New growth of extraocular muscle in peripheral nerve autografts. Ultrastructural relationships

We assessed the ultrastructural relationships of extraocular muscle (eom) fibers grown in a nonmuscle, extracellular matrix. Free sections of autogenous, extraorbital, peripheral nerve were implanted between the cut edge of a healthy eom and a denervated eom in four dogs. Light microscopy at 4 and 8 weeks demonstrated muscle fiber growth throughout the length of the implanted segments. Electron microscopy showed muscle fibers surrounded by collagen, frequently beside degenerating myelinated nerve fibers, but never growing within Schwann tubes or completely surrounded by the basal lamina of one nerve or Schwann cell. The muscle fibers were, however, bordered by abundant fibroblast processes (always separated by collagen), which often partially encircled the fiber. All muscle fiber growth occurred in parallel with the nerve axis. These findings indicate that peripheral nerve may contain factors conducive to the growth and orderly alignment of eom fibers. The identification of these factors may be helpful in the development of a synthetic matrix for eom graft growth.