Harvesting Techniques of Cutaneous Nerves for Grafting

The advent of nerve grafts has revolutionized the treatment of nerve injuries. Before nerve grafts, techniques such as extreme limb flexion or limb shortening were used with a high degree of morbidity and low success rates. Hanno Millesi pioneered the use of free nerve grafts in the 1970s. ¹ Traditionally, the sural nerve has been the gold standard for harvesting autograft, due to the ease of the approach, length of graft, and minimal complications. Practically, any cutaneous nerve can be used as a donor graft. In this chapter, we will address some of the more commonly used ones. Recently, allografts have also been made available.

74.2 Patient Selection

Sharp nerve injuries should be repaired immediately. Blunt and stretch injuries can be treated conservatively for 3 to 6 months. If no spontaneous recovery occurs, surgery is recommended. Direct repair is the best method if performed without tension. Otherwise nerve grafts should be considered.

74.3 Preoperative Preparation

When counseling patients, it is important to explain how lengthy the recovery process is so that patients and families are not frustrated postoperatively. The patient positioning is dictated mainly by the recipient nerve to repair, since this involves microsurgical skills requiring good surgeon ergonomics. Sural nerve harvest for example can be done in prone, lateral, or most of the time in a supine position.

74.4 Operative Procedure (See Video 74.1)

74.4.1 Sural Nerve

For sural nerve harvesting the patient may be positioned lateral decubitus, supine with the leg medial rotated, or prone with the limb laterally rotated. Patient positioning should be based on optimal access of the nerve repair site. Three methods for sural nerve harvest have been established including: full incision to expose the nerve, segmented or “stepladder” incisions, and minimally invasive endoscopic harvest. A tourniquet may be placed for each technique but is not necessary.

Single Incision

A tourniquet is placed on the proximal thigh and inflated to a pressure of 250–300mmHg. ² The posterior aspect of the patient’s leg is prepped from the calcaneus to the distal portion of the thigh. For harvest of the sural nerve using a full incision, a pen is used to mark the incision site just posterior and proximal to the lateral malleolus ( ▶ Fig. 74.1). A vertical incision is made using a scalpel taking care to remain superficial to avoid incising the short saphenous vein. A retractor is placed and blunt dissection is performed until the short saphenous vein and distal sural nerve are visualized ( ▶ Fig. 74.2). The incision is continued proximally along the leg, retractors are placed as necessary, and the sural nerve is continuously dissected and mobilized from the surrounding tissue. At the level of the gastrocnemius muscle bellies the sural nerve commonly splits into its two contributions: medial (from the tibial nerve) and lateral (from the common peroneal nerve) sural cutaneous nerves. The medial sural nerve dives into the deep fascia of the leg and travels between the gastrocnemius muscle bellies. ³ To follow this course, the deep fascia of the leg is incised with scissors. Dissection is continued until the medial sural nerve can no longer be mobilized without excessive damage of the gastrocnemius muscles. The medial sural nerve is sharply transected proximally at the groove of the gastrocnemius bellies, and distally at the initial incision. Minor cutaneous branches are also transected along the course of the nerve as necessary. If more nerve graft is needed, the lateral sural nerve may be harvested as well. The tourniquet is removed and the incision is irrigated and closed appropriately in layers. The sural nerve will provide graft material of approximately 35 cm³ ( ▶ Fig. 74.3).

Fig. 74.1 For sural nerve harvest, an incision is made midway between the Achilles tendon and the lateral malleolus. The patient here is positioned lateral for a sural nerve biopsy. For grafting, the patient can be prone, lateral, or supine, depending on the recipient nerve to be exposed.

Fig. 74.2 (a) Once the skin is retracted, the short saphenous vein is usually evident by its blue color (single arrow). The sural nerve (double arrows) is posterior to it. (b) The dissection is carried on, and the vein is surrounded by a red loop while the nerve is surrounded by a blue loop.

Fig. 74.3 Up to 35 to 40 cm of sural nerve can be harvested, once followed up to its origins from tibial and peroneal nerves.

