJ instability. Diagnosis: fovea sign (tenderness between ulnar styloid and FCU — most sensitive clinical test), MRI arthrography (gold standard imaging), wrist arthroscopy (gold standard overall). Treatment: IB tears (ulnar peripheral) → arthroscopic repair (good healing due to peripheral blood supply). IA tears (central) → debridement (avascular central zone — won't heal with repair).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Flexor Tendons",
          "range": "Q1077-Q1080",
          "questions": [
            {
              "number": 1077,
              "stem": "A jersey finger is an avulsion of which tendon from the distal phalanx?",
              "options": [
                "FDS",
                "Terminal extensor tendon",
                "Central slip",
                "EPL",
                "FDP"
              ],
              "answer": "E",
              "explanation": "A jersey finger is a closed avulsion of the FDP tendon from its insertion on the distal phalanx, caused by forced extension of a flexed finger (e.g., grabbing a jersey in rugby/football). The ring finger is most commonly affected (75%). The patient cannot actively flex the DIP joint. Leddy and Packer classification: Type I = tendon retracts to palm (no vincular blood supply, urgent repair within 7–10 days). Type II = retracts to PIP (short vinculum intact, repair within 3 months). Type III = bony avulsion stays at A4 pulley (repair at leisure).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1078,
              "stem": "The flexor tendon zone of 'no man's land' (Zone II) extends from:",
              "options": [
                "The A1 pulley to the FDS insertion (middle phalanx)",
                "Wrist crease to mid-palm",
                "The FDS insertion to the DIP joint",
                "The carpal tunnel to the wrist",
                "The forearm to the carpal tunnel"
              ],
              "answer": "A",
              "explanation": "Zone II ('no man's land', named by Bunnell) extends from the proximal edge of the A1 pulley to the insertion of FDS at the middle phalanx. In this zone, both FDP and FDS tendons run together within the flexor sheath beneath the pulley system. Repairs in this zone are technically demanding due to the confined space and risk of adhesion formation between the two tendons and the sheath. Modern results with early active mobilisation protocols have greatly improved outcomes.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1079,
              "stem": "The A2 and A4 pulleys are the most important pulleys for flexor tendon function. They are located over:",
              "options": [
                "The MCP joint and DIP joint",
                "The wrist and palm",
                "The PIP joint and DIP joint",
                "The proximal phalanx (A2) and middle phalanx (A4)",
                "The metacarpal and proximal phalanx"
              ],
              "answer": "D",
              "explanation": "The A2 pulley is located over the proximal phalanx and the A4 over the middle phalanx. They are the critical pulleys that prevent bowstringing of the flexor tendons during finger flexion. Loss of either A2 or A4 significantly impairs grip strength and tendon excursion. During flexor tendon surgery, these pulleys must be preserved or reconstructed. There are 5 annular (A1–A5) and 3 cruciate (C1–C3) pulleys. A1 pulley involvement causes trigger finger.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1080,
              "stem": "The modified Kessler technique is most commonly used for:",
              "options": [
                "Extensor tendon repair",
                "Nerve repair",
                "Flexor tendon core suture repair",
                "Ligament reconstruction",
                "Skin closure"
              ],
              "answer": "C",
              "explanation": "The modified Kessler suture is the most widely used core suture technique for flexor tendon repair. It is a grasping suture that provides a 2-strand repair. Modern practice favours 4-strand or 6-strand repairs (e.g., modified Kessler + epitendinous suture, or cruciate repair) which are stronger and permit early active mobilisation. The epitendinous (peripheral) suture adds 10–50% to repair strength and smooths the repair surface.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Hand Infections",
          "range": "Q1081",
          "questions": [
            {
              "number": 1081,
              "stem": "Kanavel signs are used to diagnose which hand infection?",
              "options": [
                "Flexor tendon sheath infection (suppurative tenosynovitis)",
                "Paronychia",
                "Felon (pulp space infection)",
                "Web space infection",
                "Deep space infection"
              ],
              "answer": "A",
              "explanation": "Kanavel signs diagnose flexor tendon sheath infection (suppurative/pyogenic tenosynovitis): (1) fusiform (sausage-shaped) swelling of the finger, (2) flexed posture of the finger, (3) tenderness along the entire flexor tendon sheath, (4) pain on passive extension of the finger (most reliable sign). This is a surgical emergency requiring urgent incision, drainage, and irrigation of the tendon sheath, combined with IV antibiotics. Delay leads to tendon necrosis and loss of finger function.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Swan Neck",
          "range": "Q1082",
          "questions": [
            {
              "number": 1082,
              "stem": "A swan-neck deformity of the finger consists of:",
              "options": [
                "PIP flexion and DIP hyperextension",
                "MCP hyperextension and PIP flexion",
                "MCP flexion and IP extension",
                "DIP hyperextension and MCP flexion",
                "PIP hyperextension and DIP flexion"
              ],
              "answer": "E",
              "explanation": "Swan-neck deformity: PIP hyperextension + DIP flexion. It is the REVERSE pattern of boutonnière. Causes include: (1) FDS rupture or laxity (rheumatoid arthritis), (2) intrinsic muscle tightness (cerebral palsy, intrinsic-plus), (3) volar plate laxity at PIP, (4) untreated mallet finger (DIP flexion leads to compensatory PIP hyperextension via retinacular ligament imbalance). Treatment depends on the cause and whether the PIP is passively correctable.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Scaphoid",
          "range": "Q1083",
          "questions": [
            {
              "number": 1083,
              "stem": "The Herbert classification of scaphoid fractures divides fractures into:",
              "options": [
                "Displaced and undisplaced only",
                "Proximal, waist, and distal",
                "Acute and chronic only",
                "Stable (Type A) and unstable (Type B)",
                "Open and closed"
              ],
              "answer": "D",
              "explanation": "Herbert classification: Type A = stable acute (A1 = tubercle fracture, A2 = incomplete waist fracture). Type B = unstable acute (B1 = distal oblique, B2 = complete waist, B3 = proximal pole, B4 = trans-scaphoid perilunate fracture-dislocation). Type C = delayed union. Type D = established non-union (D1 = fibrous, D2 = sclerotic). The Herbert screw (headless compression screw) was designed specifically for scaphoid fracture fixation, providing compression without a protruding head.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Extensor Tendons",
          "range": "Q1084-Q1085",
          "questions": [
            {
              "number": 1084,
              "stem": "A mallet finger deformity results from disruption of the:",
              "options": [
                "Central slip of the extensor tendon at the PIP joint",
                "Terminal extensor tendon at the DIP joint",
                "FDP tendon at the DIP joint",
                "Sagittal band at the MCP joint",
                "Volar plate at the PIP joint"
              ],
              "answer": "B",
              "explanation": "Mallet finger is caused by disruption of the terminal extensor tendon at its insertion on the distal phalanx, resulting in a flexion deformity at the DIP joint and inability to actively extend the DIP. It can be tendinous (closed injury from forced flexion of the extended DIP) or bony (avulsion fracture of the dorsal base of the distal phalanx). Treatment: continuous splinting of the DIP in extension for 6–8 weeks. Bony mallet with >30% articular involvement or volar subluxation may need surgical fixation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1085,
              "stem": "A boutonnière deformity consists of:",
              "options": [
                "DIP flexion and PIP hyperextension",
                "MCP hyperextension and PIP flexion",
                "PIP flexion and DIP hyperextension",
                "DIP hyperextension and MCP flexion",
                "PIP and DIP flexion"
              ],
              "answer": "C",
              "explanation": "Boutonnière deformity: PIP joint flexion (from disruption of the central slip of the extensor mechanism at the PIP) and DIP joint hyperextension (from volar migration of the lateral bands, which then act as DIP extensors rather than PIP extensors). The PIP 'buttonholes' through the torn central slip. Acute treatment: PIP splinting in extension. Chronic fixed deformity may require surgical reconstruction.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Carpal Instability",
          "range": "Q1086",
          "questions": [
            {
              "number": 1086,
              "stem": "A scapholunate ligament injury results in which pattern on plain radiograph?",
              "options": [
                "Narrowed scapholunate gap",
                "Ulnar translocation of the carpus",
                "Volar intercalated segment instability (VISI)",
                "Normal radiograph always",
                "Widened scapholunate gap >3 mm (Terry-Thomas sign)"
              ],
              "answer": "E",
              "explanation": "Scapholunate ligament disruption produces a widened scapholunate interval (>3 mm on PA radiograph) — the Terry-Thomas sign (named after the gap-toothed comedian). The scaphoid flexes (becomes more vertical) and the lunate extends, producing a DISI pattern (dorsal intercalated segment instability) with a scapholunate angle >60° on lateral view (normal 30–60°). Untreated, this progresses to SLAC (scapholunate advanced collapse) arthritis.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Trigger Finger",
          "range": "Q1087-Q1088",
          "questions": [
            {
              "number": 1087,
              "stem": "Trigger finger is caused by a size mismatch between the flexor tendon and which pulley?",
              "options": [
                "A1 pulley",
                "A2 pulley",
                "A4 pulley",
                "C1 pulley",
                "A5 pulley"
              ],
              "answer": "A",
              "explanation": "Trigger finger (stenosing tenosynovitis) is caused by thickening of the A1 pulley at the MCP joint level, creating a size mismatch with the underlying flexor tendon. The tendon develops a nodule that catches as it passes through the constricted A1 pulley during flexion/extension, producing clicking, locking, and eventually a fixed flexion deformity. Treatment: splinting → steroid injection (1–2 attempts) → surgical A1 pulley release.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1088,
              "stem": "Trigger finger is caused by:",
              "options": [
                "Extensor tendon subluxation",
                "Fracture of the proximal phalanx",
                "Dupuytren contracture",
                "Stenosis of the A1 pulley with a thickened flexor tendon nodule catching on entry",
                "Carpal tunnel compression"
              ],
              "answer": "D",
              "explanation": "Trigger finger (stenosing flexor tenosynovitis) is caused by a mismatch between the flexor tendon and the A1 pulley at the level of the MCP joint. The A1 pulley narrows or the tendon develops a nodular thickening — the tendon catches on the proximal edge of the pulley during flexion, then suddenly releases (triggering) during extension, producing a painful click or locking. The ring finger is most commonly affected, followed by the thumb ('trigger thumb'). Treatment: splinting (MCP extension splint), steroid injection into the A1 pulley sheath (60-70% cure rate with 1-2 injections), or surgical A1 pulley release (percutaneous or open — 95-100% cure). In diabetics: lower response to injection, higher recurrence.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Tendon Transfer",
          "range": "Q1089",
          "questions": [
            {
              "number": 1089,
              "stem": "In a high radial nerve palsy causing wrist and finger drop, which tendon transfer restores wrist extension?",
              "options": [
                "FDS ring finger to EDC",
                "Pronator teres to ECRB",
                "FCR to EDC",
                "Palmaris longus to EPL",
                "FDS middle finger to EPL"
              ],
              "answer": "B",
              "explanation": "The classic tendon transfer set for high radial nerve palsy (wrist drop + finger/thumb extension loss) is: (1) Pronator teres → ECRB (restores wrist extension), (2) FCR or FCU → EDC (restores finger extension), (3) Palmaris longus → rerouted EPL (restores thumb extension). Requirements for tendon transfer: expendable donor, adequate strength (≥MRC 4), synergistic function (wrist flexor → wrist extensor), sufficient excursion, and supple joints. Jones, Boyes, and Brand described various transfer combinations.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            }
          ]
        },
        {
          "title": "Anatomy",
          "range": "Q1090-Q1094",
          "questions": [
            {
              "number": 1090,
              "stem": "The anatomical snuffbox is bordered by which tendons?",
              "options": [
                "FPL and FPB",
                "ECRL and ECRB",
                "EPL (ulnar border) and APL + EPB (radial border)",
                "EDC and EIP",
                "FCR and PL"
              ],
              "answer": "C",
              "explanation": "The anatomical snuffbox is bordered by EPL (extensor pollicis longus) on the ulnar (dorsal) side, and APL (abductor pollicis longus) and EPB (extensor pollicis brevis) on the radial (volar) side. The floor contains the scaphoid and trapezium. The radial artery crosses the snuffbox floor. Tenderness in the anatomical snuffbox after a fall is the hallmark clinical finding for a suspected scaphoid fracture. The cephalic vein crosses superficially and the superficial branch of the radial nerve is at risk during surgery.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1091,
              "stem": "The carpal tunnel contains how many tendons plus the median nerve?",
              "options": [
                "4 tendons + median nerve",
                "6 tendons + median nerve",
                "10 tendons + median nerve",
                "9 tendons + median nerve",
                "12 tendons + median nerve"
              ],
              "answer": "D",
              "explanation": "The carpal tunnel contains 10 structures: 9 tendons + the median nerve. The tendons are: 4 × FDS (flexor digitorum superficialis), 4 × FDP (flexor digitorum profundus), and 1 × FPL (flexor pollicis longus). The median nerve is the most superficial structure in the tunnel, lying just beneath the transverse carpal ligament (flexor retinaculum). FCR travels in a separate fibro-osseous tunnel. The ulnar nerve and artery travel through Guyon canal (separate from the carpal tunnel, superficial to the retinaculum).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1092,
              "stem": "Cleland ligaments and Grayson ligaments are found in the digits. Which statement is correct?",
              "options": [
                "Cleland ligaments are volar to the neurovascular bundle, Grayson are dorsal",
                "Both are dorsal",
                "Cleland ligaments are dorsal to the NV bundle, Grayson ligaments are volar",
                "Both are volar",
                "Neither exists — they are fictional structures"
              ],
              "answer": "C",
              "explanation": "Cleland ligaments are dorsal to the neurovascular bundle (they hold the skin to the skeleton dorsally). Grayson ligaments are volar to the neurovascular bundle (they hold the skin volarly). Mnemonic: 'C comes before G, Ceiling before Ground' — Cleland is dorsal (ceiling), Grayson is volar (ground). In Dupuytren disease, the Grayson ligament (volar) becomes part of the spiral cord, but the Cleland ligament (dorsal) is NOT involved in Dupuytren contracture. The neurovascular bundle lies between the two ligaments.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1093,
              "stem": "The flexor tendon pulley system — the most important pulleys for preventing bowstringing are:",
              "options": [
                "A2 (over the proximal phalanx) and A4 (over the middle phalanx) annular pulleys",
                "C1 and C2 cruciate pulleys",
                "A1 and A3 annular pulleys",
                "A5 annular pulley only",
                "All pulleys are equally important"
              ],
              "answer": "A",
              "explanation": "The A2 and A4 annular pulleys are the most critical pulleys for preventing flexor tendon bowstringing during finger flexion. They are the longest and strongest pulleys: A2 is over the proximal phalanx (attached to bone), A4 is over the middle phalanx (attached to bone). If A2 and/or A4 are disrupted or released surgically, significant bowstringing occurs → loss of flexion power and range. During flexor tendon surgery, A2 and A4 must be PRESERVED. A1 pulley can be released safely (trigger finger release). A3 and A5 are over the PIP and DIP joints respectively and can be released if needed for exposure. C1, C2, and C3 cruciate pulleys are between the annular pulleys and allow tendon gliding during flexion.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1094,
              "stem": "The flexor digitorum superficialis (FDS) tendon splits around the FDP tendon at the level of the proximal phalanx before inserting on the middle phalanx. This arrangement is called the:",
              "options": [
                "Vincula system",
                "Chiasma of Camper (decussation of FDS)",
                "Pulley system",
                "Retinacular system",
                "Sheath system"
              ],
              "answer": "B",
              "explanation": "The chiasma of Camper is the decussation (crossing) of the two slips of the FDS tendon around the FDP tendon. At the level of the proximal phalanx, the FDS tendon splits into two slips, the FDP passes through the gap, and the two FDS slips then reunite before inserting on the middle phalanx (palmar surface, lateral ridges). This arrangement places the FDP deep to the FDS proximally, then superficial to the FDS in the digit — creating the complex arrangement that makes Zone II flexor tendon surgery challenging ('no man's land'). The FDS flexes the PIP joint, while the FDP flexes the DIP joint. Testing: hold other fingers in extension (blocks the common FDP muscle belly) → isolated PIP flexion confirms FDS function.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Thumb",
          "range": "Q1095",
          "questions": [
            {
              "number": 1095,
              "stem": "Gamekeeper's thumb (skier's thumb) involves injury to which structure?",
              "options": [
                "Radial collateral ligament of the thumb MCP joint",
                "Volar plate of the thumb MCP joint",
                "Extensor pollicis longus",
                "First dorsal interosseous",
                "Ulnar collateral ligament (UCL) of the thumb MCP joint"
              ],
              "answer": "E",
              "explanation": "Gamekeeper's/skier's thumb involves injury to the UCL of the thumb MCP joint, caused by forced abduction/valgus stress. The critical concern is a Stener lesion — where the torn UCL displaces superficial to the adductor aponeurosis, preventing healing (the aponeurosis acts as a physical block between the ligament and its insertion). A Stener lesion requires surgical repair. Without a Stener lesion, immobilisation in a thumb spica for 4-6 weeks usually suffices.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Extensor Zones",
          "range": "Q1096",
          "questions": [
            {
              "number": 1096,
              "stem": "Extensor tendon injuries are classified into zones I-VIII. Zone III is located over the:",
              "options": [
                "PIP joint (central slip area)",
                "DIP joint",
                "MCP joint",
                "Wrist",
                "Forearm"
              ],
              "answer": "A",
              "explanation": "Extensor tendon zones (dorsal hand): I = DIP joint (mallet finger). II = middle phalanx. III = PIP joint (boutonnière if central slip disrupted). IV = proximal phalanx. V = MCP joint (human bite injury/fight bite, sagittal band disruption). VI = dorsum of hand (metacarpals). VII = wrist (beneath extensor retinaculum). VIII = forearm. Odd numbers are over joints, even numbers are between joints. Zone III injuries (central slip) are particularly important — missed diagnosis leads to chronic boutonnière deformity.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Rheumatoid",
          "range": "Q1097",
          "questions": [
            {
              "number": 1097,
              "stem": "In the rheumatoid hand, the typical MCP joint deformity is:",
              "options": [
                "Hyperextension with radial deviation",
                "Volar plate injury with hyperextension",
                "Ankylosis in extension",
                "Dorsal dislocation",
                "Ulnar drift with volar subluxation"
              ],
              "answer": "E",
              "explanation": "The classic rheumatoid MCP deformity is ulnar drift (ulnar deviation of the fingers at the MCP joints) with volar subluxation of the proximal phalanges. This occurs due to: (1) synovitis destroying the capsule and collateral ligaments, (2) extensor tendon subluxation ulnarly (off the metacarpal heads), (3) weakening of the radial sagittal bands, (4) the pull of intrinsic muscles in an ulnar direction, and (5) the normal ulnar bias of finger tendons during power grip. Surgery may include synovectomy, extensor tendon centralisation, or MCP arthroplasty (Swanson silicone implants).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Wrist Anatomy",
          "range": "Q1098",
          "questions": [
            {
              "number": 1098,
              "stem": "The scaphoid fracture is at high risk of avascular necrosis, particularly proximal pole fractures, because the blood supply enters:",
              "options": [
                "Proximally from the radiocarpal joint",
                "Distally through the dorsal ridge (retrograde blood supply)",
                "Equally from all directions",
                "Through the palmar surface only",
                "Through the volar carpal ligaments"
              ],
              "answer": "B",
              "explanation": "The scaphoid receives its blood supply primarily through the dorsal ridge from branches of the radial artery, which enter distally and supply the bone in a retrograde (distal to proximal) fashion. The proximal pole has the most tenuous blood supply — a fracture through the waist can disrupt the retrograde flow to the proximal pole, leading to AVN. AVN risk: proximal pole fractures ~30-40%, waist fractures ~10-20%, tubercle fractures ~0%. MRI is the gold standard for detecting occult scaphoid fractures and early AVN.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Fracture",
          "range": "Q1099-Q1100",
          "questions": [
            {
              "number": 1099,
              "stem": "A Bennett fracture is:",
              "options": [
                "A transverse fracture of the 5th metacarpal neck (boxer's fracture)",
                "A fracture of the scaphoid waist",
                "An intra-articular fracture-subluxation of the base of the 1st metacarpal (thumb CMC joint)",
                "A fracture of the hamate hook",
                "A comminuted intra-articular fracture of the 1st metacarpal base"
              ],
              "answer": "C",
              "explanation": "A Bennett fracture is an intra-articular fracture-subluxation of the base of the 1st metacarpal at the trapeziometacarpal (thumb CMC) joint. A small volar-ulnar fragment remains attached to the trapezium (via the strong volar oblique/beak ligament), while the metacarpal shaft subluxes dorsally and proximally (pulled by APL). This is unstable and requires anatomical reduction + fixation (closed reduction + percutaneous K-wires or ORIF). A Rolando fracture is a comminuted (Y- or T-shaped) intra-articular fracture of the same location — worse prognosis.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1100,
              "stem": "A boxer's fracture is a fracture of which bone and where?",
              "options": [
                "5th metacarpal shaft",
                "4th metacarpal base",
                "Distal phalanx of the index finger",
                "5th metacarpal neck",
                "Proximal phalanx of the ring finger"
              ],
              "answer": "D",
              "explanation": "A boxer's fracture is a fracture of the neck of the 5th metacarpal, caused by a punch or direct impact with a closed fist. The distal fragment typically angulates volarly (apex dorsal). Up to 40° of volar angulation is acceptable in the 5th metacarpal because the 5th CMC joint has ~30° of compensatory flexion-extension motion. Less angulation is tolerated in the 2nd and 3rd metacarpals (10-15°) because their CMC joints are rigid. Treatment: neighbour strapping or ulnar gutter splint for 3-4 weeks. Operative fixation only for >40° angulation, rotational deformity, or open fractures. Always examine for fight bite (tooth laceration over MCP — needs washout).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Ganglion",
          "range": "Q1101",
          "questions": [
            {
              "number": 1101,
              "stem": "The most common soft tissue tumour of the hand and wrist is:",
              "options": [
                "Lipoma",
                "Giant cell tumour of tendon sheath",
                "Epidermoid inclusion cyst",
                "Haemangioma",
                "Ganglion cyst"
              ],
              "answer": "E",
              "explanation": "Ganglion cysts are the most common soft tissue 'tumour' (actually a cyst, not a true neoplasm) of the hand and wrist, accounting for 50-70% of hand/wrist masses. They arise from joint capsules or tendon sheaths and contain thick, mucinous fluid. The most common location is the dorsal wrist (scapholunate interval, 60-70%). Volar wrist ganglions arise from the radiocarpal or STT joint and are near the radial artery. Treatment: observation (50% resolve spontaneously), aspiration (high recurrence ~50%), or surgical excision (recurrence ~5-10%, risk of neurovascular injury with volar ganglions).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Nail Bed",
          "range": "Q1102",
          "questions": [
            {
              "number": 1102,
              "stem": "A subungual haematoma involving >50% of the nail with an associated distal phalanx fracture should be treated with:",
              "options": [
                "Observation only",
                "Trephination (drilling a hole in the nail) only",
                "Nail removal, nail bed repair, and fracture stabilisation if needed",
                "Amputation of the fingertip",
                "IV antibiotics and no surgery"
              ],
              "answer": "C",
              "explanation": "When a subungual haematoma involves >50% of the nail area AND there is an underlying distal phalanx fracture, this constitutes an open fracture (the nail bed laceration communicates with the fracture through the nail bed). Management: nail removal, repair of the nail bed laceration (using absorbable sutures under loupe magnification), and replace the nail (or use a silicone spacer) under the eponychial fold to maintain the nail fold space and act as a splint. The fracture is typically stabilised by the nail bed repair or a K-wire for displaced fractures. Simple trephination alone risks missing a significant nail bed injury.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Kienbock",
          "range": "Q1103",
          "questions": [
            {
              "number": 1103,
              "stem": "Kienböck disease is avascular necrosis of which carpal bone?",
              "options": [
                "Lunate",
                "Scaphoid",
                "Triquetrum",
                "Capitate",
                "Hamate"
              ],
              "answer": "A",
              "explanation": "Kienböck disease is AVN of the lunate, associated with ulna minus variance (short ulna relative to the radius), which may create uneven load distribution across the radiocarpal joint. Lichtman classification: Stage I = normal XR, MRI shows marrow oedema. Stage II = lunate sclerosis on XR. Stage IIIA = lunate collapse, no carpal collapse (scaphoid rotation). Stage IIIB = lunate collapse WITH carpal collapse (fixed scaphoid rotation). Stage IV = generalised arthritis. Treatment: I-II = unloading (radial shortening osteotomy if ulna minus, joint levelling). IIIA = revascularisation or PRC. IIIB-IV = salvage (proximal row carpectomy, wrist fusion).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Injury",
          "range": "Q1104",
          "questions": [
            {
              "number": 1104,
              "stem": "A gamekeeper's thumb (skier's thumb) involves injury to which structure?",
              "options": [
                "Radial collateral ligament of the thumb MCP",
                "Scapholunate ligament",
                "TFCC",
                "UCL (ulnar collateral ligament) of the thumb MCP joint",
                "Volar plate of the PIP joint"
              ],
              "answer": "D",
              "explanation": "Gamekeeper's/skier's thumb is an injury to the UCL (ulnar collateral ligament) of the thumb MCP joint, typically from forced abduction/valgus stress (fall onto an outstretched thumb, classically while holding a ski pole). The Stener lesion is a critical complication: the torn UCL flips over the adductor aponeurosis, placing the aponeurosis between the torn ligament end and its bony insertion — this prevents healing without surgery (the aponeurosis acts as a physical block to reattachment). Clinical examination: laxity to valgus stress at the thumb MCP (>30° opening or >15° greater than contralateral). MRI or USS can identify a Stener lesion. Treatment: partial tear without Stener → thumb spica cast for 4-6 weeks. Complete tear with Stener lesion → surgical repair/reattachment + K-wire.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Wrist Instability",
          "range": "Q1105",
          "questions": [
            {
              "number": 1105,
              "stem": "Scapholunate dissociation is diagnosed on a PA wrist radiograph by a scapholunate gap (Terry Thomas sign) of greater than:",
              "options": [
                "1 mm",
                "3 mm",
                "2 mm",
                "5 mm",
                "10 mm"
              ],
              "answer": "B",
              "explanation": "Scapholunate dissociation: a gap >3 mm between the scaphoid and lunate on a PA grip (clenched fist) radiograph is diagnostic (Terry Thomas/Madonna sign — gap between the bones like the gap between the teeth of these celebrities). The scapholunate ligament (SL) is the most important intrinsic ligament of the wrist. When ruptured: the scaphoid flexes (ring sign on PA view — foreshortened scaphoid showing a ring-shaped cortical outline) and the lunate extends → DISI (dorsal intercalated segment instability) pattern on lateral view (SL angle >70°, normal 30-60°). Untreated SL dissociation progresses to SLAC (scapholunate advanced collapse) wrist: Stage I = radial styloid-scaphoid OA, II = radioscaphoid OA, III = midcarpal OA (capitolunate).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            }
          ]
        },
        {
          "title": "Trauma",
          "range": "Q1106",
          "questions": [
            {
              "number": 1106,
              "stem": "A fight bite (human bite wound over the MCP joint) is an orthopaedic emergency because:",
              "options": [
                "It is always a simple laceration",
                "It never involves the joint",
                "Human oral flora (including Eikenella corrodens) can penetrate the MCP joint capsule, causing rapidly progressive septic arthritis and osteomyelitis",
                "Antibiotics alone are always sufficient",
                "The wound always heals spontaneously"
              ],
              "answer": "C",
              "explanation": "A fight bite (clenched fist injury) occurs when a tooth penetrates the skin over the MCP joint during a punch. In the clenched fist position, the extensor tendon hood and joint capsule slide distally — when the fist opens, the wound no longer aligns with the deeper penetration site, creating a 'trapdoor' effect that seals bacteria within the joint. Human oral flora (Eikenella corrodens, Streptococci, anaerobes, Staphylococcus) can cause rapidly destructive septic arthritis and osteomyelitis. Treatment: urgent surgical exploration, washout of the MCP joint, debridement of devitalised tissue, IV co-amoxiclav (covers Eikenella), and leave the wound open. NEVER close a fight bite primarily. Always X-ray to exclude a retained tooth fragment or fracture.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        }
      ]
    },
    {
      "title": "Paediatrics",
      "chapters": [
        {
          "title": "Knee",
          "range": "Q1107",
          "questions": [
            {
              "number": 1107,
              "stem": "Osteochondritis dissecans (OCD) of the knee most commonly affects the:",
              "options": [
                "Lateral tibial plateau",
                "Patella",
                "Fibular head",
                "Lateral femoral condyle exclusively",
                "Lateral aspect of the MEDIAL femoral condyle (the most common location — the 'classic' OCD site, affecting the posterolateral aspect of the medial condyle in ~75% of cases)"
              ],
              "answer": "E",
              "explanation": "OCD of the knee: a localised condition where a segment of articular cartilage and underlying subchondral bone becomes separated (partially or completely) from the surrounding bone. Most common location: posterolateral aspect of the MEDIAL femoral condyle (~75% — the 'classic' location visible on the AP XR and tunnel/notch view). Other locations: lateral femoral condyle (~15-20%), patella (~5%). Typically affects adolescents (10-20 years, males > females). Aetiology: likely multifactorial (repetitive microtrauma + focal ischaemia → subchondral bone necrosis → cartilage separation). Classification: Stable (intact cartilage covering — good prognosis in juveniles with open physes, ~50% heal with activity modification + NWB 6-12 weeks) vs Unstable (cartilage flap/loose body — requires surgery: fixation if fragment is viable, excision + microfracture/OATS/MACI if not). MRI is essential: T2-weighted shows high signal behind the lesion (fluid = unstable). Juvenile OCD (open physes): better prognosis than adult OCD (closed physes — higher rate of non-healing, more likely to need surgery).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Congenital",
          "range": "Q1108-Q1120",
          "questions": [
            {
              "number": 1108,
              "stem": "Congenital talipes equinovarus (clubfoot) managed by the Ponseti method — after correction of the cavus, adductus, and varus components, the equinus is corrected by:",
              "options": [
                "Serial casting alone in all cases",
                "Percutaneous Achilles tenotomy (required in ~80-90% of cases to correct the residual equinus after serial casting has corrected the other components)",
                "Open posterior release in all cases",
                "No treatment needed for equinus",
                "Botox injection only"
              ],
              "answer": "B",
              "explanation": "The Ponseti method corrects clubfoot components in a specific order: (1) cavus (corrected FIRST by supinating the forefoot — aligning it with the hindfoot), (2) adductus and varus (corrected simultaneously by abducting the foot around the talar head in sequential weekly casts — typically 4-6 casts), (3) equinus (corrected LAST). After serial casting corrects the cavus, adductus, and varus, residual equinus persists in ~80-90% of cases because the tight Achilles tendon cannot be fully stretched by casting alone. A percutaneous Achilles tenotomy (done in clinic under local anaesthesia in infants) allows the final correction of equinus. After tenotomy: the foot is casted in maximum dorsiflexion and abduction for 3 weeks. Then: foot abduction brace (Denis Browne bar) — full-time for 3 months, then night and nap time until age 4-5 years (prevents relapse). Relapse rate: ~5-10% with compliant bracing.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1109,
              "stem": "In congenital vertical talus, the hindfoot is in equinus and the forefoot is dorsally dislocated at which joint?",
              "options": [
                "Talonavicular joint",
                "Subtalar joint",
                "Calcaneocuboid joint",
                "Ankle joint",
                "Lisfranc joint"
              ],
              "answer": "A",
              "explanation": "Congenital vertical talus (CVT) is characterised by a rigid rocker-bottom flatfoot with dorsolateral dislocation of the navicular on the talar head at the talonavicular joint. The talus is vertically oriented (hence the name). The hindfoot is in equinus and valgus. It is differentiated from oblique talus (which reduces on plantarflexion — the lateral radiograph shows the navicular articulating with the talar head in plantarflexion). CVT is associated with neuromuscular conditions (spina bifida, arthrogryposis) and chromosomal abnormalities (trisomy 13, 18).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1110,
              "stem": "Congenital muscular torticollis is most commonly caused by:",
              "options": [
                "Cervical vertebral anomaly",
                "Klippel-Feil syndrome",
                "Atlantoaxial rotatory subluxation",
                "Sternocleidomastoid muscle fibrosis",
                "Posterior fossa tumour"
              ],
              "answer": "D",
              "explanation": "Congenital muscular torticollis results from fibrosis of the sternocleidomastoid (SCM) muscle, often presenting as a palpable 'pseudotumour' in the SCM at 2–4 weeks of age. The head tilts towards the affected side with the chin rotated to the opposite side. It is associated with DDH (10–20%) and should prompt hip screening. ~90% resolve with stretching exercises. Persistent cases may need surgical SCM release after 12 months.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1111,
              "stem": "Congenital radial club hand (radial longitudinal deficiency) is associated with which systemic condition?",
              "options": [
                "Down syndrome",
                "Thrombocytopenia-absent radius (TAR) syndrome and Fanconi anaemia",
                "Achondroplasia",
                "Osteogenesis imperfecta",
                "Ehlers-Danlos syndrome"
              ],
              "answer": "B",
              "explanation": "Radial longitudinal deficiency (radial club hand) is associated with several systemic conditions: TAR syndrome (thrombocytopenia with absent radius — characteristically the thumb is present despite absent radius), Fanconi anaemia (aplastic anaemia, increased cancer risk — requires blood tests to exclude), Holt-Oram syndrome (cardiac septal defects), and VACTERL association (Vertebral, Anorectal, Cardiac, Tracheoesophageal, Renal, Limb anomalies). All children with radial deficiency must have haematological investigation (FBC, chromosomal breakage studies for Fanconi) and cardiac assessment.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1112,
              "stem": "Poland syndrome is characterised by:",
              "options": [
                "Bilateral absence of the radius",
                "Bilateral clubfeet",
                "Unilateral absence of the sternal head of pectoralis major with ipsilateral hand anomalies (symbrachydactyly)",
                "Congenital hip dislocation with torticollis",
                "Multiple enchondromas with haemangiomas"
              ],
              "answer": "C",
              "explanation": "Poland syndrome: unilateral absence of the sternal head of pectoralis major (sternocostal portion) with ipsilateral upper limb anomalies — typically symbrachydactyly (short, webbed fingers). May also include chest wall anomalies (rib hypoplasia, breast hypoplasia), absence of latissimus dorsi, and rarely renal anomalies. It is sporadic (not inherited). Right side more commonly affected. Diagnosed clinically — asymmetric anterior axillary fold with hand anomalies. Treatment: reconstructive surgery (pectoralis transfer, hand reconstruction) as needed.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1113,
              "stem": "Arthrogryposis multiplex congenita is characterised by:",
              "options": [
                "Excessive joint hypermobility",
                "Brittle bones and frequent fractures",
                "Progressive muscle weakness starting in adolescence",
                "Multiple congenital joint contractures with loss of normal skin creases",
                "Joint hypermobility with skin hyperextensibility"
              ],
              "answer": "D",
              "explanation": "Arthrogryposis multiplex congenita (AMC) is a clinical syndrome characterised by multiple congenital joint contractures affecting ≥2 body areas. Features: stiff joints, loss of normal skin creases (waxy, featureless skin), atrophic muscles replaced by fibrous/fatty tissue. Intelligence is usually normal. Aetiology: anything causing fetal akinesia (neuromuscular disease, maternal disease, oligohydramnios, uterine anomalies). Treatment is challenging — serial casting, physiotherapy, surgical releases, tendon transfers. Recurrence of deformity after surgery is common.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1114,
              "stem": "Congenital pseudarthrosis of the tibia is most commonly associated with:",
              "options": [
                "Down syndrome",
                "Osteogenesis imperfecta",
                "Turner syndrome",
                "Marfan syndrome",
                "Neurofibromatosis type 1 (NF1)"
              ],
              "answer": "E",
              "explanation": "Congenital pseudarthrosis of the tibia is strongly associated with neurofibromatosis type 1 (NF1) — approximately 50% of children with this condition have NF1. The tibia shows anterolateral bowing, cortical thickening, and eventually develops a fracture that fails to unite (pseudarthrosis). It is one of the most challenging paediatric orthopaedic conditions to treat. Management options include: Ilizarov technique (bone transport/compression), intramedullary rodding (Williams rod), vascularised fibula graft, or BMP augmentation. Amputation may be necessary for refractory non-union.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1115,
              "stem": "Proximal femoral focal deficiency (PFFD) is a congenital limb deficiency classified by:",
              "options": [
                "Aitken classification (A-D based on femoral head/acetabular presence and subtrochanteric connection)",
                "Salter-Harris classification",
                "Gustilo-Anderson classification",
                "Enneking staging",
                "Catterall classification"
              ],
              "answer": "A",
              "explanation": "The Aitken classification grades PFFD based on radiographic appearance: Type A = femoral head present, adequate acetabulum, subtrochanteric connection present (bony connection between head and shaft will develop). Type B = femoral head present, adequate acetabulum, but NO bony connection to shaft (pseudarthrosis). Type C = femoral head absent/severely deficient, dysplastic acetabulum. Type D = femoral head and acetabulum absent. Treatment depends on severity and predicted LLD: mild (Type A) with adequate femoral length → limb lengthening. Severe (Type C-D) with major LLD → rotationplasty (Van Nes) or amputation + prosthesis.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            },
            {
              "number": 1116,
              "stem": "In a child with congenital talipes equinovarus (clubfoot) treated by the Ponseti method, a percutaneous Achilles tenotomy is required in approximately what percentage of cases?",
              "options": [
                "10%",
                "30%",
                "80%",
                "50%",
                "100%"
              ],
              "answer": "C",
              "explanation": "Percutaneous Achilles tenotomy is required in approximately 80-90% of clubfoot cases treated with the Ponseti method. It is performed after the cavus, adductus, and varus have been corrected by serial casting (usually 4-6 casts), but residual equinus persists. The tenotomy is performed under local anaesthesia as an outpatient procedure — the tendon regenerates within 3-4 weeks in the corrected (lengthened) position. After tenotomy, the final cast is applied for 3 weeks, then boots-and-bars (FAO) are worn 23 hours/day for 3 months, then nights-and-naps only until age 4-5.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1117,
              "stem": "Achondroplasia is the most common skeletal dysplasia. It is caused by a mutation in:",
              "options": [
                "COL1A1 (Type I collagen)",
                "COL2A1 (Type II collagen)",
                "EXT1 (exostosin)",
                "FGFR3 (fibroblast growth factor receptor 3) — gain-of-function mutation",
                "GNAS1"
              ],
              "answer": "D",
              "explanation": "Achondroplasia is caused by a gain-of-function mutation in FGFR3 (fibroblast growth factor receptor 3) — the mutation causes constitutive activation of the receptor, which INHIBITS chondrocyte proliferation in the growth plate → impaired endochondral ossification → shortened long bones (rhizomelic shortening — proximal segments most affected). Autosomal dominant, but ~80% are new mutations (unaffected parents). Features: rhizomelic short stature, macrocephaly, frontal bossing, midface hypoplasia, trident hand, genu varum, lumbar hyperlordosis with spinal stenosis (narrowed spinal canal from shortened pedicles). Intelligence is normal. Complications: foramen magnum stenosis (cervicomedullary compression in infancy — may need decompression), spinal stenosis (lumbar — progressive, may need decompression in adulthood), and recurrent otitis media.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1118,
              "stem": "Sprengel deformity is characterised by:",
              "options": [
                "Congenital high (undescended) scapula",
                "Congenital absence of the clavicle",
                "Congenital hip dislocation",
                "Congenital vertical talus",
                "Congenital knee dislocation"
              ],
              "answer": "A",
              "explanation": "Sprengel deformity is a congenital undescended (elevated) scapula — the scapula fails to descend from its embryological position at C4-C5 to its normal position at T2-T7. It causes: asymmetric shoulder height, restricted shoulder abduction, cosmetic deformity, and may have a bony bridge (omovertebral bone) connecting the scapula to the cervical spine. It is associated with Klippel-Feil syndrome (30%), congenital scoliosis, and renal anomalies. Cavendish grading (I-IV) assesses severity based on cosmetic appearance and shoulder function. Surgical treatment (Woodward or Green procedure): scapular repositioning for severe cases.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1119,
              "stem": "Tarsal coalition is an abnormal bony, cartilaginous, or fibrous connection between tarsal bones. The two most common types are:",
              "options": [
                "Talonavicular and calcaneocuboid",
                "Cuneiform-metatarsal and cuboid-metatarsal",
                "Navicular-cuneiform and cuboid-calcaneal",
                "Talus-tibia and fibula-calcaneal",
                "Calcaneonavicular and talocalcaneal (sustentaculum tali)"
              ],
              "answer": "E",
              "explanation": "The two most common tarsal coalitions are: (1) Calcaneonavicular (most common, ~53%) — best seen on oblique foot radiograph (the 'anteater nose' sign — elongated anterior process of calcaneus reaching towards the navicular). CT confirms. (2) Talocalcaneal (second most common, ~37%) — involves the sustentaculum tali (middle facet). Difficult to see on plain radiographs — the C-sign (a continuous C-shaped line on lateral XR formed by the outline of the dome of the talus and sustentaculum) is suggestive. CT or MRI confirms. Coalitions become symptomatic at age 8-12 (calcaneonavicular) or 12-16 (talocalcaneal) as they ossify. Presents: rigid painful flat foot, peroneal spasm, reduced subtalar motion. Treatment: orthoses → excision of coalition + interposition fat graft (if <50% of facet involved, no secondary OA) → triple arthrodesis (if extensive coalition or secondary OA).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1120,
              "stem": "Congenital muscular torticollis presents in infancy with the head tilted to one side and the chin rotated to the opposite side. It is caused by fibrosis of which muscle?",
              "options": [
                "Trapezius",
                "Sternocleidomastoid (SCM)",
                "Levator scapulae",
                "Scalene muscles",
                "Platysma"
              ],
              "answer": "B",
              "explanation": "Congenital muscular torticollis (CMT) is caused by fibrosis and shortening of the sternocleidomastoid (SCM) muscle, resulting in the head tilting TOWARDS the affected side (shortened SCM pulls the mastoid down) and the chin rotating AWAY (to the opposite side). A firm, non-tender 'tumour' or lump may be palpable within the SCM in early infancy (sternocleidomastoid tumour of infancy — fibromatosis colli). It is thought to result from intrauterine positioning or birth trauma causing compartment syndrome of the SCM. Treatment: ~90% resolve with physiotherapy (stretching — parents taught to stretch the SCM by gently rotating the chin towards the affected side and tilting the head away). Surgical release (bipolar SCM release): for persistent torticollis beyond 12-18 months despite physiotherapy. Check for DDH (associated in 5-20% of cases — similar intrauterine moulding mechanism).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Developmental",
          "range": "Q1121-Q1128",
          "questions": [
            {
              "number": 1121,
              "stem": "Rickets in children is caused by deficiency of vitamin D or calcium, leading to defective mineralisation of the growth plate. The characteristic radiographic finding is:",
              "options": [
                "Sclerotic metaphyses",
                "Dense epiphyses",
                "Periosteal new bone formation only",
                "Normal radiographic appearance",
                "Widened, frayed, and cupped metaphyses with indistinct zone of provisional calcification"
              ],
              "answer": "E",
              "explanation": "Rickets causes defective mineralisation of the growth plate (physis) — the zone of provisional calcification cannot mineralise properly, leading to accumulation of unmineralised osteoid and hypertrophied cartilage. Radiographic findings: (1) widened growth plates (excess unmineralised tissue), (2) frayed/irregular metaphyses (uneven mineralisation), (3) cupped metaphyses (concave deformity of the metaphyseal end), (4) indistinct/absent zone of provisional calcification (normally a dense white line — becomes invisible), (5) generalised osteopaenia, (6) bowing deformities (genu varum or valgum — weakened bone bends under weight-bearing). Laboratory: low Ca²⁺ (or normal if compensated by secondary hyperPTH), low phosphate, elevated ALP (osteoblast activity attempting to mineralise), elevated PTH, low 25(OH)D. Treatment: vitamin D supplementation (cholecalciferol), calcium, dietary advice. Refractory rickets: consider genetic causes (X-linked hypophosphataemia — FGF23-related).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1122,
              "stem": "Blount disease (tibia vara) is a pathological bowing of the proximal tibia caused by:",
              "options": [
                "Rickets only",
                "Growth disturbance of the posteromedial proximal tibial physis (medial tibial plateau growth plate suppression from excessive compressive loading)",
                "Vitamin D excess",
                "Femoral deformity only",
                "Normal physiological development"
              ],
              "answer": "B",
              "explanation": "Blount disease is a progressive varus deformity of the proximal tibia caused by growth disturbance (suppression) of the posteromedial proximal tibial physis due to excessive compressive loading (Hueter-Volkmann law: increased pressure inhibits growth, decreased pressure stimulates growth). It must be differentiated from physiological genu varum (normal in children <2 years — resolves spontaneously). Two forms: (1) Infantile Blount (1-3 years) — often bilateral, associated with obesity, early walking, African descent. Langenskiöld classification (I-VI) guides severity and treatment. (2) Adolescent Blount (>10 years) — usually unilateral, strongly associated with obesity. Treatment: bracing (for Langenskiöld I-III in <3yr), proximal tibial valgus osteotomy (Langenskiöld III+ or failed bracing), guided growth (8-plate/tension band hemiepiphysiodesis for milder cases with remaining growth).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1123,
              "stem": "Leg length discrepancy in children — the Shapiro classification guides management based on the pattern of growth inhibition. The most reliable method for predicting leg length at skeletal maturity is:",
              "options": [
                "Clinical estimation alone",
                "Single standing radiograph",
                "Guessing based on current discrepancy",
                "The Moseley straight-line graph or multiplier method (Anderson-Green data — using serial scanogram measurements plotted against skeletal age to predict final discrepancy at maturity)",
                "No prediction is possible"
              ],
              "answer": "D",
              "explanation": "Predicting final LLD at skeletal maturity requires serial measurements over time because the discrepancy may increase as the child grows (the inhibited limb falls further behind). Methods: (1) Moseley straight-line graph — plots serial scanogram leg length measurements against skeletal age to predict final discrepancy (most widely used graphic method), (2) Anderson-Green growth-remaining tables (the original data underlying Moseley), (3) Multiplier method (Paley) — uses a simple multiplier based on age/sex to predict final discrepancy from a single measurement (increasingly popular due to simplicity). Scanogram (CT or standard): measures each bone individually (femur + tibia = total leg length). Treatment thresholds: <2cm → shoe raise. 2-5cm → epiphysiodesis (guided growth: 8-plate, or percutaneous epiphysiodesis to shorten the longer leg at the right timing) or limb lengthening. >5cm → limb lengthening (Ilizarov/lengthening nail). Timing of epiphysiodesis: critical — use growth data to determine when to intervene.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1124,
              "stem": "Fibrous dysplasia is a benign bone condition where normal bone is replaced by fibrous tissue and immature woven bone. It is caused by a mutation in:",
              "options": [
                "COL1A1 (Type I collagen)",
                "FGFR3 (fibroblast growth factor receptor 3)",
                "GNAS1 gene (activating mutation of the Gsα subunit causing constitutive cAMP signalling in osteoblast precursors)",
                "EXT1 (exostosin)",
                "RB1 (retinoblastoma)"
              ],
              "answer": "C",
              "explanation": "Fibrous dysplasia results from a post-zygotic somatic activating mutation in the GNAS1 gene (chromosome 20q13) — this encodes the Gsα subunit of the stimulatory G-protein. The mutation causes constitutive activation of adenylyl cyclase → increased cAMP → disordered osteoblast differentiation → normal bone replaced by fibrous tissue containing immature woven bone and characteristically 'Chinese character' or 'alphabet soup' trabecular bone on histology. Forms: monostotic (most common, ~75%), polyostotic (~25%), and McCune-Albright syndrome (polyostotic fibrous dysplasia + café-au-lait spots with irregular 'coast of Maine' borders + precocious puberty — triad). Radiographic: 'ground glass' or 'smoky' appearance, well-defined expansile lesion, shepherd's crook deformity (proximal femur varus). Treatment: observation (most), internal fixation for fractures/impending fractures, corrective osteotomy for deformity. Bisphosphonates may reduce pain. Malignant transformation: <1% (usually to osteosarcoma).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1125,
              "stem": "Skeletal fluorosis is caused by chronic excessive fluoride intake and is endemic in parts of India, China, and East Africa. The orthopaedic manifestation includes:",
              "options": [
                "Osteosclerosis (increased bone density with thickened but brittle bones), ligament calcification, restricted joint motion, and spinal cord compression from posterior longitudinal ligament ossification",
                "Osteoporosis only",
                "Only dental changes without bone effects",
                "Improved bone quality and strength",
                "No orthopaedic consequences"
              ],
              "answer": "A",
              "explanation": "Skeletal fluorosis results from chronic ingestion of excessive fluoride (>4mg/day — commonly from high-fluoride groundwater in endemic regions). Fluoride replaces hydroxyl groups in hydroxyapatite → fluorapatite, which is DENSER but more BRITTLE (increased crystal size, decreased elasticity). Orthopaedic effects: (1) OSTEOSCLEROSIS (generalised increased bone density on XR — particularly axial skeleton, ribs, pelvis), (2) ligament CALCIFICATION (particularly paravertebral, iliolumbar), (3) RESTRICTED joint motion (particularly spine — 'poker back'), (4) OSSIFICATION of PLL/ALL → spinal canal stenosis → myelopathy/radiculopathy, (5) stress fractures (dense but brittle bone), (6) secondary hyperparathyroidism (fluoride inhibits mineraliasation at very high doses). XR: 'chalky white' dense bones, paravertebral calcification. Treatment: remove fluoride source (clean water), calcium + vitamin D supplementation, decompressive surgery if myelopathy. Prevention: defluoridation of water supplies, alternative water sources.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1126,
              "stem": "The Cobb angle is the standard measurement for scoliosis severity. It is measured on a standing PA spine radiograph between:",
              "options": [
                "The two vertebrae with the most rotation",
                "The apex vertebra and the sacrum",
                "The most tilted upper end vertebra and the most tilted lower end vertebra (the vertebrae most tilted towards the concavity at each end of the curve)",
                "C7 and S1 only",
                "The two vertebrae closest to the rib hump"
              ],
              "answer": "C",
              "explanation": "The Cobb angle is measured between the superior endplate of the UPPER END VERTEBRA (most tilted towards the concavity at the top of the curve) and the inferior endplate of the LOWER END VERTEBRA (most tilted towards the concavity at the bottom of the curve). Lines are drawn along these endplates (or perpendicular to them), and the angle between the intersecting lines is the Cobb angle. It is measured on a standing posteroanterior (PA) radiograph (PA to reduce breast radiation in adolescent girls). Significance: <10° = spinal asymmetry (not true scoliosis). 10-25° = observe. 25-40° in growing patients (Risser 0-2) = brace. >45-50° = consider surgical correction and fusion. Inter-observer reliability: moderate (~5° measurement error — changes must exceed this to be considered significant progression).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1127,
              "stem": "The Dimeglio classification is used as an alternative to the Pirani score for assessing severity of which condition?",
              "options": [
                "DDH",
                "SUFE",
                "Scoliosis",
                "Congenital talipes equinovarus (clubfoot)",
                "Perthes disease"
              ],
              "answer": "D",
              "explanation": "The Dimeglio classification is an alternative scoring system for assessing clubfoot (CTEV) severity. It evaluates four parameters (each scored 0-4): equinus, varus (heel), midfoot rotation/deformity (forefoot relative to hindfoot), and adduction of the forefoot. Four additional points for deep posterior crease, medial crease, cavus, and poor muscle condition (1 point each). Total score 0-20: Benign (0-5), Moderate (5-10), Severe (10-15), Very severe (15-20). It is used alongside or instead of the Pirani score to guide treatment and monitor response to Ponseti casting.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1128,
              "stem": "Multiple hereditary exostoses (MHE/diaphyseal aclasis) is an autosomal dominant condition characterised by multiple osteochondromas. The risk of malignant transformation to secondary chondrosarcoma is approximately:",
              "options": [
                "0%",
                "1%",
                "30%",
                "50%",
                "5-10%"
              ],
              "answer": "E",
              "explanation": "Multiple hereditary exostoses (MHE, also called diaphyseal aclasis or hereditary multiple osteochondromas) involves multiple osteochondromas (cartilage-capped bony projections) arising from the metaphyses of long bones. Caused by mutations in EXT1 (chromosome 8) or EXT2 (chromosome 11) tumour suppressor genes. The risk of malignant transformation (secondary chondrosarcoma arising from the cartilage cap) is approximately 5-10% for MHE (compared to <1% for a solitary osteochondroma). Warning signs of malignant transformation: growth of a previously stable lesion after skeletal maturity, increasing pain, cartilage cap thickness >2cm on MRI. Complications: cosmetic deformity, short stature, limb malalignment, neurovascular compression, restricted joint motion.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Trauma",
          "range": "Q1129-Q1133",
          "questions": [
            {
              "number": 1129,
              "stem": "Supracondylar fractures of the humerus in children — the Gartland classification Type III is:",
              "options": [
                "Completely displaced with NO cortical contact (highest risk of neurovascular injury)",
                "Undisplaced (Type I)",
                "Displaced with intact posterior cortex (Type II)",
                "A fracture of the lateral condyle",
                "An olecranon fracture"
              ],
              "answer": "A",
              "explanation": "Gartland classification of paediatric supracondylar humerus fractures: Type I = undisplaced (only a subtle anterior humeral line abnormality — the anterior humeral line should pass through the middle third of the capitellum; if it passes anterior to it, suspect an occult extension-type fracture). Type II = displaced with an INTACT posterior cortex (hinged — can be reduced closed in most cases). Type III = completely displaced with NO cortical contact (most severe, highest complication rate — neurovascular injury in ~15-20%). Type IV (added later): multidirectional instability (unstable in both flexion and extension). Nerve at risk: anterior interosseous nerve (AIN — MOST COMMONLY injured, test OK sign), median nerve, radial nerve (with posterolateral displacement), ulnar nerve (with posteromedial displacement or after medial pin placement). Brachial artery: at risk in displaced fractures → check pulse, perfusion.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1130,
              "stem": "Toddler's fracture is a non-displaced spiral fracture of the tibial shaft in a walking child aged 1-3 years. The characteristic feature is:",
              "options": [
                "Obvious deformity with massive swelling",
                "A subtle oblique/spiral fracture of the distal tibial shaft that may be invisible on initial radiographs — the child presents with an unexplained limp or refusal to bear weight",
                "Bilateral fractures always present",
                "Open fracture with bone exposure",
                "Pathological fracture through a tumour"
              ],
              "answer": "B",
              "explanation": "A toddler's fracture is a non-displaced, often hairline spiral/oblique fracture of the distal tibial shaft in children aged 9 months to 3 years. It results from a low-energy rotational mechanism (twisting while walking/running — may be unwitnessed). The child presents with an unexplained limp or refusal to bear weight, with no obvious deformity or significant swelling. The fracture may be INVISIBLE on initial radiographs (particularly AP view — the oblique fracture line may only be visible on the lateral or internal oblique view). If initial XR is normal but clinical suspicion is high: treat as a fracture (below-knee walking cast) and repeat XR at 10-14 days (periosteal new bone formation confirms the fracture). Differential: consider NAI (non-accidental injury) if the history is inconsistent, multiple fractures, or unusual fracture patterns. Treatment: below-knee walking cast for 3-4 weeks → complete healing.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1131,
              "stem": "Non-accidental injury (NAI) in children — which fracture pattern is MOST suspicious?",
              "options": [
                "Distal radius torus fracture from a witnessed fall",
                "Supracondylar fracture from a playground fall",
                "Corner/bucket-handle metaphyseal fractures (classic metaphyseal lesions), posterior rib fractures, and multiple fractures at different stages of healing",
                "Simple clavicle fracture from a bicycle accident",
                "Single tibial shaft fracture with a consistent mechanism"
              ],
              "answer": "C",
              "explanation": "Classic metaphyseal lesions (CMLs — corner fractures or bucket-handle fractures of the metaphyses) are HIGHLY SPECIFIC for NAI (~95-100% specificity) — they result from violent shaking or pulling/twisting forces on the limbs (the metaphyseal-physeal junction fractures at the subperiosteal bone collar). Other high-specificity fractures: posterior rib fractures (from squeezing during shaking — the ribs fracture at the costovertebral junction), scapular fractures, spinous process fractures, and sternal fractures. Multiple fractures at DIFFERENT STAGES OF HEALING (indicating repeated injury at different times) are also highly suspicious. Moderate specificity: multiple fractures, bilateral fractures, complex skull fractures. Low specificity: clavicle, long bone shaft fractures (can occur from both abuse and accidental trauma). Management: safeguarding referral, skeletal survey (full body XR series — detect occult fractures), ophthalmology (retinal haemorrhages), CT head (intracranial injury), blood tests (exclude OI, metabolic bone disease).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1132,
              "stem": "Pulled elbow (nursemaid's elbow/radial head subluxation) typically occurs in children aged:",
              "options": [
                "10-15 years",
                "Only in adults",
                "Only in neonates",
                "6-12 months only",
                "1-4 years (the annular ligament is lax and can slip over the radial head when longitudinal traction is applied to the extended pronated arm — e.g., pulling a child by the hand)"
              ],
              "answer": "E",
              "explanation": "Pulled elbow (subluxation of the radial head from beneath the annular ligament) is extremely common in children aged 1-4 years (peak ~2-3 years). The annular ligament is relatively lax in this age group and can slip over the radial head when longitudinal traction is applied to the extended, PRONATED forearm (e.g., parent pulling a reluctant child by the hand, swinging a child by the arms, catching a falling child by the wrist). The child: holds the arm still by the side in PRONATION, refuses to use the arm, and cries with any attempt at supination. There may be no significant swelling or deformity. XR is usually NORMAL (diagnosis is clinical). Reduction: the SUPINATION-FLEXION manoeuvre (the most reliable — supinate the forearm while flexing the elbow → a palpable 'click' is felt as the radial head reduces beneath the annular ligament) or the HYPERPRONATION technique (also effective). After reduction: the child typically uses the arm normally within minutes (no immobilisation needed). Recurrence: ~5-30% — most outgrow it by age 5-6 (annular ligament strengthens).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1133,
              "stem": "Lateral condyle fractures of the humerus in children are important because:",
              "options": [
                "They involve the physis and articular surface, are inherently UNSTABLE (pulled by the extensor muscles), and have a high risk of non-union if displaced and not fixed — non-union leads to progressive cubitus valgus and tardy ulnar nerve palsy",
                "They are always undisplaced and heal without problems",
                "They only cause cosmetic problems",
                "They heal faster than other fractures",
                "No treatment is ever needed"
              ],
              "answer": "A",
              "explanation": "Lateral condyle fractures (Milch classification: Type I — fracture lateral to trochlear groove, Type II — through trochlear groove) are the SECOND most common elbow fracture in children (after supracondylar). They are critical because: (1) involve the PHYSIS (growth plate — risk of growth disturbance), (2) involve the ARTICULAR SURFACE (intra-articular — must achieve anatomical reduction for congruent joint), (3) are inherently UNSTABLE — the common extensor muscles originate from the lateral epicondyle and PULL the fragment laterally and distally (displacement can increase in cast). (4) HIGH NON-UNION risk if displaced >2mm and not fixed (the fracture surfaces are bathed in synovial fluid which prevents callus formation + the extensor pull separates the fragment). Non-union consequences: progressive cubitus VALGUS (loss of lateral condyle growth) → TARDY ULNAR NERVE PALSY (the ulnar nerve is progressively stretched over the medial epicondyle as valgus increases — may present years after the injury). Treatment: undisplaced (<2mm) → above-elbow cast with close follow-up XR (watch for displacement). Displaced (≥2mm) → ORIF (K-wires or screws — anatomical reduction essential).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Hip",
          "range": "Q1134-Q1138",
          "questions": [
            {
              "number": 1134,
              "stem": "Transient synovitis of the hip in children — the key clinical feature that differentiates it from septic arthritis is:",
              "options": [
                "Always bilateral",
                "Fever >39°C and inability to weight-bear (more suggestive of septic arthritis)",
                "Transient synovitis causes permanent joint damage",
                "Transient synovitis typically presents with mild/no fever, the child is often still able to weight-bear (though with a limp), and inflammatory markers are only mildly elevated or normal",
                "Transient synovitis only affects adults"
              ],
              "answer": "D",
              "explanation": "Transient synovitis (irritable hip) is the most common cause of acute hip pain and limp in children (peak age 3-8 years, boys > girls). It is a self-limiting inflammatory condition (viral aetiology suspected) that resolves spontaneously within 7-10 days. Key differentiating features from septic arthritis: transient synovitis has MILD or NO fever, the child is often still ABLE to weight-bear (though with an antalgic gait), and inflammatory markers (WCC, ESR, CRP) are normal or only MILDLY elevated. Septic arthritis: HIGH fever (>38.5°C), REFUSES to weight-bear, markedly elevated inflammatory markers. Kocher criteria help differentiate: 0 criteria = <0.2% risk of septic arthritis (treat as transient synovitis). ≥2 criteria → aspirate the hip. If in doubt: ASPIRATE (septic arthritis is a joint-destroying emergency that must not be missed).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1135,
              "stem": "The Graf classification is used to assess:",
              "options": [
                "Perthes disease severity",
                "Infant hip maturity and DDH on ultrasound (classifying alpha and beta angles of the acetabulum to determine hip type)",
                "SUFE stability",
                "Clubfoot severity",
                "Scoliosis curve magnitude"
              ],
              "answer": "B",
              "explanation": "The Graf classification assesses infant hip development and DDH on ULTRASOUND (the primary imaging modality for infant hips from birth to ~4-6 months, before ossification of the femoral head makes XR more useful). It measures two angles on a standardised coronal ultrasound image: ALPHA ANGLE (bony acetabular roof angle — measures bony coverage of the femoral head) and BETA ANGLE (cartilaginous acetabular roof angle). Classification: Type I (alpha ≥60°) = mature, normal hip. Type IIa (alpha 50-59°, age <3 months) = physiologically immature (may mature spontaneously — observe). Type IIb (alpha 50-59°, age >3 months) = deficient — needs treatment. Type IIc (alpha 43-49°) = critical zone — unstable, needs treatment. Type III (alpha <43°) = dislocated, femoral head displacing. Type IV = dislocated, labrum inverted. Types IIb-IV require treatment (Pavlik harness for types IIb-III if reducible). USS screening: universal (Austria, Germany) vs selective/targeted (UK — risk factors or clinical concern).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1136,
              "stem": "Perthes disease — the Herring lateral pillar classification is based on the height of the lateral pillar of the femoral epiphysis on AP radiograph. Group B indicates:",
              "options": [
                "No involvement of the lateral pillar (Group A)",
                "Complete lateral pillar collapse <50% (Group C)",
                "Normal hip",
                "Only metaphyseal involvement",
                "Lateral pillar height maintained >50% but with some lucency/collapse (mild to moderate involvement)"
              ],
              "answer": "E",
