EFFECT OF SCIATIC-NERVE SECTION ON NEURAL INGROWTH INTO THE RAT TIBIAL FRACTURE CALLUS

Neural influences have been associated with fracture healing through c linical observations and experimental procedures. This work was intend ed to study the reliability of sciatic nerve section as a model of den ervation of tibial fracture. Rats were subjected to a standardized fra cture with or without simultaneous nerve resection. The fractures were fixed by intramedullary nails, and the legs were immobilized to preve nt differential loading. On Day 25 posttrauma, nerve fibers were found in the periosteum, fracture callus, and bone-marrow space. Most fiber s expressed growth-associated protein 43 (GAP-43/B-50), suggesting act ively ongoing neural regeneration. Additional characterization of the type of innervation revealed an extensive distribution of sensory fibe rs containing calcitonin gene-related peptide, a neuropeptide with pot ent vasodilatory actions. Sciatic nerve section reduced all free and s ome perivascular calcitonin gene-related peptide-containing fibers, al though regenerating nerve fibers still were evident in the bone marrow . Radiographs showed an increased callus formation in rats with sciati c nerve section, suggesting involvement of neural factors in the heali ng process. The results show that sciatic nerve section is not a relia ble model for a total denervation of tibial fracture, Hard tissue inju ry induces proliferation of nerves, probably by production of chemotac tic factors to attract neural targeting and regeneration of injured ne rves.