Biomechanical reconstruction parameters obtained after direct anterior approach total hip arthroplasty do not compromise clinical outcome

Introduction: Accurate reconstruction of biomechanical parameters following total hip arthroplasty (THA) is crucial for good joint function. We investigated how reconstruction parameters achieved by minimally invasive anterior (MIS) THA may influence function and patient-related outcomes. Methods: A consecutive series of 95 patients treated by MIS THA for primary osteoarthritis were retrospectively reviewed. Primary outcome measures were Harris Hip Score (HHS), hip disability and osteoarthritis outcome score (HOOS) and EQ-5D. Femoral offset (FO), abductor lever arm (ALA), centre of rotation (CoR), leg length discrepancy (LLD), cup version and stem alignment were measured pre- and post-operatively. Obtained reconstruction parameters compared to the contralateral hip were used as independent variables in a multivariate regression with each primary outcome measure as dependent variable. Results: Mean age at surgery was 69 years. HHS rated 94.7% of patients as good/excellent and mean EQ-5D was 0.82. Post-operative HOOS subscales showed no statistical difference compared to the Italian benchmark population. Stem alignment averaged 0.2° valgus, mean cup inclination was 37.8° and mean anteversion was 12.8°. When compared to the contralateral side, CoR was post-operatively elevated by 2.6 mm and medialized by 2.4 mm averagely. An average FO reduction of −0.5 mm was observed while FO ratio increased by 1.9% averagely. ALA decreased by −3.3 mm while LLD was 2.3 mm averagely. Multivariate regression analysis revealed a significant contribution of ALA to HHS only. Conclusions: Biomechanical parameters achieved by MIS THA are satisfactory with negligible impact on functional results and no impact on patient-related outcomes certifying the high quality achieved in THA.