Three-Dimensional Analysis of Scapular Kinematics During Arm Elevation in Baseball Players With Scapular Dyskinesis: Comparison of Dominant and Nondominan Arms

Background: The knowledge of 3-dimensional scapular kinematics is essential for understanding the pathological lesions of the shoulder and elbow in throwing athletes. Many studies about alterations of the resting scapular position, dynamic scapular motion, or scapular dyskinesis (SD) have been conducted, yet none of them have identified a consistent pattern of altered scapular kinematics in throwing athletes. Hypothesis/Purpose: To analyze the 3-dimensional scapular kinematics of dominant and nondominant arms in baseball players with a pathological condition of the shoulder or elbow. Study Design: Cross-sectional study. Methods: Bilateral scapular positions, consisting of upward rotation (UR), superior translation (Si), internal rotation (IR), protraction (PRO), and anterior tilting (Al) with an arm at rest and at 150 degrees forward elevation, were measured among 319 baseball players with SD using 3-dimensional computed tomography. Angular values of scapula were compared between dominant and nondominant arms with statistical analysis. Level of Evidence: Level III, diagnostic study. Results: The scapular position of dominant arms showed significantly more AT, less ST at rest and more UR and IR and less ST, PRO, and AT at 150 degrees full forward elevation compared with the nondominant arms. The magnitude of mean change of UR, IR, PRO, and AT during arm elevation increased significantly between the paired arms (P value: UR, ST, PRO, and AT: <.001 and IR: .001). Conclusion: When compared with the nondominant arms, UR, AT, and PRO with the arm at 150 degrees forward elevation of dominant symptomatic arms in baseball players tilted toward positive compensation, whereas IR altered toward negative decompensation. In addition, the angular increment of the scapula increased significantly in dominant symptomatic arms compared with the nondominant arms.