The primary lesion is either a caseating focus in one of the bones--most often in the upper end of the humerus--or it is of the nature of caries sicca. The greater part of the head may disappear, and the upper end of the shaft be drawn against the socket. In exceptional cases, portions of the glenoid or humerus are found separated as sequestra, or the disease involves parts outside the joint, such as the acromion or coracoid process. Hydrops with melon-seed bodies is rare. In young subjects, destruction of the tissues at the ossifying junction may result in considerable shortening of the arm.
The _diagnosis_ is to be made from (1) arthritis deformans, in which the movements are less restricted, and are attended with grating and cracking; (2) paralysis involving the deltoid and scapular muscles--by the absence of pain, and the flail-like character of the movements; (3) disease in the sub-deltoid bursa--by the absence of rigidity and other evidence of implication of the articular surfaces; and (4) sarcoma of the upper end of the humerus--by the history of the case, the use of the X-rays or an exploratory incision. Injuries in the region of the upper epiphysis resulting in loss of movement, may, in the absence of a reliable history, be mistaken for tuberculous disease.
While the _prognosis_ is favourable on the whole, recovery is usually attended with fibrous ankylosis and incapacity to raise the arm above the level of the shoulder. The disease often progresses slowly, and may last for years.
_Treatment._--The limb should be immobilised in the position of abduction with the forearm and hand directed forwards; the most efficient apparatus is a plaster spica embracing the thorax and the upper limb down as far as the wrist. If the articular surfaces are affected and the disease is likely to lead to ankylosis, the arm should be abducted to a right angle. The severe pain of caries sicca may be relieved by blistering or by the application of the cautery. To inject iodoform, the needle is introduced either immediately outside the coracoid process, or just below the junction of the acromion process and spine of the scapula. When the disease does not yield to conservative measures, or the X-rays show a gross lesion in the bone, excision of the joint should be performed; a close fibrous ankylosis usually results, and the arm is quite a useful one provided the abducted position has been maintained throughout.