Association Between Metabolic Syndrome, Radiographic Knee Osteoarthritis, and Intensity of Knee Pain: Results of a National Survey

Context: Although osteoarthritis (OA) has been suggested as another component of metabolic syndrome (MetS), weight-independent associations between MetS and knee OA or intensity of arthritic knee pain remain unclear. Objective: The objective of the study was to evaluate the above associations and suggest possible mechanisms. Design and Setting: This was a cross-sectional study using the fifth Korean National Health and Nutrition Examination Survey (2010). Participants: A total of 2363 adults (>= 50 y of age) who had completed both laboratory examinations and an evaluation for radiographic knee OA participated in the study. Main Outcome and Measures: Radiographic knee OA was defined as a Kellgren/Lawrence grade of 2 or greater, and the intensity of arthritic knee pain was assessed using a self-reported numeric rating scale. MetS was diagnosed based on National Cholesterol Education Program-Adult Treatment Panel III criteria, and insulin resistance was evaluated using the homeostasis model assessment-estimated insulin resistance index. Results: In a multivariable logistic regression analysis, MetS was associated with radiographic knee OA(adjusted odds ratio 1.49; 95% confidence interval 1.23-1.79; P < .001). This association was not changed significantly after further adjusting for homeostasis model assessment-estimated insulin resistance but became nonsignificant after adjusting for weight or body mass index. Age-, sex-, and weight (or body mass index)-adjusted mean score of knee pain was significantly higher in subjects with more components of MetS (P for trend = .010 or .035, respectively). Conclusions: The association between MetS and radiographic knee OA can be largely explained by an excessive weight but not by insulin resistance, a key pathophysiology of MetS. Because accumulation of MetS components appears to be associated with a higher intensity of knee pain, independently of weight, appropriate treatment for MetS may be helpful for subjects with knee pain.