Surgical Techniques for Peripheral Nerve Repair

Surgical repair of peripheral nerves is a well-researched technique to improve motor and sensory function after injury. Surgical intervention should not be attempted without complete understanding of the nerve anatomy ( ▶ Fig. 73.1). The external epineurium is connective tissue that encases the nerve to serve as protection and strength and provide vascular supply with longitudinal vessels. The internal epineurium further divides the nerve into groups of fascicles, and the perineurium surrounds individual fascicles. This layer provides significant tensile strength and can withstand suture placement, making the fascicle the smallest component of any peripheral nerve that can be repaired. ¹^, ²^, ³ The axons lie within the fascicle, alongside Schwann cells, held together with basal endoneurium.

Fig. 73.1 (a) External epineurium, (b) internal epineurium, (c) perineurium, and (d) endoneurium.

73.2 Patient Selection

Nerve repair may be attempted immediately in the case of sharp, complete transection. ¹ Nerve injuries by other mechanisms require close observation, as some may experience spontaneous recovery; but those that do not should undergo surgical repair within the first 3 to 6 months after the injury. Fibrosis at the motor end plate increases significantly after 3 to 6 months, and surgical repair after 12 months is rarely clinically successful. ²^, ⁴

73.3 Preoperative Preparation

Before proceeding with surgical intervention, detailed examination of the patient’s nerve function must be completed. This may be supplemented with electromyography (EMG) testing when appropriate. Assessment for primary repair should be completed, with secondary evaluation for possible nerve transfers and grafting procedures in case primary repair is not feasible. The incision must be planned to allow for adequate proximal and distal exposure to ensure the reanastomosis is without tension. Utility of intraoperative neuromuscular monitoring or stimulation must be considered; the anesthesiologist should be prepared to limit the use of paralytic agents and/or inhalational anesthetics, depending on the monitoring modality needed.

73.4 Operative Procedure

Several techniques for nerve repair have been described. Nerve injuries that are sustained with sharp force, with minimal gap of less than 2 cm between severed ends, are generally amenable to primary end-to-end reapproximation. ² If dissection of the injured nerve has left a significant gap, the length may be made up by extension of the circumferential nerve dissection. If the gap is excessive, leading to tension on the reapproximated nerve ends, nerve grafting or nerve transfer should be considered. Nerve injuries that leave the nerve in continuity should be examined with the operative microscope to identify the segment of injured tissue, sometimes manifesting as a neuroma in continuity. The nerve is circumferentially exposed with sharp dissection, and function across the injury may be assessed with intraoperative nerve action potentials (NAPs). If NAPs are found across the injury site, this provides evidence of spontaneous regeneration and the nerve should not be transected. If no conduction is found, the nerve should be transected just proximal and distal to the injury site.

73.4.1 Direct Repair

The injured ends should be resected further in a stepwise fashion with a fresh, sharp blade, until healthy tissue is appreciated at either both ends. Healthy ends show sprouting fascicles, bleed, and can be confirmed histologically intraoperatively. Any retained scar tissue will limit recovery and is a major cause of nerve repair failure. The healthy nerve ends should be realigned, with surfaces touching but not taut, with retention of fascicular anatomical orientation. Fascicular realignment can be guided by the surface vessels, as well as the cross-sectional size of the nerve endings.

Once the proximal and distal nerve ends have been appropriately dissected and reapproximated, sutures are placed with the use of operating microscope. Sutures can be applied through the outer epineurium using an 8–0 to 10–0 monofilament, nonabsorbable, simple sutures, with a final product free of tension. This is most appropriate for monofascicular nerves (e.g., digital nerves) or diffusely grouped polyfascicular nerves. Two sutures are initially applied opposite one another, with square knots lying flat on the nerve surface, sometimes followed by two more sutures evenly spaced, if deemed necessary by the diameter and fascicular alignment. Excess sutures may lead to scarring and should not be placed if not absolutely necessary.

The epineural technique allows the least injury possible to the nervous tissues, but it does not always give reliable fascicular alignment ( ▶ Fig. 73.2). Dissection of the fascicles, anatomical realignment, and suture through the perineurium allow more control over retention of the chosen fascicular alignment and increase the strength of the repair; however, this technique simultaneously increases likelihood of injury to the nerve fibers. ³^, ⁵ Alternatively, fascicles may be grouped, realigned, and sutured using internal epineurium. This approach is particularly useful in a mixed peripheral nerve, where conservation of motor-to-motor and sensory-to-sensory function is of utmost importance. The antebrachial portions of the median and ulnar nerves fall into this category. For grouped fascicular repair, the process mirrors that described for epineurial repair. The ends should be debrided sharply until healthy neural anatomy is appreciated under the operative microscope. Internal neurolysis for isolation of the fascicles is completed with blunt dissection techniques using microinstruments. The ends are realigned using surface landmarks, as well as intraoperative stimulation techniques, to ensure matching of the appropriate fascicles. Once reapproximated, the internal epineurium is sutured using techniques described above.

Fig. 73.2 (a) Suture applied epineurium to fascicle, fascicle to epineurium. (b) Instrument tie with a square, flat knot. (c) Tighten the knot without applying stress to the nervous tissue. (d). Two final knots lay square and flat on the surface of the nerve. This is a perineural technique; some surgeons may use epineural suture techniques.

73.4.2 Grafting

Nerve grafts are used to bridge a gap between two nerve ends requiring repair. Autografts or allografts can be used. A separate chapter (Chapter 74) is dedicated to nerve autograft harvesting techniques. Allografts may be fresh or processed to remove immunogenic cells and proteins. The use of fresh allografts will require 18 months of immunosuppression associated with increased infection risk and healing time; this should be considered strongly in patient and procedure selection. ⁶ Processed allografts are stripped of the cellular components that activate adverse immunogenic reactions that normally induce scarring and fibrosis, impeding axonal growth. Processed allografts retain a collagen scaffold containing laminin, which together promote cell migration, nerve fiber elongation, diffusion of growth factors, and axonal outgrowth. When allograft tissue is selected, the surgeon should also consider that increased vascularity and complementary diameter of the allograft to the host nerve are associated with successful axonal growth and reinnervation. ⁶

Whether an autograft or allograft is used, the proximal and distal stumps of the injured nerve are prepared for coaptation as previously described. The graft is positioned and trimmed to the appropriate length for coaptation of the ends with the proximal and distal host nerves. Appropriate graft length is crucial to preventing undue tension on the nerve (short graft) or displacement and kinking of the nerve (long graft) after anastomosis is complete. Multiple nerve graft cables can be used to match the whole cross-sectional area of the recipient nerve. This should be taken into consideration when harvesting. If fresh allograft is being used, attention should be directed to ensure approximation of the vessels and fascicles, sensory and motor, with the appropriate host structures. After approximating the graft ends with the host nerve, end-to-end anastomosis is performed as previously described. Sutures should be 8–0 or smaller, monofilament, nonabsorbable, simple sutures, with an end product free of tension and eversion ( ▶ Fig. 73.3). Outcomes data reveal similar results between allografting and autografting procedures when the gap is small and greater functional recovery in autografts over allografts when the gap is longer. ⁶

Fig. 73.3 Allograft material is approximated across the nerve gap. Inset: Suture is applied from the epineurium through the fascicle and subsequently through the allograft. A square, flat knot lays on the surface of the nerve.

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