27 Pain following Nerve Repair
27.1 History
A 40-year-old right-hand-dominant woman was accepted in transfer with subacute left, greater than right, neuropathic arm pain. Five days prior to presentation, the patient had fallen on the stairs and sustained bilateral upper extremity lacerations from broken glass. She sustained bilateral arterial, nerve, and tendinous injuries and presented to an outside facility for emergent management. Perfusion was restored, tendons were repaired, and major nerve branches were temporarily coapted using conduit. On transfer, she presented with tachycardia and 10 out of 10 pain.
27.2 Anatomic Description of the Patient’s Current Status
27.2.1 Examination Findings
The left arm had a stapled transverse laceration spanning the antecubital fossa with significant edema, no signs of infection, intact distal perfusion, pain with attempted elbow flexion, and absent distal median and radial nerve function. There was exquisite sensitivity to light touch at the medial and lateral aspects of the proximal staple line with loss of sensation in the medial antebrachial (MABC) and lateral antebrachial (LABC) cutaneous nerve distributions. Distal ulnar nerve function was preserved.
Fig. 27.1 Left upper extremity after extension of the laceration, exposure and removal of the previously interposed nerve conduits. The transected median and radial nerves are visible. The biceps was transected at the musculotendinous junction; the brachialis was partially transected; the proximal muscle bellies were coapted under tension to the distal brachialis muscle. The distal biceps tendon had not been included in the repair. The nerve stumps are contused and show some evidence of a more avulsive mechanism of injury. (Reproduced with permission of nervesurgery.wustl.edu)
The right arm had a stapled oblique laceration that crossed the ulnar aspect of the forearm. Distal function of the ulnar nerve was absent.
27.2.2 Intraoperative Findings
In the left upper extremity, after extending the previous laceration significantly to allow for better exposure, the ends of the transected left median and radial nerves were exposed. They had been approximated, under moderate tension, with nerve conduits (▶Fig. 27.1). In addition, after meticulous and tedious dissection through the subcutaneous tissue, the proximal ends of the transected LABC and MABC were identified; the distal stumps could not be easily identified. A laceration through the biceps musculotendinous junction and brachialis muscle belly was also noted.
In the right upper extremity, the previous laceration was extended slightly, and the transected ulnar nerve (with interposed conduit) was exposed. The muscle bellies of the flexor digitorum superficialis (FDS) and flexor carpi ulnaris (FCU) were partially transected (▶Fig. 27.2).
27.2.3 Physiologic Explanation of Problem
Following laceration, the proximal nerve end undergoes axonal sprouting, and, if left unrepaired, it can generate a traumatic neuroma. Stimulation of this traumatized proximal stump leads to pain and paresthesias. If the proximal end is appropriately approximated to a recipient scaffold for ingrowth (i.e., distal stump of the transected nerve, autograft, allograft, etc.), regeneration occurs, preventing neuroma formation and its accompanying pain.
Furthermore, when a traumatized nerve is repaired, the coapted ends must be healthy, and outside of the zone of injury. Coaptation of damaged fascicles will prohibit healthy nerve regeneration, resulting in a segment of abnormal fascicular sprouting and scar (neuroma in continuity). Tension across a nerve repair also inhibits axonal outgrowth and promotes gapping, both of which further contribute to neuroma-in-continuity formation. For these reasons, acute repair of nerve injuries requires aggressive trimming of traumatically transected nerve ends and, often, interposition grafting to avoid tension.
Fig. 27.2 Right upper extremity. The transected ulnar nerve is visible, still attached to the previously interposed conduit proximally. Lacerated flexor digitorum superficialis (FDS) and flexor carpi ulnaris (FCU) muscle bellies are noted. The distal nerve stump appears to be of poor quality—ecchymotic, with evidence of an avulsive mechanism. (Reproduced with permission of nervesurgery.wustl.edu.)
27.3 Recommended Solution to the Problem
Anticipating and addressing the potential for neuropathic pain at the time of nerve injury, through pharmacologic, surgical, and therapeutic interventions can help prevent this problem. Nerves of critical function must be repaired, tension free, with interposed graft material if a tension-free primary repair is not possible. Distal compression points, which add additional insult to an injured nerve (the double-crush phenomenon), should be released to assist distal regeneration and potentially decrease pain or dysfunction.
There must be a high index of suspicion for injured cutaneous nerves (such as the LABC and MABC), which can also lead to painful neuroma formation. Diligent dissection to identify at least the proximal nerve end is important. If the distal ends cannot be found, then the proximal end should be cauterized, crushed proximally (to move the regeneration front away from the cut end), and transposed in a loose loop, deeper into a relatively immobile muscle plane. These injured cutaneous nerves may also be harvested for use as “spare parts” graft material for repair of nerves of more critical function.
Neuropathic pain medications, such as gabapentin, nortriptyline, or pregabalin, should be started at the time of injury and titrated as needed to control pain after surgery. These should be used in conjunction with anti-inflammatories, muscle relaxants, and narcotics. Early referral to a pain specialist can be helpful not only for medication management but also for performance of both pre- and postoperative nerve blocks. Indwelling supraclavicular catheters can also be placed for instillation of continuous local anesthetic perioperatively. Later, stellate (sympathetic) ganglion blocks can provide significant pain relief and even help prevent progression to complex regional pain syndrome (CRPS).
Finally, physical therapy can be a powerful adjunct. Techniques such as desensitization and graded motor imagery can assist with pain control. Additionally, following repair, institution of early nerve gliding exercises (even within the limited movement required to protect muscle and/or tendon repairs) helps ensure that newly repaired nerves do not heal encased and tethered in scar.
27.4 Technique for Nerve Harvest and Repair
27.4.1 Sural Nerve Harvest
The patient may be positioned prone for bilateral harvest (supine may be used for one-sided harvest or in children/smaller patients). The sural nerve is identified, through an incision posterior to the lateral malleolus (▶Fig. 27.3) running with the lesser saphenous vein, just lateral to the Achilles tendon. Harvest is performed with the assistance of a nerve stripper (do not substitute the tendon stripper, which will transect the nerve) to free the nerve from surrounding tissues without requiring an extensive incision along the posterior leg. Several small incisions may be needed proximally along the course of the sural nerve to free branches that prohibit smooth use of the stripper. The proximal end of each harvested nerve is marked.
