Acetabular cup orientation differs across surgical approaches in primary total hip arthroplasty: a retrospective analysis

Abstract Purpose Accurate acetabular cup positioning is crucial in primary total hip arthroplasty (THA), as malposition is associated with instability and early failure. We hypothesized that acetabular cup orientation may differ according to the surgical approach used. The aim of this study was to assess whether acetabular anteversion and inclination vary according to surgical approach and whether these differences affect the proportion of acetabular cups positioned outside reference orientation zones. Materials and methods A retrospective single-centre comparative study was conducted including 300 primary THAs performed between 2018 and 2022. A stratified random sample of 100 hips per approach was selected: posterolateral (PLA), direct lateral (DLA), and direct anterior (DAA). Cup inclination and anteversion were measured on standardized postoperative radiographs using calibrated digital software. Positioning was analyzed according to the safe zones described by Lewinnek and Reina, as well as the zone corresponding to the lowest observed dislocation ratio reported by Esposito et al. Continuous and categorical variables were compared using appropriate statistical tests ( p < 0.05). Results Mean inclination and anteversion for the overall cohort were 41.5° and 17.6°, respectively. Significant differences were observed between approaches for both inclination ( p < 0.001) and anteversion ( p = 0.011), with the DLA demonstrating lower mean anteversion compared with the PLA and DAA. No significant differences were observed in the proportion of cups positioned within the Lewinnek safe zone ( p = 0.276). However, significant differences were observed in the proportion of cups within the Reina target zone ( p = 0.0015) and within the zone centred on 48° inclination and 24° anteversion (± 10°) derived from Esposito et al. ( p = 0.0004). Conclusion Acetabular cup positioning appears to vary according to surgical approach in primary THA, particularly regarding anteversion, with the PLA demonstrating higher mean anteversion and the DLA lower values. However, these differences did not translate into clinically relevant differences in positioning within established reference orientation zones according to widely used criteria.