Total hip arthroplasty restores population health-related quality of life norms : a propensity-matched study with mediation analysis of BMI.

Abstract

This study compares health-related quality of life (HRQoL) between patients undergoing primary total hip arthroplasty (THA) for osteoarthritis (OA) and a propensity-matched general population cohort. We also aimed to clarify the relationship between BMI and postoperative improvements, mediated via preoperative HRQoL. In this retrospective study using the Edinburgh Arthroplasty database (1 January 2013 to 31 December 2022; n = 3,495) and Health Survey for England data (2010 to 2012; n = 25,320), propensity score matching (1:1) was performed based on age, sex, and BMI. The primary outcome was EuroQol five-dimension three-level questionnaire (EQ-5D-3L) index score. Secondary outcomes included EuroQol-visual analogue scale (EQ-VAS) and mediation analysis examining how preoperative EQ-5D-3L mediated the relationship between BMI and postoperative improvement. Preoperatively, THA patients had significantly lower EQ-5D-3L scores compared with matched general population (median difference: 0.280, bootstrapped 95% CIs; 0.258 to 0.306; p < 0.001). At one-year follow-up, THA patients exceeded population norms (THA median: 0.814 vs general population: 0.796, p = 0.014). Patients aged > 85 years showed the greatest magnitude of improvements, restoring EQ-5D-3L scores equivalent with their age-matched general population peers (preoperative: 0.189 vs postoperative: 0.796, general population: 0.696). Mediation analysis revealed that BMI's negative direct effect on improvements in EQ-5D-3L was counterbalanced by stronger indirect effects transmitted through preoperative scores (indirect effects: obesity I (30 to 34.9 kg/m²): β = 0.038, p < 0.001; obesity II (35 to 39.9 kg/m²): β = 0.086, p < 0.001; obesity III (≥ 40 kg/m²): β = 0.123, p < 0.001). THA was shown to restore HRQoL to that expected of a matched normal population, but in younger patients this was less than expected. Patients aged > 85 years had the greatest magnitude of restoration. Postoperative HRQoL improvement was predominantly influenced by preoperative functional status, rather than BMI alone. These findings challenge current BMI-based eligibility thresholds and support surgical prioritization based on functional impairment severity.