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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. bilateral computed tomography (CT) scans to determine the angle of humeral head version. Maximal shoulder internal and external rotation ROM at 90 degrees 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 10.60 greater retroversion in their throwing arm compared to their nonthrowing arm. A significant side-to-side difference was not observed in the control group (average difference, 2.30; 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.