Optimal position and apex-subchondral bone distance of cannulated screws for internal fixation of femoral neck fracture: A radiological study.

ABSTRACT

To determine the optimal position of three cannulated screws in an inverted triangle pattern for internal fixation of femoral neck fractures, including the apex-subchondral bone distance, computed tomography (CT) images of the hip were processed using the MIMICS (Materialize Interactive Medical Image Control System) Research software. Points adjacent to the inferior, anterosuperior, and posterior cortex of the femoral neck were selected on the axial view. Subsequently, the positions of these points were adjusted to maximize the area between them, and splines were drawn in the coronal and sagittal planes to represent the cannulated screws. Finally, the virtual anteroposterior and lateral fluoroscopy images of the proximal femur and splines were created and the parameters calculated. Finite element analysis showed this fixation scheme provides stronger fracture support and stability. Twenty patients with femoral neck fractures (Modified group), with the area and perimeter of the triangle formed on axial postoperative CT images, including the shortest distance from the tip of the screw to the subchondral bone was compared with 23 matched patients for whom the conventional inverted isosceles triangle configuration of screws for internal fixation was used (Conventional group). The area and perimeter of the stabilization screws were larger, with a shorter apex-subchondral bone distance for the Modified group. There was no incidence of screw penetration in the femoral neck or head in either group, and all fractures healed within a follow-up period of 10 months. The modified screw placement method is simple and safe and provides greater fracture stability than the conventional empirical method of fixation.