SHOULDER-JOINT (AS. sculdor, 0110.. sealtin.a,( h-r. Schuller; of unknown etymology). A ball-and-socket joint formed at the junction of the humerus and scapula. The large globular head of the humerus is received into the shallow• glenoid cavity of the scapula, by which arrange ment extreme freedom of tnotion is obtained, while the apparent insecurity of the joint is pre vented by the strong ligaments and tendons which surround it, and also by the arched vault above formed by the under surface of the acromion and co•acoid processes. (See SCAPULA.) As in movable joints generally, the articular surfaces are covered with cartilage, and there is a synovial membrane which lines the interior of the joint. The most important connecting medium between the two bones is the capsular ligament, which is a fibrinous expansion embracing the margin of the glenoid cavity above, while it is prolonged upon the tuberosities of the humerus below.
The morbid affections of the shoulder-joint may be divided into (1) those arising from disease and (2) those dependent on an accident. The shoulder-joint is not as liableto disease as the other articulations; it may, however, become the seat of a synovial inflammation, active, subacute, or chronic, and less often of tubercular syphilitic o• rheumatic disease. There may be fracture
(1) of the acromion process, o• (2) of the cora coid process, or (3) of the neck of the scapula, or (4) of the superior extremity of the humerus; or two or more of these accidents may be asso ciated. Again, the head of the humerus may lie dislocated from the glenoid cavity in a direc tion above, below, in front, o• behind this cavity. The anterior variety is most frequent. The fol lowing are the most prominent symptoms: The arm is lengthened; a hollow' may be felt under the acromion, where the head of the bone ought to be; the shoulder seems flattered; the elbow sticks out from the side, and cannot be made to touch the ribs: and the head of the hone can be felt if the limb be raised, although such an at tempt causes great pain and weakness from the pressure exerted on the axillary plexus of nerves. For a description of the symptoms and mode of treatment of fractures and dislocations, consult Park, Surgery by American Authors (New York, 1901).