Improved fracture healing with less rigid plates. A biomechanical study in dogs.

The effect of axial plate flexibility on bone healing was investigated with four experimental plating systems using elastic inserts to manage their axial flexibility in compression. The plates were tested in 72 dogs that underwent unilateral femoral osteotomy and noncompression plating on alternate sides. The femurs of 18 dogs were plated with each of the four plating systems: six for 8 weeks, six for 16 weeks, and six 6 for 24 weeks. Each osteotomized femur and its contralateral control were removed at the end of the plating periods and tested in multidirectional nondestructive bending to evaluate the polar distributions of their flexural rigidity. Results from each pair of bones were used to calculate parameters defining the relative mechanical status of the healing bone. These parameters were used to evaluate the effects of plating system axial flexibility and time on healing. It was found that: within the selected range of axial flexibility there was an optimal value that produced the best healing; healing progressed with a diminishing rate leading to a steady state; and all four plating systems produced healing superior to that obtained with dynamic compression plates.