Ancient Principles, Modern Impact: Increased Femoral Offset Demonstrates Decreased Load to Failure in Total Hip Arthroplasty.

Abstract

Background: A critical decision in total hip arthroplasty implant selection is the choice of femoral offset. Femoral offset lateralizes the femoral shaft, tensioning the abductor mechanism providing stability and reducing joint reactive forces. Variations in offset may affect hip biomechanics, potentially influencing the risk of periprosthetic fractures. This study aimed to evaluate the forces required for implant failure and fracture in two femoral stems with different neck angles.

Methods: Twenty osteoporotic composite femurs were prepared and implanted with either a Stryker Accolade II stem with 132° (standard offset) or 127° neck angle (high offset). Femurs were subjected to an axial load using a biaxial servohydroaulic testing machine until failure. Maximum load to failure was recorded. Finite element analysis was conducted to assess stress and strain distributions with the femurs for both implant types.

Results: Femurs with a 132° neck angle exhibited significantly higher mean load to failure compared with those with a 127° neck angle (3,537.8 ± 627.9 vs. 2,947.6 ± 507.6 N, P = 0.032). Finite element analysis revealed that maximum stress in femurs with a high offset implant was 9.5% higher than the standard offset (135.9 vs. 124.1 N/m2) and maximum strain was 25.1% higher in the high offset stem compared with the standard offset (1.580e-8 vs. 1.263e-8).

Conclusion: Higher femoral stem offset decreases the ultimate load to failure of the femur. Although high offset stems offer benefits in hip stability and abductor lever arm enhancement, their potential to increase fracture risk must be further explored.