Long-term evaluation of rat peripheral nerve repair with end-to-side neurorrhaphy

This study was designed to assess long-term reinnervation of end-to-side neurorrhaphy in the rat. The cut right peroneal nerve was repaired and sutured to the side of the intact tibial nerve. Both the extent of reinnervation and the integrity of the intact donor nerve were evaluated in 48 Sprague-Dawley rats randomly treated with fresh or delayed nerve repair with or without perineurotomy. Evaluations included nerve conduction velocity (NCV) of both the peroneal and tibial nerves, dry muscle weight, and histologic examination (neurofilament stain and morphometric assessment) at 8 and 12 months postoperatively. Although animals treated with perineurotomy tended to have better NCV and dry muscle weight recovery than those without, the difference was not statistically significant. No difference was observed between fresh and predegenerated nerve repair. The mean total (all four subgroups) NCV recovery rates were 87 percent and 94 percent for the peroneal nerve, and 93 percent and 95 percent for the tibial nerve, compared to the contralateral intact nerves, at 8 and 12 months, respectively. Tibialis anterior muscle mass measurements revealed a recovery in dry muscle weight of about 85 percent and 89 percent at 8 and 12 months, respectively, compared to the intact contralateral tibialis anterior muscles. Histologic studies with neurofilament staining revealed numerous axons at the distal end of the peroneal nerve in all groups, indicative of myelinated axonal regeneration. Morphometric analysis demonstrated that the presence of a window in the perioneurium improved the histologic picture. The mean number of myelinated fibers at 12 months postoperatively was significantly higher in animals with a perineurotomy window (compared to without) in both fresh and predegenerated nerve repair subgroups, respectively (p <0.05). These results indicated that end-to-side neurorrhaphy permits axonal regeneration from the intact donor nerve and is associated with satisfactory recovery. The effect of the procedure on the donor nerve was negligible.