Biomechanical evaluation of the proximal femoral nail.

In 1997, the proximal femoral nail was introduced for treatment of peritrochanteric femoral fractures. Treatment results show a low complication rate. The most serious complication is cutout of the hip pin and femoral neck screw. Considerable load on the hip pin is thought to facilitate cutout. The biomechanical behavior of the hip pin and the femoral neck screw as part of the standard proximal femoral nail, and of an experimentally modified proximal femoral nail (in which the hole through the nail for the hip pin is modified to a slot) was studied. In the standard proximal femoral nail, the amount of the total load carried by the hip pin varies between 8% and 39% (mean, 21%). If the hip pin passes through a slot in the nail, it carries 2% to 8% (mean, 5%) of the load. The nonconstrained lateral end of the hip pin reduces the bending load applied to the implant. The slotted hole for the hip pin also allows the femur and the nail to medialize, even if the hip pin and femoral neck screw lose parallelism. The prevalence of cutout of the proximal femoral nail may be reduced by introduction of this mechanism.