A scanning electron microscopy evaluation of peripheral nerve regeneration.

Regeneration of a transected peripheral nerve following repair is often impeded by scar formation and misdirection of axon sprouts. This paper describes the use of the scanning electron microscope (SEM) in conjunction with other physiologic tests to evaluate nerve regeneration. A central one centimeter segment was removed from the peroneal branch of both sciatic nerves in 37 white New Zealand rabbits. Sectioned nerves were divided into four experimental groups according to type of repair performed: (A) no repair; (B) mobilization and direct epineural repair; (C) interpositional nerve graft repair; (D) polyglycolic acid (PGA) conduit repair. Each animal was reexplored eight months later and nerves examined by electrophysiologic testing and scanning electron microscopy. Unrepaired nerves viewed by SEM showed impaired axonal regeneration and loss of fascicular morphology with increased scar tissue. Nerve sections of direct epineural and interpositional graft repairs showed the best return of axonal morphology. Nerves regenerated across a one centimeter gap through a PGA conduit demonstrated regrowth of small and large myelinated axons grouped into "mini-fascicles" with increased connective tissue. PGA conduit repairs were electrically inferior to graft and direct repairs as measured by conduction velocity and the amplitude of evoked response. These findings correlated well with anatomy seen on scanning electron micrographs. The scanning electron microscope proved an excellent adjunctive tool for the study of peripheral nerve regeneration.