Ratio between 3D glenohumeral and scapulothoracic motions in individuals without shoulder pain

This study determined the ratio between glenohumeral and three-dimensional scapular motion during arm elevation and lowering in 91 individuals without shoulder pain. Scapular kinematics were assessed using an electromagnetic tracking device. Individuals performed 3 repetitions of elevation and lowering of the arm in the sagittal plane. Two-way ANOVAs (interval: 30-60°, 60-90°, 90-120° x phase: elevation and lowering) and paired t-tests were used for data analysis. For scapular internal/external rotation, lesser scapular internal rotation contribution was found during the 60-90° interval as compared to the 90-60° interval. Lesser scapular external rotation was identified in the 60-30° interval of arm lowering. The ratio was greater during arm elevation (1.89) compared to lowering (1.74) across the entire motion arc. For scapular upward rotation, greater upward rotation contribution was observed during arm elevation at the 30-60° interval, and less scapular downward rotation contribution in the final range of arm lowering. For scapular tilt, lesser scapular posterior tilt contribution during arm elevation was observed compared to arm lowering. The ratios between glenohumeral elevation/lowering and each individual scapulothoracic motion showed either differences between intervals and/or between elevation and lowering during specific intervals in healthy individuals.