FIG. 42.

Triceps

Subcoracoid dislocation, reduced; in cadaver; the humerus has been rotated outward to show the rent in the capsule. (B. ANGER.)

backward, and that thus the elbow is pressed toward the spine, outward rotation of the arm. It is impossible in most cases to determine the exact position and attitude of the limb at the moment the dislocation occurs, and the relative parts taken by abduction, rotation, muscular action, and direct impulsion in its production. At present it can only be said that every one of the four has proved sufficient by itself, and that they have been found to coöperate in varying degrees.

Pathology. The results of experiments upon the cadaver are in harmony with those of post-mortem examination in recent and in old cases. The capsule is torn at its inner and lower portion between the tendon of the subscapularis and the triceps, and the rent extends usually along the inner and lower border of the glenoid fossa for half, sometimes even twothirds, of the entire periphery. In other cases the rent extends outward and backward, rather than upward, and near the insertion of the capsule upon the humerus. Exceptionally, the rent is very small, or may even be entirely lacking. Eve' reported a case of subcoracoid dislocation in a man thirty-six years old, who had been knocked down by a railway train and died a few hours afterward. The capsule was untorn but was separated from the anterior border of the glenoid fossa, remaining continuous with the periosteum which was stripped up from the costal surface of the scapula. On the posterior surface of the head of the humerus was a deep vertical indentation made by impact against the anterior margin of the glenoid fossa. In 1880 I presented to the New York Surgical Society the shoulder-joint of an old man who had died of pneumonia a week after he had dislocated the shoulder by falling from the fourth story of a building. The dislocation was well marked, the shoulder was flattened, the head of the humerus could he distinctly felt in the axilla, and reduction was effected with the aid of ether. The joint was opened from behind, and the capsule was found untorn; the tendon of the subscapularis was partly detached at its insertion, but at no point throughout its entire thickness, and the upper facet of the greater tuberosity was broken off in several pieces but not widely separated. Such cases of slight or no injury to the capsule are classed by some writers as "incomplete" dislocations.

The outer and upper portion of the capsule, when untorn, is drawn tightly across the glenoid fossa.

The subscapularis muscle is sometimes simply pressed inward and separated from the scapula by the interposed head of the humerus, but in most cases it is torn more or less widely from its lower border upward, and its upper portion may lie upon the head of the humerus and separate it from the coracoid process. Occasionally, instead of being ruptured the muscle is torn away from its attachment to the humerus, perhaps bringing with it the lesser tuberosity.

The supraspinatus is sometimes, probably often, torn from its attachment to the humerus, and the same is true in a less degree of the infraspinatus, and occasionally even of the teres minor.

The teres major is sometimes slightly torn, apparently by the partial passage of the head of the humerus between it and the subscapularis.

1 Eve: Trans. Path. Soc. of London, 1880, vol. 63, p. 317.

The anterior edge of the glenoid fossa is occasionally broken off; the acromion and coracoid process have both been found broken, but such injury appears to have been purely incidental and should be classed as a complication.

The head of the humerus lies against the edge of the glenoid fossa, or further back against the side of the neck of the scapula, and either close up against the beak of the coracoid process behind the coracobrachialis and the short head of the biceps, or lower down at a distance determined by its relations to the subscapularis and by the tension of the

untorn portion of the capsule. It may lie on the outer side of the coracoid process, "incomplete dislocation," or immediately below it, or it may pass entirely to its inner side (intracoracoid dislocation), and it may be in outward or inward rotation (Fig. 46) or in any intermediate attitude. As has been already said, avulsion of the tuberosities may take the place of laceration of the muscles attached to them; this has been rarely

FIG. 46.

noted of the lesser tuberosity, but frequently of the greater, and especially of its upper and middle facets. Von Thaden,' who made a study of this feature, found that the upper and middle facets were each sometimes torn off separately, but the lower one only in connection with the other two. The complication is of importance because of the consequent loss of the control of the attached muscles over the humerus and the consequent exposure to recurrence of the dislocation (see Chapter III.), and because it opens the way for the escape of the long tendon of the biceps from its groove and its inter

Scapula

Subcoracoid dislocation; to show the different degrees of rotation of the humerus in different positions.