              "explanation": "Herring lateral pillar classification (assessed during the fragmentation phase): Group A = lateral pillar INTACT (full height maintained, no density change) → best prognosis (>95% good outcomes regardless of treatment). Group B = lateral pillar maintained at >50% of original height but with some lucency/loss of density (moderate involvement) → prognosis depends on age and treatment. Group B/C border = lateral pillar exactly 50% height or thin/poorly mineralised. Group C = lateral pillar <50% height (severe collapse) → worst prognosis (>50% poor outcomes). Treatment decisions: children <8 years (especially Group A-B) → generally good outcomes regardless of treatment (observation usually sufficient). Children >8 years with Group B or B/C border → containment treatment may improve outcomes (abduction bracing, femoral varus osteotomy, or Salter innominate osteotomy). Group C in any age → poor prognosis regardless of treatment. The Stulberg classification describes the final shape of the healed femoral head (I-V: spherical → aspherical → flat).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1137,
              "stem": "Slipped upper femoral epiphysis (SUFE) — the most serious complication is:",
              "options": [
                "Mild hip pain only",
                "Temporary limp",
                "Avascular necrosis of the femoral head (risk increases with: unstable SUFE, forceful reduction attempts, and delay in treatment — AVN rate ~10-50% for unstable SUFE vs <5% for stable SUFE treated with in-situ fixation)",
                "Minor stiffness only",
                "Cosmetic concern only"
              ],
              "answer": "C",
              "explanation": "AVN is the most feared complication of SUFE — it results from disruption of the retinacular blood supply to the femoral head (particularly the lateral epiphyseal arteries from the MFCA). AVN risk by stability: STABLE SUFE (can weight-bear, Loder classification) treated with in-situ fixation → AVN rate <5%. UNSTABLE SUFE (cannot weight-bear, acute or acute-on-chronic) → AVN rate 10-50% even with optimal treatment. Factors increasing AVN risk: (1) UNSTABLE slip (most important factor), (2) forceful/closed reduction ATTEMPTS (manipulating the slip damages remaining retinacular vessels — GENTLE positioning only, accept the deformity and fix in-situ), (3) delay in treatment, (4) high-grade slip (Southwick angle >60°). Treatment: in-situ fixation with a single cannulated screw (for stable slips — DO NOT REDUCE). Unstable slips: gentle capsulotomy to decompress intracapsular haematoma (may improve femoral head perfusion) + in-situ fixation (avoid forced reduction). Prophylactic contralateral pinning: controversial (risk of bilateral slip ~20-40%).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1138,
              "stem": "In DDH, the Ortolani test is positive when:",
              "options": [
                "A dislocated hip is pushed OUT of the acetabulum",
                "A dislocated hip is REDUCED back INTO the acetabulum with a palpable 'clunk' during abduction",
                "The hip is stiff and cannot be abducted",
                "There is a 'click' only",
                "The knee hyperextends"
              ],
              "answer": "B",
              "explanation": "Ortolani test: with the infant supine, hips and knees flexed to 90°, gently ABDUCT the hips while lifting the greater trochanter anteriorly with the middle fingers. A positive test = a palpable 'CLUNK' as the dislocated femoral head REDUCES back into the acetabulum. This indicates a dislocated but REDUCIBLE hip. The Barlow test is the opposite: apply gentle posterior and lateral pressure to a LOCATED hip — if it dislocates (subluxes posteriorly), it is Barlow-positive (DISLOCATABLE). Remember: 'Ortolani = Out and then back IN' (reduces), 'Barlow = hip is pushed Back and OUT' (dislocates). A 'click' is common and usually benign (ligament/tendon snapping) — only a CLUNK is significant. Both tests are most reliable in the first few weeks of life (become less useful after 8-12 weeks as the hip tightens).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Fractures",
          "range": "Q1139-Q1149",
          "questions": [
            {
              "number": 1139,
              "stem": "Greenstick fractures are unique to paediatric bone because:",
              "options": [
                "Children have denser bone than adults",
                "Children's bone is identical to adult bone",
                "Children never sustain complete fractures",
                "Children's bone has a higher proportion of collagen relative to mineral (and a thicker periosteum) — making it more flexible and allowing it to bend and crack on one side (tension cortex) while bending on the other (compression cortex) rather than breaking completely",
                "Greenstick fractures only occur after age 10"
              ],
              "answer": "D",
              "explanation": "Children's bone differs from adult bone in several ways that affect fracture patterns: (1) HIGHER COLLAGEN:MINERAL ratio (more collagen = more flexibility/elasticity, less brittleness) → bone bends before it breaks, creating unique fracture patterns (greenstick, torus/buckle, plastic deformation). (2) THICKER PERIOSTEUM — stronger, more biologically active periosteal sleeve that: (a) prevents complete displacement of fracture fragments (acts as a hinge in greenstick and periosteal sleeve in buckle fractures), (b) contributes to faster fracture healing (rich osteogenic cambium layer), (c) provides greater remodelling potential. (3) GROWTH PLATES (physes) — zone of relative weakness (Salter-Harris fractures). Greenstick: the tension cortex fractures (fails in tension) while the compression cortex bends (plastic deformation without complete fracture). Treatment: may need reduction if angulated >acceptable thresholds → complete the fracture (break the intact cortex) to prevent recurrence of angulation, then cast.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1140,
              "stem": "Salter-Harris Type II fractures are the most common physeal fractures. They involve:",
              "options": [
                "Physis + metaphysis (a metaphyseal fragment — the Thurston-Holland fragment — remains attached to the epiphysis; the fracture exits through the metaphysis)",
                "Physis only (Type I)",
                "Physis + epiphysis (Type III)",
                "Physis + metaphysis + epiphysis (Type IV)",
                "Crush injury to the physis (Type V)"
              ],
              "answer": "A",
              "explanation": "Salter-Harris classification of physeal (growth plate) fractures: Type I = through the PHYSIS only (no metaphyseal or epiphyseal fracture visible on XR — may be XR-occult, diagnosed clinically by tenderness over the physis). Type II = through the physis + exits through the METAPHYSIS (the triangular metaphyseal fragment = THURSTON-HOLLAND fragment; most common type ~75% of all physeal fractures; generally good prognosis). Type III = through the physis + exits through the EPIPHYSIS (intra-articular — needs anatomical reduction). Type IV = through the physis + BOTH metaphysis AND epiphysis (intra-articular + crosses the physis — ORIF essential to prevent physeal bar formation). Type V = CRUSH/COMPRESSION injury to the physis (rare, often diagnosed retrospectively when growth arrest occurs — worst prognosis). Mnemonic: SALTR — Straight across (I), Above (II — metaphysis), beLow (III — epiphysis), Through all (IV), Rammed/crushed (V). Prognosis worsens I→V. Anatomical reduction essential for Types III and IV (articular + physeal).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1141,
              "stem": "The anterior humeral line on a lateral elbow radiograph normally passes through which structure?",
              "options": [
                "The olecranon fossa",
                "The radial head",
                "The trochlea",
                "The coronoid process",
                "The middle third of the capitellum"
              ],
              "answer": "E",
              "explanation": "The anterior humeral line (AHL) is drawn along the anterior cortex of the humerus on a true lateral radiograph. It should pass through the middle third of the capitellum. In a posteriorly displaced supracondylar fracture (extension type), the capitellum lies posterior to the AHL (the line passes through the anterior third or misses the capitellum entirely). The radiocapitellar line (drawn through the centre of the radial shaft) should pass through the centre of the capitellum on ALL views — malalignment suggests radial head dislocation (Monteggia).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1142,
              "stem": "The ossification centres of the elbow appear in a predictable sequence during childhood. The correct order of appearance is:",
              "options": [
                "Trochlea, Capitellum, Radial head, Olecranon, Medial epicondyle, Lateral epicondyle",
                "Olecranon first, then all others simultaneously",
                "Random order with no predictable sequence",
                "Capitellum, Radial head, Internal (medial) epicondyle, Trochlea, Olecranon, Lateral (external) epicondyle (CRITOL/CRITOE)",
                "Lateral epicondyle, Medial epicondyle, Capitellum, Trochlea, Olecranon, Radial head"
              ],
              "answer": "D",
              "explanation": "The elbow ossification centres appear in the CRITOL/CRITOE sequence: Capitellum (~1 year), Radial head (~3 years), Internal (medial) epicondyle (~5 years), Trochlea (~7 years), Olecranon (~9 years), Lateral (external) epicondyle (~11 years). Mnemonic: CRITOE or CRITOL. Ages roughly 1-3-5-7-9-11. Knowing this sequence is clinically important — if a later-appearing centre is visible but an earlier one is not, the 'missing' centre may be trapped in the joint (e.g., medial epicondyle trapped in joint after elbow dislocation).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1143,
              "stem": "In a paediatric supracondylar fracture, the brachial artery and median nerve are most at risk in which type?",
              "options": [
                "Gartland Type I (undisplaced)",
                "Extension-type posteromedially displaced fracture",
                "Extension-type posterolaterally displaced fracture",
                "Flexion-type fracture",
                "All types equally"
              ],
              "answer": "B",
              "explanation": "In extension-type supracondylar fractures with posteromedial displacement of the distal fragment, the brachial artery and median nerve (specifically the AIN) are at greatest risk because they are stretched over the sharp proximal spike as it displaces anterolaterally. In posterolateral displacement, the radial nerve is more at risk. In flexion-type fractures (rare, ~2%), the ulnar nerve is at risk. Overall, the anterior interosseous nerve (AIN branch of median) is the most commonly injured nerve in supracondylar fractures — test with the 'OK sign' (pinch between thumb IP and index DIP).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1144,
              "stem": "A greenstick fracture is unique to paediatric bone because:",
              "options": [
                "The thick periosteum and higher plasticity allow the bone to bend and break on one cortex while the other cortex remains intact",
                "Children's bones are purely cancellous",
                "Children's bones have no cortex",
                "Paediatric fractures never fully displace",
                "The growth plate is involved"
              ],
              "answer": "A",
              "explanation": "Greenstick fractures occur exclusively in children because paediatric bone has: (1) thicker, stronger, more osteogenic periosteum (acts as a hinge/restraint), (2) higher water content and lower mineral content than adult bone → greater plasticity/ductility, and (3) more porous cortex. The bone bends, breaking on the tension (convex) side while the cortex on the compression (concave) side remains intact (like bending a green twig). Angulation >15-20° typically requires reduction. The intact periosteum aids stability and healing.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1145,
              "stem": "The peak age for paediatric supracondylar humeral fractures is:",
              "options": [
                "1-2 years",
                "10-12 years",
                "5-7 years",
                "14-16 years",
                "Adults over 30"
              ],
              "answer": "C",
              "explanation": "Paediatric supracondylar fractures peak at 5-7 years of age. At this age, the distal humerus is remodelling from round to flattened shape, and the olecranon fossa thins as it deepens — creating a structural weak point. The ligaments are stronger than bone in this age group, so forces that would cause elbow dislocation in adults cause supracondylar fractures in children. Extension-type (98%): fall on outstretched hand → posteriorly displaced distal fragment. Flexion-type (2%): fall on flexed elbow → anteriorly displaced distal fragment.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1146,
              "stem": "The most common paediatric fracture overall is:",
              "options": [
                "Femoral shaft fracture",
                "Supracondylar fracture",
                "Clavicle fracture",
                "Tibial fracture",
                "Distal radius/forearm fracture"
              ],
              "answer": "E",
              "explanation": "Distal radius/forearm fractures are the most common fractures in children, accounting for approximately 25-30% of all paediatric fractures. The distal radius metaphysis is particularly vulnerable during falls onto an outstretched hand (FOOSH). Fracture types include: torus (buckle) fractures (compression of the cortex, stable — removable splint for 3 weeks), greenstick fractures (one cortex breaks, other bends — may need reduction if angulation >15-20°), complete fractures (both cortices — may need reduction and casting, or MUA + K-wires if significantly displaced/unstable), and Salter-Harris physeal injuries. The distal radial physis contributes ~80% of radial growth, so remodelling potential here is excellent — accept more angulation in younger children.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1147,
              "stem": "A toddler's fracture is a spiral fracture of which bone, caused by a low-energy rotational mechanism?",
              "options": [
                "Tibial shaft (undisplaced spiral fracture in a young child learning to walk)",
                "Distal radius",
                "Femoral shaft",
                "Fibula",
                "Clavicle"
              ],
              "answer": "A",
              "explanation": "A toddler's fracture is an undisplaced or minimally displaced spiral fracture of the tibial shaft in a child aged 1-3 years who is learning to walk or has just started walking. It results from a low-energy rotational/twisting mechanism (e.g., catching a foot while walking/running). The child presents with refusal to weight-bear, limping, and tenderness over the tibia. Radiographs may initially be normal — a subtle oblique lucency or periosteal reaction may only become visible on repeat films at 10-14 days. If clinical suspicion is high with negative XRs: treat with a below-knee walking cast for 3 weeks, then reassess. Important: always consider NAI if the history is inconsistent with the injury pattern or if the child is non-ambulatory.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1148,
              "stem": "A Monteggia fracture-dislocation in a child differs from an adult in that in children:",
              "options": [
                "The radial head dislocation cannot be reduced",
                "The ulnar fracture always needs plating",
                "Accurate anatomical reduction of the ulnar fracture (closed or open) usually results in spontaneous reduction of the radial head dislocation",
                "Radial head excision is the treatment of choice",
                "The injury never occurs in children"
              ],
              "answer": "C",
              "explanation": "In children, accurate anatomical reduction of the ulnar fracture (which can often be achieved by closed reduction and casting, or with flexible IM nails for unstable patterns) usually leads to spontaneous and stable reduction of the radial head dislocation. This is because the annular ligament is usually intact (stretched but not torn) — once the ulnar length and alignment are restored, the radial head relocates. If the radial head does not reduce after anatomical ulnar reduction, suspect soft tissue interposition (annular ligament, joint capsule) and proceed to open reduction. In adults, the ulnar fracture requires ORIF with plate fixation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1149,
              "stem": "The Salter-Harris classification of physeal fractures — Type II is the most common and involves:",
              "options": [
                "Fracture through the physis only (Type I pattern)",
                "Fracture through the physis with a metaphyseal fragment (Thurston-Holland fragment)",
                "Fracture through the physis into the epiphysis",
                "Fracture through the physis, metaphysis, AND epiphysis",
                "Crush injury to the physis"
              ],
              "answer": "B",
              "explanation": "Salter-Harris classification: I = Straight across (through physis only — may be radiographically occult, diagnosed clinically by physeal tenderness). II = Above (fracture exits through the metaphysis, creating a triangular metaphyseal fragment — Thurston-Holland fragment, MOST COMMON ~75%). III = beLow (fracture exits through the epiphysis — intra-articular). IV = Through (fracture crosses from metaphysis through physis into epiphysis — intra-articular). V = cRush/Rammed (compression injury to the physis — often diagnosed retrospectively by growth arrest). Mnemonic: SALTR. Types I-II: generally good prognosis (fracture through hypertrophic zone, germinal layer intact). Types III-V: risk growth disturbance (germinal layer disrupted). Types III-IV need anatomical reduction (articular and physeal).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Spine",
          "range": "Q1150-Q1152",
          "questions": [
            {
              "number": 1150,
              "stem": "Adolescent idiopathic scoliosis (AIS) — the Cobb angle measured on a standing PA radiograph is the standard method for quantifying curve magnitude. Surgical treatment is typically recommended when the Cobb angle exceeds:",
              "options": [
                "10° (this is the minimum threshold to diagnose scoliosis, not a surgical indication)",
                "20° (bracing threshold, not surgical)",
                "Any visible asymmetry",
                "45-50° in a skeletally immature patient (or progressing despite bracing — curves >50° tend to progress even after skeletal maturity)",
                "90° only"
              ],
              "answer": "D",
              "explanation": "AIS treatment thresholds: <25° → OBSERVATION (serial radiographs every 4-6 months until skeletal maturity). 25-45° in a skeletally immature patient (Risser 0-2) → BRACING (thoracolumbosacral orthosis — TLSO/Milwaukee brace, worn 18-23 hours/day; BrAIST trial 2013 showed bracing is effective in reducing progression). >45-50° → SURGICAL consideration (posterior spinal fusion with instrumentation — pedicle screw constructs, derotation, correction, and fusion). Rationale for surgery at 45-50°: curves >50° in the thoracic spine are likely to PROGRESS even after skeletal maturity (~1° per year in adulthood), leading to cosmetic deformity, reduced pulmonary function (severe curves >80°), and back pain. The goal of surgery: arrest progression, correct the deformity (typically 50-70% correction achievable), and achieve balanced spinal fusion. Risser sign (iliac apophysis ossification): guides skeletal maturity and progression risk — lower Risser + larger curve = higher progression risk.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1151,
              "stem": "Back pain in a child under 10 years should be treated with a high index of suspicion because:",
              "options": [
                "It is always benign and self-limiting",
                "It is caused by poor posture only",
                "No investigation is needed",
                "It always resolves with physiotherapy",
                "It is much more likely to have a serious underlying cause than in adults"
              ],
              "answer": "E",
              "explanation": "Back pain in children under 10 is rare and should prompt thorough investigation — significant pathology is found in up to 50% of cases (compared to adult back pain which is usually mechanical). Causes to exclude: infection (discitis, osteomyelitis), tumour (osteoid osteoma, osteoblastoma, Ewing sarcoma, leukaemia, spinal cord tumours), spondylolysis/spondylolisthesis, Scheuermann disease, and inflammatory conditions. Red flags: age <10, night pain, systemic symptoms, neurological signs, constant pain. Investigation: bloods (FBC, CRP, ESR), plain XR, MRI if suspicious.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1152,
              "stem": "Scheuermann disease is a developmental kyphosis of the thoracic spine. The diagnostic criterion requires anterior wedging of at least 5° in how many consecutive vertebrae?",
              "options": [
                "3",
                "1",
                "2",
                "4",
                "5"
              ],
              "answer": "A",
              "explanation": "Scheuermann disease is defined radiographically by anterior vertebral body wedging of ≥5° in at least 3 consecutive vertebrae (Sorensen criteria). It causes a rigid hyperkyphosis (usually thoracic, T7-T10 apex) that does not correct on hyperextension. Additional radiographic features: irregular endplates, Schmorl nodes (disc herniations through endplates), disc space narrowing. Differentiate from postural kyphosis (flexible, corrects on hyperextension, no vertebral wedging). Treatment: observation/physiotherapy for mild curves. Bracing for curves 45-70° in growing patients. Surgery for curves >70° or progressive deformity.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Screening",
          "range": "Q1153",
          "questions": [
            {
              "number": 1153,
              "stem": "DDH screening in the UK follows a selective USS screening policy. Universal clinical screening (Barlow and Ortolani tests) is performed:",
              "options": [
                "Only at school entry",
                "At the newborn check (within 72 hours) AND at the 6-8 week check — with SELECTIVE USS for babies with risk factors (breech presentation, family history of DDH, clinical instability/click)",
                "Only at 12 months",
                "Never — DDH screening is not performed in the UK",
                "Only by ultrasound without any clinical examination"
              ],
              "answer": "B",
              "explanation": "UK DDH screening programme: (1) UNIVERSAL clinical examination: Barlow test (adduction + posterior pressure → hip dislocates posteriorly out of the acetabulum = positive = unstable hip) and Ortolani test (abduction + anterior lift → a clunk felt as the dislocated hip REDUCES back into the acetabulum = positive = dislocated but reducible). Performed at: newborn check (within 72 hours of birth) AND 6-8 week check. (2) SELECTIVE USS (not universal in the UK): offered to babies with RISK FACTORS — breech presentation (at or after 36 weeks), family history of DDH (first-degree relative), clinical instability/abnormality on examination. USS at 6 weeks of age (or 2 weeks if clinically dislocated). The UK uses selective USS because: the false-positive rate of universal USS is high (many 'abnormal' hips at birth normalise spontaneously → leads to unnecessary treatment). Countries using UNIVERSAL USS: Austria, Germany, Switzerland. Treatment: if DDH confirmed — Pavlik harness (dynamic flexion-abduction device, used from birth to ~6 months, ~90-95% success for Graf Type IIb-III reducible hips).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Angular Deformity",
          "range": "Q1154",
          "questions": [
            {
              "number": 1154,
              "stem": "Physiological genu varum in a toddler typically corrects to neutral alignment by age:",
              "options": [
                "6 months",
                "12–18 months",
                "3–4 years",
                "18–24 months",
                "7–8 years"
              ],
              "answer": "D",
              "explanation": "Normal physiological limb alignment progresses through predictable phases: genu varum at birth (0–18 months), transitions to neutral at 18–24 months, then genu valgum (peaks at 3–4 years), and finally achieves adult alignment (5–7° valgus) by age 7–8 years. Pathological causes of persistent varus beyond age 2 include: Blount disease (infantile tibia vara), rickets, skeletal dysplasias, and physeal injury. Any unilateral, progressive, or severe deformity warrants investigation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Limb Length",
          "range": "Q1155",
          "questions": [
            {
              "number": 1155,
              "stem": "A predicted limb length discrepancy of 2–5 cm at maturity in a growing child is most commonly managed with:",
              "options": [
                "Shoe raise only",
                "Limb lengthening of the short limb",
                "Epiphysiodesis (guided growth/physeal arrest) of the longer limb",
                "Immediate THA",
                "No intervention needed"
              ],
              "answer": "C",
              "explanation": "Epiphysiodesis (surgical arrest or retardation of the growth plate in the longer limb) is the most commonly used method for predicted LLD of 2–5 cm. Timing is critical — it must be performed when sufficient growth remains to equalise the discrepancy but not so early that over-correction occurs. The Paley multiplier method or Anderson-Green growth remaining charts guide timing. LLD <2 cm: shoe raise. LLD >5 cm: consider limb lengthening (Ilizarov/Taylor Spatial Frame). LLD >15–20 cm: may need amputation + prosthesis.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Bone Cysts",
          "range": "Q1156",
          "questions": [
            {
              "number": 1156,
              "stem": "A simple (unicameral) bone cyst in the proximal humerus of a 10-year-old is best characterised by which radiographic feature?",
              "options": [
                "Aggressive periosteal reaction with cortical destruction",
                "A well-defined, centrally located, lytic lesion in the metaphysis with thinned cortex",
                "A sclerotic lesion with matrix calcification",
                "An expansile lesion with fluid-fluid levels on MRI",
                "A diaphyseal lesion with onion-skin periosteal reaction"
              ],
              "answer": "B",
              "explanation": "Simple (unicameral) bone cysts are benign, fluid-filled lesions that occur centrally in the metaphysis of long bones, most commonly the proximal humerus and proximal femur in children (age 4–10). Radiographically: well-defined, centrally located, mildly expansile, lytic lesion with thinned but intact cortex. The 'fallen fragment sign' (a cortical fracture fragment falls to the dependent portion of the cyst) is pathognomonic. Active cysts abut the physis; latent cysts migrate away with growth. Treatment: observation if stable; aspiration + steroid/BMP injection or curettage + grafting if symptomatic/pathological fracture.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "DDH",
          "range": "Q1157-Q1165",
          "questions": [
            {
              "number": 1157,
              "stem": "After failed Pavlik harness treatment for DDH, the next step in management for an infant aged 6-18 months is:",
              "options": [
                "Continue Pavlik harness indefinitely",
                "Open reduction immediately",
                "Total hip arthroplasty",
                "Closed reduction under GA with arthrogram and hip spica",
                "Observation until walking age"
              ],
              "answer": "D",
              "explanation": "If Pavlik harness fails (no reduction by 3 weeks), it should be discontinued to avoid Pavlik harness disease (AVN from forced abduction). For infants 6-18 months, the next step is closed reduction under general anaesthesia with arthrogram (to confirm concentric reduction and assess obstacles), followed by hip spica immobilisation in the human position for 12 weeks. If closed reduction fails due to soft tissue interposition (limbus, inverted labrum, hypertrophied ligamentum teres, pulvinar, psoas tendon), open reduction is required.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1158,
              "stem": "Risk factors for developmental dysplasia of the hip (DDH) include all of the following EXCEPT:",
              "options": [
                "Female sex",
                "Breech presentation",
                "Prematurity",
                "First-born child",
                "Family history"
              ],
              "answer": "C",
              "explanation": "DDH risk factors: female sex (F:M = 6:1), breech presentation (highest risk factor), first-born (tight uterus), family history (positive in ~20%), oligohydramnios, and left hip (most common side — left hip against mother's sacrum in utero). Prematurity is NOT a recognised risk factor for DDH — in fact, premature infants may have less intrauterine moulding. Associated conditions include torticollis, metatarsus adductus, and other 'packaging' disorders.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1159,
              "stem": "The Galeazzi sign (Allis sign) in an infant with DDH demonstrates:",
              "options": [
                "Asymmetric skin folds",
                "A palpable clunk on hip abduction",
                "Limited hip abduction",
                "Trendelenburg sign",
                "Apparent femoral shortening with knees at different heights"
              ],
              "answer": "E",
              "explanation": "The Galeazzi (Allis) sign is positive when the infant lies supine with hips and knees flexed to 90°, and the knees are at different heights — the affected side is lower due to proximal migration of the femoral head (apparent femoral shortening). It indicates a dislocated hip. This sign is useful after 2–3 months when the Ortolani and Barlow tests become negative (as the hip becomes fixed in the dislocated position).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1160,
              "stem": "The Severin classification is used to assess the radiographic outcome of DDH treatment. Severin Grade I indicates:",
              "options": [
                "Normal hip (concentrically reduced, normal CE angle, spherical head)",
                "Complete dislocation with no acetabular coverage",
                "Mild residual dysplasia with CE angle 15-20°",
                "AVN changes with head deformity",
                "Subluxation with lateralised head"
              ],
              "answer": "A",
              "explanation": "Severin classification grades the radiographic outcome of DDH treatment at skeletal maturity: I = normal (spherical femoral head, concentric reduction, normal CE angle ≥25°). II = mild deformity (slight head/acetabular abnormality, CE angle 15-25°). III = dysplasia without subluxation (CE angle <15°). IV = subluxation. V = head articulating with secondary acetabulum. VI = redislocation. The goal of DDH treatment is to achieve Severin I or II.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            },
            {
              "number": 1161,
              "stem": "The most appropriate treatment for a newborn diagnosed with DDH (Ortolani-positive, reducible dislocated hip) is:",
              "options": [
                "Immediate surgery",
                "No treatment — it will resolve spontaneously in all cases",
                "Spica cast immediately",
                "Skeletal traction",
                "Pavlik harness (dynamic flexion-abduction splint worn 23 hours/day)"
              ],
              "answer": "E",
              "explanation": "The Pavlik harness is the first-line treatment for DDH diagnosed in the neonatal period (0-6 months). It maintains the hip in flexion (100°) and abduction (the position of stability), allowing the femoral head to reduce into the acetabulum and the acetabulum to develop normally around the concentric femoral head. It is worn 23 hours/day (removed only for bathing) and is used until the hip is clinically and sonographically stable (typically 6-12 weeks full-time, then weaning). Success rate: ~90-95% for Ortolani-positive (reducible) hips when started before 6 months. If the hip is not reduced within 3-4 weeks of Pavlik harness use → discontinue (risk of Pavlik harness disease — AVN from forced abduction) and proceed to examination under anaesthesia + closed reduction + arthrogram + spica cast.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1162,
              "stem": "After treatment of DDH, the radiographic outcome at skeletal maturity is assessed using the centre-edge (CE) angle of Wiberg. A normal CE angle in an adult is:",
              "options": [
                "<10°",
                "10-15°",
                "≥25°",
                "15-20°",
                "≥45°"
              ],
              "answer": "C",
              "explanation": "The centre-edge (CE) angle of Wiberg measures the lateral coverage of the femoral head by the acetabulum on an AP pelvis radiograph. Normal adult CE angle: ≥25°. Borderline: 20-25°. Dysplastic: <20°. It is measured between a vertical line through the centre of the femoral head and a line from the centre of the head to the lateral edge of the acetabular sourcil (weight-bearing surface). A reduced CE angle indicates insufficient lateral coverage of the femoral head (acetabular dysplasia) — predisposing to labral tears, cartilage damage, and early-onset OA. Periacetabular osteotomy (PAO/Ganz) can be performed to increase coverage in symptomatic dysplasia in young adults.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1163,
              "stem": "Graf classification of infant hip ultrasound — a Type IIa hip indicates:",
              "options": [
                "Physiologically immature hip in an infant <3 months (expected to mature normally)",
                "Normal mature hip",
                "Subluxed hip requiring treatment",
                "Dislocated hip",
                "Teratological dislocation"
              ],
              "answer": "A",
              "explanation": "Graf ultrasound classification: Type I = mature normal hip (alpha angle >60°). Type IIa = physiologically immature hip in infant <3 months (alpha angle 50-59°, adequate but immature bony roof — expected to mature spontaneously, recheck at 6 weeks). Type IIb = same morphology but in infant >3 months (abnormal, requires treatment). Type IIc = critical hip (alpha angle 43-49°, deficient bony roof). Type D = decentring (subluxing). Type III = dislocated (labrum everted). Type IV = dislocated (labrum inverted). Alpha angle measures bony acetabular roof coverage. Beta angle measures cartilaginous roof. Screening USS indicated for: breech, family history, clinical concern.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1164,
              "stem": "The Pavlik harness is the first-line treatment for DDH in infants. It works by maintaining the hip in:",
              "options": [
                "Full extension and adduction",
                "Maximum internal rotation",
                "Full extension and external rotation",
                "Flexion and abduction (the position of stability)",
                "Neutral position only"
              ],
              "answer": "D",
              "explanation": "The Pavlik harness maintains the hip in flexion (90-100°) and abduction (allowing the femoral head to reduce into and remain seated in the acetabulum). It allows active hip motion within a safe zone while preventing extension and adduction (the positions of instability/dislocation). Success rate: 90-95% for Barlow-positive (dislocatable) and Ortolani-positive (dislocated but reducible) hips when commenced before 6 months of age. Worn 23 hours/day for 6-12 weeks (until stability confirmed on USS). Complications: Pavlik harness disease (forced excessive abduction → AVN of the femoral head — must avoid over-tightening the abduction straps). If Pavlik fails (hip not reduced by 3-4 weeks): discontinue and proceed to closed or open reduction under GA.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1165,
              "stem": "In DDH management, the Barlow test assesses:",
              "options": [
                "Whether a dislocated hip can be reduced",
                "Whether a located but unstable hip can be DISLOCATED (provoked out of the acetabulum) by adduction and posterior pressure",
                "The range of hip abduction only",
                "The stability of the knee",
                "The presence of femoral anteversion"
              ],
              "answer": "B",
              "explanation": "Barlow test: assesses whether a LOCATED (currently in the acetabulum) but potentially unstable hip can be provoked to dislocate posteriorly. Technique: with the hip flexed to 90° and in neutral abduction, apply gentle posterior and lateral pressure — if the hip dislocates (the femoral head is felt to sublux or dislocate posteriorly), it is Barlow-positive (dislocatable). Ortolani test: assesses whether an already DISLOCATED hip can be REDUCED back into the acetabulum. Technique: abduct the hip with gentle anterior pressure on the greater trochanter — a palpable 'clunk' as the head reduces into the acetabulum is Ortolani-positive (reducible). Both tests must be performed gently. BARLOW = hip can be PUSHED OUT. ORTOLANI = hip can be PUT BACK IN.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "SUFE",
          "range": "Q1166-Q1169",
          "questions": [
            {
              "number": 1166,
              "stem": "The Loder classification of SUFE divides slips into stable and unstable based on:",
              "options": [
                "Whether the patient can weight-bear",
                "Slip angle on radiograph",
                "Duration of symptoms",
                "Patient's age",
                "Degree of femoral head coverage"
              ],
              "answer": "A",
              "explanation": "The Loder classification: Stable SUFE = patient CAN weight-bear (with or without crutches). Unstable SUFE = patient CANNOT weight-bear. This is clinically important because unstable slips have a much higher AVN rate (~10-50%) compared to stable slips (<1-2%). Unstable slips require urgent gentle reduction and fixation. Stable slips are treated with in situ fixation without reduction attempt.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1167,
              "stem": "Chondrolysis is a recognised complication of SUFE treatment. It is characterised by:",
              "options": [
                "Overgrowth of articular cartilage",
                "Calcification of the labrum",
                "Ossification of the joint capsule",
                "Progressive loss of articular cartilage with joint space narrowing",
                "Hypertrophy of synovial villi"
              ],
              "answer": "D",
              "explanation": "Chondrolysis is progressive destruction of the articular cartilage of the hip following SUFE (or its treatment), characterised by diffuse joint space narrowing (<3 mm or >50% reduction compared to the normal side) and progressive loss of movement. It is associated with unrecognised pin penetration, cast immobilisation, and prolonged immobilisation. Treatment is supportive (physiotherapy, anti-inflammatory drugs) but the prognosis is poor.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1168,
              "stem": "Slipped upper femoral epiphysis (SUFE) occurs most commonly in which demographic?",
              "options": [
                "Thin prepubertal girls",
                "Neonates",
                "Overweight adolescent boys (peak 10-16 years, during the pubertal growth spurt)",
                "Elderly women",
                "Young athletic adults"
              ],
              "answer": "C",
              "explanation": "SUFE typically affects overweight/obese adolescents during the pubertal growth spurt — the combination of increased body weight, hormonal changes (decreased sex hormones relative to growth hormone), and the reorientation of the physis from horizontal to more oblique all contribute to the slip. Boys are more commonly affected (2:1 male:female). Left hip is slightly more common. Bilateral involvement in 20-40% (sequential or simultaneous). Presentation: hip/groin/thigh/knee pain (referred knee pain is a common diagnostic pitfall — ALWAYS examine the hip in a child with knee pain), antalgic gait, obligatory external rotation with hip flexion (Drehmann sign). Treatment: urgent in situ fixation with a single cannulated screw (to prevent further slip). DO NOT attempt reduction of a chronic slip (risk of AVN).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1169,
              "stem": "An unstable SUFE (patient cannot weight-bear, even with crutches) is classified as Loder unstable. The significance of instability is:",
              "options": [
                "No prognostic significance",
                "Unstable SUFE always heals without complications",
                "Unstable SUFE does not require surgery",
                "Instability indicates a benign course",
                "The AVN rate is approximately 47% in unstable SUFE (compared to <5% in stable)"
              ],
              "answer": "E",
              "explanation": "Loder classification: Stable SUFE = patient can weight-bear (with or without crutches). Unstable SUFE = patient CANNOT weight-bear at all. The critical significance: unstable SUFE has an AVN rate of approximately 47% regardless of treatment, compared to <5% for stable SUFE. This is because the unstable slip disrupts the retinacular blood supply to the femoral epiphysis (similar mechanism to displaced intracapsular NOF fractures). Treatment for unstable SUFE: urgent gentle reduction (if possible, not forced) and single screw fixation in the ED/theatre. Some advocate gentle positioning on the fracture table rather than active manipulation to minimise additional vascular damage. The Southwick slip angle is used to quantify the severity of the slip on the frog-lateral radiograph.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Perthes",
          "range": "Q1170-Q1172",
          "questions": [
            {
              "number": 1170,
              "stem": "The principle of containment treatment in Perthes disease aims to:",
              "options": [
                "Reduce the blood supply to the femoral head",
                "Keep the femoral head fully seated within the acetabulum to act as a mould during reossification",
                "Increase hip joint pressure",
                "Restrict all hip movement",
                "Accelerate the fragmentation phase"
              ],
              "answer": "B",
              "explanation": "Containment maintains the femoral head concentrically within the acetabulum, using the acetabulum as a biological mould during the reossification phase. This aims to achieve a spherical femoral head at healing. Methods include: abduction bracing (Scottish Rite orthosis — less commonly used now), femoral varus osteotomy (redirects the head into the acetabulum), or innominate osteotomy (Salter — increases acetabular coverage). Containment is most effective in children >8 years with Herring B or B/C lateral pillar involvement.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1171,
              "stem": "In Perthes disease, the Herring lateral pillar classification assesses the lateral pillar of the femoral epiphysis during the fragmentation phase. Group C indicates:",
              "options": [
                "No involvement of the lateral pillar",
                "Lateral pillar maintains >50% of its original height",
                "Normal hip",
                "Only trochanteric involvement",
                "Lateral pillar height is <50% of the original (worst prognosis)"
              ],
              "answer": "E",
              "explanation": "Herring lateral pillar classification (assessed during fragmentation phase on AP radiograph): Group A = lateral pillar fully maintained (no loss of height) — best prognosis, almost all do well regardless of treatment. Group B = lateral pillar maintains >50% of its original height — prognosis depends on age (>8 years at onset have worse outcomes). Group B/C = exactly 50% height or a very narrow maintained pillar. Group C = lateral pillar height <50% of original — worst prognosis, most likely to develop femoral head deformity and secondary OA. Prognostic factors: age at onset (>8yr worse), lateral pillar classification, and range of motion (loss of abduction/IR suggests hinge abduction and poor outcome).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1172,
              "stem": "Perthes disease progresses through four radiographic stages. The correct sequence is:",
              "options": [
                "Fragmentation → initial/necrosis → reossification → remodelling",
                "Reossification → fragmentation → necrosis → remodelling",
                "Initial/necrosis → fragmentation → reossification → remodelling (healing)",
                "Remodelling → necrosis → fragmentation → reossification",
                "No recognisable radiographic stages exist"
              ],
              "answer": "C",
              "explanation": "Waldenstrom radiographic stages of Perthes: (1) Initial/necrosis stage: epiphysis appears smaller and denser (sclerotic) than contralateral side, Gage sign (lateral epiphyseal lucency), widened medial joint space. (2) Fragmentation stage: epiphysis fragments into areas of sclerosis and lucency — Herring lateral pillar classification is applied at THIS stage (determines prognosis). (3) Reossification (re-ossification/healing): new bone formation begins, femoral head gradually re-forms (shape depends on containment during fragmentation). (4) Remodelling (residual): final shape of the femoral head is established by skeletal maturity — ranges from normal spherical (Stulberg I) to severely flattened (Stulberg V, aspherical congruent or incongruent → early OA). Total disease duration: 2-4 years.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Skeletal Dysplasia",
          "range": "Q1173-Q1175",
          "questions": [
            {
              "number": 1173,
              "stem": "Hereditary multiple exostoses (HME/MHE) is inherited in which pattern?",
              "options": [
                "Autosomal dominant",
                "Autosomal recessive",
                "X-linked recessive",
                "X-linked dominant",
                "Mitochondrial"
              ],
              "answer": "A",
              "explanation": "HME/MHE (also called diaphyseal aclasis) is autosomal dominant, caused by mutations in EXT1 (chromosome 8) or EXT2 (chromosome 11) genes. It produces multiple osteochondromas (cartilage-capped bony exostoses) growing away from the nearest joint. Complications: cosmetic deformity, mechanical impingement, forearm deformity (relative ulnar shortening), and malignant transformation to secondary chondrosarcoma in 5-10% (compared to ~1% for solitary osteochondroma).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1174,
              "stem": "Achondroplasia is characterised by which pattern of limb shortening?",
              "options": [
                "Mesomelic (middle segment short)",
                "Acromelic (distal segment short)",
                "Proportionate shortening",
                "Rhizomelic (proximal segment short)",
                "No limb shortening"
              ],
              "answer": "D",
              "explanation": "Achondroplasia produces rhizomelic shortening — the proximal segments (humeri and femora) are disproportionately short compared to the forearms/legs. This is because endochondral ossification (responsible for longitudinal growth of long bones) is impaired by constitutive activation of FGFR3, but intramembranous ossification (periosteal appositional growth) is unaffected. Features include frontal bossing, midface hypoplasia, trident hand, lumbar lordosis, and spinal stenosis.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1175,
              "stem": "Osteogenesis imperfecta Type I (Sillence classification) is characterised by:",
              "options": [
                "Lethal in the perinatal period",
                "Blue sclerae with mild bone fragility",
                "Severe progressive deformity with normal sclerae",
                "Moderate deformity with dentinogenesis imperfecta",
                "No fractures until adulthood"
              ],
              "answer": "B",
              "explanation": "OI Type I (Sillence) is the mildest form: blue sclerae (due to thin scleral collagen allowing choroidal pigment to show through), mild bone fragility with few fractures, near-normal stature, and autosomal dominant inheritance. Type II is lethal perinatally. Type III is the most severe surviving form with progressive deformity and normal sclerae. Type IV is moderate severity with normal sclerae. Treatment includes bisphosphonates, physiotherapy, and orthopaedic management of fractures/deformities.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Paediatric Fractures",
          "range": "Q1176-Q1179",
          "questions": [
            {
              "number": 1176,
              "stem": "A lateral condyle fracture of the distal humerus in a child is classified as Milch Type II when the fracture line runs through:",
              "options": [
                "The capitellar ossification centre only",
                "The trochlear groove (lateral to the trochlear ridge)",
                "The medial epicondyle",
                "The olecranon fossa",
                "Through the trochlea (medial to the trochlear ridge)"
              ],
              "answer": "E",
              "explanation": "Milch classification of lateral condyle fractures: Type I = fracture line lateral to the trochlear ridge (through the capitello-trochlear groove) — the trochlear ridge is intact, providing some elbow stability. Type II = fracture line through or medial to the trochlear ridge — the elbow is potentially unstable (equivalent to a Salter-Harris IV physeal injury). Lateral condyle fractures are the second most common paediatric elbow fracture. They are prone to non-union because the fracture is intra-articular and bathed in synovial fluid (inhibits healing).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1177,
              "stem": "A buckle (torus) fracture of the distal radius in a child is best managed with:",
              "options": [
                "Open reduction and internal fixation",
                "Manipulation under anaesthesia and casting",
                "Removable splint for 3–4 weeks",
                "Intramedullary nailing",
                "Skeletal traction"
              ],
              "answer": "C",
              "explanation": "Buckle (torus) fractures are incomplete fractures where the cortex buckles on the compression side without cortical disruption on the tension side. They are inherently stable and do not displace further. Current evidence supports treatment with a removable wrist splint for 3–4 weeks rather than rigid casting, allowing earlier return to function without risk of displacement. This represents a significant change in practice from routine casting.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1178,
              "stem": "The most common elbow fracture in children is:",
              "options": [
                "Olecranon fracture",
                "Radial head fracture",
                "Lateral condyle fracture",
                "Supracondylar fracture",
                "Medial epicondyle fracture"
              ],
              "answer": "D",
              "explanation": "Supracondylar fractures account for approximately 60% of elbow fractures in children, with a peak age of 5–7 years. Extension-type injuries (98%) result from a fall on an outstretched hand. The Gartland classification guides management: Type I (undisplaced) = collar and cuff/backslab, Type II (angulated with intact posterior cortex) = MUA + K-wire if unstable, Type III (completely displaced) = MUA + percutaneous K-wire fixation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1179,
              "stem": "In children, fractures remodel more effectively in which plane?",
              "options": [
                "Rotational plane",
                "Sagittal plane (plane of joint motion)",
                "Coronal plane",
                "Axial plane",
                "All planes equally"
              ],
              "answer": "B",
              "explanation": "Fractures in children remodel most effectively in the plane of motion of the adjacent joint (sagittal plane for most limb fractures). Remodelling is also better in younger children and when the fracture is closer to the physis (where more growth occurs). Rotational deformity does NOT remodel and must be corrected. Angular deformity in the coronal plane remodels less well than in the sagittal plane.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Clubfoot (CTEV)",
          "range": "Q1180-Q1181",
          "questions": [
            {
              "number": 1180,
              "stem": "The Ponseti method of clubfoot correction involves serial manipulation and casting. The order of correction is:",
              "options": [
                "Cavus first, then adductus and varus together, equinus last",
                "Equinus first, then cavus, adductus, varus",
                "Adductus first, then varus, cavus, equinus",
                "Equinus and varus simultaneously, then adductus",
                "All deformities corrected simultaneously"
              ],
              "answer": "A",
              "explanation": "The Ponseti method corrects deformities in a specific sequence: (1) Cavus is corrected first by supinating the forefoot relative to the hindfoot. (2) Adductus and varus are corrected simultaneously by abducting the foot with counter-pressure on the lateral talar head. (3) Equinus is corrected last, often requiring a percutaneous Achilles tenotomy (needed in ~80% of cases). The cavus must be corrected first because it locks the forefoot, preventing correction of the other deformities.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1181,
              "stem": "The Pirani scoring system for clubfoot assesses severity based on how many clinical signs?",
              "options": [
                "3",
                "6",
                "4",
                "8",
                "10"
              ],
              "answer": "B",
              "explanation": "The Pirani score evaluates 6 clinical signs, 3 in the hindfoot (posterior crease, empty heel, rigid equinus) and 3 in the midfoot (curved lateral border, medial crease, lateral head of talus coverage). Each sign is scored 0 (normal), 0.5, or 1 (most severe), giving a total score of 0–6. A score of 0 indicates a fully corrected foot. The score guides treatment decisions and monitors progress during serial casting.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Salter-Harris",
          "range": "Q1182-Q1183",
          "questions": [
            {
              "number": 1182,
              "stem": "A Salter-Harris Type II physeal fracture involves:",
              "options": [
                "Fracture through the physis only",
                "Fracture through the physis and epiphysis",
                "Fracture through the physis, metaphysis, and epiphysis",
                "Crush injury of the physis",
                "Fracture through the physis with a metaphyseal fragment (Thurston-Holland)"
              ],
              "answer": "E",
              "explanation": "Salter-Harris classification: Type I = through the physis only (may be radiographically occult). Type II = through the physis with a triangular metaphyseal fragment (Thurston-Holland fragment) — this is the MOST COMMON type (~75%). Type III = through the physis and epiphysis (intra-articular). Type IV = through the metaphysis, physis, and epiphysis. Type V = crush/compression of the physis. Mnemonic: SALTR — Straight across, Above, Lower, Through, Ruined.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1183,
              "stem": "Which Salter-Harris type carries the highest risk of growth arrest?",
              "options": [
                "Type V",
                "Type I",
                "Type II",
                "Type III",
                "Type IV"
              ],
              "answer": "A",
              "explanation": "Type V (crush injury) carries the highest risk of growth arrest because the germinal cells of the physis are directly damaged by compression. However, Type V injuries are rare and often diagnosed retrospectively when growth arrest becomes apparent. Types III and IV also carry significant risk because they cross the physis and disrupt the growth mechanism. Type II has the lowest growth arrest risk (~1–2%). Physeal arrest can cause angular deformity (partial arrest) or limb length discrepancy (complete arrest).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "NAI",
          "range": "Q1184-Q1185",
          "questions": [
            {
              "number": 1184,
              "stem": "Which fracture pattern in a child under 18 months is most specific for non-accidental injury (NAI)?",
              "options": [
                "Spiral femoral shaft fracture in a walking toddler",
                "Clavicle fracture from a fall",
                "Greenstick forearm fracture",
                "Classic metaphyseal corner fracture (bucket-handle/corner fracture)",
                "Supracondylar fracture"
              ],
              "answer": "D",
              "explanation": "Classic metaphyseal lesions (CML), also called corner fractures or bucket-handle fractures, are highly specific for NAI. They result from shearing/avulsion forces at the metaphyseal-physeal junction from violent pulling, twisting, or shaking. Other high-specificity fractures: posterior rib fractures (from squeezing), scapular fractures, spinous process fractures, and sternal fractures. Multiple fractures at different stages of healing are a red flag.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1185,
              "stem": "A skeletal survey in a child suspected of NAI should include radiographs of:",
              "options": [
                "Only the injured limb",
                "Chest and abdomen only",
                "The entire skeleton including oblique views of the ribs",
                "Long bones only",
                "Skull and spine only"
              ],
              "answer": "C",
              "explanation": "A full skeletal survey for NAI includes AP views of all long bones (individually, not babygram), AP and lateral skull, AP and lateral spine, AP chest, oblique views of the ribs (to detect posterior rib fractures), AP pelvis, and AP views of hands and feet. Repeat skeletal survey at 11–14 days may reveal healing fractures not visible initially. A bone scan can supplement but does not replace the skeletal survey.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Perthes Disease",
          "range": "Q1186",
          "questions": [
            {
              "number": 1186,
              "stem": "The Catterall classification of Perthes disease divides involvement of the femoral head into how many groups?",
              "options": [
                "2",
                "3",
                "5",
                "4",
                "6"
              ],
              "answer": "D",
              "explanation": "Catterall classification: Group I = anterior epiphysis only (<25% involvement), Group II = anterior half involved with sequestrum (25–50%), Group III = large sequestrum involving most of the head (50–75%), Group IV = total head involvement (>75%). Catterall 'head at risk' signs include: lateral subluxation, Gage sign (lateral physeal lucency), lateral calcification, horizontal physis, and metaphyseal cysts. The Herring lateral pillar classification is now more commonly used.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Cerebral Palsy",
          "range": "Q1187",
          "questions": [
            {
              "number": 1187,
              "stem": "In cerebral palsy, the GMFCS (Gross Motor Function Classification System) has how many levels?",
              "options": [
                "5",
                "3",
                "4",
                "6",
                "7"
              ],
              "answer": "A",
              "explanation": "The GMFCS classifies gross motor function in children with cerebral palsy into 5 levels: Level I = walks without limitations. Level II = walks with limitations (difficulty outdoors/stairs). Level III = walks with hand-held mobility devices (crutches/walker). Level IV = self-mobility with limitations, may use powered wheelchair. Level V = transported in a manual wheelchair (severely limited self-mobility). The classification is age-dependent and does not change with treatment.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Rickets",
          "range": "Q1188",
          "questions": [
            {
              "number": 1188,
              "stem": "The radiographic hallmark of rickets at the growth plate is:",
              "options": [
                "Sclerotic metaphysis",
                "Physeal closure",
                "Widened, irregular, cupped metaphysis with physeal widening",
                "Periosteal reaction only",
                "Normal growth plate appearance"
              ],
              "answer": "C",
              "explanation": "Rickets produces characteristic radiographic changes at the growth plate: widening and irregularity of the physis, cupping and fraying of the metaphysis, osteopenia, and bowing deformities. The growth plate appears widened because unmineralised osteoid (hypertrophic zone) accumulates due to failure of provisional calcification. The zone of provisional calcification is absent or poorly defined. Biochemistry: low calcium, low phosphate, raised ALP, raised PTH.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "CP",
          "range": "Q1189",
          "questions": [
            {
              "number": 1189,
              "stem": "In spastic diplegic cerebral palsy, the typical gait pattern includes:",
              "options": [
                "Steppage gait (high-stepping to clear foot)",
                "Antalgic gait on the right",
                "Normal gait pattern",
                "Trendelenburg gait only",
                "Scissoring gait with crouched posture (hip flexion/adduction/IR, knee flexion, equinus)"
              ],
              "answer": "E",
              "explanation": "Spastic diplegia (the most common pattern of CP in premature infants) produces bilateral lower limb spasticity with relatively spared upper limbs. The typical gait pattern: hip flexion/adduction/internal rotation (tight hamstrings, adductors, medial hamstrings → internal rotation), knee flexion (tight hamstrings, rectus femoris spasticity), and equinus (tight gastrocnemius/soleus → toe-walking). Scissoring occurs from adductor spasticity. Gait analysis (instrumented 3D gait analysis) is essential for surgical planning.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Physeal Injury",
          "range": "Q1190",
          "questions": [
            {
              "number": 1190,
              "stem": "The physis (growth plate) is weakest in which zone, making it the most common site of failure?",
              "options": [
                "Reserve (resting) zone",
                "Hypertrophic zone (particularly the zone of provisional calcification)",
                "Proliferative zone",
                "Zone of ossification",
                "Groove of Ranvier"
              ],
              "answer": "B",
              "explanation": "The hypertrophic zone is the weakest zone of the physis because the chondrocytes are enlarged, the matrix is poorly mineralised (provisional calcification zone), and the intercellular matrix is sparse. This is where the majority of physeal fractures propagate (Salter-Harris fractures pass through the hypertrophic zone). The reserve zone provides stem cells. The proliferative zone provides longitudinal growth. The zone of provisional calcification is where mineralisation begins and is the specific weak point within the hypertrophic zone.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Blount Disease",
          "range": "Q1191",
          "questions": [
            {
              "number": 1191,
              "stem": "Blount disease (tibia vara) involves abnormal growth of which part of the proximal tibia?",
              "options": [
                "Lateral tibial physis",
                "Tibial tuberosity apophysis",
                "Medial proximal tibial physis (and metaphysis)",
                "Fibular physis",
                "Entire tibial shaft"
              ],
              "answer": "C",
              "explanation": "Blount disease (infantile tibia vara) involves abnormal endochondral ossification of the medial proximal tibial physis and metaphysis, leading to progressive varus deformity. It differs from physiological genu varum (which corrects by age 2) in that it is progressive, often unilateral, and shows radiographic changes (beaking of the medial metaphysis, fragmentation, widening of the medial physis). The Langenskiöld classification stages I-VI guides treatment. Risk factors: obesity, early walking, African descent. Treatment: bracing (Stages I-II, <3 years) or proximal tibial valgus osteotomy (Stages III+).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Pulled Elbow",
          "range": "Q1192",
          "questions": [
            {
              "number": 1192,
              "stem": "A pulled elbow (subluxation of the radial head) in a toddler is reduced by:",
              "options": [
                "Supination of the forearm with pressure over the radial head while flexing the elbow",
                "Open reduction in theatre",
                "Pronation and extension of the forearm",
                "Skeletal traction",
                "Casting in extension for 3 weeks"
              ],
              "answer": "A",
              "explanation": "Pulled elbow (nursemaid's elbow) is subluxation of the radial head through the annular ligament, caused by a longitudinal traction force on the extended forearm (e.g., pulling a child by the hand). The child holds the arm in pronation and refuses to use it. Reduction: supinate the forearm fully while applying gentle pressure over the radial head, then flex the elbow — a palpable click confirms reduction. The child typically uses the arm within minutes. No radiograph is needed if the history and presentation are classic. Immobilisation is not required after reduction.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Apophysitis",
          "range": "Q1193-Q1194",
          "questions": [
            {
              "number": 1193,
              "stem": "Osgood-Schlatter disease is a traction apophysitis affecting which structure?",
              "options": [
                "Inferior pole of the patella",
                "Tibial tuberosity apophysis",
                "Greater trochanter apophysis",
                "Calcaneal apophysis",
                "Iliac crest apophysis"
              ],
              "answer": "B",
              "explanation": "Osgood-Schlatter disease is a traction apophysitis of the tibial tuberosity caused by repetitive stress from the patellar tendon during the adolescent growth spurt. It presents with anterior knee pain, swelling, and tenderness over the tibial tuberosity, worsened by activity (running, jumping, kneeling). Lateral radiograph may show fragmentation or prominence of the tibial tuberosity. It is self-limiting and resolves with skeletal maturity. Treatment: activity modification, stretching (quadriceps/hamstrings), ice, NSAIDs. A residual bony prominence may persist.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1194,
              "stem": "Sever disease is a calcaneal apophysitis presenting with heel pain in which age group?",
              "options": [
                "Neonates",
                "Adults aged 30-50",
                "Elderly >70",
                "Adolescents aged 16-18",
                "Children aged 8-13"
              ],
              "answer": "E",
              "explanation": "Sever disease (calcaneal apophysitis) affects children aged 8-13 during the growth spurt. It is caused by traction of the Achilles tendon on the calcaneal apophysis (secondary ossification centre). Presents with posterior heel pain worse with activity (running, jumping), tenderness on medial-lateral calcaneal squeeze test. Self-limiting — resolves when the apophysis fuses. Treatment: activity modification, heel raises, stretching (calf), cushioned heel inserts, ice. Differentiate from: calcaneal stress fracture, plantar fasciitis (rare in children), and tumour (if persistent/atypical).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Radial Neck",
          "range": "Q1195",
          "questions": [
            {
              "number": 1195,
              "stem": "Radial neck fractures in children are common. The acceptable angulation before operative intervention is needed is approximately:",
              "options": [
                "Any angulation requires surgery",
                "≤60° angulation",
                "≤90° angulation",
                "≤30° angulation (>30° needs reduction)",
                "Only completely displaced fractures need surgery"
              ],
              "answer": "D",
              "explanation": "In children, radial neck fractures with ≤30° angulation and ≤3mm translation can be managed non-operatively (collar and cuff, early mobilisation). Fractures with >30° angulation or >3mm translation need reduction. Reduction techniques: Patterson manoeuvre (direct pressure over the radial head), Israeli technique (flexible IM wire inserted retrograde via the distal radius to lever the head), or ORIF (as a last resort — open reduction risks AVN and stiffness). The radial head ossification centre appears at ~5 years (don't confuse a normal ossification centre for a fracture). Cross-table lateral view is essential.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Bone Disease",
          "range": "Q1196-Q1197",
          "questions": [
            {
              "number": 1196,
              "stem": "Fibrous dysplasia is caused by a mutation in which gene?",
              "options": [
                "COL1A1 (collagen Type I)",
                "FGFR3 (fibroblast growth factor receptor 3)",
                "EXT1 (exostosin 1)",
                "GNAS1 (guanine nucleotide-binding protein α-stimulating)",
                "TP53 (tumour protein 53)"
              ],
              "answer": "D",
              "explanation": "Fibrous dysplasia is caused by an activating mutation in the GNAS1 gene (encodes the Gsα subunit of the G-protein signalling pathway), leading to constitutive activation of adenylyl cyclase and abnormal osteoblast differentiation. Normal bone is replaced by fibrous tissue containing immature woven bone trabeculae. Monostotic (70-80%): single bone (rib, proximal femur most common). Polyostotic (20-30%): multiple bones. McCune-Albright syndrome: polyostotic FD + café-au-lait spots (coast of Maine borders, irregular) + precocious puberty. Mazabraud syndrome: FD + intramuscular myxomas. Malignant transformation <1%.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1197,
              "stem": "Osteogenesis imperfecta (OI) is caused by defects in which molecule?",
              "options": [
                "Type II collagen",
                "Type I collagen (COL1A1 or COL1A2 gene mutations)",
                "Fibrillin",
                "Elastin",
                "Keratin"
              ],
              "answer": "B",
              "explanation": "Osteogenesis imperfecta (brittle bone disease) is caused by mutations in the COL1A1 or COL1A2 genes, which encode the alpha chains of Type I collagen. Since Type I collagen is the primary structural protein of bone (90% of organic bone matrix), tendon, ligament, skin, sclera, and dentin, defects lead to: frequent fractures from minimal trauma, blue sclerae (thin sclera allows choroidal pigment to show through), dentinogenesis imperfecta (discoloured, fragile teeth), hearing loss (otosclerosis), joint hypermobility, and easy bruising. Sillence classification: Type I = mild (normal stature, blue sclerae, autosomal dominant). Type II = lethal perinatal (most severe, multiple fractures in utero). Type III = severe progressive deforming (most severe compatible with survival). Type IV = moderate (variable severity, normal sclerae). Treatment: bisphosphonates (reduce fracture rate), IM rodding (telescoping rods for long bone protection).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Orthopaedic Assessment",
          "range": "Q1198",
          "questions": [
            {
              "number": 1198,
              "stem": "In a child with a limping gait, the most common cause varies by age. In a child aged 3-8 years, the most common cause of a painful limp is:",
              "options": [
                "Transient synovitis (irritable hip)",
                "DDH",
                "Septic arthritis",
                "Slipped upper femoral epiphysis",
                "Perthes disease"
              ],
              "answer": "A",
              "explanation": "Transient synovitis (irritable hip) is the most common cause of a painful limp in children aged 3-8 years. It is a self-limiting inflammatory synovitis typically following a viral illness. Presents with: acute onset hip/thigh/knee pain, antalgic gait or refusal to weight-bear, restricted ROM (especially internal rotation), low-grade or no fever, normal or mildly elevated inflammatory markers. The KEY differential is septic arthritis — use Kocher criteria (fever >38.5°, non-WB, ESR >40, WCC >12,000) to guide aspiration. Transient synovitis: settles within 7-10 days with rest and NSAIDs. Perthes should be considered if symptoms persist >2 weeks (get repeat XR).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Infection",
          "range": "Q1199",
          "questions": [
            {
              "number": 1199,
              "stem": "The most common organism causing osteomyelitis in ALL paediatric age groups is:",
              "options": [
                "Group B Streptococcus",
                "Kingella kingae",
                "Haemophilus influenzae",
                "Pseudomonas aeruginosa",
                "Staphylococcus aureus"
              ],
              "answer": "E",
              "explanation": "Staphylococcus aureus is the most common causative organism of osteomyelitis across ALL paediatric age groups and in adults. However, age-specific patterns exist: Neonates (0-3 months): S. aureus, Group B Streptococcus, gram-negatives (E. coli). Children (3 months-5 years): S. aureus (most common), Kingella kingae (increasingly recognised, especially in <5 years — difficult to culture, PCR needed), Streptococcus pyogenes. Older children/adolescents: S. aureus, Streptococcus pyogenes. Sickle cell disease: Salmonella (most common in sickle cell, NOT S. aureus — this is a frequently tested exam trap).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        }
      ]
    },
    {
      "title": "Upper Limb",
      "chapters": [
        {
          "title": "Shoulder",
          "range": "Q1200-Q1218",
          "questions": [
            {
              "number": 1200,
              "stem": "A Hill-Sachs lesion is:",
              "options": [
                "A fracture of the acromion",
                "A tear of the rotator cuff",
                "A compression FRACTURE of the POSTEROSUPERIOR humeral head caused by impaction against the anterior glenoid rim during anterior shoulder dislocation",
                "A fracture of the clavicle",
                "A tear of the long head of biceps"
              ],
              "answer": "C",
