Chap, xi.] THE SHOULDER JOINT. 215 



of the joint, keeps the humerus against the glenoid 

 cavity in the various positions of the limb, and pre- 

 vents the head of the bone from being pulled too 

 closely upwards under the acromion. The tendon 

 may be ruptured, and in such a case, in addition to 

 the general weakening of the limb and the peculiar 

 projection formed by the contraction of the muscle, 

 the head of the humerus is usually drawn upwards 

 and forwards until arrested by the coraco-acromial 

 arch. Thus, a kind of slight false dislocation may be 

 produced. In certain violent wrenches of the limb the 

 tendon may slip from its groove and be displaced to 

 one or other side, usually to the inner side. In these 

 cases also the head is drawn up under the acromion, 

 and is prominent in front, while abduction is rendered 

 less free than is normal owing to the great tuberosity 

 being sooner brought in contact with tho acromion. 



Joint disease. This articulation is liable to all 

 forms of joint disease. The capsule, as just stated, is 

 very lax, but the humerus is kept in contact with the 

 glenoid cavity by atmospheric pressure. In joint 

 disease, however, the effusion may effect a considerable 

 separation of the two bones. Braune, having pierced 

 the glenoid cavity through the supraspinous fossa, 

 injected tallow at considerable pressure into the joint. 

 When fully distended the humerus was found to be 

 separated from the scapula by more than half an inch, 

 and this may serve to explain the lengthening of the 

 limb often noted in joint disease of this part with 

 much effusion. When the greatest degree of disten- 

 sion of the capsule was reached the humerus became 

 slightly extended and rotated in. It is significant that 

 in shoulder- joint disease it is com-inon for the arm to 

 be found close to the side, the elbow carried a little 

 back (extension), and the limb rotated inwards. This 

 position may also be due to the rigid contraction of 

 the muscles about the joint that is usually observed. 



