2004 Volume 28 Issue 3 Pages 427-431
The Purpose of this study was to analyze the articular contact pattern of the normal glenohumeral joint. There are few previous papers concerning the dynamic contact patterns, although the studies of using the cadaver or the tracking device have been reported. The subjects consisted of 10 normal volunteers. The subjects were fixed on a tilted stand with free motion around the scapula.3D MRI images were extracted at the scapular plane at every 30° between 30° and 150° in the supine position. The images obtained at each position were transmitted to a personal computer and the description of the bony frame by digitizing methods using the analyzing software were developed. Three dimensional reconstruction of the glenohumeral joint were performed. The items of measurement were the following (1)The contact area; the distances between the humeral head and the glenoid surface were calculated and the distribution set at the distances were considered to be the contact area. The shortest distance was regarded as the proximity of the joint. The change of the center of the distribution was investigated. (2)The center of the humeral head (3) Kinematics of the humerus; (from the aspect of the scapula) Results: (1)In the contact area; the minimum contact area had shifted superiorly up to 90 or 120° elevation, but after 120° it shifted inferiorly. Concerning the antero-posterior direction of the glenoid, it shifted antero-inferiorly at the elevated position compared to that of the 30Thlevation. (2)In the center of the humeral head; it shifted superiorly at 120° or 150° compaired to the 30° elevation. Its change was within 3mm. (3)In the Kinematics of the humerus; although the glenohumeral movement was totally 66°, it was only 17' after 90° elevation. We conclude that although the contact area shifted superior until 90°, it shifted to the central part of the glenoid over 120°, because the centripetal force might have worked at the elevated position. The distribution of the contact area was assumed to be reflected as a result of seeking a good congruity of the humeral head and the glenoid.
