Axilla

The axilla is a space located between the upper limb and thorax, which permits the passage of major neurovascular structures.

Gross anatomy

The axilla is pyramidal in shape with its apex opening superiorly towards the base of the neck between the subclavius muscle, first rib, superior border of the scapula and clavicle. The base/floor is composed of tough axillary fascia, which extends between the chest wall (at the level of the 4 rib), arm, and the posterior boundary.

The intercostobrachial nerve supplies the skin of the axilla.

Boundaries

• anteriorly: pectoralis minor, clavipectoral fascia, clavicle, pectoralis major (forming the anterior axillary fold)
• posteriorly: subscapularis, teres major, scapula, latissimus dorsi (forming the posterior axillary fold)
• medially: serratus anterior overlying chest wall to the level of the 4 rib
• laterally: intertubercular groove of the humerus

Contents

The axilla has an abundance of fat, which surrounds the following structures to allows movement during scapulothoracic motion:

• vessels
  • axillary artery and branches
  • axillary vein and branches
• nerves
  • brachial plexus
  • long thoracic nerve
• axillary lymph nodes
• muscles and tendons
  • tendons of the long and short heads of biceps brachialis
  • pectoralis minor
  • coracobrachialis

A safe technique for insertion of intercostal catheters describes anatomical landmarks involving the axilla and a 'triangle of safety'.