How does changing femoral component anteversion affect biomechanics in cementless total hip arthroplasty?

Adjustment of femoral stem anteversion can be used to create a more stable hip to reduce the risk of dislocation in total hip arthroplasty. Depending on the amount of version, forces transmitted to the proximal femur may vary and alter the biomechanical behavior. The purpose of this study was to determine the effect of anteversion on the stiffness of the construct and femoral stem subsidence.

A biomechanical study was performed using Sawbones composite femurs and a flat taper-wedge stem to assess loading and implant subsidence. Sawbones femurs were prepared with 0-, 15-, or 30 degrees of anteversion relative to the native femur version and tested in cyclic compression for 7200 cycles. Outcomes measured included stem size, initial stiffness, change in stiffness, final stiffness, and amount of subsidence.

Stem size decreased incrementally with the addition of anteversion. There was a statistical difference in subsidence between the constructs placed at 0-, 15-, and 30-degrees of anteversion (in mm, 0-degrees 0.778, 15-degrees 1.045, 30-degrees 0.648, p < 0.006). The construct with the femoral stem placed at 15° anteversion had lower initial stiffness, greater subsidence, and greater Δstiffness relative to the 0- and 30-degree constructs.

Increasing femoral anteversion relative to the native anteversion leads to decreased stem size. Changing the stem anteversion relative to the native femoral anteversion affected the initial stiffness, final stiffness, change in stiffness, and subsidence; however, the differences may not be clinically different.