Motion analysis assessment of alterations in the scapulo-humeral rhythm after throwing in baseball pitchers

Purpose: Throwing a baseball requires a coordinated sequence of scapula and humerus movements also called scapulo-humeral rhythm (SHR). Fatigue associated with repetitive throwing can lead to scapular dyskinesia, a recognized cause of shoulder disability in pitchers and overhead athletes. We introduce a novel device, the Xbus Kit, which can objectively assess scapular biomechanics and the effect of pitching on SHR. Methods: SHR was studied using the Xbus Kit (Xsens Technologies B.V., NL). Thirteen collegiate baseball pitchers (aged 20 ± 2.6) were studied, evaluating SHR in forward elevation and abduction in three sessions: before throwing (S1), after 60 pitches (S2) and 24 h after a pitching session (S3). Results: SHR changes were found in 85 % of pitchers (11 cases), and no changes were observed in 2 cases (15 %). We were able to subdivide pitchers into four groups, based on their response to pitching. Conclusion: Repetitive movement of pitching leads to SHR changes and sometimes, incomplete restoration of normal shoulder biomechanics. © 2013 Istituto Ortopedico Rizzoli.