Metabolic syndrome and trajectory of knee pain in older adults.

Objectives: To examine the association of metabolic syndrome (MetS) and its components with knee pain severity trajectories.

Methods: Data from a population-based cohort study were utilised. Baseline blood pressure, glucose, triglycerides and high-density lipoprotein (HDL) cholesterol were measured. MetS was defined according to the National Cholesterol Education Program-Adult Treatment Panel III criteria. Radiographic knee osteoarthritis (ROA) was assessed by X-ray. Pain severity was measured by the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain questionnaire at each time-point. Group-based trajectory modelling was used to identify pain trajectories and multi-nominal logistic regression was used for analysis. Mediation analysis was performed to assess whether body mass index (BMI)/central obesity mediated the association between MetS, its components and pain trajectories.

Results: Among 985 participants (Mean ± SD age: 62.9 ± 7.4, 50% female), 32% had MetS and 60% had ROA. Three pain trajectories were identified: 'Minimal pain' (52%), 'Mild pain' (33%) and 'Moderate pain' (15%). After adjustment for potential confounders, central obesity increased risk of belonging to both 'Mild pain' and 'Moderate pain' trajectories as compared to the 'Minimal pain' trajectory group, but MetS [relative risk ratio (RRR): 2.26, 95%CI 1.50-3.39], hypertriglyceridemia (RRR: 1.75, 95%CI 1.16-2.62) and low HDL (RRR: 1.67, 95%CI 1.10-2.52) were only associated with 'Moderate pain' trajectory. BMI/central obesity explained 37-70% of these associations. Results were similar in those with ROA.

Conclusion: MetS and its components are predominantly associated with worse pain trajectories through central obesity, suggesting that the development and maintenance of worse pain trajectories may be caused by MetS.