Determinants of disability in osteoarthritis of the knee.

OBJECTIVES To evaluate the influences of radiographic severity, quadriceps strength, knee pain, age, and gender on functional ability in patients with osteoarthritis of the knee. METHODS Equal numbers of knee pain positive and negative respondents to a survey of registrants aged more than 55 years at a general practice were invited to attend for knee radiographs and quadriceps femoris isometric strength estimations. Disability was measured using the Stanford Health Assessment Questionnaire. RESULTS Complete data were available on 70 men (mean age 72.7 years) and 89 women (mean age 68.1 years); 44% reported knee pain, 48% had radiographic features of osteoarthritis, and 32% reported some degree of disability. Significant correlations were observed between disability and radiographic score, quadriceps strength, and knee pain. Logistic regression analysis, however, showed significant independent contributions from quadriceps strength (odds ratio 0.84 kgF), knee pain (odds ratio 1.67), and age (odds ratio 1.06 per year) only; the radiographic score had no influence on the model. These results were not influenced by confining the analysis to the group with radiographic features of osteoarthritis. CONCLUSIONS Quadriceps strength, knee pain, and age are more important determinants of functional impairment in elderly subjects than the severity of knee osteoarthritis as assessed radiographically. Strategies designed to optimise muscle strength may have the potential to reduce a vast burden of disability, dependency, and cost.