Effect of Acetabular Component Positioning on Functional Outcomes in Primary Total Hip Arthroplasty

BACKGROUND: Acetabular component positioning is crucial to a successful total hip arthroplasty (THA). This study evaluated the effect of absolute acetabular component position as well as acetabular position relative to bony anatomy on patient-reported functional outcomes after primary THA. METHODS: Primary, press fit, hemispherical metal-on-polyethylene THA performed between 2003 and 2011 were analyzed. Western Ontario and McMaster Osteoarthritis Index (WOMAC), Harris Hip Score (HHS), Short Form-12 scores, and radiographs between 2 and 3 years after the index procedure were assessed. RESULTS: Of the 1241 primary THA included, the mean abduction and anteversion angles were 44.4 ± 6.94 and 21.7 ± 11.9 degrees, respectively. The mean anterior and lateral overhang were 1.9 ± 3.6 and 2.5 ± 3.4 mm, respectively. There was no correlation between functional outcomes and acetabular inclination. A weak positive correlation between anteversion and HHS (P < .001) and WOMAC (P = .02) scores was found. For relative position, anterior overhang of the acetabular component beyond the bone resulted in inferior Short Form-12 physical function (P = .001), HHS (P = .004), and WOMAC (P < .001) scores compared to those with bony coverage. Mean HHS pain score was 41.20 ± 5.69 in patients with lateral overhang and 41.97 ± 5.04 in those who had bony coverage of the lateral edge of the acetabular component (P = .02). CONCLUSION: The tribology and biomechanics of acetabular component position have been extensively studied without examination of how it affects patient function. Although statistical significance was seen, clinical outcome scores were not sensitive enough to show a clinically significant effect of the absolute or relative position of the acetabular component.