LAUSR

To describe the association between body weight change and the risk of knee replacement and hip replacement. Time-to-event survival analysis from a population-based cohort of participants who had or were at risk of clinically significant knee osteoarthritis at baseline. Data from the Osteoarthritis Initiative (OAI), which collected data from four clinical centres in the United States. A total of 8069 knees from 4081 participants, and 8076 hips from 4064 participants (59.3% female) aged 45–79 years, with mean ± SD body mass index (BMI) of 28.7 ± 4.8 kg/m2, were included in the knee and hip analyses, respectively. Body weight change from baseline as a percentage of baseline at repeated follow-up visits over 8 years. Incidence of primary knee or hip replacement during 8-year follow-up. Body weight change had a small, positive, linear association with the risk of knee replacement (adjusted hazard ratio [HR] 1.02; 95% confidence interval [CI] 1.00–1.04). Body weight change was also positively and linearly associated with the risk of hip replacement in hips that were persistently painful at baseline (adjusted HR 1.03; 95% CI 1.01–1.05), but not in hips that were not persistently painful at baseline. There were no significant interactions between body weight change and baseline BMI in the association with knee or hip replacement. In people with or at risk of clinically significant knee osteoarthritis, every 1% weight loss was associated with a 2% reduced risk of knee replacement and – in those people who also had one or more persistently painful hips – a 3% reduced risk of hip replacement, regardless of baseline BMI. Public health strategies that incorporate weight loss interventions have the potential to reduce the burden of knee and hip replacement surgery.