Distraction physiolysis in the rabbit.

Axial forces across the growth plate of the upper tibia during controlled distraction were studied in 24 rabbits close to skeletal maturity. Distraction rates of 0.13, 0.26, and 0.53 mm every 24 hours were applied through a dual-frame external fixator. Strain gauges were bonded to the fixator, and axial forces were estimated prior to and following distraction. The results demonstrate two distinct patterns. In one group, forces increased to maximum values of 20-32 newtons and then suddenly decreased on subsequent distraction. This force pattern indicated fracture of the growth plate with associated hyperplasia. In the other group, lower maximum forces of 6-18 newtons were produced at the end of the distraction period, which were associated with physeal hyperplasia without fracture. These results showed that response to controlled distraction was dependent upon both the level of force acting across the growth plate and the rate of distraction; hyperplasia was achieved with lower rates of distraction up to a critical peak force above which fracture occurred.