End-to-Side Nerve Transfer: An Evaluation of Its Efficacy and Functional Impact

Background Peripheral nerve injury is common, effecting 3% of the population. While surgery can be effective in moderate cases, complete neurologic and functional recovery are often not possible in severe cases of proximal nerve injury. Poor outcomes are attributable to the long-distance nerves must regenerate to reach their targets. End-to-end (ETE) nerve transfer surgery can shorten the distance of regeneration by bridging a dispensable donor nerve to the end of the injured nerve that is closer to the denervated target. Unfortunately, these procedures involve cutting the injured nerve, preventing the possibility for native nerve regeneration, and making in unfeasible for incomplete injuries. Reverse end-to-side (RETS) nerve transfers is an increasingly utilized technique that involves connecting the donor nerve to the side of the injured nerve, which preserves the injured nerve continuity, and potentially allows for donor nerve (1) axonal crossover and the (2) babysitting effect. However, the source of regenerating nerve fibres in the RETS transfer has been inconsistent with some studies that show benefits and others that did not find efficacy in the surgery. Objective To evaluate the amount of (1) axonal crossover from the donor nerve in the RETS transfer using a novel electrophysiology technique. To evaluate the (2) babysitting effect by comparing the RETS transfer to a decompression surgery. Aim 1 — A novel electrophysiological technique to quantify axonal crossover. Seven Martin-Gruber anastomosis (MGA) and nine anterior interosseous nerve (AIN) to ulnar nerve ETE nerve transfer patients were recruited. Motor nerve conduction studies were performed, and the novel digital subtraction technique was compared against the collision technique and innervation ratio method, previous techniques to measure crossover. The digital subtraction method was highly correlated with the collision technique and has several practical advantages. With the increasing use of nerve transfer surgery in severe high ulnar nerve injury, this could be a useful method to identify the presence of MGA prior to surgery and for evaluating nerve recovery following surgery. Aim 2 — A prospective clinical trial comparing RETS with ETE and decompression surgery. Sixty-two subjects (RETS=25 | ETE=16 | decompression=21) from four centres in Western Canada were enrolled. All subjects with severe ulnar nerve injury had nerve compression at the elbow except 10 in the ETE group had nerve laceration or traction injury. The novel digital subtraction technique was used to quantify the regeneration of AIN and ulnar nerve fibers while functional recovery was evaluated using key pinch and Semmes-Weinstein monofilaments. The subjects were followed post-surgically for 3 years. Post-surgically, no reinnervation from the AIN to the abductor digiti minimi muscles was seen in any of the RETS subjects. Significance While clinical translation of RETS has been increasing, the results from published clinical trials has been conflicting, in part because crossover regeneration from the donor nerve has never been measured. From applying the novel electrophysiological technique in the multicentre prospective study, we found there was no crossover regeneration in patients that underwent RETS compared to ETE nerve surgery. The extent of reinnervation from RETS surgery was also no different compared to decompression surgery alone. Based on these findings, the justification for the RETS surgical technique needs to be further evaluated.

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