258 The Shoulder Joint 



may easily slip from the axilla, and be dragged and thrust beneath 

 the origin of the infra-spinatus, to form a sub-spinous dislocation. 

 But, as in the other instances, the capsule is rent in the lowest 

 part. 



As the roundness of the shoulder is due to the presence of the 

 head of the humerus, flatness of the shoulder is one of the characteristic 

 signs of dislocation ', the end of the acromion stands out conspicuously, 

 and the fingers may be thrust in beneath it towards the empty 

 socket. 



The humerus is hung, as it were, by the insertion of the over- 

 stretched deltoid, and when its head is carried inwards, as in the sub- 

 coracoid dislocation, the lower end is necessarily thrust outwards. 

 So the man usually has his elbow abducted, and, the arm being thus 

 fixed, the hand cannot be laid upon the opposite shoulder whilst tJic 

 elbow is touching the chest. Lastly, the head of the bone may be 

 detected in the infra-clavicular hollow, in the axilla, or bulging in the 

 infra-spinous fossa. 



Reduction of the dislocation is effected by first bending the elbow, 

 to take tension off the longhead of the biceps ; the arm is then drawn 

 from the side to relax the supra-spinatus, which is tightly stretched, 

 and to ' unhitch ' the margin of the humeral head from the border 

 of the glenoid cavity. The arm is then forcibly adducted over a firm 

 pad in the axilla, and thus, when the lower end of the humerus is 

 forcibly brought forwards and inwards, the upper end is tilted back- 

 wards and outwards against and into the socket. 



This can also be effected by putting the shoeless heel or the knee 

 into the axilla, the patient in the latter case being in the sitting 

 posture, and by then using the lower end of the humerus as a lever 

 the elbow being kept bent. 



Sir Astley Cooper showed that the chief impediment to the 

 reduction is the supra-spinatus locking the head beneath the glenoid 

 cavity hence the need of abduction in replacing the bone. 



As the axillary vessels and the brachial plexus lie close on the inner 

 side of the head of the humerus, they are apt to be pressed upon in 

 subcoracoid or subglenoid dislocation ; thus the limb becomes cedema- 

 tous (from obstruction of the vein) and pulseless, or painful and numb 

 (from pressure against the artery or nerves). 



In the case of an old-standing dislocation violent attempts to re- 

 duce the luxation by the heel in the axilla are apt to rupture the artery, 

 which by that time may have become adherent in its new bed, and 

 indirectly affixed to the head of humerus. It has happened also that 

 in such efforts to replace the bone fracture has occurred at the surgu-al 

 neck, or even that the heel has been thrust through the skin and 

 fasciae into the space. In the case of an old dislocation, therefore, it 

 is better to excise the head of the bone than subject the patient to such 

 serious risks. 



