Scapular kinematics in constrained and functional upper extremity movements.

STUDY DESIGN Controlled laboratory study using a single-group, repeated-measures design. OBJECTIVES To investigate scapular kinematics during both constrained and functional shoulder movements. BACKGROUND Abnormal scapulothoracic joint motion has been associated with pathologies such as shoulder impingement. Constrained protocols are commonly used in the measurement of shoulder kinematics; however, few studies have measured motion during functional tasks. METHODS Twenty-five healthy subjects participated in this study. Three-dimensional kinematic data from the scapula and humerus with respect to the thorax were collected with a magnetic tracking system. Functional testing consisted of 6 different tasks representing common activities of daily living. Constrained testing consisted of at least 42 arm elevations in various planes. Two-way analyses of variance with repeated measures were used to compare scapular rotations between constrained and functional movements at the same humeral elevation and plane of elevation angles. Intersubject variability was compared between the overhead tasks and the constrained humeral elevation in the scapular plane by using the coefficient of multiple correlations. RESULTS Significant differences between constrained trials and functional tasks were found for all scapular rotations. A similar pattern was observed for scapular rotations variability between overhead tasks and constrained arm elevation in the scapular plane. CONCLUSION Care needs to be taken when comparing and generalizing scapular kinematic data from constrained humeral movements and applying it to functional humeral movements.