Generic and condition-specific outcome measures for people with osteoarthritis of the knee

Objectives. The aims of this study were to evaluate two condition-specific and two generic health status questionnaires for measuring health-related quality of life in patients with osteoarthritis (OA) of the knee, and to offer guidance to clinicians and researchers in choosing between them. Methods. Patients were recruited from two settings: 118 from knee surgery waiting lists and 112 from rheumatology clinics. Four self-completion questionnaires [Western Ontario and McMaster University Osteoarthritis Index (WOMAC), Health Assessment Questionnaire (HAQ), Short Form-36 (SF-36) and Euroqol] were sent to subjects on two occasions 6 months apart. Construct validity, convergent validity, internal consistency and responsiveness were examined using primarily non-parametric methods. Results. All instruments proved satisfactory in terms of ease of use, acceptability to patients, internal consistency and reliability. In the surgical group, the OA-specific WOMAC performed better than the HAQ and the generic measures in terms of validity and responsiveness to change, whereas in the rheumatology group the SF-36 was more responsive. Conclusion. WOMAC is the instrument of choice for evaluating the outcome of knee replacement surgery in OA. The SF-36 provides a more general insight into patients' health and may be more responsive to change than the WOMAC in a heterogeneous rheumatology clinic population. Researchers wishing to undertake an economic evaluation might consider the EQ-5D for a surgical, but not a rheumatology clinic group.