3 – Anatomy of the axilla

The axilla (armpit) is bound medially by the rib cage and the serratus anterior muscles, anteriorly by the anterior axillary fold (the major and minor pectoral muscles – yellow and cyan asterixs in the picture), laterally by humerus and the tendons of the coracobrachialis muscle (green asterix) and of the short head of biceps brachii muscle (blue asterix), and posteriorly by the subscapularis (white asterix) and the posterior axillary fold

The posterior axillary fold is the latissimus dorsi muscle (not shown) and the teres major muscle (magenta asterix)

The triceps muscle is shown with a black asterix

The ultrasound-guided axillary block is performed in cross-section along the lower border of the teres minor muscle, where the ulnar nerve, median nerve, radial nerve, and medial and antebrachial cutaneous nerves run in close proximity to the axillary artery and veins (see figure and text). The musculocutaneous nerve has branched off and has to be blocked separately at this level. The axillary nerve is not blocked with the axillary block.