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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 
    • location 
      • lateral to triangular space and medial to triangular interval 
    • boundaries
      • superior - subscapularis and teres minor
      • inferior - teres major
      • medial - long head of triceps brachii
      • lateral - surgical neck of the humerus
    • contents
      • axillary nerve (C5 nerve root, posterior cord) 
      • posterior circumflex humeral artery
  • 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
        • anterior branch has been shown to run 3-5 cm from the acromion in 20% of patients
          • arm abduction to 90° REDUCES distance between acromion and nerve by 30%
        • 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
        • branch to the teres minor is closest to glenoir labrum and most susceptible during arthroscopy
      • 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
Injury & Clinical Conditions
  • Hornblower's test indicates teres minor pathology
    • shoulder placed in 90 degrees of abduction, 90 degrees of external rotation
    • positive if patient falls into internal rotation
 

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