Axillary Nerve

Anatomy

  • Terminal branch of the posterior cord of the brachial plexus, root values C5 and C6
  • Passes anterior to subscapularis, then runs close to the inferior shoulder capsule
  • Leaves the axilla through the quadrangular space with the posterior circumflex humeral artery
  • Anterior branch winds around the surgical neck on the deep surface of deltoid, about 5 cm below the acromion
  • Posterior branch supplies teres minor and posterior deltoid, then becomes the superior lateral cutaneous nerve of the arm

Motor Supply

  • Deltoid
  • Teres minor

Sensory Supply

  • Skin over the lower deltoid (regimental badge area)

Clinical Features

  • Injured with anterior shoulder dislocation and proximal humerus fractures, more often in older patients
  • Weak abduction and loss of deltoid contour
  • Sensation can be preserved despite complete motor loss, so test deltoid power
  • Quadrilateral space syndrome compresses the nerve in throwing athletes

Investigations

Radial Nerve, the suprascapular, axillary and radial nerves, gray’s anatomy plate 818
The suprascapular, axillary and radial nerves, Gray’s Anatomy plate 818. Image by Henry Vandyke Carter, Wikimedia Commons, Public domain.
  • Nerve conduction studies and EMG at 3 to 4 weeks give a baseline
  • MRI for a paralabral cyst or mass in quadrilateral space syndrome

Management

  • Most traction injuries after dislocation recover
  • EMG if there is no clinical recovery by 3 months
  • Nerve grafting or a triceps branch radial to axillary nerve transfer when recovery fails by 6 months

Structures at Risk

  • Deltoid splitting approaches extended more than 5 cm below the acromion
  • Inferior capsular shift and low posterior arthroscopic portals
  • Inferior glenoid during capsular release

Reviewed by Professor Phong Tran, Head of Orthopaedic Surgery, Western Health. Last updated 10 October 2026.