Subtrochanteric fixation stability depends on discrete fracture surface points.

Fixation of subtrochanteric femur fractures may present complications, including malunion, delayed union, or nonunion, and is thought to be related to early fracture stability. To examine the initial stability of subtrochanteric fracture fixation, we investigated construct stiffness, interfragmentary gaps, and overall and point-wise interfragmentary motion (ie, axial and shear displacements) in synthetic composite femurs fixed with a cephalomedullary nail or condylar blade plate. Simulated stable and unstable subtrochanteric femur fractures were created in composite femurs, anatomically reduced, fixed with either a long Gamma nail or a blade plate, and subjected to combined axial, bending, and torsional loading. The long Gamma nail group consistently showed greater displacement magnitudes than the blade plate group; these differences included axial and shear displacement magnitudes in the stable fracture group and shear displacement magnitudes in the unstable fracture group. Overall differences in fixation stability were dependent on discrete points around the periphery of the contiguous fracture surfaces, especially in the unstable fracture group. These differences in interfragmentary motion patterns between implant constructs were detected despite the lack of difference in combined axial, bending, and torsional construct stiffness or initial interfragmentary gap.