              "explanation": "Hill-Sachs lesion (Hill and Sachs, 1940): a compression fracture (impaction defect) of the POSTEROSUPERIOR humeral head. It occurs during ANTERIOR shoulder dislocation — as the humeral head dislocates anteriorly, the posterior aspect of the head impacts against the hard anterior-inferior glenoid rim, creating a dent/concavity in the posterosuperior humeral head. Incidence: ~65-70% of first-time anterior dislocations, up to ~90-100% in recurrent dislocators. Clinical significance: an 'engaging' Hill-Sachs lesion (one that catches on the anterior glenoid rim during external rotation in abduction) contributes to recurrent instability. Treatment: small non-engaging lesions → no specific treatment (Bankart repair alone may suffice). Large engaging lesions → remplissage (French for 'filling' — the infraspinatus tendon and posterior capsule are packed into the Hill-Sachs defect to prevent engagement) or Latarjet (the bone block extends the glenoid arc, preventing the Hill-Sachs from reaching the glenoid). Reverse Hill-Sachs (McLaughlin lesion): compression of the ANTEROINFERIOR humeral head from POSTERIOR dislocation (impaction against the posterior glenoid).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1201,
              "stem": "The Neer classification of proximal humerus fractures is based on the number of displaced parts. A fracture is considered 'displaced' when there is:",
              "options": [
                "Displacement >1cm or angulation >45° between the fragments",
                "Any visible fracture line",
                "Displacement >1mm",
                "Displacement >5cm",
                "No specific criteria exist"
              ],
              "answer": "A",
              "explanation": "Neer classification defines a 'part' as displaced when it is separated by >1cm or angulated >45° from the adjacent fragment. The four potential parts are: (1) greater tuberosity, (2) lesser tuberosity, (3) humeral head (articular segment), (4) humeral shaft. A 1-part fracture: no displaced parts (regardless of fracture lines — the fragments are in acceptable position). 2-part: one part is displaced. 3-part: two parts are displaced. 4-part: all four parts are displaced (worst — highest AVN risk). Treatment: 1-part (85% of proximal humerus fractures): non-operative (sling, early mobilisation — supported by PROFHER trial). 2-part GT: ORIF if >5mm displacement (particularly in active patients). 3-part: ORIF (locking plate) or hemiarthroplasty (older patients). 4-part: rTSA (elderly) or ORIF (young patients with adequate bone quality).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1202,
              "stem": "The most common shoulder arthroplasty procedure performed worldwide is now:",
              "options": [
                "Hemiarthroplasty",
                "Anatomical total shoulder arthroplasty",
                "Reverse total shoulder arthroplasty (rTSA — has surpassed anatomical TSA in volume due to expanding indications beyond cuff tear arthropathy)",
                "Resurfacing arthroplasty",
                "Shoulder fusion"
              ],
              "answer": "C",
              "explanation": "Reverse total shoulder arthroplasty (rTSA) has become the most commonly performed shoulder arthroplasty worldwide, surpassing anatomical TSA and hemiarthroplasty. Originally designed by Grammont for cuff tear arthropathy (irreparable cuff + OA), its indications have EXPANDED significantly to include: (1) cuff tear arthropathy (original indication), (2) complex proximal humerus fractures in the elderly (better function than hemiarthroplasty), (3) failed anatomical TSA (revision to rTSA), (4) massive irreparable cuff tears WITHOUT arthritis (augmented with tendon transfer), (5) tumour reconstruction of the proximal humerus. The expanding indications have driven the volume growth. NJR and US registry data confirm rTSA now accounts for >50% of all shoulder arthroplasties. Key contraindication: absent deltoid function (axillary nerve palsy — the deltoid is the ONLY motor for rTSA). Complication rates are higher than anatomical TSA: scapular notching (~50%), instability, infection, acromial fracture.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1203,
              "stem": "The supraspinatus muscle is innervated by the:",
              "options": [
                "Axillary nerve (C5-C6)",
                "Suprascapular nerve (C5-C6 — passes through the suprascapular notch under the transverse scapular ligament to supply supraspinatus, then through the spinoglenoid notch to supply infraspinatus)",
                "Subscapular nerve",
                "Musculocutaneous nerve",
                "Long thoracic nerve"
              ],
              "answer": "B",
              "explanation": "The suprascapular nerve (C5-C6) innervates BOTH the supraspinatus and infraspinatus. It originates from the upper trunk of the brachial plexus, passes through the SUPRASCAPULAR NOTCH (under the transverse scapular ligament — the artery passes OVER the ligament: 'army over the bridge, navy under the bridge') to supply the supraspinatus (initiates abduction 0-15°), then continues through the SPINOGLENOID NOTCH to supply the infraspinatus (external rotation). Suprascapular nerve palsy: causes supraspinatus and infraspinatus weakness/atrophy → difficulty initiating abduction, weak ER. Causes: suprascapular notch entrapment (ganglion cyst from labral tear compressing the nerve — MRI diagnosis), traction injuries (overhead athletes — volleyball), Parsonage-Turner syndrome (neuralgic amyotrophy). The nerve also provides sensory branches to the AC and GH joints (~70% of shoulder joint proprioception).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1204,
              "stem": "The apprehension test for anterior shoulder instability is positive when:",
              "options": [
                "The patient reports pain only without any fear of dislocation",
                "The patient cannot flex the shoulder",
                "Only during a posterior force on the shoulder",
                "The patient demonstrates apprehension (fear/anxiety that the shoulder is about to dislocate) when the arm is placed in 90° abduction and externally rotated — the position that recreates the anterior dislocation mechanism",
                "When the arm is in full adduction"
              ],
              "answer": "D",
              "explanation": "The apprehension test: the patient's arm is placed in 90° abduction and maximal external rotation (the 'position of vulnerability' for anterior dislocation). A positive test = the patient demonstrates APPREHENSION — a look of fear, resistance, or anxiety that the shoulder is about to dislocate (not just pain). The relocation test: with the arm in the same apprehension position, the examiner applies a POSTERIOR force on the humeral head → the apprehension is RELIEVED (the humeral head is pushed back into the glenoid → the patient feels more secure). If apprehension is relieved by posterior force → confirms anterior instability. The release test (surprise test): the posterior force is suddenly removed while still in the provocative position → apprehension returns abruptly. All three tests together have very high diagnostic accuracy for anterior instability. Important: apprehension ≠ pain. The test is specifically looking for FEAR OF DISLOCATION, not just pain (pain with ER can occur in impingement, cuff pathology, and other conditions).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1205,
              "stem": "Calcific tendinitis of the shoulder — the tendon most commonly affected is the:",
              "options": [
                "Infraspinatus",
                "Subscapularis",
                "Teres minor",
                "Long head of biceps",
                "Supraspinatus (~80% of cases — calcium hydroxyapatite deposits within the tendon substance, typically in the critical zone of relative hypovascularity)"
              ],
              "answer": "E",
              "explanation": "Calcific tendinitis most commonly affects the SUPRASPINATUS tendon (~80%), particularly in the 'critical zone' — an area of relative hypovascularity approximately 1-2cm from the tendon insertion (described by Codman). Calcium hydroxyapatite crystals deposit within the tendon substance during a formative phase (often asymptomatic). The condition becomes acutely painful during the RESORPTIVE phase — when the body mounts a vascular inflammatory response to absorb the deposits (macrophage invasion, hyperaemia, oedema → severe pain, sometimes the most intense shoulder pain a patient has ever experienced). Three phases (Uhthoff): (1) Pre-calcific (fibrocartilaginous transformation), (2) Calcific (formative — often asymptomatic, then resorptive — acutely painful), (3) Post-calcific (healing, tendon reconstitution). XR: well-defined radio-opaque deposit within the supraspinatus (formative — dense, well-defined; resorptive — fluffy, ill-defined). Treatment: most resolve spontaneously (the resorptive phase is actually HEALING). Conservative: NSAIDs, subacromial injection, physiotherapy. Barbotage: US-guided needle lavage + aspiration of calcium (effective for large/persistent deposits). Surgery (rare): arthroscopic excision if refractory.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1206,
              "stem": "Multidirectional instability (MDI) of the shoulder is characterised by:",
              "options": [
                "Instability in only one direction (anterior)",
                "Only posterior instability",
                "Symptomatic glenohumeral instability in two or more directions (anterior, posterior, and/or inferior — sulcus sign positive)",
                "Rotator cuff tear with instability",
                "Acromioclavicular joint instability"
              ],
              "answer": "C",
              "explanation": "MDI is symptomatic instability in at least TWO directions (typically inferior + anterior, or inferior + posterior, or all three). The sulcus sign is the key clinical test: apply a downward (inferior) traction force on the arm in neutral rotation — a visible sulcus (dimple) appearing between the acromion and humeral head indicates inferior capsular laxity (Grade 1 = <1cm, Grade 2 = 1-2cm, Grade 3 = >2cm). MDI is typically atraumatic (generalised ligamentous laxity, often bilateral), unlike unidirectional traumatic instability (Bankart lesion). The Stanmore classification triangulates instability: Polar Type I = traumatic structural (Bankart), Polar Type II = atraumatic structural (capsular laxity/MDI), Polar Type III = muscle patterning/habitual. Treatment: prolonged physiotherapy (rotator cuff and scapular stabiliser strengthening — 6-12 months). If failed: inferior capsular shift (tighten the redundant capsule inferiorly).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1207,
              "stem": "Calcific tendinitis of the shoulder most commonly affects which tendon?",
              "options": [
                "Supraspinatus",
                "Infraspinatus",
                "Subscapularis",
                "Teres minor",
                "Long head of biceps"
              ],
              "answer": "A",
              "explanation": "Calcific tendinitis most commonly affects the supraspinatus tendon (~70-80% of cases). It involves deposition of calcium hydroxyapatite crystals within the tendon substance. The resorptive (acute) phase produces severe pain, warmth, and erythema (can mimic septic arthritis). Radiographs show calcific deposits in the supraspinatus region on AP shoulder view in external rotation. Treatment: acute pain = NSAIDs, subacromial steroid injection. Persistent: barbotage (needle aspiration of calcium under ultrasound guidance), shockwave therapy, or arthroscopic excision.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1208,
              "stem": "The long head of biceps tendon originates from the:",
              "options": [
                "Coracoid process",
                "Superior glenoid labrum (supraglenoid tubercle) and superior labrum",
                "Acromion",
                "Inferior glenoid",
                "Greater tuberosity of the humerus"
              ],
              "answer": "B",
              "explanation": "The long head of biceps (LHB) originates from the supraglenoid tubercle and the superior glenoid labrum (this is why SLAP lesions involve the biceps anchor). The tendon passes through the glenohumeral joint, over the humeral head, and exits through the bicipital groove (between the greater and lesser tuberosities), held in place by the transverse humeral ligament. The short head of biceps originates from the coracoid process (with coracobrachialis — the conjoint tendon). LHB pathology: tendinopathy, instability (subluxation from groove), and rupture (Popeye deformity). Biceps tenotomy or tenodesis for symptomatic LHB pathology.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1209,
              "stem": "Posterior shoulder dislocation is classically missed on AP radiograph. The diagnostic radiographic sign on AP view is:",
              "options": [
                "Hill-Sachs lesion",
                "Bankart fragment",
                "Calcification in the supraspinatus",
                "Normal appearance in all cases",
                "Lightbulb sign (internally rotated humeral head appearing rounded like a lightbulb, loss of normal greater tuberosity profile)"
              ],
              "answer": "E",
              "explanation": "Posterior shoulder dislocations are missed in up to 50-60% of initial presentations. On standard AP radiograph, the humeral head appears ROUNDED ('lightbulb sign') because it is LOCKED in internal rotation — the normal GT profile (which creates the lateral convexity on AP view in external rotation) is lost. Other radiographic clues: loss of the half-moon overlap sign (normal overlap between humeral head and posterior glenoid rim), widened glenohumeral joint space (>6mm = rim sign), trough line (reverse Hill-Sachs — anteromedial impaction fracture, 'McLaughlin lesion'). The diagnosis is CONFIRMED on axillary lateral or scapular Y view — always obtain a second view perpendicular to the AP. Causes: seizures (most common, bilateral in 50%), electrocution, and direct anterior force. Clinical: arm held in adduction and internal rotation, LOSS OF EXTERNAL ROTATION (pathognomonic).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1210,
              "stem": "The critical angle of Goll (CSA — Critical Shoulder Angle) is measured on AP shoulder radiographs. A CSA >35° is associated with:",
              "options": [
                "Reduced risk of rotator cuff tears",
                "Only cosmetic implications",
                "Increased risk of instability without cuff pathology",
                "Increased risk of rotator cuff tears (greater supraspinatus moment arm demand)",
                "No clinical significance"
              ],
              "answer": "D",
              "explanation": "The Critical Shoulder Angle (CSA) measures the combined effect of glenoid inclination and lateral acromial extent on an AP shoulder radiograph. CSA >35°: associated with increased risk of rotator cuff tears (the more lateral acromion increases the deltoid moment arm, which increases the shearing force on the supraspinatus tendon during abduction). CSA <30°: associated with increased risk of glenohumeral OA (more concentric compressive loading). CSA 30-35°: normal range. This metric is increasingly used in clinical practice to understand the biomechanical predisposition to cuff disease and may guide surgical decisions (lateral acromial extension → consider acromioplasty to reduce CSA, though evidence for this approach is still evolving).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1211,
              "stem": "The safe zone for deltoid splitting in the anterolateral approach to the proximal humerus is limited to how far distal from the acromion to avoid axillary nerve injury?",
              "options": [
                "2 cm",
                "3 cm",
                "7 cm",
                "10 cm",
                "5 cm"
              ],
              "answer": "E",
              "explanation": "The axillary nerve crosses the deep surface of the deltoid approximately 5 cm (range 5-7 cm) distal to the lateral edge of the acromion. In the deltoid-splitting (anterolateral/Mackenzie) approach, the split must NOT extend more than 5 cm distal to the acromion to avoid injuring the axillary nerve. A stay suture is placed at the distal extent of the split to prevent inadvertent extension. This approach is commonly used for proximal humerus fracture fixation (plates, nails) and rotator cuff repair. The same 5 cm rule applies to the lateral (Hardinge) approach to the hip for the superior gluteal nerve and gluteus medius.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1212,
              "stem": "The most common shoulder pathology presenting to an orthopaedic clinic is:",
              "options": [
                "Shoulder dislocation",
                "Rotator cuff disease (tendinopathy, impingement, tears)",
                "Acromioclavicular joint injury",
                "Adhesive capsulitis",
                "Glenohumeral arthritis"
              ],
              "answer": "B",
              "explanation": "Rotator cuff disease (including subacromial impingement, tendinopathy, partial and full-thickness tears) is the most common shoulder pathology presenting to orthopaedic clinics. The spectrum ranges from subacromial bursitis and tendinopathy (younger patients, overuse) through partial tears to massive irreparable tears (elderly, degenerative). Supraspinatus is the most commonly affected tendon. The Neer impingement classification stages the process: Stage I = oedema and haemorrhage (reversible, <25 years). Stage II = fibrosis and tendinitis (25-40 years). Stage III = tendon degeneration and tears (>40 years).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1213,
              "stem": "The most important static stabiliser of the glenohumeral joint in the apprehension position (90° abduction, external rotation) is the:",
              "options": [
                "Inferior glenohumeral ligament (anterior band)",
                "Superior glenohumeral ligament",
                "Middle glenohumeral ligament",
                "Coracohumeral ligament",
                "Rotator cuff"
              ],
              "answer": "A",
              "explanation": "The inferior glenohumeral ligament (IGHL), specifically its anterior band, is the primary static stabiliser against anterior glenohumeral translation when the arm is in 90° abduction and maximum external rotation (the apprehension position for anterior instability). It forms a hammock-like support for the humeral head. The Bankart lesion (avulsion of the anteroinferior labrum with attached IGHL from the glenoid rim) is the essential lesion in anterior shoulder instability. The SGHL stabilises in adduction/ER. The MGHL stabilises in mid-range abduction/ER. The rotator cuff provides dynamic stabilisation. The capsulolabral complex works together but the IGHL anterior band is most critical in the position of vulnerability.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1214,
              "stem": "A massive irreparable rotator cuff tear in an elderly patient with pseudoparalysis (inability to actively elevate the arm) and cuff tear arthropathy is best treated with:",
              "options": [
                "Arthroscopic rotator cuff repair",
                "Anatomic total shoulder arthroplasty",
                "Hemiarthroplasty",
                "Reverse total shoulder arthroplasty (rTSA)",
                "Steroid injection alone"
              ],
              "answer": "D",
              "explanation": "Reverse total shoulder arthroplasty (rTSA, Grammont design) is the treatment of choice for massive irreparable cuff tears with pseudoparalysis and cuff tear arthropathy (Hamada Grade 4-5). The reverse design places the ball (glenosphere) on the glenoid and the socket on the humerus — this medialises and distalises the centre of rotation, tensioning the deltoid and allowing it to compensate for the absent rotator cuff. The deltoid becomes the primary elevator via a lengthened lever arm. Anatomic TSA requires a functioning rotator cuff and is contraindicated in cuff tear arthropathy (risk of superior migration/rocking horse loosening). Hemiarthroplasty gives unpredictable results with a deficient cuff.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1215,
              "stem": "Adhesive capsulitis (frozen shoulder) passes through three clinical stages. The correct sequence is:",
              "options": [
                "Thawing → freezing → frozen",
                "Frozen → freezing → thawing",
                "Freezing (painful) → frozen (stiff) → thawing (recovery)",
                "Recovery → pain → stiffness",
                "No recognisable stages — it is constant"
              ],
              "answer": "C",
              "explanation": "Adhesive capsulitis progresses through three overlapping stages: (1) Freezing/painful stage (2-9 months): progressive pain, particularly at night, with gradually increasing stiffness. (2) Frozen/adhesive stage (4-12 months): pain diminishes but stiffness is maximal — significant restriction in all planes, particularly external rotation. (3) Thawing/resolution stage (5-24 months): gradual spontaneous recovery of motion and resolution of pain. Total duration: typically 12-36 months (may take up to 3 years). Most patients recover near-normal function. Risk factors: diabetes (most significant — 10-20% of diabetics, often bilateral, resistant to treatment), thyroid disease, female, age 40-60. Treatment: analgesia, physiotherapy (within pain limits), steroid injection (subacromial or intra-articular hydrodilatation), MUA (frozen stage), arthroscopic capsular release (refractory).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1216,
              "stem": "The suprascapular nerve (C5, C6) innervates supraspinatus and infraspinatus. It is at risk of compression at which two anatomical locations?",
              "options": [
                "Carpal tunnel and Guyon canal",
                "Suprascapular notch (beneath the transverse scapular ligament) and spinoglenoid notch",
                "Cubital tunnel and arcade of Struthers",
                "Triangular interval and quadrilateral space",
                "Thoracic outlet and first rib"
              ],
              "answer": "B",
              "explanation": "The suprascapular nerve passes through the suprascapular notch (beneath the transverse scapular ligament) where it innervates supraspinatus, then continues around the lateral border of the scapular spine to the spinoglenoid notch where it innervates infraspinatus. Compression at the suprascapular notch → supraspinatus AND infraspinatus weakness/atrophy. Compression at the spinoglenoid notch (often by a paralabral cyst from a posterior labral tear) → ISOLATED infraspinatus weakness/atrophy (supraspinatus is spared because the branch to supraspinatus has already left proximally). Presents: dull posterior shoulder pain, ER weakness, muscle wasting. MRI shows cyst (if present) + denervation oedema/atrophy in affected muscles.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1217,
              "stem": "The Latarjet procedure for recurrent anterior shoulder instability involves transfer of which structure to the anterior glenoid?",
              "options": [
                "Acromion",
                "Olecranon",
                "Greater tuberosity",
                "Coracoid process (with the conjoint tendon still attached) to the anteroinferior glenoid rim",
                "Clavicle"
              ],
              "answer": "D",
              "explanation": "The Latarjet procedure transfers the coracoid process (with the attached conjoint tendon — short head of biceps and coracobrachialis) to the anteroinferior glenoid rim. This provides a triple stabilising effect: (1) bone block — extends the glenoid surface area (addresses glenoid bone loss), (2) sling effect — the conjoint tendon passes over the subscapularis and acts as a dynamic anterior sling when the arm is in abduction and external rotation, (3) capsular repair — the coracoacromial ligament (attached to the coracoid) is sutured to the capsule. Indications: recurrent anterior instability with significant glenoid bone loss (>20-25%), failed Bankart repair, engaging Hill-Sachs, contact athletes with high recurrence risk. Complications: non-union of coracoid, hardware failure, musculocutaneous nerve injury, recurrence (~5%), OA.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1218,
              "stem": "The rotator cuff consists of four muscles. Which is NOT part of the rotator cuff?",
              "options": [
                "Supraspinatus",
                "Infraspinatus",
                "Teres minor",
                "Subscapularis",
                "Deltoid"
              ],
              "answer": "E",
              "explanation": "The rotator cuff consists of four muscles: Supraspinatus (initiates abduction, most commonly torn), Infraspinatus (external rotation, second most commonly torn), Teres minor (external rotation), and Subscapularis (internal rotation, most powerful cuff muscle). Mnemonic: SITS (Supraspinatus, Infraspinatus, Teres minor, Subscapularis). The DELTOID is NOT part of the rotator cuff — it is the prime mover of shoulder abduction (after the first 15-30° initiated by supraspinatus) and is innervated by the axillary nerve (C5-C6). The cuff muscles originate from the scapula and insert on the greater tuberosity (supraspinatus, infraspinatus, teres minor) and lesser tuberosity (subscapularis), forming a tendinous 'cuff' around the humeral head.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Elbow",
          "range": "Q1219-Q1230",
          "questions": [
            {
              "number": 1219,
              "stem": "Heterotopic ossification (HO) prophylaxis after elbow surgery — the most commonly used pharmacological agent is:",
              "options": [
                "Indomethacin (NSAID — inhibits prostaglandin-mediated osteoblast differentiation, given for 2-6 weeks post-operatively)",
                "Aspirin",
                "Paracetamol",
                "Methotrexate",
                "Bisphosphonate"
              ],
              "answer": "A",
              "explanation": "Indomethacin (25mg TDS for 2-6 weeks) is the most commonly used pharmacological agent for HO prophylaxis after elbow surgery and other high-risk procedures (acetabular surgery, burns). It works by inhibiting prostaglandin synthesis (COX inhibition) — prostaglandins stimulate mesenchymal stem cell differentiation into osteoblasts and promote bone formation at ectopic sites. Alternative: single-dose radiation therapy (700-800 cGy within 24 hours post-operatively — prevents MSC differentiation). Both methods inhibit early-stage HO formation. Risk factors for elbow HO: burns, head injury, high-energy elbow trauma, delayed surgery, and certain genetic predispositions. Once established HO has matured (typically 6-12 months — confirmed by normalised ALP and mature appearance on bone scan), it can be excised surgically if causing functional limitation. Brooker classification (hip): grades HO severity I-IV.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1220,
              "stem": "The carrying angle of the elbow is:",
              "options": [
                "0° in all individuals",
                "Always exactly 30°",
                "The normal valgus angle of the elbow when the arm is fully extended and supinated — approximately 11-14° in males and 13-16° in females",
                "A varus angle of 20°",
                "Only measurable under anaesthesia"
              ],
              "answer": "C",
              "explanation": "The carrying angle is the valgus angle between the longitudinal axis of the humerus and the forearm when the elbow is fully extended and the forearm fully supinated. Normal values: ~11-14° in males, ~13-16° in females (females have slightly more valgus — thought to be related to the wider pelvis requiring greater arm clearance during walking). Increased carrying angle (cubitus valgus): may result from lateral condyle non-union, growth plate injury to the lateral condyle, or Turner syndrome. Decreased carrying angle or varus (cubitus varus/gunstock deformity): most commonly results from malunion of a supracondylar fracture in children (the most common complication of supracondylar fractures). Cubitus valgus can lead to tardy ulnar nerve palsy (the nerve is progressively stretched over the medial epicondyle with increasing valgus).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1221,
              "stem": "Olecranon fractures in adults are most commonly treated with:",
              "options": [
                "Cast immobilisation only (for displaced fractures — leads to extensor mechanism dysfunction)",
                "Tension band wiring (TBW) — two parallel K-wires + a figure-of-eight wire that converts the triceps pull (distraction force) into a dynamic compression force across the fracture",
                "Intramedullary nail always",
                "Total elbow replacement for all fractures",
                "No treatment is needed"
              ],
              "answer": "B",
              "explanation": "The olecranon is the insertion of the TRICEPS — any displaced fracture disrupts the extensor mechanism of the elbow. Tension band wiring (TBW) is the classic fixation: two parallel K-wires are driven across the fracture into the anterior ulnar cortex, and a figure-of-eight cerclage wire is passed around the K-wire ends and through a hole in the ulna distal to the fracture. The principle: the triceps pulls on the posterior olecranon (creating a distraction force) — the figure-of-eight wire converts this tensile force into a COMPRESSIVE force on the articular side (anterior cortex). This is the essence of the tension band principle — the posterior tensile force is converted to anterior compression. Indications for TBW: simple transverse or short oblique fractures with minimal comminution and good bone quality. Alternatives: plate fixation (for comminuted fractures, Monteggia fracture-dislocations, or poor bone quality — provides more stable fixation), suture fixation (in osteoporotic bone), and excision + triceps advancement (only for elderly/low-demand patients with severe comminution — excise up to 50% of the olecranon).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1222,
              "stem": "The lateral epicondyle is the common origin of which group of forearm muscles?",
              "options": [
                "Forearm flexors and pronators",
                "Forearm flexors only",
                "Intrinsic hand muscles",
                "Forearm extensors and supinator",
                "Biceps and brachialis"
              ],
              "answer": "D",
              "explanation": "The lateral epicondyle is the common extensor origin for the forearm extensor muscles: ECRB (extensor carpi radialis brevis — most commonly involved in tennis elbow), EDC, ECU, EDM, and supinator. The medial epicondyle is the common flexor origin for the forearm flexor-pronator group (pronator teres, FCR, palmaris longus, FDS, FCU).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1223,
              "stem": "The carrying angle of the elbow is the valgus angle between the arm and forearm in full extension. The normal value is approximately:",
              "options": [
                "0° (neutral)",
                "5-7° valgus",
                "20-25° valgus",
                "5° varus",
                "11-14° valgus"
              ],
              "answer": "E",
              "explanation": "The carrying angle is the valgus angle at the elbow in full extension and supination. Normal: ~11-14° (slightly greater in females, ~13-16°). It allows the forearm to clear the body during the swing phase of gait while carrying objects. Cubitus valgus (increased carrying angle) can result from lateral condyle fracture non-union or malunion and may cause a delayed (tardy) ulnar nerve palsy. Cubitus varus (gunstock deformity) results from malunion of supracondylar fractures and is primarily a cosmetic concern (though it may predispose to posterolateral rotatory instability).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1224,
              "stem": "The most common cause of medial epicondylitis (golfer's elbow) involves degeneration at the origin of which muscle?",
              "options": [
                "Extensor carpi radialis brevis",
                "Extensor digitorum communis",
                "Pronator teres and flexor carpi radialis (common flexor origin)",
                "Biceps brachii",
                "Supinator"
              ],
              "answer": "C",
              "explanation": "Medial epicondylitis (golfer's elbow) involves degeneration of the common flexor origin on the medial epicondyle, primarily the pronator teres and FCR (and to a lesser extent FDS and FCU). Like lateral epicondylitis (tennis elbow), it is an angiofibroblastic tendinopathy rather than an inflammatory tendinitis. It is less common than lateral epicondylitis (~1:7 ratio). The ulnar nerve runs behind the medial epicondyle and may be involved in up to 50% of cases (cubital tunnel symptoms). Treatment: physiotherapy (eccentric exercises), activity modification, steroid injection (avoid ulnar nerve), surgical debridement for refractory cases.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1225,
              "stem": "Olecranon bursitis (student's elbow) is inflammation of the bursa overlying the:",
              "options": [
                "Olecranon process",
                "Lateral epicondyle",
                "Medial epicondyle",
                "Radial head",
                "Coronoid process"
              ],
              "answer": "A",
              "explanation": "Olecranon bursitis is inflammation/infection of the subcutaneous bursa overlying the olecranon process. It may be: (1) traumatic (direct blow or repetitive pressure — 'student's elbow', 'miner's elbow'), (2) inflammatory (gout, RA), or (3) septic (~30% of acute bursitis cases — S. aureus most common). Septic bursitis: erythema, warmth, tenderness, ± cellulitis. Always aspirate if septic bursitis is suspected (cell count, Gram stain, crystals, culture). Treatment: non-septic = compression, ice, NSAIDs, aspiration if tense. Septic = antibiotics (flucloxacillin) ± surgical drainage/bursectomy for refractory cases.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1226,
              "stem": "The Kocher interval for the lateral approach to the elbow uses the plane between which two muscles?",
              "options": [
                "Brachioradialis and ECRL",
                "Anconeus and extensor carpi ulnaris (ECU)",
                "Triceps and brachialis",
                "Pronator teres and brachioradialis",
                "Biceps and brachialis"
              ],
              "answer": "B",
              "explanation": "The Kocher approach to the lateral elbow uses the interval between anconeus (radial nerve) and ECU (posterior interosseous nerve). It provides access to the radial head, lateral collateral ligament complex, and lateral epicondyle. The forearm must be kept in PRONATION to protect the PIN which wraps around the radial neck within the supinator muscle. The Kaplan approach (direct lateral, splitting the common extensor origin/EDC) is an alternative lateral approach. The posterior approach (triceps-splitting or olecranon osteotomy) provides access to the distal humerus articular surface.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1227,
              "stem": "The most common peripheral nerve injury associated with elbow dislocation is:",
              "options": [
                "Ulnar nerve (stretched over the medial epicondyle during dislocation)",
                "Radial nerve",
                "Musculocutaneous nerve",
                "Median nerve",
                "Axillary nerve"
              ],
              "answer": "A",
              "explanation": "The ulnar nerve is the most commonly injured nerve in elbow dislocations (~10-15% incidence) because it passes directly behind the medial epicondyle in the cubital tunnel, making it vulnerable to stretching during the dislocation and reduction. Most injuries are neurapraxia and recover spontaneously within 3-6 months. The median nerve can also be injured (particularly in children — may become entrapped in the joint during reduction). Brachial artery injury is uncommon but must be assessed (check radial pulse pre- and post-reduction). After reduction: assess and document ulnar nerve function (little finger sensation, interossei power, Froment sign). If ulnar nerve palsy develops after reduction (was not present before) → suspect nerve entrapment → early exploration may be needed.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1228,
              "stem": "A patient with a stiff elbow after fracture fixation has a functional arc of motion if they have at least:",
              "options": [
                "0-30° flexion",
                "0-60° flexion",
                "Full ROM only",
                "Any motion at all",
                "30-130° flexion (100° arc) with 50° pronation and 50° supination"
              ],
              "answer": "E",
              "explanation": "The Morrey functional arc of the elbow: 30-130° flexion-extension (100° arc) and 50° pronation-50° supination (100° rotational arc). This range allows performance of most activities of daily living (eating, personal hygiene, reaching overhead). Loss of the last 30° of extension is usually well tolerated, but loss of flexion below 130° significantly impairs function (cannot reach the mouth). Stiffness is common after elbow fractures/dislocations. Treatment: aggressive physiotherapy, static progressive or dynamic splinting, and surgical release (capsulectomy ± HO excision) if plateau reached and functional arc not achieved.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1229,
              "stem": "Lateral epicondylitis (tennis elbow) primarily involves degenerative change at the origin of which muscle?",
              "options": [
                "Pronator teres",
                "Flexor carpi radialis",
                "Extensor carpi radialis brevis (ECRB)",
                "Extensor digitorum communis",
                "Triceps"
              ],
              "answer": "C",
              "explanation": "Lateral epicondylitis involves angiofibroblastic tendinopathy (NOT inflammation — hence 'tendinopathy' rather than 'tendinitis') primarily at the origin of ECRB on the lateral epicondyle. Histologically: disordered collagen, mucoid degeneration, neovascularisation, and fibroblast hyperplasia — but notably NO inflammatory cells. It affects 1-3% of the population, peak age 35-55. Treatment: 90% resolve with non-operative management (activity modification, eccentric strengthening exercises, counterforce brace, steroid injection for short-term relief but poorer long-term outcomes). Surgical debridement (open or arthroscopic) reserved for refractory cases (>6-12 months failed conservative treatment).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1230,
              "stem": "The most common complication following elbow fracture-dislocation surgery is:",
              "options": [
                "Infection",
                "Nerve palsy",
                "Non-union",
                "Stiffness (loss of motion/arthrofibrosis)",
                "Implant failure"
              ],
              "answer": "D",
              "explanation": "Stiffness (loss of motion/arthrofibrosis) is the most common complication following elbow fracture-dislocation surgery. The elbow is particularly prone to stiffness due to: (1) the highly congruent joint anatomy (humeroulnar joint), (2) the close relationship between the capsule and surrounding muscles (capsular adhesions form quickly), (3) propensity for heterotopic ossification (HO), and (4) patient reluctance to mobilise due to pain or fear of re-dislocation. Prevention: early ROM exercises (within a stable arc determined intra-operatively), adequate pain management, static progressive splinting if plateauing, and HO prophylaxis (indomethacin or single-dose radiation in high-risk cases). The Morrey functional arc (30-130° flexion + 50/50° rotation) is the minimum goal.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Wrist",
          "range": "Q1231-Q1234",
          "questions": [
            {
              "number": 1231,
              "stem": "Scaphoid fractures heal slowly due to the retrograde blood supply. The blood supply to the scaphoid enters primarily through:",
              "options": [
                "The proximal pole (proximal to distal)",
                "The distal pole directly",
                "The dorsal ridge (waist region) via branches of the radial artery — supplying the proximal pole in a retrograde fashion",
                "The volar surface only",
                "Multiple equally distributed arteries around the entire circumference"
              ],
              "answer": "C",
              "explanation": "The scaphoid receives its blood supply primarily through branches of the dorsal carpal branch of the radial artery, entering through the dorsal ridge at the WAIST of the scaphoid (~70-80% of the blood supply enters here). This blood supply is RETROGRADE — it enters distally/at the waist and flows PROXIMALLY to supply the proximal pole. Proximal pole fractures (fractures proximal to the blood entry point) disrupt this retrograde supply → the proximal pole becomes avascular → high risk of AVN and non-union. This is analogous to the talar blood supply. AVN risk by fracture location: distal pole/tubercle = 0-5%, waist = 10-20%, proximal pole = 30-100%. Treatment: undisplaced waist → thumb spica cast 8-12 weeks (with serial XR). Displaced (>1mm step or gap, humpback deformity) or proximal pole → ORIF with headless compression screw (Herbert screw). Non-union: ORIF + bone graft (vascularised or non-vascularised).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1232,
              "stem": "De Quervain tenosynovitis affects which tendons?",
              "options": [
                "FDS and FDP in the carpal tunnel",
                "APL (abductor pollicis longus) and EPB (extensor pollicis brevis) in the first dorsal compartment of the wrist",
                "ECRB and ECRL at the lateral epicondyle",
                "FPL in the thumb",
                "EDC over the dorsal hand"
              ],
              "answer": "B",
              "explanation": "De Quervain tenosynovitis is stenosing tenosynovitis of the FIRST DORSAL COMPARTMENT of the wrist, containing APL (abductor pollicis longus) and EPB (extensor pollicis brevis). These tendons pass through a tight fibro-osseous tunnel over the radial styloid. Inflammation, thickening of the tendon sheath, and narrowing of the compartment cause pain on the radial side of the wrist, particularly with thumb movements and gripping. Finkelstein test: the thumb is tucked into the palm, the fingers close over it, and the examiner ulnar-deviates the wrist → reproduction of radial wrist pain is positive. This test stretches the APL and EPB across the radial styloid. Risk factors: female, 30-50 years, repetitive thumb use (texting thumb, new mothers — repetitive lifting). Treatment: thumb spica splint, NSAIDs, corticosteroid injection into the first compartment (80-90% success — note: there may be a separate sub-compartment for EPB requiring a second injection), and surgical release (if injection fails).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1233,
              "stem": "De Quervain tenosynovitis affects which tendons at the wrist?",
              "options": [
                "FCR and FCU",
                "ECRL and ECRB",
                "EDC",
                "APL and EPB (first extensor compartment)",
                "FPL"
              ],
              "answer": "D",
              "explanation": "De Quervain tenosynovitis involves stenosing tenosynovitis of the first dorsal extensor compartment, which contains the APL (abductor pollicis longus) and EPB (extensor pollicis brevis) tendons. Finkelstein test: the patient makes a fist over the thumb and the examiner ulnar deviates the wrist — reproduction of pain at the radial styloid is positive. Treatment: splinting + NSAIDs → steroid injection into the first compartment sheath → surgical decompression of the first compartment (if injection fails). Must check for a separate EPB sub-compartment (present in ~30%, can cause injection failure).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1234,
              "stem": "Perilunate and lunate dislocations are high-energy wrist injuries. In a perilunate dislocation, which structure remains articulated with the radius?",
              "options": [
                "Capitate",
                "Scaphoid",
                "Triquetrum",
                "Hamate",
                "Lunate (the lunate stays in the lunate fossa of the radius while the rest of the carpus dislocates dorsally)"
              ],
              "answer": "E",
              "explanation": "In a perilunate dislocation, the LUNATE remains in the lunate fossa of the radius (articulated with the radius), while the rest of the carpus (capitate, scaphoid, triquetrum, and all distal carpal bones) dislocates DORSALLY relative to the lunate. In a lunate dislocation (more severe), the lunate itself is squeezed VOLARLY out of the lunate fossa (into the carpal tunnel — may compress the median nerve), while the rest of the carpus remains aligned with the radius. On lateral radiograph: perilunate = capitate behind the lunate (the rest of the carpus is dorsal). Lunate dislocation = lunate volarly rotated ('spilled teacup' sign) into the carpal tunnel. Both are frequently missed on initial radiographs (~25%). Mayfield stages describe the progressive perilunar instability pattern: Stage I (scapholunate dissociation) → II (lunocapitate dislocation) → III (lunotriquetral disruption) → IV (lunate dislocation).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Nerve Transfer",
          "range": "Q1235",
          "questions": [
            {
              "number": 1235,
              "stem": "For a high (C5-C6) brachial plexus injury with loss of elbow flexion, the most commonly performed nerve transfer is:",
              "options": [
                "Oberlin transfer — fascicles of the ulnar nerve (to FDP/FCU) are transferred to the musculocutaneous nerve branch to biceps, restoring elbow flexion",
                "Sural nerve graft only",
                "Tendon transfer of the triceps",
                "Direct nerve repair at the root level in all cases",
                "No surgical treatment is available"
              ],
              "answer": "A",
              "explanation": "The Oberlin transfer (Oberlin, 1994): motor fascicles of the ULNAR nerve (specifically those supplying FCU — an expendable function) are transferred directly to the motor branch of the musculocutaneous nerve to the BICEPS. This provides a short, direct nerve coaptation (no graft needed) with a powerful donor nerve → fast reinnervation of the biceps (~6-9 months) → restored elbow flexion. Success rate: ~80-90% achieve ≥M3+ (anti-gravity) biceps strength. The double fascicular transfer (Mackinnon modification): adds a median nerve fascicle (to FDS) transfer to the brachialis branch → powers both biceps AND brachialis → stronger elbow flexion. Advantages over nerve grafting from C5-C6 roots: shorter reinnervation distance (transfer is near the target muscle), faster recovery, avoids root-level surgery (which has worse outcomes for distal targets). Timing: ideally within 3-6 months of injury (before motor endplates degenerate — critical 12-18 month window).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            }
          ]
        },
        {
          "title": "Nerve",
          "range": "Q1236-Q1238",
          "questions": [
            {
              "number": 1236,
              "stem": "Erb-Duchenne palsy (upper brachial plexus injury, C5-C6) results in the 'waiter's tip' position. The affected movements are:",
              "options": [
                "Wrist and finger extension only",
                "Shoulder abduction, shoulder external rotation, elbow flexion, and forearm supination (the arm hangs in adduction, internal rotation, elbow extension, and forearm pronation)",
                "Intrinsic hand muscle function only",
                "Only sensation without motor loss",
                "Hip flexion and knee extension"
              ],
              "answer": "B",
              "explanation": "Erb-Duchenne palsy (C5-C6 injury — upper trunk) classically results from birth injury (shoulder dystocia with lateral neck traction), motorcycle accidents (shoulder depression with lateral neck force), or falls. The 'waiter's tip' position: arm hangs at the side in ADDUCTION (loss of deltoid/supraspinatus — C5), INTERNAL ROTATION (loss of infraspinatus/teres minor — C5,C6), ELBOW EXTENSION (loss of biceps/brachialis — C5,C6), and FOREARM PRONATION (loss of supinator/biceps supination — C5,C6). Hand function is typically PRESERVED (C8-T1 intact). Compare: Klumpke palsy (C8-T1, lower trunk — intrinsic hand muscle paralysis, claw hand, ± Horner syndrome if T1 sympathetic affected). In neonates: most Erb's palsies (~80-90%) recover spontaneously within 3-6 months. Those without biceps recovery by 3-6 months → consider microsurgery (nerve repair/graft/transfer).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1237,
              "stem": "Posterior interosseous nerve (PIN) palsy causes loss of finger and thumb MCP extension but preserves wrist extension because:",
              "options": [
                "The PIN innervates ECRL which extends the wrist",
                "The wrist extensors are innervated by the median nerve",
                "Wrist extension uses gravity only",
                "ECRL is innervated by the radial nerve PROXIMAL to the PIN branch point, so it is spared",
                "PIN only innervates sensory fibres"
              ],
              "answer": "D",
              "explanation": "ECRL (extensor carpi radialis longus) is innervated by the radial nerve proper BEFORE it divides into the superficial branch and the PIN. Therefore, even when the PIN is injured (e.g., entrapment at the arcade of Frohse within the supinator), ECRL function is preserved, maintaining wrist extension (with radial deviation). The PIN innervates: ECRB, supinator, EDC, EDM, ECU, APL, EPB, EPL, and EIP. PIN palsy: loss of finger/thumb extension at MCPs + loss of thumb retropulsion (EPL) + wrist extension preserved but with radial deviation (ECRL pulls radially without ECRB/ECU balance). There is NO sensory loss (PIN is a pure motor nerve).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1238,
              "stem": "Cubital tunnel syndrome (ulnar nerve compression at the elbow) presents with which typical findings?",
              "options": [
                "Thenar muscle wasting and thumb weakness",
                "Numbness in the thumb and index finger",
                "Numbness in the ring and little finger, weakness of intrinsic hand muscles (interossei, hypothenar), and possible clawing of the ring and little fingers",
                "Wrist drop",
                "Shoulder weakness"
              ],
              "answer": "C",
              "explanation": "Cubital tunnel syndrome (ulnar nerve compression at the elbow, behind the medial epicondyle) presents with: (1) sensory: numbness/tingling in the little finger and ulnar half of the ring finger (dorsal and palmar). (2) Motor: weakness/wasting of the intrinsic hand muscles (interossei, hypothenar, 3rd/4th lumbricals, adductor pollicis) → weak grip and pinch, difficulty with fine motor tasks. (3) Clawing: ring and little finger MCP hyperextension + IP flexion (ulnar claw — 'claw hand'). The ulnar paradox: the claw is WORSE in low ulnar nerve lesions (at the wrist) than high lesions (at the elbow) because in high lesions, FDP to the ring and little fingers is also paralysed → no IP flexion → less obvious clawing.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Frozen Shoulder",
          "range": "Q1239",
          "questions": [
            {
              "number": 1239,
              "stem": "Adhesive capsulitis (frozen shoulder) typically progresses through how many clinical phases?",
              "options": [
                "2",
                "4",
                "5",
                "1 (single phase)",
                "3"
              ],
              "answer": "E",
              "explanation": "Adhesive capsulitis progresses through 3 phases: (1) Freezing/painful phase (2–9 months): gradual onset of diffuse shoulder pain, worse at night, progressive loss of motion. (2) Frozen/stiff phase (4–12 months): pain diminishes but stiffness persists with significant loss of active AND passive range of motion (especially external rotation). (3) Thawing phase (5–24 months): gradual return of motion. Total duration: 12–36 months. Most patients recover near-full function, though some have residual stiffness.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Distal Biceps",
          "range": "Q1240",
          "questions": [
            {
              "number": 1240,
              "stem": "Rupture of the distal biceps tendon is diagnosed clinically using the hook test. A positive hook test is:",
              "options": [
                "Inability to hook a finger under the intact biceps tendon in the antecubital fossa",
                "Inability to supinate the forearm",
                "Visible 'Popeye' deformity of the arm",
                "Weakness of elbow flexion only",
                "Pain on resisted pronation"
              ],
              "answer": "A",
              "explanation": "The hook test (O'Driscoll): the examiner attempts to hook their index finger under the lateral edge of the biceps tendon in the antecubital fossa with the elbow flexed to 90° and the forearm supinated. If the tendon is intact, a cord-like structure can be hooked. If ruptured, nothing can be hooked (positive test — 100% sensitive and specific in O'Driscoll's study). Distal biceps rupture causes loss of supination power (~40% loss) more than flexion (~30% loss).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "TFCC",
          "range": "Q1241",
          "questions": [
            {
              "number": 1241,
              "stem": "The triangular fibrocartilage complex (TFCC) is the primary stabiliser of which joint?",
              "options": [
                "Radiocarpal joint",
                "Midcarpal joint",
                "Proximal radioulnar joint",
                "Distal radioulnar joint (DRUJ)",
                "Carpometacarpal joint"
              ],
              "answer": "D",
              "explanation": "The TFCC is the primary stabiliser of the distal radioulnar joint (DRUJ). It consists of the articular disc (triangular fibrocartilage), dorsal and volar radioulnar ligaments, meniscus homologue, ECU subsheath, and ulnocarpal ligaments. Palmer classified TFCC injuries: Class 1 = traumatic (A=central perforation, B=ulnar avulsion, C=distal avulsion, D=radial avulsion); Class 2 = degenerative (A–E). Central tears (1A) can be debrided. Peripheral tears (1B, 1D) should be repaired for DRUJ stability.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Rotator Cuff",
          "range": "Q1242-Q1249",
          "questions": [
            {
              "number": 1242,
              "stem": "The rotator cuff consists of four muscles. Which of the following is NOT a rotator cuff muscle?",
              "options": [
                "Supraspinatus",
                "Infraspinatus",
                "Teres minor",
                "Subscapularis",
                "Teres major"
              ],
              "answer": "E",
              "explanation": "The four rotator cuff muscles are supraspinatus (initiates abduction, most commonly torn), infraspinatus (external rotation), teres minor (external rotation), and subscapularis (internal rotation). Teres major is NOT part of the rotator cuff — it is an adductor and internal rotator that inserts onto the medial lip of the bicipital groove but does not attach to the humeral head.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1243,
              "stem": "Supraspinatus is innervated by which nerve?",
              "options": [
                "Axillary nerve",
                "Musculocutaneous nerve",
                "Suprascapular nerve",
                "Long thoracic nerve",
                "Subscapular nerve"
              ],
              "answer": "C",
              "explanation": "The suprascapular nerve (C5, C6) innervates both supraspinatus and infraspinatus. It passes through the suprascapular notch (under the transverse scapular ligament) to reach supraspinatus, then through the spinoglenoid notch to reach infraspinatus. Entrapment at either notch can cause denervation and wasting.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1244,
              "stem": "The most commonly used clinical test for supraspinatus pathology is:",
              "options": [
                "Jobe test (empty can test)",
                "Belly-press test",
                "Lift-off test",
                "Gerber test",
                "Bear-hug test"
              ],
              "answer": "A",
              "explanation": "The Jobe test (empty can test) is the most commonly used test for supraspinatus pathology. The arm is positioned in 90° abduction, 30° forward flexion (scapular plane), and full internal rotation (thumb pointing down). The examiner applies a downward force. Pain suggests tendinopathy; weakness suggests a tear. The full can test (thumb up) is an alternative that may be more specific.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1245,
              "stem": "A massive rotator cuff tear in an elderly patient with pseudoparalysis of the shoulder and glenohumeral arthritis (cuff arthropathy) is best treated with:",
              "options": [
                "Arthroscopic cuff repair",
                "Reverse total shoulder arthroplasty",
                "Hemiarthroplasty",
                "Anatomical total shoulder arthroplasty",
                "Subacromial decompression"
              ],
              "answer": "B",
              "explanation": "Reverse total shoulder arthroplasty (RTSA) is the treatment of choice for cuff tear arthropathy with pseudoparalysis. The reverse design (convex glenosphere on the glenoid, concave socket on the humerus) medialises and distalises the centre of rotation, increasing the moment arm of the deltoid and allowing active abduction without a functioning rotator cuff. Grammont designed the original reverse prosthesis.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1246,
              "stem": "The critical zone of the supraspinatus tendon (area most prone to degeneration and tears) is located:",
              "options": [
                "At the musculotendinous junction",
                "At the bony insertion on the greater tuberosity",
                "In the supraspinous fossa",
                "Approximately 1 cm proximal to the insertion on the greater tuberosity",
                "At the acromial attachment"
              ],
              "answer": "D",
              "explanation": "The critical zone (described by Codman) is an area of relative avascularity approximately 1 cm proximal to the insertion on the greater tuberosity. This hypovascular zone is where most degenerative tears initiate. The blood supply comes from both the osseous insertion and the muscular end, creating a watershed area in between. Moseley and Goldie confirmed this hypovascular zone histologically.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1247,
              "stem": "Impingement of the rotator cuff under the coracoacromial arch is tested clinically using the Neer test. How is this performed?",
              "options": [
                "Passive external rotation with arm at side",
                "Resisted internal rotation",
                "Active abduction against resistance in the scapular plane",
                "Passive horizontal adduction",
                "Passive forward flexion with the scapula stabilised"
              ],
              "answer": "E",
              "explanation": "The Neer impingement test involves passive forward flexion of the arm with the scapula stabilised by the examiner's other hand. This compresses the supraspinatus tendon and subacromial bursa against the anterior undersurface of the acromion. Pain reproduced by this manoeuvre is a positive test, suggesting subacromial impingement. The Hawkins-Kennedy test (passive internal rotation with the arm at 90° forward flexion) is another impingement test.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1248,
              "stem": "The subscapularis muscle is tested using the lift-off test (Gerber test). What does a positive test indicate?",
              "options": [
                "Supraspinatus tear",
                "Infraspinatus tear",
                "Subscapularis tear or insufficiency",
                "Biceps tendon rupture",
                "Deltoid weakness"
              ],
              "answer": "C",
              "explanation": "The lift-off test (Gerber) tests subscapularis integrity. The patient places the dorsum of their hand on their lower back and attempts to lift the hand away from the back (internal rotation). Inability to maintain this position indicates subscapularis insufficiency. Other subscapularis tests include the belly-press test (pressing the palm against the abdomen using internal rotation) and the bear-hug test.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1249,
              "stem": "In the Goutallier classification of fatty infiltration of the rotator cuff muscles on CT/MRI, Stage 3 indicates:",
              "options": [
                "Equal amounts of fat and muscle",
                "Normal muscle, no fatty streaks",
                "Some fatty streaks",
                "Significant fat but less fat than muscle",
                "More fat than muscle"
              ],
              "answer": "A",
              "explanation": "Goutallier classification of fatty infiltration: Stage 0 = normal muscle, no fat. Stage 1 = some fatty streaks. Stage 2 = significant fat but less fat than muscle. Stage 3 = equal amounts of fat and muscle. Stage 4 = more fat than muscle. Stages 3 and 4 indicate irreversible muscular degeneration — rotator cuff repair is less likely to heal and functional outcomes are poorer.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            }
          ]
        },
        {
          "title": "Shoulder Instability",
          "range": "Q1250-Q1257",
          "questions": [
            {
              "number": 1250,
              "stem": "A Bankart lesion is:",
              "options": [
                "An impaction fracture of the posterolateral humeral head",
                "An avulsion of the anteroinferior glenoid labrum from the glenoid rim",
                "A tear of the superior labrum",
                "A fracture of the coracoid process",
                "A tear of the rotator interval"
              ],
              "answer": "B",
              "explanation": "A Bankart lesion is an avulsion of the anteroinferior glenoid labrum (along with the attached inferior glenohumeral ligament) from the glenoid rim. It is the essential lesion in traumatic anterior shoulder instability. A bony Bankart involves a fracture of the anteroinferior glenoid rim with the labrum. Surgical repair (arthroscopic or open Bankart repair) reattaches the labrum to the glenoid rim.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1251,
              "stem": "A Hill-Sachs lesion is:",
              "options": [
                "A fracture of the anterior glenoid rim",
                "A tear of the biceps anchor",
                "A fracture of the greater tuberosity",
                "An avulsion of the subscapularis",
                "An impaction fracture of the posterolateral humeral head caused by anterior dislocation"
              ],
              "answer": "E",
              "explanation": "A Hill-Sachs lesion is a compression fracture of the posterolateral humeral head caused by impaction against the anteroinferior glenoid rim during anterior dislocation. Large engaging Hill-Sachs lesions (>25–30% of the articular surface) that engage the glenoid rim in functional positions can contribute to recurrent instability. Treatment options for large lesions include remplissage (infraspinatus tenodesis into the defect) or humeral-side bone grafting.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1252,
              "stem": "The Latarjet procedure is indicated for anterior shoulder instability when there is:",
              "options": [
                "Isolated labral tear without bone loss",
                "Significant anterior glenoid bone loss (>20–25%)",
                "Posterior instability only",
                "Multidirectional instability with muscle patterning",
                "Rotator cuff tear only"
              ],
              "answer": "B",
              "explanation": "The Latarjet procedure involves transfer of the coracoid process (with its attached conjoint tendon — short head of biceps and coracobrachialis) to the anterior glenoid rim. It is indicated when there is significant glenoid bone loss (>20–25%) which precludes a successful soft tissue Bankart repair. The procedure provides both a bony buttress (bone block) and a dynamic sling effect from the conjoint tendon across the inferior subscapularis.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1253,
              "stem": "The TUBS acronym for traumatic anterior instability stands for:",
              "options": [
                "Traumatic, Unilateral, Bilateral, Surgery",
                "Traumatic, Unstable, Bilateral, Stabilisation",
                "Traumatic, Unidirectional, Bankart lesion, Surgery",
                "Traumatic, Unilateral, Bankart, Suture",
                "Traction, Unilateral, Bilateral, Sling"
              ],
              "answer": "C",
              "explanation": "TUBS: Traumatic, Unidirectional (anterior), Bankart lesion, treated with Surgery. This describes the classic traumatic anterior instability pattern. It contrasts with AMBRI: Atraumatic, Multidirectional, Bilateral, treated with Rehabilitation, and Inferior capsular shift if rehabilitation fails. The Stanmore classification provides a more nuanced framework recognising overlap between these patterns.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1254,
              "stem": "The apprehension test for anterior shoulder instability is performed with the shoulder in which position?",
              "options": [
                "Adduction and internal rotation",
                "Forward flexion with internal rotation",
                "Extension with adduction",
                "90° abduction and maximum external rotation",
                "Neutral position with axial load"
              ],
              "answer": "D",
              "explanation": "The anterior apprehension test places the shoulder in 90° abduction with progressive external rotation. In patients with anterior instability, this reproduces the at-risk position for anterior dislocation, causing apprehension (not just pain). A positive Jobe relocation test (relief of apprehension when posterior pressure is applied to the humeral head) confirms anterior instability.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1255,
              "stem": "Following a first-time traumatic anterior dislocation, the recurrence rate is highest in which age group?",
              "options": [
                "Under 20 years",
                "Over 60 years",
                "40–50 years",
                "30–40 years",
                "Age does not affect recurrence"
              ],
              "answer": "A",
              "explanation": "The recurrence rate after first-time traumatic anterior dislocation is strongly age-dependent. Patients under 20 years have a recurrence rate of 80–90%. The rate decreases with age: 20–30 years ≈ 60%, 30–40 years ≈ 30%, over 40 years ≈ 10–15%. However, older patients have a much higher rate of associated rotator cuff tear with dislocation (>40% in patients over 40). This is a frequently tested exam fact.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1256,
              "stem": "A posterior shoulder dislocation classically shows which radiographic sign on the AP radiograph?",
              "options": [
                "Bankart sign",
                "Hill-Sachs sign",
                "Lightbulb sign (fixed internal rotation)",
                "Sail sign",
                "Fat pad sign"
              ],
              "answer": "C",
              "explanation": "The lightbulb sign on AP radiograph is caused by fixed internal rotation of the humerus — the humeral head appears rounded and symmetrical like a lightbulb (rather than the normal asymmetric outline seen with a normally positioned humerus in external rotation). Posterior dislocations are missed in up to 50% of initial assessments. An axillary or Velpeau view is essential to confirm the diagnosis.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1257,
              "stem": "A SLAP lesion (Superior Labrum Anterior to Posterior) involves a tear of the superior labrum at the attachment of which structure?",
              "options": [
                "Supraspinatus tendon",
                "Long head of biceps tendon",
                "Infraspinatus tendon",
                "Subscapularis tendon",
                "Coracoacromial ligament"
              ],
              "answer": "B",
              "explanation": "A SLAP lesion is a tear of the superior labrum at the biceps anchor (where the long head of biceps tendon attaches to the superior glenoid labrum). Snyder classified SLAP lesions into 4 types: I=degenerative fraying, II=detachment of labrum and biceps anchor (most common, most clinically significant), III=bucket-handle tear with intact biceps anchor, IV=bucket-handle extending into biceps tendon. Type II requires surgical repair.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Nerve Palsies",
          "range": "Q1258-Q1265",
          "questions": [
            {
              "number": 1258,
              "stem": "Radial nerve palsy produces which characteristic clinical finding?",
              "options": [
                "Claw hand",
                "Ape hand deformity",
                "Hand of benediction",
                "Erb-Duchenne palsy",
                "Wrist drop with inability to extend the wrist and fingers"
              ],
              "answer": "E",
              "explanation": "Radial nerve palsy causes wrist drop (loss of wrist extension), finger drop (loss of MCP extension via EDC), and loss of thumb extension (EPL). Sensation is lost over the first dorsal web space (superficial branch of radial nerve). The radial nerve is most commonly injured at the spiral groove of the humerus (mid-distal junction) in humeral shaft fractures.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1259,
              "stem": "An ulnar nerve lesion at the wrist (Guyon canal) would produce clawing of which fingers?",
              "options": [
                "Index and middle fingers",
                "All four fingers",
                "Thumb only",
                "Ring and little fingers",
                "Index finger only"
              ],
              "answer": "D",
              "explanation": "Ulnar nerve palsy at the wrist produces clawing of the ring and little fingers (hyperextension at MCP, flexion at IP joints) due to loss of the 3rd and 4th lumbricals and interossei. FDP to the ring and little fingers is still functioning (supplied by the ulnar nerve more proximally in the forearm) so the clawing is MORE pronounced with a distal lesion (ulnar paradox). A proximal lesion loses FDP function too, so there is LESS clawing.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1260,
              "stem": "The anterior interosseous nerve (AIN) is a pure motor branch of which nerve?",
              "options": [
                "Median nerve",
                "Radial nerve",
                "Ulnar nerve",
                "Musculocutaneous nerve",
                "Axillary nerve"
              ],
              "answer": "A",
              "explanation": "The AIN is a pure motor branch of the median nerve arising in the proximal forearm. It innervates FPL (flexor pollicis longus), FDP to the index finger (and sometimes middle finger), and pronator quadratus. AIN palsy presents with inability to make an 'OK' sign (pinch grip between thumb IP and index DIP) and weakness of forearm pronation. There is NO sensory loss (pure motor nerve).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1261,
              "stem": "Froment sign is positive in which nerve palsy?",
              "options": [
                "Radial nerve",
                "Median nerve",
                "Posterior interosseous nerve",
                "Musculocutaneous nerve",
                "Ulnar nerve"
              ],
              "answer": "E",
              "explanation": "Froment sign tests adductor pollicis (ulnar nerve innervated). When asked to grip a piece of paper between the thumb and index finger, a patient with ulnar nerve palsy cannot adduct the thumb and compensates by flexing the thumb IP joint using FPL (median nerve). This compensatory flexion at the IP joint is a positive Froment sign.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1262,
              "stem": "Carpal tunnel syndrome is caused by compression of which nerve?",
              "options": [
                "Ulnar nerve",
                "Median nerve",
                "Radial nerve",
                "Posterior interosseous nerve",
                "Anterior interosseous nerve"
              ],
              "answer": "B",
              "explanation": "Carpal tunnel syndrome is compression of the median nerve beneath the flexor retinaculum (transverse carpal ligament) at the wrist. It is the most common compression neuropathy. Symptoms: pain, numbness, and tingling in the median nerve distribution (thumb, index, middle, and radial half of ring finger). Thenar wasting occurs in advanced cases. Night symptoms are characteristic.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1263,
              "stem": "Winging of the scapula is caused by paralysis of which muscle due to long thoracic nerve injury?",
              "options": [
                "Serratus anterior",
                "Trapezius",
                "Rhomboid major",
                "Levator scapulae",
                "Pectoralis minor"
              ],
              "answer": "A",
              "explanation": "The long thoracic nerve (C5, C6, C7 — nerve of Bell) innervates serratus anterior, which protracts the scapula and holds it against the chest wall. Palsy causes medial winging of the scapula, most evident when pushing against a wall with outstretched arms. Causes include traction injuries, viral neuritis, and iatrogenic injury (axillary surgery, first rib resection).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1264,
              "stem": "An Erb-Duchenne palsy (upper brachial plexus injury, C5–C6) produces which characteristic arm position?",
              "options": [
                "Arm abducted and externally rotated",
                "Claw hand",
                "Wrist drop",
                "Arm adducted, internally rotated, forearm pronated (waiter's tip position)",
                "Total flail arm"
              ],
              "answer": "D",
              "explanation": "Erb-Duchenne palsy (C5–C6) produces the classic 'waiter's tip' position: the arm hangs at the side in adduction (loss of deltoid/supraspinatus), internal rotation (loss of infraspinatus/teres minor), with the forearm pronated (loss of biceps/supinator) and the wrist flexed. It occurs in birth injuries (shoulder dystocia) and in adults from motorcycle/traction injuries affecting the upper trunk.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1265,
              "stem": "In a high median nerve palsy (above the elbow), the hand adopts a 'hand of benediction' posture when attempting to make a fist because:",
              "options": [
                "The interossei are paralysed",
                "The lumbricals are paralysed",
                "FDP to the index and middle fingers is paralysed (can't flex DIP)",
                "FDS to ring and little fingers is lost",
                "Thenar muscles are paralysed"
              ],
              "answer": "C",
