Shoulder kinematics, including scapular rotation relative to the trunk and humeral rotation relative to the scapula, were examined during humeral elevation in three vertical planes via video analysis of intracortical pins. Helical axis parameters provided an easily interpretable description of shoulder motion not subject to the limitations associated with Cardan/Euler angles. Between 30 and 150° of elevation in each plane, the scapula rotated almost solely about an axis perpendicular to the scapula. Additional scapular rotation appeared to support the notion that the scapula moves “toward” the plane of elevation. Humeral rotation took place mainly in the plane of the scapula independent of the plane of elevation. Many parameters of shoulder complex kinematics were quite similar across all planes of elevation, suggesting a consistent movement pattern with subtle differences associated with the plane of elevation.
Timothy J. Koh and Mark D. Grabiner are with the Department of Biomedical Engineering, and John J. Brems is with the Department of Orthopedic Surgery, The Cleveland Clinic Foundation, Cleveland, OH 44195. Direct correspondence to Timothy J. Koh, Department of Physiological Science, University of California, Los Angeles, 405 Hilgard Ave., Los Angeles, CA 90095-1527.