In the true subspinous dislocation the head rests on the dorsum scapulae under the spine, the infraspinatus and teres minor muscles being pushed before it, while the subscapularis is drawn across the glenoid, and is frequently torn. The supraspinatus, biceps, and pectoralis major are rendered tense, the latter producing inward rotation and forward adduction of the humerus, while the teres major and latissimus dorsi are relaxed. The circumflex nerve is frequently torn. A modified subspinous or subacromial displacement is said to be more common, the head resting on the posterior surface of the neck of the scapula.
In reducing dislocations of the shoulder, especially those of old standing, the axillary artery is not infrequently damaged, the vein and nerves generally escaping. The glenoid cavity is capable of very considerable distension, the humerus being separated from the glenoid by nearly ½ inch in extreme cases, and thus giving rise to lengthening, while slight extension (arm carried back) and rotation inwards take place, possibly in part due to the action of the latissimus dorsi. When the joint is distended, the diverticula also become affected, a swelling sometimes appearing between the pectoralis major arid the deltoid, from distension of the intertubercular bursa, overlaid by the unyielding biceps tendon ; and when rupture occurs it is frequently through one of the diverticula that it takes place, most often through the intertubercular one. Here the pus presents in front, generally below the pectoralis major tendon. When it escapes through the subscapular bursa, it tends to spread between the muscle and vertebral surface of the scapula, and point at the lower and back part of the axilla.
Excision of the shoulder is frequently performed for tubercular disease, or even rheumatoid arthritis, a false joint, with practically perfect movement, generally resulting. A vertical incision is made over the head of the bone midway between the coracoid and the acromion, the humerus being fully rotated outwards, so as to remove the long head of the biceps from injury. This incision goes through the superficial tissues, deltoid, and capsule of the joint, and the head is then cut off with a fan-shaped osteotome, and the wound stitched up. In some cases of myeloid sarcoma of the upper end of the humerus an amputation of the head of the bone through the surgical neck is performed, a fairly useful limb resulting.
Amputation at the shoulder may be performed by making a racket-shaped incision to include a deltoid flap, from the outer side of the coracoid down to the lower border of the pectoralis major, then outwards across the limb through the lower portion of the deltoid to the posterior axillary fold, the limb being abducted and rotated outwards. As the first part of this incision is practically that for excision, it enables the conditions of the parts about the joint to be examined before proceeding to amputate, in cases of doubt. The racket is now completed across the superficial tissues on the inner side of the limb. The deltoid flap containing the posterior circumflex vessels and circumflex nerve is now raised, the capsular muscles, capsule, and biceps tendon divided, and the head disarticulated. The triceps, latissimus dorsi, and teres major are next cut, and the limb being drawn from the side, the axillary vessels may be ligatured, and then along with the nerves, cephalic vein, humeral branch of the acromio-thoracic artery, some fibres of the deltoid and biceps and coraco-brachialis, divided by a transverse incision.