SITBACROMIAL DISLOCATIONS.-A few cases are recorded in which the outer end of the clavicle was forced down and caught under the acromion. Direct vio lence and muscular action are the re applied obliquely in the bony surface and directly on the capsule of the joint, through which the head of the bone is then forced.
divisions may be made according to the direction in which the head of the bone leaves the socket, and these subdivided according to the point at which it comes to rest, or accord ing to the position of the limb, as fol lows:— corded causes. Reduction was easy by drawing the shoulder outward, and there was tendency to recurrence in only one case.
DisLocAnoNs OF THE SHOULDE'R. These dislocations are as numerous as all other dislocations taken together. They are rare in youth and old age, and more frequent in men than in women. This frequency is explicable by the exposure of the joint to trauma and its conforma tion. The glenoid cavity covers such a small part of the head of the humerus that, in extreme degrees of abduction, extension, or flexion, any force trans mitted through the shaft of the bone is In the anterior dislocations the dis placement is also more or less downward (and, of course, inward), and in the down ward ones it is usually also forward and inward. Thus, the two classes merge into cach other. The term "subglenoid" is restricted to those cases in which the head of the bone is very low, others of this class being called "subcoracoid." The accompanying figure (Fig. 4) will demonstrate the different positions as sumed by the head of the bone in the anterior-and-downward dislocation.
Anterior Dislocations. sub divisions of this variety are dependent on the increasing amount of inward dis placement of the head of the bone, and grow less frequent in the same order; namely, subcoracoid, intracoracoid, and subclavicular.
Subcoracoid. — The head of the hu merus lies beneath the coracoid process, in contact with it or at a variable dis tance—a finger's breadth at most—below I it. The head may be displaced inward until three-fourths of its diameter lies to the inner side of the process (farther in ward would be subcoracoid) or it may be simply balanced on the anterior edge of the glenoid fossa. The elbow hangs away
from the side and the deltoid fullness of the shoulder is lost (Fig. 5). The axis of the humerus is sure to pass to the in ner side of the glenoid fossa, and palpa tion reveals the absence of the usual bony resistance below the outer side of the acromion, and the presence of an abnormal resistance below the coracoid process, in the axilla, which partakes of rotary movements communicated to the arm. Voluntary movement is usually lost. Passively the arm can be abducted, but not adducted; so that the elbow touches the chest, while the fingers rest on the opposite shoulder. Measurement in abduction shows shortening.
The diag,nosis is usually easily made by finding the glenoid cavity empty, the head of the bone beneath the coracoid, and by eliciting the above-mentioned sign. If there be fracture of the ana tomical neck the head will not partici pate in movements imparted to the shaft, and crepitus can usually be elicited.
violence, by a blow under the shoulder, indirect, as by a fall upon the hand; by leverage in forcible abduction and outward rotation; or by muscular action in any of the above ways.
capsule is torn at its inner and lower portion, or, more rarely, stripped up, and with it may be torn the circumflex nerve, the posterior circum flex artery, and subscapularis (Fig. 6). In "typical" eases the outer and upper portions of the capsule remain untorn and aid in determinine-, the abduction.
The supraspinatus, infraspinatus, and teres minor may be torn away (in decreas ing order of frequency) from the great trochanter or there may be avulsion of more or less of the trochanter itself. With avulsion of the trochanter the ten don of the long head of the biceps may slip to the outer side of the bone and oppose reduction (rarely). This tendon may also be torn. The head of the humerus is often bruised and ground by impact with the edge of the glenoid cavity, which, in turn, is splintered.