THE SHOULDER-GIRDLE. 



2 53 



It is to be remembered that rotation inward is mostly performed by the sub- 

 scapularis and outward rotation by the infraspinatus and teres minor. The supra- 

 spinatus aids abduction. A too free excision is liable to be followed by a flail-joint, 

 in which case the limb hangs helplessly by the side with the dorsum pointing forward. 



The axillary fold muscles insert on the anterior surface of the bone and hence 

 turn the arm inward and draw it in toward the body, they do not compensate for 

 the loss of the muscles attached to the tuberosities. 



The bleeding in the operation will be mainly from the acromial branches of the 

 acromial thoracic artery and the bicipital branch of the anterior circumflex artery, 

 which runs in the bicipital groove. 



DISEASES OF THE JOINT AND BURS^E. 



The shoulder-joint, like other joints, is subject to inflammatory and other diseases. 

 These may be ( i) traumatic and later septic; (2) rheumatic or gouty; (3) tuberculous, 

 with suppuration. 



These affections result in an effusion within the joint-cavity which distends the 

 capsule and finally tends to escape at the weakest points. The joint is not a 



Supraspinatus Acromion process 



Subacromial bursa space 

 Capsule of joint 

 Long head of biceps 



Capsule of joint 

 Glenoid cavity 

 Long head of triceps 



FIG. 266. Transverse section of shoulder-joint, illustrating the laxity of the capsule of the joint. 



complicated one, like the knee, and its synovial membrane is neither so extensive 

 nor so elaborate. 



Traumatism may give rise to a synovitis, an inflammation of the synovial mem- 

 brane, or an arthritis involving the entire joint structures. Sprains and other injuries 

 are not uncommon. A sprain will be caused by a force which acts to a greater 

 extent than the normal movements of the joint will allow. 



Movements of the Joint. In abduction the capsule becomes tense at its lower 

 portion when the arm is at 90 degrees to the trunk, greater abduction is resisted by the 

 greater tuberosity impinging on the acromion process and the scapula begins to revolve. 



Adduction is resisted both by the muscles and by the ligaments. When the 

 ligaments only remain, the head can be separated for 2 cm. or more from the glenoid 

 cavity (see Fig. 266). Marked adduction is usually limited by the arm coming in 

 contact with the side of the body. 



If the humerus is brought diagonally across the chest the scapula begins to 

 move and its posterior edge and lower angle turn forward. As the humerus is 

 adducted the deltoid and supraspinatus are made tense and the head is drawn up in 

 its socket. When the muscles are paralyzed the weight of the upper extremity 

 allows the head to fall and a distinct depression can be seen beneath the acromion 

 process. In paralysis of the deltoid this is particularly noticeable. 



