Effect of sciatic nerve section on neural ingrowth into the rat tibial fracture callus

Neural influences have been associated with fracture healing through clinical observations and experimental procedures. This work was intended to study the reliability of sciatic nerve section as a model of denervation of tibial fracture. Rats were subjected to a standardized fracture with or without simultaneous nerve resection. The fractures were fixed by intramedullary nails, and the legs were immobilized to prevent differential loading. On Day 25 posttrauma, nerve fibers were found in the periosteum, fracture callus, and bone-marrow space. Most fibers expressed growth-associated protein 43 (GAP-43/B-50), suggesting actively ongoing neural regeneration. Additional characterization of the type of innervation revealed an extensive distribution of sensory fibers containing calcitonin gene-related peptide, a neuropeptide with potent vasodilatory actions. Sciatic nerve section reduced all free and some perivascular calcitonin gene-related peptide-containing fibers, although regenerating nerve fibers still were evident in the bone marrow. Radiographs showed an increased callus formation in rats with sciatic nerve section, suggesting involvement of neural factors in the healing process. The results show that sciatic nerve section is not a reliable model for a total denervation of tibial fracture. Hard tissue injury induces proliferation of nerves, probably by production of chemotactic factors to attract neural targeting and regeneration of injured nerves.