Humeral head retroversion in competitive baseball players and its relationship to glenohumeral rotation range of motion

DESIGN: Prospective case series. OBJECTIVE: To determine if an osseous component in the form of increased humeral head retroversion may contribute to observed differences in the amount of rotation between the throwing and nonthrowing shoulders of competitive baseball players. BACKGROUND: Differences in side-to-side shoulder rotation range of motion (ROM) are seen in throwing athletes. In the past, these differences have been attributed to adaptive changes to the surrounding soft tissue structures, including attenuation of the anteroinferior capsule and ligaments, and tightening of the posterior capsule. Recent studies, however, suggest that a possible osseous adaptation in the form of increased humeral head retroversion may be the cause of this side-to-side ROM difference. METHODS AND MEASURES: Twenty-five individuals (19 competitive baseball players, 6 controls with no history of specific overhead sports activity) with no previous shoulder surgery and free of any symptomatic shoulder pathology at the time of testing participated. All subjects underwent bilateral computed tomography (CT) scans to determine the angle of humeral head version. Maximal shoulder internal and external rotation ROM at 901 abduction were measured both passively and actively for both shoulders. RESULTS: Players had statistically significant (P<.001) side-to-side difference in humeral head version, with an average of 10.61 greater retroversion in their throwing arm compared to their non-throwing arm. A significant side-to-side difference was not observed in the control group (average difference, 2.31; P = .197). Greater humeral head retroversion was associated with greater external rotation ROM and lesser internal rotation ROM in the throwing arm of the throwers. CONCLUSIONS: Our results indicated that highly competitive baseball players do have greater humeral head retroversion in their dominant arm, which can partially explain the observed differences in side-to-side shoulder rotation ROM.