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 degrees to 11 degrees. The major portion of the correction (14 degrees of 16 degrees) occurred within 3 weeks, concomitantly with fracture healing. The angle of the proximal growth plate changed 8 degrees 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.