Shoulder morphology and throwing shoulder pain: Associations with humeral retroversion angle and posterior glenohumeral distance

To examine the association between shoulder joint morphology and a history of throwing shoulder pain. Male collegiate and corporate league baseball players (n&#x2009;=&#x2009;21; 20.2&#x2009;&#xb1;&#x2009;1.5 years) underwent bilateral shoulder imaging using open magnetic resonance imaging (MRI) in simulated abduction-external rotation positions replicating the late cocking phase. The posterior glenohumeral distance (PGHD) and humeral retroversion angle were measured. Side-to-side measures were calculated as the %PGHD and the difference in the humeral retroversion angle; higher values indicated greater morphological changes in the posterior glenoid rim and increased humeral retroversion in the throwing shoulder, respectively. Structural equation modelling examined the relationships among the %PGHD, the difference in the humeral retroversion angle, and a history of throwing shoulder pain. The difference in the humeral retroversion angle was 8.0&#xb0;&#x2009;&#xb1;&#x2009;4.9&#xb0;, and the %PGHD was 187.1%&#x2009;&#xb1;&#x2009;76.2%. A history of throwing shoulder pain was present in 8 of 21 athletes. A larger %PGHD was significantly associated with a smaller difference in the humeral retroversion angle (&#x3b2;&#x2009;=&#x2009;-0.506, p&#x2009;=&#x2009;0.012), which, in turn, was significantly associated with a history of throwing shoulder pain (&#x3b2;&#x2009;=&#x2009;-0.885, p&#x2009;<&#x2009;0.001). Reduced humeral retroversion may be accompanied by morphological changes in the posterior glenoid rim, which may be associated with an increased risk of throwing shoulder injury. MRI&#x2011;based morphological assessment is useful as a research tool to understand the pathomechanisms of throwing&#x2011;related shoulder injury and to validate potential clinical markers. Level IV, cross-sectional observational study.