It is unclear what impact obesity has on the progression of knee osteoarthritis (OA) from diagnosis to knee replacement surgery. This study was undertaken to examine the relative risk of knee replacement surgery in overweight and obese patients who were newly diagnosed as having knee OA in a community setting.
Subjects were selected from the Information System for Development of Primary Care Research database, which compiles comprehensive clinical information collected by health care professionals for >5.5 million people in Catalonia, Spain (80% of the population). Patients newly diagnosed as having knee OA in primary care between 2006 and 2011 were included. Knee replacement was ascertained using International Classification of Diseases, Ninth Revision, Clinical Modification codes from linked hospital admissions data. Multivariable Cox regression models were fitted for knee replacement according to body mass index (BMI), and were adjusted for relevant confounders. Population proportional attributable risk was calculated.
A total of 105,189 participants were followed up for a median of 2.6 years (interquartile range 1.3-4.2). Of these patients, 7,512 (7.1%) underwent knee replacement. Adjusted hazard ratios and 95% confidence intervals (95% CIs) for knee replacement for the World Health Organization BMI categories were 1.41 (95% CI 1.27-1.57) for overweight, 1.97 (95% CI 1.78-2.18) for obese I, 2.39 (95% CI 2.15-2.67) for obese II, and 2.67 (95% CI 2.34-3.04) for obese III compared to normal weight. The effect of BMI on risk of knee replacement was stronger among younger participants. The population attributable risk of obesity for knee OA-related knee replacement was 31.0%.
Overweight and obese patients are at >40% and 100% increased risk of knee replacement surgery, respectively, compared to patients with normal weight. This association is even stronger in younger patients. Weight reduction strategies could potentially reduce the need for knee replacement surgery by 31% among patients with knee OA.