SHOULDER-70INT, THE, is a ball-and-socket joint. The bones entering into its com position are the humerus or arm-bone, and the scapula or shoulder-blade, the large globular head of the former being received into the shallow glenoid cavity of the latter, an arrangement by which extreme freedom of motion is obtained, while the apparent. insecurity of the joint is guarded against by the strong ligaments and tendons which surround it, mid above, by the arched vault formed by the under surface of the aeromion and coracoid processes. See FCAPULA. As in movable joints generally, the articular surfaces are covered with cartilage, and there is a synodal membrane which lines the interior of the joint. The most important connecting medium between the two bones is the capsular liirantent, which is a fibrinous expansion embracing the margin of the glenoid cavity above, while it is prolonged upon the tuberosities of the humerus below. From its relations wills the surrounding muscles, the ligament derives much of its strength. Accordingly, in paralysis of the arm, one or two fingers can often he pressed into tile joint toward the head of the glenoid cavity, from which the head of the humerus IS now separated.
The shoulder-joint exhibits the following varieties of motion. 1. Flexion, to a great extent; 2. Extension, in a much more limited degree; 8. At!cluetion, in an direc tion, forward and inward; 4. Abduction, very freely: 5. Ciremnduction; and C. Rota tion slightly.
The morbid affections of the shoulder-joint may he divided Into (1) those arising from disease, and (2) thosii dependent on all accident. The most common disms•s are nettle and chronic inflammation of the joint, which often terminate in its anchylosia er immo biiity. The principal accidents arc fractures and dislocations. There may be fracture (1) of the aeromion process, or (2) of the eoracoid process, or (3) of the neck of the reap- ula, or (1) of the superior extremity of the humerus; or two or more of these accidents may be associated. Again, the head of the humerus may be dislocated from the glenoid
cavity as the result of accident in three different directions—viz. (1) Downward and inward into the axilla, which is by far the most common form; (2) Forward and inward; and (3) Backward on the infra-sphums fossil, or the dorsi= of the scapula. The first of these varieties is of such common occurrence that persons of ordinary intelligence should know how to recognize, and even (in an emergency) to treat it. The folio wiag DM the most prominent 83'1111)(0111S: arm is lengthened; a hollow may he felt under the itgrondou, where the head of the bone ought to be; the shoulder scents flattened; the elbow sticks out from the side, and cannot be made to touch the ribs; and the bead of the bone can be felt if the limb be raised, although such an attempt causes great pain and weakness from the pressure exerted on the axillary plexus of nerves."— Druitt's Surgeon's rade-mecum, 8th ed. p. 282. There are at least five methods of treat ing this form of dislocation. It is sufficient to notice two of them. 1. Reduction by the heel in the axilla. The patient lies on a couch, and the operator sits at the edge and puts his heel (the shoe or boot being previously removed) into the axilla, to press the head of the bone upward and outward, and at the same time pulls the limb downward by means of a towel fastened above the elbow. 2. Reduction by the knee in the The patient being seated in a chair, the surgeon places one of his knees in the axilla, resting his foot on the chair. He then puts one hand on the shoulder to fix the se twilit, and with the other depresses the elbow over his knee.—For a description of the symp toms and mode of treatment of the other forms of dislocation, and of the different van-. etics of practice, we must refer the reader to any systematic treatise on surgery.