              "explanation": "In high median nerve palsy, FDS (all fingers) and FDP to the index and middle fingers are paralysed. When attempting to make a fist, the ring and little fingers flex (via intact ulnar-innervated FDP) but the index and middle fingers remain extended, creating the 'hand of benediction'. This differs from the 'ape hand' (thenar wasting with loss of opposition) seen in low median nerve palsy at the wrist.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            }
          ]
        },
        {
          "title": "Carpal/Cubital Tunnel",
          "range": "Q1266-Q1270",
          "questions": [
            {
              "number": 1266,
              "stem": "Cubital tunnel syndrome is the second most common compression neuropathy. At the elbow, the ulnar nerve passes behind which bony landmark?",
              "options": [
                "Lateral epicondyle",
                "Medial epicondyle",
                "Olecranon",
                "Radial head",
                "Coronoid process"
              ],
              "answer": "B",
              "explanation": "The ulnar nerve passes behind the medial epicondyle in the cubital tunnel (formed by the medial epicondyle, olecranon, and Osborne's ligament/cubital tunnel retinaculum). The tunnel narrows with elbow flexion, which increases both tunnel and intraneural pressure. Sites of compression include the medial intermuscular septum, arcade of Struthers, Osborne's ligament, and the two heads of FCU.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1267,
              "stem": "The sensory distribution of the median nerve in the hand includes:",
              "options": [
                "Little finger and ulnar half of ring finger",
                "First dorsal web space only",
                "Thumb, index, middle, and radial half of ring finger (palmar)",
                "Entire dorsum of the hand",
                "All five fingers"
              ],
              "answer": "C",
              "explanation": "The median nerve provides sensory innervation to the palmar aspect of the thumb, index, middle, and radial half of the ring finger, plus the dorsal fingertips of these fingers. The palmar cutaneous branch (which branches BEFORE the carpal tunnel) supplies the thenar eminence — this is why thenar sensation is preserved in carpal tunnel syndrome even though the digital sensation is affected.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1268,
              "stem": "The most reliable investigation to confirm carpal tunnel syndrome is:",
              "options": [
                "Plain radiograph",
                "Ultrasound",
                "MRI of the wrist",
                "CT scan",
                "Nerve conduction studies"
              ],
              "answer": "E",
              "explanation": "Nerve conduction studies (NCS) / electromyography (EMG) are the gold standard investigation to confirm CTS. They demonstrate prolonged distal motor and sensory latencies of the median nerve across the wrist. NCS has ~85–90% sensitivity and >95% specificity. However, clinical diagnosis remains paramount — NCS can be false negative in early/mild CTS. NCS also helps exclude other causes (cervical radiculopathy, polyneuropathy).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1269,
              "stem": "How do you differentiate a T1 nerve root lesion from an ulnar nerve palsy at the elbow?",
              "options": [
                "Both present identically and cannot be differentiated",
                "Ulnar palsy at elbow has Horner syndrome",
                "T1 lesion affects only the hypothenar muscles",
                "T1 lesion may have Horner syndrome and affects ALL intrinsic hand muscles",
                "NCS cannot help differentiate them"
              ],
              "answer": "D",
              "explanation": "A T1 root lesion affects ALL intrinsic hand muscles (both ulnar and median-innervated), causes paraesthesia over the medial forearm (T1 dermatome), and may be associated with Horner syndrome (ptosis, miosis, anhidrosis) if the sympathetic chain is involved (e.g., Pancoast tumour). Ulnar nerve palsy at the elbow affects only ulnar-innervated muscles and has no Horner syndrome. NCS helps localise the lesion.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1270,
              "stem": "Wartenberg sign is a clinical finding in ulnar nerve palsy. What does it demonstrate?",
              "options": [
                "Persistent abduction of the little finger",
                "Thumb IP flexion on attempted key pinch",
                "Inability to cross the fingers",
                "Wasting of the first dorsal interosseous",
                "Claw hand deformity"
              ],
              "answer": "A",
              "explanation": "Wartenberg sign is the persistent abduction of the little finger at rest, caused by paralysis of the 3rd palmar interosseous muscle (ulnar nerve) which normally adducts the little finger. The unopposed action of extensor digiti minimi (radial nerve) keeps the little finger abducted. It is an early sign of ulnar nerve palsy that patients may notice as the finger catches on objects.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Surgical Approaches",
          "range": "Q1271-Q1272",
          "questions": [
            {
              "number": 1271,
              "stem": "The deltopectoral approach to the shoulder uses the interval between which two muscles?",
              "options": [
                "Deltoid and pectoralis major",
                "Deltoid and supraspinatus",
                "Deltoid and infraspinatus",
                "Pectoralis major and pectoralis minor",
                "Deltoid and trapezius"
              ],
              "answer": "A",
              "explanation": "The deltopectoral approach uses the intermuscular interval between deltoid (axillary nerve) and pectoralis major (pectoral nerves). The cephalic vein runs in this interval and is usually retracted laterally (with the deltoid) to preserve its drainage into the axillary vein. This approach provides access to the anterior shoulder for fracture fixation, arthroplasty, Bankart repair (open), and Latarjet procedures.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1272,
              "stem": "During the posterior approach to the elbow, which nerve must be identified and protected?",
              "options": [
                "Median nerve",
                "Musculocutaneous nerve",
                "Radial nerve",
                "Anterior interosseous nerve",
                "Ulnar nerve"
              ],
              "answer": "E",
              "explanation": "The ulnar nerve must be identified and protected in the posterior approach to the elbow. It runs in the cubital tunnel behind the medial epicondyle. Whether the nerve is transposed or simply identified and protected in situ depends on the surgeon's preference and the nature of the pathology. The radial nerve is at risk in the lateral approach (particularly the PIN during the Kocher approach to the radial head).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Shoulder Arthroplasty",
          "range": "Q1273",
          "questions": [
            {
              "number": 1273,
              "stem": "In anatomical total shoulder arthroplasty, the most common cause of failure requiring revision is:",
              "options": [
                "Infection",
                "Glenoid component loosening",
                "Instability",
                "Humeral component loosening",
                "Periprosthetic fracture"
              ],
              "answer": "B",
              "explanation": "Glenoid component loosening is the most common cause of long-term failure in anatomical TSA ('the glenoid problem'). Eccentric loading from rotator cuff deficiency or component malpositioning accelerates polyethylene wear and loosening (the 'rocking horse' phenomenon). This is why anatomical TSA requires a functioning rotator cuff — without it, asymmetric loading causes early glenoid failure.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Brachial Plexus",
          "range": "Q1274",
          "questions": [
            {
              "number": 1274,
              "stem": "The brachial plexus is formed from the ventral rami of which nerve roots?",
              "options": [
                "C3-C7",
                "C4-T1",
                "C6-T2",
                "C5-T1",
                "C5-C8 only"
              ],
              "answer": "D",
              "explanation": "The brachial plexus is formed from the ventral rami of C5, C6, C7, C8, and T1. It follows the sequence: Roots → Trunks → Divisions → Cords → Branches (mnemonic: 'Robert Taylor Drinks Cold Beer'). Upper trunk = C5+C6. Middle trunk = C7. Lower trunk = C8+T1. Each trunk divides into anterior and posterior divisions. Lateral cord = anterior divisions of upper and middle trunks. Posterior cord = all posterior divisions. Medial cord = anterior division of lower trunk. Major terminal branches: musculocutaneous (lateral cord), median (lateral + medial), ulnar (medial), radial (posterior), axillary (posterior).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        }
      ]
    },
    {
      "title": "Sports Medicine",
      "chapters": [
        {
          "title": "ACL Reconstruction",
          "range": "Q1275",
          "questions": [
            {
              "number": 1275,
              "stem": "ACL graft choices — the main advantage of bone-patellar tendon-bone (BPTB) autograft over hamstring tendon autograft is:",
              "options": [
                "Lower donor site morbidity",
                "Greater graft diameter",
                "Bone-to-bone healing in the tunnels (faster, more reliable integration — regarded as the 'gold standard' graft)",
                "No risk of graft failure",
                "Better cosmesis"
              ],
              "answer": "C",
              "explanation": "BPTB autograft provides bone-to-bone healing at both the femoral and tibial tunnel ends (bone plugs from the patella and tibial tubercle integrate within 6-8 weeks, faster than soft tissue-to-bone healing of hamstring grafts which takes 8-12 weeks). This is why BPTB has historically been considered the gold standard, particularly for high-demand athletes and revision ACL surgery. Disadvantages: anterior knee pain (~15-20%), kneeling pain, patellar fracture risk (~1%), patellar tendon rupture (rare), and quadriceps weakness. Hamstring autograft advantages: less anterior knee pain, less kneeling pain, better cosmesis. Hamstring disadvantages: slower graft incorporation (soft tissue-to-bone), potential hamstring weakness (particularly deep flexion), and variable graft diameter (if <8mm, may need augmentation).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Meniscus",
          "range": "Q1276",
          "questions": [
            {
              "number": 1276,
              "stem": "Meniscal root tears are biomechanically equivalent to:",
              "options": [
                "Total meniscectomy (the meniscus loses its hoop stress function and extrudes, unable to convert compressive loads into circumferential tension)",
                "A partial meniscal tear with preserved function",
                "Normal meniscal function",
                "A stable longitudinal tear",
                "Discoid meniscus"
              ],
              "answer": "A",
              "explanation": "Meniscal root tears (avulsion of the meniscal attachment at the tibial plateau) are biomechanically equivalent to a total meniscectomy because the meniscus can no longer generate hoop stresses. The root anchors the meniscus to bone — without this anchor, axial loads push the meniscus peripherally (extrusion) rather than being converted into circumferential (hoop) tension within the meniscal ring. This results in rapid increase in peak contact pressures on the articular cartilage, accelerating OA progression. Posterior root tears of the medial meniscus are most common (associated with degenerative knee, middle-aged women, and acute 'pop' while squatting). Treatment: surgical root repair (pull-out suture technique re-anchoring the root to bone through a tibial tunnel) if the cartilage is still preserved. If already established OA → root repair won't help.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Shoulder",
          "range": "Q1277-Q1280",
          "questions": [
            {
              "number": 1277,
              "stem": "A SLAP (superior labrum anterior to posterior) tear is classified by Snyder. Type II is the most common type and involves:",
              "options": [
                "Degenerative fraying of the superior labrum (Type I)",
                "Bucket-handle tear extending into the middle glenohumeral ligament (Type III)",
                "Extension of the SLAP into the subscapularis (Type IV)",
                "Detachment of the superior labrum AND long head of biceps anchor from the glenoid (bucket-handle tear of superior labrum with unstable biceps anchor)",
                "Complete labral avulsion circumferentially"
              ],
              "answer": "D",
              "explanation": "Snyder SLAP classification: Type I = degenerative fraying of the superior labrum (biceps anchor intact — treat with debridement). Type II = detachment of the superior labrum AND biceps anchor from the glenoid (MOST COMMON, ~55% — the biceps anchor is unstable, the labrum peels off the glenoid rim). Type III = bucket-handle tear of the superior labrum (biceps anchor intact — resect the torn fragment). Type IV = bucket-handle tear extending INTO the biceps tendon. Type II is the most clinically significant because the biceps anchor is destabilised → pain, clicking, and instability symptoms (particularly in overhead athletes). Treatment of Type II: SLAP repair with suture anchors (in young athletes) OR biceps tenodesis (in patients >35-40 years, where outcomes of tenodesis are more predictable and reliable than repair). Active compression test (O'Brien) and biceps load test help diagnose SLAP lesions.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1278,
              "stem": "Rotator cuff tear arthropathy is best treated with which arthroplasty option?",
              "options": [
                "Anatomical total shoulder arthroplasty",
                "Reverse total shoulder arthroplasty (rTSA — Grammont design, medialised centre of rotation increases deltoid lever arm)",
                "Hemiarthroplasty",
                "Resurfacing arthroplasty",
                "Arthrodesis in all cases"
              ],
              "answer": "B",
              "explanation": "Rotator cuff tear arthropathy (RCTA — massive irreparable cuff tear + glenohumeral arthritis + superior migration of the humeral head) is the primary indication for reverse total shoulder arthroplasty (rTSA). The Grammont design reverses the ball-and-socket anatomy: a hemisphere (glenosphere) is fixed to the glenoid, and a polyethylene cup is placed on the humeral side. This MEDIALISES and DISTALISES the centre of rotation, dramatically increasing the deltoid moment arm — allowing the deltoid alone to power shoulder elevation without a functioning rotator cuff. Anatomical TSA fails in RCTA (no cuff to stabilise → superior instability, 'rocking horse' loosening of the glenoid). Hemiarthroplasty gives poor functional results. rTSA contraindications: absent deltoid function (axillary nerve palsy), active infection. Complications: scapular notching (~50%), instability, infection, acromial fracture.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1279,
              "stem": "The Bristow-Latarjet procedure transfers the coracoid to the anterior glenoid. The 'sling effect' refers to:",
              "options": [
                "The coracoacromial ligament creating a hammock",
                "The glenosphere stabilising the humeral head",
                "The conjoint tendon (short head of biceps + coracobrachialis) crossing over the subscapularis and acting as a dynamic anterior restraint when the arm is abducted and externally rotated",
                "The capsule alone providing stability",
                "The rotator cuff creating a sling"
              ],
              "answer": "C",
              "explanation": "The sling effect is one of three stabilising mechanisms of the Latarjet procedure. When the arm is abducted and externally rotated (the apprehension position), the conjoint tendon (attached to the transferred coracoid) tightens across the lower portion of the subscapularis, creating a dynamic muscular 'sling' that reinforces the anterior capsule and prevents anterior translation of the humeral head. The effect is DYNAMIC — it increases as the arm moves into the at-risk position. The three effects: (1) bone block (extends the glenoid arc), (2) sling effect (conjoint tendon dynamic stabiliser), (3) capsular repair (coracoacromial ligament sutured to remaining capsule). This triple mechanism explains the low recurrence rate (~5%) even in high-demand contact athletes with significant bone loss.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            },
            {
              "number": 1280,
              "stem": "Shoulder impingement syndrome — the Neer classification describes three stages of impingement. Stage I is:",
              "options": [
                "Full-thickness rotator cuff tear",
                "Partial-thickness rotator cuff tear with fibrosis and tendinitis",
                "Massive irreparable cuff tear with arthropathy",
                "Complete shoulder fusion",
                "Oedema and haemorrhage of the rotator cuff (reversible — typically in patients <25 years)"
              ],
              "answer": "E",
              "explanation": "Neer impingement stages: Stage I = oedema and haemorrhage of the supraspinatus tendon (REVERSIBLE — typically in patients <25 years, from overuse/overhead activity). Treatment: rest, NSAIDs, physiotherapy. Stage II = fibrosis and tendinitis of the rotator cuff (typically 25-40 years — thickening and fibrosis of the bursa and tendon from repeated mechanical irritation). Treatment: physiotherapy, subacromial injection, activity modification. Stage III = bone spurs and tendon rupture (partial or full-thickness tears, typically >40 years — the final stage of the impingement continuum). Treatment: surgical (acromioplasty ± cuff repair). Clinical tests: Neer test (passive forward flexion with scapula stabilised — arm impacts against the anterior acromion), Hawkins-Kennedy test (forward flexion to 90° with forced IR — greater tuberosity impacts against the coracoacromial ligament).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Knee",
          "range": "Q1281-Q1287",
          "questions": [
            {
              "number": 1281,
              "stem": "Posterolateral corner (PLC) injuries of the knee — the three main structures of the PLC are:",
              "options": [
                "ACL, PCL, and MCL",
                "Medial meniscus, lateral meniscus, and ACL",
                "LCL (fibular collateral ligament), popliteus tendon, and popliteofibular ligament",
                "Quadriceps tendon, patellar tendon, and retinaculum",
                "ITB, biceps femoris, and gastrocnemius"
              ],
              "answer": "C",
              "explanation": "The posterolateral corner (PLC) consists of three primary stabilisers: (1) LCL (fibular/lateral collateral ligament — primary restraint to varus), (2) popliteus tendon (resists ER + posterior translation of the lateral tibial plateau), (3) popliteofibular ligament (connects popliteus to fibular head — resists ER). Together, they resist varus, external rotation, and posterior translation. The dial test (30° and 90° flexion) assesses PLC: increased external rotation asymmetry at 30° ONLY = isolated PLC. Increased ER at BOTH 30° and 90° = combined PLC + PCL. Isolated PLC injuries are rare — most are combined with PCL (Grade III PCL sag >10mm suggests combined PLC involvement). Treatment: acute (<3 weeks) → direct repair. Chronic → reconstruction (fibular-based techniques: LaPrade anatomical reconstruction).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1282,
              "stem": "Patellofemoral instability — the primary medial soft tissue restraint preventing lateral patellar dislocation is the:",
              "options": [
                "MCL (medial collateral ligament of the knee)",
                "Medial retinaculum",
                "VMO only",
                "MPFL (medial patellofemoral ligament — provides ~50-60% of the total medial restraining force against lateral patellar displacement)",
                "Iliotibial band"
              ],
              "answer": "D",
              "explanation": "The MPFL (medial patellofemoral ligament) is the primary medial stabiliser of the patella, providing ~50-60% of the total medial restraint against lateral patellar displacement (particularly in the first 0-30° of flexion, before the patella engages in the trochlear groove). The MPFL originates from the medial femoral epicondyle (between the adductor tubercle and medial epicondyle) and inserts on the superomedial border of the patella. Acute patellar dislocation ALWAYS tears or stretches the MPFL. In recurrent patellar instability, MPFL reconstruction (using gracilis autograft or allograft) is the cornerstone of surgical treatment — often combined with tibial tubercle transfer (medialisation/distalisation) and/or trochleoplasty (for severe trochlear dysplasia, Dejour classification). Risk factors for recurrent instability: trochlear dysplasia, patella alta, increased tibial tubercle-trochlear groove distance (TT-TG >20mm), MPFL insufficiency.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1283,
              "stem": "Return to sport after ACL reconstruction — current evidence suggests the minimum time before return to pivoting/contact sports should be:",
              "options": [
                "3 months",
                "6 months",
                "2 years",
                "Return immediately after surgery",
                "9-12 months (with evidence suggesting lower re-rupture rates with longer rehabilitation before return)"
              ],
              "answer": "E",
              "explanation": "Current evidence strongly supports a minimum of 9 months before return to pivoting/contact sports after ACL reconstruction, with many authorities now recommending 12 months or longer. The Grindem et al. (2016) study showed that each month of delay in return to sport (up to 9 months) reduced the re-rupture rate by 51%. The overall ACL graft re-rupture rate is ~6-15% (higher in young athletes <20 years, early return, hamstring graft). Criteria-based return (not just time-based): (1) no effusion, (2) full ROM, (3) quadriceps strength ≥90% of contralateral (LSI — limb symmetry index), (4) hop test performance ≥90% LSI, (5) sport-specific agility testing, (6) psychological readiness (ACL-RSI scale). Psychological readiness is the most commonly overlooked factor.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1284,
              "stem": "Discoid lateral meniscus is a congenital variant where the meniscus is:",
              "options": [
                "Thicker and disc-shaped (covers more of the tibial plateau than normal), rather than the normal crescent shape — it is prone to tearing and may cause snapping/clicking in children",
                "Absent",
                "Calcified throughout",
                "Located medially instead of laterally",
                "Fused to the ACL"
              ],
              "answer": "A",
              "explanation": "Discoid lateral meniscus is a congenital variant (incidence ~3-5% overall, higher in Asian populations ~15-20%) where the lateral meniscus is thicker and more disc-shaped than the normal crescent, covering a larger portion of the lateral tibial plateau. Watanabe classification: Type I = complete (covers entire lateral plateau — most common). Type II = incomplete (larger than normal but doesn't cover the entire plateau). Type III = Wrigley (hypermobile — normal size but lacks posterior capsular attachment → snaps over the lateral femoral condyle during flexion/extension, causing the 'snapping knee syndrome' in children). Symptoms: mechanical symptoms (clicking, locking, snapping), pain, effusion. Many are asymptomatic and discovered incidentally. Treatment: if asymptomatic → observe. Symptomatic → arthroscopic saucerisation (reshape to a stable crescent rim, preserving the peripheral vascularised portion) ± repair if torn. Complete excision leads to early OA.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1285,
              "stem": "The anterolateral ligament (ALL) of the knee has been increasingly recognised as important for controlling:",
              "options": [
                "Valgus stability",
                "Rotational stability (internal rotation of the tibia — contributing to pivot shift control alongside the ACL)",
                "Posterior translation",
                "Flexion range",
                "Patellar tracking"
              ],
              "answer": "B",
              "explanation": "The ALL (anterolateral ligament) runs from the lateral femoral epicondyle to the lateral tibial plateau (between Gerdy's tubercle and the fibular head), with connections to the lateral meniscus. It acts as a secondary restraint to internal rotation of the tibia, particularly between 20-90° of flexion. Its role is most significant in controlling the PIVOT SHIFT phenomenon — the anterolateral rotatory subluxation that characterises ACL-deficient knees. When the ACL is torn AND the ALL is also injured (associated with a Segond fracture — the ALL avulsion from the tibia), the pivot shift is more pronounced and rotational instability is greater. This has led to the concept of combined ACL + ALL reconstruction (lateral extra-articular tenodesis — modified Lemaire or Ellison procedure) for high-risk patients (young athletes, hypermobile, pivot sport, large pivot shift).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1286,
              "stem": "Stress fractures of the tibia — the most common location is the:",
              "options": [
                "Distal metaphysis",
                "Proximal epiphysis",
                "Posteromedial cortex of the proximal-middle tibial diaphysis (compression side, common in runners — 'shin splints' may represent a spectrum from periostitis to stress reaction to stress fracture)",
                "Anterior cortex (tension side — has worse healing potential and may require surgery)",
                "Fibular head"
              ],
              "answer": "C",
              "explanation": "Tibial stress fractures most commonly occur in the POSTEROMEDIAL cortex of the proximal-to-middle tibial diaphysis — the COMPRESSION side. These are the 'typical' stress fractures seen in runners and military recruits (overuse + repetitive loading). They generally heal well with activity modification, protected weight-bearing, and gradual return to activity (6-12 weeks). ANTERIOR CORTEX stress fractures (tension side — the 'dreaded black line') are LESS common but have WORSE healing potential — the tension forces on the anterior cortex tend to propagate the fracture rather than compress it. These may require surgical intervention (IM nail or anterior tension band plate) because they have a high rate of delayed union/non-union with conservative treatment. MRI: most sensitive investigation (bone marrow oedema before fracture line visible on XR). Bone scan: sensitive but less specific. Risk factors: female athlete triad (disordered eating, menstrual dysfunction, low bone density), rapid training increase, hard running surfaces, inappropriate footwear.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1287,
              "stem": "Meniscal repair (rather than meniscectomy) is preferred when:",
              "options": [
                "The tear is in the red-red or red-white zone (peripheral vascularised zone), is a longitudinal/vertical pattern, the patient is young, and the tear is ≥1cm — particularly when performed concurrently with ACL reconstruction",
                "The tear is in the white-white (avascular) zone only",
                "All meniscal tears should be excised regardless",
                "Only in patients over 70 years",
                "Only for degenerative horizontal cleavage tears"
              ],
              "answer": "A",
              "explanation": "Meniscal repair is preferred over meniscectomy when conditions for healing are favourable. Favourable factors: (1) LOCATION: red-red zone (peripheral, well-vascularised — best healing, ~90% success) or red-white zone (intermediate vascularity — ~60-70% success). White-white zone (central, avascular) has the poorest healing potential (~10-30% — repair rarely attempted here). (2) TEAR PATTERN: longitudinal/vertical tears (fibres run parallel to the circumferential collagen — can be sutured together). Complex, degenerative, horizontal cleavage, or radial tears in the avascular zone do NOT heal well with repair. (3) PATIENT AGE: younger patients heal better. (4) TEAR LENGTH: ≥1cm (smaller tears may heal spontaneously or be stable). (5) CONCURRENT ACL RECONSTRUCTION: the blood from the ACL drilling creates a healing environment that ENHANCES meniscal repair healing (~90-95% success when combined with ACLR vs ~60-70% isolated meniscal repair). Meniscectomy consequences: loss of load-bearing function → increased contact pressures → accelerated OA (meniscectomy is a risk factor for OA — save the meniscus whenever possible).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Ankle",
          "range": "Q1288",
          "questions": [
            {
              "number": 1288,
              "stem": "The anterior talofibular ligament (ATFL) is the most commonly injured ligament in ankle sprains. It is injured by which mechanism?",
              "options": [
                "Dorsiflexion and eversion",
                "Pure external rotation",
                "Direct trauma to the medial side",
                "Plantarflexion and inversion (the most common ankle sprain mechanism)",
                "Hyperextension of the ankle"
              ],
              "answer": "D",
              "explanation": "The ATFL is the weakest and most commonly injured lateral ankle ligament, torn in ~70% of ankle sprains. Mechanism: INVERSION of the plantarflexed foot. In plantarflexion, the ATFL becomes the primary restraint against inversion (the wider anterior body of the talus is no longer engaged in the mortise, and the ATFL is taut). The sequence of lateral ligament injury with increasing severity: ATFL (first, weakest) → CFL (calcaneofibular ligament, second) → PTFL (posterior talofibular ligament, third — strongest, rarely torn). Ottawa Ankle Rules: determine whether XR is needed (tenderness at posterior edge of malleolus, inability to WB 4 steps). Treatment: most lateral ankle sprains heal with functional rehabilitation (RICE + early mobilisation + proprioceptive exercises). Chronic lateral ankle instability (recurrent sprains): Broström-Gould repair (direct repair of ATFL + reinforcement with inferior extensor retinaculum).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Cartilage Repair",
          "range": "Q1289",
          "questions": [
            {
              "number": 1289,
              "stem": "Microfracture for articular cartilage defects works by:",
              "options": [
                "Transplanting mature hyaline cartilage",
                "Injecting synthetic cartilage into the defect",
                "Applying growth factors without any bony penetration",
                "Replacing the entire joint surface",
                "Creating small holes in the subchondral bone plate to allow marrow elements (MSCs, growth factors, blood) to fill the defect and form fibrocartilage repair tissue"
              ],
              "answer": "E",
              "explanation": "Microfracture (Steadman technique): small awl holes (3-4mm apart, 2-4mm deep) are made through the subchondral bone plate at the base of a prepared cartilage defect. This breaches the subchondral bone → allows marrow elements (MSCs, platelets, growth factors) to fill the defect → a 'super clot' forms → MSCs differentiate into chondrocyte-like cells → FIBROCARTILAGE fills the defect. Key limitation: fibrocartilage is predominantly Type I collagen (unlike hyaline cartilage which is Type II) — it is biomechanically inferior, less durable, and deteriorates over time (particularly >2 years and in defects >2-4cm²). Best results: young patients, small focal defects (<2cm²), intact menisci, normal alignment. Larger or failed defects → consider OATS (osteochondral autograft), ACI/MACI (autologous chondrocyte implantation), or osteochondral allograft.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Tendon",
          "range": "Q1290",
          "questions": [
            {
              "number": 1290,
              "stem": "Eccentric exercises are the evidence-based first-line treatment for:",
              "options": [
                "Acute fractures",
                "Achilles tendinopathy and patellar tendinopathy (the Alfredson protocol for Achilles and the Stanish/Curwin protocol)",
                "Ligament ruptures",
                "Bone tumours",
                "Joint dislocations"
              ],
              "answer": "B",
              "explanation": "Eccentric exercises (muscle lengthens under load — the opposite of concentric contraction) are the gold-standard conservative treatment for tendinopathy, with the strongest evidence for Achilles mid-portion tendinopathy (Alfredson protocol: 3×15 reps of eccentric heel drops, twice daily, for 12 weeks) and patellar tendinopathy (decline squat eccentric protocol). The mechanism: controlled loading stimulates tendon remodelling — collagen synthesis, improved fibre alignment, and neovascularisation regression. Success rates: ~60-90% for Achilles tendinopathy at 12 weeks. The key principle: eccentric loading must be performed INTO PAIN (mild-moderate discomfort is expected and beneficial — pain-free exercises are less effective for tendinopathy). This differentiates tendinopathy rehabilitation from most other musculoskeletal protocols where pain is avoided.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Hip",
          "range": "Q1291-Q1292",
          "questions": [
            {
              "number": 1291,
              "stem": "In hip arthroscopy for FAI, the procedure typically involves:",
              "options": [
                "Cam resection (femoral osteochondroplasty to restore the head-neck offset) and labral repair (± pincer rim trimming)",
                "Total hip replacement",
                "Fusion of the hip joint",
                "Removal of the femoral head",
                "External fixation of the hip"
              ],
              "answer": "A",
              "explanation": "Hip arthroscopy for FAI addresses the mechanical impingement by: (1) CAM resection — osteochondroplasty of the aspherical bump on the femoral head-neck junction using a high-speed burr, restoring the normal concavity and head-neck offset (guided by intra-operative fluoroscopy to confirm adequate resection without over-resection). (2) LABRAL REPAIR — the damaged labrum is reattached to the acetabular rim using suture anchors (preservation of the labral seal is preferred over debridement — the labrum acts as a suction seal maintaining negative intra-articular pressure and joint stability). (3) PINCER rim trimming — excess acetabular rim bone is removed (for pincer morphology). Post-operative: protected weight-bearing 2-4 weeks, ROM exercises, gradual return to sport 4-6 months. Contraindications: established OA (Tönnis Grade 2-3), minimal joint space (<2mm), dysplasia.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1292,
              "stem": "Femoroacetabular impingement (FAI) — CAM morphology is characterised by:",
              "options": [
                "Overcoverage of the femoral head by the acetabulum (that's PINCER)",
                "An aspherical bump on the anterolateral femoral head-neck junction that reduces the normal concavity — causing abutment against the acetabular rim with flexion + IR, damaging the labrum and cartilage",
                "Normal hip anatomy",
                "A fracture of the femoral neck",
                "Femoral head AVN"
              ],
              "answer": "B",
              "explanation": "CAM morphology: an aspherical bump/prominence on the anterolateral femoral head-neck junction that reduces the normal head-neck offset. During hip flexion + internal rotation, this bump abuts against the acetabular rim → shear forces damage the labrum (detachment) and adjacent cartilage (delamination — the 'carpet' of cartilage is peeled off the subchondral bone). CAM is more common in MALES, young athletes (develops during skeletal maturation — association with high-impact sport during adolescence). Measured by: ALPHA ANGLE on axial MRI or lateral XR (Dunn view): normal <50-55°, CAM >55°. PINCER morphology: excessive acetabular overcoverage (global — coxa profunda/protrusio, or focal — acetabular retroversion/crossover sign on AP pelvis XR) → the labrum is crushed between the acetabular rim and the femoral neck → labral degeneration/ossification. MIXED: most patients have BOTH cam and pincer components (~70%). Treatment: hip arthroscopy (cam osteochondroplasty + labral repair ± pincer rim trimming).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Rotator Cuff",
          "range": "Q1293-Q1294",
          "questions": [
            {
              "number": 1293,
              "stem": "The most important prognostic factor for successful rotator cuff repair healing is:",
              "options": [
                "Patient age alone",
                "Type of suture anchor used",
                "Whether the surgery is done in the morning or afternoon",
                "Tear size and tissue quality (larger tears with fatty infiltration — Goutallier Grade 3-4 — have significantly higher retear rates regardless of surgical technique)",
                "Blood type"
              ],
              "answer": "D",
              "explanation": "The two most important prognostic factors for cuff repair healing are: (1) TEAR SIZE — massive tears (>5cm or ≥2 tendons involved) have retear rates of 40-90% vs ~10-20% for small tears. (2) FATTY INFILTRATION (Goutallier classification on CT/MRI): Grade 0 = no fat, Grade 1 = some fatty streaks, Grade 2 = less fat than muscle, Grade 3 = equal fat and muscle, Grade 4 = more fat than muscle. Grades 3-4 represent irreversible muscle degeneration — even if the tendon is reattached, the muscle cannot generate meaningful force. These tears are often considered IRREPARABLE. Other factors: patient age (older = worse healing), smoking (impairs healing), diabetes, chronic tear duration, and retraction. Modern repair: double-row (suture bridge) technique provides superior footprint compression vs single-row. Biological augmentation (PRP, patches) — evidence still evolving.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1294,
              "stem": "After arthroscopic rotator cuff repair, the standard rehabilitation protocol restricts active overhead motion for:",
              "options": [
                "24 hours",
                "1 week",
                "6 months",
                "No restrictions at all",
                "6 weeks (allowing passive ROM only initially to protect the repair during the critical early healing phase)"
              ],
              "answer": "E",
              "explanation": "Post-arthroscopic rotator cuff repair rehabilitation follows a phased approach: Phase 1 (0-6 weeks): sling immobilisation + PASSIVE ROM only (pendulum exercises, passive forward flexion, passive ER within limits). NO active motion — the repair must be protected during the early healing phase when the tendon-to-bone healing is weakest (the tendon is only mechanically secured by sutures during this period — biological integration occurs over 6-12 weeks). Phase 2 (6-12 weeks): active-assisted ROM progressing to active ROM (the repair has achieved some biological fixation). Phase 3 (12-16 weeks): progressive strengthening (isotonic exercises, resistance bands). Phase 4 (4-6 months): full strengthening and return to functional activities. Return to sport/heavy labour: typically 6-9 months. Over-aggressive early rehabilitation → retear. Too conservative → stiffness. Balance is key.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Elbow",
          "range": "Q1295",
          "questions": [
            {
              "number": 1295,
              "stem": "Medial epicondylitis (golfer's elbow) primarily involves the origin of:",
              "options": [
                "ECRB (lateral epicondyle)",
                "Triceps",
                "Pronator teres and flexor carpi radialis (common flexor-pronator origin at the medial epicondyle)",
                "Biceps",
                "Supinator"
              ],
              "answer": "C",
              "explanation": "Medial epicondylitis affects the common flexor-pronator origin at the medial epicondyle — primarily the pronator teres and FCR (with possible involvement of palmaris longus, FDS, and FCU). Like lateral epicondylitis, it is a TENDINOPATHY (angiofibroblastic degeneration) rather than a true inflammatory tendinitis. It is ~7× LESS COMMON than lateral epicondylitis. Associated with: golf (trailing arm during downswing), throwing sports (valgus stress during acceleration phase), and occupational activities (repetitive wrist flexion/pronation). The ulnar nerve runs in the cubital tunnel directly posterior to the medial epicondyle — ~50% of patients with medial epicondylitis have concurrent ulnar nerve symptoms (paraesthesiae in ring/little finger). Treatment: activity modification, eccentric exercises, counterforce brace, corticosteroid injection (cautious — ulnar nerve proximity). Surgery: rare (debridement of degenerate tissue ± ulnar nerve decompression if symptomatic).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Cartilage",
          "range": "Q1296",
          "questions": [
            {
              "number": 1296,
              "stem": "MACI (matrix-assisted autologous chondrocyte implantation) differs from traditional ACI in that:",
              "options": [
                "Chondrocytes are seeded onto a collagen scaffold/membrane before implantation (eliminating the need for a periosteal flap and simplifying the surgical technique)",
                "No cartilage biopsy is needed",
                "It uses synthetic cartilage without any biological component",
                "It requires total joint replacement",
                "It only works for patients over 60"
              ],
              "answer": "A",
              "explanation": "MACI is the evolution of autologous chondrocyte implantation (ACI). Traditional ACI (Brittberg, 1994): Stage 1 — arthroscopic cartilage biopsy from a non-weight-bearing area → chondrocytes isolated and expanded in culture (3-6 weeks). Stage 2 — open surgery, periosteal flap harvested and sutured over the defect → chondrocyte suspension injected beneath the flap. MACI improvement: the expanded chondrocytes are seeded onto a collagen scaffold/membrane BEFORE implantation → the membrane is trimmed to fit the defect and secured with fibrin glue (no periosteal flap needed, no suturing to cartilage rim needed → simpler, can be done arthroscopically in some cases). Results: hyaline-like repair tissue (Type II collagen) — biomechanically superior to microfracture fibrocartilage (Type I collagen). Indications: focal full-thickness chondral defects 2-10cm² in young/active patients with normal alignment and stable joint.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            }
          ]
        }
      ]
    },
    {
      "title": "Infection",
      "chapters": [
        {
          "title": "Prophylaxis",
          "range": "Q1297-Q1299",
          "questions": [
            {
              "number": 1297,
              "stem": "Surgical antibiotic prophylaxis for elective arthroplasty should be administered:",
              "options": [
                "After skin closure",
                "The day before surgery",
                "24 hours after surgery",
                "Only if infection develops",
                "Within 60 minutes before skin incision (to ensure therapeutic tissue concentrations at the time of incision)"
              ],
              "answer": "E",
              "explanation": "Antibiotic prophylaxis must be administered within 60 minutes before skin incision to achieve therapeutic tissue concentrations at the surgical site BEFORE bacterial contamination occurs. For most orthopaedic procedures: IV cefuroxime 1.5g (first-generation cephalosporin in some centres — e.g., cefazolin 2g in the US) at induction of anaesthesia. Re-dose every 3-4 hours for prolonged procedures (or if blood loss >1500ml). Vancomycin (for penicillin-allergic patients or MRSA carriers): requires infusion starting 60-120 minutes before incision (slow infusion to avoid red man syndrome). Duration: NICE recommends discontinuation within 24 hours (single dose is often sufficient for clean surgery). Extended prophylaxis beyond 24 hours has NOT been shown to reduce SSI rates and increases antibiotic resistance. WHO and NICE both emphasise pre-incision timing.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1298,
              "stem": "Antibiotic-loaded cement (ALC) in primary THA/TKA uses a LOW dose of antibiotic for prophylaxis. The most commonly used antibiotic in cement is:",
              "options": [
                "Vancomycin only",
                "Gentamicin (typically 0.5-1g per 40g packet of cement — provides local antibiotic delivery to reduce deep infection rate without compromising cement mechanical properties)",
                "Ciprofloxacin",
                "Metronidazole",
                "Fluconazole"
              ],
              "answer": "B",
              "explanation": "Gentamicin is the most commonly used antibiotic in prophylactic cement (low-dose: 0.5-1g per 40g PMMA packet). It provides local antibiotic delivery directly to the cement-bone interface — achieving concentrations far higher than systemic administration alone. Evidence: the use of antibiotic-loaded cement in primary arthroplasty reduces the rate of deep periprosthetic infection (NJR data supports this). Key distinction: LOW-dose antibiotic cement (for prophylaxis in primary arthroplasty) uses ~0.5-1g per 40g packet — this does NOT significantly affect the mechanical properties of the cement (compressive strength, fatigue resistance). HIGH-dose antibiotic cement (for treatment — spacers in two-stage revision) uses ~4-8g total antibiotics per 40g packet — this DOES reduce mechanical properties (the spacer is temporary, so mechanical strength is less critical). Alternative antibiotics: tobramycin, vancomycin (added for MRSA coverage in high-risk patients). Heat-stable antibiotics only (gentamicin, vancomycin, tobramycin — survive the exothermic polymerisation).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1299,
              "stem": "The most common organism causing periprosthetic joint infection is:",
              "options": [
                "Pseudomonas aeruginosa",
                "Escherichia coli",
                "Clostridium difficile",
                "Coagulase-negative staphylococci (e.g., S. epidermidis) and S. aureus (together account for ~60-70% of PJI)",
                "Mycobacterium tuberculosis"
              ],
              "answer": "D",
              "explanation": "Staphylococci are the dominant organisms in PJI: coagulase-negative staphylococci (CoNS, predominantly S. epidermidis — ~30-40%) and S. aureus (~20-30%) together account for ~60-70% of all PJI. S. epidermidis is particularly important because: (1) it is a skin commensal (easily introduced during surgery), (2) it is an excellent biofilm former, (3) it often causes low-grade chronic infection (subtle presentation — persistent pain, loosening), and (4) it is frequently resistant to multiple antibiotics (including methicillin → MRSE). Other organisms: streptococci (~10%), gram-negatives (~5-10%), anaerobes, polymicrobial (~10-15%), culture-negative (~5-10%). Fungal PJI is rare but devastating.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "TB",
          "range": "Q1300-Q1301",
          "questions": [
            {
              "number": 1300,
              "stem": "In skeletal tuberculosis, the most commonly affected joint (after the spine) is:",
              "options": [
                "Shoulder",
                "Elbow",
                "Hip joint (second most common site of skeletal TB after the spine)",
                "Ankle",
                "Wrist"
              ],
              "answer": "C",
              "explanation": "Skeletal TB accounts for ~10% of all TB cases. The spine (Pott disease) is the most common skeletal site (~50%), followed by the HIP (~15%) and KNEE (~10%). TB arthritis of the hip presents with: insidious onset hip pain, limp, night sweats, weight loss, and progressive ROM restriction. Phemister triad (radiographic): juxta-articular osteopaenia, peripheral erosions, and gradual joint space narrowing (cartilage destroyed slowly — unlike pyogenic arthritis which destroys cartilage rapidly). TB hip progresses through three stages: synovitis (early — joint effusion, osteopaenia) → arthritis (cartilage destruction, erosions) → advanced (fibrous ankylosis, significant destruction, cold abscess). Treatment: anti-tuberculous chemotherapy (ATT) for 12-18 months (RIPE: rifampicin, isoniazid, pyrazinamide, ethambutol) ± surgical debridement/drainage if abscess or failed medical treatment.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1301,
              "stem": "Spinal tuberculosis differs from pyogenic spinal infection in that TB characteristically:",
              "options": [
                "Destroys the disc space first",
                "Causes only posterior element involvement",
                "Is always limited to a single vertebral level",
                "Does not form abscesses",
                "Preserves the disc space initially and involves the anterior vertebral body"
              ],
              "answer": "E",
              "explanation": "Spinal TB classically involves the anterior vertebral body with relative preservation of the disc space initially (because TB is an avascular organism that reaches the vertebral body via Batson's plexus, and the avascular disc is secondarily involved). Pyogenic discitis typically destroys the disc space first (bacteria access the disc via the endplate vessels). TB also produces cold abscesses (paravertebral collections without acute inflammatory signs), skip lesions, and kyphotic deformity (gibbus).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Chronic",
          "range": "Q1302",
          "questions": [
            {
              "number": 1302,
              "stem": "Antibiotic-impregnated cement spacers used during two-stage revision for PJI typically contain:",
              "options": [
                "Oral antibiotics embedded in plaster of Paris",
                "Only systemic IV antibiotics without local delivery",
                "Antifungal agents only",
                "High-dose gentamicin and vancomycin mixed into PMMA cement (providing local antibiotic delivery at concentrations far exceeding systemic levels)",
                "No antibiotics — the spacer is inert"
              ],
              "answer": "D",
              "explanation": "Antibiotic-loaded cement spacers (ALCS) deliver extremely high LOCAL antibiotic concentrations at the infection site (100-1000× higher than achievable systemically) while maintaining joint space and some function during the antibiotic treatment interval (typically 6-12 weeks between stages). Standard loading: vancomycin 2-4g + gentamicin/tobramycin 2.4-4.8g per 40g packet of PMMA cement (high-dose protocol — much more than the low-dose used for prophylaxis in primary arthroplasty). The combination provides broad-spectrum cover (vancomycin = gram-positives/MRSA, gentamicin = gram-negatives). Spacer types: static (non-articulating — better antibiotic delivery, simpler) or articulating (maintains ROM, easier second-stage surgery). The cement acts as a carrier for sustained antibiotic elution over weeks.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Tropical",
          "range": "Q1303-Q1304",
          "questions": [
            {
              "number": 1303,
              "stem": "Chronic osteomyelitis with a draining sinus in a tropical setting — the most common infecting organism worldwide remains:",
              "options": [
                "Staphylococcus aureus (remains the predominant organism globally, though polymicrobial infections are more common in tropical settings)",
                "Pseudomonas aeruginosa",
                "Escherichia coli",
                "Mycobacterium leprae",
                "Candida albicans"
              ],
              "answer": "A",
              "explanation": "S. aureus remains the most common organism in chronic osteomyelitis worldwide, including tropical settings (~40-60% of cases). However, in developing countries, several additional factors increase the complexity: (1) polymicrobial infections are more common (mixed gram-positive + gram-negative organisms due to delayed presentation, open fractures treated without debridement, and traditional remedies applied to wounds), (2) Salmonella osteomyelitis is classically associated with sickle cell disease (prevalent in tropical Africa), (3) extended-spectrum beta-lactamase (ESBL) producing gram-negatives are increasingly common, (4) TB osteomyelitis must always be considered (particularly spine, hip), and (5) fungal osteomyelitis (rare but seen in immunocompromised). Treatment challenges in low-resource settings: limited access to prolonged IV antibiotics, culture/sensitivity testing, advanced imaging, and specialised surgical expertise.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1304,
              "stem": "Mycetoma (Madura foot) is a chronic granulomatous infection of the foot endemic to tropical regions. It is characterised by:",
              "options": [
                "Acute onset with rapid resolution",
                "A chronic triad of painless swelling, draining sinuses with coloured discharge containing grains (colonies of the organism), and tissue destruction with bone involvement",
                "Only skin involvement without bone",
                "Bilateral symmetric presentation",
                "Self-limiting in all cases"
              ],
              "answer": "B",
              "explanation": "Mycetoma is a chronic, progressive, destructive granulomatous infection affecting the subcutaneous tissue and eventually invading bone. The classic triad: (1) painless SWELLING (firm, lobulated mass — the foot is the most common site, hence 'Madura foot'), (2) DRAINING SINUSES with coloured discharge containing GRAINS (granules — colonies of the causative organism: yellow/white = actinomycetoma/fungal, black = eumycetoma/fungal, red = actinomycetoma/bacterial), (3) progressive TISSUE DESTRUCTION including bone involvement (lytic lesions on XR). Two types: EUMYCETOMA (true fungal — Madurella mycetomatis — treated with prolonged antifungals ± surgery, poorer response) and ACTINOMYCETOMA (bacterial — Nocardia, Streptomyces, Actinomadura — treated with prolonged antibiotics, better response). Endemic: tropical 'mycetoma belt' (India, Sudan, Mexico, sub-Saharan Africa). Barefoot walking on thorny ground is the typical mechanism of inoculation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Septic Arthritis",
          "range": "Q1305-Q1310",
          "questions": [
            {
              "number": 1305,
              "stem": "Kocher criteria for differentiating septic arthritis from transient synovitis of the hip in children include all of the following EXCEPT:",
              "options": [
                "Non-weight-bearing",
                "ESR >40 mm/hr",
                "Radiographic joint destruction",
                "WCC >12,000",
                "Fever >38.5°C"
              ],
              "answer": "C",
              "explanation": "Kocher criteria (4 predictors for septic arthritis vs transient synovitis in children): (1) Non-weight-bearing (refusal to bear weight), (2) ESR >40 mm/hr, (3) WCC >12,000 (serum white cell count), (4) Fever >38.5°C. Probability of septic arthritis: 0 criteria = <0.2%, 1 = 3%, 2 = 40%, 3 = 93%, 4 = 99.6%. Caird later added CRP >20 mg/L as a 5th predictor (most sensitive single marker). Radiographic joint destruction is NOT one of the Kocher criteria — it is a LATE finding of untreated septic arthritis. If clinical suspicion is high (≥2 Kocher criteria), urgent joint ASPIRATION under USS guidance is mandatory. Turbid aspirate with >50,000 WCC and >75% PMNs = presumed septic arthritis → urgent washout (arthroscopic or open). S. aureus: most common organism at all ages. Kingella kingae: important in <5yr (may need prolonged culture/PCR).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1306,
              "stem": "Septic arthritis of a native joint is a surgical emergency. The first-line treatment is:",
              "options": [
                "Urgent joint washout (arthroscopic or open) with IV antibiotics",
                "IV antibiotics alone for 6 weeks",
                "Oral antibiotics alone",
                "Observation with serial aspiration",
                "Steroid injection into the joint"
              ],
              "answer": "A",
              "explanation": "Septic arthritis requires urgent joint washout (arthroscopic or open) with synovial fluid culture and targeted IV antibiotics. Delay in washout leads to irreversible cartilage destruction (proteolytic enzymes from bacteria and inflammatory cells destroy cartilage within hours). Empirical IV antibiotics are started immediately after synovial fluid aspiration and adjusted once culture results are available. The hip in children must always be washed out as an emergency.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1307,
              "stem": "In adult septic arthritis, the most commonly affected joint is:",
              "options": [
                "Hip",
                "Knee",
                "Shoulder",
                "Ankle",
                "Wrist"
              ],
              "answer": "B",
              "explanation": "The knee is the most commonly affected joint in adult septic arthritis (~50% of cases), followed by the hip (~20%), shoulder, ankle, and wrist. Risk factors: pre-existing joint disease (RA, OA), diabetes, immunosuppression, IV drug use, skin infection, recent joint procedure, prosthetic joint. The knee is vulnerable because it is the largest synovial joint with a large surface area for haematogenous seeding. In children, the hip is the most important joint (risk of AVN and growth disturbance if diagnosis delayed).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1308,
              "stem": "The Kocher criteria for differentiating septic arthritis from transient synovitis of the hip in children include all EXCEPT:",
              "options": [
                "Fever >38.5°C",
                "Non-weight-bearing on the affected limb",
                "ESR >40 mm/hr",
                "WCC >12,000/mm³",
                "Positive family history of arthritis"
              ],
              "answer": "E",
              "explanation": "Kocher criteria (4 predictors of septic arthritis vs transient synovitis in children): (1) Fever >38.5°C, (2) non-weight-bearing, (3) ESR >40 mm/hr, (4) WCC >12,000/mm³. With 4/4 criteria present: ~99% probability of septic arthritis. 3/4: ~93%. 2/4: ~40%. CRP >20 mg/L has been added as a 5th predictor (Caird modification). If septic arthritis is suspected: urgent hip aspiration (under GA or USS guidance) → synovial fluid MC&S + cell count → washout if confirmed.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1309,
              "stem": "In a child presenting with an irritable hip, the differential diagnosis between transient synovitis and septic arthritis is critically important. The most important initial investigation after clinical assessment is:",
              "options": [
                "Plain radiograph",
                "MRI of the hip",
                "Blood tests (FBC, CRP, ESR) followed by guided hip aspiration if suspicious",
                "CT scan",
                "Bone scan"
              ],
              "answer": "C",
              "explanation": "In a child with an acute irritable hip, blood tests (WCC, CRP, ESR) are essential to help differentiate transient synovitis from septic arthritis using the Kocher criteria. If 2 or more Kocher criteria are met (or clinical suspicion is high), urgent hip aspiration (under USS guidance or GA) is mandatory. Aspirate is sent for MC&S, cell count, and crystal analysis. Plain radiograph may show joint space widening or a soft tissue shadow but is not sensitive for early infection. MRI/USS can show effusion but aspiration is the definitive diagnostic investigation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1310,
              "stem": "In neonatal septic arthritis, which joint is most commonly affected?",
              "options": [
                "Knee",
                "Ankle",
                "Shoulder",
                "Hip",
                "Elbow"
              ],
              "answer": "D",
              "explanation": "The hip is the most commonly affected joint in neonatal septic arthritis. In neonates, unique features make hip septic arthritis particularly dangerous: (1) transphyseal blood vessels allow infection to spread from metaphysis to epiphysis and into the joint, (2) the femoral neck is entirely intracapsular (metaphyseal infection easily enters the joint), (3) the hip joint capsule distends rapidly with pus → increased intracapsular pressure → vascular compromise to the femoral head → AVN. Organisms: S. aureus, Group B Streptococcus, gram-negatives. Emergency washout is MANDATORY — delay leads to permanent femoral head destruction, growth arrest, and LLD.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Principles",
          "range": "Q1311-Q1315",
          "questions": [
            {
              "number": 1311,
              "stem": "The most common organism causing septic arthritis in adults (non-gonococcal) is:",
              "options": [
                "Staphylococcus aureus (~60-70% of non-gonococcal septic arthritis in adults)",
                "Streptococcus pneumoniae",
                "Haemophilus influenzae",
                "Neisseria gonorrhoeae",
                "Escherichia coli"
              ],
              "answer": "A",
              "explanation": "S. aureus is the most common organism in non-gonococcal septic arthritis in adults (~60-70%), followed by streptococci (~15-20%). In young sexually active adults: Neisseria gonorrhoeae is the most common cause of septic arthritis (gonococcal arthritis — typically migratory polyarthritis with dermatitis → settles into monoarthritis). In children <5 years: Kingella kingae is increasingly recognised (may need prolonged culture or PCR for detection). In neonates: Group B streptococcus and gram-negatives. In IVDU: Pseudomonas (especially sternoclavicular/sacroiliac joints). In immunocompromised: atypical organisms (fungi, mycobacteria). The knee is the most commonly affected joint (~50%). Treatment: joint aspiration + urgent surgical washout (arthroscopic or open) + IV antibiotics (empiric: flucloxacillin ± gentamicin → organism-directed when sensitivities available).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1312,
              "stem": "Culture-negative periprosthetic joint infection occurs in approximately what percentage of PJI cases?",
              "options": [
                "0% — an organism is always identified",
                "50%",
                "80%",
                "5-10% (despite appropriate sampling techniques, some PJIs remain culture-negative due to prior antibiotics, fastidious organisms, or biofilm bacteria)",
                "100% — organisms are never identified"
              ],
              "answer": "D",
              "explanation": "Culture-negative PJI occurs in approximately 5-10% of cases (some studies report up to 15%). Causes: (1) prior antibiotic therapy (most common reason — antibiotics suppress bacterial growth in culture, particularly if given before adequate tissue samples are obtained), (2) fastidious organisms (Cutibacterium acnes — previously Propionibacterium acnes — requires prolonged culture up to 14 days, and is often missed with standard 5-day incubation), (3) biofilm bacteria (may not grow on standard media), (4) inadequate sampling technique (fewer than 5 tissue samples, swabs instead of tissue, contamination). Improving detection: hold antibiotics for 2 weeks before aspiration/surgery (if clinically safe), obtain ≥5 intra-operative tissue samples, extend culture to 14 days, use sonication of explanted components (disrupts biofilm), and molecular techniques (16S rRNA PCR — identifies bacterial DNA).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1313,
              "stem": "Biofilm formation on orthopaedic implants — the critical time window after which biofilm becomes mature and resistant to antibiotics is approximately:",
              "options": [
                "1 hour",
                "2-4 weeks (mature biofilm develops over this period — after which antibiotic penetration is significantly reduced and DAIR becomes less effective)",
                "12 hours",
                "6 months",
                "Only forms after years"
              ],
              "answer": "B",
              "explanation": "Biofilm is a structured community of bacteria enclosed in a self-produced extracellular polysaccharide matrix (glycocalyx) that adheres to implant surfaces. Timeline: (1) Within MINUTES to HOURS: planktonic (free-floating) bacteria adhere to the implant surface (initial attachment — potentially reversible). (2) Over DAYS to WEEKS: bacteria multiply, produce glycocalyx, and form a structured biofilm community. (3) By 2-4 WEEKS: the biofilm is MATURE — it becomes a complex, multi-layered structure with water channels, gene transfer, and quorum sensing. Mature biofilm is 10-1000× more resistant to antibiotics than planktonic bacteria (the glycocalyx acts as a physical barrier, bacteria within are in a dormant/slow-growing state resistant to most antibiotics). This is why: DAIR works for acute PJI (<4 weeks — immature biofilm) but fails for chronic PJI (>4 weeks — mature biofilm → need two-stage revision with implant removal). Rifampicin is the only antibiotic with significant biofilm penetration (for staphylococci).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1314,
              "stem": "DAIR (debridement, antibiotics, and implant retention) for periprosthetic joint infection is most successful when performed within:",
              "options": [
                "6 months of symptom onset",
                "1 year",
                "Any time after diagnosis regardless of duration",
                "Only after 2 years",
                "4 weeks of symptom onset (acute infection — immature biofilm on the implant can still be disrupted by thorough debridement + appropriate antibiotics, with 60-80% success)"
              ],
              "answer": "E",
              "explanation": "DAIR is the treatment for ACUTE PJI — either early post-operative infection (<4 weeks from surgery) or acute haematogenous infection (symptoms <4 weeks duration in a previously well-functioning joint). Success rate: 60-80% when performed within the 4-week window. Why 4 weeks? The biofilm on the implant is still IMMATURE (forming but not yet mature) — it can be partially disrupted by thorough surgical debridement + exchange of modular components (liner, head, insert — these harbour the densest biofilm) + intensive antibiotic therapy. After 4 weeks: the biofilm MATURES → becomes 10-1000× more resistant to antibiotics → DAIR failure rate rises dramatically (>70% failure) → requires implant removal (two-stage revision or one-stage revision). DAIR protocol: (1) thorough debridement + washout, (2) exchange ALL modular components, (3) take ≥5 tissue samples for culture, (4) IV antibiotics 2-6 weeks → oral antibiotics 3-6 months (organism-directed, include rifampicin for staphylococci — the only antibiotic with significant biofilm penetration). Rifampicin: NEVER use as monotherapy (rapid resistance development) — always combine with another antibiotic.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1315,
              "stem": "The WHO surgical safety checklist has three phases. The correct sequence is:",
              "options": [
                "Time-out → Sign-in → Sign-out",
                "Sign-out → Sign-in → Time-out",
                "SIGN-IN (before induction of anaesthesia) → TIME-OUT (before skin incision) → SIGN-OUT (before patient leaves the operating room)",
                "No specific phases exist",
                "Only Time-out is performed"
              ],
              "answer": "C",
              "explanation": "The WHO Surgical Safety Checklist (introduced 2008, based on the Haynes/Gawande 'Safe Surgery Saves Lives' campaign) has THREE PHASES: (1) SIGN-IN (before induction of anaesthesia): confirms patient identity, procedure, site marked, consent, anaesthetic safety check, allergies, airway assessment, blood loss risk, pulse oximetry. (2) TIME-OUT (before skin incision — all team members pause): confirms team introduction (all members), patient identity, procedure, site, anticipated critical events (surgeon, anaesthetist, nursing team), antibiotic prophylaxis given within 60 minutes, essential imaging displayed, equipment/implants available. (3) SIGN-OUT (before patient leaves the OR): confirms procedure name recorded, instrument/sponge/needle counts correct, specimen labelling, any equipment problems documented, key concerns for recovery/ward management communicated. Implementation of the WHO checklist has been shown to reduce surgical morbidity by 36% and mortality by 47% (Haynes 2009, NEJM). It is now mandatory in all NHS operating theatres.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Classification",
          "range": "Q1316-Q1317",
          "questions": [
            {
              "number": 1316,
              "stem": "The Cierny-Mader classification of chronic osteomyelitis considers both the anatomical type of bone involvement AND the host physiological status. A Type III (localised) infection in a B-host means:",
              "options": [
                "Diffuse infection in a healthy patient",
                "Medullary infection only",
                "Superficial infection in a healthy patient",
                "Localised (segmental) cortical involvement in a patient with LOCAL or SYSTEMIC compromise (one or more comorbidities that impair healing — diabetes, immunosuppression, vascular disease, malnutrition)",
                "No infection present"
              ],
              "answer": "D",
              "explanation": "Cierny-Mader classification: ANATOMICAL TYPE: Type I = medullary (endosteal infection — e.g., infected IM nail), Type II = superficial (cortical surface — e.g., contiguous focus from soft tissue), Type III = localised (SEGMENTAL — full-thickness cortical involvement but in a localised segment, stable bone before and after debridement), Type IV = diffuse (extensive, full-thickness involvement affecting the entire circumference — the bone is mechanically unstable after debridement, requiring stabilisation). HOST STATUS: A-host = healthy, normal immune function. B-host = compromised — Bs (systemic: diabetes, immunosuppression, malnutrition, renal failure, smoking) or Bl (local: chronic lymphoedema, venous stasis, arterial insufficiency, scarring/radiation, neuropathy). C-host = treatment worse than disease (treatment morbidity would exceed the benefit — e.g., terminally ill). Treatment is guided by combining type + host: e.g., Type III + B-host = localised debridement + local antibiotic delivery + systemic antibiotics, with optimisation of host factors (glycaemic control, nutrition, smoking cessation).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1317,
              "stem": "The McPherson classification of periprosthetic hip infection stratifies patients by:",
              "options": [
                "Only the organism identified",
                "Infection type (acute/chronic/positive cultures only), host grade (uncompromised/compromised/significant compromise), and extremity grade (not compromised/compromised/significant compromise)",
                "Only the timing of infection",
                "Only the implant type",
                "Only the surgical approach used"
              ],
              "answer": "B",
              "explanation": "The McPherson classification comprehensively stratifies PJI by three parameters: (1) Infection type: Type I = positive intra-operative cultures only (≥2 positive cultures from revision for presumed aseptic failure). Type II = early post-operative (<4 weeks from index surgery). Type III = acute haematogenous. Type IV = late chronic (>4 weeks, insidious onset). (2) Host grade: A = uncompromised (no significant comorbidities). B = compromised (1-2 comorbidities: diabetes, immunosuppression, etc.). C = significantly compromised (>2 comorbidities — treatment risk may exceed benefit). (3) Extremity grade: 1 = not compromised (no local factors). 2 = compromised (prior surgery, skin quality issues). 3 = significantly compromised (active infection, sinus, poor soft tissue). This guides treatment decisions: DAIR for Type II-III with good host/extremity, two-stage for Type IV, and consideration of suppression/amputation for Type C hosts.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Biofilms",
          "range": "Q1318",
          "questions": [
            {
              "number": 1318,
              "stem": "A biofilm on an orthopaedic implant is significant because:",
              "options": [
                "It protects bacteria from antibiotics and the host immune system, making eradication extremely difficult",
                "It makes the implant stronger",
                "It improves bone ingrowth",
                "It is easily destroyed by oral antibiotics",
                "It only forms on cemented implants"
              ],
              "answer": "A",
              "explanation": "Biofilms are structured communities of bacteria encased in a self-produced extracellular polysaccharide matrix (glycocalyx) that adheres to implant surfaces. Within the biofilm, bacteria exist in a metabolically quiescent state and are protected from both systemic antibiotics (1000× higher MIC required) and host immune cells (phagocytes cannot penetrate the matrix). This is why chronic PJI requires implant removal — antibiotics alone cannot eradicate biofilm bacteria. DAIR (debridement, antibiotics, implant retention) is only successful in acute infections before mature biofilm forms.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Antibiotics",
          "range": "Q1319-Q1323",
          "questions": [
            {
              "number": 1319,
              "stem": "The recommended antibiotic prophylaxis for elective joint arthroplasty is:",
              "options": [
                "No antibiotics needed",
                "Oral amoxicillin 2 hours before surgery",
                "IV gentamicin after the operation only",
                "Topical antibiotics applied to the wound",
                "IV cefuroxime (or teicoplanin if penicillin allergy) given within 60 minutes before skin incision"
              ],
              "answer": "E",
              "explanation": "Prophylactic IV cefuroxime (1.5g) should be administered within 60 minutes before skin incision (ideally at induction of anaesthesia). For penicillin/cephalosporin allergy, teicoplanin or vancomycin is used (vancomycin must be started 90–120 minutes before incision due to slow infusion rate). Additional doses may be given intra-operatively for prolonged procedures (>2 hours) or significant blood loss. NICE and BOAST guidelines recommend a maximum of 24 hours of prophylactic antibiotics.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1320,
              "stem": "In prosthetic joint infection caused by MRSA, the antibiotic of choice is:",
              "options": [
                "Flucloxacillin",
                "Amoxicillin",
                "Vancomycin (with consideration of rifampicin combination for biofilm)",
                "Metronidazole",
                "Ciprofloxacin"
              ],
              "answer": "C",
