In rare cases habitual luxation results; the only successful method of treating it is a surgical operation consisting in resecting portions of the capsule for the purpose of shortening it.

Modifications and Complications of Preglenoid Dislocation. If the head of the humerus escapes from the glenoid fossa in a direct line forward, it sometimes lies so close to the fossa, between the scapula and the subscapular muscle, that the articular surface of the head still remains in relation with the edge of the glenoid fossa. In these cases, which are produced chiefly by direct violence, a groove is formed in both bones by attrition within a few weeks. In old cases of this kind the wearing away may be very considerable, forming a deep groove on the head of the humerus and completely wearing away the anterior half of the glenoid fossa. At the same time the usual periosteal proliferation takes place, forming a kind of new joint for the head in its abnormal position (see Plate 31). Reduction in such cases is, as a rule, extremely difficult, and often impossible without arthrotomy. Supracoracoid dislocations are extremely rare, and always combined with fracture of the coracoid process.

Dislocation with simultaneous fracture of the neck of the humerus: This constitutes a very grave injury. If the attempts at reduction by abduction and extension, supplemented by direct manipulations, fail even under full anesthesia, arthrotomy is indicated for the purpose of forcing the bones into place, or, if necessary, removing the fragment, especially if it is small and principally intra-articular. The treatment formerly recommended was to aim at producing a false joint at the seat of fracture without attempting to correct the position of the head of the bone. [Without much doubt, in this injury the seat of fracture should be explored by an open incision, and if the fragment cannot be properly fixed with a fair hope of its union with good function of the joint, the head of the bone should be removed.-ED.]

(b) Downward or subglenoid dislocation of the humerus (luxatio infraglenoidalis or axillaris). In this [rare. ED.] dislocation the head is often found at the lower border of the glenoid fossa, and is accordingly felt through the axilla. The appearance of the patient is most characteristic when he stands with his hands extended from the body, as in this position the line of the shoulder resembles a bayonet in shape. In this variety also there are prominence of

the acromion; absence of the head from the glenoid fossa; and functional disturbances. Sometimes the arm is elevated (luxatio erecta), or in horizontal extension. Reduction is effected by extension and direct pressure against the head through the axilla, with the thumb pressed against the acromion.

Fig. 54.-Horizontal section through the shoulder-joint and adjacent half of the thorax in retroglenoid dislocation. (Compare Fig. 47, p. 141, after Anger.)

(c) Backward or subacromial dislocation of the humerus (luxatio retroglenoidalis, subacromialis, infraspinata). This form is rarely met with and is mostly produced by direct violence. The head is readily seen and felt in its abnormal position. The coracoid process forms a distinct prominence. Reduction is effected by extension, with the arm in abduction, and by direct pressure.

PLATE 32.

Fracture of the Surgical Neck of the Humerus, with Marked Displacement of the Fragments and Abduction of the Arm.

Fig. 1. The specimen represents the anatomic conditions most faithfully. We see the head of the humerus with its tuberosities in the normal position. The end of the lower fragment is displaced inward as in a subcoracoid luxation. The possibility of injury to the plexus and the large vessels, and the strain and displacement of the tendon of the biceps, are seen at a glance. Above and medial to the head of the humerus is the coracoid process, where the short head of the biceps has its origin; the pectoralis minor has been removed. Above the coracoid process we see the clavicle, the outer extremity of which articulates with the acromion. Parts of the deltoid and pectoralis major muscles have been removed; the latter has been pushed out of the way so that the second, third, and fourth ribs are exposed.

Fig. 2.-Upper extremity of the humerus, from the right side, showing a united fracture. Anterior view. The fracture included not only the surgical neck, but also the region of the tuberosities and the anatomic neck. There is great inward and upward displacement of the lower fragment; the arm is in abduction. The two fragments are united by an abundant mass of not very condensed callus. The fracture was evidently produced by great violence; it presents the appearance of a compression-fracture. (Author's collection.)

4. HUMERUS

(A) Fractures of the Upper End of the Humerus The upper extremity of the humerus presents the following parts: the anatomic neck; the region of the tuberosities; and, below the latter, the surgical neck. Fracture may take place in any one of these regions; as a rule, the line of fracture is not confined to one, but extends more or less into neighboring parts.

Fracture of the upper end of the humerus may be due to direct or to indirect violence. Indirect violence may produce it by compressing the bone in its long axis against the glenoid fossa or the arch of the acromion, as in a fall