Review Question - QID 4591

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. Illustration A shows a diagram of the branches of the axillary nerve.

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.