606 



ABNORMAL CONDITIONS OF THE SHOULDER JOINT. 



may be dislocated from the glenoid cavity of 

 the scapula as the result of accident, in three 

 different directions ; namely, downwards and 

 inwards, into the axilla. 



Secondly, forwards and inwards. 



Thirdly, backwards on the infra-spinatus 

 fossa, or on the dorsum of the scapula. 



Partial dislocations, or subluxations of the 

 head of the humerus, as the result of acci- 

 dent, have been much spoken of, and accounts 

 of such supposed accidents are to be found 

 in the works of practical surgeons. While 

 we would not deny that cases deserving the 

 name of partial luxations of the head of the 

 humerus do occasionally present themselves 

 to the surgeon, in our experience all such 

 cases have been found, on strict inquiry, not 

 to have been the direct effect of accident, but 

 the result of chronic disease, or of congenital 

 malformation of the shoulder joint. And we 

 here formally deny that the case of partial 

 luxation of the head of the humerus, as the 

 result of accident, has ever been satisfactorily 

 proved, either in the living or the dead sub- 

 ject. 



1. Dislocation downwards and inwards 

 into the axilla. The dislocation of the hu- 

 merus downwards is unquestionably the most 

 common, and is generally produced by a 

 fall on the elbow, or palm of the hand, the 

 arm being at the time extended from the 

 body. The humerus, therefore, immediately 

 prior to the accident, would be so related to 

 the glenoid cavity as to form with it an acute 

 angle inverted ; and the head of the bone, 

 thus gliding from above downwards, is forced 

 violently against the lower part of the cap- 

 sule, which is stretched and lacerated so as 

 to allow the head of the humerus to escape ; 

 this result is further aided by the weight of 

 the body, and by the contraction of the great 

 pectoral, latissimus dorsi, and teres major 

 muscles. The new position assumed by the 

 head of the dislocated bone is on the inner 

 side of the anterior margin of the scapula, 

 between the subscapular muscle anteriorly, 

 and the long head of the triceps, posteriorly. 

 The pectoralis major, latissimus dorsi, and 

 teres major muscles act upon the arm as on a 

 lever, of which the elbow is the fulcrum, and 

 the point of resistance is at the articulation ; 

 while the elbow rests on the ground, and the 

 weight of the body presses on the lower part 

 of the capsular ligament of the shoulder joint, 

 the muscular folds of the axilla being in- 

 stinctively thrown into violent action, make 

 an effort to approximate the arm to the side ; 

 but as these muscles cannot move the lower 

 extremity of the humerus, on account of the 

 elbow resting on the ground, the head of the 

 bone becomes the moving point, and bursts 

 through the lower part of the capsular liga- 

 ment, and is dislocated into the axilla. Dis- 

 location doiumuards may. according to some 

 authors, be produced by a violent blow on 

 the outer part of the shoulder, below the 

 acromion ; but in that case it is often compli- 

 cated with fracture of the scapula or humerus. 

 It is further possible that it may result from 



simple muscular action, as in the act of lift- 

 ing a heavy weight, or during an attack of 

 epilepsy ; in either case a violent effort is re- 

 quired, whether the effect be attributed to the 

 agency of the deltoid, in depressing the head 

 of the bone, or, as Boyer supposes, to the 

 action of the great pectoral, latissimus dorsi, 

 and teres major muscles, simultaneously co- 

 operating with the elevators of the arm. 



Symptoms. The usual signs of this disloca- 

 tion into the axilla, are the following : A hol- 

 low is formed below the acromion, in conse- 

 quence of the displacement of the head of the 

 humerus from the glenoid cavity. The deltoid 

 muscle is flattened and dragged down with the 

 depressed head of the bone, so that the na- 

 tural roundness of the region of the shoulder 

 is lost. The arm is somewhat longer, and the 

 anterior fold of the axilla is deeper than na- 

 tural, because the new situation occupied by 

 the head of the bone on the subscapular fossa 

 of the scapula, is below the level of its na- 

 tural position in the glenoid cavity {fig. 

 434-.). The elbow is with difficulty made to 

 touch the patient's side; this movement is 

 the source of much pain, as it causes the 

 head of the dislocated bone to compress the 

 nerves in the axilla; and upon this account 

 the patient himself supports his arm at the 

 wrist with the other hand. The head of the 

 os humeri can be felt in the axilla, but not 

 except the elbow be considerably removed 

 from the side. " I have," says Sir Astley 

 Cooper, " several times seen surgeons de- 

 ceived in these accidents, by thrusting the 

 fingers into the axilla, when the arm is close 

 to the side, when they have directly said, ' This 

 is not a dislocation;' but upon raising the 

 elbow from the side, the head of the bone 

 could be distinctly felt ; for that movement 

 throws the head of the bone downwards, and 

 more into the axilla." The surgeon finds some 

 difficulty in overcoming the fixedness of posi- 

 tion of the humerus in its new situation. The 

 patient's voluntary power of abduction of the 

 arm, and of rotation, are lost; the motion of 

 the limb forwards and backwards is preserved. 

 There is great difference in respect to the 

 movements which can be communicated to 

 the limb, depending on the tone of the mus- 

 cles ; because, if the muscles are relaxed and 

 feeble, from age or any other cause, the sur- 

 geon may be able to move the patient's arm 

 freely, and to raise it up to the head, and even 

 press the elbow close to the side. On moving 

 the limb, a slight crepitus will sometimes be 

 felt, but by a continuance of the motion, this 

 soon ceases ; the crepitus, however, in these 

 cases is never like the rough grating which is 

 felt when a fracture is examined. The direc- 

 tion of the longitudinal axis of the arm is 

 changed ; for the lower extremity of the hu- 

 merus being placed outwards from the side, 

 its longitudinal axis, if prolonged upwards, 

 instead of passing towards the glenoid cavity, 

 may be observed to be directed inwards to- 

 wards the axilla. In this accident, numbness 

 of the fingers is sometimes complained of, 

 arising from the pressure of the head of the 



