Habitual or recurrent dislocation is almost exclusively met with in the shoulder, and will be described with the injuries of that joint.

Pathological Dislocations.—Joints may become dislocated in the course of certain diseases. These pathological dislocations fall into different groups: (1) those due to gradual stretching of the capsular and other ligaments weakened by inflammatory and suppurative processes, such as sometimes follow on typhoid, scarlet fever, or diphtheria, and in pyæmia; (2) those due to destructive changes in the ligaments and bones—typically seen in tuberculous arthritis, in arthritis deformans, in Charcot's disease, and in nerve lesions, e.g. dislocation of the hip in spastic conditions, such as Little's disease; (3) those associated with deformed attitudes of the limb; (4) those due to changes in the articular surfaces, e.g. the phalanges in arthritis deformans. These will be considered with the conditions which give rise to them.

Congenital Dislocations.—Congenital dislocations are believed to be the result of abnormal or arrested development in utero, and are to be distinguished from dislocations occurring during birth, which are essentially traumatic in origin. They will be described along with the Deformities of the Extremities.

CHAPTER III
INJURIES IN THE REGION OF THE SHOULDER AND UPPER ARM

The injuries met with in the region of the shoulder include fractures and dislocations of the clavicle, fractures of the scapula, dislocations and sprains of the shoulder-joint, and fractures of the upper end of the humerus.

Surgical Anatomy.—For the examination of an injury in the region of the shoulder the patient should be seated on a low stool or chair. After inspecting the parts from the front, the surgeon stands behind the patient and systematically examines by palpation the shoulder girdle and upper end of the humerus. The uninjured side should be examined along with the other for purposes of comparison.

Immediately lateral to the supra-sternal notch, the sterno-clavicular articulation may be felt, the large end of the clavicle projecting to a varying degree beyond the margins of the small and shallow articular surface on the sternum. Any dislocation of this joint is at once recognised. The clavicle being subcutaneous throughout its whole length, any irregularity in its outline can be easily detected. A small tubercle (deltoid tubercle) which frequently exists near the acromial end is liable to suggest the presence of a fracture. The lateral end forms with the acromion the acromio-clavicular joint, which, however, is not always readily identified. The fingers are now carried over the acromion, which often exhibits in the situation of its epiphysial cartilage a prominent ridge, which must not be mistaken for a fracture. The tip of the acromion is usually employed as a fixed point in measuring the length of the upper arm.

The outline of the spine of the scapula can be traced back to the vertebral border; and the body of the bone may be manipulated, and its movements tested by moving the arm.

The coracoid process can be recognised in the upper and lateral angle of the triangular depression bounded by the pectoralis major, the deltoid, and the clavicle.