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.