Investigation of a trochanteric Fi-nail intramedullary implant fixation using the finite element method

The efficiency of an intramedullary nail fixation device, used in cases of trochanteric and subtrochanteric fractures, is defined by several parameters, two of which are the location and the number of distal screws that are used. Towards this direction, the present paper investigated the effect of the two aforementioned characteristics implementing the finite element method (FEM). The left proximal femur of a 93-year old man was scanned and two series of full 3D models, introducing an intramedullary Fi-nail, were developed. The first series, consisting of five models, concerned the use of a single distal screw inserted in five different distal locations. The second series, consisting of four models, concerned the use of four different pairs of distal screws. Each model was analyzed with the FEM twice, first considering that the femur is fractured and then considering that the fracture is healed. The main conclusion derived from this investigation was that, for Fi-nails with a single distal screw, stresses around the nail hole were reduced with proximal placement of the distal screw but the area around the nail hole where the lag screw is inserted becomes more stressed. Furthermore, for Fi-nails with a pair of distal screws, placing the pair of distal screws at a specific location is most beneficial for the mechanical behavior of the femur/Fi-nail assembly.