What is the origin and course of the axillary nerve?

The axillary nerve originates from the posterior cord of the brachial plexus (C5, C6 fibers). It travels posteriorly through the quadrangular space with the posterior circumflex humeral artery, near the surgical neck of the humerus, and divides into branches deep to the deltoid muscle.

What are the main branches of the axillary nerve and what do they supply?

The axillary nerve has three main branches: the articular branch supplies the shoulder joint capsule; the posterior branch supplies the teres minor and posterior deltoid, and continues as the upper lateral cutaneous nerve for skin over the lower deltoid; and the anterior branch supplies the anterior and middle deltoid, with small cutaneous branches.

What causes axillary nerve injury and what are the symptoms?

Axillary nerve injury is commonly caused by shoulder dislocation or fracture of the surgical neck of the humerus. Symptoms include weakness in shoulder abduction (15–90°), sensory loss over the lower deltoid (the 'regimental badge' area), and loss of shoulder contour with prominence of the greater tubercle.

What is the 'regimental badge' area and why is it important?

The 'regimental badge' area refers to the skin over the lower deltoid region, which is supplied by the upper lateral cutaneous nerve from the posterior branch of the axillary nerve. It's important because sensory loss in this area is a key clinical sign of axillary nerve injury.

How does the axillary nerve relate to the quadrangular space?

The axillary nerve travels posteriorly through the quadrangular space alongside the posterior circumflex humeral artery. This anatomical passage is crucial as it positions the nerve near the surgical neck of the humerus and shoulder joint, making it vulnerable to injury in this region.

What muscles are innervated by the axillary nerve?

The axillary nerve innervates two key shoulder muscles: the deltoid muscle (all parts: anterior, middle, and posterior) and the teres minor muscle (supplied by the posterior branch). This innervation is essential for shoulder abduction and external rotation.

Axillary Nerve Anatomy – Course, Branches & Injury