1 Von Thaden: Arch. für klin. Chir., vol. 6, p. 67.

position between the humerus and its socket in such a way as to constitute a serious obstacle to reduction. In the specimens Von Thaden examined he found the tendon thus interposed three times. Körte' reported a similar case in which the tendon had slipped entirely out of its groove and was wound around the outer and posterior side of the head. He adds that Stromeyer quotes from Curling a case in which the tendon had to be lifted back over the head with a spatula before reduction could be made.

FIG. 47.

Old unreduced dislocation of the right humerus, with interposition of the capsule. At the inner side of the head of the humerus is the rent in the capsule through which it passed, and above the rent is the greater tuberosity which had been torn off. At the outer side of the coracoid process is an opening in the capsule which had been produced by the pressure of the humerus; through it the glenoid fossa is seen. (HILTON.)

When the tuberosity or a portion of it is thus broken off, the fragment lies over or in the glenoid fossa, and the broken surface of the humerus rests against the inner surface of the neck of the scapula or engages the edge of the fossa. The upper and outer portion of the capsule thus separated from the humerus may remain interposed between the head of the humerus and its socket and prevent reduction. After reduction of the dislocation the tuberosity reunites with the humerus with more or less irregularity and deformity.

Except in connection with fracture of one or the other tuberosity the long tendon of the biceps is rarely dislocated, but it is sometimes torn away from its insertion or ruptured.

In some specimens of old unreduced dislocation a vertical groove has been found on the articular surface of the head of the humerus which was thought to have been caused by prolonged contact with the edge of the glenoid fossa. Malgaigne, who took a special interest in the specimens

1 Körte: Arch. für klin. Chir., vol. 27, p. 747.

as supposed examples of incomplete dislocation, suggested that the groove might have been caused at the time the injury was received by the forcible impact of one bone against the other. It is interesting to find that this suggestion has been recently confirmed by the autopsy in Eve's case men

FIG. 48.

tioned above and by two specimens of recent dislocation preserved in the Museum of the University of Edinburgh and reported in an interesting and valuable paper by Caird; the indentation lay wholly or in part along the junction of the head and shaft, was from one to one and a half inches long, and from onequarter to one-half an inch deep. The indentations accurately fitted the inner lip of the glenoid fossa, and the latter was bruised or chipped. The suggestion that the causation. of fracture of the anatomical neck may be referred to the same mechanism seems very plausible.

The large axillary vessels and nerves are pressed inward and are rarely injured. Examples of the injuries that may be done them have been given in Chapter III., and the subject has been more freely discussed in Chapter VIII.

The axillary artery may be torn across in part or completely, probably by being stretched around the head of the humerus while the arm is abducted, or its branches, especially the subscapular and circumflex, ruptured or torn away at their origin. In Körte's case, just mentioned, the anterior circumflex was ruptured half an inch from its origin. The main nerves also may be compressed or stretched, and it is not uncommon to find the circumflex more or less disabled, as shown by loss of sensation in the cutaneous region supplied by it.

SYMPTOMS AND DIAGNOSIS.

The description of the symptoms will be made simpler by limiting it at first to those commonly found in the medium displacements, and subsequently indicating the differences or modifications peculiar to the exceptional grades and conditions.

The patient sits with his head and trunk inclined toward the injured side, and supports the forearm with the other hand. The shoulder is flattened on the outer side so that the line of the deltoid runs straight down from the acromion and makes a more marked angle with the arm at its insertion than is usual. The anterior fold of the axilla lies lower, further from the clavicle than its fellow of the opposite side, and its creases appear deeper, as if the arm were applied more closely against the chest, and the outer part of the subclavicular fossa appears more full. The elbow stands a little away from the side and can be easily abducted,

1 Caird: Edinburgh Med. Journ., Feb. 1887.