Symptom severity of osteoarthritis of the knee: a patient-based measure developed in the veterans health study.

BACKGROUND Our objective was to develop a patient-based measure of the severity of osteoarthritis of the knee, focusing on symptomatology, that may be used in conjunction with measures of health-related quality of life in monitoring the health status of outpatients. METHODS We surveyed a random sample of male outpatients at Boston-area Veterans Affairs medical centers who were identified as having osteoarthritis of the knee according to a three-question screen. Structured interviews included 12 items covering five domains of symptoms (global severity, 4 items; pain with activity, 3 items; pain at rest, 2 items; impaired mobility, 2 items; and sensations of crepitus, 1 item), which were derived from clinical texts, consensus statements, and previously developed severity indices. Interviews also included a detailed medical history. Health-related quality of life was measured by the Medical Outcomes Study Health Status Survey (SF-36). Factor analysis and evaluation of multiattribute scales were used to evaluate the structural relationships between and within the five domains of symptoms. RESULTS We identified 415 of the 1770 screened outpatients as having osteoarthritis of the knee. Internal consistencies of the five domains ranged from .50 to .72, with substantial convergence between domains. The 12 items comprise a summary index with high internal consistency (alpha = .88). Overall severity, defined as the mean of the 12 items after standardization, was moderately correlated with the SF-36 component summaries: r = -.48 for physical; r = -.30 for mental. CONCLUSIONS Our measure provides a reliable index that represents symptomatic severity of osteoarthritis of the knee, which may be useful in comparing patient groups and assessing health outcomes; subscales may help characterize temporal changes, including responses to treatment.