Spontaneous correction of angular fracture deformity in the rat

Background: The different parts of long bone are known to participate in the spontaneous correction of fracture deformity. However, the relative contribution of growth plate, epiphysis and diaphysis of bone during the correction process is not clear. Animals and methods: We used a rat model of tibial fracture fixed with a semi-rigid intramedullary pin in anterior angulation, and evaluated the magnitude, temporal course and pertinent sites of spontaneous deformity correction by means of radiography and bone mineral uptake. Results: Over a 12-week period, the mean angular deformity was corrected from 27° to 11°. The major portion of the correction (14° of 16°) occurred within 3 weeks, concomitantly with fracture healing. The angle of the proximal growth plate changed 8° over the study period. The first 3 weeks were characterized by intense bone formation on the concave side of the fracture. From weeks 3-8, signs of resorption predominated on the corresponding convex side. On the concave side, the front of new bone formation in the proximal diaphysis moved in the opposite direction to that at the fracture level, so that both sites contributed to deformity correction. Interpretation: We found that different sites of a diaphyseal bone fractured in angulation respond quite differently, but still in an orchestrated way to promote correction by modeling. Notably, most of the spontaneous correction occurred during the reparative phase, the major contributor being the diaphysis, not the growth plate. Compared to other reports on angulated fracture using rigid fixation and limb immobilization, our data suggest that semi-rigid fixation and early weight bearing is more efficient in enhancing not only healing, but also deformity correction.