A segmental defect in a nerve can result from the following:

Nerve grafting should be considered in the following cases:

A variety of substitutes have been described for reconstituting nerve defects. They include nerve (autograft/allograft), biological conduits (e.g., vein, muscle), and artificial conduits (e.g., polyglycolic acid, nanofiber).

The available nerve autografts include the posterior interosseous nerve (PIN), superficial radial nerve, medial and lateral antebrachial cutaneous nerves, and sural nerve (Fig. 16-4). We do not use the superficial radial nerve or the lateral antebrachial cutaneous nerves because they provide innervation to potentially valuable areas of skin.

PIN: The distal portion of the PIN is a purely sensory nerve that innervates the wrist joint. It is identified in the radial aspect of the floor of the fourth extensor compartment deep to the tendons of the extensor digitorum communis (EDC) and the extensor indicis proprius (EIP). It can then be followed proximally for a distance of 5 to 7 cm adjacent to the posterior interosseous artery on the dorsal aspect of the interosseous membrane. It has a cross-sectional area of approximately 0.5 to 0.8 mm² and contains one to two fascicles.

Medial antebrachial cutaneous nerve (MABCN): This is a purely sensory nerve that arises directly from the medial cord of the brachial plexus (C8, T1) and runs along the axillary vein. It then accompanies the basilic vein in the proximal half of the arm and pierces the deep fascia in the midarm. It splits into anterior and posterior branches in the distal third of the arm. The anterior branch innervates the anteromedial surface of the forearm, whereas the posterior branch innervates the posterior and ulnar aspect of the elbow and forearm (Fig. 16-5). The anterior branch of MABCN is used for nerve graft harvest to avoid sensory loss over the elbow. The anterior branch crosses the elbow between the medial epicondyle and the biceps tendon, usually in front of the antecubital vein, and courses superficial to the flexor carpi ulnaris muscle, ending 10 cm from the wrist. A 20-cm long graft can be harvested based on the anterior branch. It has a cross-sectional area of approximately 0.6 to 1 mm² and contains three to four fascicles.

Sural nerve: The sural nerve is a purely sensory nerve formed by the union of the medial and lateral sural cutaneous nerves (sural communicating nerve). The medial sural cutaneous nerve arises from the tibial nerve and pierces the deep fascia of the leg between the heads of the gastrocnemius in the upper third of the leg. It is then joined by the lateral sural cutaneous nerve branch of the peroneal nerve to form the sural nerve. The sural nerve descends along the lateral margin of the Achilles tendon with the small saphenous vein between the lateral malleolus and the calcaneus (Fig. 16-6). It innervates the lateral aspect of the lower third of the leg and the lateral aspect of the ankle, heel, and foot. A 40-cm–long graft can be harvested based on the sural nerve and medial sural cutaneous nerves. The sural nerve has a cross-sectional area of approximately 2.5 to 3.0 mm² and contains six to eight fascicles.

The procedure is performed under tourniquet control using 3.0× to 3.5× loupe magnification for the initial dissection and an operating microscope for the nerve repairs.

The patient is positioned supine with the affected extremity on a hand table.

The leg must be prepared and a thigh tourniquet applied, if a sural nerve graft is anticipated.

A Bruner zigzag incision that incorporates any previous lacerations is made. Thick skin flaps are raised in a plane superficial to the tendon sheath (Fig. 16-7B).

Nerve grafts should not be harvested until the divided nerve ends have been exposed, the ends have been débrided, and the required length of nerve graft has been calculated.

The PIN is exposed by a longitudinal incision ulnar to the Lister tubercle. The extensor retinaculum over the fourth compartment is incised, and the tendons of the EDC and EIP are retracted. The PIN is found on the radial aspect of the floor of fourth compartment. Depending on the length of the nerve required, the skin incision can be extended proximally. There is often a bulbous dilation at the distal termination of the PIN. This should be excised. The average length of a PIN graft is usually 4 to 5 cm.

The MABCN is exposed by a longitudinal incision on the anteromedial aspect of the forearm at the junction of the proximal and middle third of the forearm. This incision begins 2 cm anterior and 2 to 3 cm distal to the medial epicondyle. The anterior branch of the MABCN can be found within the subcutaneous tissue (Fig. 16-8). If more than one branch is found, the branch that better matches the recipient nerve diameter is selected. Depending on the length of nerve required, the skin incision can be extended proximally.

The sural nerve is exposed by a 2-cm longitudinal incision midway between the lateral malleolus and the calcaneus. It is close to the lateral margin of the Achilles tendon and lies lateral to the small saphenous vein. The required length of the nerve is then dissected proximally. The use of multiple transverse 1-cm stepladder incisions gives a more aesthetic result compared with a single longitudinal incision.

The patient is started on early mobilization within the splint. There should be no tension at the repair site in a nerve graft, and patients can be mobilized early, as opposed to after a primary repair, which would require a longer period of immobilization. The splint can be discontinued after 2 to 3 weeks, and patients are advised to avoid hyperextension for another 2 to 3 weeks.

More than 90% of patients (<65 years) get S3 or greater sensory recovery after a nerve graft (Fig. 16-15—late postoperative result of patient in Figs. 16-1 and 16-12). This equates to recovery of pain and touch sensation, disappearance of hyperesthesia, and ability to localize stimulus. However, there is imperfect recovery of two-point discrimination.