TOTAL HIP ARTHROPLASTY RESTORES POPULATION HEALTH-RELATED QUALITY OF LIFE NORMS: A PROPENSITY-MATCHED STUDY WITH MEDIATION ANALYSIS OF BMI

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 body mass index (BMI) and postoperative improvements, mediated via preoperative HRQoL. In this retrospective case-controlled study using the Edinburgh Arthroplasty database (2013-22; n=3495) and Health Survey for England (2010-12; n=25,320), propensity score matching (1:1) was performed based on age, sex, and BMI. The primary outcome was EQ-5D-3L index score. Secondary outcomes included 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% confidence intervals; 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 >85 years showed the greatest relative improvements compared with the age-matched general population (THA median: 0.796 vs. general population: 0.696, p=0.142). 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 (30-34.9kg/m2): β=0.048, p<0.01; Obesity II (35-39.9kg/m2): β=0.108, p<0.001; Obesity III (□40kg/m2): β=0.151, p<0.001). THA was shown to restore HRQoL to that expected of a matched normal population. 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.