The broken end of the os humeri is drawn somewhat forwards, but is easily pushed into the glenoid cavity, from which, unless it be supported, it is again drawn by the pecto ralis and coraco-brachialis muscles.
The arm, measured from the acromion to the elbow, is shorter than the other.* As this accident is produced by great vio lence, the parts are much obscured by the effusion of blood, and by the inflammation which speedily follows; but, for the first three hours, the muscles are so lax, that but for the pain it occasions, considerable motions of the limb might be produced.
In one case detailed by Sir A. Cooper, the tubercles were broken off' with the head of the bone, and the fractured extremity of the neck of the os humeri was placed in the glenoid cavity of the scapula. In another case, the fracture was intra-capsular, and the head of the bone was at the same time dis located forwards, under the pectoral muscle, and placed at the inner side of the coracoid process.
Delpech* gives the history of a case of fracture of the anatomical neck of the hu merus, combined with a dislocation. The case was remarkable, and differed from all the others recorded, in being an example of that rare form of dislocation, where the bone is thrown on the dorsum of the scapula. The history of the case is accompanied with an engraving.
With reg,ard to the case of dislocation into the axilla, complicated with fracture, Sir A. Cooper says, " I would observe that in this case the fall and depression of the shoulder is less striking than in the case of simple ax illary dislocation, as the shaft of the bone fills up the glenoid cavity ; also, that in the case complicated with fracture, the head of the bone can still be distinctly felt in the axilla, and that as it does not move when the os humeri is rotated from the elbow, this be comes the principal diagnostic mark.
" That a grating sensation can generally- be felt, and sometimes a very' distinct crepitus, especially if the elbow be raised outwards during the rotation of the arm.
" That the upper extremity of the shaft of the humerus can be felt advancing to the coracoid process ; but that it is easily re turned into the glenoid cavity, and that it there rotates with the arm, but easily again slips forward.
" That the accident which produces it is much more severe than that by which simple dislocation into the axilla is produced ; and there is, therefore, more contusion, more swelling, and more pain." Muscles. —If in some cases the tuberosities of the humerus are broken off and reniain connected with the muscles when the head of the humerus is dislocated, in others, we may be prepared to expect that in the dis section of cases of dislocation, the capsular and other muscles will be found lacerated. g as has been stated, the supra-spinatus be the muscle which is most put on the stretch In hen the head of the humerus is dislocated down wards, we need not be surprised to learn that this muscle is very frequently found to have been ruptured, or to have torn away a frag rnent of bone from the head of the humerus.
In the dislocation on the dorsurn of the scapula, the dissection of which is detailed in Sir A. Cooper's work, we find the following observations made by Mr. Key, with reference to a very peculiar phenomenon noticed in that case : namely," that, during the patient's life-time it was thought probable that a portion of the glenoid cavity had been broken off, or a piece of the head of the os humeri, or perhaps the smaller tubercle ; and that any of these injuries would account for the head of the bone not remaining in its natural cavity when reduced ; but the inspection post mortem proved that the cause of this symptom was the laceration of the tendon of the sub scapularis muscle, which was found to adhere to the edge of the glenoid cavity, and much thickened and altered in its character from its laceration, and very imperfect and irregular union." The tendon of the long head of the biceps is sometimes altered, as to its direction, in cases of complete dislocation, and adhesions between it and the contiguous parts occur ; but there are very few cases recorded, or to be found in museums, which prove that in true dislocation from accident, the tendon was found ruptured. In this respect, the effects of accident and disease on this tendon are strongly contrasted ; for, as the result of disease, the tendon, so far as its articular por tion is concerned, is very generally removed altogether.