              "explanation": "MRSA prosthetic joint infections are treated with vancomycin (or teicoplanin) as the glycopeptide of choice. For biofilm-associated infections (chronic PJI), rifampicin is added in combination (rifampicin has unique ability to penetrate biofilms and kill stationary-phase bacteria). Rifampicin must NEVER be used as monotherapy (rapid resistance develops). Linezolid and daptomycin are alternatives for vancomycin-resistant organisms. Duration: typically 6 weeks IV + oral combination.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1321,
              "stem": "Rifampicin is particularly useful in prosthetic joint infection because of its ability to:",
              "options": [
                "Kill gram-negative organisms exclusively",
                "Achieve high serum concentrations rapidly",
                "Replace vancomycin in all cases",
                "Treat fungal infections",
                "Penetrate and act against bacteria within biofilms"
              ],
              "answer": "E",
              "explanation": "Rifampicin has a unique ability among antibiotics to penetrate biofilms and kill bacteria in stationary phase (slow-growing/dormant bacteria within biofilms that are resistant to most other antibiotics). This makes it invaluable in PJI treatment, particularly in DAIR protocols for acute infections where the implant is retained. However, rifampicin must NEVER be used as monotherapy because resistance develops rapidly (within 1-2 days). It is always combined with another active antibiotic (e.g., flucloxacillin, vancomycin, or a fluoroquinolone).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1322,
              "stem": "The empirical antibiotic of choice for acute haematogenous osteomyelitis in an otherwise healthy child is:",
              "options": [
                "IV flucloxacillin (anti-staphylococcal penicillin)",
                "Metronidazole",
                "Ciprofloxacin",
                "Gentamicin",
                "Trimethoprim"
              ],
              "answer": "A",
              "explanation": "S. aureus is the most common organism in all age groups, so empirical treatment is with an anti-staphylococcal penicillin: IV flucloxacillin (or nafcillin). If MRSA is suspected (high prevalence area, previous MRSA, failed treatment): vancomycin or clindamycin. In neonates: add gentamicin or cefotaxime (covers gram-negatives and GBS). Duration: typically 4-6 weeks total (IV for 2-4 weeks, then oral switch when CRP normalising and clinical improvement). Serial CRP monitoring guides treatment duration.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1323,
              "stem": "In the management of open fractures, the BOAST-recommended empirical antibiotic regimen is:",
              "options": [
                "Oral amoxicillin only",
                "IV co-amoxiclav (or cefuroxime + metronidazole if penicillin allergy)",
                "IV vancomycin and gentamicin",
                "Topical antibiotics only",
                "No antibiotics needed if the wound is clean"
              ],
              "answer": "B",
              "explanation": "BOAST (British Orthopaedic Association Standards for Trauma) recommends IV co-amoxiclav 1.2g TDS for open fractures, starting as early as possible (ideally in the Emergency Department within 1 hour). If penicillin-allergic: cefuroxime 1.5g TDS + metronidazole 500mg TDS. Antibiotics are continued until definitive wound closure or for a maximum of 72 hours after each debridement (whichever is shorter). Tetanus status must be checked and updated. Gentamicin may be added for gross contamination (soil, farm injuries).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Antibiotic",
          "range": "Q1324-Q1325",
          "questions": [
            {
              "number": 1324,
              "stem": "Vancomycin is used in orthopaedic practice primarily for:",
              "options": [
                "All infections regardless of organism",
                "Only gram-negative infections",
                "Only fungal infections",
                "MRSA infections and penicillin-allergic patients with serious gram-positive infections (glycopeptide antibiotic inhibiting cell wall synthesis)",
                "Prophylaxis in all routine cases"
              ],
              "answer": "D",
              "explanation": "Vancomycin is a glycopeptide antibiotic that inhibits bacterial cell wall synthesis by binding to D-Ala-D-Ala terminal of the peptidoglycan precursor, preventing cross-linking. It is bactericidal for most gram-positive organisms. Primary indications in orthopaedics: (1) MRSA infection (PJI, osteomyelitis, SSI), (2) penicillin/cephalosporin allergy in patients needing gram-positive cover, (3) high-dose in antibiotic-loaded cement spacers for PJI (combined with gentamicin for broad cover). Administered IV (poor oral absorption — oral vancomycin is only used for C. difficile colitis). Requires therapeutic drug monitoring (TDM) — trough levels to ensure therapeutic range and avoid nephrotoxicity and ototoxicity. Slow infusion required (rapid infusion → 'red man syndrome' — histamine-mediated flushing, NOT true allergy).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1325,
              "stem": "Rifampicin is particularly valuable in the treatment of staphylococcal periprosthetic joint infection because it:",
              "options": [
                "Is the best monotherapy antibiotic available",
                "Is only effective against gram-negative organisms",
                "Penetrates and acts against bacteria within biofilm",
                "Has no side effects",
                "Is the only oral antibiotic available"
              ],
              "answer": "C",
              "explanation": "Rifampicin has a unique ability to penetrate biofilm and kill sessile (biofilm-embedded) staphylococci — a property not shared by most other antibiotics. This makes it invaluable in the treatment of staphylococcal PJI, particularly in DAIR and one-stage revision protocols where the implant is retained or immediately replaced. CRITICAL RULE: rifampicin must NEVER be used as monotherapy — staphylococci develop resistance to rifampicin rapidly if used alone (single-step mutation). It must always be combined with another active antibiotic (e.g., fluoroquinolone, doxycycline, cotrimoxazole, fusidic acid). Duration of treatment for PJI: typically 3 months for hip, 6 months for knee (longer for knee due to worse biofilm penetration). Side effects: hepatotoxicity (monitor LFTs), red/orange discolouration of bodily fluids, drug interactions (potent CYP450 inducer).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Osteomyelitis",
          "range": "Q1326-Q1330",
          "questions": [
            {
              "number": 1326,
              "stem": "The Brodie abscess is a form of:",
              "options": [
                "Acute osteomyelitis with septicaemia",
                "Septic arthritis",
                "Chronic subacute osteomyelitis (localised intraosseous abscess)",
                "Soft tissue abscess",
                "Spinal epidural abscess"
              ],
              "answer": "C",
              "explanation": "A Brodie abscess is a localised form of subacute osteomyelitis characterised by an intraosseous abscess, usually in the metaphysis of long bones (commonly distal/proximal tibia). It has a well-defined lytic lesion with surrounding sclerosis on radiograph, and a characteristic penumbra sign on MRI (T1-bright rim around the abscess). S. aureus is the most common organism. Treatment: usually requires surgical curettage and antibiotics, though some respond to prolonged antibiotics alone.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1327,
              "stem": "In children, acute haematogenous osteomyelitis most commonly affects which region of the bone?",
              "options": [
                "Epiphysis",
                "Diaphysis",
                "Physis directly",
                "Periosteum",
                "Metaphysis"
              ],
              "answer": "E",
              "explanation": "The metaphysis is the most common site because the terminal branches of the metaphyseal arteries form slow-flowing sinusoidal loops, creating an environment where bacteria can settle and multiply. The capillaries lack phagocytic lining cells in this region. In neonates (<18 months), transphyseal vessels may allow spread from the metaphysis into the epiphysis and joint (causing septic arthritis). In adults, the physis has closed and haematogenous spread typically affects the vertebral bodies.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1328,
              "stem": "The Cierny-Mader classification of adult chronic osteomyelitis classifies the disease based on:",
              "options": [
                "Anatomical type of bone involvement and physiological class of patient",
                "Organism and antibiotic sensitivity",
                "Duration of infection only",
                "Radiographic appearance only",
                "White cell count and ESR"
              ],
              "answer": "A",
              "explanation": "Cierny-Mader classifies chronic osteomyelitis using two axes: Anatomical type (1=medullary, 2=superficial/cortical, 3=localised full-thickness, 4=diffuse with circumferential instability) and Physiological host class (A=healthy host, B=compromised locally/systemically/both, C=treatment would be worse than the disease). This combined classification guides treatment decisions and predicts outcomes.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1329,
              "stem": "The investigation of choice for diagnosing acute osteomyelitis is:",
              "options": [
                "Plain radiograph (changes visible within 24 hours)",
                "MRI (most sensitive and specific)",
                "CT scan",
                "Bone scan",
                "Blood cultures alone"
              ],
              "answer": "B",
              "explanation": "MRI is the investigation of choice for acute osteomyelitis (sensitivity ~82-100%, specificity ~75-99%). It detects bone marrow oedema, periosteal reaction, soft tissue changes, and abscesses earlier than any other modality. Plain radiographs are NORMAL for the first 10-14 days (periosteal reaction and lytic changes take 2 weeks to appear). Bone scan (Tc-99m) is sensitive but non-specific (positive in many conditions). CT shows bony changes well but is less sensitive than MRI for early disease. Blood cultures are positive in only ~50% of haematogenous osteomyelitis.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1330,
              "stem": "Acute haematogenous osteomyelitis in children most commonly affects which anatomical region of the bone?",
              "options": [
                "Epiphysis",
                "Diaphysis",
                "Physis directly",
                "Metaphysis (rich blood supply with slow-flowing sinusoidal vessels where bacteria settle)",
                "Apophysis"
              ],
              "answer": "D",
              "explanation": "The metaphysis of long bones is the most common site for acute haematogenous osteomyelitis in children. The metaphyseal region has a rich blood supply with tortuous sinusoidal vessels (end-arteries) where blood flow slows — bacteria settle and proliferate in this low-flow environment. The most commonly affected bones: distal femur, proximal tibia (around the knee = most common site), proximal femur, distal tibia, and proximal humerus. In neonates: the infection can cross the physis via transphyseal vessels (which are present until ~18 months) → epiphyseal involvement and septic arthritis of the adjacent joint. In adults: haematogenous osteomyelitis is less common (direct/contiguous spread predominates), and when it occurs, it typically affects the vertebral body (discitis/osteomyelitis).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "PJI",
          "range": "Q1331-Q1334",
          "questions": [
            {
              "number": 1331,
              "stem": "The gold standard investigation for diagnosing prosthetic joint infection before revision surgery is:",
              "options": [
                "Plain radiograph",
                "Joint aspiration with synovial fluid analysis",
                "Bone scan",
                "Blood culture",
                "MRI"
              ],
              "answer": "B",
              "explanation": "Joint aspiration with synovial fluid analysis (cell count, differential, culture, and increasingly alpha-defensin or leucocyte esterase) is the gold standard pre-operative investigation for PJI. The MSIS/ICM criteria combine synovial markers with blood inflammatory markers (ESR, CRP). Intraoperative frozen section histology and multiple tissue cultures (≥3, using separate instruments) confirm the diagnosis at the time of surgery.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1332,
              "stem": "The most common organism causing prosthetic joint infection is:",
              "options": [
                "Escherichia coli",
                "Pseudomonas aeruginosa",
                "Streptococcus pneumoniae",
                "Candida albicans",
                "Coagulase-negative staphylococci"
              ],
              "answer": "E",
              "explanation": "Coagulase-negative staphylococci (particularly S. epidermidis) are the most common organisms causing PJI overall, followed closely by S. aureus. CoNS are low-virulence organisms that form biofilms on implant surfaces, making eradication difficult. S. aureus causes more acute, aggressive infections. Polymicrobial infections account for ~10–20%. Culture-negative PJI occurs in 5–10% of cases (often due to prior antibiotic use).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1333,
              "stem": "Alpha-defensin is a synovial fluid biomarker used to diagnose periprosthetic joint infection. Its main advantage is:",
              "options": [
                "It is always positive in OA",
                "It only works for fungal infections",
                "It replaces the need for cultures entirely",
                "It is the most specific synovial biomarker for PJI (>95% specificity), and is NOT affected by systemic inflammatory conditions, recent antibiotics, or non-infectious causes of inflammation",
                "It is measured in the blood, not synovial fluid"
              ],
              "answer": "D",
              "explanation": "Alpha-defensin is an antimicrobial peptide produced by neutrophils in response to the presence of a pathogen. It is measured in synovial fluid aspirated from the joint. Key advantages: (1) very high specificity (>95%) and sensitivity (~95%) for PJI, (2) NOT affected by systemic inflammatory conditions (RA, gout, crystal arthropathy), systemic infections (UTI, chest infection), recent antibiotics, or metallosis — making it superior to ESR/CRP which can be elevated from non-infectious causes, (3) results available within hours (lateral flow immunoassay) or days (lab ELISA). It does NOT replace cultures (cultures identify the organism and guide antibiotic therapy) — it complements them. Included as a minor criterion in the 2018 ICM/MSIS PJI diagnostic criteria.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1334,
              "stem": "The most commonly used diagnostic criterion for periprosthetic joint infection (PJI) is based on the 2018 ICM criteria. Which of the following is considered a MAJOR criterion (alone sufficient for PJI diagnosis)?",
              "options": [
                "Elevated CRP only",
                "Elevated ESR only",
                "Two positive cultures of the same organism from synovial fluid or tissue",
                "Single positive culture",
                "Positive histology only"
              ],
              "answer": "C",
              "explanation": "The 2018 International Consensus Meeting (ICM/MSIS) criteria for PJI diagnosis: MAJOR criteria (either one alone = PJI confirmed): (1) Two positive cultures of the same organism from periprosthetic tissue/fluid. (2) Sinus tract communicating with the joint. MINOR criteria are scored using a weighted system: elevated CRP, elevated ESR, elevated synovial WCC, elevated synovial PMN%, positive alpha-defensin, elevated synovial CRP, positive histology, positive purulence, single positive culture. A combined score ≥6 = PJI confirmed. Alpha-defensin is the most specific synovial fluid biomarker for PJI.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Discitis",
          "range": "Q1335",
          "questions": [
            {
              "number": 1335,
              "stem": "Childhood discitis most commonly presents at which spinal level?",
              "options": [
                "Lumbar (L2-L4 most common)",
                "Cervical",
                "Upper thoracic",
                "Lower thoracic",
                "Sacral"
              ],
              "answer": "A",
              "explanation": "Childhood discitis most commonly affects the lumbar spine (particularly L2-L4). In children, the intervertebral disc has a blood supply (unlike adults where the disc is avascular), making it susceptible to haematogenous infection. Presentation: back pain, refusal to walk, irritability, low-grade fever (may be afebrile). Elevated ESR/CRP. MRI is the investigation of choice (shows disc destruction, endplate changes, paraspinal abscess). Most cases respond to IV then oral antibiotics (S. aureus most common). Surgery is rarely needed in children.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "HO Prevention",
          "range": "Q1336",
          "questions": [
            {
              "number": 1336,
              "stem": "Heterotopic ossification can be prevented following THA using which NSAID?",
              "options": [
                "Paracetamol",
                "Ibuprofen",
                "Aspirin 75mg",
                "Celecoxib",
                "Indomethacin (75mg daily for 6 weeks)"
              ],
              "answer": "E",
              "explanation": "Indomethacin is the most widely used NSAID for HO prophylaxis following THA. It inhibits prostaglandin synthesis via COX inhibition, which reduces the differentiation of mesenchymal cells into osteoblasts. Standard dose: 75mg daily (or 25mg TDS) for 6 weeks post-operatively. Alternative: single-dose radiotherapy (700 cGy within 24-72 hours post-op). Risk factors for HO: male sex, previous HO, hypertrophic OA, ankylosing spondylitis, post-trauma. NSAIDs may impair fracture healing — use cautiously in fracture patients.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Pharmacology",
          "range": "Q1337",
          "questions": [
            {
              "number": 1337,
              "stem": "Bisphosphonates treat osteoporosis by which mechanism?",
              "options": [
                "Stimulating osteoblast formation",
                "Inhibiting osteoclast-mediated bone resorption",
                "Increasing vitamin D synthesis",
                "Stimulating PTH secretion",
                "Increasing calcium absorption from the gut"
              ],
              "answer": "B",
              "explanation": "Bisphosphonates (alendronate, risedronate, zoledronic acid) are anti-resorptive agents that bind to hydroxyapatite on bone surfaces. During resorption, they are ingested by osteoclasts and inhibit the mevalonate pathway (farnesyl pyrophosphate synthase), leading to osteoclast apoptosis. This reduces bone resorption and increases bone mineral density. Side effects: oesophagitis (oral preparations — take upright with water), atypical femoral fractures (long-term use >5 years), osteonecrosis of the jaw (ONJ, rare, higher with IV bisphosphonates), flu-like reaction (IV zoledronic acid).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Theatre",
          "range": "Q1338-Q1340",
          "questions": [
            {
              "number": 1338,
              "stem": "Laminar flow ventilation in orthopaedic theatres aims to reduce surgical site infection by:",
              "options": [
                "Increasing the temperature in theatre",
                "Humidifying the air",
                "Providing unidirectional, filtered air flow over the operative field to reduce airborne bacterial contamination",
                "Sterilising instruments faster",
                "Reducing noise levels for better concentration"
              ],
              "answer": "C",
              "explanation": "Laminar flow provides unidirectional HEPA-filtered air flowing vertically or horizontally over the operative field, displacing airborne particles and bacteria away from the wound. It reduces the airborne bacterial count from ~90 CFU/m³ (conventional theatre) to <10 CFU/m³. Charnley pioneered ultraclean air enclosures for arthroplasty. However, more recent evidence (including NJR data by Hooper et al.) has questioned whether laminar flow provides additional benefit over modern conventional ventilation with appropriate antibiotic prophylaxis. It remains standard in many arthroplasty theatres.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1339,
              "stem": "The most effective skin preparation agent for reducing surgical site infection in orthopaedic surgery is:",
              "options": [
                "Povidone-iodine (aqueous)",
                "Soap and water alone",
                "Hydrogen peroxide",
                "Chlorhexidine in 70% isopropyl alcohol",
                "No skin preparation is needed"
              ],
              "answer": "D",
              "explanation": "Chlorhexidine in 70% isopropyl alcohol is superior to povidone-iodine for skin antisepsis in reducing SSI — demonstrated in several RCTs and endorsed by NICE and WHO guidelines. Chlorhexidine has: broader antimicrobial spectrum, more rapid onset, longer residual activity on the skin (persistent effect), and is not inactivated by blood/serum (unlike povidone-iodine). The alcohol component provides additional rapid bactericidal activity. Precautions: allow the solution to dry completely before draping (fire risk with diathermy if alcohol vapour trapped under drapes). Chlorhexidine is avoided on the face, eyes, and mucous membranes.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1340,
              "stem": "The WHO Surgical Safety Checklist 'time-out' phase occurs:",
              "options": [
                "Before skin incision (after anaesthesia, before cutting)",
                "Before induction of anaesthesia",
                "After the operation in recovery",
                "The following day on the ward round",
                "Only if a complication occurs"
              ],
              "answer": "A",
              "explanation": "The Time-out occurs immediately before skin incision. The entire operating team pauses and confirms: (1) all team members have introduced themselves and their roles, (2) the surgeon states the patient's name, planned procedure, and operative site, (3) anticipated critical events are discussed (surgeon: critical steps, equipment, anticipated blood loss; anaesthetist: patient-specific concerns; nursing: sterility, equipment issues), (4) antibiotic prophylaxis has been given within the last 60 minutes, (5) essential imaging is displayed. The three WHO checklist phases: Sign-in (before anaesthesia), Time-out (before incision), Sign-out (before leaving theatre). Compliance with the WHO checklist has been shown to reduce surgical mortality by up to 47% and complications by 36%.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "SSI",
          "range": "Q1341",
          "questions": [
            {
              "number": 1341,
              "stem": "The most important modifiable risk factor for surgical site infection in elective orthopaedic surgery is:",
              "options": [
                "Patient age",
                "Diabetes (HbA1c optimisation)",
                "Gender",
                "Previous surgery at the same site",
                "Hospital type"
              ],
              "answer": "B",
              "explanation": "Diabetes (particularly poorly controlled diabetes with HbA1c >53 mmol/mol or 7%) is one of the most important modifiable risk factors for SSI. Hyperglycaemia impairs neutrophil function, reduces wound healing, and increases susceptibility to infection. Pre-operative HbA1c optimisation is recommended before elective surgery. Other modifiable risk factors: smoking (cessation 4-8 weeks before surgery), obesity (BMI >35), malnutrition, S. aureus nasal carriage (eradication with mupirocin nasal ointment + chlorhexidine body wash), and skin preparation (chlorhexidine-alcohol is superior to povidone-iodine for skin antisepsis — NICE).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Antibiotic Cement",
          "range": "Q1342",
          "questions": [
            {
              "number": 1342,
              "stem": "Antibiotic-loaded bone cement (ALBC) is used in arthroplasty. The most commonly used antibiotic in cement is:",
              "options": [
                "Vancomycin only",
                "Rifampicin",
                "Ciprofloxacin",
                "Metronidazole",
                "Gentamicin"
              ],
              "answer": "E",
              "explanation": "Gentamicin is the most commonly used antibiotic in bone cement (e.g., Palacos R+G, CMW3 Gentamicin). It provides broad-spectrum cover against common periprosthetic organisms (staphylococci, many gram-negatives), is thermally stable during cement polymerisation (exothermic reaction reaches 70-80°C), and elutes well from the cement surface. In revision for PJI, higher doses of antibiotic can be mixed into the cement spacer (often gentamicin + vancomycin for broader cover including MRSA). The antibiotic must be in powder form (not liquid) to avoid weakening the cement.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "HIT",
          "range": "Q1343",
          "questions": [
            {
              "number": 1343,
              "stem": "Heparin-induced thrombocytopenia Type II (HIT) is characterised by:",
              "options": [
                "Mild platelet drop in first 2 days that resolves spontaneously",
                "Platelet count increase",
                "Immune-mediated thrombocytopenia occurring 5-14 days after heparin exposure with PARADOXICAL thrombosis risk",
                "Only occurs with unfractionated heparin, never LMWH",
                "Treated by increasing the heparin dose"
              ],
              "answer": "C",
              "explanation": "HIT Type II is a serious immune-mediated complication: antibodies form against heparin-PF4 (platelet factor 4) complexes → platelet activation → thrombocytopenia (platelet count drops >50% from baseline or <150 × 10⁹/L) AND paradoxical THROMBOSIS (not bleeding). It typically occurs 5-14 days after heparin exposure (or within 24 hours if prior heparin exposure within 100 days). Can occur with BOTH UFH and LMWH (less common with LMWH). Management: STOP ALL heparin immediately, switch to alternative anticoagulant (fondaparinux, argatroban, danaparoid), do NOT give warfarin until platelet count recovers (risk of warfarin-induced skin necrosis/venous limb gangrene). 4T score guides clinical probability.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            }
          ]
        },
        {
          "title": "Antibiotic Stewardship",
          "range": "Q1344",
          "questions": [
            {
              "number": 1344,
              "stem": "Antibiotic prophylaxis for elective orthopaedic surgery should be administered:",
              "options": [
                "At the time of skin incision or within 60 minutes before incision (at induction of anaesthesia)",
                "24 hours before surgery",
                "Only after the operation in recovery",
                "1 week before surgery",
                "No prophylaxis is needed for elective orthopaedic surgery"
              ],
              "answer": "A",
              "explanation": "Prophylactic antibiotics should be administered at induction of anaesthesia, within 60 minutes before skin incision, to ensure adequate tissue levels at the time of surgical exposure. This timing is critical — too early and levels may have dropped; too late and the bacteria have already been introduced. For cefuroxime (most common): IV at induction (half-life ~1.5 hours). For vancomycin: must start infusion 90-120 minutes before incision (slow infusion required). Repeat doses for prolonged operations (>2 hours for cefuroxime) or significant blood loss. NICE recommends stopping prophylaxis within 24 hours (no prolonged courses for clean elective surgery).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Biofilm",
          "range": "Q1345",
          "questions": [
            {
              "number": 1345,
              "stem": "Biofilm formation on orthopaedic implants is clinically significant because:",
              "options": [
                "It makes the implant stronger",
                "It has no clinical significance",
                "It improves bone integration",
                "Bacteria within biofilm are protected from antibiotics and host immune responses, making eradication extremely difficult without implant removal",
                "It prevents corrosion"
              ],
              "answer": "D",
              "explanation": "Biofilm is a structured community of bacteria encased in an extracellular polymeric substance (EPS) matrix adherent to the implant surface. Bacteria within biofilm are 100-1000× more resistant to antibiotics than planktonic (free-floating) bacteria, and are protected from phagocytosis and antibody-mediated killing. This is why chronic PJI (established biofilm) typically requires implant removal (DAIR may work in acute infections <4 weeks when biofilm is immature). Biofilm forms within hours of bacterial contamination — prevention (meticulous aseptic technique, antibiotic prophylaxis, antibiotic cement) is far better than treatment. Rifampicin has biofilm-penetrating properties and is added to the regimen for staphylococcal PJI.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Chronic Osteomyelitis",
          "range": "Q1346-Q1347",
          "questions": [
            {
              "number": 1346,
              "stem": "The Cierny-Mader classification of adult osteomyelitis combines anatomical type with host physiological status. The four anatomical types are:",
              "options": [
                "Acute, subacute, chronic, and recurrent",
                "Haematogenous, post-traumatic, contiguous, and vascular",
                "Medullary, superficial, localised, and diffuse",
                "Type I-IV by bone affected",
                "Classified by organism only"
              ],
              "answer": "C",
              "explanation": "Cierny-Mader classification — Anatomical types: Type I = medullary (infection confined to the medullary canal). Type II = superficial (infection of the cortical surface, e.g., from an overlying soft tissue wound). Type III = localised (full-thickness cortical involvement but stable bone — can be debrided without compromising stability). Type IV = diffuse (circumferential instability after debridement — requires stabilisation). Host classification: A = normal host (good immune function). B = compromised host: Bs = systemic (diabetes, immunosuppression), Bl = local (scarring, lymphoedema), Bsl = both. C = treatment worse than disease (too sick for surgery). Treatment escalates with type and host status.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1347,
              "stem": "A Brodie abscess is:",
              "options": [
                "A subacute osteomyelitis presenting as a well-defined intramedullary abscess (typically metaphyseal) with sclerotic margins, often indolent",
                "An acute haematogenous osteomyelitis with systemic sepsis",
                "A soft tissue abscess only",
                "An epidural abscess",
                "A lung abscess from haematogenous spread"
              ],
              "answer": "A",
              "explanation": "A Brodie abscess is a localised form of subacute osteomyelitis — a well-circumscribed intramedullary abscess, typically in the metaphysis of long bones (most commonly distal/proximal tibia in children and young adults). It has an insidious onset with mild/intermittent pain, low-grade or absent systemic features, and often normal inflammatory markers. Radiographically: a well-defined radiolucent lesion with sclerotic margins (the body has attempted to wall off the infection). The differential includes benign bone tumours (NOF, chondroblastoma, osteoid osteoma). MRI shows a classic 'penumbra sign' (bright rim on T1 between the abscess and sclerotic bone). Treatment: curettage + culture + prolonged antibiotics (organism-directed). S. aureus is the most common organism.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "SSI Prevention",
          "range": "Q1348",
          "questions": [
            {
              "number": 1348,
              "stem": "Double gloving in orthopaedic surgery is recommended because:",
              "options": [
                "It improves surgical dexterity",
                "It keeps hands warmer",
                "It is purely aesthetic",
                "It increases infection rates",
                "The outer glove perforation rate is high (~30% in arthroplasty), and the inner glove provides a second barrier reducing contamination when the outer glove is breached"
              ],
              "answer": "E",
              "explanation": "Glove perforation rates in orthopaedic surgery are high: ~30% for single gloves during arthroplasty (sharp instruments, bone edges, implant handling). With double gloving, the outer glove perforates at a similar rate but the inner glove perforation rate is only 2-4% — providing a second barrier against contamination. Indicator glove systems (coloured inner glove showing through a perforation in the outer clear glove) allow early detection of outer glove breaches so they can be changed promptly. NICE and WHO recommend double gloving for orthopaedic procedures, particularly arthroplasty and procedures involving sharp implants.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "PJI Management",
          "range": "Q1349",
          "questions": [
            {
              "number": 1349,
              "stem": "DAIR (Debridement, Antibiotics, and Implant Retention) for periprosthetic joint infection is most likely to succeed when:",
              "options": [
                "The infection is chronic (>4 weeks since onset)",
                "The infection is acute (<4 weeks from onset or <4 weeks from last surgery), the implant is well-fixed, and the organism is susceptible to biofilm-active antibiotics",
                "There is sinus tract formation",
                "The organism is highly resistant to all antibiotics",
                "The implant is loose"
              ],
              "answer": "B",
              "explanation": "DAIR is most successful for ACUTE PJI — either early post-operative infection (<4 weeks from surgery) or acute haematogenous infection (<4 weeks of symptoms) with a WELL-FIXED implant. In acute infection, the biofilm is immature and more susceptible to debridement and antibiotics. During DAIR: thorough surgical debridement, exchange of all modular components (polyethylene liner, femoral head — these are easily exchanged and remove the surface biofilm), multiple tissue cultures (≥5 samples), and prolonged organism-directed antibiotics with a biofilm-active agent (rifampicin for staphylococci). Success rate for acute DAIR: 60-80%. For chronic infection (>4 weeks, mature biofilm): DAIR success drops to <30% → two-stage revision is preferred (explant → antibiotic spacer → 6-12 weeks antibiotics → reimplantation).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        }
      ]
    },
    {
      "title": "Spine",
      "chapters": [
        {
          "title": "Surgery",
          "range": "Q1350-Q1355",
          "questions": [
            {
              "number": 1350,
              "stem": "Pedicle screw fixation in the spine — the pedicle screw traverses the pedicle to anchor in the vertebral body. The at-risk structure with a medially malpositoned screw is:",
              "options": [
                "Aorta (laterally malpositioned)",
                "Oesophagus",
                "Kidney",
                "Spinal cord or nerve root (medial breach of the pedicle places the screw into the spinal canal)",
                "Liver"
              ],
              "answer": "D",
              "explanation": "Pedicle screws pass through the vertebral pedicle (the strongest part of the vertebra) into the vertebral body, providing three-column fixation. The pedicle has a cortical wall — if the screw breaches this wall: MEDIAL breach → the screw enters the SPINAL CANAL (risk of cord/nerve root injury — the most dangerous direction). LATERAL breach → the screw may impinge on the segmental vessels or nerve root in the foramen (usually less catastrophic). INFERIOR breach → nerve root in the foramen. ANTERIOR perforation (over-penetration into the vertebral body) → risk of great vessel injury (aorta/IVC — particularly in the thoracic/lumbar spine). Intra-operative assessment of screw position: palpate the pedicle walls with a ball-tipped probe before screw insertion (feel for breach), fluoroscopy (AP — screws should converge but not cross midline; lateral — screws fully within vertebral body), and CT post-operatively if concern. Navigation/robotics improve accuracy.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1351,
              "stem": "The most feared complication of posterior cervical spine surgery at C1-C2 (e.g., Harms/Goel technique for atlantoaxial fixation) is:",
              "options": [
                "Wound infection",
                "Sore throat",
                "Vertebral artery injury (the vertebral artery runs on the superior surface of C1 posterior arch and through the C2 pars/pedicle — at risk during screw placement)",
                "Mild headache",
                "Skin irritation from dressings"
              ],
              "answer": "C",
              "explanation": "The vertebral artery is at significant risk during C1-C2 posterior fixation. At C1: the artery runs in the vertebral artery groove on the SUPERIOR surface of the C1 posterior arch — C1 lateral mass screws must be placed with precise knowledge of this anatomy (the entry point, trajectory, and length are critical to avoid arterial injury). At C2: the artery runs through the C2 transverse foramen and is at risk with C2 pedicle screws (the C2 pedicle is small and the artery runs just lateral). Injury to the vertebral artery can cause: massive haemorrhage (difficult to control in the posterior cervical spine), posterior circulation stroke (brainstem infarction — potentially fatal), and vertebrobasilar insufficiency. Pre-operative CT angiography (CTA) is MANDATORY to assess: vertebral artery size, dominance (one artery may be larger/dominant — injury to the dominant artery is more catastrophic), and anatomical variations (high-riding vertebral artery on C2 — seen in ~20%, makes pedicle screw insertion dangerous).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1352,
              "stem": "Adjacent segment disease (ASD) after cervical or lumbar spinal fusion is thought to be caused by:",
              "options": [
                "The fusion itself resolving all spinal pathology permanently",
                "Improved blood supply to adjacent levels",
                "Natural ageing that would have occurred regardless",
                "Increased mechanical stress and motion at the levels immediately above and below the fusion (compensatory hypermobility leading to accelerated degeneration)",
                "Only seen in cervical spine, never lumbar"
              ],
              "answer": "D",
              "explanation": "Adjacent segment disease (ASD) is accelerated degeneration at the spinal levels immediately adjacent to a fusion construct. The biomechanical theory: fusion eliminates motion at the operated level → the adjacent segments must compensate with increased motion and stress → this accelerates disc degeneration, facet arthropathy, and potential stenosis/instability at those levels. Radiographic ASD (changes visible on imaging) occurs in up to 25-30% at 10 years, but symptomatic ASD (requiring treatment) occurs in approximately 3% per year (~22-30% at 10 years). It occurs in BOTH cervical and lumbar spine. Debate exists: is ASD truly caused by the fusion (altered biomechanics) or simply the natural progression of a spine predisposed to degeneration? Likely both factors contribute. Prevention strategies: motion-preserving alternatives (cervical disc replacement, dynamic stabilisation) — theoretical advantage but long-term evidence still accumulating.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1353,
              "stem": "Laminoplasty is a posterior cervical decompression technique that differs from laminectomy in that it:",
              "options": [
                "Removes the lamina entirely (that's laminectomy)",
                "PRESERVES the lamina by hinging it open on one side and propping it open (expanding the spinal canal without removing the posterior elements — maintaining posterior stability and reducing post-laminectomy kyphosis risk)",
                "Only decompresses a single nerve root",
                "Is an anterior approach",
                "Is only used in the lumbar spine"
              ],
              "answer": "B",
              "explanation": "Laminoplasty (open-door or French-door technique) is a POSTERIOR cervical spine decompression that expands the spinal canal WITHOUT removing the lamina. Open-door technique: the lamina is cut on one side (opening side), hinged on the other (hinge side), and propped open with a small plate or bone spacer → the spinal canal is expanded by 4-6mm, allowing the cord to drift posteriorly away from anterior compressive pathology (disc/osteophyte). Advantages over laminectomy: (1) preserves the posterior elements (lamina stays attached as a door → maintains posterior stability), (2) lower risk of POST-LAMINECTOMY KYPHOSIS (a significant problem after multilevel laminectomy — loss of posterior tension band → progressive cervical kyphosis). Indications: multilevel cervical myelopathy (≥3 levels) with maintained or lordotic cervical alignment. Contraindication: pre-existing cervical kyphosis (laminoplasty/laminectomy won't work if the cord is draped over the anterior pathology in kyphosis → needs anterior approach). Disadvantage: reduced neck ROM post-procedure (~50% reduction in extension).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1354,
              "stem": "Cervical disc replacement (CDR/arthroplasty) compared to ACDF for single-level cervical radiculopathy — the theoretical advantage of CDR is:",
              "options": [
                "CDR preserves segmental MOTION at the operated level (potentially reducing stress on adjacent segments and lowering the rate of adjacent segment disease compared to fusion)",
                "CDR is always superior in all patients",
                "CDR has a lower cost",
                "CDR never needs revision",
                "CDR is easier to perform technically"
              ],
              "answer": "A",
              "explanation": "CDR preserves segmental motion at the operated level (~8-12° preserved ROM) — this is its theoretical advantage over ACDF (which eliminates motion at the fused level). By maintaining motion: CDR may reduce the stress transferred to adjacent segments → potentially lowering the rate of adjacent segment disease (ASD, which occurs at ~3% per year after fusion). Evidence: RCTs (Prestige, Bryan, ProDisc, Mobi-C trials) show CDR is NON-INFERIOR to ACDF for clinical outcomes at 5-10 years, with some showing lower reoperation rates at adjacent levels with CDR. However: definitive proof that CDR REDUCES ASD compared to ACDF is still accumulating (the difference may take 10-20 years to become clinically significant). Contraindications for CDR: significant facet arthropathy (motion through arthritic facets → pain), instability, ossification of PLL, osteoporosis (poor fixation), multilevel disease (>2 levels — less evidence), myelopathy (relative — some centres use CDR for mild myelopathy). CDR is NOT cheaper (implants are more expensive). Technical demands are similar to ACDF.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1355,
              "stem": "Anterior cervical discectomy and fusion (ACDF) is performed through an approach between which two structures?",
              "options": [
                "Sternocleidomastoid and trapezius",
                "Posterior midline through the ligamentum nuchae",
                "Between the vertebral arteries posteriorly",
                "Through the oral cavity",
                "Carotid sheath (laterally) and midline visceral structures — trachea, oesophagus, thyroid (medially) — the Smith-Robinson approach"
              ],
              "answer": "E",
              "explanation": "ACDF uses the anterior Smith-Robinson approach: a transverse skin crease incision, dissection through the platysma, then developing the interval between the carotid sheath LATERALLY (containing the carotid artery, internal jugular vein, vagus nerve) and the midline visceral structures MEDIALLY (trachea, oesophagus, thyroid, recurrent laryngeal nerve). The longus colli muscles are elevated to expose the anterior cervical spine. Key structures at risk: recurrent laryngeal nerve (RLN — more at risk on the RIGHT side because of its aberrant course around the subclavian artery rather than the aortic arch, so LEFT-sided approach is conventionally preferred to reduce RLN risk), oesophagus (retraction injury), carotid/vertebral arteries, spinal cord (during discectomy/decompression), and sympathetic chain (Horner syndrome).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Deformity",
          "range": "Q1356-Q1361",
          "questions": [
            {
              "number": 1356,
              "stem": "Scheuermann disease is a structural kyphosis of the thoracic spine in adolescents. The radiographic diagnostic criteria include:",
              "options": [
                "Lateral listhesis of vertebral bodies",
                "Anterior wedging of ≥5° in at least 3 consecutive vertebral bodies (Sorensen criteria), with associated endplate irregularity and Schmorl nodes",
                "Bilateral spondylolysis",
                "Complete vertebral body collapse",
                "Normal radiographic appearance"
              ],
              "answer": "B",
              "explanation": "Scheuermann disease (juvenile kyphosis) is a structural, rigid thoracic kyphosis caused by abnormal endochondral ossification of the vertebral ring apophyses. Sorensen diagnostic criteria: anterior wedging of ≥5° in at least 3 CONSECUTIVE vertebral bodies. Additional radiographic features: endplate irregularity (wavy/scalloped endplates), Schmorl nodes (disc material herniating through weakened endplates into the vertebral body), increased thoracic kyphosis (>45° on lateral XR using the Cobb angle method), and disc space narrowing. The apex is typically T7-T9. Differentiate from postural kyphosis (flexible, corrects with hyperextension — Scheuermann does NOT correct). Treatment: mild (<60°) = physiotherapy (extension exercises) + observation. Moderate (60-75°) in a growing patient = bracing (Milwaukee brace). Severe (>75° or progressive despite bracing, or neurological deficit) = posterior spinal fusion ± anterior release.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1357,
              "stem": "Congenital scoliosis is caused by vertebral anomalies present from birth. The type with the WORST prognosis for curve progression is:",
              "options": [
                "Block vertebra (failure of segmentation — least progressive)",
                "Butterfly vertebra",
                "Unilateral unsegmented bar with contralateral hemivertebra (asymmetric growth — worst prognosis, ~5-10° per year progression)",
                "Isolated hemivertebra without bar",
                "Spina bifida occulta"
              ],
              "answer": "C",
              "explanation": "Congenital scoliosis results from vertebral formation defects (hemivertebra, wedge vertebra) and/or segmentation defects (unsegmented bar, block vertebra). The WORST prognosis for progression: UNILATERAL UNSEGMENTED BAR + CONTRALATERAL HEMIVERTEBRA — this creates maximal growth asymmetry (the bar tethers growth on one side while the hemivertebra adds growth on the opposite side → rapid, relentless progression at ~5-10° per year). Progression rates: block vertebra (failure of segmentation bilaterally) = least progressive (~1°/yr). Unilateral unsegmented bar alone = ~5°/yr. Isolated hemivertebra = variable (2-3°/yr depending on location). Unilateral bar + contralateral hemivertebra = WORST (~5-10°/yr). Treatment: observation if non-progressive, early posterior hemivertebra excision or short-segment fusion (convex hemiepiphysiodesis/concave distraction) to prevent severe deformity. MRI MANDATORY before surgery (40% have associated intraspinal anomalies — diastematomyelia, tethered cord, syrinx).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1358,
              "stem": "Spondylolisthesis — the Meyerding classification grades the percentage of forward slip. Grade II indicates:",
              "options": [
                "25-50% slip of the superior vertebral body on the inferior",
                "0-25% slip (Grade I)",
                "50-75% slip (Grade III)",
                "75-100% slip (Grade IV)",
                "Complete slip beyond 100% (spondyloptosis, Grade V)"
              ],
              "answer": "A",
              "explanation": "Meyerding classification (measured on lateral XR): Grade I = 0-25% slip, Grade II = 25-50%, Grade III = 50-75%, Grade IV = 75-100%, Grade V (spondyloptosis) = >100% (the vertebral body has slipped completely beyond the inferior body). Most common type: isthmic (pars interarticularis defect/spondylolysis — usually L5-S1, common in young athletes, especially gymnasts/fast bowlers). Degenerative spondylolisthesis: most common at L4-L5 in older adults, associated with facet arthropathy (no pars defect — the slip occurs through the degenerate facet joint). Treatment: Grade I-II asymptomatic → observation, activity modification. Grade I-II symptomatic (radiculopathy/neurogenic claudication) → decompression + instrumented fusion (pedicle screws + posterolateral fusion ± interbody). Grade III-IV → reduction + instrumented fusion (higher complication rate, including L5 nerve root injury during reduction). Spondyloptosis → circumferential (anterior + posterior) surgery.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1359,
              "stem": "The normal thoracic kyphosis range in an adult is approximately:",
              "options": [
                "0-10°",
                "50-70°",
                "80-90°",
                "20-45°",
                ">90°"
              ],
              "answer": "D",
              "explanation": "Normal thoracic kyphosis: 20-45° (measured T1-T12 by Cobb angle on lateral standing radiograph). Normal cervical lordosis: 20-40°. Normal lumbar lordosis: 40-60°. The sum of thoracic kyphosis should approximately equal lumbar lordosis to maintain sagittal balance. The C7 plumb line (vertical line dropped from C7) should fall within 2 cm of the posterior corner of the sacrum in normal sagittal balance. Sagittal malalignment (loss of lordosis, increased kyphosis) is associated with pain, disability, and poor quality of life.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1360,
              "stem": "Klippel-Feil syndrome is characterised by:",
              "options": [
                "Multiple hemivertebrae",
                "Atlantoaxial rotatory fixation",
                "Achondroplasia of the cervical spine",
                "Cervical disc herniation",
                "Congenital fusion of two or more cervical vertebrae"
              ],
              "answer": "E",
              "explanation": "Klippel-Feil syndrome involves congenital fusion (failure of segmentation) of two or more cervical vertebrae. The classic clinical triad: (1) short neck, (2) low posterior hairline, (3) restricted cervical movement — though the full triad is present in <50% of cases. Commonly associated conditions: scoliosis (60%), renal anomalies (35%), Sprengel deformity (congenital high scapula, 30%), congenital hearing impairment (30%), cardiac anomalies. Adjacent segment hypermobility above and below the fusion may predispose to early degenerative disease and instability at these levels. Management is primarily monitoring with intervention for instability or neurological compromise.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1361,
              "stem": "The Lenke classification of adolescent idiopathic scoliosis guides surgical planning. It classifies curves based on:",
              "options": [
                "Cobb angle alone",
                "Patient age only",
                "Risser sign alone",
                "Curve type (1-6 based on major curve location), lumbar spine modifier (A-C), and thoracic sagittal modifier (−, N, +)",
                "MRI findings of the spinal cord"
              ],
              "answer": "D",
              "explanation": "The Lenke classification is the current standard for AIS surgical planning. It uses three components: (1) Curve type (1-6): based on the location of the major (largest) curve and the structural nature of minor curves — Type 1 = main thoracic, Type 2 = double thoracic, Type 3 = double major (thoracic + lumbar), Type 4 = triple major, Type 5 = thoracolumbar/lumbar, Type 6 = thoracolumbar/lumbar + structural thoracic. (2) Lumbar spine modifier (A, B, C): based on the relationship of the CSVL (centre sacral vertical line) to the lumbar apical vertebra — A = CSVL between pedicles, B = CSVL between medial border and lateral pedicle, C = CSVL lateral to apical vertebral body. (3) Thoracic sagittal modifier: (−) = hypo-kyphotic (<10°), N = normal (10-40°), (+) = hyper-kyphotic (>40°). This determines which curves need to be included in the fusion.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Cauda Equina",
          "range": "Q1362-Q1363",
          "questions": [
            {
              "number": 1362,
              "stem": "Cauda equina syndrome (CES) is a surgical emergency. The most important clinical feature that mandates urgent investigation is:",
              "options": [
                "Mild back pain alone",
                "Bilateral sciatica, bladder dysfunction (urinary retention or incontinence), saddle anaesthesia, and/or progressive neurological deficit — requiring emergency MRI and surgical decompression within 24-48 hours",
                "Isolated knee pain",
                "Normal neurological examination with mild back ache",
                "Chronic back pain without leg symptoms"
              ],
              "answer": "B",
              "explanation": "CES results from compression of the cauda equina nerve roots (below the conus medullaris, typically L1-L2 level) — most commonly from a large central lumbar disc herniation (L4-L5 or L5-S1). Red flag symptoms: (1) bilateral leg pain/sciatica, (2) urinary retention or incontinence (loss of bladder control — the most significant symptom), (3) faecal incontinence, (4) saddle anaesthesia (numbness in the perineal/perianal region — S2-S4 distribution), (5) progressive bilateral lower limb weakness, (6) reduced anal tone (on PR examination). CES-incomplete (urinary difficulties without retention) and CES-retention (actual urinary retention — worse prognosis) must be distinguished. Management: EMERGENCY MRI → surgical decompression (laminectomy + discectomy) ideally within 24-48 hours (earlier decompression associated with better outcomes, particularly for bladder recovery). Delay → permanent neurological deficit (particularly bladder dysfunction).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1363,
              "stem": "The most important clinical feature differentiating cauda equina syndrome requiring emergency surgery from simple radiculopathy is:",
              "options": [
                "Unilateral leg pain",
                "Reduced knee jerk",
                "Back pain alone",
                "Reduced straight leg raise",
                "Bladder dysfunction (urinary retention or incontinence) with saddle anaesthesia"
              ],
              "answer": "E",
              "explanation": "Cauda equina syndrome (CES) is a surgical emergency characterised by bilateral radiculopathy, bladder dysfunction (retention → overflow incontinence), bowel dysfunction, saddle anaesthesia (perineum, perianal), and bilateral lower limb weakness. CES-Incomplete (CESI) has altered bladder sensation/urgency but not retention — outcomes better with early surgery. CES-Retention (CESR) has urinary retention with overflow — outcomes worse. Emergency MRI and surgical decompression (within 24-48 hours, ideally as soon as possible) are mandatory.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Cord Injury",
          "range": "Q1364-Q1369",
          "questions": [
            {
              "number": 1364,
              "stem": "The ASIA (American Spinal Injury Association) Impairment Scale — ASIA A indicates:",
              "options": [
                "Complete injury — no sensory or motor function preserved in the sacral segments (S4-S5)",
                "Normal function",
                "Sensory incomplete (sensory but no motor function below the level)",
                "Motor incomplete with >50% of key muscles below the level having MRC ≥3",
                "Motor incomplete with <50% of key muscles having MRC ≥3"
              ],
              "answer": "A",
              "explanation": "ASIA Impairment Scale: A = COMPLETE — no sensory or motor function preserved in the lowest sacral segments (S4-S5, tested by perianal sensation and voluntary anal contraction). B = Sensory INCOMPLETE — sensory function preserved below the level (including S4-S5) but no motor function. C = Motor INCOMPLETE — motor function preserved below the level, but <50% of key muscles below the level have MRC grade ≥3 (can't overcome gravity). D = Motor INCOMPLETE — motor function preserved and ≥50% of key muscles have MRC grade ≥3 (can overcome gravity). E = NORMAL — full motor and sensory function. The assessment MUST be performed AFTER spinal shock has resolved (bulbocavernosus reflex returned) — spinal shock mimics a complete injury but may recover. Sacral sparing (any S4-S5 function — perianal sensation, voluntary anal contraction) = INCOMPLETE injury (even if everything else is absent).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1365,
              "stem": "Central cord syndrome is the most common INCOMPLETE spinal cord injury. It is characterised by:",
              "options": [
                "Complete loss of all motor and sensory function below the injury",
                "Only lower limb weakness",
                "Greater weakness in the UPPER limbs than the lower limbs (the centrally located cervical cord tracts for the arms are more affected than the peripherally located tracts for the legs), with variable sensory loss and bladder dysfunction",
                "Only sensory loss without any motor deficit",
                "Isolated loss of proprioception"
              ],
              "answer": "C",
              "explanation": "Central cord syndrome typically occurs in elderly patients with pre-existing cervical spondylosis/stenosis after a hyperextension injury (e.g., forward fall striking the face/chin). The narrowed spinal canal buckles the ligamentum flavum inward, compressing the CENTRAL portion of the cord. The corticospinal tracts are arranged somatotopically with the cervical (arm) fibres CENTRALLY and the sacral/lumbar (leg) fibres PERIPHERALLY — so central compression preferentially affects the arm tracts. Pattern: upper limb weakness > lower limb weakness (the 'man in a barrel' — arms paralysed, legs relatively spared), variable sensory loss, and bladder dysfunction (urinary retention). Prognosis: best of all incomplete cord syndromes — lower limbs recover first, then bladder, then upper limbs. Proximal upper limb recovery before distal (hands recover last and often incompletely). Treatment: decompressive surgery (if structural compression identified on MRI) — early surgery (<24h) may improve outcomes (STASCIS study evidence supports this).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1366,
              "stem": "Brown-Séquard syndrome (cord hemisection) produces:",
              "options": [
                "Bilateral complete paralysis",
                "Only sensory loss bilaterally",
                "IPSILATERAL motor loss (corticospinal tract) and proprioception/vibration loss (dorsal columns), with CONTRALATERAL pain and temperature loss (spinothalamic tract crosses 1-2 levels above entry)",
                "Only motor loss bilaterally",
                "No neurological deficit"
              ],
              "answer": "C",
              "explanation": "Brown-Séquard syndrome results from HEMISECTION (one side) of the spinal cord — classically from penetrating trauma (stab wound) but also from tumour, MS, or disc herniation. The neurological pattern reflects the anatomy of the cord tracts: (1) IPSILATERAL motor loss (corticospinal tract — descends ipsilaterally, having already crossed in the brainstem). (2) IPSILATERAL proprioception/vibration/fine touch loss (dorsal columns — ascend ipsilaterally, crossing in the brainstem medulla). (3) CONTRALATERAL pain and temperature loss (spinothalamic tract — crosses to the opposite side 1-2 levels above entry, then ascends contralaterally). Prognosis: second best of the incomplete syndromes (after central cord) — >90% of patients regain functional ambulation. The ipsilateral leg (motor loss) is more functionally limiting than the contralateral sensory loss.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1367,
              "stem": "Anterior cord syndrome has the WORST prognosis among incomplete spinal cord injuries because:",
              "options": [
                "Only proprioception is affected",
                "Both motor function (corticospinal tracts) AND pain/temperature sensation (spinothalamic tracts) are lost bilaterally — only the posterior columns (proprioception, vibration, fine touch) are preserved",
                "Only one limb is affected",
                "All functions are completely preserved",
                "It only affects the upper limbs"
              ],
              "answer": "B",
              "explanation": "Anterior cord syndrome results from injury to the ANTERIOR two-thirds of the spinal cord (supplied by the anterior spinal artery). Causes: anterior spinal artery occlusion/infarction, burst fracture with retropulsed fragment compressing the anterior cord, aortic surgery complications, disc herniation. Pattern: BILATERAL loss of motor function (corticospinal tracts in the lateral columns) + bilateral loss of pain/temperature (spinothalamic tracts in the anterolateral columns). PRESERVED: posterior columns (proprioception, vibration, fine touch — supplied by the posterior spinal arteries, which are intact). This syndrome has the WORST prognosis of all incomplete SCI — only ~10-20% recover functional motor ability. The extensive bilateral motor loss (both upper and lower limbs) makes functional recovery extremely limited. Compare: central cord (best prognosis), Brown-Séquard (second best), anterior cord (worst).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1368,
              "stem": "Anterior cord syndrome is characterised by loss of motor function and pain/temperature sensation below the level of injury, with PRESERVATION of:",
              "options": [
                "Motor function",
                "Pain sensation",
                "All function is lost",
                "Proprioception and vibration (dorsal columns)",
                "Temperature sensation"
              ],
              "answer": "D",
              "explanation": "Anterior cord syndrome results from damage to the anterior two-thirds of the spinal cord (anterior spinal artery occlusion, burst fracture with retropulsed fragment, disc herniation). This damages the corticospinal tracts (bilateral motor loss), spinothalamic tracts (bilateral pain/temperature loss), but SPARES the dorsal columns (proprioception, vibration, fine touch — which are supplied by the posterior spinal arteries and located posteriorly). It has the WORST prognosis of the incomplete cord syndromes — only ~10-20% recover functional motor strength. Compare: central cord (UL>LL, best hand recovery), Brown-Séquard (best prognosis ~90% ambulate), posterior cord (proprioception loss only, rare).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1369,
              "stem": "Spinal shock differs from neurogenic shock in that spinal shock is:",
              "options": [
                "A cardiovascular problem with hypotension and bradycardia",
                "Permanent paralysis",
                "Only present in cervical cord injuries",
                "A psychological reaction to injury",
                "A transient loss of ALL neurological function (motor, sensory, reflex) below the level of spinal cord injury, with areflexia and flaccidity"
              ],
              "answer": "E",
              "explanation": "Spinal shock is a transient physiological state following acute spinal cord injury characterised by complete loss of motor function, sensory function, AND reflexes below the level of injury — the cord appears 'stunned'. There is flaccid paralysis (not spastic) and areflexia (absent bulbocavernosus reflex, absent deep tendon reflexes). It typically lasts 24-72 hours (can be days to weeks). Resolution is marked by the return of the bulbocavernosus reflex (S2-S4 arc — the first reflex to return). Once spinal shock has resolved, the TRUE neurological status can be assessed (ASIA grading). If no function returns after spinal shock resolves → complete injury (ASIA A). Neurogenic shock is a SEPARATE cardiovascular problem (hypotension + bradycardia from loss of sympathetic tone).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Cervical Myelopathy",
          "range": "Q1370-Q1374",
          "questions": [
            {
              "number": 1370,
              "stem": "Cervical spondylotic myelopathy (CSM) — the most common presenting feature is:",
              "options": [
                "Gait disturbance (clumsy, broad-based, spastic gait — often the earliest and most common symptom, sometimes described as 'walking on cotton wool')",
                "Severe neck pain only",
                "Isolated arm pain only",
                "Headache only",
                "Normal neurological examination always"
              ],
              "answer": "A",
              "explanation": "CSM is caused by degenerative narrowing of the cervical spinal canal (disc bulging + ligamentum flavum hypertrophy + osteophytes + ossification of PLL) compressing the cervical spinal cord. GAIT DISTURBANCE is the most common presenting feature (~80%) — patients describe: clumsy walking, unsteadiness, feeling of walking on cotton wool, broad-based gait, and difficulty with stairs. Upper limb symptoms: loss of manual dexterity (difficulty with buttons, writing, chopsticks), grip weakness, numb/clumsy hands. Lower limb: spastic paraparesis (hyperreflexia, clonus, upgoing plantars/Babinski positive, increased tone). Hoffman sign: flicking the DIP of the middle finger → involuntary flexion of the thumb IPJ (upper motor neuron sign in cervical myelopathy). Lhermitte sign: electric shock sensation down the spine/limbs with neck flexion. Natural history: stepwise deterioration (most patients worsen without treatment). Treatment: surgical decompression (anterior ACDF/corpectomy or posterior laminoplasty/laminectomy+fusion — depending on pathology and alignment).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1371,
              "stem": "Cervical spondylotic myelopathy presents with which combination of clinical features?",
              "options": [
                "Unilateral arm pain with normal reflexes",
                "Upper motor neuron signs in the legs with lower motor neuron signs at the level of compression",
                "Isolated lower motor neuron signs in both arms",
                "Normal neurological examination",
                "Pure sensory loss with no motor involvement"
              ],
              "answer": "B",
              "explanation": "Cervical myelopathy (cord compression) characteristically produces upper motor neuron (UMN) signs below the level of compression (spasticity, hyperreflexia, upgoing plantars, clonus in the legs) with lower motor neuron (LMN) signs at the level of compression (weakness, wasting, hyporeflexia in the arms at that myotomal level). Gait disturbance (broad-based, spastic) is often the presenting feature. Lhermitte sign (electric shock sensation down the spine on neck flexion) may be positive.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1372,
              "stem": "An inverted brachioradialis reflex is a sign of cord compression at which level?",
              "options": [
                "C3/C4",
                "C4/C5",
                "C7/T1",
                "T1/T2",
                "C5/C6"
              ],
              "answer": "E",
              "explanation": "An inverted brachioradialis reflex occurs with cord compression at C5/C6. When the brachioradialis (C5/C6) reflex is tested by tapping the distal radius, instead of the normal brachioradialis contraction (elbow flexion and forearm supination), finger flexion occurs due to hyperactive C7/C8 segments below the compressed level. The brachioradialis reflex itself may be diminished (LMN at the level) while the finger flexors are brisk (UMN below).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1373,
              "stem": "The anterior approach to the cervical spine (Smith-Robinson) utilises the interval between:",
              "options": [
                "Sternocleidomastoid and strap muscles",
                "Trachea and oesophagus",
                "Carotid sheath and midline viscera",
                "Longus colli muscles bilaterally",
                "Posterior triangle structures"
              ],
              "answer": "C",
              "explanation": "The Smith-Robinson anterior cervical approach uses the interval between the carotid sheath (laterally) and the midline visceral structures — trachea, oesophagus, thyroid (medially). Three fascial layers are traversed: investing layer of deep cervical fascia, pretracheal fascia, and prevertebral fascia. The recurrent laryngeal nerve is at risk, particularly on the right side (where it loops around the subclavian artery and has a more oblique course).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1374,
              "stem": "Anterior cervical discectomy and fusion (ACDF) is preferred over posterior decompression when cervical myelopathy involves:",
              "options": [
                "More than 3 levels of compression",
                "Fixed cervical lordosis",
                "Ossification of the ligamentum flavum only",
                "Compression at 1–2 disc levels with anterior pathology",
                "Congenital stenosis without disc disease"
              ],
              "answer": "D",
              "explanation": "ACDF is preferred for 1–2 level compression where the pathology is predominantly anterior (disc herniation, anterior osteophytes). It allows direct removal of the compressing pathology and restoration/maintenance of cervical lordosis. For multilevel disease (≥3 levels) or when pathology is predominantly posterior, posterior decompression (laminectomy + fusion, or laminoplasty) is preferred. Isolated laminectomy without fusion risks post-laminectomy kyphosis.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Trauma",
          "range": "Q1375-Q1377",
          "questions": [
            {
              "number": 1375,
              "stem": "A Chance fracture (flexion-distraction injury) of the thoracolumbar spine is classically associated with:",
              "options": [
                "A seatbelt injury (lap-belt only restraint — flexion-distraction force around the seatbelt fulcrum causes horizontal splitting of the vertebra through all three columns)",
                "Axial compression mechanism",
                "Penetrating trauma",
                "Extension injury",
                "Rotational mechanism only"
              ],
              "answer": "A",
              "explanation": "The Chance fracture (first described by GQ Chance, 1948) is a horizontal splitting fracture through ALL THREE COLUMNS of the vertebra — the vertebral body (anterior column), pedicles (middle column), and spinous process/lamina (posterior column). It results from FLEXION-DISTRACTION around a fulcrum (the seatbelt). Classic association: LAP-BELT only restraint (no shoulder strap) in RTA — the patient flexes violently around the lap belt, creating a distraction force posteriorly and compression anteriorly. The fracture line runs horizontally from posterior to anterior. Bony Chance fractures (through bone only) have good healing potential with extension bracing. Ligamentous Chance variants (through disc/ligaments) are UNSTABLE and typically require surgical fixation. CRITICAL: ~50% of Chance fractures are associated with ABDOMINAL injuries (bowel, mesenteric, solid organ) — ALWAYS assess the abdomen (CT abdomen). TLICS score: distraction morphology (4) → operative threshold often met.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1376,
              "stem": "The TLICS (Thoracolumbar Injury Classification and Severity) score guides operative vs non-operative management. A total score ≥5 indicates:",
              "options": [
                "Conservative management only",
                "Operative treatment is recommended (unstable injury requiring surgical stabilisation)",
                "Equivocal management — can go either way",
                "No treatment at all",
                "Only bracing"
              ],
              "answer": "B",
              "explanation": "TLICS scores THREE parameters: (1) MORPHOLOGY: compression (1), burst (2), translational/rotational (3), distraction (4). (2) POSTERIOR LIGAMENTOUS COMPLEX (PLC) integrity: intact (0), suspected/indeterminate (2), injured (3). (3) NEUROLOGICAL STATUS: intact (0), nerve root injury (2), cord/conus — incomplete (3), cord/conus — complete (2), cauda equina (3). Total score interpretation: ≤3 = NON-OPERATIVE (brace/orthosis). 4 = EQUIVOCAL (surgeon discretion — either operative or non-operative acceptable). ≥5 = OPERATIVE (surgical stabilisation recommended). The PLC is the KEY determinant of stability — PLC injury (3 points) almost always pushes the score to operative threshold. MRI is essential for assessing PLC integrity (disrupted supraspinous/interspinous ligaments, ligamentum flavum, facet capsules). The TLICS system simplifies decision-making for thoracolumbar fractures compared to older, more complex systems (Denis, AO).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1377,
              "stem": "A hangman's fracture is a bilateral pars interarticularis fracture of which vertebra?",
              "options": [
                "C1",
                "C3",
                "C2",
                "C5",
                "C7"
              ],
              "answer": "C",
              "explanation": "A hangman's fracture is a bilateral fracture of the pars interarticularis (or pedicles) of C2, caused by hyperextension with axial loading. Despite the dramatic name, most modern cases are from motor vehicle accidents and falls, not judicial hanging. Levine-Edwards classification: Type I = <3mm displacement, no angulation (stable, rigid collar). Type II = >3mm displacement with angulation (halo or surgery). Type IIa = no translation but significant angulation (do NOT apply traction — disc disruption). Type III = bilateral facet dislocation at C2-C3 (highly unstable, requires surgery). Paradoxically, the fracture often widens the canal, so neurological injury is uncommon.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Degeneration",
          "range": "Q1378",
          "questions": [
            {
              "number": 1378,
              "stem": "Lumbar spinal stenosis typically causes:",
              "options": [
                "Constant severe pain unrelated to activity",
