A quantitative assessment of extraocular muscle growth in peripheral nerve autografts

In previous studies, we have documented new growth of extraocular muscle fibers within axon-depleted motor neurons of denervated muscle. This study was designed to quantitate the regenerative growth of extraocular muscle within autologous peripheral sensory nerve transplants and to determine whether acutely denervated extraocular muscle affects this growth. Fifteen anesthetized beagles were subjected to an intracranial lesion of the left third cranial nerve. Segments of the infraorbital sensory nerve were removed from the nose and implanted between the lateral rectus and inferior oblique muscles in both orbits. At 2, 4 and 8 weeks postoperatively, five dogs were killed and the nerve grafts were removed. Muscle fibers were counted at four levels along each nerve segment. Fiber number increased significantly at each successive postoperative interval in implanted nerve segments on both the denervated and nondenervated side. At 8 weeks, fiber number was significantly greater on the denervated side. These results indicate that autologous peripheral sensory nerve is capable of supporting regenerative growth of extraocular muscle and that denervation has a significant positive influence on muscle fiber growth.