Axillary neuropathy

A.N. can be caused by direct trauma with or without humeral fracture, anterior or posterior shoulder dislocation, and quadrilateral space syndrome. Direct shouder injury (the usual mechanism of the stinger) can cause it. There is about 50 % association of axillary injury with humerus fracture (proximal) and anterior shoulder dislocation. AN can also occur as part of brachial neuritis. Other causes are crutches causing pressure, hyperextension of shoulder during wrestling. The quadrilateral space syndrome involves the a.n. and the posterior circumflex artery in posterior axilla, bound by long head of triceps (medially), surgical neck of the humerus (laterally), teres minor and subscapularis (superiorly), and teres major (inferiorly). Syndrome may be due to muscle hypertrophy, fibrous bands, gunshot wounds, neuralgic amyotrophy, iatrogenic injury during shoulder surgery (up to 8 %).

Clinical presentation is inability to elevate and abduct the shoulder due to deltoid weakness (ie limited abduction after the first 30 degrees which is subsumed by the supraspinatus). By contrast, C-5 radiculopathy cause weak shoulder abduction for all 180 degrees subsumed by both muscles. An isolated teres minor lesion (also AN inn.) may escape detection since infraspinatus also rotates arm outward, but is detected by EMG. Teres minor is localized immediately lateral to middle third of the lateral scapular border. There may be numbness over the deltoid muscle belly. There may be tenderness in the quadrilateral space. The deltoid extension lag sign occurs when the arm is placed in a position of maximal extension and the patient is asked to maintain the position, and the degree of drop correlates with the extent of AN injury. MRI may show teres minor atrophy. Dynamic MRA can show compression of the circumflex artery with shoulder movements (abduction and external rotation) but angiography is not indicated. Shoulder dislocation AN injury recovers more than blunt trauma to the shoulder. Rest is usually adequate Surgery can be considered after three months. Less than 20 % require surgery. NCS show normal sensory responses, and decreased CMAP over deltoid with supraclavicular stimulation. Needle affects only deltoid and teres minor. Pitfalls-- C5-6; upper trunk/ posterior cord. The prognosis is good for recovery after fracture or dislocation of the humerus but not as good after blunt trauma to the shoulder