the Axillary and Circumflex Nerves
Axillary or circumflex nerve is an important nerve because it supplies the deltoid muscle which is the main abductor of the arm. Surgically it is important, because it is commonly involved in dislocations of the shoulder and in fractures of the surgical neck of the humerus. The axillary nerve is a smaller terminal branch of the posterior cord of the brachial plexus (C5, C6). Root aalue: Its root value is ventral rami of cervical 5, 6 segments of spinal cord (see Fig. a.7\.
Course
Axillary nerve courses through lower part of axilla into the quadrangular space where it terminates by dividing into two branches (Fig. 6.6).
Relotions ond Blonches
a. In the lower part of the axilla, the nerve runs downwards behind the third part of the axillary artery. Here it lies on the subscapularis muscle. It is related medially to the median nerve, and laterally to the coracobrachialis. The nerve leaves the axilla by winding round the lower border of the subscapularis in close relation to the lowest part of the capsule of the shoulder joint where it gives a branch to the capsule of the joint and enters the quadrangular space (Fig. 6.8).
b. The nerve then passes backwards through the quadrangular space. Here it is accompanied by the posterior circumflex humeral vessels and has the following relations (Fig. 6.72).
. Superiorly:
i. Subscapularis or teres minor.
ii. Lowest part of the capsule of the shoulder joint. o Laterally: Surgical neck of humerus.
. lnferiorly; Teres major.
. Medially: Long head of the triceps brachii. In the quadrangular space, the nerve divides into anterior and posterior branches in relation to the deltoid muscle (Fig. 6.6)
c. The anterior branch is accompanied by the posterior circumflex humeral vessels. It winds round the surgical neck of the humerus, deep to the deltoid, reaching almost up to the anterior border of the muscle. It supplies the deltoid and the skin over its anteroinferior part.
d. The posterior branch supplies the teres minor and the posterior part of the deltoid. The nerve to the teres minor bears a pseudoganglion, i.e. fibrous tissue and fat without any neurons (Fig. 6.6). The posterior branch then pierces the deep fascia at the lower part of the posterior border of the deltoid and continues as the upper lateral cutaneous nerve of the arm.
