Background: Increased external rotation and decreased internal rotation have been noted to occur progressively in the throwing shoulder of baseball pitchers.
Hypothesis: Proximal remodeling of the humerus contributes to the rotational asymmetry between shoulders in pitchers.
Study design: Descriptive anatomic study.
Methods: Both shoulders of 19 male college baseball pitchers were evaluated and retroversion of the humerus calculated by using the technique of Söderlund et al. Measurements were taken of passive glenohumeral external rotation at 0 degrees and 90 degrees of abduction and internal rotation at 90 degrees of abduction under a 3.5-kg load. Subjects completed a questionnaire on the amount and duration of overhead throwing performed during the ages 8 through 16 years.
Results: All of the subjects had greater external rotation at 0 degrees and 90 degrees of abduction, decreased internal rotation at 90 degrees of abduction, and greater retroversion of the humerus in their dominant compared with nondominant shoulders. A significant difference was found between dominant and nondominant external rotation at 0 degrees and 90 degrees of abduction, internal rotation at 90 degrees of abduction, and retroversion of the humerus. In the dominant arm, there was a significant correlation between retroversion of the humerus and external rotation at 0 degrees and 90 degrees of abduction. There was also a significant correlation between the side-to-side difference in retroversion of the humerus compared with the side-to-side difference in external rotation at 90 degrees of abduction.
Conclusions: Rotational changes in the throwing shoulder are due to bony as well as soft tissue adaptations.