Objectives: To compare piriformis fossa to greater trochanteric entry cephalomedullary implants in an evaluation of femoral neck load to failure when the device is used for femoral shaft fractures with prophylaxis of an associated femoral neck fracture.
Methods: Thirty fourth-generation synthetic femur models were separated into 5 groups: intact femora, entry sites alone at the piriformis fossa or greater trochanter, and piriformis fossa and greater trochanteric entry sites after the insertion of a cephalomedullary nail. Each model was mechanically loaded with a flat plate against the superior femoral head along the mechanical axis and load to failure was recorded.
Results: Mean load to failure was 5487 ± 376 N in the intact femur, 3126 ± 387 N in the piriformis fossa entry site group, 3772 ± 558 N in the piriformis entry nail, 5332 ± 292 N for the greater trochanteric entry site, and 5406 ± 801 N for the greater trochanteric nail group. Both piriformis groups were significantly lower compared with the intact group. Both greater trochanteric groups were similar to the intact group and were statistically higher than the piriformis groups.
Conclusions: A piriformis fossa entry site with or without an intramedullary implant weakens the femoral neck in load to failure testing. A greater trochanteric entry yields a load to failure equivalent to that of an intact femoral neck. Instrumentation with a greater trochanteric cephalomedullary nail is significantly stronger than a piriformis fossa cephalomedullary nail during axial loading in a composite femur model.
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