71.8 Anterior dislocation of the shoulder

Dislocation is the most common shoulder injury. It is usually anterior and only occasionally posterior. In an anterior dislocation the head of a patient’s humerus passes forwards and downwards to lie in front of his scapula. In the common subcoracoid variety, the normal outline of his shoulder is broken by the two sharp angles shown in Fig. 71-4. He is in great pain.

This dislocation is often missed because nobody examines the patient for loss of movement, which is the critical sign. Typically, he holds his elbow fixed away from his side, and he cannot make it touch his chest. His injured arm looks longer than his normal one, his shoulder joint is fixed, his elbow is flexed, and his forearm is internally rotated. Although you can make his scapula move over his chest, you cannot make his humerus move on his scapula. If his shoulder is not too swollen, you may be able to feel the displaced head of his humerus below his coracoid process.

The main differential diagnoses of an anterior dislocation are: (1) a fracture of the neck of the humerus, and (2) a fracture dislocation. Both are much less common than a simple dislocation. The treatment for these injuries differs. If you treat either of the latter two injuries as if it were a simple dislocation, the results can be disastrous, so always take an AP and an oblique view before you try to reduce what might seem to be an ordinary dislocation. If you take an oblique view routinely, you will not miss a rare posterior dislocation (71.9). An oblique view is more difficult to take than a true lateral view but is easier to interpret.

Three signs will help you in the differential diagnosis: (1) Can you make the patient’s elbow touch his side? (2) Will his humerus move on his scapula? If one or both these signs are present, he may have fractured the neck of his humerus, or he may have a fracture dislocation. (3) Much swelling also makes a simple dislocation unlikely.

We have not described Kocher’s method for reducing a dislocated shoulder. If you use it and are inexperienced, you may fracture the neck of a patient’s humerus.