The deltoid and teres minor are critical for normal shoulder function and are innervated by the axillary nerve. Compression of the axillary nerve can result in pain, weakness, and atrophy in some patients. Humeral osteophytes, malignancies, hyper- trophied musculature, malunited scapular fractures, and fibrous bands in quadrilateral space syndrome have all been identified as causes of axillary nerve compression (Table 1). Although axillary nerve compression is infrequent, accurate and timely diagnosis is critical to prevent chronic atrophy and weak- ness of the shoulder girdle.
When axillary nerve compression is present, patients often describe posterior shoulder pain, weakness, and decreased athletic performance. In chronic cases, deltoid atrophy and weakness may be present on examination. Magnetic resonance imaging can be useful to confirm the diagnosis by showing neurogenic edema or fatty infiltration of the deltoid or teres minor. It also provides the opportunity to evaluate soft-tissue causes of compression and the presence of concomitant shoulder pathology.
The indications for axillary nerve decompression are not completely defined and continue to evolve. For this reason, the initial treatment of patients diagnosed with axillary nerve compression is usually nonoperative. Patients are directed to discontinue aggravating activities, and a general shoulder rehabilitation program is initiated that includes shoulder strengthen- ing and scapular stabilization exercises. Failure to improve over a 3- to 6-month period or the presence of large compressive lesions may necessitate surgical intervention. Arthroscopic axillary nerve decompression is a novel procedure that we have primarily used to treat recalcitrant quadrilateral space syndrome and as a joint preservation procedure in young patients with large impinging humeral osteophytes.