Achieving stability at the site of a femoral neck fracture is an important factor for callus formation in the postoperative period. For minimally displaced fractures, cannulated screws are commonly used in North-East England. However, the placement of the screws currently is based on the surgeon's choice. The purpose of this study was to quantify the stability of a simulated fracture for a range of fracture orientations to determine optimal configuration.
Finite element analysis was employed to create a model of the proximal femur. A fracture was created at 50° to the horizontal, which was rotated to give an orientation range of 40–60°. The femur was subjected to two loading regimes representing joint contact force and the action of the abductor muscles during slow-walking. Interfragmentary movement was quantified by the amount of relative motion occurring between paired nodes on either side of the fracture.
Greater amounts of movement were found at more vertical obliquities, indicating a more unstable fracture from reduction in the amount of compression across the fracture. For fractures at 58°or less, a triangular configuration with a superior apical screw achieved the greatest stability, while for fractures above 58° the triangular configuration with an inferior apical screw achieved the greatest stability.
The findings of this study provide an empirical base from which surgeons can make informed decisions of the choice about femoral neck fracture fixation. The results demonstrate the important interaction between loading direction during the gait cycle and fracture orientation.