Introduction. End-to-side neurorrhaphy (ESN) has reemerged as a potential alternative technique in nerve repair. This study seeks to determine whether collateral axonal sprouting can occur across gaps in end-to-side neurorrhaphy and to compare the functional recovery of gap repaired lesions to those repaired by direct suture.

Methods: The right peroneal nerve of 80 female Lewis rats (200g ±25) was transected 3mm distal to the bifurcation of the sciatic nerve. A perineurial window sized to match the distal peroneal stump was made in the tibial nerve of each rat. The rats were then divided into four groups of twenty-four each. In the direct suture group, ESN repair was made by suturing the distal stump to the epineurium surrounding the window by 12-0 nylon suture. The remaining three groups were connected through an ultra thin-walled PTFE plastic tube with a gap of 2mm, 4mm, or 6mm. Results were assessed by (1) walking track test calculated by the peroneal functional index (PFI) and the tibial functional index (TFI); (2) wet weight ratio of the extensor digitorum longus (EDL) muscle; (3) contractile functional testing of EDL; and (4) histological examination.

Results: The PFI recovered to the normal range in all groups by week 12, with the first significant improvement in the direct ESN group at week 4, followed by the 2mm group at week 5, the 4mm group at week 6, and the 6mm group at week 8. From week 5 onward, there was no significant difference between the Direct and 2mm groups, but both of these groups was significantly better than the 4mm and 6mm groups. By week 9 there was no significant difference in the PFI between the groups. The TFI demonstrated some initial impairment in donor nerve function, but recovering to the normal range by week 5. Muscle atrophy was noted in EDL at 8 and 12 weeks. At week 12, there was a significant difference between the wet weight ratios of EDLs, with the Direct>2mm>4mm>6mm. Contractile testing revealed greater muscle force in the Direct and 2mm groups at each stimulation frequency at each time period. Histology demonstrated sprouting axons in the tubes of each gap group and regenerated axons in the distal peroneal nerve in all groups.

Discussion: This study demonstrated successful nerve regeneration and considerable motor functional recovery across a conduit up to 6mm in end-to-side nerve repair, indicating a potential clinical alternation when direct suture is not possible.