A MECHANICAL COMPARISON OF SUBTROCHANTERIC FEMUR FRACTURE FIXATION

Objective: To determine whether the mechanical properties of first-gen eration interlocking femoral nails are different from those of second- generation interlocking femoral nails in a subtrochanteric femur fract ure model. Design: Randomized laboratory investigation using a synthet ic subtrochanteric femur fracture model. Setting: Simulated stable and unstable fractures were created at three levels in the subtrochanteri c region of synthetic femora. Instrumented specimens were tested elast ically in a biomaterials testing system. Intervention: Synthetic femor a were instrumented with either a statically locked first-generation f emoral nail or a statically locked second-generation femoral nail. Mai n Outcome Measurements: Elastic stiffness for both the stable and unst able fracture groups was measured in both compression and torsion. Uns table fracture specimens were tested to failure in compression, and lo ad to failure was measured. Results: Throughout the subtrochanteric re gion, second-generation femoral nail constructs were consistently stif fer in compression and torsion than were statically locked first-gener ation femoral nail constructs. In general, second-generation construct s also withstood larger loads to failure in the unstable fracture mode l. Conclusions: Second-generation nails provided significantly enhance d mechanical stiffness compared with first-generation femoral nails wh en used to treat both stable and unstable subtrochanteric femur fractu res. Although these results were obtained by using a well-controlled, mechanically consistent model, clinical validation of an increased inc idence of fracture unions or of decreased time to union is required be fore we can recommend that second-generation nails be used routinely t o treat subtrochanteric femur fractures.