Nailing and occlusion of the medullary cavity. Flow and mechanical changes in rat femora

25 rats were bilaterally operated on and the femoral canal nailed, nailed and plugged with silicone or only plugged with silicone after intramedullary nailing. A fourth group was intramedullary reamed without any other intervention. The bones were evaluated after 12 weeks, including flow measurements, mechanical properties and bone dimensions. There were no differences between the groups in total bone or cortical bone blood flow. There were only marginal changes in outer and inner anteroposterior diameters and the area moment of inertia. The maximum bending stress in bones that had been both nailed and silicone-plugged was decreased compared to the other groups, except the nailed bones. In the silicone/nail group, energy absorption was less than in the other groups, except the nailed group. We conclude that modest intramedullary reaming, nailing or plugging of the femoral canal do not change the mechanical properties of the bone, nor do they induce chronic vascular changes in bone. However, when the medullary cavity is filled with both a nail and silicone, mechanical as well as structural changes may ensue.