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.

Internal fixation of fragility fracturesof the femoral neck

“…This puts great demand to both the design of the implant's anchor and to the local bone quality. Regarding fixation with three screws, experimental studies have shown increased mechanical stability using a triangular pattern compared to a vertical screw orientation and that the apex down configuration reduces the risk of a later subtrochanteric fracture compared to apex up configuration (Selvan et al 2004, Oakey et al 2006, Lichtblau et al 2008. A recent clinical report including 202 patients treated for a femoral neck fracture with either a triangle screw configuration or an inverted triangle configuration, found a significant difference in union rate in favor of the inverted triangle configuration (Yang et al 2013).…”

“…Some research groups prefer to keep the diaphysis in a neutral position without adduction, abduction, flexion or extension (Brandt et al 2010). Others again use a calculated mechanical axis for each single femur (Oakey et al 2006). A distal anchorage that allows angulations and rotations of the femurs opens the possibility of simulating abductor muscles and the iliotibial tract.…”

Contemporary management of femoral neck fractures: the young and the old

“…Typically, three cancellous lag screws oriented along the femoral neck axis and parallel to each other are placed in an inverted triangle. This configuration is biomechanically superior to any other orientation and decreases the risk of subtrochanteric fracture [36][37][38][39][40][41][42][43]. As demonstrated by Lindequist et al [44••] and other previous authors, the first screw should be placed within 3 mm of the cortical calcar femorale to allow a three-point buttressing effect (with fixation in the dense subcortical femoral head, the calcar, and the lateral femoral cortex of entry) [45].…”

Biomechanical comparison of different pin configurations during percutaneous pinning for the treatment of proximal humeral fractures

“…7,9 The anatomy of the proximal humerus is similar to that of the proximal femur to a certain extent. Theoretically, a parallel pin construct should have a better mechanical advantage than the convergent pin construct.…”