                "Only back pain without leg symptoms",
                "Cauda equina syndrome in all cases",
                "Upper limb symptoms",
                "Neurogenic claudication — bilateral leg pain, heaviness, and weakness with walking that is relieved by sitting or leaning forward (flexion opens the spinal canal)"
              ],
              "answer": "E",
              "explanation": "Lumbar spinal stenosis (LSS) causes NEUROGENIC CLAUDICATION — bilateral leg pain, heaviness, numbness, and/or weakness that develops with WALKING or standing (extension narrows the spinal canal further) and is RELIEVED by SITTING, squatting, or leaning forward (FLEXION opens the spinal canal by increasing the cross-sectional area). The 'shopping trolley sign': patients can walk further when leaning forward on a trolley (flexed posture opens the canal). Differentiate from VASCULAR claudication: vascular = calf-predominant pain, absent pulses, normal spinal exam, relieved by stopping walking (doesn't need to sit). Neurogenic = thigh/buttock-predominant, normal pulses, positive spine exam, must SIT (not just stop) for relief. MRI: confirms stenosis (central canal <10mm AP diameter = absolute stenosis). Treatment: conservative (physiotherapy — flexion-based exercises, epidural injections) → surgical decompression (laminectomy ± fusion) if conservative treatment fails after 3-6 months. SPORT trial extension data: surgery provides greater improvement than conservative treatment for LSS.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Fractures",
          "range": "Q1379",
          "questions": [
            {
              "number": 1379,
              "stem": "Osteoporotic vertebral compression fractures (VCFs) — the initial treatment for acute painful VCFs is:",
              "options": [
                "Immediate surgical fusion in all cases",
                "Bed rest for 6 months",
                "Only physiotherapy without any analgesia",
                "Conservative management: analgesia (WHO pain ladder), early mobilisation, anti-osteoporotic treatment (bisphosphonates + calcium + vitamin D), and spinal orthosis (bracing) for comfort",
                "Ignore the fracture entirely"
              ],
              "answer": "D",
              "explanation": "Acute osteoporotic VCFs cause significant pain and disability, particularly in elderly patients. INITIAL treatment is CONSERVATIVE: (1) ANALGESIA (multimodal — paracetamol, NSAIDs if tolerated, opioids short-term for severe pain, calcitonin nasal spray may provide analgesic benefit). (2) EARLY MOBILISATION (avoid prolonged bed rest — increases osteoporosis, DVT, pneumonia, deconditioning). (3) BRACING (thoracolumbosacral orthosis/TLSO — provides comfort and reduces pain with activity, though evidence for improved fracture healing is limited). (4) ANTI-OSTEOPOROTIC TREATMENT — essential (treat the underlying cause): bisphosphonates (alendronate or zoledronic acid), calcium + vitamin D, fall prevention. For severe pain REFRACTORY to conservative treatment (typically 6-8 weeks trial): vertebral augmentation procedures — vertebroplasty (PMMA cement injection into the fractured vertebra) or balloon kyphoplasty (balloon inflation → cavity creation → cement injection — may restore height and reduce kyphosis). Evidence: controversial (VERTOS II showed benefit for vertebroplasty, but Australian sham-controlled trials showed no significant benefit).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "DISH",
          "range": "Q1380",
          "questions": [
            {
              "number": 1380,
              "stem": "Diffuse idiopathic skeletal hyperostosis (DISH) is characterised by flowing ossification along the anterolateral aspect of at least how many contiguous vertebral bodies?",
              "options": [
                "4",
                "2",
                "3",
                "6",
                "8"
              ],
              "answer": "A",
              "explanation": "DISH (Forestier disease) is characterised by flowing ossification along the anterolateral aspect of ≥4 contiguous vertebral bodies (Resnick diagnostic criteria). Disc spaces are preserved (unlike AS where disc spaces are involved). SI joints are NOT affected (unlike AS). DISH affects the right side of the thoracic spine preferentially (left side protected by the aortic pulsation). Associated: diabetes, obesity, older males. Fracture risk: long lever arms → unstable fractures (like AS).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Ankylosing Spondylitis",
          "range": "Q1381-Q1382",
          "questions": [
            {
              "number": 1381,
              "stem": "Ankylosing spondylitis is associated with which HLA type?",
              "options": [
                "HLA-B7",
                "HLA-DR4",
                "HLA-B27",
                "HLA-A2",
                "HLA-DQ2"
              ],
              "answer": "C",
              "explanation": "Ankylosing spondylitis is strongly associated with HLA-B27 (~90% of AS patients are HLA-B27 positive, though only 5–10% of HLA-B27 positive individuals develop AS). It predominantly affects young males (M:F = 3:1, though increasingly recognised in females). Features: bilateral sacroiliitis (earliest and most consistent finding), syndesmophytes, bamboo spine, enthesopathy, anterior uveitis (25–30%), and aortic regurgitation. Spinal fractures: treat as unstable (three-column injury through rigid spine).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1382,
              "stem": "Ankylosing spondylitis (AS) is a seronegative spondyloarthropathy. Fractures in AS patients are high-risk because:",
              "options": [
                "The fractures always heal without complications",
                "The fused, osteoporotic spine behaves as a long bone — fractures are highly unstable and act like long bone fractures (three-column injury through a rigid lever arm), with high risk of neurological injury",
                "Fractures in AS are extremely rare",
                "AS does not affect the spine",
                "Fractures only occur in the cervical spine"
              ],
              "answer": "B",
              "explanation": "In AS, the entire spine may become fused (bamboo spine) — a rigid, osteoporotic bar. When a fracture occurs (even from minor trauma like a ground-level fall), it typically extends through ALL THREE COLUMNS (the rigid spine cannot absorb energy — the fracture propagates completely through). This creates a highly unstable, transverse fracture that behaves like a long bone fracture through a lever arm. The spinal cord/cauda equina is at significant risk (~65% neurological injury rate with displaced fractures). CT of the ENTIRE spine is mandatory (multiple non-contiguous fractures occur in ~5%). The most common fracture location: cervicothoracic junction (C6-T1). Treatment: avoid manipulation (risk of cord injury), surgical stabilisation (long posterior instrumented fusion spanning the fracture). Mortality: up to 30% in the acute phase.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Spinal Infections",
          "range": "Q1383",
          "questions": [
            {
              "number": 1383,
              "stem": "Spinal tuberculosis (Pott disease) most commonly affects which region of the spine?",
              "options": [
                "Cervical",
                "Upper thoracic",
                "Lumbar",
                "Lower thoracic/thoracolumbar junction",
                "Sacral"
              ],
              "answer": "D",
              "explanation": "Spinal TB most commonly affects the lower thoracic spine and thoracolumbar junction. It typically involves the anterior vertebral body, spreading under the anterior longitudinal ligament to adjacent vertebrae (skip lesions can occur). Disc space narrowing occurs as the avascular disc is destroyed. Paravertebral abscess ('cold abscess') and kyphotic deformity (gibbus) are characteristic. Neurological deficit from cord compression may occur. Treatment: anti-TB chemotherapy (standard regimen: isoniazid, rifampicin, pyrazinamide, ethambutol). Surgery for neurological deficit, instability, or significant deformity.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Infection",
          "range": "Q1384-Q1385",
          "questions": [
            {
              "number": 1384,
              "stem": "Discitis (infective spondylodiscitis) most commonly involves which organism in adults?",
              "options": [
                "Mycobacterium tuberculosis in all cases",
                "Pseudomonas in all cases",
                "Fungal organisms only",
                "No organism is ever identified",
                "Staphylococcus aureus (most common organism, typically haematogenous spread)"
              ],
              "answer": "E",
              "explanation": "S. aureus is the most common organism causing pyogenic discitis/spondylodiscitis in adults (~40-50%), typically via haematogenous spread from a distant focus (UTI, skin infection, dental procedure, IVDU). Other organisms: streptococci, E. coli and other gram-negatives (urinary source, elderly), coagulase-negative staphylococci (post-operative), Pseudomonas (IVDU), and TB (important in endemic areas and immunocompromised patients). Presentation: insidious back pain (worse at night, not relieved by rest), malaise, low-grade fever, elevated ESR/CRP. MRI: disc signal change (loss of intranuclear cleft on T2), endplate erosion, enhancement with gadolinium, paravertebral/epidural abscess. Treatment: CT-guided biopsy for organism identification → prolonged IV then oral antibiotics (6-12 weeks). Surgery: for epidural abscess with neurological deficit, spinal instability, or failure of medical treatment.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1385,
              "stem": "Spinal tuberculosis (Pott disease) classically affects which part of the vertebra?",
              "options": [
                "Anterior vertebral body (paradiscal region)",
                "Spinous process",
                "Posterior elements only",
                "Lamina",
                "Pedicle only"
              ],
              "answer": "A",
              "explanation": "Spinal TB (Pott disease) characteristically affects the anterior vertebral body, typically starting in the paradiscal region (near the endplates) and spreading to the adjacent disc and vertebral body. Multiple contiguous vertebral bodies may be involved. The anterior column destruction leads to kyphotic deformity (gibbus). Cold abscesses (paravertebral/psoas abscesses) are characteristic — they track along fascial planes and may present as a groin or thigh mass (psoas abscess tracking to the inguinal region). Thoracolumbar junction is the most common spinal level. Treatment: anti-tuberculous chemotherapy for 12+ months (rifampicin, isoniazid, pyrazinamide, ethambutol). Surgery for: cord compression with neurological deficit, progressive kyphosis >40°, failure of medical treatment, abscess drainage.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Anatomy",
          "range": "Q1386-Q1395",
          "questions": [
            {
              "number": 1386,
              "stem": "How many cervical vertebrae are there in the human spine?",
              "options": [
                "5",
                "7",
                "6",
                "8",
                "9"
              ],
              "answer": "B",
              "explanation": "There are 7 cervical vertebrae (C1-C7), 12 thoracic (T1-T12), 5 lumbar (L1-L5), 5 sacral (fused into sacrum), and 3-5 coccygeal (fused into coccyx). There are 8 cervical nerve roots (C1-C8) despite only 7 vertebrae — C1-C7 nerves exit above their corresponding vertebra, and C8 exits below C7/above T1. From T1 downward, nerve roots exit below their corresponding vertebra.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1387,
              "stem": "The spinal cord typically terminates (conus medullaris) at which vertebral level in adults?",
              "options": [
                "T10",
                "T12",
                "L1-L2",
                "L3-L4",
                "S1"
              ],
              "answer": "C",
              "explanation": "The conus medullaris (terminal end of the spinal cord) is at approximately L1-L2 in adults. Below this level, the spinal canal contains the cauda equina (nerve roots only, not cord). In neonates, the conus is at L3, rising to the adult level by age 2. This is clinically important: injuries above L1-L2 produce cord injury (UMN signs), while injuries below produce cauda equina injury (LMN signs).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1388,
              "stem": "The ligamentum flavum connects adjacent:",
              "options": [
                "Laminae",
                "Vertebral bodies anteriorly",
                "Spinous processes",
                "Transverse processes",
                "Pedicles"
              ],
              "answer": "A",
              "explanation": "The ligamentum flavum connects the laminae of adjacent vertebrae posteriorly. It has the highest proportion of elastic fibres of any ligament in the body (~80% elastin, 20% collagen), which prevents buckling into the spinal canal during extension. With degeneration, it hypertrophies and loses elasticity, contributing to spinal stenosis (particularly in the lumbar spine). The ligaments of the spine from anterior to posterior: ALL → PLL → ligamentum flavum → interspinous → supraspinous.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1389,
              "stem": "The anterior cervical spine approach (Smith-Robinson) typically accesses the spine from which side of the neck?",
              "options": [
                "Right side always",
                "Either side equally",
                "Posterior midline",
                "Left side preferably",
                "Through the mouth (transoral)"
              ],
              "answer": "D",
              "explanation": "The left side is generally preferred for the anterior cervical approach because the recurrent laryngeal nerve (RLN) has a more predictable course on the left (it loops around the aortic arch and ascends in the tracheo-oesophageal groove). On the right, the RLN loops around the subclavian artery and has a more variable, oblique course, making it more susceptible to injury during retraction. However, revision surgery or previous left-sided approach may necessitate a right-sided approach.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1390,
              "stem": "The atlas (C1) vertebra differs from other cervical vertebrae in that it:",
              "options": [
                "Has the largest spinous process",
                "Has a vertebral body and a dens",
                "Has the widest spinal canal",
                "Has bilateral transverse foramina larger than C2",
                "Has NO vertebral body and NO spinous process"
              ],
              "answer": "E",
              "explanation": "The atlas (C1) is a ring-shaped vertebra with NO vertebral body (its embryological body has become the dens of C2) and NO spinous process (it has a posterior tubercle instead). It has two lateral masses connected by anterior and posterior arches. The superior articular facets are concave and articulate with the occipital condyles (nodding — 'yes' movement). The transverse ligament of the atlas holds the dens against the anterior arch, preventing anterior subluxation. A Jefferson fracture (burst fracture of C1) disrupts the ring at 2-4 points.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1391,
              "stem": "The intervertebral disc consists of two main components. The nucleus pulposus is composed primarily of:",
              "options": [
                "Type I collagen with low water content",
                "Dense bone",
                "Elastic fibres only",
                "Fat and blood vessels",
                "Type II collagen and proteoglycans with high water content (~80% in young adults)"
              ],
              "answer": "E",
              "explanation": "The nucleus pulposus is a gelatinous core rich in Type II collagen, proteoglycans (predominantly aggrecan), and water (~80% water content in young adults, decreasing with age). The high proteoglycan content creates osmotic pressure that attracts and retains water, giving the disc its load-bearing capacity. The annulus fibrosus surrounds the nucleus and consists of concentric lamellae of Type I collagen fibres arranged at alternating angles (~30° to the horizontal). With degeneration: water content decreases, proteoglycan content decreases, disc height reduces, and fissures develop in the annulus → disc herniation becomes possible.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1392,
              "stem": "The most mobile segment of the cervical spine for flexion-extension is:",
              "options": [
                "C5-C6",
                "Occiput-C1",
                "C1-C2",
                "C3-C4",
                "C7-T1"
              ],
              "answer": "A",
              "explanation": "C5-C6 is the most mobile segment of the subaxial cervical spine for flexion-extension, which is why it is the most common level for cervical disc degeneration, disc herniation, and spondylotic myelopathy. The occiput-C1 (atlanto-occipital) joint accounts for approximately 50% of total cervical flexion-extension (nodding 'yes'). C1-C2 (atlanto-axial) accounts for approximately 50% of cervical rotation (turning 'no'). The subaxial spine (C3-C7) provides the remaining flexion-extension and rotation, with C5-C6 being the most mobile subaxial segment.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1393,
              "stem": "The vertebral artery enters the transverse foramina at which cervical vertebral level?",
              "options": [
                "C1",
                "C3",
                "C6 (ascends through C6-C1 transverse foramina before entering the foramen magnum)",
                "C7",
                "T1"
              ],
              "answer": "C",
              "explanation": "The vertebral artery (branch of the subclavian artery) enters the transverse foramen of C6 and ascends through the transverse foramina of C6, C5, C4, C3, C2, and C1 before winding around the posterior arch of the atlas (C1) to enter the foramen magnum and unite with the contralateral vertebral artery to form the basilar artery. The vertebral artery is at risk during cervical spine surgery, particularly: anterior cervical approaches (ACDF — at risk with lateral dissection beyond the longus colli), posterior C1-C2 fixation (Harms technique — artery runs on the superior surface of C1 posterior arch), and trauma (fractures involving the transverse foramina). C7 has a transverse foramen but it typically transmits only veins (not the vertebral artery in most individuals).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1394,
              "stem": "The posterior longitudinal ligament (PLL) is narrowest at which spinal level, contributing to the high frequency of posterolateral disc herniations at this region?",
              "options": [
                "Cervical spine",
                "Lumbar spine",
                "Upper thoracic spine",
                "Lower thoracic spine",
                "Sacral spine"
              ],
              "answer": "B",
              "explanation": "The PLL is broadest in the cervical spine and becomes progressively narrower in the lumbar spine — it is narrowest at the L4-L5 and L5-S1 levels. At these levels, the PLL does not fully cover the posterior aspect of the disc, leaving the posterolateral portions relatively unprotected. This anatomical narrowing contributes to the high frequency of posterolateral disc herniations in the lumbar spine (the disc herniates where the PLL is weakest/absent). In contrast, central disc herniations are less common because the PLL provides some midline reinforcement. The ALL (anterior longitudinal ligament) is the strongest spinal ligament and is broadest in the lumbar spine.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1395,
              "stem": "The spinal nerve root that exits between L5 and S1 vertebrae is:",
              "options": [
                "L4",
                "S1",
                "S2",
                "L5",
                "L3"
              ],
              "answer": "D",
              "explanation": "In the lumbar spine (below C8), nerve roots exit BELOW their corresponding vertebra (through the neural foramen below the pedicle). Therefore: the L5 nerve root exits between L5 and S1 (below the L5 pedicle). The L4 root exits between L4 and L5. The S1 root exits through the S1 foramen. This differs from the cervical spine where roots exit ABOVE their vertebra (C6 root exits between C5 and C6). The transition occurs at C7/T1 (C8 root exits below C7 — there is no C8 vertebra).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Stenosis",
          "range": "Q1396-Q1398",
          "questions": [
            {
              "number": 1396,
              "stem": "Neurogenic claudication (from lumbar spinal stenosis) differs from vascular claudication in that neurogenic claudication is:",
              "options": [
                "Relieved by sitting or flexing the spine (e.g., leaning on a shopping trolley)",
                "Relieved by standing still",
                "Worse walking uphill",
                "Associated with absent peripheral pulses",
                "Always unilateral"
              ],
              "answer": "A",
              "explanation": "Neurogenic claudication (from lumbar stenosis) is characteristically relieved by spinal flexion (sitting, leaning forward, cycling) because flexion opens the spinal canal and lateral recesses. It is worsened by extension (standing upright, walking downhill). Vascular claudication is relieved by standing still (reducing muscle oxygen demand) and is associated with absent pulses, cool/pale limbs, and trophic skin changes. Neurogenic claudication patients can often cycle long distances without symptoms.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1397,
              "stem": "Degenerative lumbar spinal stenosis most commonly occurs at which level?",
              "options": [
                "L1-L2",
                "L2-L3",
                "L4-L5",
                "L3-L4",
                "L5-S1"
              ],
              "answer": "C",
              "explanation": "L4-L5 is the most common level for degenerative lumbar stenosis, followed by L3-L4. This is due to the combination of disc degeneration, facet joint hypertrophy, and ligamentum flavum thickening that occurs with age. Degenerative spondylolisthesis (which contributes to stenosis) also most commonly occurs at L4-L5. The stenosis can be central (neurogenic claudication), lateral recess (radiculopathy), or foraminal (exiting root compression).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1398,
              "stem": "Lumbar spinal stenosis typically presents with neurogenic claudication. This is characterised by:",
              "options": [
                "Calf pain on walking that is relieved by standing still (vascular claudication)",
                "Sudden onset paraplegia",
                "Isolated back pain without leg symptoms",
                "Bilateral lower limb pain, heaviness, and paraesthesiae on walking that is relieved by sitting down or leaning forward (flexion), and worsened by extension",
                "Unilateral sharp shooting pain"
              ],
              "answer": "D",
              "explanation": "Neurogenic claudication: bilateral (or asymmetric) lower limb pain, heaviness, weakness, numbness, and/or paraesthesiae brought on by walking or prolonged standing, RELIEVED by sitting or leaning forward (flexion opens the spinal canal, increasing the space available for the cauda equina). Patients classically describe being able to walk further pushing a shopping trolley (flexed posture) than walking upright. This differentiates it from VASCULAR claudication (calf pain on walking, relieved by standing still, absent pulses, ABI <0.9). Lumbar stenosis is caused by: ligamentum flavum hypertrophy, facet joint hypertrophy, disc bulging, and spondylolisthesis. Treatment: non-operative (physiotherapy, epidural steroid injection). Surgical: decompressive laminectomy (± fusion if concomitant instability/spondylolisthesis).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Disc Prolapse",
          "range": "Q1399-Q1405",
          "questions": [
            {
              "number": 1399,
              "stem": "A far lateral (foraminal) disc prolapse at L4/5 will compress which nerve root?",
              "options": [
                "L3",
                "L4 (exiting root)",
                "L5 (traversing root)",
                "S1",
                "L2"
              ],
              "answer": "B",
              "explanation": "A far lateral (foraminal) disc prolapse compresses the EXITING nerve root at that level. At L4/5, the exiting root is L4. This is in contrast to a posterolateral disc prolapse at the same level, which compresses the TRAVERSING L5 root. Far lateral herniations are less common (~10%) but important to recognise because they produce a different clinical picture (L4 radiculopathy rather than the expected L5).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1400,
              "stem": "L4 radiculopathy produces weakness of which movement and which reflex is reduced?",
              "options": [
                "Ankle dorsiflexion, ankle jerk",
                "Hip flexion, cremasteric reflex",
                "Ankle plantarflexion, ankle jerk",
                "Great toe extension, no reliable reflex",
                "Knee extension, knee jerk (patellar reflex)"
              ],
              "answer": "E",
              "explanation": "L4 radiculopathy: motor = knee extension (quadriceps), hip adduction. Reflex = knee jerk (patellar reflex) reduced/absent. Sensory = medial leg and medial foot. The L4 dermatome wraps around from the lateral thigh to the medial leg. L3/4 disc prolapse compresses the L4 traversing root. L4/5 far lateral disc compresses the L4 exiting root.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1401,
              "stem": "L5 radiculopathy typically produces weakness of:",
              "options": [
                "Hip flexion",
                "Ankle dorsiflexion and great toe extension (EHL)",
                "Knee extension",
                "Ankle plantarflexion",
                "Knee flexion"
              ],
              "answer": "B",
              "explanation": "L5 radiculopathy causes weakness of ankle dorsiflexion (tibialis anterior), great toe extension (EHL — most sensitive muscle to test), foot eversion (peronei), and hip abduction (gluteus medius). The L5 dermatome covers the lateral leg, dorsum of the foot, and great toe. The reflex is difficult to test (medial hamstring reflex may be reduced). L5 root is the most commonly affected root in the lumbar spine.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1402,
              "stem": "S1 radiculopathy characteristically produces reduced or absent:",
              "options": [
                "Ankle jerk (Achilles reflex)",
                "Knee jerk (patellar reflex)",
                "Biceps reflex",
                "Supinator reflex",
                "Abdominal reflexes"
              ],
              "answer": "A",
              "explanation": "S1 radiculopathy characteristically reduces or abolishes the ankle jerk (Achilles tendon reflex). S1 motor function includes ankle plantarflexion (gastrocnemius-soleus) and foot eversion (peronei). The S1 dermatome covers the lateral border and sole of the foot, posterior calf, and lateral malleolus. The L5/S1 disc prolapse is the most common cause of S1 radiculopathy.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1403,
              "stem": "In the cervical spine, a C5/C6 disc prolapse compresses which nerve root?",
              "options": [
                "C5",
                "C7",
                "C4",
                "C6",
                "C8"
              ],
              "answer": "D",
              "explanation": "In the cervical spine (unlike the lumbar spine), the nerve root exits ABOVE the pedicle of its corresponding vertebra. Therefore, a C5/C6 disc prolapse compresses the C6 nerve root (the root exits between C5 and C6). This is because cervical nerve roots are numbered above the vertebra (C6 root exits above C6 pedicle/below C5 pedicle). The transition occurs at C7/T1 (C8 root has no corresponding vertebra).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1404,
              "stem": "C7 radiculopathy produces weakness of which movement and loss of which reflex?",
              "options": [
                "Elbow flexion and biceps reflex",
                "Shoulder abduction and deltoid reflex",
                "Elbow extension and triceps reflex",
                "Wrist extension and brachioradialis reflex",
                "Finger abduction and no standard reflex"
              ],
              "answer": "C",
              "explanation": "C7 radiculopathy: motor = triceps (elbow extension), wrist flexors, finger extensors. Reflex = triceps jerk reduced/absent. Sensory = middle finger. C7 is the most commonly affected cervical nerve root. C6/C7 disc prolapse is the most common cervical disc herniation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1405,
              "stem": "The straight leg raise (SLR/Lasègue) test is positive for lumbar radiculopathy when it reproduces leg pain at what angle range?",
              "options": [
                "0–10°",
                "10–30°",
                "70–90°",
                ">90°",
                "30–70°"
              ],
              "answer": "E",
              "explanation": "A positive SLR reproduces the patient's radicular leg pain between 30° and 70° of hip flexion. Below 30°, there is insufficient tension on the nerve root. Above 70°, pelvic rotation and hamstring stretch can cause non-specific pain. The crossed SLR (raising the unaffected leg reproduces pain in the affected leg) is less sensitive but more specific for disc herniation (~90% specificity).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Scoliosis",
          "range": "Q1406-Q1412",
          "questions": [
            {
              "number": 1406,
              "stem": "The Risser sign (iliac apophysis ossification) is used to assess skeletal maturity in scoliosis. Risser 5 indicates:",
              "options": [
                "No ossification of the iliac apophysis",
                "25% ossification",
                "50% ossification",
                "Complete ossification and fusion of the apophysis (skeletal maturity)",
                "75% ossification"
              ],
              "answer": "D",
              "explanation": "Risser grading: 0 = no ossification (most growth remaining), 1 = 0-25% ossification, 2 = 25-50%, 3 = 50-75%, 4 = 75-100% ossification but not fused, 5 = complete fusion of apophysis to iliac crest (skeletal maturity). Ossification progresses from anterolateral to posteromedial. Risser 0-1 = highest risk of curve progression in scoliosis. Bracing is most effective in Risser 0-2.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1407,
              "stem": "The King classification of adolescent idiopathic thoracic scoliosis was largely replaced by the Lenke classification. The Lenke system classifies curves based on:",
              "options": [
                "Curve magnitude only",
                "Age and sex of patient",
                "Curve type (1-6), lumbar modifier (A, B, C), and sagittal thoracic modifier (-, N, +)",
                "Risser sign and curve flexibility",
                "Aetiology of the scoliosis"
              ],
              "answer": "C",
              "explanation": "The Lenke classification uses three components: (1) Curve type (1-6): based on which curves are structural (major and minor curves assessed on bending films). Type 1 = main thoracic. Type 5 = thoracolumbar/lumbar. (2) Lumbar modifier (A, B, C): based on the position of the CSVL (centre sacral vertical line) relative to the lumbar apex. (3) Sagittal thoracic modifier (-, N, +): T5-T12 kyphosis (<10° = -, 10-40° = N, >40° = +). Total 42 possible curve types.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            },
            {
              "number": 1408,
              "stem": "Adolescent idiopathic scoliosis (AIS) most commonly occurs in which demographic?",
              "options": [
                "Girls aged 10–16",
                "Boys aged 5–10",
                "Boys aged 10–16",
                "Neonates of either sex",
                "Adults over 50"
              ],
              "answer": "A",
              "explanation": "AIS predominantly affects girls during the adolescent growth spurt, typically between 10–16 years. The female:male ratio increases with curve magnitude — small curves have nearly equal sex distribution, but curves requiring treatment are approximately 8–10× more common in girls. Right thoracic curves are the most common pattern. Screening is typically performed using the Adams forward bend test to detect a rib hump (rotational prominence).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1409,
              "stem": "The Cobb angle is measured between the endplates of which vertebrae?",
              "options": [
                "The two most tilted vertebrae in the curve",
                "The most superior and most inferior end vertebrae of the curve",
                "The apex vertebra and the vertebra above",
                "C7 and L5",
                "T1 and S1"
              ],
              "answer": "B",
              "explanation": "The Cobb angle is measured between the superior endplate of the most tilted vertebra at the top of the curve (upper end vertebra) and the inferior endplate of the most tilted vertebra at the bottom of the curve (lower end vertebra). Lines are drawn along these endplates, and the angle between them (or their perpendiculars) is the Cobb angle. Curves >10° are defined as scoliosis. Curves >40–50° in skeletally immature patients typically require surgical correction.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1410,
              "stem": "In AIS, bracing is typically recommended for curves between:",
              "options": [
                "5–10°",
                "10–20°",
                "40–50° regardless of maturity",
                ">50° as a definitive treatment",
                "25–40° in a skeletally immature patient"
              ],
              "answer": "E",
              "explanation": "Bracing (typically a TLSO/Boston brace) is recommended for curves between 25–40° in skeletally immature patients (Risser 0–2, premenarchal or within 1 year of menarche). The BrAIST study (2013) demonstrated that bracing significantly reduces curve progression compared to observation. Bracing does not correct the curve — it aims to prevent progression until skeletal maturity. Compliance (>18 hours/day) is critical for effectiveness.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1411,
              "stem": "Which type of congenital scoliosis has the worst prognosis for curve progression?",
              "options": [
                "Block vertebra (failure of segmentation)",
                "Unilateral unsegmented bar with contralateral hemivertebra",
                "Hemivertebra alone",
                "Wedge vertebra",
                "Butterfly vertebra"
              ],
              "answer": "B",
              "explanation": "A unilateral unsegmented bar with a contralateral hemivertebra produces the most rapid curve progression because it combines a tethered growth plate on one side (unsegmented bar prevents growth) with an extra growth centre on the opposite side (hemivertebra adds growth). This combination produces relentless, severe curve progression requiring early surgical intervention. Block vertebra (bilateral failure of segmentation) produces the least progression.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1412,
              "stem": "In the assessment of adolescent idiopathic scoliosis, skeletal maturity is assessed using the Risser sign. Risser Grade 5 indicates:",
              "options": [
                "No ossification of the iliac apophysis (skeletally immature)",
                "25% ossification",
                "50% ossification",
                "75% ossification",
                "Complete apophysis fusion to the ilium (skeletally mature)"
              ],
              "answer": "E",
              "explanation": "The Risser sign assesses skeletal maturity by observing the progression of ossification of the iliac crest apophysis on AP pelvis/spine radiographs: Grade 0 = no ossification (most immature, highest risk of curve progression). Grade 1 = 25% ossification (anterolateral). Grade 2 = 50%. Grade 3 = 75%. Grade 4 = 100% ossification (complete capping but not fused). Grade 5 = apophysis FUSED to the ilium (skeletally mature, minimal progression risk). Curve progression risk is greatest at Risser 0-1 (rapid growth phase). Bracing is indicated for curves 25-40° in Risser 0-2 (growing patients). Surgery for curves >45-50° or progressive despite bracing.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Spondylolisthesis",
          "range": "Q1413-Q1416",
          "questions": [
            {
              "number": 1413,
              "stem": "The Meyerding classification grades spondylolisthesis based on:",
              "options": [
                "Aetiology of the slip",
                "Neurological status",
                "Disc degeneration grade",
                "Percentage of anterior translation of the superior vertebra on the inferior",
                "Patient age"
              ],
              "answer": "D",
              "explanation": "Meyerding classification: Grade I = 0-25% slip, Grade II = 25-50%, Grade III = 50-75%, Grade IV = 75-100%, Grade V = spondyloptosis (complete displacement, >100%). Most isthmic spondylolisthesis in children presents as Grade I or II. Grades III-V are high-grade slips with higher risk of progression and neurological compromise. L5 spondylolysis/spondylolisthesis at L5/S1 is the most common pattern.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1414,
              "stem": "Isthmic spondylolisthesis involves a defect (spondylolysis) in which part of the vertebra?",
              "options": [
                "Pars interarticularis",
                "Vertebral body",
                "Pedicle",
                "Transverse process",
                "Spinous process"
              ],
              "answer": "A",
              "explanation": "Isthmic spondylolisthesis results from a defect (stress fracture or elongation) of the pars interarticularis. This allows the vertebral body to slip forward relative to the vertebra below. The most common level is L5/S1. It is common in young athletes (gymnasts, fast bowlers, football linemen) due to repetitive hyperextension loading. The Wiltse classification divides spondylolisthesis into five types: isthmic, dysplastic, degenerative, traumatic, and pathological.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1415,
              "stem": "Degenerative spondylolisthesis most commonly occurs at which level?",
              "options": [
                "L3/L4",
                "L5/S1",
                "L4/L5",
                "L2/L3",
                "L1/L2"
              ],
              "answer": "C",
              "explanation": "Degenerative spondylolisthesis occurs most commonly at L4/L5 due to the sagittal orientation of the facet joints at this level (which allows more anterior translation) and the relative stability of L5/S1 provided by the iliolumbar ligament and the deep seating of L5 within the pelvis. It is more common in females, the elderly, and those with facet joint arthropathy. It causes central canal stenosis and neurogenic claudication.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1416,
              "stem": "Meyerding grading of spondylolisthesis — Grade III indicates:",
              "options": [
                "0-25% slip",
                "25-50% slip",
                "50-75% slip",
                "75-100% slip",
                "Complete slip (spondyloptosis)"
              ],
              "answer": "C",
              "explanation": "Meyerding classification grades the percentage of anterior translation of one vertebra over the one below: Grade I = 0-25% slip. Grade II = 25-50%. Grade III = 50-75%. Grade IV = 75-100%. Grade V = >100% (spondyloptosis — the vertebra has slipped completely off the one below). Most commonly at L5-S1 (isthmic) or L4-L5 (degenerative). Wiltse classification of spondylolisthesis types: I = dysplastic, II = isthmic (IIA = pars stress fracture/spondylolysis, IIB = elongated pars, IIC = acute pars fracture), III = degenerative, IV = traumatic, V = pathological. Treatment: Grade I-II asymptomatic → conservative. Symptomatic or high-grade (III-V) → posterior fusion ± decompression ± reduction.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Myelopathy",
          "range": "Q1417",
          "questions": [
            {
              "number": 1417,
              "stem": "Hoffmann sign is a clinical test for cervical myelopathy. A positive test is:",
              "options": [
                "Pain on neck flexion (Lhermitte sign)",
                "Wrist drop on extension",
                "Loss of finger abduction",
                "Flicking the middle finger DIP causes reflexive flexion of the thumb and index finger",
                "Positive Phalen test"
              ],
              "answer": "D",
              "explanation": "Hoffmann sign: the examiner flicks (snaps) the distal phalanx of the middle finger into extension. A positive test produces involuntary flexion of the thumb and index finger. It indicates upper motor neuron pathology (cervical myelopathy) and is the upper limb equivalent of the Babinski sign. It is not specific for myelopathy (can be present in 2-3% of normal individuals) but in the context of other UMN signs, it supports the diagnosis.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Rheumatoid",
          "range": "Q1418",
          "questions": [
            {
              "number": 1418,
              "stem": "In rheumatoid arthritis of the cervical spine, the atlanto-dens interval (ADI) is considered abnormal when it exceeds:",
              "options": [
                "1 mm",
                "3 mm in adults (or 5 mm in children)",
                "2 mm",
                "7 mm",
                "10 mm"
              ],
              "answer": "B",
              "explanation": "The ADI is measured between the posterior border of the anterior arch of C1 and the anterior surface of the odontoid (dens) on lateral flexion-extension radiographs. Normal ADI: <3 mm in adults (<5 mm in children). ADI >3 mm indicates atlantoaxial instability (AAI) from transverse ligament incompetence. However, the space available for the cord (SAC = distance from posterior dens to posterior ring of C1) is more clinically relevant: SAC <14 mm suggests cord compression risk. The Ranawat classification grades RA cervical involvement by neurological status.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Tumour",
          "range": "Q1419",
          "questions": [
            {
              "number": 1419,
              "stem": "The Tokuhashi scoring system is used to guide treatment decisions in patients with:",
              "options": [
                "Spinal metastases (predicts survival and guides surgical vs conservative management)",
                "Primary bone tumours of the spine",
                "Scoliosis severity",
                "Spinal trauma",
                "Spinal infections"
              ],
              "answer": "A",
              "explanation": "The Tokuhashi score (revised version) predicts survival in patients with spinal metastases and guides treatment decisions. It scores 6 parameters (0-2 each): general condition (KPS), number of extraspinal bone mets, number of vertebral body mets, metastases to major internal organs, primary site of cancer, and neurological deficit. Total 0-8 = <6 months survival (conservative/palliative). 9-11 = 6-12 months (palliative surgery). 12-15 = >12 months (excisional surgery may be appropriate).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Clinical",
          "range": "Q1420",
          "questions": [
            {
              "number": 1420,
              "stem": "Brown-Séquard syndrome (hemisection of the spinal cord) produces:",
              "options": [
                "Bilateral motor and sensory loss below the level",
                "Bilateral pain and temperature loss with preserved motor function",
                "Complete sensory loss with preserved motor function",
                "Pure motor loss without sensory involvement",
                "Ipsilateral motor loss and proprioception loss with CONTRALATERAL pain and temperature loss"
              ],
              "answer": "E",
              "explanation": "Brown-Séquard (cord hemisection): Ipsilateral findings: (1) motor paralysis below the level (lateral corticospinal tract), (2) loss of proprioception and vibration below the level (dorsal columns), (3) LMN signs at the level of the lesion. Contralateral findings: (1) loss of pain and temperature 1-2 levels below the lesion (lateral spinothalamic tract — crosses in the anterior commissure). Brown-Séquard has the BEST prognosis of all incomplete cord syndromes (~90% regain ambulatory function). Causes: penetrating trauma (stab wound), tumour, demyelination.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Spondylolysis",
          "range": "Q1421",
          "questions": [
            {
              "number": 1421,
              "stem": "Spondylolysis is a defect in the pars interarticularis. On oblique lumbar radiograph, it is classically seen as the:",
              "options": [
                "Codman triangle",
                "Bamboo spine",
                "Scotty dog sign — the pars defect appears as a 'collar' or 'broken neck' on the Scotty dog",
                "Rugger jersey appearance",
                "Ivory vertebra"
              ],
              "answer": "C",
              "explanation": "On the oblique lumbar radiograph, the posterior elements of the vertebra create the appearance of a 'Scotty dog' (or Scottish terrier): the nose = transverse process, eye = pedicle, ear = superior articular facet, front leg = inferior articular facet, body = lamina, tail = contralateral superior articular facet, neck = PARS INTERARTICULARIS. A pars defect (spondylolysis) appears as a lucent line through the 'neck' of the Scotty dog — the dog appears to be wearing a 'collar' or has a 'broken neck'. Spondylolysis is most common at L5 (~85-90% of cases) and is believed to result from repetitive hyperextension stress (stress fracture of the pars). Common in gymnasts, fast bowlers (cricket), dancers, and football linemen. Bilateral spondylolysis allows the vertebral body to slip forward (spondylolisthesis).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "RA Spine",
          "range": "Q1422",
          "questions": [
            {
              "number": 1422,
              "stem": "In rheumatoid arthritis of the cervical spine, cranial settling (basilar invagination) is assessed using which measurement?",
              "options": [
                "Atlanto-dens interval (ADI)",
                "Cobb angle",
                "Torg ratio",
                "Ranawat classification criteria and McGregor line/Redlund-Johnell measurement",
                "Powers ratio"
              ],
              "answer": "D",
              "explanation": "Cranial settling (vertical translocation/basilar invagination) occurs when the C1-C2 complex migrates superiorly due to erosion of the lateral masses of C1 and the occipital condyles, causing the odontoid peg to protrude through the foramen magnum. Measurements include: McGregor line (drawn from posterior hard palate to the most caudal point of the occiput — the tip of the dens should not project >4.5mm above this line), Redlund-Johnell measurement (distance from McGregor line to the midpoint of the inferior endplate of C2 — <34mm men or <29mm women is abnormal), and Ranawat criteria (distance from centre of C2 pedicle to a transverse axis of C1). MRI is essential to assess brainstem/cord compression.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Imaging",
          "range": "Q1423",
          "questions": [
            {
              "number": 1423,
              "stem": "The Torg (Pavlov) ratio is used to assess cervical spinal canal stenosis. It is calculated as:",
              "options": [
                "Canal diameter divided by disc height",
                "AP diameter of the canal divided by the AP diameter of the vertebral body (on lateral XR)",
                "Vertebral body height divided by canal width",
                "Spinous process length divided by body width",
                "ADI divided by SAC"
              ],
              "answer": "B",
              "explanation": "The Torg (Pavlov) ratio = AP diameter of the spinal canal / AP diameter of the vertebral body, measured on a lateral cervical radiograph. Normal ratio: ≥0.8 (or >1.0 in some references). A ratio <0.8 suggests relative stenosis and increased risk of cord injury from minor trauma or spondylotic changes. The ratio corrects for radiographic magnification (both measurements are affected equally). It was originally described in American football players to assess the risk of cervical cord neurapraxia (Stinger/transient quadriplegia). MRI is the definitive investigation for stenosis assessment — the Torg ratio is a screening tool only.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Fracture",
          "range": "Q1424",
          "questions": [
            {
              "number": 1424,
              "stem": "A Chance fracture is a flexion-distraction injury of the thoracolumbar spine. It is characteristically associated with:",
              "options": [
                "Seatbelt injuries (lap belt) in motor vehicle accidents",
                "Gunshot wounds",
                "Diving injuries",
                "Osteoporotic vertebral compression",
                "High-velocity sports"
              ],
              "answer": "A",
              "explanation": "A Chance fracture is a horizontal fracture through the vertebral body extending through the pedicles and posterior elements — a flexion-distraction injury caused by a fulcrum effect over a lap seatbelt during deceleration (MVA). The fracture line passes horizontally through bone (bony Chance) or through soft tissues (ligamentous equivalent — more unstable, poorer healing). It is strongly associated with intra-abdominal injuries (mesenteric tears, bowel perforation, pancreatic injury) in up to 50% of cases — always perform abdominal CT. Bony Chance fractures (through bone) may be treated in a TLSO/hyperextension brace if stable. Ligamentous injuries require surgical stabilisation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Cord Monitoring",
          "range": "Q1425",
          "questions": [
            {
              "number": 1425,
              "stem": "Intraoperative neuromonitoring during spinal surgery uses which combination of techniques?",
              "options": [
                "Only somatosensory evoked potentials (SSEPs)",
                "Only motor evoked potentials (MEPs)",
                "EEG only",
                "No monitoring is used in modern spinal surgery",
                "Combined SSEPs (monitoring dorsal columns/sensory) and MEPs (monitoring corticospinal/motor tracts)"
              ],
              "answer": "E",
              "explanation": "Combined SSEP + MEP monitoring is the current standard for intraoperative spinal cord monitoring during high-risk spinal surgery (deformity correction, tumour resection, cord decompression). SSEPs monitor the dorsal columns (proprioception/vibration pathway) by stimulating peripheral nerves and recording cortical responses — they detect sensory pathway injuries but can MISS isolated motor cord injury (anterior cord syndrome). MEPs monitor the corticospinal tracts (motor pathway) by stimulating the motor cortex and recording muscle responses — they detect motor cord injuries. Combined monitoring captures both pathways. A significant change (>50% amplitude drop or >10% latency increase) warrants immediate communication with the surgeon.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Disc Disease",
          "range": "Q1426",
          "questions": [
            {
              "number": 1426,
              "stem": "A posterolateral lumbar disc herniation at L4-L5 most commonly compresses which nerve root?",
              "options": [
                "L3",
                "L4",
                "S1",
                "L2",
                "L5 (the traversing root)"
              ],
              "answer": "E",
              "explanation": "A posterolateral disc herniation at L4-L5 compresses the L5 TRAVERSING nerve root (the root that is descending to exit at the next level below, L5-S1). The L4 root (EXITING root) exits above the disc at the L4-L5 foramen and is typically spared by a standard posterolateral herniation. A far lateral (foraminal) disc herniation at L4-L5 would compress the L4 EXITING root instead. This distinction is crucial: posterolateral herniation → traversing root. Far lateral herniation → exiting root. L5 root compression: weakness of ankle/great toe dorsiflexion (EHL, tibialis anterior), numbness on the dorsum of the foot and great toe, preserved ankle jerk (L5 has no reliable reflex).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Cord Syndrome",
          "range": "Q1427",
          "questions": [
            {
              "number": 1427,
              "stem": "Brown-Séquard syndrome (hemisection of the spinal cord) produces which pattern of deficit?",
              "options": [
                "Bilateral motor and sensory loss below the level",
                "Bilateral loss of pain and temperature with preserved motor function",
                "Ipsilateral motor loss and proprioception loss, with CONTRALATERAL pain and temperature loss (beginning 1-2 segments below the level)",
                "Complete loss of all function below the level",
                "Pure motor loss without sensory changes"
              ],
              "answer": "C",
              "explanation": "Brown-Séquard syndrome (cord hemisection) produces: (1) IPSILATERAL motor loss (corticospinal tract — already crossed at medullary pyramids, so damage below the decussation causes ipsilateral deficit). (2) IPSILATERAL loss of proprioception, vibration, and fine touch (dorsal columns — uncrossed at cord level, cross at medulla). (3) CONTRALATERAL loss of pain and temperature (spinothalamic tract — crosses in the cord 1-2 segments above, so contralateral loss begins 1-2 segments below the lesion). Brown-Séquard has the BEST prognosis of all incomplete cord syndromes — approximately 90% of patients regain independent ambulation. Most commonly caused by penetrating trauma (stab wounds), but also occurs with lateral cord compression (tumour, disc).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Disc",
          "range": "Q1428",
          "questions": [
            {
              "number": 1428,
              "stem": "A far lateral (foraminal) disc herniation at L4-L5 compresses which nerve root?",
              "options": [
                "L3",
                "L4 (the EXITING root at that level, not the traversing root)",
                "L5",
                "S1",
                "L2"
              ],
              "answer": "B",
              "explanation": "A far lateral (foraminal) disc herniation at L4-L5 compresses the L4 EXITING nerve root — the root that exits through the L4-L5 foramen (above the disc). This is DIFFERENT from a posterolateral disc at the same level, which would compress the L5 TRAVERSING root. This distinction is frequently tested and clinically critical: L4 root signs (quadriceps weakness, reduced knee jerk, anteromedial thigh/shin numbness) are different from L5 root signs (EHL weakness, foot dorsiflexion weakness, dorsal foot numbness, no reliable reflex). Far lateral herniations account for ~10% of lumbar disc herniations but are frequently missed on standard imaging if not specifically looked for. They may require a different surgical approach (far lateral approach rather than standard interlaminar/discectomy).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        }
      ]
    },
    {
      "title": "Foot & Ankle",
      "chapters": [
        {
          "title": "Deformity",
          "range": "Q1429-Q1431",
          "questions": [
            {
              "number": 1429,
              "stem": "Cavovarus foot deformity — the Coleman block test is used to determine:",
              "options": [
                "Whether the hindfoot varus is flexible (correctable) or rigid — by placing a block under the lateral forefoot to assess if the hindfoot corrects to neutral when the plantarflexed 1st ray is unloaded",
                "The severity of hallux valgus",
                "The degree of ankle arthritis",
                "The presence of a stress fracture",
                "Ligament laxity"
              ],
              "answer": "A",
              "explanation": "The Coleman block test differentiates FOREFOOT-DRIVEN hindfoot varus (flexible/correctable) from FIXED (rigid) hindfoot varus in cavovarus deformity. Technique: the patient stands with the lateral border of the foot on a 2.5cm block, allowing the plantarflexed 1st ray to drop off the edge (unloaded). If the hindfoot CORRECTS to neutral/valgus: the varus is forefoot-driven (the plantarflexed 1st ray is forcing the hindfoot into varus compensatorily — address the forefoot: 1st MT dorsiflexion osteotomy ± peroneus longus to brevis transfer). If the hindfoot REMAINS in varus: the deformity is fixed/rigid (the hindfoot itself is structurally deformed — requires calcaneal osteotomy: Dwyer lateral closing wedge or lateral slide). Most cavovarus is forefoot-driven. Causes: CMT (Charcot-Marie-Tooth — most common), cerebral palsy, sequelae of clubfoot, post-polio, idiopathic.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1430,
              "stem": "Hallux valgus (bunion) — the intermetatarsal angle (IMA) between the 1st and 2nd metatarsals is the key measurement for surgical planning. An IMA >15° typically indicates:",
              "options": [
                "Normal alignment",
                "Mild deformity treatable with distal osteotomy only",
                "No treatment needed",
                "Moderate to severe deformity requiring a proximal metatarsal osteotomy or Lapidus (1st TMT fusion) to correct the increased intermetatarsal divergence",
                "Only shoe modification"
              ],
              "answer": "D",
              "explanation": "Hallux valgus assessment (weight-bearing AP foot XR): (1) HVA (hallux valgus angle — between 1st MT and proximal phalanx): normal <15°, mild 15-30°, moderate 30-40°, severe >40°. (2) IMA (intermetatarsal angle — between 1st and 2nd MT axes): normal <9°, mild 9-13°, moderate 13-15°, severe >15°. The IMA guides the level of the corrective osteotomy: IMA <13° (mild): DISTAL osteotomy (chevron/scarf — corrects at the MT head level, limited correction ~5-7° IMA improvement). IMA 13-15° (moderate): SCARF osteotomy (versatile, moderate correction) or proximal osteotomy. IMA >15° (severe): PROXIMAL osteotomy (base of 1st MT — greater correction) or LAPIDUS procedure (1st TMT arthrodesis — corrects at the source of the deformity if 1st TMT joint hypermobility is present). Treatment: non-operative first (wide shoes, toe spacers, orthotics). Surgery: if symptomatic despite conservative measures.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1431,
              "stem": "A cavovarus foot deformity is most commonly associated with which underlying condition?",
              "options": [
                "Diabetes mellitus",
                "Rheumatoid arthritis",
                "Charcot-Marie-Tooth disease (CMT/hereditary motor sensory neuropathy)",
                "Osteoarthritis",
                "Gout"
              ],
              "answer": "C",
              "explanation": "Cavovarus foot (high arch + hindfoot varus) is most commonly caused by Charcot-Marie-Tooth disease (CMT/HMSN Type 1), a hereditary motor sensory neuropathy. The muscle imbalance (peroneus brevis weakens before tibialis posterior, and intrinsics weaken causing clawing) drives the deformity. Other causes: polio, spinal cord pathology (tethered cord, syringomyelia, Friedreich ataxia), cerebral palsy, and idiopathic. Coleman block test: determines whether the hindfoot varus is forefoot-driven (flexible, corrects when the 1st ray is allowed to drop off the block) or fixed (requires hindfoot osteotomy). Treatment: address muscle balance (tendon transfers) + correct bony deformity (calcaneal osteotomy, 1st MT osteotomy, midfoot osteotomy).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Trauma",
          "range": "Q1432-Q1434",
          "questions": [
            {
              "number": 1432,
              "stem": "A Jones fracture is a fracture of the:",
              "options": [
                "1st metatarsal base",
                "5th metatarsal tuberosity (avulsion — actually a different fracture, not Jones)",
                "Midshaft of the 3rd metatarsal",
                "Navicular",
                "Proximal diaphysis of the 5th metatarsal at the meta-diaphyseal junction (Zone II) — an area of vascular watershed prone to non-union"
              ],
              "answer": "E",
              "explanation": "The Jones fracture is a transverse fracture at the meta-diaphyseal junction of the 5th metatarsal (Zone II — at the junction of the proximal metaphysis and diaphysis, approximately 1.5cm distal to the tuberosity). It occurs in a VASCULAR WATERSHED area (between the proximal metaphyseal blood supply and the nutrient artery supply of the diaphysis) — this is why it has a high non-union rate (~25-30% with non-operative treatment). DO NOT confuse with: (1) 5th MT tuberosity avulsion fracture (Zone I — 'pseudo-Jones' or dancer's fracture, peroneus brevis avulsion, heals well non-operatively), (2) 5th MT diaphyseal stress fracture (Zone III — further distal, chronic stress fracture, also high non-union risk). Treatment: Jones fracture (Zone II) → non-operative in low-demand patients (NWB cast 6-8 weeks, high non-union risk), SURGICAL fixation recommended for athletes and active patients (intramedullary screw — high union rate ~95%).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1433,
              "stem": "A pilon fracture (tibial plafond fracture) typically results from:",
              "options": [
                "Twisting injury (like ankle fracture)",
                "Axial compression (high-energy — fall from height or RTA — driving the talus into the tibial plafond and shattering the articular surface)",
                "Direct lateral blow",
                "Stress fracture from running",
                "Avulsion injury"
              ],
              "answer": "B",
              "explanation": "Pilon fractures (tibial plafond/distal tibial articular fractures) result from AXIAL COMPRESSION forces — the talus is driven superiorly into the tibial plafond, shattering the articular surface. High-energy mechanisms: fall from height (most common), RTA (dashboard with feet on floorboard). The soft tissue envelope around the distal tibia is thin and vulnerable — high-energy pilon fractures cause significant soft tissue injury (swelling, blistering, open wounds). This is why the management strategy is typically STAGED: (1) Initial: spanning external fixator (delta frame or ankle-spanning) + fibula ORIF (restores length and alignment as a template), (2) Delay 10-14 days: allow soft tissue swelling to settle (wrinkle sign = ready for definitive surgery), (3) Definitive: ORIF of the tibial plafond through an appropriate approach (anterolateral or posteromedial) with articular reduction + metaphyseal fixation. CT is ESSENTIAL for operative planning. Direct ORIF in the acute setting through swollen tissue → wound complications (dehiscence, infection) in up to 30-40%.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1434,
              "stem": "A Lisfranc injury involves disruption of the tarsometatarsal joint complex. The key ligament that stabilises this joint is the:",
              "options": [
                "Lisfranc ligament — a strong oblique ligament running from the medial cuneiform to the base of the 2nd metatarsal (there is NO intermetatarsal ligament between the 1st and 2nd MT bases — making this the weak point)",
                "Spring ligament",
                "Deltoid ligament",
                "Calcaneofibular ligament",
                "Bifurcate ligament"
              ],
              "answer": "A",
              "explanation": "The Lisfranc ligament is the strongest of the tarsometatarsal ligaments — it runs obliquely from the lateral surface of the medial cuneiform to the plantar base of the 2nd metatarsal. Critically, there is NO intermetatarsal ligament connecting the 1st and 2nd metatarsal bases — the Lisfranc ligament is the ONLY structure bridging this gap. When it ruptures, the 2nd MT base can displace laterally from the medial cuneiform, destabilising the entire tarsometatarsal complex. Clinical: often missed on initial XR (~20% missed). Subtle signs: fleck sign (small avulsion fracture between 1st and 2nd MT bases — pathognomonic), widening >2mm between 1st and 2nd MT bases on AP XR, disruption of the 2nd MT-middle cuneiform line on AP and the 4th MT-cuboid line on oblique. Weight-bearing XR essential for subtle injuries. Treatment: undisplaced stable → cast/boot. Displaced/unstable → ORIF (anatomical reduction of the medial column is critical) or primary arthrodesis (emerging evidence favours fusion for purely ligamentous injuries).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Surgery",
          "range": "Q1435",
          "questions": [
            {
              "number": 1435,
              "stem": "Ankle arthrodesis (fusion) is considered the gold standard treatment for end-stage ankle arthritis. The optimal fusion position is:",
              "options": [
                "Plantarflexion and varus",
                "Maximum dorsiflexion and valgus",
                "Full equinus",
                "Neutral dorsiflexion (0-5° DF), 5° hindfoot valgus, 5-10° external rotation, and slight posterior translation of the talus",
                "Any position — it doesn't matter"
              ],
              "answer": "D",
              "explanation": "The optimal ankle fusion position balances function and gait: (1) Neutral dorsiflexion or 0-5° DF (allows heel strike and foot clearance during swing — excessive equinus causes toe walking, excessive DF causes back-knee thrust). (2) 5° hindfoot VALGUS (normal physiological valgus — varus causes lateral border loading, pain, and instability). (3) 5-10° EXTERNAL ROTATION (matches the normal foot progression angle during gait — internal rotation causes toe-in gait). (4) Slight posterior translation of the talus (centres the talus under the tibial axis for optimal load transfer). Position is critical: a fusion in the wrong position is worse than the arthritis it replaced. Fusion rates: ~90-95% with modern techniques (arthroscopic or open, compression screws ± plate). Long-term consequence: increased stress on adjacent joints (subtalar, talonavicular) → accelerated adjacent joint degeneration (~70% at 20 years). Total ankle replacement (TAR): motion-preserving alternative for lower-demand patients (expanding indications but higher revision rates than TKA/THA).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Tendon",
          "range": "Q1436-Q1441",
          "questions": [
            {
              "number": 1436,
              "stem": "Tibialis posterior tendon dysfunction (TPTD) is the most common cause of acquired adult flatfoot. The Johnson-Strom classification Stage II is characterised by:",
              "options": [
                "Tenosynovitis with normal tendon length (Stage I)",
                "Rigid hindfoot valgus deformity with subtalar arthritis (Stage III)",
                "Elongated/degenerate tendon with flexible hindfoot valgus deformity (the tendon is functionally incompetent, the foot can still be passively corrected to normal alignment)",
                "Rigid valgus with ankle arthritis (Stage IV)",
                "Normal tendon and foot"
              ],
              "answer": "C",
              "explanation": "Johnson-Strom TPTD staging: Stage I = tenosynovitis, tendon length NORMAL, no deformity (pain + swelling along the medial ankle/tendon, single-leg heel raise possible but painful). Treatment: orthotics (UCBL/Arizona brace), physiotherapy (tibialis posterior strengthening), ± tenosynovectomy. Stage II = tendon ELONGATED/degenerate (may be partially torn), FLEXIBLE hindfoot valgus, forefoot abduction, arch collapse. Single-leg heel raise WEAK or IMPOSSIBLE. Can still be passively corrected. Treatment: FDL (flexor digitorum longus) tendon transfer + medial displacement calcaneal osteotomy ± spring ligament repair ± lateral column lengthening (Evans). Stage III = RIGID hindfoot valgus with subtalar arthritis. Cannot be passively corrected. Treatment: triple arthrodesis (talonavicular, subtalar, calcaneocuboid). Stage IV (added by Myerson) = Stage III + ANKLE VALGUS tilt (deltoid incompetence). Treatment: triple arthrodesis + deltoid reconstruction or pantalar fusion.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1437,
              "stem": "Acute Achilles tendon rupture — the Simmonds (Thompson) test involves:",
              "options": [
                "Palpating for tenderness along the tendon only",
                "Testing ankle dorsiflexion strength",
                "Assessing the knee reflex",
                "Checking for swelling behind the heel",
                "Squeezing the calf with the patient prone and knee flexed — normally this plantar-flexes the foot; ABSENCE of plantarflexion indicates rupture"
              ],
              "answer": "E",
              "explanation": "The Simmonds (Thompson) test: the patient lies PRONE with feet hanging off the end of the bed. The examiner SQUEEZES the calf muscles. Normal response: the foot PLANTARFLEXES (because squeezing the gastrocnemius-soleus complex transmits force through the intact Achilles tendon). Positive test (rupture): NO plantarflexion occurs when the calf is squeezed — the tendon is disrupted and cannot transmit force. Additional signs of Achilles rupture: palpable gap in the tendon (~2-6cm above the calcaneal insertion — the watershed zone), increased passive dorsiflexion compared to the other side, and inability to perform a single-leg heel raise. Treatment: non-operative (functional rehabilitation with early weight-bearing in an equinus boot, sequential wedge removal — Exeter protocol) OR operative (open or minimally invasive repair). Meta-analyses show similar re-rupture rates (~5%) for operative and non-operative treatment with modern functional protocols. Operative: lower re-rupture rate (~2-3%) but higher wound complication risk (~5-10%). Young/athletic patients may benefit from surgical repair.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1438,
              "stem": "Peroneal tendon subluxation/dislocation occurs with rupture of which structure?",
              "options": [
                "Superior peroneal retinaculum",
                "Achilles tendon",
                "Posterior tibial tendon",
                "Inferior extensor retinaculum",
                "Plantar fascia"
              ],
              "answer": "A",
              "explanation": "The superior peroneal retinaculum (SPR) holds the peroneal tendons (peroneus longus and brevis) in the retromalleolar groove behind the lateral malleolus. Rupture or avulsion of the SPR (typically from a forced dorsiflexion-eversion injury, common in skiing) allows the tendons to sublux or dislocate anteriorly over the lateral malleolus. This is often misdiagnosed as an ankle sprain. Treatment: acute → immobilisation in cast (may heal). Recurrent → surgical repair/reconstruction of the SPR ± groove deepening.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1439,
              "stem": "Rupture of the tibialis posterior tendon results in which clinical finding?",
              "options": [
                "High-arched (cavus) foot",
                "Foot drop",
                "Equinus deformity",
                "Unilateral acquired flatfoot with inability to perform single heel-rise",
                "Claw toes only"
              ],
              "answer": "D",
              "explanation": "Tibialis posterior is the primary dynamic stabiliser of the medial longitudinal arch. Its rupture or degeneration leads to acquired flatfoot (arch collapse), hindfoot valgus, and forefoot abduction. The patient cannot perform a single heel-rise on the affected side (or it is weak and asymmetric). The 'too many toes' sign is positive (more toes visible laterally when viewed from behind due to forefoot abduction). Johnson-Strom classification guides treatment. This is the most common cause of adult acquired flatfoot.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1440,
              "stem": "Peroneus brevis tendon tears are most commonly found at which location?",
              "options": [
                "Musculotendinous junction",
                "At or just below the fibular tip (retrofibular groove — compressed between peroneus longus and the fibula)",
                "At the cuboid tunnel",
                "At the base of the 5th metatarsal",
                "In the mid-calf"
              ],
              "answer": "B",
              "explanation": "Peroneus brevis tears most commonly occur in the retrofibular groove at or just below the tip of the fibula. At this location, the peroneus brevis tendon is compressed between the peroneus longus tendon (posteriorly) and the posterior surface of the fibula (anteriorly). The tendon wraps around the fibular tip in this groove (held by the superior peroneal retinaculum). Chronic lateral ankle instability leads to repetitive subluxation of the tendons over the fibular tip → peroneus brevis develops longitudinal split tears. A peroneus quartus (accessory peroneal muscle, present in ~10-20%) or a prominent peroneal tubercle can also contribute. The tear is typically a longitudinal split (not a transverse rupture). Treatment: debridement of degenerate tissue + tubularisation of the remaining tendon ± groove deepening. If >50% of the tendon is affected: consider tenodesis to peroneus longus.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1441,
              "stem": "The Achilles tendon is formed by the combined tendons of which muscles?",
              "options": [
                "Tibialis posterior and FHL",
                "Peroneus longus and brevis",
                "Tibialis anterior and EHL",
                "Gastrocnemius and soleus (triceps surae)",
                "Quadriceps femoris"
              ],
              "answer": "D",
              "explanation": "The Achilles tendon (calcaneal tendon) is formed by the combined tendons of the gastrocnemius (two heads — medial and lateral, crossing the knee and ankle) and the soleus (crosses the ankle only). Together these are called the triceps surae. Plantaris (a vestigial muscle) also contributes a small tendinous slip. The Achilles is the strongest and thickest tendon in the body, transmitting forces up to 12× body weight during running. The Silfverskiöld test differentiates gastrocnemius tightness (equinus that corrects with knee flexion, as gastrocnemius is relaxed) from combined gastrocnemius-soleus tightness (equinus persists in knee flexion).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Arthroplasty",
          "range": "Q1442",
          "questions": [
            {
              "number": 1442,
              "stem": "Total ankle replacement (TAR) compared to ankle fusion — the main advantage of TAR is:",
              "options": [
                "TAR is always superior in all patient groups",
                "TAR has better long-term survival than hip or knee replacement",
                "Preservation of ankle motion (reducing stress on adjacent joints and potentially lowering the rate of adjacent joint degeneration compared to fusion)",
                "TAR is cheaper",
                "TAR never needs revision"
