Acute Versus Delayed Experimental Obturator to Femoral Nerve End-Side Transfers

University of Calgary

Tak-Ho Chu, Amanda McConnachie, Nicolas Lasaleta, Saud Alzahrani

INTRODUCTION: Reverse end-to-side (RETS) nerve transfer aims to augment injured nerve function by supplying a dispensable donor motor nerve to the side of the distal injured nerve. Although clinical studies have suggested efficacy of RETS transfer, uncertainties remain regarding its underlying mechanism (reinnervation from donor vs. augmentation of the distal nerve and muscle- “babysitting” effect). Indeed, our recent clinical studies in chronic ulnar neuropathy patients, using electrophysiological examination, revealed no reinnervation contribution from the donor nerve, despite functional improvement.

OBJECTIVE: Our objective is to assess the effectiveness of RETS transfer in chronic experimental nerve injury and to examine for evidence of a babysitter effect. Methods Rat obturator and femoral nerve were used as donor and recipient nerves, respectively. Electromyogram (EMG), retrograde labeling of regenerated motoneurons and neuromuscular junction (NMJ) formation were used to compare regenerative ability of donor nerve in acute RETS transfer and delayed RETS transfer (injured 8 weeks prior). Nerve- babysitting effect on injured nerve was investigated by 1) no intervention; 2) perineurial window creation; and 3) RETS transfer to femoral nerve in delayed repair model. The effects of availability of regeneration from the native femoral nerve were investigated by severing proximal femoral nerve with subsequent acute and delayed repairs.

RESULTS: EMG and motoneuron quantification confirmed significant inferiority of donor nerve regeneration into recipient nerve in delayed RETS transfer compared to acute repair. Yet some donor axons reached targeted muscle and formed NMJs in both. Similar functional assessments revealed no appreciable evidence of babysitting effects contributing to RETS success. The availability of regenerating axons from the recipient nerve profoundly influenced the final outcomes.

CONCLUSIONS: Our study offers insights into the discrepancy between clinical outcomes and experimental findings, underscoring the compounded impact of delayed intervention and native nerve regeneration which both affect the efficacy of RETS nerve transfer.