Axillary nerve

Innervation

• Motor
  • deltoid
  • teres minor
• Sensory 
  • superficial lateral cutaneous nerve of arm
• lateral shoulder sensation 

Origin

• Originates from the brachial plexus 
  • middle trunk, posterior division, posterior cord
• Carries fibers from C5 and C6

Course

• Comes off posterior cord behind the axillary artery, anterior to the subscapularis muscle
• Travels through the quadrangular space 
  • runs here with the posterior circumflex humeral artery and vein
• Gives off an anterior, posterior, and articular terminal branch
• Terminal branches
  • anterior branch
    • wraps around the surgical neck of the humerus on the undersurface of the deltoid
    • supplies the anterior deltoid muscle 
    • traditional “safe zone” from lateral acromion is 5 cm
      • axillary nerve has been shown to run 3-5 cm from the acromion in 20% of patients
      • damage to nerve with a muscle split here will denervate the anterior deltoid
    • terminates in small cutaneous branches for the anterior/anterolateral skin
  • posterior branch
    • supplies the teres minor and posterior deltoid muscles
    • pierces the deep fascia and terminates as the superior lateral cutaneous nerve of the arm
  • articular branch
    •  enters the shoulder joint inferior to the subscapularis