• Motor
    • deltoid
    • teres minor
  • Sensory
    • superficial lateral cutaneous nerve of arm
      • lateral shoulder sensation
  • Originates from the brachial plexus 
    • middle trunk, posterior division, posterior cord  
  • Carries fibers from C5 and C6
  • 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
        • 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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Questions (1)

(OBQ12.231) A 32-year-old female sustains a proximal humerus fracture shown in Figure A. This fracture goes on to uneventful union, but she complains of a lack of sensation over the lateral deltoid and has weakness with the Hornblower's test at final follow-up. Which of the following structures is most likely injured in this patient? Review Topic


Anterior branch of the axillary nerve




Posterior branch of the axillary nerve




Posterior cord of the brachial plexus




Suprascapular nerve




Musculocutaneous nerve



Select Answer to see Preferred Response


The patient scenario above describes an injury to the posterior branch of the axillary nerve.

The axillary nerve divides into an anterior, a posterior, and a collateral branch to the long head of the triceps brachii. The anterior branch winds around the surgical neck of the humerus to provide innervation to the anterior deltoid and overlaying skin. The posterior branch supplies the teres minor and the posterior part of the deltoid and supplies the skin over the lower two-thirds of the posterior deltoid.

Ball et al. performed a cadaveric study of 19 specimens and found that the posterior branch of the axillary nerve separates from the main nerve anterior to the origin of the long head of the triceps. They also found that the superolateral brachial cutaneous nerve and motor innervation of the teres minor always arises from the posterior branch.

Uno et al. performed cadaveric dissection of 12 shoulders and found that the axillary nerve is adjacent to the shoulder capsule at the 5 to 7 o'clock position during arthroscopy when the shoulder is in neutral, extension, or internal rotation. However, they found that shoulder abduction, external rotation, and traction increases the distance from the capsule to the nerve.

Price et al. performed cadaveric dissection of nine shoulders and found that the branch to the teres minor is the closest to the glenoid rim with all shoulder motion. They also found that the distance from the axillary nerve to the glenoid rim at the 6 o'clock position is 12.4mm and the axillary nerve is only 2.5mm away from the inferior glenohumeral ligament.

Figure A shows a left-sided proximal humeral greater tuberosity fracture with minimal displacement. Video V demonstrates how to perform Hornblower's test.

Incorrect Answers:
Answer 1: The anterior branch of the axillary nerve has motor fibers for the anterior deltoid.
Answer 3: A posterior cord injury would lead to more dysfunction than just the two findings listed.
Answer 4: The suprascapular nerve innervates the supraspinatus and infraspinatus.
Answer 5: The musculocutaneous nerve provides innervation to the coracobrachialis, biceps brachii, and medial brachialis.


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