Misconceptions about the mechanical advantages of intramedullary devices for treatment of proximal femur fractures

摘要

Implant options for internal fixation of extracapsu-lar proximal femur fractures include extramedul-lary and intramedullary devices (plates vs. nails) with different neck-shaft angles, most commonly 130deg to 150deg for plates and 130deg for nails. The argument in favor of intramedullary devices stems, in part, from the commonly held belief that intramedullary devices offer the theoretical advantage of a shorter moment arm at the plate-screw or nail-screw junction (Koval and Zuckerman 2002, Baumgaertner 2003, Lorich et al. 2004). Koval and Zuckerman (2002) stated that intramedullary devices are subject to smaller bending moments than plate-screw devices because they are positioned closer to the mechanical axis of the femur. Rosenblum et al. (1992) reported that the shorter lever arm of the Gamma nail should reduce the tensile strain on the implant and reduce the risk of failure. Jacobs et al. (1980) found that the shortened lever arm reduces the bending moment and avoids cutout from the femoral head.