• The coracoid process of the scapula is a key landmark in axillary nerve dissection. It is palpable throughout every stage of the operation (Figure 8-1).

• The glenoid articular surface of the scapula is relatively small compared with the articular surface of the humerus. The integrity of the shoulder joint is much dependent on large and small muscles and their nerve supply. The spinal nerves exit the plane between the scalenus anterior and scalenus medius, and their fibers traverse the trunks, divisions, and cords to reach the named nerves that supply the muscles (Figures 8-2 and 8-3).

• The costal, concave surface of the scapula is covered by the subscapularis, which in turn is covered by thick fascia (Figure 8-4). The dorsal surface is covered by the supraspinatus and infraspinatus. The latter is crucial for external rotation of the humerus (Figure 8-5). Even if shoulder abduction and elbow flexion are restored after surgery, in the absence of external rotation the patient will have difficulty bringing food to the mouth.

• The origin of the teres major from the lateral side of the inferior angle of the scapula and the insertion of that muscle below the subscapularis into the humerus should be studied. The deltoid suspends the humerus at the shoulder joint, pulling it upward, and the teres major has the reverse action. Paralysis of the deltoid thins the muscle to reveal that the head of the humerus is being pulled down by the teres major and gravity.

• The origin of the deltoid, from the clavicle and the acromion and spine of the scapula, should be reviewed. The anterior origin does not impede the surgeon’s view of the brachial plexus, but the origin of the posterior deltoid may occasionally need partial division to make it easier to see the axillary nerve from the posterior approach. The deltoid is inserted into the deltoid tuberosity of the humerus. (This is a useful level at which to study the cross-sectional anatomy of the arm, because many relationship changes occur at this level: the median nerve in its relationship to the brachial artery, the ulnar nerve to the medial intermuscular septum, and the radial nerve to the humerus.)

• The fibers of the deltoid are bunched into anterior, lateral, and posterior components. These three segments should be observed individually in cases of deltoid paralysis and in reinnervation following axillary nerve repair (Figure 8-6). The skin over the deltoid is supplied by C5 fibers, by way of the axillary and superior lateral brachial cutaneous nerves.

• The massive latissimus dorsi narrows to a shiny tendon of insertion, which winds around the inferior border of teres major en route to its insertion in the humerus. The quadrilateral space is bounded by the subscapularis above and the teres major below, but the surgeon uses the upper border of the thin, shiny tendon of latissimus dorsi, winding around teres major, as the guide to the space (Figure 8-7; see also Figure 8-3).

• The three muscles of the posterior wall of the axilla are all supplied by the posterior cord (subscapular nerve, nerve to latissimus dorsi, and nerve to teres major). When operating from the front, however, the fascia over the subscapularis and the tendon of latissimus dorsi form the background to the plexus.

• Passing a fingertip above the upper border of the latissimus dorsi tendon leads the surgeon into the quadrangular space. Gentle tenting of the axillary artery will put tension on the posterior circumflex artery (which is of variable size). This vessel also leads to the quadrangular space and the identification of the axillary nerve (Figures 8-8 and 8-9).