End-to-side neurorrhaphy and lateral axonal sprouting in a long graft rat model

Controversy exists regarding collateral axonal sprouting across an end-to-side neurorrhaphy to provide functional motor reinnervation of a target organ without compromise of the donor nerve. Rat models may be limited in the study of end-to-side repair given potential contamination from the proximal nerve stump of the recipient distal nerve and the use of antagonistic muscle groups for donor and recipient. The current study attempts to address these issues by using a rat model in which an end-to-side coaptation is performed with a long graft interposed between the intact donor tibial nerve and the divided, distal contralateral tibial nerve.

The graft used in proximal end-to-side coaptation consisted of both sciatic nerves in a donor syngeneic animal. The distal repair to the contralateral tibial nerve was done immediately or in a delayed fashion to allow potential motor axons to transverse the graft before division of the recipient tibial nerve.

After 24 weeks, axons were noted to transverse the entire distance of the graft and into the contralateral distal posterior tibial nerve. A significant increase in axonal numbers was observed in the immediate repairs compared with the delayed. No animal recovered functional motor ability on the contralateral side as assessed by walking tracks.

These findings suggest the importance of immediate distal neurotrophic factors in encouraging nerve regeneration even in a long graft end-to-side repair. Our model is successful in demonstrating innervation through an end-to-side coaptation but questions its use given the lack of motor recovery.