Do knee osteoarthritis and fat-free mass interact in their impact on health-related quality of life in men? Results from a population-based cohort.

Objective: To investigate whether obesity and other risk factors interact with knee osteoarthritis (OA) in its adverse impact on health-related quality of life (HRQOL).

Methods: In 1,262 participants of the Netherlands Epidemiology of Obesity Study, a population-based cohort (age 45-65 years, 53% women, and median body mass index [BMI] 27 kg/m(2) ), knee OA was defined following modified American College of Rheumatology criteria. BMI and fat-free mass (as proxy for muscle mass) were assessed by bioelectrical impedance analysis, and comorbidities by self-report. HRQOL was assessed using the Short Form 36 physical component summary (PCS) score. Linear regression analyses were performed to examine associations between knee OA and PCS score, adjusting for age and sex and stratified for BMI, fat-free mass, and comorbidities.

Results: Knee OA (prevalence 16%) was associated with a 7.2-points lower PCS score (95% confidence interval -9.5, -4.8). PCS score was also negatively associated with obesity and comorbidities; however, no interaction with knee OA was seen. Low fat-free mass was associated with a lower PCS score and interacted with knee OA in men. Interaction between concurring OA and low fat-free mass attributed to 64% of the decrease in PCS score, as compared with men without OA and with high fat-free mass.

Conclusion: Knee OA was associated with a lower HRQOL, as were its risk factors, obesity, comorbidities, and low fat-free mass. In men, fat-free mass interacted with knee OA, leading to an additional decrease of HRQOL in the case of concurrence. Especially in the former, improvement of fat-free mass may improve HRQOL in knee OA patients.