              ],
              "answer": "C",
              "explanation": "TAR preserves ankle joint motion (average ~25-30° arc post-TAR vs 0° after fusion), which theoretically reduces stress on adjacent joints (subtalar, talonavicular) and may lower the rate of adjacent joint degeneration (a significant long-term problem after ankle fusion — ~70% at 20 years). However: TAR has HIGHER revision rates than THA/TKA (~10-year survival 78-90% for TAR vs ~95-97% for THA/TKA) and is technically more demanding. Complications: aseptic loosening, subsidence, bearing wear, wound complications (thin soft tissue envelope), and fracture. Ideal TAR candidate: lower-demand patient (>55 years), good bone quality, no significant deformity (<15° varus/valgus), intact soft tissue envelope, BMI <30. Modern TAR designs (3rd generation — STAR, Infinity, Salto Talaris) have improved outcomes but still lag behind hip/knee arthroplasty. Ankle fusion remains the gold standard for younger, active, heavy patients, and those with significant deformity or bone loss.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Nerve",
          "range": "Q1443",
          "questions": [
            {
              "number": 1443,
              "stem": "Morton's neuroma is a compression neuropathy of the:",
              "options": [
                "Common digital nerve, most frequently in the THIRD web space (between the 3rd and 4th metatarsal heads) — causing forefoot pain, numbness, and a clicking sensation",
                "Tibial nerve at the ankle",
                "Sural nerve",
                "Saphenous nerve",
                "Deep peroneal nerve"
              ],
              "answer": "A",
              "explanation": "Morton's neuroma (more accurately an interdigital neuroma or perineural fibrosis) is NOT a true neuroma — it is perineural fibrosis and degeneration of the common digital nerve as it passes beneath the intermetatarsal ligament between the metatarsal heads. The THIRD web space (between 3rd and 4th MT heads) is most commonly affected (~65-70%), followed by the second web space (~25-30%). Symptoms: forefoot pain (burning, shooting, electric — worsened by tight shoes and walking, relieved by removing shoes and massaging the foot), numbness/tingling in the affected web space. Clinical tests: Mulder click (squeeze the forefoot while simultaneously compressing the affected web space — a palpable/audible click indicates the neuroma popping between the metatarsal heads). Treatment: wide shoes, metatarsal pad (placed PROXIMAL to the metatarsal heads to offload), corticosteroid injection (50-70% improvement), US-guided injection. Surgery: neurectomy (excision of the affected nerve segment — ~80% good results, but leaves permanent numbness in the web space).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Soft Tissue",
          "range": "Q1444",
          "questions": [
            {
              "number": 1444,
              "stem": "Plantar fasciitis — the most effective first-line treatment is:",
              "options": [
                "Immediate surgery",
                "Stretching exercises (Achilles tendon and plantar fascia stretching — particularly the Digiovanni protocol of plantar fascia-specific stretching, combined with supportive footwear and activity modification)",
                "Only rest without any exercise",
                "IV antibiotics",
                "Casting for 12 weeks"
              ],
              "answer": "B",
              "explanation": "Plantar fasciitis is the most common cause of plantar heel pain (~80%). It is a degenerative enthesopathy of the plantar fascia origin at the medial calcaneal tuberosity (NOT inflammation — histology shows collagen degeneration without inflammatory cells). Classic symptom: START-UP PAIN — severe heel pain with the first few steps in the morning or after sitting (the fascia contracts during rest and is painfully stretched on initial weight-bearing). Treatment (90% resolve within 12-18 months with conservative measures): (1) STRETCHING (most important — Achilles + plantar fascia-specific stretching: Digiovanni protocol — cross leg, pull toes into dorsiflexion, stretch the arch × 10 repetitions, 3 times daily). (2) Supportive footwear (cushioned heel, arch support). (3) NSAIDs short course. (4) Night splint (maintains fascia in stretched position overnight). (5) Corticosteroid injection (short-term relief, risk of fat pad atrophy + fascia rupture with repeated injections). (6) ESWT (extracorporeal shockwave therapy — evidence for refractory cases). Surgery (rare, <5%): partial plantar fasciotomy.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Neuroarthropathy",
          "range": "Q1445",
          "questions": [
            {
              "number": 1445,
              "stem": "Charcot neuroarthropathy (diabetic Charcot foot) in the acute stage presents with:",
              "options": [
                "A cold, pale, pulseless foot",
                "Only bony deformity without any swelling",
                "No clinical signs",
                "Blue discolouration only",
                "A hot, swollen, erythematous foot that mimics infection (but without systemic sepsis markers or wound — the key is to differentiate from osteomyelitis/cellulitis, which can be extremely difficult)"
              ],
              "answer": "E",
              "explanation": "Acute Charcot neuroarthropathy presents as a RED, HOT, SWOLLEN foot in a patient with peripheral neuropathy (most commonly diabetic) — mimicking infection. The key challenge: differentiating Charcot from osteomyelitis/cellulitis (both can coexist). Clinical clues for Charcot: (1) absent/minimal pain (neuropathy → patient doesn't feel the inflammation), (2) no wound/ulcer overlying the swelling, (3) no systemic sepsis markers (normal WCC, only mildly elevated CRP — though ESR may be elevated in both), (4) good pulses (Charcot patients typically have intact vascular supply). MRI: can be difficult (both Charcot and infection show marrow oedema). Eichenholtz staging: Stage 0 = pre-clinical (hot foot, normal XR), Stage 1 = fragmentation (joint destruction, debris), Stage 2 = coalescence (healing, sclerosis, bone formation), Stage 3 = consolidation/remodelling (stable deformity). Treatment: ACUTE — total contact cast (TCC) or removable walker until the acute phase resolves (foot temperature equals contralateral side → healing). AVOID surgery in the acute phase (bone is too soft for fixation). Chronic: if deformity causes plantar bony prominence → ulceration → reconstructive surgery (midfoot fusion).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Ankle Arthroplasty",
          "range": "Q1446",
          "questions": [
            {
              "number": 1446,
              "stem": "The main advantage of total ankle arthroplasty (TAA) over ankle arthrodesis is:",
              "options": [
                "Lower complication rate",
                "Preservation of ankle joint motion",
                "Better long-term survival",
                "Lower cost",
                "No risk of loosening"
              ],
              "answer": "B",
              "explanation": "TAA preserves ankle joint motion, which may reduce stress on adjacent joints (subtalar, talonavicular, calcaneocuboid) and potentially slow the progression of adjacent joint arthritis. Ankle arthrodesis provides reliable pain relief but eliminates ankle motion and transfers stress to adjacent joints (with reported rates of adjacent joint arthritis up to 70% at 22 years). Modern 3rd-generation TAA designs (3-component mobile-bearing) show improved survivorship (78–80% at 10 years), but complications remain significant.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Tarsal Coalition",
          "range": "Q1447",
          "questions": [
            {
              "number": 1447,
              "stem": "The most common type of tarsal coalition is:",
              "options": [
                "Calcaneocuboid",
                "Talonavicular",
                "Talocalcaneal",
                "Cubonavicular",
                "Calcaneonavicular"
              ],
              "answer": "E",
              "explanation": "Calcaneonavicular coalition is the most common type (~53%), followed by talocalcaneal (middle facet) coalition (~37%). Tarsal coalition is an abnormal bony, cartilaginous, or fibrous connection between tarsal bones that restricts subtalar motion. It typically presents in adolescence (when ossification occurs) with a rigid painful flatfoot and limited subtalar motion. The C-sign on lateral radiograph and anteater nose on oblique view suggest calcaneonavicular coalition. CT or MRI confirms the diagnosis.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Lesser Toes",
          "range": "Q1448",
          "questions": [
            {
              "number": 1448,
              "stem": "A hammer toe deformity is characterised by:",
              "options": [
                "MTP hyperextension, PIP flexion, DIP extension",
                "MTP extension, PIP extension, DIP flexion",
                "MTP flexion, PIP flexion, DIP flexion",
                "MTP neutral, PIP hyperextension, DIP flexion",
                "MTP extension, PIP flexion, DIP flexion"
              ],
              "answer": "A",
              "explanation": "Hammer toe: MTP hyperextension (dorsal subluxation), PIP flexion (the dominant deformity), DIP extension or neutral. Claw toe: MTP hyperextension, PIP flexion, AND DIP flexion (involves both IP joints). Mallet toe: isolated DIP flexion with normal MTP and PIP. Understanding these three patterns and their differences is regularly tested.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Anatomy",
          "range": "Q1449",
          "questions": [
            {
              "number": 1449,
              "stem": "The spring ligament (calcaneonavicular ligament) supports which structure?",
              "options": [
                "Lateral malleolus",
                "Achilles tendon",
                "Cuboid",
                "Head of the talus (maintains the medial longitudinal arch)",
                "5th metatarsal"
              ],
              "answer": "D",
              "explanation": "The spring ligament (plantar calcaneonavicular ligament) extends from the sustentaculum tali of the calcaneus to the navicular, forming a fibrocartilaginous sling that supports the HEAD OF THE TALUS. It is a critical component of the medial longitudinal arch and is supported dynamically by the tibialis posterior tendon (which inserts partially into the navicular and the spring ligament). Failure of the spring ligament (often in combination with tibialis posterior tendon dysfunction) leads to acquired adult flatfoot deformity — the talar head drops plantarly and medially, collapsing the arch. Treatment of acquired flatfoot addresses both the tibialis posterior (FDL transfer) and the spring ligament (reconstruction or augmentation) along with corrective osteotomies.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Achilles",
          "range": "Q1450-Q1451",
          "questions": [
            {
              "number": 1450,
              "stem": "The Achilles tendon is the strongest tendon in the body. It most commonly ruptures at which location?",
              "options": [
                "Calcaneal insertion",
                "Musculotendinous junction",
                "2-6 cm proximal to the calcaneal insertion (watershed zone)",
                "Mid-tendon (10 cm from insertion)",
                "At the level of the ankle joint"
              ],
              "answer": "C",
              "explanation": "The Achilles tendon most commonly ruptures 2-6 cm proximal to the calcaneal insertion in the 'watershed zone' — an area of relative hypovascularity (blood supply from both the musculotendinous junction and the calcaneal insertion creates a watershed area in between). This hypovascularity predisposes to degeneration and rupture. Risk factors: age 30-50, male, recreational athletes ('weekend warriors'), fluoroquinolone antibiotics, corticosteroid injections, prior tendinopathy.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1451,
              "stem": "The management of acute Achilles tendon rupture — the most important clinical test is:",
              "options": [
                "Ankle radiograph",
                "Simmonds-Thompson test (calf squeeze test — absence of passive plantarflexion when the calf is squeezed confirms rupture)",
                "MRI (always required before deciding treatment)",
                "Blood tests",
                "Nerve conduction studies"
              ],
              "answer": "B",
              "explanation": "The Simmonds-Thompson test (calf squeeze test) is the most important clinical test for Achilles tendon rupture. With the patient prone and feet hanging off the bed, squeezing the calf should produce passive plantarflexion of the ankle. ABSENCE of plantarflexion = positive test = Achilles tendon rupture. It is highly sensitive and specific when performed correctly. Achilles rupture is a CLINICAL diagnosis — MRI is not routinely required (it may be used when the diagnosis is uncertain, or to assess the gap between tendon ends). USS can assess the gap in equinus position (guides whether non-operative management is appropriate). Treatment: non-operative (functional rehabilitation in an equinus boot with progressive dorsiflexion) or operative (open repair or percutaneous repair). Current evidence (UKSTAR trial): no significant difference in outcomes between operative and non-operative treatment with functional rehabilitation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Diabetic Foot",
          "range": "Q1452-Q1454",
          "questions": [
            {
              "number": 1452,
              "stem": "The most common site of diabetic foot ulceration is:",
              "options": [
                "Plantar surface of the metatarsal heads",
                "Heel",
                "Lateral border of the foot",
                "Dorsum of the toes",
                "Achilles tendon area"
              ],
              "answer": "A",
              "explanation": "The plantar surface beneath the metatarsal heads is the most common site of diabetic foot ulceration, particularly under the 1st and 2nd metatarsal heads. This is due to the combination of peripheral neuropathy (loss of protective sensation), motor neuropathy (intrinsic muscle wasting → claw toes → prominent metatarsal heads → increased plantar pressure), and autonomic neuropathy (dry skin, loss of sweating). The Wagner classification grades ulcer severity (0-5).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1453,
              "stem": "Charcot neuroarthropathy in the diabetic foot most commonly affects which area?",
              "options": [
                "Ankle joint",
                "Subtalar joint",
                "Tarsometatarsal (Lisfranc) joints",
                "Metatarsophalangeal joints",
                "Calcaneus"
              ],
              "answer": "C",
              "explanation": "The tarsometatarsal (Lisfranc) joints are the most commonly affected area in diabetic Charcot neuroarthropathy (~60% of cases). The Eichenholtz classification stages the process: Stage 0 = pre-Charcot (hot, swollen foot, normal XR); Stage I = development/fragmentation (joint destruction); Stage II = coalescence (healing begins); Stage III = reconstruction (remodelling/consolidation). Treatment centres on offloading (total contact cast) in acute phase and surgical reconstruction for deformity causing ulceration.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1454,
              "stem": "The diabetic foot is at risk of ulceration primarily because of:",
              "options": [
                "Only vascular disease",
                "Only infection",
                "Only poor footwear",
                "Only poor hygiene",
                "Peripheral neuropathy (loss of protective sensation) combined with deformity, vascular disease, and impaired wound healing"
              ],
              "answer": "E",
              "explanation": "The diabetic foot is at risk due to a combination of factors: (1) peripheral neuropathy (most important — loss of protective sensation means injuries are not felt, repetitive trauma causes tissue breakdown without pain warning). (2) Peripheral vascular disease (reduced blood flow impairs wound healing). (3) Motor neuropathy (intrinsic muscle wasting → claw toes → altered pressure distribution → callus → ulceration under metatarsal heads). (4) Autonomic neuropathy (loss of sweating → dry, cracked skin → entry points for infection). (5) Impaired immune function (poor neutrophil function, hyperglycaemia). The combination creates a cascade: neuropathy → unrecognised injury → ulcer → infection → potential amputation. Prevention: annual foot screening (sensation testing with 10g Semmes-Weinstein monofilament + pulse palpation), appropriate footwear, foot care education, regular podiatry.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Ankle Anatomy",
          "range": "Q1455-Q1456",
          "questions": [
            {
              "number": 1455,
              "stem": "The deltoid ligament is the primary medial stabiliser of the ankle. Its deep component primarily resists:",
              "options": [
                "Inversion",
                "Eversion",
                "Plantarflexion",
                "External rotation and lateral talar shift",
                "Dorsiflexion"
              ],
              "answer": "D",
              "explanation": "The deltoid ligament has superficial and deep components. The deep deltoid (anterior and posterior tibiotalar ligaments) is the primary restraint to lateral talar shift (widening of the medial clear space) and external rotation of the talus. It is the strongest ankle ligament. An isolated deltoid rupture without associated lateral or syndesmotic injury is uncommon. On stress views, medial clear space >4mm indicates deltoid injury. The superficial deltoid resists eversion.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1456,
              "stem": "The ankle syndesmosis is primarily stabilised by which ligament?",
              "options": [
                "Anterior inferior tibiofibular ligament (AITFL), posterior inferior tibiofibular ligament (PITFL), and interosseous membrane",
                "Deltoid ligament",
                "Anterior talofibular ligament",
                "Calcaneofibular ligament",
                "Spring ligament"
              ],
              "answer": "A",
              "explanation": "The ankle syndesmosis (the fibrous joint between the distal tibia and fibula) is stabilised by: (1) AITFL (anterior inferior tibiofibular ligament — weakest, tears first), (2) PITFL (posterior inferior tibiofibular ligament — strongest syndesmotic ligament), (3) interosseous membrane (IOM), and (4) transverse tibiofibular ligament (deep component of PITFL). Syndesmotic injuries are common in ankle fractures (especially Weber C/pronation-external rotation patterns) and high ankle sprains. Assessment: squeeze test, external rotation stress test. Fixation: syndesmotic screw(s) or suture button device if unstable after fracture fixation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Hallux Valgus",
          "range": "Q1457-Q1458",
          "questions": [
            {
              "number": 1457,
              "stem": "In hallux valgus, the hallux metatarsophalangeal angle (HVA) that defines a moderate deformity is approximately:",
              "options": [
                "<15°",
                "15–20°",
                "40–60°",
                ">60°",
                "20–40°"
              ],
              "answer": "E",
              "explanation": "Hallux valgus severity: mild = HVA 15–20° (IMA <11°), moderate = HVA 20–40° (IMA 11–16°), severe = HVA >40° (IMA >16°). The intermetatarsal angle (IMA) between the 1st and 2nd metatarsals is also important for surgical planning. Mild deformity may be treated with a distal metatarsal osteotomy (e.g., chevron). Moderate may need a proximal osteotomy (e.g., scarf, proximal crescentic). Severe may need a basal osteotomy or Lapidus (1st TMT fusion).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1458,
              "stem": "The intermetatarsal angle (IMA) in hallux valgus is measured between:",
              "options": [
                "The 1st metatarsal and the proximal phalanx",
                "The medial cuneiform and the 1st metatarsal",
                "The talus and the calcaneus",
                "The 1st and 2nd metatarsal shafts on a weight-bearing AP foot radiograph",
                "The 1st and 5th metatarsals"
              ],
              "answer": "D",
              "explanation": "The intermetatarsal angle (IMA) is measured between the longitudinal axes of the 1st and 2nd metatarsal shafts on a weight-bearing AP foot radiograph. Normal IMA: <9°. Mild hallux valgus: IMA 9-13°. Moderate: IMA 13-20°. Severe: IMA >20°. The hallux valgus angle (HVA) is measured between the 1st metatarsal and the proximal phalanx (normal <15°). These angles guide surgical decision-making: distal osteotomy (chevron/scarf) for mild-moderate HV with IMA <15-20°. Proximal osteotomy or Lapidus (1st TMT fusion) for severe HV with IMA >20°. MTP fusion (1st MTP arthrodesis) for severe deformity with OA.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Hallux Rigidus",
          "range": "Q1459",
          "questions": [
            {
              "number": 1459,
              "stem": "Hallux rigidus is osteoarthritis of which joint?",
              "options": [
                "First interphalangeal joint",
                "First tarsometatarsal joint",
                "First metatarsophalangeal joint",
                "Subtalar joint",
                "Ankle joint"
              ],
              "answer": "C",
              "explanation": "Hallux rigidus is OA of the 1st MTP joint, characterised by dorsal osteophytes (which limit dorsiflexion), pain, stiffness, and progressive loss of motion. It is the most common arthritic condition of the foot. Grading: mild = pain at extremes of motion, dorsal osteophyte; moderate = significant motion loss; severe = near-complete loss of motion. Treatment: stiff-soled shoes/rocker bottom → cheilectomy (dorsal osteophyte excision, good for mild-moderate) → 1st MTP fusion (gold standard for severe).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Adult Flatfoot",
          "range": "Q1460",
          "questions": [
            {
              "number": 1460,
              "stem": "Adult acquired flatfoot deformity is most commonly caused by dysfunction of which tendon?",
              "options": [
                "Achilles tendon",
                "Tibialis posterior",
                "Peroneus longus",
                "Tibialis anterior",
                "Flexor hallucis longus"
              ],
              "answer": "B",
              "explanation": "Tibialis posterior tendon dysfunction (TPTD) is the most common cause of adult acquired flatfoot. The tibialis posterior is the primary dynamic stabiliser of the medial longitudinal arch. Progressive tendon degeneration leads to arch collapse, hindfoot valgus, and forefoot abduction. Johnson and Strom classification: Stage I = tendinopathy without deformity; Stage II = flexible flatfoot; Stage III = fixed flatfoot; Stage IV (added by Myerson) = + ankle valgus.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Cavus Foot",
          "range": "Q1461",
          "questions": [
            {
              "number": 1461,
              "stem": "The most common neurological cause of pes cavus is:",
              "options": [
                "Cerebral palsy",
                "Poliomyelitis",
                "Friedreich ataxia",
                "Charcot-Marie-Tooth disease (CMT/HMSN)",
                "Spinal cord tumour"
              ],
              "answer": "D",
              "explanation": "Charcot-Marie-Tooth disease (hereditary motor and sensory neuropathy, HMSN) is the most common neurological cause of pes cavus. The cavus foot develops due to imbalance between the intrinsic (weak) and extrinsic muscles: peroneus longus overpowers the weak tibialis anterior, causing forefoot-driven cavus with a plantarflexed 1st ray. All patients with bilateral cavus feet should be investigated for an underlying neurological cause. The Coleman block test determines whether the hindfoot varus is forefoot-driven (flexible) or fixed.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Achilles Tendon",
          "range": "Q1462",
          "questions": [
            {
              "number": 1462,
              "stem": "The Thompson (Simmonds) test for Achilles tendon rupture is performed by:",
              "options": [
                "Asking the patient to stand on tiptoes",
                "Palpating for a gap in the tendon",
                "Dorsiflexing the ankle against resistance",
                "Testing knee flexion in prone position",
                "Squeezing the calf with the patient prone — observing for absence of plantarflexion"
              ],
              "answer": "E",
              "explanation": "The Thompson (Simmonds) test: patient lies prone with feet over the edge of the bed. The examiner squeezes the calf. In a normal tendon, this produces passive plantarflexion. With a complete rupture, the foot does not plantarflex (positive test). It is the most reliable clinical test for complete Achilles tendon rupture. Other signs: palpable gap in the tendon, increased passive dorsiflexion (Matles test), and loss of resting tendon tension.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Morton Neuroma",
          "range": "Q1463",
          "questions": [
            {
              "number": 1463,
              "stem": "Morton neuroma most commonly occurs in which web space of the foot?",
              "options": [
                "First (between 1st and 2nd toes)",
                "Second (between 2nd and 3rd toes)",
                "Third (between 3rd and 4th toes)",
                "Fourth (between 4th and 5th toes)",
                "Equally in all spaces"
              ],
              "answer": "C",
              "explanation": "Morton neuroma (interdigital neuroma) most commonly occurs in the third web space (between the 3rd and 4th metatarsal heads), followed by the second web space. It is not a true neuroma but a perineural fibrosis of the common digital nerve caused by compression between the metatarsal heads. Symptoms: burning pain in the forefoot radiating to the toes, worse with tight shoes, relieved by removing shoes and massaging the foot. Mulder click (palpable click on lateral compression of the forefoot) is the clinical test.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Ankle Fracture",
          "range": "Q1464-Q1465",
          "questions": [
            {
              "number": 1464,
              "stem": "The Lauge-Hansen classification of ankle fractures is based on the mechanism of injury. The most common type is:",
              "options": [
                "Pronation-external rotation (PER)",
                "Supination-external rotation (SER)",
                "Supination-adduction (SA)",
                "Pronation-abduction (PA)",
                "Pronation-dorsiflexion"
              ],
              "answer": "B",
              "explanation": "SER (supination-external rotation) is the most common Lauge-Hansen pattern (~40-75% of ankle fractures). It produces a progressive injury sequence: Stage I = AITFL disruption. Stage II = oblique/spiral fibular fracture at or below the syndesmosis (Weber B). Stage III = posterior malleolus fracture or PITFL disruption. Stage IV = deltoid ligament rupture or medial malleolus fracture. Understanding the mechanism helps predict the extent of injury — if you see the fibular fracture (Stage II), look for evidence of Stages III and IV.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1465,
              "stem": "An isolated undisplaced lateral malleolus fracture below the syndesmosis (Weber A) is typically caused by which mechanism?",
              "options": [
                "Supination-adduction (inversion)",
                "Pronation-external rotation",
                "Pronation-abduction",
                "Vertical compression",
                "Hyperextension"
              ],
              "answer": "A",
              "explanation": "Weber A fractures occur BELOW the ankle syndesmosis and are caused by a supination-adduction (inversion) mechanism — the lateral ligaments fail first, then the fibula fractures by avulsion at or below the level of the tibial plafond. The syndesmosis is INTACT, making these injuries stable. Treatment: symptomatic (walking boot or below-knee cast, weight-bearing as tolerated). Prognosis is excellent. Weber B: at the syndesmosis level (SER mechanism, stability depends on medial side). Weber C: above the syndesmosis (PER mechanism, always unstable — syndesmosis disrupted).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Lisfranc",
          "range": "Q1466-Q1467",
          "questions": [
            {
              "number": 1466,
              "stem": "The Lisfranc ligament connects which two bones?",
              "options": [
                "Medial cuneiform to the base of the 2nd metatarsal",
                "Navicular to cuboid",
                "Calcaneus to navicular",
                "Talus to 1st metatarsal",
                "Cuboid to 5th metatarsal"
              ],
              "answer": "A",
              "explanation": "The Lisfranc ligament is a strong interosseous ligament connecting the medial (1st) cuneiform to the base of the 2nd metatarsal. It is the key stabiliser of the tarsometatarsal (Lisfranc) joint complex. There is no ligament connecting the 1st and 2nd metatarsal bases directly — the Lisfranc ligament serves this role. Injury disrupts the tarsometatarsal alignment. Weight-bearing radiographs showing >2mm diastasis between the 1st and 2nd MT bases or malalignment of the 2nd MT with the middle cuneiform confirm the injury.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1467,
              "stem": "The Lisfranc joint complex is the articulation between the:",
              "options": [
                "Talus and calcaneus (subtalar)",
                "Metatarsal heads and proximal phalanges (MTP joints)",
                "Navicular and cuneiforms",
                "Tarsals and metatarsal bases (tarsometatarsal joints)",
                "Cuboid and calcaneus"
              ],
              "answer": "D",
              "explanation": "The Lisfranc joint is the tarsometatarsal (TMT) joint complex — the articulation between the tarsal bones (3 cuneiforms + cuboid) and the bases of the 5 metatarsals. The Lisfranc ligament is the key stabiliser — it connects the medial cuneiform to the base of the 2nd metatarsal (there is NO intermetatarsal ligament between the 1st and 2nd MT bases, making this the weakest link). Lisfranc injuries range from subtle sprains to complete fracture-dislocations. They are frequently missed (up to 20% initially) — leading to chronic pain and midfoot arthritis. Weight-bearing radiographs are essential. The fleck sign (avulsion of the Lisfranc ligament) is pathognomonic. Treatment: anatomical ORIF or primary fusion (purely ligamentous injuries may do better with primary fusion).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Ankle Instability",
          "range": "Q1468",
          "questions": [
            {
              "number": 1468,
              "stem": "The most commonly injured ligament in an ankle sprain is the:",
              "options": [
                "Deltoid ligament",
                "Posterior talofibular ligament (PTFL)",
                "Calcaneofibular ligament (CFL)",
                "Spring ligament",
                "Anterior talofibular ligament (ATFL)"
              ],
              "answer": "E",
              "explanation": "The ATFL is the most commonly injured ligament in ankle sprains (~85% of ankle sprains are lateral/inversion injuries). The ATFL is the weakest of the three lateral ligaments and is taut in plantarflexion and inversion — the typical mechanism of injury. The sequence of injury with increasing severity: ATFL alone (Grade I-II) → ATFL + CFL (Grade II-III) → ATFL + CFL + PTFL (Grade III — severe instability). The PTFL is the strongest lateral ligament and is rarely injured in isolation. Treatment: most ankle sprains respond to functional rehabilitation (early mobilisation, physiotherapy).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Metatarsal",
          "range": "Q1469",
          "questions": [
            {
              "number": 1469,
              "stem": "A stress fracture of the proximal 5th metatarsal diaphysis (Jones fracture) is at high risk of non-union because:",
              "options": [
                "It is always an open fracture",
                "The diaphyseal region has a watershed area of poor blood supply",
                "The patient is always diabetic",
                "The fracture is intra-articular",
                "It is caused by infection"
              ],
              "answer": "B",
              "explanation": "The Jones fracture (stress or acute fracture at the proximal 5th MT metaphyseal-diaphyseal junction, Zone 2) is at high risk of non-union and refracture because this area is a vascular watershed zone between the diaphyseal nutrient artery and the metaphyseal blood supply. Lawrence and Botte classified proximal 5th MT fractures into: Zone 1 = tuberosity avulsion (peroneus brevis, heals well non-operatively). Zone 2 = Jones fracture (metaphyseal-diaphyseal junction, high non-union risk). Zone 3 = diaphyseal stress fracture (highest non-union risk). Athletes with Zone 2-3 fractures are often treated with intramedullary screw fixation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Plantar Fasciitis",
          "range": "Q1470",
          "questions": [
            {
              "number": 1470,
              "stem": "Plantar fasciitis classically presents with heel pain that is:",
              "options": [
                "Worst at night and relieved by walking",
                "Constant throughout the day without variation",
                "Worst with the first steps in the morning and after rest, improving with activity",
                "Only present during running",
                "Associated with visible swelling and erythema"
              ],
              "answer": "C",
              "explanation": "Plantar fasciitis (plantar fasciopathy) classically presents with 'start-up pain' — pain with the first steps in the morning or after prolonged sitting, which improves with activity but may worsen again with prolonged standing/walking. The pain is typically at the medial calcaneal tubercle (origin of the plantar fascia). Risk factors: obesity, pes planus/cavus, tight Achilles, prolonged standing occupations. Treatment: stretching (calf and plantar fascia), orthotics, NSAIDs, night splints, steroid injection (risk of fat pad atrophy/rupture), shockwave therapy. ~90% resolve with non-operative treatment within 12 months.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Stress Fracture",
          "range": "Q1471",
          "questions": [
            {
              "number": 1471,
              "stem": "The most common site for a stress fracture in a military recruit or runner is:",
              "options": [
                "Femoral neck",
                "Calcaneus",
                "Navicular",
                "Tibial shaft (posteromedial cortex)",
                "5th metatarsal base"
              ],
              "answer": "D",
              "explanation": "The tibial shaft (particularly the posteromedial cortex of the proximal-middle tibia) is the most common site for stress fractures overall (~50% of all stress fractures), particularly in military recruits and runners. They result from repetitive submaximal loading exceeding the bone's capacity for remodelling. Presentation: localised pain worse with activity, relieved by rest, progressing to pain at rest if not addressed. Plain radiographs may be normal initially — MRI is the gold standard for early detection (bone marrow oedema before cortical changes). High-risk sites (require aggressive management): femoral neck (tension side), navicular, anterior tibial cortex, 5th MT (Jones), sesamoids.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Pes Planus",
          "range": "Q1472",
          "questions": [
            {
              "number": 1472,
              "stem": "A flexible flatfoot in a child is differentiated from a rigid flatfoot by:",
              "options": [
                "The arch is absent in both weight-bearing and non-weight-bearing",
                "The arch reconstitutes on tiptoeing or when the great toe is dorsiflexed (Jack test)",
                "The subtalar joint is completely fixed",
                "Neurological signs are present",
                "It always requires surgical treatment"
              ],
              "answer": "B",
              "explanation": "In a flexible (physiological) flatfoot, the arch is absent on weight-bearing but reconstitutes when the child stands on tiptoes (heel inverts into varus) or when the great toe is dorsiflexed (Jack test/Hubscher manoeuvre — windlass mechanism reconstitutes the arch by tightening the plantar fascia). In a rigid flatfoot, the arch does NOT reconstitute on tip-toe and subtalar motion is restricted. Causes of rigid flatfoot: tarsal coalition, congenital vertical talus, inflammatory arthritis, tibialis posterior dysfunction. Flexible flatfoot in children is usually physiological and requires no treatment. Rigid flatfoot always needs investigation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Paediatric",
          "range": "Q1473",
          "questions": [
            {
              "number": 1473,
              "stem": "Freiberg disease is avascular necrosis of which metatarsal head?",
              "options": [
                "1st metatarsal head",
                "3rd metatarsal head",
                "2nd metatarsal head (most commonly)",
                "4th metatarsal head",
                "5th metatarsal head"
              ],
              "answer": "C",
              "explanation": "Freiberg disease (Freiberg infraction) is AVN of the metatarsal head, most commonly the 2nd metatarsal head (~68%). It typically affects adolescent girls (12-18 years) and presents with forefoot pain and swelling localised to the affected MTP joint. Radiographically: flattening, sclerosis, and collapse of the metatarsal head with joint widening. Smillie classified stages I-V (I=fissure fracture, V=articular destruction + loose bodies). Treatment: stiff-soled shoes + metatarsal pad (offload) for early stages. Advanced stages: debridement, dorsal closing wedge osteotomy of the metatarsal, or joint replacement/excision arthroplasty.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            }
          ]
        },
        {
          "title": "Fracture",
          "range": "Q1474",
          "questions": [
            {
              "number": 1474,
              "stem": "The most common ankle fracture pattern is:",
              "options": [
                "Weber B (transsyndesmotic — at the level of the syndesmosis, most commonly from a supination-external rotation mechanism)",
                "Weber A (infrasyndesmotic)",
                "Weber C (suprasyndesmotic)",
                "Pilon fracture",
                "Talus fracture"
              ],
              "answer": "A",
              "explanation": "Weber B fractures (transsyndesmotic — fibular fracture at the level of the syndesmosis) are the most common ankle fracture pattern, accounting for approximately 60-70% of all ankle fractures. The most common mechanism is supination-external rotation (SER in the Lauge-Hansen classification). The key clinical question with Weber B fractures is whether the ankle is STABLE or UNSTABLE: stability depends on the integrity of the MEDIAL side (deltoid ligament or medial malleolus). If the medial structures are intact → stable → non-operative (below-knee cast/boot). If the deltoid is disrupted (medial clear space >4mm on mortise view, positive stress test, medial malleolus fracture) → unstable → ORIF. Weber A: usually stable (conservative). Weber C: syndesmosis disrupted → unstable → ORIF + syndesmotic fixation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Rheumatoid",
          "range": "Q1475",
          "questions": [
            {
              "number": 1475,
              "stem": "In the rheumatoid forefoot, the characteristic deformity pattern includes:",
              "options": [
                "Hallux valgus and fixed flexion of all toes",
                "Hallux varus with plantar fibromatosis",
                "Normal forefoot alignment",
                "Cavus foot with hammer toes",
                "Hallux valgus, lesser toe MTP dorsal subluxation/dislocation, and claw toes with prominent metatarsal heads plantarly"
              ],
              "answer": "E",
              "explanation": "The classic rheumatoid forefoot deformity: hallux valgus (MTP joint erosion and medial capsule attenuation), lesser toe MTP subluxation/dislocation (synovitis → capsule/collateral ligament destruction → extensor tendon bowstringing → dorsal subluxation of proximal phalanges with plantar plate disruption), claw/hammer toes, and prominent metatarsal heads on the plantar surface (with overlying painful callosities/bursae). This causes significant pain on weight-bearing ('walking on pebbles'). Treatment: insoles + metatarsal bar (offload metatarsal heads). Surgical: forefoot reconstruction (1st MTP fusion + lesser MTP excision arthroplasty/Stainsby procedure).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Tibialis Anterior",
          "range": "Q1476",
          "questions": [
            {
              "number": 1476,
              "stem": "Rupture of the tibialis anterior tendon results in:",
              "options": [
                "Loss of ankle plantarflexion",
                "Loss of ankle inversion",
                "Loss of toe flexion",
                "Steppage gait (foot drop — loss of ankle dorsiflexion)",
                "Loss of ankle eversion"
              ],
              "answer": "D",
              "explanation": "Tibialis anterior is the primary ankle dorsiflexor and foot invertor. Its rupture (usually degenerative in elderly patients, or from laceration) results in a foot drop (inability to dorsiflex the ankle) and a compensatory steppage gait (exaggerated hip and knee flexion to clear the foot during swing phase). This must be differentiated from common peroneal nerve palsy (also causes foot drop but additionally loses ankle eversion due to peroneal muscle paralysis, and has sensory loss on the dorsum of the foot). Tibialis anterior rupture: isolated loss of dorsiflexion with preserved eversion (peronei intact). Treatment: direct repair if acute. Chronic/degenerative: EHL transfer or reconstruction.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Ankle OA",
          "range": "Q1477",
          "questions": [
            {
              "number": 1477,
              "stem": "The most common cause of ankle osteoarthritis is:",
              "options": [
                "Primary/idiopathic (like hip and knee OA)",
                "Rheumatoid arthritis",
                "Post-traumatic (previous ankle fracture or ligament injury)",
                "Gout",
                "Haemochromatosis"
              ],
              "answer": "C",
              "explanation": "Unlike the hip and knee (where primary/idiopathic OA predominates), ankle OA is MOST COMMONLY post-traumatic (~70-80%). Previous ankle fractures (malleolar, pilon, talus), chronic ligament instability, and osteochondral injuries lead to abnormal joint mechanics and progressive cartilage loss. Primary ankle OA is relatively uncommon (~10%). RA accounts for ~10%. This post-traumatic predominance is important: it means ankle OA patients are often younger and more active than hip/knee OA patients, influencing treatment decisions (ankle fusion vs replacement vs conservative). Treatment: ankle arthrodesis (gold standard for end-stage) or total ankle arthroplasty (preserves motion, protects adjacent joints).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Charcot",
          "range": "Q1478",
          "questions": [
            {
              "number": 1478,
              "stem": "Charcot neuroarthropathy (Charcot foot) in diabetic patients is characterised by:",
              "options": [
                "Progressive destructive arthropathy with fracture, dislocation, and deformity in a neuropathic foot, often triggered by minor trauma",
                "Normal bone and joint architecture",
                "Only superficial skin ulceration",
                "Isolated tendon rupture",
                "Acute septic arthritis"
              ],
              "answer": "A",
              "explanation": "Charcot neuroarthropathy is a progressive destructive condition affecting bones and joints in a neuropathic foot (peripheral neuropathy, most commonly diabetic). It is triggered by repetitive unrecognised trauma in a sensory-deficient limb. The neurotraumatic theory (repeated mechanical damage to insensate joints) and neurovascular theory (autonomic neuropathy → increased blood flow → osteoclastic resorption) both contribute. Eichenholtz classification: Stage 0 = prodromal (warm swollen foot, normal XR, MRI shows oedema). Stage 1 = development/fragmentation (periarticular fractures, subluxation). Stage 2 = coalescence (bone healing, reduced swelling). Stage 3 = reconstruction (remodelling, sclerosis, residual deformity). The midfoot (Lisfranc region) is most commonly affected. Treatment: total contact casting (TCC) during acute phase (immobilisation until quiescent), then accommodative footwear. Surgery for unstable deformity.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Morton",
          "range": "Q1479",
          "questions": [
            {
              "number": 1479,
              "stem": "Morton neuroma is NOT a true neuroma but a perineural fibrosis. It most commonly occurs in which web space?",
              "options": [
                "1st web space",
                "3rd web space (between the 3rd and 4th metatarsal heads)",
                "2nd web space",
                "4th web space",
                "5th web space"
              ],
              "answer": "B",
              "explanation": "Morton neuroma (interdigital neuroma) is a compressive neuropathy with perineural fibrosis (NOT a true neuroma — no axonal proliferation) of the common digital nerve. The 3rd web space is the most common location (~65%), followed by the 2nd web space (~32%). It is thought to occur at this location because the common digital nerve in the 3rd web space receives contributions from BOTH the medial and lateral plantar nerves, making it thicker and more susceptible to compression between the metatarsal heads. Presentation: forefoot pain radiating to the toes, burning/tingling, sensation of 'walking on a pebble'. Mulder click: palpable/audible click when squeezing the metatarsal heads together while pressing the web space. Treatment: wider footwear + metatarsal pad → steroid injection → surgical excision (through dorsal approach, neurectomy ~80% satisfaction).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Ankle",
          "range": "Q1480",
          "questions": [
            {
              "number": 1480,
              "stem": "The deltoid ligament is the primary medial stabiliser of the ankle. It has deep and superficial components. The DEEP deltoid primarily resists:",
              "options": [
                "Ankle plantarflexion",
                "Ankle dorsiflexion",
                "Ankle inversion",
                "Midfoot pronation",
                "Talar lateral shift and external rotation (primary restraint against lateral displacement of the talus within the mortise)"
              ],
              "answer": "E",
              "explanation": "The deep deltoid ligament (anterior and posterior tibiotalar ligaments) is the primary restraint against lateral translation (shift) and external rotation of the talus within the ankle mortise. It is the strongest component of the deltoid complex. The superficial deltoid (tibionavicular, tibiocalcaneal, tibiospring) primarily resists eversion. In ankle fractures, the integrity of the deltoid determines stability: if the deep deltoid is torn (medial clear space >4mm on mortise view, or widening on external rotation stress test), the ankle is UNSTABLE even with an isolated lateral malleolus fracture (Weber B with deltoid disruption requires ORIF). MRI and intra-operative stress testing assess deltoid integrity.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        }
      ]
    },
    {
      "title": "Oncology",
      "chapters": [
        {
          "title": "Staging",
          "range": "Q1481-Q1485",
          "questions": [
            {
              "number": 1481,
              "stem": "The most common primary malignant bone tumour in children and adolescents is:",
              "options": [
                "Ewing sarcoma",
                "Chondrosarcoma",
                "Myeloma",
                "Fibrosarcoma",
                "Osteosarcoma (peak incidence 10-25 years, most commonly around the knee — distal femur and proximal tibia)"
              ],
              "answer": "E",
              "explanation": "Osteosarcoma is the most common primary malignant bone tumour in children and adolescents (peak incidence 10-25 years during the pubertal growth spurt), and the second most common primary malignant bone tumour overall (after myeloma in adults). Most common locations: around the knee (distal femur ~40%, proximal tibia ~20%), followed by proximal humerus. Radiographic features: aggressive periosteal reaction (Codman triangle — elevated periosteum at tumour margins, sunburst pattern — radiating spicules of new bone), mixed lytic/sclerotic destruction, and soft tissue mass. Treatment: neoadjuvant chemotherapy (MAP protocol: methotrexate, doxorubicin/Adriamycin, cisPlatin) → wide excision (limb salvage in ~90% of cases now) → adjuvant chemotherapy. Tumour necrosis after neoadjuvant chemo is the single best prognostic indicator (>90% necrosis = excellent prognosis). 5-year survival: ~60-70% for localised disease.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1482,
              "stem": "The Enneking staging system for musculoskeletal tumours classifies tumours based on which three factors?",
              "options": [
                "Histological grade, local extent (intra/extracompartmental), and metastasis",
                "Size, lymph node status, and metastasis",
                "Age, tumour location, and treatment response",
                "Histological type, size, and depth",
                "Tumour markers, imaging, and biopsy"
              ],
              "answer": "A",
              "explanation": "The Enneking (MSTS) staging system uses three factors: (1) Histological grade (G): low grade (G1) vs high grade (G2). (2) Local extent (T): intracompartmental (T1) vs extracompartmental (T2). (3) Metastasis (M): absent (M0) vs present (M1). Stage IA = G1T1M0, IB = G1T2M0, IIA = G2T1M0, IIB = G2T2M0, III = any G, any T, M1. Stage IIB is the most common presentation for osteosarcoma.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1483,
              "stem": "When performing a biopsy of a suspected bone tumour, the biopsy track should be:",
              "options": [
                "Transverse to the limb for maximum tissue sampling",
                "In line with the planned definitive surgical incision (longitudinal)",
                "Through multiple compartments for better sampling",
                "Through the joint for access",
                "Randomly placed for convenience"
              ],
              "answer": "B",
              "explanation": "The biopsy track must be longitudinal and in line with the planned definitive surgical incision so that the entire biopsy track can be excised en bloc with the tumour during definitive surgery. A transverse or poorly placed biopsy contaminates additional compartments and may necessitate a wider resection or even amputation. Mankin's study showed that errors in biopsy technique led to adverse outcomes in up to 19% of patients. The biopsy should be performed at the tumour referral centre.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1484,
              "stem": "The Musculoskeletal Tumor Society (MSTS) functional outcome scoring system assesses which domains?",
              "options": [
                "Only pain",
                "Only range of motion",
                "Pain, function, emotional acceptance, use of supports, walking ability, and gait (6 domains scored 0-5 each)",
                "Only radiographic outcomes",
                "Only survival"
              ],
              "answer": "C",
              "explanation": "The MSTS (Enneking) functional outcome scoring system evaluates 6 domains for lower extremity tumour patients: (1) pain, (2) function (activities), (3) emotional acceptance, (4) use of supports (walking aids), (5) walking ability (distance), (6) gait (limp). Each domain is scored 0-5 (5 = best). Total maximum score = 30 (expressed as a percentage: e.g., 24/30 = 80%). For upper extremity: the domains are pain, function, emotional acceptance, hand positioning, manual dexterity, and lifting ability. It is the most widely used patient-reported outcome measure in musculoskeletal oncology.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1485,
              "stem": "The Enneking staging system for primary malignant musculoskeletal tumours classifies tumours by:",
              "options": [
                "Size only",
                "Patient age and gender",
                "Response to chemotherapy only",
                "Grade (low/high), site (intra/extracompartmental), and presence of metastases",
                "Radiographic appearance only"
              ],
              "answer": "D",
              "explanation": "Enneking surgical staging system: (1) Grade: I = low-grade (slow-growing, well-differentiated, low metastatic potential), II = high-grade (fast-growing, poorly differentiated, high metastatic potential). (2) Site: A = intracompartmental (confined within the compartment of origin — within bone cortex, within a single muscle compartment), B = extracompartmental (extends beyond the compartment — through cortex into soft tissues, across fascial boundaries). (3) Metastases: III = any grade or site with distant metastases. Staging guides surgical margins: Stage IA (low-grade, intracompartmental) → wide margin adequate. Stage IIB (high-grade, extracompartmental) → wide margin + adjuvant chemotherapy. Stage III → palliative or aggressive surgery depending on resectability.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Imaging",
          "range": "Q1486",
          "questions": [
            {
              "number": 1486,
              "stem": "The investigation sequence for a suspected primary malignant bone tumour is:",
              "options": [
                "Biopsy first, then imaging",
                "CT chest only",
                "Bone scan only",
                "No imaging needed — treat empirically",
                "Plain radiograph → MRI of the entire bone (local staging) → CT chest (lung metastases) → biopsy LAST (after all staging imaging is complete)"
              ],
              "answer": "E",
              "explanation": "The correct staging sequence for a suspected primary malignant bone tumour (e.g., osteosarcoma, Ewing sarcoma) is critically important: (1) PLAIN RADIOGRAPH (initial — identifies the lesion, assesses aggressiveness: periosteal reaction, matrix, margins), (2) MRI of the ENTIRE affected bone (local staging — assesses intramedullary extent, skip lesions, soft tissue mass, neurovascular involvement, joint involvement), (3) CT CHEST (metastatic staging — lungs are the most common site for bone sarcoma metastases), (4) BONE SCAN or PET-CT (whole-body screening for distant bony metastases), (5) BIOPSY LAST — after all staging imaging is complete. Why biopsy last? The biopsy disrupts tissue planes and creates a haematoma that can contaminate additional compartments on MRI — if MRI is done AFTER biopsy, the post-biopsy changes obscure the tumour margins, making surgical planning more difficult.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Principles",
          "range": "Q1487-Q1489",
          "questions": [
            {
              "number": 1487,
              "stem": "Limb salvage surgery for primary malignant bone tumours (e.g., osteosarcoma) is now possible in approximately what percentage of cases?",
              "options": [
                "10%",
                "85-90% (advances in neoadjuvant chemotherapy, imaging, and surgical techniques have made limb salvage the standard of care over amputation in most cases)",
                "30%",
                "100% — amputation is never needed",
                "50%"
              ],
              "answer": "B",
              "explanation": "Limb salvage surgery is now possible in approximately 85-90% of primary malignant bone tumours (compared to near-universal amputation before the 1970s). This improvement is due to: (1) neoadjuvant chemotherapy (shrinks the tumour, creates a pseudocapsule, kills micrometastases), (2) advances in imaging (MRI precisely defines tumour extent, allowing accurate pre-operative planning of margins), (3) improved reconstruction options (endoprosthetic replacement/megaprostheses, allografts, vascularised fibula grafts, 3D-printed custom implants), and (4) microsurgical techniques for soft tissue reconstruction. The key principle: the surgical MARGIN must not be compromised — a wide margin (≥2cm of normal tissue around the tumour in all directions, or an intact anatomical barrier like fascia/cortex) must be achieved regardless of whether limb salvage or amputation is performed. If a wide margin cannot be achieved with limb salvage → amputation remains the correct choice (survival > limb). Oncological outcomes (survival) are equivalent between limb salvage and amputation when margins are adequate.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1488,
              "stem": "In a patient with a suspected primary bone tumour, the biopsy should be performed by:",
              "options": [
                "The definitive treating surgeon (or by a specialist at the tumour centre, in line with the planned definitive surgical incision)",
                "The GP",
                "Any surgeon available",
                "The radiographer",
                "The anaesthetist"
              ],
              "answer": "A",
              "explanation": "The biopsy of a suspected primary bone tumour should ideally be performed by the surgeon who will perform the definitive resection, or at the specialist bone tumour centre under the guidance of the MDT. This is because: (1) the biopsy track must be placed in line with the planned definitive surgical incision — a poorly placed biopsy track can contaminate additional tissue compartments, potentially converting a limb-salvage case to an amputation. (2) The Mankin study (1982, updated 1996) showed that referring centre biopsies had a 3× higher complication rate and a 5× higher rate of unnecessary amputation compared to tumour centre biopsies. Poorly performed biopsies adversely affected outcomes in up to 19% of patients. (3) The biopsy should be at the tumour CENTRE (most representative tissue), using a longitudinal incision, within a single compartment, with meticulous haemostasis.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1489,
              "stem": "Osteosarcoma is the most common primary malignant bone tumour in children and adolescents. It typically arises in the:",
              "options": [
                "Diaphysis of long bones",
                "Epiphysis",
                "Flat bones exclusively",
                "Metaphysis of long bones around the knee (distal femur > proximal tibia > proximal humerus)",
                "Spine"
              ],
              "answer": "D",
              "explanation": "Osteosarcoma (conventional high-grade intramedullary type) arises in the metaphysis of long bones, most commonly around the knee: distal femur (most common single site, ~40%), proximal tibia (~20%), proximal humerus (~15%). Peak incidence: 10-20 years (during the adolescent growth spurt — rapid bone growth zone). A second peak occurs in the elderly (secondary osteosarcoma arising in Paget disease or post-radiation). It produces osteoid/bone matrix. Radiographic features: aggressive permeative/moth-eaten destruction, periosteal reaction (Codman triangle, sunburst/sunray), soft tissue mass. Treatment: neoadjuvant chemotherapy → wide excision (limb salvage or amputation) → adjuvant chemotherapy. Survival: ~60-70% 5-year with current protocols.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Benign",
          "range": "Q1490-Q1495",
          "questions": [
            {
              "number": 1490,
              "stem": "Non-ossifying fibroma (NOF / fibrous cortical defect) is the most common benign bone lesion in children. Its characteristic radiographic appearance is:",
              "options": [
                "Dense sclerotic mass",
                "Permeative destruction with periosteal reaction",
                "Eccentric, well-defined, cortically-based lucent lesion with sclerotic scalloped margins in the metaphysis of long bones (typically around the knee — distal femur, proximal tibia)",
                "Central medullary expansile lesion",
                "Ivory vertebra"
              ],
              "answer": "C",
              "explanation": "NOF (also called fibrous cortical defect when <3cm) is the most common incidental bone lesion in children, found in up to 30-40% of normal children. Radiographic appearance: eccentric (off-centre), well-defined, cortically-based, multiloculated lucent lesion with thin sclerotic scalloped ('soap bubble') margins, located in the METAPHYSIS of long bones — most commonly around the knee (distal femur, proximal tibia). It is ALWAYS benign — no malignant transformation occurs. Most are asymptomatic and discovered incidentally. Natural history: spontaneously REGRESSES (fills in with normal bone) during skeletal maturation — no treatment needed in the vast majority. Only intervene if: (1) pathological fracture (rare, usually in large lesions >50% of bone width), (2) uncertainty about diagnosis (biopsy if atypical features). Histology: spindle cells in a storiform/whorled pattern, giant cells, haemosiderin. DO NOT biopsy/treat a classic NOF unless atypical features are present.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1491,
              "stem": "An aneurysmal bone cyst (ABC) characteristically shows which finding on MRI?",
              "options": [
                "Homogeneous solid enhancement",
                "Ground glass appearance",
                "Fluid-fluid levels within a multiloculated expansile lesion",
                "Dense sclerosis",
                "Central calcification only"
              ],
              "answer": "C",
              "explanation": "ABCs characteristically show fluid-fluid levels on MRI (from layering of blood products of different densities within the cystic spaces). They are expansile, multiloculated, lytic lesions with a thin shell of reactive bone ('eggshell' or 'blown-out' appearance on XR). They can be primary or secondary (arising within another lesion: GCT, chondroblastoma, osteoblastoma). Treatment: curettage + adjuvant (phenol, cryotherapy) + bone graft. Recurrence rate ~20-30%. Denosumab and selective arterial embolisation are emerging treatments.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1492,
              "stem": "A non-ossifying fibroma (NOF/fibrous cortical defect) is:",
              "options": [
                "A malignant tumour requiring wide excision",
                "A benign tumour requiring urgent biopsy",
                "A metastatic lesion",
                "A common benign developmental lesion found incidentally in children that resolves spontaneously",
                "A precursor to osteosarcoma"
              ],
              "answer": "D",
              "explanation": "Non-ossifying fibroma (NOF, or fibrous cortical defect if <3 cm) is the most common incidental bone lesion in children, found in up to 30-40% of children's knee radiographs. It is an eccentric, well-defined cortical lytic lesion with a sclerotic (scalloped) border, located in the metaphysis of long bones (typically distal femur or proximal tibia). It is NOT a true neoplasm but a developmental abnormality. Most resolve spontaneously by skeletal maturity (replaced by normal bone). No treatment needed unless pathological fracture risk (>50% of bone width). NEVER biopsy — the diagnosis is made radiographically.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1493,
              "stem": "Enchondroma is a benign cartilage tumour most commonly found in the:",
              "options": [
                "Small bones of the hands (phalanges and metacarpals)",
                "Vertebral body",
                "Pelvis",
                "Skull",
                "Scapula"
              ],
              "answer": "A",
              "explanation": "Enchondroma is the most common benign tumour of the hand (and the most common primary bone tumour of the hand overall). It is a benign intramedullary cartilage tumour typically found in the metaphysis/diaphysis of the small tubular bones of the hands (proximal phalanges most common, then metacarpals). Radiographically: well-defined central lytic lesion with chondroid calcification (stippled/popcorn/ring-and-arc pattern). Usually asymptomatic (discovered incidentally or after pathological fracture). Solitary enchondroma: <1% malignant transformation risk. Ollier disease: multiple enchondromas (non-hereditary, 25-30% malignant transformation to secondary chondrosarcoma). Maffucci syndrome: multiple enchondromas + soft tissue haemangiomas (highest malignant transformation risk ~100% develop a malignancy by age 40).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1494,
              "stem": "An osteoid osteoma classically presents with:",
              "options": [
                "Painless mass",
                "Constitutional symptoms (weight loss, fever)",
                "Progressive deformity without pain",
                "Pulsatile mass",
                "Night pain that is dramatically relieved by NSAIDs (particularly aspirin)"
              ],
              "answer": "E",
              "explanation": "Osteoid osteoma classically presents with nocturnal pain that is dramatically and specifically relieved by NSAIDs (particularly aspirin/ibuprofen — through prostaglandin inhibition). The tumour produces prostaglandins (PGE2) within the nidus, causing local vasodilation and pain. Radiographically: a small radiolucent nidus (<1.5 cm) surrounded by dense reactive sclerosis (may be difficult to see on XR — thin-cut CT best demonstrates the nidus). Most common in the cortex of the femur and tibia, with a peak age of 10-25 years. Treatment: NSAIDs (if tolerable), or CT-guided radiofrequency ablation (RFA) of the nidus (>90% success rate, minimally invasive). Spinal osteoid osteoma: causes painful scoliosis (concavity towards the lesion).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1495,
              "stem": "Giant cell tumour (GCT) of bone typically occurs in which location and age group?",
              "options": [
                "Diaphysis of long bones in children",
                "Epiphysis/subarticular region of long bones in skeletally mature adults (20-40 years)",
                "Metaphysis of long bones in adolescents",
                "Vertebral body in elderly patients",
                "Flat bones in infants"
              ],
              "answer": "B",
              "explanation": "GCT (osteoclastoma) occurs in the epiphysis (subarticular region) of long bones in skeletally mature adults (peak 20-40 years, closed physes). The most common sites: around the knee (distal femur and proximal tibia account for ~50%), followed by distal radius and proximal humerus. Radiographically: eccentric, lytic, expansile lesion extending to the subchondral bone (right up to the articular surface) without sclerotic margin ('soap bubble' appearance). Locally aggressive (Campanacci Grade 1-3). Treatment: extended curettage + adjuvant (phenol, liquid nitrogen, or PMMA cement packing) + bone graft. Denosumab (anti-RANKL) can be used neoadjuvantly to reduce tumour bulk. Recurrence: ~15-25% after curettage.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Metastases",
          "range": "Q1496",
          "questions": [
            {
              "number": 1496,
              "stem": "The most common primary cancers that metastasise to bone are:",
              "options": [
                "Brain and liver cancers",
                "Breast, lung, prostate, kidney, and thyroid (mnemonic: 'BLT with a Kosher Pickle' or 'Pb KTL' — Lead Kettle)",
                "Skin melanoma only",
                "Pancreatic cancer only",
                "Colon cancer only"
              ],
              "answer": "B",
              "explanation": "The five most common cancers that metastasise to bone: Breast, Lung, Prostate (Thyroid, Kidney — 'BLT-KP' or various other mnemonics). Breast: most common overall source of skeletal metastases in women (typically lytic or mixed). Prostate: most common in men (typically OSTEOBLASTIC/sclerotic — the classic exception to the rule that most metastases are lytic). Lung: aggressive, typically lytic, poor prognosis (median survival ~6 months with skeletal mets). Kidney (renal cell): characteristically HYPERVASCULAR (pre-operative embolisation essential before surgery to reduce intra-operative blood loss). Thyroid: also hypervascular (embolise), relatively good prognosis if differentiated type. Distribution: metastases occur preferentially in the axial skeleton and proximal long bones (red marrow distribution — Batson's vertebral venous plexus facilitates haematogenous spread). Spine is the most common site (~70%), followed by pelvis, proximal femur, ribs, and proximal humerus.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Benign Tumours",
          "range": "Q1497-Q1498",
          "questions": [
            {
              "number": 1497,
              "stem": "The most common benign bone tumour is:",
              "options": [
                "Osteochondroma (exostosis)",
                "Giant cell tumour",
                "Osteoid osteoma",
                "Enchondroma",
                "Fibrous dysplasia"
              ],
              "answer": "A",
              "explanation": "Osteochondroma (osteocartilaginous exostosis) is the most common benign bone tumour, accounting for 35–45% of all benign bone tumours. It consists of a cartilage-capped bony protuberance arising from the surface of bone near the physis. The cartilage cap should be <2 cm in adults — a cap >2 cm raises concern for malignant transformation to secondary chondrosarcoma (occurs in ~1% of solitary osteochondromas and ~5–10% of hereditary multiple exostoses). Complications: cosmetic, mechanical impingement, fracture, vascular compression.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1498,
              "stem": "An osteoid osteoma characteristically presents with pain that is:",
              "options": [
                "Constant and unresponsive to any medication",
                "Worse during the day and relieved by rest",
                "Only present with weight-bearing",
                "Associated with joint effusion",
                "Worse at night and relieved by NSAIDs (aspirin/ibuprofen)"
              ],
              "answer": "E",
              "explanation": "Osteoid osteoma classically presents with well-localised pain that is worse at night and dramatically relieved by NSAIDs (particularly aspirin). This is because the tumour nidus produces prostaglandins (PGE₂) that cause pain and local vasodilation. Radiographically it shows a small (<1.5 cm) radiolucent nidus with surrounding reactive sclerosis. CT is the best imaging modality to identify the nidus. Treatment: NSAIDs (if tolerable), or CT-guided radiofrequency ablation (RFA) for persistent symptoms. It may spontaneously regress over 3–5 years.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Soft Tissue",
          "range": "Q1499",
          "questions": [
            {
              "number": 1499,
              "stem": "The most common soft tissue sarcoma in adults is:",
              "options": [
                "Liposarcoma",
                "Synovial sarcoma",
                "Rhabdomyosarcoma",
                "Malignant fibrous histiocytoma (undifferentiated pleomorphic sarcoma)",
                "Fibrosarcoma"
              ],
              "answer": "D",
              "explanation": "Undifferentiated pleomorphic sarcoma (UPS, formerly called malignant fibrous histiocytoma/MFH) is the most common soft tissue sarcoma in adults (previously, MFH was the most commonly diagnosed, now reclassified as UPS). Liposarcoma is the second most common. In children, rhabdomyosarcoma is the most common soft tissue sarcoma. Synovial sarcoma affects young adults (misnomer — does not arise from synovium). The 2× rule for soft tissue masses: >5 cm, deep to fascia, increasing in size, painful → refer to tumour centre.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Fibrous Dysplasia",
          "range": "Q1500",
          "questions": [
            {
              "number": 1500,
              "stem": "The characteristic radiographic appearance of fibrous dysplasia is:",
              "options": [
                "Sunburst periosteal reaction",
                "Onion-skin periosteal reaction",
                "Ground glass (hazy, smoky) appearance with endosteal scalloping",
                "Soap bubble expansile lytic lesion",
                "Dense sclerotic lesion with no lytic component"
              ],
              "answer": "C",
              "explanation": "Fibrous dysplasia produces a characteristic ground glass (hazy, smoky) radiographic appearance due to replacement of normal bone with fibrous tissue containing immature woven bone trabeculae. Endosteal scalloping may be present. It can be monostotic (70-80%, most common in ribs and proximal femur — 'shepherd's crook' deformity) or polyostotic (20-30%, may be part of McCune-Albright syndrome: polyostotic FD + café-au-lait spots + precocious puberty). Histology shows Chinese letter/alphabet soup pattern of woven bone.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Enchondroma",
          "range": "Q1501",
          "questions": [
            {
              "number": 1501,
              "stem": "The most common bone tumour of the hand is:",
              "options": [
                "Osteochondroma",
                "Osteoid osteoma",
                "Giant cell tumour",
                "Enchondroma",
                "Osteosarcoma"
              ],
              "answer": "D",
              "explanation": "Enchondroma is the most common bone tumour of the hand (and also the most common primary tumour of the phalanges). It presents as a well-defined central lytic lesion with stippled calcification (chondroid matrix) in the metaphysis or diaphysis. In the hand, enchondromas are virtually always benign. Ollier disease = multiple enchondromatosis. Maffucci syndrome = multiple enchondromas + soft tissue haemangiomas (higher malignant transformation risk ~25%).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Bone Tumour Basics",
          "range": "Q1502",
          "questions": [
            {
              "number": 1502,
              "stem": "The most common primary malignant bone tumour is:",
              "options": [
                "Osteosarcoma",
                "Ewing sarcoma",
                "Multiple myeloma",
                "Chondrosarcoma",
                "Fibrosarcoma"
              ],
              "answer": "C",
              "explanation": "Multiple myeloma is the most common primary malignant bone tumour overall if haematological malignancies are included. If considering only solid primary bone tumours, osteosarcoma is the most common in young patients (10–25 years) and chondrosarcoma in older adults (>40 years). Ewing sarcoma is the second most common solid primary malignant bone tumour in children/adolescents. The answer depends on the question framing — read carefully.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Osteosarcoma",
          "range": "Q1503",
