Isolated axillary neuropathy is a somewhat uncommon diagnosis, but it may not be as rare as might be expected. Given a thorough clinical history, physical examination, and timely studies, the diagnosis needs to be considered in the differential in the proper setting. Sports and other activities in which this injury might occur include overhead sports (eg, volleyball, javelin), racquet sports, gymnastics, rock climbing, workouts that involve shoulder traction (eg, pullups), and contact sports that involve tackling with an extended arm (eg, rugby, American football).
A comprehensive understanding of the anatomy and function is critical to making a definitive diagnosis and formulating an appropriate treatment plan. Most patients with axillary nerve injuries do well with conservative treatment and make a full recovery over a reasonable period; surgical intervention rarely is necessary. In this article, we report cases of axillary nerve injury in an elite teenage baseball pitcher and in a middle-aged recreational cyclist.
Figure 1 – For axillary nerve injury, a comprehensive understanding of the anatomy and function is critical to making a definitive diagnosis and formulating an appropriate treatment plan. The axillary nerve has its origin at the posterior cord of the brachial plexus and innervates the deltoid and the teres minor. It passes obliquely across the anteroinferolateral aspect of the subscapularis muscle before it enters into the quadrilateral space, accompanied by the posterior humeral circumflex artery. Most injuries arise from closed trauma that involves a traction-type mechanism.
ANATOMY AND FUNCTION
The axillary nerve has its origin at the posterior cord of the brachial plexus (C5-6 nerve roots) and innervates the deltoid and the teres minor. Along its anatomical course, it passes obliquely across the anteroinferolateral aspect of the subscapularis muscle before it enters into the quadrilateral space (QS), accompanied by the posterior humeral circumflex artery (Figure 1).
The QS is defined superiorly by the teres minor (when the vantage point of the shoulder is posterior), anteriorly by the subscapularis, inferiorly by the teres major and latissimus dorsi, medially by the long head of the triceps, and laterally by the proximal humerus.1-3 Within the QS, the nerve lies in close proximity to the inferior shoulder joint capsule and exits posteriorly around the humeral neck. It then splits into the anterior branch (innervates the anterior and middle deltoid bundles) and posterior branch (innervates the posterior deltoid bundle and teres minor). A terminal branch (superior lateral cutaneous nerve) of the posterior branch provides sensory innervation to the lateral deltoid region.3
In axillary nerve injuries, the clinical history is important in determining the cause (Table) and developing an appropriate and timely treatment plan. Most injuries arise from closed trauma that involves a traction-type mechanism. The location of the pain typically is lateral or deep to the shoulder, with occasional radiation to the proximal arm. The pain, which may be mild to severe, often worsens in extreme ranges of motion. The pain tends to be type II neurological pain—dull and aching’rather than the type I “zinger” neurologi-cal pain. However, patients often complain of only mild pain and more of weakness or inability to perform in their sport.
On physical evaluation, clinicians need to pay particular attention to the cervical, shoulder, and neurological examinations. Baseline plain radiographs of the neck and shoulder as well as more comprehensive testing (eg, MRI) may be valuable. Nerve testing with electromyography and nerve conduction studies (EMG/NCS) may help confirm the diagnosis and may be needed to monitor the treatment and, ultimately, the recovery process.
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