A new animal model to investigate axonal sprouting after end-to-side neurorrhaphy.

End-to-side neurorrhaphy is a technique that may provide a solution for the problem of distal target reinnervation without injury to the original donor nerve. The technique drew extensive attention after Viterbo reported his experiments in 1992; however, to date, the animal models used to elucidate the process of lateral axon sprouting had the disadvantage of substantial injury to the donor nerve, raising questions about the origin of axons reinnervating the nerve graft. In this report, a new model in the rat is introduced, in which the donor nerve is not damaged and an additional target can be innervated via a nerve graft. The saphenous nerve represents the axonal conduit; the proximal end is coapted end-to-side to the sciatic nerve at the site of a perineurial window. The distal end is passed through the adductor muscles and coapted distally in an end-to-end fashion with the obturator nerve. In one group, a partial neurectomy was performed at the site of coaptation, which led to a lower Sciatic Functional Index (SFI). In the second group, the creation of a perineurial window yielded a normal SFI after end-to-side neurorrhaphy. Compared to the partial neurectomy group, the perineurial window end-to-side neurorrhaphy resulted in significantly less axons in the graft. The new model has the following advantages: (a) minimal injury to the donor nerve; (b) provision of a single additional target (gracilis) whose functional recovery can be assessed morphologically and behaviorally; (c) an opportunity to understand lateral sprouting by providing a non-injury model in which axonal invasion of the graft can originate from nodal axonal outgrowth; and (d) establishment of a noninjury model that can have widespread clinical applications.