Posterior dislocation of the shoulder.

Abstract

The shoulder is the most frequently dislocated joint in the body (6). Ninety-five per cent of all its dislocations are anterior. Certain rare dislocations—superior, inferior, and intrathoracic (9)—and osterior dislocations account for the remainder. The latter constitute approximately 2 per cent of the total. The lowest incidence reported is just under 1 per cent, in a series reviewed by Ellerbrolk and cited by Dardel (Thomas, 11). Ellerbrolk is said to have seen only 4 instances in 404 cases of shoulder dislocation. The highest incidence, 3.78 per cent, is reported by McLaughlin (7), who saw a total of 22 cases in a series of 581 dislocations involving the shoulder joint. Wilson and McKeever (14) found 4 examples in 260 cases of shoulder dislocation. In fifteen years at Massachusetts General Hospital (15), there were 5 instances in 200 shoulder dislocations, an incidence of 2.5 per cent, or about one case every three years. Posterior shoulder dislocation thus accounts for such a small percentage in most series that it automatically recedes into the background as a possibility (9, 13) and is therefore often overlooked, with dire consequences, as will be demonstrated in the cases to be presented. This point is stressed almost unanimously in the literature, especially in pathological descriptions of chronic or recurrent dislocation (4, 9, 13). Bilateral posterior dislocation has been reported by Coover (3), McLaughlin, Wilson and McKeever, and Thomas (quoting Mynter). A bilateral dislocation reported by McLaughlin had gone undiagnosed for thirty-five years. Less severe degrees of posterior dislocation—so-called subacromial dislocation (11)—may be missed either when they are associated with other severe bodily injuries, coma, shock, etc., or with a fracture of the upper humerus. This lesser degree of displacement is the subject of an unusually thorough review by Thomas. When such dislocation occurs alone, it is extremely difficult to demonstrate even with stereoscopic films, as noted in the literature (8, 11, 14, 15). Posterior dislocations are the result of forces the opposite of those producing anterior dislocation. There is usually a history of internal rotation and adduction, as noted in all series and most isolated case reports, and the clinical deformity is of that type. At times there is complete loss of ability to abduct the arm (8). This is not invariably the case, however, and some patients with posterior dislocation can abduct the arm well enough to allay suspicion as well as permit easy examination of the shoulder by means of a view axially directed with reference to the trunk of the body. This view, called the lateral view by some reporters, may be unobtainable (8). Where conditions permit, it is invaluable. Posterior dislocations of the shoulder are often associated with convulsive seizures, especially those of epilepsy and electric shock, both accidental and therapeutic (7, 9, 10, 11).