Combined anteversion in natural Asian hips is lower than conventional targets and is predominantly determined by femoral anteversion.

PURPOSE: Combined anteversion (CA), integrating acetabular (AA) and femoral anteversion (FA), is crucial for total hip arthroplasty (THA) stability. We evaluated CA distribution in natural Asian hips, AA and FA contributions to CA variance, and sex and age effects.

METHODS

We retrospectively analysed 200 normal contralateral hips from patients with femoral neck fractures. Using CT-based 3D models, we calculated AA and FA. CA was determined using the Widmer equation (CA = AA + 0.7 × FA). We evaluated sex and age differences and used standardised regression coefficients to identify CA variance determinants.

RESULTS

Mean values were AA 16.3° ± 5.4°, FA 18.8° ± 11.2°, and CA 29.4° ± 9.6°. Standardised regression coefficients for CA variance were β = 0.822 for FA and β = 0.580 for AA. Women had significantly higher AA, FA, and CA than men (mean CA: 30.7° vs 24.4°). Sex-specific coefficients confirmed FA as the dominant determinant (men: FA β = 0.889, AA β = 0.595; women: FA β = 0.817, AA β = 0.587). With age, AA increased (0.12°/year, P = 0.006) and FA decreased (-0.30°/year, P = 0.001), but CA remained unchanged (P = 0.256).

CONCLUSION

Mean CA in natural Asian hips (29.4°) is lower than conventional THA targets. CA variance is predominantly determined by FA. While AA and FA change with age, CA remains stable. Optimising CA in THA requires individualised strategies emphasising sex differences.