71.9 Posterior dislocation of the shoulder (rare)

If a patient has pain, swelling, and reduced movement after a shoulder injury, together with an apparently normal AP X–ray, suspect that he has a posterior dislocation. Typically, he cannot move his arm, which is locked in adduction and internal rotation. The outline of his shoulder is abnormal, but not as abnormal as in an anterior dislocation. His corticoid process is prominent, and in late cases he has a characteristic dimple on the front of his shoulder. Looked at from above, his shoulder bulges posteriorl . Also, you may be able to feel the head of his humerus posteriorly under the spine of his scapula. His shoulder movements are poor and his humerus feels as if it is fixed to his scapula. You will probably be able to reduce his dislocation without too much difficulty.

Figure 71.9: AN ALTERNATIVE METHOD FOR REDUCING A POSTERIOR DISLOCATION. Flex the patient’s elbow, and exert traction in the long axis of his arm (1). Ask an assistant to press downwards on the head of his humerus with his thumb (2). Adduct his arm while still maintaining traction (3). When the head reaches the glenoid cavity, rotate his arm externally (4), then gently rotate it internally (5). His axillary nerve may be injured, so support his arm in a sling to prevent his humerus dropping out of his glenoid. After de Palma, with kind permission.

POSTERIOR DISLOCATION OF THE SHOULDER

Give the patient a general anaesthetic. Try to put his shoulder through a normal range of movements, while pulling upwards on his humerus, with his arm above his head, and his elbow flexed to relax his biceps tendon. The dislocation will usually reduce promptly.

If this fails, try the alternative method in Fig. 71-9. If this also fails, refer him.

If reduction is successful, put his arm in a sling for 3 weeks and encourage him to move it as soon as he can.

DIFFICULTIES WITH A POSTERIOR DISLOCATION OF THE SHOULDER

If the patient’s DISLOCATION iS OLD, reduction may be possible, so refer him. If this is impractical, ignore the dislocation, and concentrate on active movements and exercises. Occasionally, an arthrodesis is necessary for severe and persistent pain. Posterior dislocations are often overlooked in early stages, so they are often diagnosed too late.