Skip Incisions ( ▶ Fig. 74.4)

A second technique for sural nerve harvest is the intermediate or segmented incision approach that uses staggered lateral incisions to expose and harvest the nerve. This technique’s greatest advantage is reduced donor site morbidity and scarring. The patient is prepped and positioned as previously discussed. The sural nerve and short saphenous vein are exposed and visualized through a small incision just posterior and proximal to the lateral malleolus, as previously described. Blunt scissors are inserted into the incision and opened as gentle pressure is applied in a cephalic direction to create a canal in the superficial fascia that is ~ 5 cm long. Instruments such as Penfields and curved and strait hemostats are used to mobilize the sural nerve from the surrounding connective tissue under direct visualization.

Fig. 74.4 Skip incisions can also be used for better cosmesis.

A vessel loop is placed around the sural nerve and gentle traction is applied to visualize the proximal course of the nerve under the skin. ³ The course of the nerve is marked on the skin, and a second horizontal incision is made along it ~ 10 cm proximal to the first. A retractor is placed, and blunt dissection is performed until the nerve is again localized. A vessel loop is placed around the nerve, and blunt dissection of the surrounding connective tissue is performed distally until the original canal is entered and the nerve is mobilized. Dissection is continued proximally, and this process of stepwise incisions is continued until the desired length of nerve is mobilized. For harvest of the nerve, the proximal end should be sharply transected. The next adjacent distal vessel loop is used to apply gentle traction to pull the proximal end of the nerve through the incision site. This process is repeated to sequentially remove the nerve through each incision site until the original incision is reached and the full length of nerve has been removed from the leg. ³ To complete the nerve harvest, the distal end of the nerve is sharply transected. Each incision site is irrigated and closed appropriately.

Endoscopic

Towels are placed under the ankle to slightly elevate the leg while retaining the knee in an extended position. This positioning reduces the pressure on the posterior and lateral compartments of the leg and aids in the establishment of a working canal for the endoscope and instruments. ² A 4-cm incision is made posterior and proximal to the lateral malleolus, and a retractor is placed. Blunt scissors are used to create a canal through the superficial fascia. The sural nerve and short saphenous vein are visualized, and a looped nerve dissector is used to dissect the nerve away from the vein under direct visualization. ² The nerve harvest unit/endoscope is inserted in combination with a laparoscopic scissors that is capable of rotating 360 degrees. Uchio et al, in 2012, describe the use of the neurotome device for harvest of the sural nerve. ⁴ This device consists of a leading cutting blade followed by a slotted tube that cradles the nerve. The nerve is freed from the surrounding tissue as the neurotome is advanced. This device may be considered for use during the remainder of this procedure to aid the mobilization of the nerve.

Under endoscopic visualization, the turndown spoon of the nerve harvest unit is used to extend the canal in the superficial fascia; dissection of the sural nerve from the lesser saphenous vein is continued until it is freed. At the level of the gastrocnemius muscle bellies, the sural nerve diverges. The medial sural nerve pierces the deep fascia of the leg to travel between the muscle bellies of the gastrocnemius while the communicating branch remains superficial and anastomosis with the lateral sural nerve. ² The laparoscopic scissors are used to transect the deep fascia. The retractor is advanced, and the course of the nerve is followed between the muscle bellies. The nerve is mobilized from the muscle, gently retracted, and transected at its proximal end using laparoscopic scissors. The scissors are used to transect the communicating branch at its distal end or more proximally if more nerve graft is required. A vessel loop is placed around the nerve at the incision site and is used to gently place traction on the nerve to pull it through the skin incision. The distal end is then cut, and the nerve is removed from the leg. The canal and incision are irrigated, and the wound is closed.

74.4.2 Saphenous Nerve ( ▶ Fig. 74.5)

The saphenous nerve is a sensory branch of the femoral nerve arising in the thigh and descends toward the medial malleolus. ⁵ It travels to supply the anteromedial aspect of the leg and ankle. This path is made up of the deep muscular fascia inferiorly, the superficial fascia superiorly, and the fusion of these planes laterally, forming a compartment. ⁶ As the saphenous nerve descends, it travels with the long saphenous vein in this partition, forming an intimate relationship in the leg.

Fig. 74.5 (a) Incision (arrowheads) for saphenous nerve harvest is anterior to the medial malleolus. (b) The saphenous nerve (single arrow) and vein (double arrow) can be dissected.

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