Medial migration or cutout of the neck helical blade has commonly occurred in the treatment of trochanteric fracture of the femur. The position of the helical blade within the femoral head is one of the influencing factors that cause the blade to perforate the intact joint surface; however, the ideal placement of the helical blade is not currently known. A finite element model of a femur/nail construct was utilized to analyze five possible blade positions in the femoral head. Normal strain at the fracture surface, the minimum principal strain in the cancellous bone, and the von Mises stress in the implant itself were calculated and compared between different blade positions. The results showed that a large area of normal compressive strain at the fracture surface was observed in the inferior and posterior blade positions. The volume of cancellous bone strained to yielding in the femoral head and neck was lower for the inferior and posterior positions, whereas it was the highest for the superior position. The inferior and posterior positions had lower von Mises stress in the implant itself. The inferior and posterior positions may be the ideal position for the intramedullary nail with a helical neck blade.
- intramedullary nail
- pertrochanteric fracture