Lesion of the axillary nerve is an indication, either from direct trauma to the nerve, from involvement of the upper roots of the brachial plexus, or from a brachial plexitis, such as in Parsonage-Turner syndrome.

If the patient is seen after 6 months in isolated injuries of the axillary nerve, our preference is for a nerve transfer. Otherwise, a nerve graft is preferable.

Nerve transfers should be performed within 6 months of the injury. From 6 to 9 months, recovery can still be obtained but with limitations. From 9 to 12 months, we attempt a nerve transfer only in patients younger than 25 years old. Beyond 12 months, upper and lower trapezius muscle transfers are preferable for shoulder reconstruction in brachial plexus injureries.7

In isolated injuries of the axillary nerve, surgery is directed to reconstruct the anterior division of the axillary nerve, which innervates the anterior and middle deltoid. In brachial plexus injuries, not only the anterior division but also the teres minor motor branch should be neurotized.

We routinely carry out nerve transfers for the reconstruction of the suprascapular and axillary nerves in brachial plexus injuries, even in the presence of nerve roots that are amenable to grafting, because of the occurrence of co-contractions and difficulties with voluntary motor control. Improved results, however, can be obtained when grafts from the roots to the divisions of the upper trunk are concomitantly performed with distal nerve transfers. Palsies of the primary abductors (i.e., deltoid and supraspinatus) are addressed by nerve transfer, while palsies of the secondary abductors (i.e., pectoralis major and coracobrachialis) are treated by root grafting. The pectoralis major and coracobrachialis are important when the arm is already abducted above 90 degrees and for the stability of the shoulder girdle. The same principle applies for external rotation. Improvement of subscapularis function by root grafting contributes to shoulder joint stability and improves the degree of recovery of external rotation.

Triceps paralysis or weak elbow extension is a contraindication.

In brachial plexus injuries, both the triceps long head and the upper medial head motor branch can be used to neurotize the anterior division of the axillary nerve and the branch to the teres minor. Before sectioning both branches, the surgeon should be confident that the triceps is fully innervated. Preoperatively, triceps strength should be at least 80% of the normal side, and intraoperatively, electrical stimulation of the radial nerve should demonstrate contractions of the lateral and medial head. If this cannot be demonstrated, only the triceps long head should be used. If the triceps is weak by examination and intraoperatively, only the triceps long head is functioning; the triceps to axillary nerve transfer should be aborted to prevent paralyzing the triceps.

Lesions older than 12 months are a contraindication.

In isolated injuries of the axillary nerve, shoulder abduction above horizontal is usually preserved. If not, an accompanying suprascapular nerve lesion should be suspected.

The presence of atrophy of the deltoid is an important physical sign in the diagnosis of axillary nerve lesions, but this is a late finding following denervation. This contributes to the delayed diagnosis of axillary nerve lesions and consequent late treatment and poor results. The typical area of sensory loss is just distal to the deltoid muscle, but this is not an invariable finding, in part because of collateral sprouting of adjacent intact sensory nerves, particularly in longstanding lesions. Due to the limitations in the clinical examination in detecting axillary nerve lesions, decisions for surgical repair traditionally have been based upon electromyograms. If signs of reinnervation are detected within 3 months of injury, surgery is not recommended. However, this approach may be misleading, because many patients show electrophysiological signs of deltoid reinnervation but do not progress to any significant clinical recovery. It is of extreme importance to look for spontaneous recovery and correlate these findings with electromyograms.

The swallow tail test, abduction in internal rotation, and the deltoid extension lag test are of value in detecting isolated axillary nerve palsies ( Figs. 20.1 , 20.2, and 20.3 ). False negatives can be observed in 15% of the patients for the swallow tail and deltoid extension lag tests. This occurs because the teres major can compensate for shoulder extension in a few cases.8

In upper-type brachial plexus injuries, the shoulder palsy is associated with an elbow flexion palsy. Triceps function is preserved but is not normal in up to 50% of patients, even in a C5–C8 root injury. In brachial plexus injuries, the examination is directed toward identifying a nerve root that is amenable to grafting.

The Tinel sign and computed tomography (CT) tomomyelograms are useful for helping to detect a nerve root that is amenable to grafting. Magnetic resonance imaging (MRI) and electromyograms are of limited help in brachial plexus injuries.9

Elbow extension strength should be assessed, and only British Medical Research Council (BMRC) M4 muscle power is considered as donor for nerve transfer. Ideally, elbow extension should be measured objectively. We found an average of 12 kg for normal strength, 8 kg in C5–C6 root injury, and 5 kg in C5–C7 root palsy. M4 corresponds to at least 30% of the normal side.

The axillary nerve emerges from the upper portion of the posterior cord at a mean distance of 49.6 ± 14.3 mm medial to the latissimus dorsi tendon. At the lateral margin of the subscapularis, the axillary nerve is in the center of a triangle bounded medially by the subscapular artery, laterally by the latissimus dorsi tendon, and cephalad by the posterior circumflex humeral artery ( Fig. 20.4 ). At this level, the axillary nerve consistently branches into anterior and posterior divisions. The anterior branch curves around the neck of the humerus, followed on its lateral aspect by the posterior circumflex humeral artery and veins ( Fig. 20.5 ). The anterior branch innervates the middle and anterior deltoid muscles. At a mean distance of 12.7 ± 2 mm distally to its origin, the posterior branch divides into a branch to the teres minor muscle and a second branch to the posterior deltoid muscle.6 The posterior division of the axillary nerve terminates as the superior lateral brachial cutaneous nerve, which traverses the posterior margin of the deltoid muscle midway between its origin and humeral insertion ( Fig. 20.6 ). The teres minor motor branch is predictably located in close contact with the triceps long head and the lateral margin of the subscapularis muscle ( Fig. 20.7 ). The branch to the posterior deltoid muscle emerges more laterally and is ~ 1–2 cm distal to the triceps long head tendon ( Fig. 20.6 ).