Reverse End-to-Side Nerve Transfer for Severe Ulnar Nerve Injury: A Western Canadian Multicentre Prospective Nonrandomized Cohort Study

Abstract

BACKGROUND: Reverse end-to-side (RETS) nerve transfer has become increasingly popular in patients with severe high ulnar nerve injury, but the reported outcomes have been inconsistent. OBJECTIVE: To evaluate the "babysitting effect," we compared outcomes after anterior interosseous nerve RETS transfer with nerve decompression alone. To evaluate the source of regenerating axons, a group with end-to-end (ETE) transfer was used for comparisons. METHODS: Electrophysiology measures were used to quantify the regeneration of anterior interosseous nerve (AIN) and ulnar nerve fibers while functional recovery was evaluated using key pinch and Semmes-Weinstein monofilaments. The subjects were followed postsurgically for 3 years. RESULTS: Sixty-two subjects (RETS = 25, ETE = 16, and decompression = 21) from 4 centers 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. Postsurgically, no reinnervation from the AIN to the abductor digiti minimi muscles was seen in any of the RETS subjects. Although there was no significant improvement in compound muscle action potentials amplitudes and pressure detection thresholds in the decompression and RETS group, key pinch strength significantly improved in the RETS group (P < .05). CONCLUSION: The results from published clinical trials are conflicting in part because crossover regeneration from the donor nerve has never been measured. Unlike those with ETE nerve transfers, we found that there was no crossover regeneration in the RETS group. The extent of reinnervation was also no different from decompression surgery alone. Based on these findings, the justifications for this surgical technique need to be carefully re-evaluated.

Perineurial Window is Critical for Experimental Reverse End-to-Side Nerve Transfer

“…In a recent clinical study, electrophysiological analysis indicated that contribution of muscle reinnervation from donor anterior interosseous nerve (AIN) is essentially absent in patients with cubital tunnel syndrome after AIN RETS nerve transfer to ulnar nerve. 22 Another clinical study also showed lack of superiority between RETS and conventional repair in ulnar nerve lesion-in-continuity injuries and lack of improvement in secondary outcomes including grip or pinch strength, 23 despite favorable outcomes in transection injuries with RETS repair. Our study may provide insights to these clinical outcomes, and we postulate that a chronically denervated recipient nerve would further decrease the likelihood of axon regeneration from donor nerve, a hypothesis that is currently under investigation in our laboratory.…”

Reverse End-to-Side Transfer to Ulnar Motor Nerve: Evidence From Preclinical and Clinical Studies

“…29 Jarvie et al 33 noted that after AIN RETS transfer, motor recovery preceded sensory recovery, suggesting that the AIN fibers were predominantly contributing to the early recovery phase. However, in a recent prospective study by Curran et al 48 (which included several patients from our center), where they tried to quantify the contributions from AIN and native ulnar nerve pool using electrophysiological parameters, the investigators found no evidence in any case of RETS transfer of muscle reinnervation from AIN. The possibility of each of the intrinsic muscles getting preferentially innervated by either AIN or ulnar fibers should also be borne in mind (Figure 3).…”

“…37 However, it is notable that these authors are comparing 2 different populations of ulnar nerve injuries, with the more severe one receiving ETE, which we too underscore in a recent prospective study of deliberate ETE and RETS transfers, depending on the type of ulnar nerve pathology. 48 In conclusion, we advise using RETS transfer (of AIN PQ to ulnar motor) as an adjunct for patients with severe traumatic in-continuity ulnar nerve injuries and severe compressive (CuTS) lesions that may have a chance for some spontaneous recovery, after ulnar nerve decompression/transposition, from the native ulnar nerve pool. We would exclude elderly and diabetic patients with severe compressive ulnar neuropathy who have no intrinsic hand muscle function.…”

“…37 However, it is notable that these authors are comparing 2 different populations of ulnar nerve injuries, with the more severe one receiving ETE, which we too underscore in a recent prospective study of deliberate ETE and RETS transfers, depending on the type of ulnar nerve pathology. 48…”

Current perspectives on peripheral nerve repair and management of the nerve gap

“…AIN transfer is typically described to augment ulnar nerve recovery but has also been described to babysit and augment median nerve repair enabling thenar recovery (Czarnecki et al., 2023). Comparative studies are small and few, such that it remains unclear as to how much recovery is dependent on RETS or regeneration of the injured nerve without further study (Curran et al., 2022; Dunn et al., 2021). A recent clinical study by Thorkildsen et al.…”