Combined Anteversion in Healthy Hips: Should There Be a Single Implant Alignment Target in Total Hip Arthroplasty?

The ideal anteversion at which the acetabular and femoral components for a total hip arthroplasty (THA) should be implanted is still a subject of debate. An alignment philosophy being explored is restoration of individual constitutional femoral and acetabular anteversion. This study aimed to measure combined anteversion in a healthy hip population and understand the expected phenotypes and ranges for constitutional hip alignment.

Computed tomography scans of 338 healthy hips were analyzed using advanced modeling and analysis software that automatically maps landmarks consistently across all scans. Four distinct methods for measuring the acetabular and femoral versions were employed, each derived from different landmark placements. Acetabular and femoral versions were classified as either normal (10 to 20°), increased (> 20°), or decreased (< 10°), resulting in nine potential hip phenotypes, and the prevalence of each in the healthy population was determined.

Femoral and acetabular version angles varied depending on the number of points used to measure them. There was wide variability in acetabular and femoral anteversion angles, ranging from 6 to 26° acetabular anteversion and from 5° retroversion to 32° femoral anteversion. Only 29% of hips were found to have constitutional combined anteversion between 20 and 40°, with acetabular version between 10° and 20° and femoral version between 10 and 20°.

There is increasing interest in individualized implant alignment for THA, since studies have shown the Lewinnek "safe zone" does not guarantee hip stability. The results found in this study suggest that a single target for implant alignment may not be optimal for recreating a patient's constitutional hip alignment. Further research should consider how changes in combined anteversion during THA implant placement can impact patient outcomes.