The quantification of health-related quality of life (HRQoL) in osteoarthritis (OA) plays a key role in determining the severity and outcome of OA. This issue is of key importance to rheumatologists as the population ages and the number of patients with OA dramatically increases. In both research and practice, the evaluation of the therapeutic benefit of interventions—used either alone or in combination—is critical. Reliability, validity, and responsiveness are essential attributes of health status measurement tools, while brevity, simplicity, and ease of scoring are regarded with high importance, particularly in clinical practice applications.1
Prior to 1981, measurement procedures for quantifying pain, stiffness, and physical disability in hip and knee OA studies lacked standardization. In 1982, with the encouragement of the late Watson Buchanan, MD, who was clinical professor of rheumatology at the University of McMaster in Hamilton, Canada, I described the development of a health status questionnaire termed the Western Ontario and McMaster Osteoarthritis Index (WOMAC) in the course of completing an MSc thesis in clinical epidemiology and biostatistics.2 The WOMAC was conceptualized and an item inventory was proposed between 1981 and 1982; the index was validated and implemented between 1982 and 1999.3,4 The original index has undergone significant refinement and there is now a broad range of WOMAC tools to meet different measurement needs.
In comparative analysis against performance-based measurement techniques, the WOMAC has frequently been superior in performance.
A Version for Every Need
The WOMAC contains five pain, two stiffness, and 17 physical function items, and is available in five-point Likert (LK), 100-mm visual analogue (VA), and 11-point numerical rating (NR) scaling formats.5 The majority of the validation work has been conducted with the LK and VA formats, although the NRS version has also been studied. There are approximately 1,500 citations (full manuscripts, abstracts, reviews) in the literature to use of the WOMAC. The WOMAC LK3.1 and WOMAC VA3.1 versions, in particular, have been extensively used, especially for assessing efficacy in clinical research environments and, increasingly, in clinical practice. (See Table 1, p. 19, for more on versions of the WOMAC.)
These are some of the features that have made the WOMAC a widely used tool:
- Extensive patient involvement in the item inventory development, which reduced the potential influence of paternalism and anchored it to aspects of the disease experience that are relevant to OA patients;
- Numerous studies that have evaluated clinimetric properties of the index (e.g., validity, reliability, and responsiveness) and issues such LK versus VA scaling and blind versus informed presentation;3-5
- Development and validation of more than 70 alternate-language forms of WOMAC VA3.1 and WOMAC LK3.1;
- Continual research and development into content and administration issues, including the application of WOMAC in telephone interviews and electronic data capture formats; 5
- Recognition by the Outcome Measures in Rheumatoid Arthritis Clinical Trials group (OMERACT), Osteoarthritis Research Society International (OARSI), and the Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials group, and regulatory agencies such as the Food and Drug Administration and European Medicines Agency, among others;6,7
- Provision of the WOMAC, in the required scaling format, alternate language form, and administration format, for academic, industrial, clinical, and educational applications, including pivotal projects and programs such as the National Institutes of Health (NIH) Osteoarthritis Initiative; and
- Ongoing user support, to provide the most appropriate form of the index to meet specific user needs.
Transcultural adaptation of WOMAC 3.1, in particular, has been a complex process spearheaded by the Health Outcomes Group in San Francisco, Calif. The impact of environmental challenges involved in, for example, stair climbing and transportation, are different in different parts of the world, and bathing and toileting habits also vary, but the WOMAC appears capable of tapping into global commonalities that exist in OA symptoms.
