DISLOCATIONS OF THE HEAD OF THE ARM-BONE (Humerus).
The head of the humerus in its natural posi tion rests in the glenoid cavity (p. 62) of the scapula immediately under the acromion pro cess (see Fig. 20, p. 61). It may be dislocated in three directions; (I) downwards, below the socket, into the armpit; (2) forwards in front of the socket, and slightly downwards ; and (3) backwards on to the scapula, beneath its spine. The first form is called sub-glenoid, under the glenoid cavity, and is rare. The second form brings the head of the bone under the corticoid process of the scapula, and is called, therefore, sub-coracoid. /i is common. The third form is called sub-spinous, because the head of the bone is under the spine of the scapula. It is very rare.
The second or sub-coracoid form is common because it is downwards and in front that the joint is least covered in and protected, muscles and bony processes guarding the joint in other directions.
The cause of the dislocation is most fre quently a fall with the arm outstretched, the force being communicated along the arm, which acts as a lever. Occasionally direct violence forces the head of the bone downwards and forwards, a blow or fall on the shoulder for instance.
It is an accident of middle and advanced life, rare in childhood, though capable of being pro duced during that period of life by palling and twisting. For instance, a mother or nurse may produce the accident when walking in the street holding a child by the hand, by suddenly and with a jerk pulling up the child if it slips, especially when stepping down off the curb stone.
The being the common form will be first described (Fig. 53).
Signs.—The roundness of the shoulder is gone, the tip of the shoulder projects outwards, and immediately beneath it, instead of the head of the bone, is a hollow.
If the limb be raised the lingers can detect, in the arm- pit, a round body which rotates when the arm is bent at the elbow and turned out wards. The elbow sticks out from the side, and cannot be brought close. There is inability to move the arm at the shoulder, pain in the region of the joint, and sometimes numbness spreading down the arm to the finger owing to the head of the bone pressing on nerves. The limb is slightly shortened. The distinguishing features be tween dislocation of the head of the humerus and fracture of its upper end have been men tioned under FRACTURE OF THE HumEnus (p. 84).
Treatment.—Strip the patient and place him sitting in the usual position in a chair. Let the operator stand behind him with one hand over the shoulder-joint to fix the shoulder blade. He then rests his foot on the edge of the chair, and thus brings his knee well up into the arm-pit, allowing the injured arm to hang over his leg. With the other hand he seizes the patient's arm near the elbow and depresses it steadily over his knee. The knee thus acts
as a fulcrum, and the bone returns to its socket with a jerk. Fig. 54 shows this method. Greater force may be obtained by laying the patient on his back on a couch. The operator sits on the edge of the couch by the affected side, and puts the heel of the foot next the patient well upwards and backwards into the arm-pit so as to fix the shoulder-blade with it. The boot must of course be removed. The arm is then grasped by both hands of the operator by the wrist or elbow, and pulled firmly and steadily downwards over the heel, which at the same time presses the head of the bone out wards. As soon as the reduction is complete, which is known by the loud snap, the extension should cease, and the forearm be brought across the chest, and there bandaged. This method is represented in Fig. 55, and is known as the method of the heel in the arm-pit. If pulling by hand on the wrist or elbow is not sufficient, greater power may be obtained by a large towel or skein of worsted arranged in a clove-hitch (see Fir.. sm fattened above the elbow. The force exerted by the clove-hitch may be further increased by tying the ends and throwing the loop over the head, letting it come round the back. The pull ing can then be done by the back. In making extension it must always be re membered that the puVinn must be steady and continuous so as to tire out the opposing muscles. If several have elapsed since the accident, chloro form is advisable, supposing one competent to administer it be present. After a longer period his dislocated shoulder by the method repre sented in Fig. 57.
Sub-glenoid Dislocation (p. 62) presents similar signs to sub-coracoid, except that the inn is lengthened ;Fig. 58). The treatment is iden tical, namely, the method by the heel in the arm pit.
Sub - spinous Dislocation is easily made out by the forward projection of the elbow, and the fulness behind the joint, where the head of the bone can be felt on the back of the shoulder-blade.
Treatment. —The extension in this case must be made forwards, but the principles on which the reduction is effected are the same. The forward extension is easily effected after rolling the patient on to the dislocated side and supporting him in that position by a pillow under the sound side.
In all these cases, after reduction, the arm should be bandaged to the side and supported by a sling for some days to permit of irritation of the joint being allayed and the healing pro cess being established. Violent exercise of the joint should be carefully avoided for months, even always, since the accident will occur again more easily. Swelling and pain after reduction should be relieved by warm fomentations and rest Neglected cases can be properly and effec tually treated only by skilful surgeons.