Abstract
Following intramedullary reaming and nailing of rat femora, in vivo changes in dynamic strain were correlated with in vitro measurements of the bones. Reaming and nailing procedures were performed 2 days after implantation of unidirectional strain gauges at the anterior, mid-diaphyseal level of the femur. Structural stiffness of poly-acetal nails were three times as stiff as intact bone. Reaming only decreased the median strain value by 26 percent, and this value was not reduced by insertion of poly-acetal nails. Steel nailing reduced the strain by 74 percent. Tested by three-point bending, reaming increased stiffness by 5 percent at the anterior aspect. The presence of nails gave stiffness values that were 9 percent (polyacetal) and 56 percent (steel) higher than the reamed only condition. Our results indicate that steel nailing following reaming causes marked reduction in strain at the anterior, mid-diaphyseal surface, whereas reduction in strain caused by polyacetal nails is negligible.