Humeral retrotorsion corrected glenohumeral external rotation deficits are present in medial ulnar collateral ligament injured and uninjured college baseball players.

Background: Glenohumeral rotational motion should be interpreted within the context of relative humeral retrotorsion (rHRT). To date, no study has investigated shoulder rotational motion within the context of rHRT in a medial ulnar collateral ligament (MUCL)-injured population. Therefore, the purpose of this study was to determine if there were differences in HRT-corrected rotational motion between MUCL-injured and uninjured college baseball players. Methods: Thirty-five baseball players diagnosed with an MUCL injury were matched with 35 uninjured controls. Glenohumeral external rotation (GER) and internal rotation (GIR), as well as anatomic HRT, were collected on both arms. Data reduction was performed for all objective rotational motions and anatomic HRT, which was used to quantify rHRT. rHRT was then used to calculate HRT-corrected GER and HRT-corrected GIR. Outcomes were compared between groups using multivariate analysis of covariance, controlling for baseline cohort differences. Results: Results indicated no significant multivariate effects of cohort, body mass index, or level of competition on HRT-corrected GER or GIR (all Pillai's Trace P > .05, partial η2 ≤ 0.019). Adjusted estimated marginal means for HRT-corrected GER were -9.99° (standard error [SE] = 2.51) for the MUCL cohort and -5.45° (SE = 2.51) for the uninjured cohort; for HRT-corrected GIR, they were 5.01° (SE = 2.46) and 2.21° (SE = 2.46), respectively. Conclusion: HRT-corrected GER deficits are more prevalent than HRT-corrected GIR deficits in both cohorts. These findings continue to highlight the importance of accounting for osseous adaptations in range of motion measurements, as GIR deficit is not as common as previously thought.