The impact of motor and sensory nerve architecture on nerve regeneration

Sensory nerve autografting is the standard of care for injuries resulting in a nerve gap. Recent work demonstrates superior regeneration with motor nerve grafts. Improved regeneration with motor grafting may be a result of the nerve's Schwann cell basal lamina tube size. Motor nerves have larger SC basal lamina tubes, which may allow more nerve fibers to cross a nerve graft repair. Architecture may partially explain the suboptimal clinical results seen with sensory nerve grafting techniques. To define the role of nerve architecture, we evaluated regeneration through acellular motor and sensory nerve grafts. Thirty-six Lewis rats underwent tibial nerve repairs with 5 mm double-cable motor or triple-cable sensory nerve isografts. Grafts were harvested and acellularized in University of Wisconsin solution. Control animals received fresh motor or sensory cable isografts. Nerves were harvested after 4 weeks and histomorphometry was performed. In 6 animals per group from the fresh motor and sensory cable graft groups, weekly walking tracks and wet muscle mass ratios were performed at 7 weeks. Histomorphometry revealed more robust nerve regeneration in both acellular and cellular motor grafts. Sensory groups showed poor regeneration with significantly decreased percent nerve, fiber count, and density (p<0.05). Walking tracks revealed a trend toward improved functional recovery in the motor group. Gastrocnemius wet muscle mass ratios show a significantly greater muscle mass recovery in the motor group (p<0.05). Nerve architecture (size of SC basal lamina tubes) plays an important role in nerve regeneration in a mixed nerve gap model.