Objective: This study examined the roles of sociodemographic factors (age, race, gender, education, marital status), obesity, and severity of radiographic knee osteoarthritis (OA) and knee pain on self-reported functional status.
Methods: The sample included 1,272 African-American and Caucasian individuals, aged 45 years or older, from the Johnston County Osteoarthritis Project. Analysis of variance was used to assess variation in mean Health Assessment Questionnaire (HAQ) scores by the above variables.
Results: Mean HAQ scores differed by severity of radiographic knee OA and knee pain, obesity, and all demographic factors (P < 0.0001), except race. Only age, female sex, obesity, and knee pain severity were independent effects (P < 0.0009). Disability associated with knee pain varied by both radiographic knee OA severity and obesity.
Conclusions: Knee pain severity was more important than radiographic knee OA severity in determining disability. Obesity was independently associated with disability and compounded disability from knee pain. Studies of disability in knee OA should include assessment of obesity, severity of radiographic knee OA, and severity of knee pain, as well as their interactions.