Humeral Retroversion and Capsule Thickening in the Overhead Throwing Athlete: A Systematic Review
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PURPOSE: To investigate the humeral and soft-tissue adaptations, including humeral retroversion, range of motion, and posterior capsule changes, in overhead throwing athletes. METHODS: We performed a systematic review in accordance with Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines. PubMed, MEDLINE, CENTRAL (Cochrane Central Register of Controlled Trials), and Embase were searched from January 1, 2011, through April 23, 2017, by 2 reviewers independently and in duplicate. The methodologic quality of all included articles was assessed using the Methodological Index for Non-randomized Studies criteria. Interobserver agreement for assessments of eligibility was calculated with the Cohen κ statistic. Descriptive statistics and raw counts were used to summarize data. RESULTS: We identified 14 studies (6 Level IV and 8 Level III) including 1,152 overhead throwing athletes. The mean age of the included athletes was 18.37 years (standard deviation, 1.52 years), with 59% of the athletes being pitchers and 41% being position players. Significantly greater humeral retroversion was found across all studies evaluating bony morphology in the dominant arm of overhead throwing athletes (range of mean differences, 9.6°-25.8°). Each of these studies also found decreased internal rotation in the dominant arm (range of mean internal rotation differences, -28° to -7.8°). Five studies found a significant negative correlation between the difference in humeral retroversion between the 2 arms and the difference in internal rotation (range of Pearson correlation coefficients, -0.56 to -0.35). Soft-tissue adaptations were assessed in 5 studies, with 4 identifying significantly thicker posterior capsules and 2 identifying significantly stiffer posterior capsules (P < .05). CONCLUSIONS: Overhead throwing athletes consistently show several distinct changes in their dominant shoulder. These include increased humeral retroversion and the presence of a thickened and stiff posterior capsule. Concomitantly, there is often reduced internal rotation and increased external rotation of the dominant arm. LEVEL OF EVIDENCE: Level IV, systematic review of Level III and IV studies.
