Knee pain and knee osteoarthritis severity in self-reported task specific disability: The Johnston County Osteoarthritis Project

Objective. To evaluate the contributions of radiographic knee osteoarthritis (OA) and knee pain severity to self-reported disability performing upper and lower extremity tasks in a rural, population based sample. Methods. Data from 1192 African-American and Caucasian participants in the Johnston County Osteoarthritis Project were analyzed with multiple logistic regression to examine the roles of Kellgren-Lawrence radiographic knee OA grade and knee pain severity in self-reported difficulty performing 20 activities of the Health Assessment Questionnaire. Potential confounders included age, sex, race, marital status, education, and body mass index. Results. Forty-three percent reported difficulty performing at least one task, Mild knee pain was independently associated with difficulty performing 16 upper and lower extremity tasks, and moderate/severe knee pain with all 20 tasks, with little change after adjustment (p < 0.0001). In contrast, mild radiographic knee OA was associated with difficulty in only 4 mobility and transfer tasks: climbing 5 steps, taking a tub bath, getting in/out of a car, and performing chores. Moderate/severe radiographic knee OA was associated with difficulty in 17 of 20 tasks (in 10 of 17, p < 0.0001), except lifting a cup, opening car doors, and turning faucets. However no associations between radiographic knee OA and difficulty were statistically significant after adjustment for knee pain and the above factors. Conclusion. Knee pain severity was the strongest risk factor for self-reported difficulty performing tasks of upper and lower extremity function. Future studies of disability should include data on knee pain severity.