Articular contact patterns of the normal glenohumeral joint.

The purpose of this study was to determine the articular contact patterns of the normal glenohumeral joint, and to correlate these findings with cartilage and subchondral bone architecture. We studied 10 normal shoulders of cadavers. We removed all soft tissues except the joint capsule and rotator cuff and then placed the shoulders on a testing apparatus that allowed freedom of translation in three planes. After the humerus was placed in a neutral position of rotation, articular contact patterns were measured with specially prepared prescale Fuji film so that it could be inserted between the joint surfaces. Articular contact was analyzed with 222 and 444 N of joint compressive load, and the humerus was positioned in scapular plane abduction of 0 degree, 45 degrees, and 90 degrees. The contact patterns were then digitized to determine percentage contact of the humeral head on the glenoid. We studied 12 additional cadaver shoulders with fine microradiographs and histologic techniques after we sectioned the glenoids in the anterior-posterior and superior-inferior planes. We then analyzed articular and subchondral architecture. We found that when the shoulder was adducted the contact area of the humeral head on the glenoid was limited to the anatomic region of the central glenoid known as the "bare area." This was histologically and radiographically an area of cartilage thinning and increased subchondral bone density. As the shoulder was abducted the articular congruity and percentage contact area increased. We concluded that there was a slight articular mismatch with the shoulder adducted in the normal shoulder. Histologic and radiographic studies suggested that the central bare area region of the glenoid was a region of increased compressive loading. As the shoulder was abducted the joint became more congruent and thus the contact area of the humeral head on the glenoid increased.