Neuroplasticity following Nerve Transfer of the Anterior Interosseous Nerve for Proximal Ulnar Nerve Injuries

Abstract

Background: Injuries to the ulnar nerve at or above proximal forearm level result in poor recovery despite early microsurgical repair, especially concerning the intrinsic motor function of the hand. To augment the numbers of regenerating axons into the targeted muscles, a nerve transfer of the distal branch of the median nerve, the anterior interosseous nerve, to the ulnar motor branch has been described. Methods: Two patients with severe atrophy of the intrinsic hand muscles following an initial proximal ulnar nerve repair had surgery with an end-to-side transfer of the anterior interosseous nerve to the ulnar motor branch at the wrist level. Outcome and neuroplasticity were prospectively studied using questionnaires, clinical examinations, electroneurography, electromyography, somatosensory evoked potentials at pre nerve transfer and 3-, 12-, and 24-months post nerve transfer as well as navigated transcranial magnetic stimulation at pre nerve transfer and 3- and 12-months post nerve transfer. Results: Successively improved motor function was observed. Complete reinnervation of intrinsic hand muscles was demonstrated at 12- to 24-months follow-up by electroneurography and electromyography. At the cortical level, navigated transcranial magnetic stimulation detected a movement of the hot-spot for the abductor digiti mini muscle, originally innervated by the ulnar nerve and the size of the area from where responses could be elicited in this muscle changed over time, indicating central plastic processes. An almost complete reinnervation of the pronator quadratus muscle was also observed. Conclusion: Both central and peripheral plastic mechanisms are involved in muscle reinnervation after anterior interosseous nerve transfer for treatment of proximal ulnar nerve injuries.

Anterior Interosseous Nerve to Ulnar Nerve Transfer: A Systematic Review

“…First dorsal interosseous (FDI) and adductor digiti minimi (ADM). Study Intrinsic Recovery BMRC ≥3 (%) End-To-End Battiston 14 86 Flores 19 100 Flores 20 80 SETS Davidge 16 70 Dengler 17 79 Doherty 18 73 (FDI & ADM) Head 22 71 (FDI) & 65 (ADM) Jarvie 23 100 Koriem 24 91 Nyman 25 100 …”

“…Amongst the 3 retrospective cohort studies, scores were 5, 7, and 9 using the Newcastle-Ottawa scale and only single study matched cohorts 13 . None of the authors in any of the articles disclosed any conflicts of interest; however, 3 articles reported an external funding source 18 , 25 , 26 . There were no clear sources of bias identified.…”

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

“…27 It was also termed "supercharged" transfer as it supplements motor fascicles to the ulnar nerve. 28 Since then, several groups have published good to excellent results with this transfer 13,[29][30][31][32][33][34][35][36][37][38][39][40] (Tables 2 and 3). In a randomized controlled trial (RCT) involving 93 subjects with advanced cubital tunnel syndrome (CuTS), the functional outcome scores, as well as the compound muscle action potential (CMAP) in ulnar intrinsics on stimulating the ulnar nerve at the wrist, were significantly higher in patients who underwent AIN RETS transfer in addition to the conventional surgery.…”

“…28,29 Motor Re-education Cortical reorganization is needed for the transfer to function well. Nyman et al 32 demonstrated cortical plasticity after the transfer using navigated transcranial magnetic stimulation, which demonstrated the "movement" of abductor digiti minimi hotspot after the transfer. Motor re-education can be started 2 weeks after the transfer.…”

“…Both preclinical and clinical studies have shown good results with epineurial 13,[20][21][22][23]35,38,42 as well as perineurial 24,27,29,[31][32][33][34]37,39,40 windows. Although a wider connective tissue window was shown to improve donor axonal regeneration into the recipient in a classical ETS transfer, 19,59 there are no published studies that look into the role of connective tissue disruption in RETS transfers.…”