256 The Shoulder Joint 



THE SHOULDER JOINT 



The shoulder-joint is formed by the glenoid cavity and the humerus, 

 the articular surfaces being enclosed in a loose capsular ligament 

 which is attached just beyond the border of the glenoid cavity, and to 

 the anatomical neck of the humerus. Its strongest part is superiorly, 

 where it receives accessory fibres from the coraco-Jnnncral ligament. 



In contact with the capsule axe the supra-spinatus above, the triceps 

 below, the subscapularis in front, and the infra-spinatus and teres 

 minor behind. Most of these muscles are blended with the capsule, 

 and thus play the part of ligaments. The axillary vessels and nerves 

 are to the inner side, separated from the capsule, however, by the sub- 

 scapularis. 



Above the joint are the acromion process and the coraco-acromial 

 ligament ; to the inner side are the coracoid process and its muscles, 

 and covering all is the deltoid. A bursa underlies the deltoid, which 

 in rheumatic subjects is often in communication with the interior 

 of the joint through an opening in the upper part of the capsule. 

 Other openings in the capsule are those by which the bursa beneath the 

 subscapularis and that beneath the infra-spinatus communicate with 

 the synovial membrane of the joint. There is also a gap between the 

 tuberosities by which the tendon of the biceps and its synovial invest- 

 ment escape into the bicipital groove. When the subdeltoid bursa is 

 in communication with the synovial membrane of the joint, the open- 

 ing in the top of the capsule is occasionally so large that the head of 

 the humerus comes into extensive contact with the under aspect of 

 the acromion. In such cases a facet is produced, so that the appear- 

 ance presented after death is of an upward partial dislocation of the 

 humerus having existed. (See * Trans. Soc. Med. Chirurg.,' 1875.) 



The glenoid ligament is the fibre-cartilaginous rim which gives a 

 pliable border to the glenoid cavity ; just inside the capsule it is lined 

 by synovial membrane. The origin of the long head of the biceps 

 blends with it above. 



The synovial membrane lines the capsule and the glenoid ligament, 

 but, though reflected on to the joint-surfaces of the bones, it cannot 

 after birth be traced over their articular cartilages. It often com- 

 municates with the subdeltoid bursa, and usually so with bursie 

 beneath the subscapularis and the teres minor. It sends a tubular 

 process between the tuberosities to line the bicipital groove and to 

 lubricate the tendon. 



Supply. The arteries supplying the joint come from the supra- 

 scapular, the anterior and posterior circumflex, and the dorsalis 

 scapulae ; the nerves are derived from the supra-scapular and the 

 circumflex. 



Movements. The humerus is raised by the supra-spinatus and 



