Are piriformis reconstruction implants ideal for prophylactic femoral neck fixation?

Objectives: Prophylactic femoral neck fixation may be performed in the setting of geriatric diaphyseal femur fracture, pathologic or impending atypical femur fractures. Fixation constructs often utilize cephalomedullary implants with one or two proximal interlocking screws into the femoral head/neck. Variations in proximal femoral anatomy and implant design can interfere with the placement of two screws in the femoral head and neck. Our objective was to assess the strength of piriformis entry reconstruction implants with one versus two proximal interlock screws for prophylactic femoral neck fixation.

Methods: Thirty fourth generation synthetic femur models were separated into 5 groups. The control group was an intact femur, and the second group was an intact femur with an entry hole in the piriformis fossa. The remaining groups had an intramedullary nail placed with either 0, 1, or 2 screws placed into the femoral head and neck. Each femur was mechanically loaded along the mechanical axis through the femoral head. Load to failure and failure displacement were recorded.

Results: Mean load to failure was 5583 ± 543 N in the intact femur. Constructs with 2 screws had a significantly higher mean load to failure (3223 ± 474 N) compared to one screw constructs (2368 ± 280 N). All of the experimental groups remained significantly lower than the intact femur model (p < 0.05).

Conclusion: Our results demonstrate that piriformis entry reconstruction implants have a significantly lower load to failure compared to an intact femur irrespective of screw construct. Further studies are needed to investigate this potential iatrogenic weakening.