The axillary nerve is the motor supply to the deltoid and teres minor and is the nerve most commonly damaged during anterior shoulder dislocation and proximal humeral fractures. Its intimate relationship with the surgical neck of the humerus and the inferior glenohumeral capsule places it at risk whenever the shoulder dislocates inferiorly, stretching the nerve around the humeral neck.
| Origin | Posterior cord of the brachial plexus (C5, C6) |
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Axillary nerve injury after shoulder dislocation produces deltoid weakness with a characteristic loss of the rounded deltoid contour and a small patch of sensory loss over the lateral deltoid. Clinical assessment of axillary nerve function is mandatory after every shoulder dislocation. The majority of stretch injuries to the axillary nerve recover spontaneously within 3 to 6 months, but recovery should be monitored with electromyography at 6 weeks if there is no clinical improvement. Quadrilateral space syndrome from the posterior circumflex humeral artery and axillary nerve being compressed in the quadrilateral space is an uncommon cause of posterior shoulder pain in overhead athletes.
Deltoid weakness and lateral shoulder sensory loss from nerve injury at the surgical neck of the humerus, classically following anterior shoulder dislocation, with most cases recovering spontaneously within 6 months.
