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 ...