In vivo three-dimensional kinematics on bilateral shoulders between body postures

Abstract

Body posture and arm dominance would change the shoulder muscle activation and the range of motion. But those altered shoulder kinematics have not been objectively assessed. The purpose of this study is to evaluate the influence between the standing and supine postures on bilateral shoulder kinematics during arm elevation. Scapular plane humeral elevation in 16 healthy volunteers, eight males and eight females (mean age, 33; range, 19-47) was analyzed using 3D model-image registration methods. Humeral head position relative to glenoid, acromiohumeral distance and scapular rotations were measured and compared between postures. Besides, the effect of arm dominance also was statistically evaluated. Humeral head position relative to glenoid had a significant difference, but acromiohumeral distance did not, between postures. Scapular rotations also were way different between postures. Especially, increasing pattern of upward rotation in supine seemed not to reflect scapulohumeral rhythm which would show almost linear increment. Asymmetries between dominant and non-dominant shoulders had small but significant differences. But the discrepancy tended to be decreased in supine. The change of gravity, scapular orientation and muscle activity might have contributed these results between postures. Our findings indicate that kinematic comparison between postures might be useful to develop diagnostic insight and physical treatment.