Does screw configuration affect subtrochanteric fracture after femoral neck fixation?

Abstract

A subtrochanteric femur fracture after cannulated screw fixation of a femoral neck fracture is a devastating complication. We hypothesized that an apex-distal screw orientation would tolerate higher loads to subtrochanteric fracture. Human cadaveric femora were instrumented with three cannulated screws in either an apex-distal or an apex-proximal configuration. Specimens were loaded along the mechanical axis to failure creating a subtrochanteric femur fracture. Ultimate load to failure and the effect of bone density on load to failure were compared between groups. There was a greater load to failure in the apex-distal group compared with the apex-proximal group. The mean force to fracture in the apex-distal group (11,330 N; standard deviation = 3151 N) was greater than the mean force to fracture in the apex-proximal group (7795 N; standard deviation = 3194 N). Previous investigations have shown improved femoral neck fixation with an apex-distal configuration, but none has examined the relationship between screw orientation and subtrochanteric fractures. Our observations support the use of an apex-distal configuration for cannulated screw fixation of femoral neck fractures.