Analysis of the scapulohumeral rhythm

The movement of the shoulder complex was once aptly described by Codman as the "scapulohumeral rhythm". To demonstrate this rhythm, 20 normal men and four patients with rotator cuff rupture were asked to elevate their arms smoothly in approximately three seconds and five seconds in front of a fluoroscope with or without load. The X-ray was irradiated perpendicularly in the scapular plane. The movements were calculated using a computer. In the normal men, the ratio of the scapular movements to humeral movements was not constant during scapular abduction. The movements of the instant center of the humerus occurred in a small area during abduction, and the result suggested that the movement of the glenohumeral joint was almost rotational. The movements of the instant center of the scapula occurred in a relatively large area during abduction. The movements of the shoulder complex with cuff rupture were quite different from those of normal men.