Three-dimensional in vivo kinematics of the shoulder during humeral elevation

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 degrees of elevation in each plane, the scapula rotated almost solely about an axis perpendicular to the scupula. 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.