OP0106 THE ASSOCIATIONS BETWEEN BARIATRIC SURGERY AND HIP OR KNEE ARTHROPLASTY, AND HIP OR KNEE OSTEOARTHRITIS: A COHORT STUDY FROM SWEDISH NATIONWIDE HEALTHCARE REGISTRIES
Authors: T. Burkard, D. Holmberg, T. Hügle, A. M. Burden
Journal: Annals of the Rheumatic Diseases (2021)

Background: Osteoarthritis (OA) is a slowly developing chronic joint disease mainly characterized by joint pain which may lead to physical disability. OA in weight bearing joints, such as the hip and knee, was suggested to be susceptible to high body weight. In end-stage disease, hip and knee OA are often treated with arthroplasty. The impact of weight loss among obese patients on hip and knee arthroplasty has not been assessed to date. Objectives: To assess the association between bariatric surgery and hip or knee arthroplasty. As a secondary aim, we assessed the association between bariatric surgery and hip or knee OA in a secondary care setting. Methods: We performed a propensity score (PS)-matched cohort study using data from Swedish nationwide healthcare registries (patient registry [secondary care], causes of death registry, prescribed drug registry). Patients aged 18-79 years who underwent bariatric surgery between 2006 and 2019 were matched to up to 2 obese bariatric surgery free patients (called unexposed patients) based on their PS. PS-matching was carried out in risk set sampling to reduce selection bias, within 4 sequential cohort entry blocks to account for time trend biases. The primary outcome was hip or knee arthroplasty. The secondary outcome was a diagnosis of hip or knee OA in secondary care. We excluded patients with differential indications for arthroplasty or OA (e.g. rheumatoid arthritis, septic arthritis). After a 1-year run-in period, patients were followed in an “as-treated” approach until the outcome or censoring due to onset of an exclusion criterion, change of exposure status, or end of study period. We applied Cox proportional hazard regression to calculate hazard ratios (HR) with 95% confidence intervals (CIs) of hip or knee arthroplasty, and separately of hip or knee OA, among bariatric surgery patients when compared to obese unexposed patients. Additionally, we performed analyses in subgroups of age, sex, joint location, bariatric surgery type, and by duration of follow-up. Results: A total of 39 392 bariatric surgery patients were PS-matched to 61 085 obese unexposed patients. The study population had a mean age of 42 years, a mean follow-up of 6.5 years, and 72.5% of patients were women. We observed 1138 and 1108 hip or knee arthroplasties among bariatric surgery and obese unexposed patients, respectively. We observed an overall increased risk of hip or knee arthroplasty among bariatric surgery patients (HR of 1.43, 95% CI 1.32-1.55), compared to obese unexposed patients. The risk for knee arthroplasty was higher than that for hip arthroplasty among bariatric surgery patients (HR of 1.58, 95% CI 1.42-1.76, and HR of 1.21, 95% CI 1.06-1.39, respectively). Patients who underwent combined malabsorptive and restrictive bariatric surgery yielded highest risks of hip or knee arthroplasty (HR of 3.58, 95% CI 1.34-9.54). Risks of hip or knee arthroplasty decreased with duration of follow-up (highest risks 1-3 years post-bariatric surgery, HR of 1.79, 95% CI 1.56-2.07). In secondary analyses, risks of secondary care hip or knee OA were decreased among bariatric surgery versus obese unexposed patients (HR of 0.84, 95% CI 0.79-0.90). We observed lower risks for knee OA (HR of 0.82, 95% CI 0.76-0.88) than for hip OA (HR of 0.90, 95% CI 0.79-1.01) and observed lowest risks of hip or knee OA in early follow-up (1-3 years post-bariatric surgery) with a HR of 0.79, 95% CI 0.71-0.88, stable thereafter at a HR of 0.87, 95% CI 0.78-0.97. Conclusion: Our results suggest that substantial weight loss among obese patients is associated with decreased risks of secondary care hip and knee OA. Increased risks of hip and knee arthroplasty after bariatric surgery are likely the result of increased operability of patients who have lost a substantial amount of excess body weight. Stronger associations for the knee than for the hip in both arthroplasty and OA are consistent with existing literature suggesting a stronger impact of body weight on knee than on hip joints. Acknowledgements: We thank Prof. Dr. Jesper Lagergren (Karolinksa Institutet, Stockholm, Sweden) for hosting Dr. Theresa Burkard for a research stay at the Upper Gastrointestinal Surgery Group and making the data available for use. Furthermore, we thank Dr. Giola Santoni (Karolinksa Institutet, Stockholm, Sweden) for her technical support. Disclosure of Interests: Theresa Burkard: None declared, Dag Holmberg: None declared, Thomas Hügle Consultant of: Pfizer, Abbvie, Novartis, Grant/research support from: GSK, Jansen, Pfizer, Abbvie, Novartis, Roche, MSD, Sanofi, BMS, Eli Lilly, UCB, Andrea Michelle Burden: None declared