          "questions": [
            {
              "number": 1503,
              "stem": "The characteristic radiographic appearance of conventional osteosarcoma includes:",
              "options": [
                "Mixed lytic and sclerotic lesion with aggressive periosteal reaction (Codman triangle, sunburst pattern)",
                "Well-defined sclerotic margins",
                "Purely lytic destruction with no matrix",
                "Ground glass appearance",
                "Soap bubble appearance"
              ],
              "answer": "A",
              "explanation": "Conventional (high-grade intramedullary) osteosarcoma typically shows an aggressive mixed lytic and sclerotic lesion with bone formation (cloud-like osteoid matrix), aggressive periosteal reaction (Codman triangle = elevation of periosteum at the lesion margin, sunburst/sunray pattern = spiculated periosteal new bone), soft tissue mass, and cortical destruction. It most commonly occurs in the metaphysis of long bones around the knee (distal femur > proximal tibia > proximal humerus) in the second decade of life.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Ewing Sarcoma",
          "range": "Q1504",
          "questions": [
            {
              "number": 1504,
              "stem": "Ewing sarcoma characteristically shows which radiographic periosteal pattern?",
              "options": [
                "Sunburst pattern",
                "Codman triangle only",
                "Solid periosteal reaction",
                "No periosteal reaction",
                "Onion-skin (lamellated) periosteal reaction"
              ],
              "answer": "E",
              "explanation": "Ewing sarcoma characteristically produces an onion-skin (lamellated) periosteal reaction — multiple layers of periosteal new bone deposited in concentric layers. It is a diaphyseal lesion (unlike osteosarcoma which is metaphyseal) that is predominantly lytic (permeative/moth-eaten pattern). It affects children and adolescents (peak 5–15 years) and has a specific translocation t(11;22)(q24;q12) producing the EWS-FLI1 fusion protein. Treatment: neoadjuvant chemo → surgery/radiotherapy → adjuvant chemo.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "GCT",
          "range": "Q1505",
          "questions": [
            {
              "number": 1505,
              "stem": "Giant cell tumour (GCT) of bone characteristically presents in which location?",
              "options": [
                "Diaphysis in a child",
                "Epiphysis/subarticular region in a skeletally mature patient",
                "Metaphysis in an adolescent",
                "Vertebral body in an elderly patient",
                "Calcaneus in a young adult"
              ],
              "answer": "B",
              "explanation": "GCT characteristically occurs in the epiphyseal/subarticular region of long bones in skeletally mature patients (20–40 years). It extends to the subchondral bone (abuts the joint surface). The most common location is the distal femur, followed by the proximal tibia and distal radius. Radiographically it appears as an eccentric, expansile, lytic lesion without matrix mineralisation ('soap bubble' appearance). It is classified as locally aggressive (Campanacci Grade 1–3). Treatment: extended curettage with adjuvant (cement, phenol, cryotherapy) ± bone graft. Denosumab used for unresectable cases.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Biopsy",
          "range": "Q1506-Q1507",
          "questions": [
            {
              "number": 1506,
              "stem": "According to Mankin's principles, a bone tumour biopsy should:",
              "options": [
                "Always be performed as an excisional biopsy",
                "Be performed at the referring centre by any available surgeon",
                "Use a transverse incision for better access",
                "Be performed at the tumour centre by or under the supervision of the surgeon who will perform the definitive surgery",
                "Always be open rather than needle biopsy"
              ],
              "answer": "D",
              "explanation": "Mankin demonstrated that incorrectly performed biopsies lead to significantly higher rates of complications, changes in surgical plan, and even unnecessary amputations. The biopsy should be performed at the specialist tumour centre by or under the direction of the surgeon who will perform definitive surgery. The biopsy track must be in line with the planned definitive incision (longitudinal) and must be excisable en bloc. Image guidance (CT/US) is increasingly used for core needle biopsy, reducing contamination risk.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1507,
              "stem": "In a patient with a suspected bone tumour, the biopsy should ideally be the:",
              "options": [
                "First investigation performed",
                "Last investigation performed, after complete imaging staging",
                "Performed before any imaging",
                "Performed at the referring hospital by the orthopaedic trainee",
                "Performed without imaging guidance"
              ],
              "answer": "B",
              "explanation": "Biopsy is always the LAST investigation performed, after ALL imaging is complete (plain XR → MRI of entire bone → CT chest → bone scan). This is because: (1) biopsy can distort anatomy and create artefact on subsequent imaging, (2) biopsy must be planned to avoid contaminating uninvolved compartments, (3) the biopsy track must be in line with the definitive surgical incision, (4) the surgeon performing the biopsy ideally performs the definitive surgery. Performing a biopsy before imaging is a common mistake that can alter management and even lead to unnecessary amputation (Mankin's study).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Metastatic Disease",
          "range": "Q1508-Q1509",
          "questions": [
            {
              "number": 1508,
              "stem": "The most common site in the skeleton for bony metastases is:",
              "options": [
                "Distal femur",
                "Proximal humerus",
                "Hands and feet",
                "Distal radius",
                "Spine (vertebral bodies)"
              ],
              "answer": "E",
              "explanation": "The spine (particularly thoracic and lumbar vertebral bodies) is the most common site for skeletal metastases, followed by the pelvis, proximal femur, ribs, and proximal humerus. The axial skeleton and proximal appendicular skeleton are preferentially affected because of their rich red marrow blood supply (Batson's vertebral venous plexus allows retrograde spread). Metastases distal to the elbows and knees are rare.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1509,
              "stem": "Sclerotic (blastic) bony metastases are characteristically seen with which primary tumour?",
              "options": [
                "Prostate carcinoma",
                "Renal cell carcinoma",
                "Thyroid carcinoma",
                "Lung carcinoma",
                "Hepatocellular carcinoma"
              ],
              "answer": "A",
              "explanation": "Prostate carcinoma characteristically produces sclerotic (osteoblastic) metastases. Breast cancer can produce lytic, sclerotic, or mixed lesions. Renal and thyroid metastases are characteristically lytic and highly vascular. Lung metastases are usually lytic. The mnemonic for sclerotic mets: 'Please Let My Bones Stay' — Prostate, Lymphoma, Medulloblastoma, Breast, Seminoma (carcinoid also).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Mirels",
          "range": "Q1510",
          "questions": [
            {
              "number": 1510,
              "stem": "In the Mirels scoring system for pathological fracture risk, which lesion TYPE scores the highest (3 points)?",
              "options": [
                "Blastic (sclerotic)",
                "Mixed",
                "Lytic",
                "All types score equally",
                "Periosteal reaction type"
              ],
              "answer": "C",
              "explanation": "Lytic lesions score 3 (highest risk) because they weaken bone more than blastic or mixed lesions. Blastic lesions score 1 (lowest risk — new bone formation actually strengthens the area somewhat). Mixed lesions score 2. The other parameters also scored 1-3: site (upper limb=1, lower limb=2, peritrochanteric=3), pain (mild=1, moderate=2, functional=3), size (<1/3=1, 1/3-2/3=2, >2/3=3).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Chondrosarcoma",
          "range": "Q1511",
          "questions": [
            {
              "number": 1511,
              "stem": "Chondrosarcoma differs from other primary malignant bone tumours in that it is:",
              "options": [
                "Radiosensitive and chemosensitive",
                "Most common in children",
                "Always benign",
                "Resistant to chemotherapy and radiotherapy — surgery is the primary treatment",
                "Associated with t(11;22) translocation"
              ],
              "answer": "D",
              "explanation": "Chondrosarcoma is characteristically resistant to both chemotherapy and radiotherapy. Wide surgical excision is therefore the only curative treatment. This differs from osteosarcoma and Ewing sarcoma (both chemosensitive) and Ewing sarcoma (radiosensitive). Chondrosarcoma is the most common primary malignant bone tumour in adults >40 years. It occurs in the pelvis, proximal femur, and proximal humerus. Grading (I-III) determines prognosis — Grade I has 5-year survival >90%, Grade III is much worse.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Bone Markers",
          "range": "Q1512",
          "questions": [
            {
              "number": 1512,
              "stem": "Elevated serum alkaline phosphatase (ALP) in a patient with a bone lesion suggests:",
              "options": [
                "Purely lytic destruction with no bone formation",
                "Infection only",
                "Normal finding in all bone tumours",
                "Renal failure",
                "Osteoblastic activity (new bone formation)"
              ],
              "answer": "E",
              "explanation": "ALP is produced by osteoblasts and elevated in conditions with increased osteoblastic activity: Paget disease (markedly elevated), osteoblastic metastases (prostate), healing fractures, osteosarcoma, and bone-forming benign conditions. In purely lytic lesions (myeloma), ALP may be normal because there is minimal osteoblastic response. ALP is also elevated in liver disease (hepatic isoenzyme) — bone-specific ALP isoenzyme can be measured to differentiate. In Paget disease, ALP is the most useful marker for monitoring disease activity and treatment response.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Investigations",
          "range": "Q1513-Q1516",
          "questions": [
            {
              "number": 1513,
              "stem": "The gold standard imaging investigation for local staging of a suspected primary bone tumour is:",
              "options": [
                "MRI of the entire bone with the adjacent joints",
                "Plain radiograph",
                "CT scan",
                "Bone scan",
                "PET-CT"
              ],
              "answer": "A",
              "explanation": "MRI of the entire involved bone including the joints above and below is the gold standard for local staging of primary bone tumours. MRI shows: intramedullary extent, soft tissue extension, neurovascular involvement, skip lesions (separate foci of tumour in the same bone — particularly important in osteosarcoma), and relationship to the joint/growth plate. Staging also requires CT chest (for pulmonary metastases) and whole-body bone scan (for skeletal metastases). PET-CT is increasingly used for staging and monitoring treatment response.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1514,
              "stem": "When evaluating a suspected primary bone tumour, the biopsy should be performed AFTER:",
              "options": [
                "No other investigation is needed — biopsy first",
                "Full staging imaging is complete (XR, MRI of entire bone, CT chest, bone scan)",
                "Only after a blood test",
                "CT of the lesion only",
                "Ultrasound only"
              ],
              "answer": "B",
              "explanation": "The biopsy must be the LAST investigation performed, after all imaging is complete. This is because: (1) the biopsy creates a haematoma that can contaminate tissue planes, making subsequent imaging less reliable, (2) the biopsy track must be planned in line with the definitive surgical incision (requires knowing the full extent of the tumour on MRI), (3) the imaging findings guide the biopsy technique (needle vs open, location of most representative tissue). Workup sequence: plain XR (first) → MRI of entire bone + adjacent joints (local staging) → CT chest (lung mets) → bone scan (skeletal mets) → BIOPSY (last, at tumour centre, by definitive surgeon).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1515,
              "stem": "PET-CT (positron emission tomography with CT) uses which radiotracer and is particularly useful for:",
              "options": [
                "Technetium-99m for bone turnover only",
                "Gadolinium for soft tissue enhancement",
                "FDG (fluorodeoxyglucose) — detects metabolically active tissue, useful for staging, monitoring treatment response, and detecting recurrence",
                "Iodine contrast for vascular assessment",
                "Barium for GI assessment"
              ],
              "answer": "C",
              "explanation": "PET-CT uses ¹⁸F-fluorodeoxyglucose (FDG) — a glucose analogue taken up preferentially by metabolically active cells (tumour cells, infection, inflammation). It provides functional and anatomical information combined (PET for metabolic activity overlaid on CT for anatomical localisation). In MSK oncology: (1) staging — detects distant metastases (more sensitive than bone scan for lytic mets), (2) monitoring treatment response (decreasing FDG uptake indicates response to chemotherapy — used to assess neoadjuvant chemo effect in osteosarcoma/Ewing), (3) detecting recurrence. Limitations: false positives (infection, inflammation, healing fracture), false negatives (low-grade tumours, small lesions).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1516,
              "stem": "The Mirels scoring system is used to predict the risk of:",
              "options": [
                "Spinal metastasis prognosis",
                "Pathological fracture through a metastatic bone lesion (guides prophylactic fixation decisions)",
                "Primary bone tumour staging",
                "Soft tissue sarcoma grading",
                "Chondrosarcoma differentiation"
              ],
              "answer": "B",
              "explanation": "The Mirels scoring system predicts the risk of pathological fracture through a metastatic bone lesion and guides the decision for prophylactic fixation. Four parameters are scored 1-3 each: (1) Site (upper limb=1, lower limb=2, peritrochanteric=3), (2) Pain (mild=1, moderate=2, functional=3), (3) Lesion type (blastic=1, mixed=2, lytic=3), (4) Size (<1/3 of cortex=1, 1/3-2/3=2, >2/3=3). Total score range: 4-12. Score ≥9: prophylactic fixation recommended (fracture risk >33%). Score ≤7: safe to irradiate/observe. Score 8: borderline (clinical judgment). Prophylactic fixation (typically an IM nail for long bones) is associated with better outcomes and shorter hospital stays than fixing an established pathological fracture.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Surgical Margins",
          "range": "Q1517",
          "questions": [
            {
              "number": 1517,
              "stem": "In musculoskeletal tumour surgery, a 'wide' margin means:",
              "options": [
                "Excision through the tumour (intralesional)",
                "Excision along the pseudocapsule (marginal)",
                "Excision of the entire compartment containing the tumour",
                "Excision through normal tissue within the same compartment, with a cuff of normal tissue around the tumour",
                "No surgery needed"
              ],
              "answer": "D",
              "explanation": "Enneking surgical margins: Intralesional = through the tumour (curettage, debulking — leaves macroscopic disease). Marginal = along the reactive zone/pseudocapsule (risk of leaving microscopic satellite lesions). Wide = through normal tissue beyond the reactive zone, with a cuff of uninvolved tissue around the tumour (standard for malignant tumours). Radical = removal of the entire compartment (rarely performed). Wide margins are the goal for primary malignant bone tumours (osteosarcoma, Ewing, chondrosarcoma). Marginal/intralesional is acceptable for benign tumours with adjuvant treatment.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Metastatic",
          "range": "Q1518-Q1519",
          "questions": [
            {
              "number": 1518,
              "stem": "The most common primary cancers metastasising to bone are (mnemonic BLT-KP):",
              "options": [
                "Brain, Liver, Thymus, Kidney, Pancreas",
                "Bone, Lung, Testis, Kidney, Pharynx",
                "Breast, Lung, Thyroid, Kidney, Prostate",
                "Breast, Liver, Trachea, Kidney, Prostate",
                "Bladder, Lung, Thyroid, Kidney, Prostate"
              ],
              "answer": "C",
              "explanation": "The BLT-KP mnemonic: Breast, Lung, Thyroid, Kidney, Prostate are the five most common primary tumours that metastasise to bone. Breast is the most common in women, prostate in men, and lung overall. Renal and thyroid metastases are characteristically hypervascular — pre-operative embolisation should be considered before surgical excision to reduce intraoperative haemorrhage. Prostate produces sclerotic (blastic) mets. Renal and thyroid produce lytic, vascular mets.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1519,
              "stem": "The most common site for skeletal metastases is the:",
              "options": [
                "Axial skeleton (spine, pelvis, proximal femur, ribs, skull — areas of red marrow)",
                "Hands and feet",
                "Distal tibia",
                "Distal forearm",
                "Fibula"
              ],
              "answer": "A",
              "explanation": "Skeletal metastases preferentially affect the axial skeleton and proximal long bones — areas where red (haematopoietic) marrow persists in adults. The most common sites: vertebral bodies (most common single site), pelvis, proximal femur, ribs, and skull. This distribution is explained by Batson's vertebral venous plexus (a valveless venous system connecting pelvic/abdominal organs to the vertebral column, allowing haematogenous spread to bypass the pulmonary filter) and the slow sinusoidal blood flow in red marrow (similar to metaphyseal haematogenous osteomyelitis in children). Metastases distal to the elbow or knee are rare ('acrometastasis' — if found, think lung or renal primary). The BLT-KP mnemonic: breast, lung, thyroid, kidney, prostate.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Chondroblastoma",
          "range": "Q1520",
          "questions": [
            {
              "number": 1520,
              "stem": "Chondroblastoma is a benign bone tumour that characteristically occurs in the:",
              "options": [
                "Diaphysis of long bones",
                "Metaphysis in adults",
                "Flat bones exclusively",
                "Vertebral body",
                "Epiphysis of skeletally immature patients"
              ],
              "answer": "E",
              "explanation": "Chondroblastoma is one of the few tumours that occurs in the EPIPHYSIS of skeletally immature patients (the other epiphyseal tumours to remember: GCT in skeletally mature, clear cell chondrosarcoma in adults). It typically affects the proximal humerus, proximal tibia, and distal femur (around the knee and shoulder). Radiographically: well-defined lytic lesion in the epiphysis with thin sclerotic rim and possible calcification. Pain is the main symptom. Treatment: curettage + adjuvant + bone graft. Recurrence rate ~10-20%.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            }
          ]
        },
        {
          "title": "Bone Tumour Approach",
          "range": "Q1521",
          "questions": [
            {
              "number": 1521,
              "stem": "In the initial evaluation of a patient with a suspected primary bone tumour, the first investigation should be:",
              "options": [
                "MRI",
                "CT scan",
                "Plain radiograph of the affected area",
                "Bone scan",
                "Biopsy"
              ],
              "answer": "C",
              "explanation": "Plain radiograph is ALWAYS the first investigation for a suspected bone lesion. It provides: location (epiphyseal, metaphyseal, diaphyseal), zone of transition (narrow = benign, wide = aggressive), matrix (osteoid, chondroid, none), periosteal reaction (solid = benign, interrupted/aggressive = malignant), cortical integrity, and soft tissue mass. The radiographic features guide the differential diagnosis and subsequent investigations. After XR: MRI for local staging → CT chest for pulmonary metastases → bone scan for skeletal survey → biopsy LAST (at tumour centre, by definitive surgeon).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Specific Tumours",
          "range": "Q1522-Q1526",
          "questions": [
            {
              "number": 1522,
              "stem": "A chordoma is a malignant tumour arising from remnants of the:",
              "options": [
                "Neural crest",
                "Apical ectodermal ridge",
                "Somites",
                "Mesoderm",
                "Notochord"
              ],
              "answer": "E",
              "explanation": "Chordoma arises from remnants of the notochord — the embryonic structure that is replaced by the vertebral column during development. It typically occurs at the two ends of the axial skeleton: sacrococcygeal region (~50%, most common site) and skull base/clivus (~35%). It is a locally aggressive, slow-growing malignant tumour that is resistant to chemotherapy and radiotherapy (proton beam therapy may help). Treatment: wide surgical excision (sacral resection for sacral chordomas). Histology: physaliferous (vacuolated/bubbly) cells. Keratin and S-100 positive on immunohistochemistry.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            },
            {
              "number": 1523,
              "stem": "Osteoblastoma is histologically identical to osteoid osteoma but differs in that it:",
              "options": [
                "Is always malignant",
                "Is always smaller than 1.5 cm",
                "Never occurs in the spine",
                "Is larger (>2 cm), may be locally aggressive, and does not typically respond to NSAIDs as dramatically",
                "Has no pain associated"
              ],
              "answer": "D",
              "explanation": "Osteoblastoma shares the same histology as osteoid osteoma (both produce osteoid and woven bone with vascularised connective tissue stroma) but is larger (>1.5-2 cm by definition), may be locally aggressive (expanding cortex, soft tissue extension), and has a less predictable response to NSAIDs. It most commonly occurs in the posterior elements of the spine (~40% of cases), unlike osteoid osteoma which is more common in the femur and tibia. Treatment: intralesional curettage + bone graft (vs RFA for osteoid osteoma). Recurrence: ~15-20%.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1524,
              "stem": "Myeloma (multiple myeloma) is the most common primary malignant bone tumour in adults overall. Characteristic laboratory findings include:",
              "options": [
                "Normal blood tests",
                "Monoclonal protein band on serum/urine electrophoresis (M-spike), elevated ESR, Bence-Jones proteinuria, NORMAL ALP (purely lytic lesions with no osteoblastic response), anaemia, renal impairment, hypercalcaemia",
                "Elevated ALP (like other bone tumours)",
                "Only elevated white cell count",
                "Elevated tumour markers (PSA, CEA)"
              ],
              "answer": "B",
              "explanation": "Myeloma is a malignancy of plasma cells producing a monoclonal immunoglobulin (M-protein). Key laboratory findings: (1) M-spike on serum protein electrophoresis (SPEP), (2) Bence-Jones protein in urine (free light chains), (3) elevated ESR (markedly), (4) NORMAL ALP — this is a classic exam point: myeloma produces purely LYTIC lesions with NO osteoblastic response, so ALP remains normal (unlike Paget, osteoblastic mets, or healing fractures which elevate ALP). (5) Anaemia (marrow infiltration), (6) hypercalcaemia (bone resorption), (7) renal impairment (light chain deposition). Diagnostic criteria (CRAB): Calcium elevation, Renal impairment, Anaemia, Bone lesions. Radiographically: 'punched-out' lytic lesions without sclerotic rim, generalised osteopaenia, vertebral compression fractures. Bone scan may be FALSE NEGATIVE (no osteoblastic activity to take up tracer).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1525,
              "stem": "Ewing sarcoma most commonly affects which age group and bone location?",
              "options": [
                "Children and adolescents (5-15 years), diaphysis of long bones and flat bones (pelvis, ribs)",
                "Adults >50, flat bones",
                "Neonates, skull",
                "Elderly, vertebral body",
                "Young adults, epiphysis"
              ],
              "answer": "A",
              "explanation": "Ewing sarcoma is the second most common primary malignant bone tumour in children and adolescents (after osteosarcoma), with peak incidence at 5-15 years. It arises in the diaphysis of long bones (femur most common long bone) and flat bones (pelvis — most common single site overall, ribs, scapula). It is extremely rare in African and Asian populations. Radiographic features: permeative/moth-eaten destruction, lamellated (onion skin) periosteal reaction, large soft tissue mass (often larger than the bony component). Genetics: t(11;22) translocation producing the EWS-FLI1 fusion protein (~85% of cases). Treatment: neoadjuvant chemotherapy → surgery ± radiotherapy (radiosensitive) → adjuvant chemotherapy.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1526,
              "stem": "Chondrosarcoma is unique among primary malignant bone tumours because it is:",
              "options": [
                "Highly chemosensitive",
                "Highly radiosensitive",
                "Only found in children",
                "Both chemoresistant AND radioresistant — surgery (wide excision) is the ONLY curative treatment",
                "Always benign"
              ],
              "answer": "D",
              "explanation": "Chondrosarcoma is the third most common primary malignant bone tumour (after myeloma and osteosarcoma). It is uniquely RESISTANT to both chemotherapy and radiotherapy — the hyaline cartilage matrix has low cellularity, poor vascularity, and the chondrocytes have a very low mitotic rate, making them insensitive to cytotoxic agents and radiation. This means SURGICAL EXCISION with WIDE margins is the ONLY curative treatment. Adequate margins are critical — local recurrence after inadequate excision is associated with tumour upgrading (becoming higher grade) and metastasis. Grade 1 (low-grade): slow-growing, rarely metastasises. Grade 2-3 (high-grade): more aggressive, metastasise. Most common sites: pelvis (most common), proximal femur, proximal humerus. Peak age: 40-60 years.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Radiology",
          "range": "Q1527",
          "questions": [
            {
              "number": 1527,
              "stem": "The 'sunburst' or 'sunray' periosteal reaction on radiograph is most commonly associated with:",
              "options": [
                "Ewing sarcoma",
                "Osteosarcoma",
                "Giant cell tumour",
                "Simple bone cyst",
                "Enchondroma"
              ],
              "answer": "B",
              "explanation": "The sunburst (sunray/hair-on-end) periosteal reaction is most commonly associated with osteosarcoma. It occurs when rapidly growing tumour penetrates the cortex and lifts the periosteum, with new bone being laid down perpendicular to the cortical surface along the tumour vessels. This is an aggressive periosteal pattern indicating a malignant or rapidly growing lesion. Other aggressive patterns: Codman triangle (periosteal elevation at the edge of the lesion — also osteosarcoma), onion-skin/lamellated (Ewing sarcoma). Benign patterns: solid/uninterrupted periosteal reaction.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Radiotherapy",
          "range": "Q1528",
          "questions": [
            {
              "number": 1528,
              "stem": "In the management of Ewing sarcoma, radiotherapy plays a role because Ewing sarcoma is:",
              "options": [
                "Completely radio-resistant",
                "Only treated with chemotherapy",
                "Radiosensitive (responds to radiotherapy)",
                "Only treated with surgery",
                "A benign condition not requiring treatment"
              ],
              "answer": "C",
              "explanation": "Ewing sarcoma is RADIOSENSITIVE — it responds well to radiotherapy, unlike most other primary bone sarcomas. Radiotherapy is used: (1) as definitive local treatment when surgical resection would cause unacceptable morbidity (e.g., pelvic Ewing, spine), (2) as adjuvant after marginal/incomplete excision, and (3) for palliation of metastatic disease. The standard treatment protocol is: neoadjuvant chemotherapy → local control (surgery and/or radiotherapy) → adjuvant chemotherapy. Surgery is preferred for local control when feasible (better local recurrence rates). Osteosarcoma and chondrosarcoma are radio-RESISTANT.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        }
      ]
    },
    {
      "title": "Rehabilitation",
      "chapters": [
        {
          "title": "Principles",
          "range": "Q1529-Q1531",
          "questions": [
            {
              "number": 1529,
              "stem": "Weight-bearing status after surgery — 'touch weight-bearing' (TWB) means:",
              "options": [
                "The foot touches the ground for balance only, with no significant load transmitted through the limb (typically <20% body weight)",
                "Full weight through the operated limb",
                "No contact with the ground at all (non-weight-bearing)",
                "50% of body weight through the limb",
                "Running on the operated limb"
              ],
              "answer": "A",
              "explanation": "Weight-bearing terminology: NWB (non-weight-bearing) = NO contact with the ground (crutches/frame, affected foot does not touch). TWB (touch/toe weight-bearing) = foot touches the ground for balance and proprioception only, <20% BW (the weight of the limb only). PWB (partial weight-bearing) = limited weight through the limb, typically 25-50% BW (difficult for patients to gauge accurately without scales). WBAT (weight-bearing as tolerated) = patient loads the limb as much as they can comfortably tolerate (most common instruction after THA/TKA — encourages early mobilisation). FWB (full weight-bearing) = normal weight through the limb. The surgeon's WB instruction depends on: fixation stability, bone quality, fracture pattern, and implant type. Modern arthroplasty: immediate WBAT is standard for cemented and most uncemented implants.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1530,
              "stem": "Heterotopic ossification prophylaxis with indomethacin should be AVOIDED in patients with:",
              "options": [
                "No contraindications — it is safe for everyone",
                "Hypertension only",
                "Diabetes only",
                "Obesity only",
                "Active fracture healing at the same surgical site (NSAIDs may inhibit prostaglandin-mediated bone healing and callus formation)"
              ],
              "answer": "E",
              "explanation": "Indomethacin (and other NSAIDs) for HO prophylaxis must be used cautiously because they inhibit prostaglandin synthesis — prostaglandins play a role in fracture healing (osteoblast recruitment, callus formation, angiogenesis). Concerns: NSAIDs may impair fracture healing, increase non-union rates, and delay union. Evidence is mixed (short courses of 2-3 weeks may be acceptable, prolonged use is more concerning). AVOID indomethacin HO prophylaxis in: (1) patients with active fracture healing at the same site (e.g., acetabular fracture ORIF — HO prophylaxis may impair the fracture union), (2) known NSAID allergy/intolerance, (3) GI ulceration/bleeding risk, (4) renal impairment, (5) patients on anticoagulants (increased bleeding). Alternative: single-dose radiation (700-800 cGy within 24-72h) — particularly useful when NSAIDs are contraindicated.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1531,
              "stem": "The Disability Assessment — the WHO ICF (International Classification of Functioning, Disability and Health) model classifies health outcomes across three domains:",
              "options": [
                "Only medical diagnosis",
                "Only surgical outcome",
                "Only radiographic result",
                "Body function/structure, Activity, and Participation (with environmental and personal factors as contextual modifiers)",
                "Only patient satisfaction"
              ],
              "answer": "D",
              "explanation": "The WHO ICF model provides a comprehensive biopsychosocial framework for understanding disability: (1) Body function and structure (impairments — e.g., loss of ROM, pain, weakness, deformity), (2) Activity (limitations in tasks — e.g., difficulty walking, dressing, gripping), (3) Participation (restrictions in life roles — e.g., unable to work, unable to participate in sport/social activities). These are modulated by: Environmental factors (physical environment, social support, healthcare access, assistive devices) and Personal factors (age, coping style, motivation, education). The ICF model moves BEYOND the traditional biomedical model (disease → impairment) to capture the full impact of musculoskeletal conditions on a person's life. PROMs (Oxford Hip Score, DASH, EQ-5D) attempt to measure across these domains. Rehabilitation should target ALL three ICF domains — not just the impairment.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Nerve Recovery",
          "range": "Q1532",
          "questions": [
            {
              "number": 1532,
              "stem": "Nerve recovery after injury — Seddon's classification of nerve injuries includes neurapraxia, axonotmesis, and neurotmesis. Neurapraxia is characterised by:",
              "options": [
                "Complete transection of the nerve requiring surgical repair",
                "Axonal disruption with intact endoneurium (Wallerian degeneration occurs)",
                "Focal demyelination with intact axons — complete recovery expected within days to weeks (maximum 12 weeks), no Wallerian degeneration",
                "Irreversible damage with no recovery possible",
                "Only sensory loss without motor involvement"
              ],
              "answer": "C",
              "explanation": "Seddon classification: (1) NEURAPRAXIA (mildest): focal demyelination or conduction block — the axon is INTACT, no Wallerian degeneration occurs. Complete recovery expected within days to 12 weeks (remyelination). Example: 'Saturday night palsy' (radial nerve compression). (2) AXONOTMESIS (moderate): axon is disrupted but the endoneurial tubes are INTACT — Wallerian degeneration occurs distal to the injury. Recovery occurs by axonal regeneration along the intact endoneurial tubes at ~1mm/day (1 inch/month). Recovery is usually good but takes months. Example: traction injuries. (3) NEUROTMESIS (most severe): complete disruption of nerve, endoneurium, and perineurium (or entire nerve transection). NO spontaneous recovery — requires surgical repair (direct repair, nerve graft, or nerve transfer). Example: sharp laceration. Sunderland expanded this into 5 degrees.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        }
      ]
    },
    {
      "title": "Applied Basic Science",
      "chapters": [
        {
          "title": "Bone Biology",
          "range": "Q1533-Q1538",
          "questions": [
            {
              "number": 1533,
              "stem": "Which cell type is derived from the monocyte-macrophage lineage and is responsible for bone resorption?",
              "options": [
                "Osteoblast",
                "Osteocyte",
                "Chondroblast",
                "Mesenchymal stem cell",
                "Osteoclast"
              ],
              "answer": "E",
              "explanation": "Osteoclasts are multinucleated cells of haemopoietic (monocyte-macrophage) origin. They resorb bone using a ruffled border, secreting H+ ions and cathepsin K into a sealed resorption lacuna (Howship lacuna). Osteoblasts are mesenchymal-derived bone-forming cells.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1534,
              "stem": "Which signalling pathway is the principal regulator of osteoclast differentiation and activation?",
              "options": [
                "Wnt/β-catenin",
                "RANK/RANKL/OPG",
                "BMP-2 pathway",
                "Hedgehog signalling",
                "Notch pathway"
              ],
              "answer": "B",
              "explanation": "The RANK/RANKL/OPG axis is the master regulator of osteoclastogenesis. RANKL (produced by osteoblasts) binds to RANK on osteoclast precursors, stimulating differentiation and activation. OPG (osteoprotegerin) is a decoy receptor that blocks RANKL, inhibiting osteoclast formation. Denosumab is a therapeutic anti-RANKL antibody used in osteoporosis.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1535,
              "stem": "Wolff's law states that bone remodels in response to mechanical loading. Which cell type acts as the primary mechanosensor in bone?",
              "options": [
                "Osteocyte",
                "Osteoblast",
                "Osteoclast",
                "Periosteal fibroblast",
                "Chondrocyte"
              ],
              "answer": "A",
              "explanation": "Osteocytes are the most abundant bone cells, embedded within lacunae and connected via canaliculi forming a lacunar-canalicular network. They detect mechanical strain (fluid shear stress within canaliculi) and signal to osteoblasts and osteoclasts to coordinate remodelling. This mechanotransduction underpins Wolff's law.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1536,
              "stem": "Woven bone differs from lamellar bone in which of the following characteristics?",
              "options": [
                "It has a higher collagen content",
                "It is found only in adults",
                "It is mechanically stronger than lamellar bone",
                "It contains no osteocytes",
                "Its collagen fibres are randomly oriented"
              ],
              "answer": "E",
              "explanation": "Woven bone has randomly oriented (disorganised) collagen fibres, making it mechanically weaker than lamellar bone. It is rapidly laid down in fracture healing, pathological states (Paget disease, tumours), and embryonic development. Lamellar bone has regularly oriented collagen in concentric layers (lamellae), providing superior mechanical properties. All bone types contain osteocytes.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1537,
              "stem": "Intramembranous ossification differs from endochondral ossification in that it:",
              "options": [
                "Requires a cartilage template",
                "Occurs in long bone diaphyses",
                "Is the mechanism of secondary fracture healing",
                "Involves direct bone formation from mesenchyme without a cartilage intermediate",
                "Only occurs in embryonic development"
              ],
              "answer": "D",
              "explanation": "Intramembranous ossification forms bone directly from condensed mesenchymal tissue without a cartilage precursor. It is responsible for formation of the flat bones of the skull, clavicle, and mandible, as well as the periosteal appositional growth of long bones. Endochondral ossification requires a cartilage template that is progressively replaced by bone — this forms long bones, vertebrae, and the base of the skull, and is the mechanism of secondary fracture healing.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1538,
              "stem": "The growth plate (physis) is divided into zones. From the epiphysis towards the metaphysis, the correct order is:",
              "options": [
                "Reserve → proliferative → hypertrophic → provisional calcification",
                "Proliferative → reserve → hypertrophic → calcification",
                "Hypertrophic → proliferative → reserve → calcification",
                "Calcification → hypertrophic → proliferative → reserve",
                "Reserve → hypertrophic → proliferative → calcification"
              ],
              "answer": "A",
              "explanation": "From epiphysis to metaphysis: (1) Reserve (germinal/resting) zone — stores stem cells, Type II collagen; (2) Proliferative zone — active chondrocyte division in columns, greatest rate of matrix production; (3) Hypertrophic zone — cells enlarge (Type X collagen), matrix calcifies; (4) Zone of provisional calcification — vascular invasion, primary spongiosa forms. Endochondral ossification then converts this to bone in the metaphysis.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            }
          ]
        },
        {
          "title": "Collagen Types",
          "range": "Q1539-Q1541",
          "questions": [
            {
              "number": 1539,
              "stem": "Type II collagen is the predominant collagen found in which tissue?",
              "options": [
                "Bone",
                "Tendon",
                "Hyaline articular cartilage",
                "Skin",
                "Ligament"
              ],
              "answer": "C",
              "explanation": "Type II collagen is the principal collagen of hyaline articular cartilage and the nucleus pulposus. It forms the Benninghoff arcade structure in cartilage. Type I collagen predominates in bone, tendon, ligament, skin, dentine, and the annulus fibrosus.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1540,
              "stem": "During the early proliferative phase of tendon healing, which collagen type is predominantly produced?",
              "options": [
                "Type I",
                "Type III",
                "Type II",
                "Type IV",
                "Type X"
              ],
              "answer": "B",
              "explanation": "Type III collagen is the first collagen laid down during tendon healing. It is produced by fibroblasts in a disorganised pattern. During the remodelling phase (weeks to months), Type III is gradually replaced by Type I collagen with improved fibre alignment, though the tendon never fully regains its pre-injury mechanical properties.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1541,
              "stem": "Type X collagen is found in which specific zone of the growth plate?",
              "options": [
                "Hypertrophic zone",
                "Reserve zone",
                "Proliferative zone",
                "Zone of provisional calcification",
                "Perichondrial ring of LaCroix"
              ],
              "answer": "A",
              "explanation": "Type X collagen is uniquely expressed in the hypertrophic zone of the physis, where chondrocytes enlarge, the matrix calcifies, and vascular invasion from the metaphysis initiates endochondral ossification. Its presence is a marker of chondrocyte hypertrophy and terminal differentiation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            }
          ]
        },
        {
          "title": "Cartilage",
          "range": "Q1542-Q1543",
          "questions": [
            {
              "number": 1542,
              "stem": "Regarding the structure of articular cartilage, which zone has the highest water content and the lowest proteoglycan concentration?",
              "options": [
                "Transitional (middle) zone",
                "Deep (radial) zone",
                "Calcified zone",
                "Superficial (tangential) zone",
                "Tidemark"
              ],
              "answer": "D",
              "explanation": "The superficial zone has the highest water content (~80%), the highest collagen content, the thinnest collagen fibrils arranged tangentially, and the lowest proteoglycan concentration. It also contains flattened chondrocytes and is responsible for the low-friction surface. The deep zone has the highest proteoglycan content and the lowest water content.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1543,
              "stem": "Articular cartilage is avascular. How does it primarily receive its nutrition?",
              "options": [
                "Through blood vessels in the perichondrium",
                "Through the subchondral bone marrow",
                "By diffusion from synovial fluid",
                "Through lymphatic drainage",
                "Via the tidemark capillaries"
              ],
              "answer": "C",
              "explanation": "Adult articular cartilage has no blood supply, lymphatic drainage, or nerve supply. It receives nutrition by diffusion and convection from the synovial fluid during joint loading and unloading (the 'sponge effect'). Intermittent loading is essential for cartilage health — prolonged immobilisation leads to cartilage atrophy.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Nerve Injury",
          "range": "Q1544",
          "questions": [
            {
              "number": 1544,
              "stem": "In the Sunderland classification, a Grade III injury involves disruption of which structures?",
              "options": [
                "Axon only (endoneurium intact)",
                "Axon and endoneurium (perineurium intact)",
                "Complete transection of all structures",
                "Conduction block only",
                "Axon, endoneurium, and perineurium (epineurium intact)"
              ],
              "answer": "E",
              "explanation": "Sunderland III: axon + endoneurium + perineurium disrupted, with only the epineurium intact. Intrafascicular scarring occurs, and recovery is unpredictable because regenerating axons may not reach appropriate endoneurial tubes. Surgical exploration may be needed.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Fracture Healing",
          "range": "Q1545-Q1548",
          "questions": [
            {
              "number": 1545,
              "stem": "Which type of fracture healing occurs without visible callus formation and requires absolute stability?",
              "options": [
                "Secondary healing",
                "Primary (direct) healing",
                "Endochondral healing",
                "Periosteal healing",
                "Distraction osteogenesis"
              ],
              "answer": "B",
              "explanation": "Primary (direct/Haversian) healing occurs under conditions of absolute stability with no interfragmentary motion. Cutting cones of osteoclasts cross the fracture line directly, followed by osteoblasts laying down new Haversian systems. No callus forms. This is achieved by compression plating and lag screw fixation.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1546,
              "stem": "The four sequential stages of secondary fracture healing are:",
              "options": [
                "Inflammation → proliferation → maturation → remodelling",
                "Haematoma → granulation → woven bone → lamellar bone",
                "Haematoma → soft callus → hard callus → remodelling",
                "Inflammation → fibrocartilage → endochondral ossification → Haversian remodelling",
                "Clot → membrane → bone → lamellar bone"
              ],
              "answer": "C",
              "explanation": "Secondary fracture healing proceeds through four overlapping stages: (1) Haematoma/inflammation — fracture haematoma forms, inflammatory cells recruited, MSCs arrive. (2) Soft callus — fibrocartilaginous tissue bridges the fracture gap. (3) Hard callus — endochondral ossification converts soft callus to woven bone. (4) Remodelling — woven bone replaced by lamellar bone along stress lines (Wolff's law). This process takes months to years.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1547,
              "stem": "Which growth factor is released from the fracture haematoma and plays a critical role in initiating the inflammatory phase of fracture healing?",
              "options": [
                "Bone morphogenetic protein 7 (BMP-7)",
                "Platelet-derived growth factor (PDGF)",
                "Insulin-like growth factor 1 (IGF-1)",
                "Fibroblast growth factor 18 (FGF-18)",
                "Parathyroid hormone (PTH)"
              ],
              "answer": "B",
              "explanation": "PDGF is released from degranulating platelets in the fracture haematoma and is one of the earliest growth factors in fracture healing. It stimulates chemotaxis of inflammatory cells and mesenchymal stem cells to the fracture site, initiating the inflammatory phase. BMPs are important later for osteoblast differentiation. TGF-β, VEGF, and other factors also contribute across different phases.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            },
            {
              "number": 1548,
              "stem": "Which of the following factors is MOST likely to impair fracture healing?",
              "options": [
                "NSAIDs administered in the acute period",
                "Use of an intramedullary nail",
                "Patient age over 50",
                "Application of a functional brace",
                "Early weight-bearing"
              ],
              "answer": "A",
              "explanation": "NSAIDs (particularly indomethacin) inhibit cyclooxygenase and prostaglandin synthesis, which are important in the inflammatory phase of fracture healing. Multiple studies have shown delayed union and non-union with NSAID use in the acute fracture period. Other factors impairing healing include smoking, diabetes, infection, excessive motion, and poor blood supply.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Metabolic Bone Disease",
          "range": "Q1549-Q1551",
          "questions": [
            {
              "number": 1549,
              "stem": "A patient has raised serum alkaline phosphatase with normal serum calcium and phosphate levels. What is the most likely diagnosis?",
              "options": [
                "Osteoporosis",
                "Osteomalacia",
                "Primary hyperparathyroidism",
                "Renal osteodystrophy",
                "Paget disease of bone"
              ],
              "answer": "E",
              "explanation": "Paget disease characteristically shows raised ALP (reflecting increased osteoblast activity) with normal calcium and phosphate. Osteoporosis has entirely normal biochemistry. Osteomalacia shows raised ALP with low calcium and/or phosphate. Primary hyperparathyroidism shows raised calcium and PTH. Renal osteodystrophy shows raised phosphate, low calcium, raised PTH.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1550,
              "stem": "In osteomalacia, the underlying pathology is:",
              "options": [
                "Increased osteoclast activity",
                "Reduced osteoid production",
                "Excessive bone remodelling",
                "Failure of mineralisation of osteoid",
                "Cortical bone thickening"
              ],
              "answer": "D",
              "explanation": "Osteomalacia (in adults) and rickets (in children) result from failure of mineralisation of osteoid, usually due to deficiency of vitamin D, calcium, or phosphate. The osteoid is produced normally but cannot mineralise. This leads to soft, weak bones prone to deformity and insufficiency fractures. Looser zones (pseudofractures) are characteristic radiographic findings.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1551,
              "stem": "A DEXA scan reports a T-score of −2.8 at the femoral neck. This finding indicates:",
              "options": [
                "Normal bone density",
                "Osteoporosis",
                "Osteopenia",
                "Severe osteoporosis",
                "Paget disease"
              ],
              "answer": "B",
              "explanation": "WHO classification: T-score ≥ −1.0 = normal; −1.0 to −2.5 = osteopenia; ≤ −2.5 = osteoporosis; ≤ −2.5 with fragility fracture = severe (established) osteoporosis. A T-score of −2.8 falls in the osteoporosis range. The T-score compares the patient's BMD to a young adult reference population.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Osteonecrosis",
          "range": "Q1552-Q1553",
          "questions": [
            {
              "number": 1552,
              "stem": "The blood supply to the femoral head is primarily from which artery?",
              "options": [
                "Medial femoral circumflex artery",
                "Lateral femoral circumflex artery",
                "Obturator artery (via ligamentum teres)",
                "Superior gluteal artery",
                "Inferior gluteal artery"
              ],
              "answer": "A",
              "explanation": "The medial femoral circumflex artery (MFCA) provides the principal blood supply to the femoral head via its deep branch, which gives rise to the lateral epiphyseal artery (the main supply to the weight-bearing portion of the head). The retinacular vessels run along the femoral neck. The lateral circumflex supplies mainly the anterior neck. The ligamentum teres artery (from obturator) provides a minor contribution in adults.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1553,
              "stem": "Which of the following bones has the highest risk of avascular necrosis following fracture due to its retrograde blood supply?",
              "options": [
                "Lunate",
                "Capitate",
                "Scaphoid proximal pole",
                "Hamate",
                "Trapezium"
              ],
              "answer": "C",
              "explanation": "The scaphoid receives 70–80% of its blood supply via the dorsal branch of the radial artery, entering at the waist and flowing retrograde to the proximal pole. Fractures at the waist or proximal pole disrupt this retrograde flow, producing AVN rates of 15–30% for displaced waist fractures and up to 100% for proximal pole fractures.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Genetics",
          "range": "Q1554-Q1556",
          "questions": [
            {
              "number": 1554,
              "stem": "Achondroplasia is caused by a gain-of-function mutation in which gene?",
              "options": [
                "COL1A1",
                "FBN1",
                "Dystrophin",
                "COL2A1",
                "FGFR3"
              ],
              "answer": "E",
              "explanation": "Achondroplasia results from a point mutation in the FGFR3 gene (fibroblast growth factor receptor 3) on chromosome 4. It is autosomal dominant. The mutation causes constitutive activation of FGFR3, which negatively regulates chondrocyte proliferation in the growth plate. Over 80% of cases are new mutations.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1555,
              "stem": "Osteogenesis imperfecta is most commonly caused by a mutation in which gene?",
              "options": [
                "FGFR3",
                "FBN1",
                "Dystrophin",
                "COL1A1",
                "EXT1"
              ],
              "answer": "D",
              "explanation": "Osteogenesis imperfecta (OI) is predominantly caused by mutations in COL1A1 or COL1A2, which encode the alpha chains of Type I collagen. Most forms are autosomal dominant. The Sillence classification divides OI into types I–IV based on severity. Type I is mildest (blue sclerae, mild fragility); Type II is lethal perinatally.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1556,
              "stem": "Duchenne muscular dystrophy is inherited in which pattern?",
              "options": [
                "Autosomal dominant",
                "Autosomal recessive",
                "X-linked dominant",
                "X-linked recessive",
                "Mitochondrial"
              ],
              "answer": "D",
              "explanation": "Duchenne muscular dystrophy (DMD) is caused by mutations in the dystrophin gene on the X chromosome, inherited as X-linked recessive. It predominantly affects males (1 in 3,500 live male births). Female carriers are usually asymptomatic. Becker muscular dystrophy involves the same gene but produces a partially functional dystrophin protein, giving a milder phenotype.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Intervertebral Disc",
          "range": "Q1557-Q1558",
          "questions": [
            {
              "number": 1557,
              "stem": "The annulus fibrosus of the intervertebral disc predominantly contains which collagen type?",
              "options": [
                "Type II",
                "Type III",
                "Type IV",
                "Type X",
                "Type I"
              ],
              "answer": "E",
              "explanation": "The annulus fibrosus is composed predominantly of Type I collagen arranged in concentric lamellae with alternating fibre orientations (approximately 30° to the horizontal, alternating between adjacent lamellae). This structure resists tensile and torsional forces. The nucleus pulposus contains predominantly Type II collagen and proteoglycans.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1558,
              "stem": "Regarding innervation of the adult intervertebral disc, nerve fibres are found in:",
              "options": [
                "The entire annulus fibrosus and nucleus pulposus",
                "The nucleus pulposus only",
                "The outer third of the annulus fibrosus only",
                "The inner two-thirds of the annulus only",
                "No part of the disc — it is entirely aneural"
              ],
              "answer": "C",
              "explanation": "Nerve fibres are restricted to the outer third of the annulus fibrosus. The sinuvertebral nerve (recurrent meningeal nerve) provides nociceptive innervation. The inner annulus and nucleus pulposus are aneural. Mechanoreceptors are also present in the outer annulus. In disc degeneration, nerve ingrowth into the inner annulus and nucleus may occur, contributing to discogenic pain.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Wound Healing",
          "range": "Q1559",
          "questions": [
            {
              "number": 1559,
              "stem": "Which phase of wound healing is characterised by fibroblast proliferation, collagen synthesis, and angiogenesis?",
              "options": [
                "Haemostasis phase",
                "Proliferative phase",
                "Inflammatory phase",
                "Remodelling phase",
                "Maturation phase"
              ],
              "answer": "B",
              "explanation": "The proliferative phase (days 3–21) involves fibroblast migration and proliferation, new collagen deposition (initially Type III), angiogenesis forming granulation tissue, and epithelial cell migration. The inflammatory phase (days 1–3) involves neutrophils and macrophages clearing debris. The remodelling phase (weeks to months) involves collagen cross-linking and Type III→I transition.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Shock",
          "range": "Q1560",
          "questions": [
            {
              "number": 1560,
              "stem": "A trauma patient has a heart rate of 130, systolic BP of 80 mmHg, respiratory rate of 35, and is confused. Estimated blood loss is 1500–2000 mL. According to the ATLS classification, this represents which class of haemorrhagic shock?",
              "options": [
                "Class III",
                "Class I",
                "Class II",
                "Class IV",
                "Not classifiable without further information"
              ],
              "answer": "A",
              "explanation": "ATLS Class III haemorrhagic shock: 30–40% blood volume loss (1500–2000 mL). Features include tachycardia >120, hypotension (SBP <90), tachypnoea >30, reduced urine output, and anxiety/confusion. Class I: <15% loss (minimal signs). Class II: 15–30% (tachycardia, anxiety). Class IV: >40% (obtunded, no urine output, severe hypotension).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Thromboembolism",
          "range": "Q1561-Q1562",
          "questions": [
            {
              "number": 1561,
              "stem": "Low molecular weight heparin primarily inhibits which clotting factor?",
              "options": [
                "Factor IIa",
                "Factor VII",
                "Factor Xa",
                "Factor IX",
                "Factor XII"
              ],
              "answer": "C",
              "explanation": "LMWH preferentially inhibits Factor Xa via potentiation of antithrombin III. Its shorter chain length (compared to unfractionated heparin) means it cannot simultaneously bridge antithrombin III and thrombin (Factor IIa). UFH has roughly equal anti-Xa and anti-IIa activity due to longer chains.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            },
            {
              "number": 1562,
              "stem": "Rivaroxaban exerts its anticoagulant effect by directly inhibiting which factor?",
              "options": [
                "Factor IIa (thrombin)",
                "Factor Xa",
                "Antithrombin III",
                "Factor VII",
                "Protein C"
              ],
              "answer": "B",
              "explanation": "Rivaroxaban is a direct oral anticoagulant (DOAC) that directly inhibits Factor Xa without requiring antithrombin III as a cofactor (unlike heparins). Dabigatran is a direct thrombin (Factor IIa) inhibitor. These agents are increasingly used for VTE prophylaxis after arthroplasty (NICE guidelines).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Infection",
          "range": "Q1563-Q1564",
          "questions": [
            {
              "number": 1563,
              "stem": "The most common causative organism in acute haematogenous osteomyelitis in children is:",
              "options": [
                "Staphylococcus aureus",
                "Streptococcus pyogenes",
                "Haemophilus influenzae",
                "Salmonella species",
                "Kingella kingae"
              ],
              "answer": "A",
              "explanation": "Staphylococcus aureus is the most common organism causing acute osteomyelitis across all age groups. In neonates, Group B Streptococcus and gram-negative organisms are also important. In children under 5, Kingella kingae has emerged as an important pathogen. In sickle cell disease, Salmonella is classically associated (though S. aureus is still the most common overall).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            },
            {
              "number": 1564,
              "stem": "In septic arthritis of the knee in a child, which combination of clinical predictors (Kocher criteria) gives the highest probability of septic arthritis?",
              "options": [
                "Fever only",
                "Non-weight-bearing and elevated ESR",
                "Elevated CRP only",
                "Joint effusion on ultrasound",
                "Non-weight-bearing, fever, WCC >12,000, ESR >40"
              ],
              "answer": "E",
              "explanation": "The Kocher criteria for septic arthritis of the hip (also applied to other joints) include four predictors: (1) non-weight-bearing, (2) fever >38.5°C, (3) WCC >12,000, (4) ESR >40 mm/hr. The probability of septic arthritis increases with each additional criterion: 1 criterion = ~3%, 2 = ~40%, 3 = ~93%, 4 = ~99%. CRP was later added by Caird et al. as a fifth predictor.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Haemophilia",
          "range": "Q1565",
          "questions": [
            {
              "number": 1565,
              "stem": "A patient with haemophilia A will have which abnormal clotting study result?",
              "options": [
                "Elevated prothrombin time (PT) with normal APTT",
                "Both PT and APTT elevated",
                "Normal PT and APTT with prolonged bleeding time",
                "Elevated APTT with normal PT",
                "Elevated thrombin time only"
              ],
              "answer": "D",
              "explanation": "Haemophilia A (Factor VIII deficiency) affects the intrinsic pathway. This prolongs the APTT (which tests the intrinsic pathway) while the PT (which tests the extrinsic pathway) remains normal. The bleeding time is normal because platelet function is unaffected. Haemophilia B (Factor IX deficiency) produces the same clotting profile.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Heterotopic Ossification",
          "range": "Q1566",
          "questions": [
            {
              "number": 1566,
              "stem": "Which of the following is the most effective prophylaxis against heterotopic ossification following total hip arthroplasty in a high-risk patient?",
              "options": [
                "Physiotherapy alone",
                "Pulsed electromagnetic therapy",
                "Single-dose perioperative radiotherapy",
                "Systemic corticosteroids",
                "Bisphosphonates"
              ],
              "answer": "C",
              "explanation": "Single-dose perioperative radiotherapy (typically 7 Gy within 72 hours of surgery, ideally pre-operatively or within 24 hours post-operatively) is the most effective prophylaxis. Indomethacin (an NSAID) is an alternative pharmacological prophylaxis but risks impaired fracture/bone healing. The Brooker classification grades HO severity (I–IV).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Muscle & Tendon",
          "range": "Q1567",
          "questions": [
            {
              "number": 1567,
              "stem": "The musculotendinous unit of the gastrocnemius-soleus complex crosses which joints?",
              "options": [
                "Knee and ankle",
                "Knee only",
                "Ankle only",
                "Hip and knee",
                "Ankle and subtalar"
              ],
              "answer": "A",
              "explanation": "Gastrocnemius originates from the posterior femoral condyles (above the knee) and the soleus from the posterior proximal tibia and fibula (below the knee). They unite to form the Achilles tendon, inserting on the calcaneus. Gastrocnemius is therefore a two-joint muscle crossing both knee and ankle. The Silfverskiöld test distinguishes gastrocnemius tightness (improves with knee flexion) from soleus/Achilles tightness (persists with knee flexion).",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Easy",
              "tags": []
            }
          ]
        },
        {
          "title": "Ligament",
          "range": "Q1568",
          "questions": [
            {
              "number": 1568,
              "stem": "The four zones of the direct (fibrocartilaginous) tendon-bone insertion (enthesis) are, from tendon to bone:",
              "options": [
                "Tendon → bone → cartilage → fibrocartilage",
                "Tendon → fibrocartilage → mineralised fibrocartilage → bone",
                "Tendon → woven bone → lamellar bone → cortical bone",
                "Tendon → hyaline cartilage → calcified cartilage → bone",
                "Tendon → periosteum → cortical bone → cancellous bone"
              ],
              "answer": "B",
              "explanation": "The direct (fibrocartilaginous) enthesis has four distinct zones providing a gradual transition from soft tissue to bone: (1) tendon/ligament, (2) unmineralised fibrocartilage, (3) mineralised fibrocartilage (separated from zone 2 by a tidemark), (4) bone. This gradual transition dissipates stress concentration at the insertion site.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Synovium",
          "range": "Q1569",
          "questions": [
            {
              "number": 1569,
              "stem": "Synovial fluid in a normal joint is produced by which cells?",
              "options": [
                "Osteoblasts",
                "Type A synoviocytes (macrophage-like)",
                "Chondrocytes",
                "Type B synoviocytes (fibroblast-like)",
                "Endothelial cells"
              ],
              "answer": "D",
              "explanation": "The synovial membrane contains two main cell types: Type A synoviocytes (macrophage-like, phagocytic, derived from monocytes) and Type B synoviocytes (fibroblast-like, produce hyaluronic acid and synovial fluid constituents). Type B cells are responsible for the production of synovial fluid including hyaluronan, which gives the fluid its viscous properties and lubrication function.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Embryology",
          "range": "Q1570",
          "questions": [
            {
              "number": 1570,
              "stem": "Limb bud development begins at which week of embryonic life?",
              "options": [
                "Week 2",
                "Week 8",
                "Week 12",
                "Week 16",
                "Week 4"
              ],
              "answer": "E",
              "explanation": "Limb buds appear at approximately week 4 of embryonic development. The upper limb buds appear slightly before the lower. The apical ectodermal ridge (AER) controls proximal-to-distal limb growth, the zone of polarising activity (ZPA) controls anterior-posterior patterning (via Sonic hedgehog), and the Wnt pathway controls dorsoventral patterning. Limb development is largely complete by week 8.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Hard",
              "tags": []
            }
          ]
        },
        {
          "title": "Bone Grafts",
          "range": "Q1571",
          "questions": [
            {
              "number": 1571,
              "stem": "Which type of bone graft possesses osteogenic, osteoinductive, AND osteoconductive properties?",
              "options": [
                "Autologous cancellous bone graft",
                "Fresh-frozen allograft",
                "Demineralised bone matrix",
                "Hydroxyapatite",
                "Tricalcium phosphate"
              ],
              "answer": "A",
              "explanation": "Autologous cancellous bone graft (e.g., from the iliac crest) is the gold standard because it possesses all three properties: osteogenic (contains living osteoblasts and MSCs), osteoinductive (contains BMPs and growth factors that stimulate new bone formation), and osteoconductive (provides a scaffold for new bone growth). Allografts lose osteogenic cells during processing. DBM is osteoinductive and osteoconductive. Synthetic substitutes are osteoconductive only.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Osteoarthritis",
          "range": "Q1572",
          "questions": [
            {
              "number": 1572,
              "stem": "In osteoarthritis, the earliest histological change in articular cartilage is:",
              "options": [
                "Subchondral sclerosis",
                "Surface fibrillation and loss of proteoglycans",
                "Osteophyte formation",
                "Full-thickness cartilage loss",
                "Synovial inflammation"
              ],
              "answer": "B",
              "explanation": "The earliest histological change in OA is surface fibrillation (disruption of the superficial tangential zone) accompanied by loss of proteoglycans (particularly aggrecan) from the cartilage matrix. This increases water content (paradoxical — swelling of early OA cartilage) and reduces compressive stiffness. Later changes include fissuring, chondrocyte clustering, and full-thickness loss. Subchondral sclerosis and osteophytes are secondary changes.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Rheumatoid Arthritis",
          "range": "Q1573",
          "questions": [
            {
              "number": 1573,
              "stem": "Rheumatoid arthritis is characterised by which primary pathological process in the joint?",
              "options": [
                "Osteophyte formation",
                "Crystal deposition",
                "Subchondral cyst formation",
                "Ligament ossification",
                "Pannus formation with synovial hyperplasia"
              ],
              "answer": "E",
              "explanation": "RA is an autoimmune inflammatory arthropathy characterised by chronic synovial hyperplasia (pannus formation). The pannus is an aggressive, vascularised granulation tissue that erodes articular cartilage and subchondral bone from the joint margins. Key features: symmetrical polyarthritis, juxta-articular osteoporosis, marginal erosions, joint subluxation. RF and anti-CCP antibodies are diagnostic markers.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Connective Tissue",
          "range": "Q1574",
          "questions": [
            {
              "number": 1574,
              "stem": "The Golgi tendon organ is a mechanoreceptor found in tendons that detects:",
              "options": [
                "Muscle length",
                "Rate of change of muscle length",
                "Joint position",
                "Muscle tension",
                "Vibration"
              ],
              "answer": "D",
              "explanation": "Golgi tendon organs (GTOs) are located at the musculotendinous junction and detect changes in muscle tension (force). They provide feedback for the inverse stretch reflex (autogenic inhibition), which causes muscle relaxation when excessive tension is detected, protecting against tendon avulsion. Muscle spindles detect muscle length (stretch) and rate of length change.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        },
        {
          "title": "Pathology",
          "range": "Q1575",
          "questions": [
            {
              "number": 1575,
              "stem": "A patient develops acute gout. The causative crystals are:",
              "options": [
                "Calcium pyrophosphate dihydrate, positively birefringent",
                "Calcium hydroxyapatite, non-birefringent",
                "Monosodium urate, negatively birefringent",
                "Calcium oxalate, positively birefringent",
                "Cholesterol crystals, variably birefringent"
              ],
              "answer": "C",
              "explanation": "Gout is caused by monosodium urate (MSU) crystals, which are needle-shaped and negatively birefringent under polarised light (yellow when parallel to the compensator axis). Pseudogout is caused by calcium pyrophosphate dihydrate (CPPD) crystals, which are rhomboid-shaped and weakly positively birefringent (blue when parallel). Hydroxyapatite crystals (Milwaukee shoulder) are not birefringent on standard polarised microscopy.",
              "distractors": "",
              "takeHome": "",
              "difficulty": "Medium",
              "tags": []
            }
          ]
        }
      ]
    }
  ]
}