Chronic Adaptations of the Shoulder in Baseball Pitchers: A Systematic Review

Abstract

Background:

Understanding clinical and tissue adaptations to the throwing shoulder is important for optimizing injury prevention and rehabilitation programs in baseball players.

Purpose/Hypothesis:

The purpose of this study was to determine the chronic clinical (range of motion [ROM] and strength) and tissue adaptations of the throwing shoulder in baseball pitchers. It was hypothesized that the throwing shoulder would have increased external rotation (ER) ROM and decreased internal rotation (IR) ROM compared with the nonthrowing shoulder, but that calculations of soft tissue glenohumeral IR deficit (GIRD) and soft tissue ER gain (ERG) would show that the true soft tissue restrictions were instead in the direction of ER ROM.

Study Design:

Systematic review; Level of evidence, 4.

Methods:

This systematic review was performed according to PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines using various keywords related to the shoulder and baseball. Studies were included if chronic adaptations of the shoulder were evaluated bilaterally in nonrecreational baseball pitchers. Outcomes of interest collected include IR and ER ROM measured in 90° of shoulder abduction, humeral retroversion (HR), GIRD, ERG, and various structural adaptations. All other chronic adaptations were compiled and reported qualitatively because of the heterogeneity of variables assessed.

Results:

Overall, 1273 studies were screened and 36 met final inclusion criteria, with 24 studies (67%) evaluating professional pitchers. Across 13 studies and 1101 professional pitchers, the mean clinical GIRD was 10.0° and the mean clinical ERG was 6.5°, leading to a total arc of ROM deficit of 3.5° in the throwing shoulder. Across 498 included pitchers with HR measures, the mean bilateral difference in HR was 15.4°. After calculating soft tissue GIRD, 3 of 4 studies found that pitchers do not have any soft tissue restrictions in IR ROM. In contrast, after calculating soft tissue ERG, all 4 studies found pitchers to have soft tissue restrictions in ER ROM with a mean of 8° to 13°.

Conclusion:

When isolating for soft tissue restrictions through calculation of soft tissue GIRD and ERG, previously reported IR ROM deficits are currently not as prevalent, and soft tissue restrictions in ER ROM are now being observed. Clinicians should focus on better isolating soft tissue restrictions to evaluate whether an athlete has deficits in IR or ER ROM.