Development, validation and globalisation of a health status measure for evaluating patients with osteoarthritis

I developed a programme of research to develop, validate and globalise a valid, reliable and responsive standard of measurement (Western Ontario and McMaster Osteoarthritis Index - WOMAC Index) for osteoarthritis (OA) clinical trials. The initial phase (1982-1992) of WOMAC development involved development and validation. Specification of the item content was achieved through face-to-face interview of 100 patients with hip and/or knee OA. The resulting test index was composed of five subscales. Two independent validation studies, involving two different scaling formats, were designed and executed, one in an orthopaedic environment involving total joint arthroplasty, and the other in a rheumatology environment involving a double-blind randomised controlled clinical trial of two nonsteroidal anti-inflammatory drugs (NSAIDs). Four of the five subscales were successfully validated, of which three were retained in the final Index. The face, content and construct validity, reliability and responsiveness of the WOMAC Index were established. The end result of the aforementioned processes was the globalisation of the WOMAC Index, international consensus on core set domains for OA outcome measurement and specification of preferred measures, one of which was the WOMAC Index. Rapidly expanding utilisation of the WOMAC Index by academically-based and industry-based researchers, was shortly thereafter followed by a sharp increase in the number of studies reporting use of the WOMAC Index, such that by 1999 it was often the most commonly used health status questionnaire in osteoarthritis clinical research reported at major rheumatology conferences in Europe, N. America and Australasia. The late phase of development (2000-2005) has involved the further development of other language forms, other scaling formats, short forms and versions amenable to telephone administration and electronic data capture. This phase has also involved using WOMAC Index data to facilitate the development, by various research groups with whom I have collaborated, of definitions of responder criteria and state-attainment criteria. In particular, we have used WOMAC data, in whole or part, in the development of the following definitions of responder criteria: OARSI responder criteria, OMERACT- OARSI responder criteria, Minimum Perceptible Clinical Improvement (MPCI), Minimal Clinically Important Improvement (MCII), and in the development of the following definition of state-attainment criteria: Patient Acceptable Symptom State (PASS). The now fully developed WOMAC Index is a tri-dimensional, disease-specific, self-administered, health status measure. It probes clinically-important, patient-relevant symptoms in the areas of pain, stiffness and physical function in patients with OA of the hip and/or knee. The index consists of 24 questions (5 pain, 2 stiffness, 17 physical function) and can be completed in less than 5 minutes. It is available in Likert (WOMAC LK-series), Visual Analogue (WOMAC VA-series) and Numerical Rating (WOMAC NRS-series) scaled formats. WOMAC is valid, reliable, and sufficiently sensitive to detect clinically-important changes in health status following a variety of interventions (pharmacologic, surgical, physiotherapy, etc). It has been translated into many different languages and has been requested for use by more than 500 researchers in over 50 different countries. The WOMAC Index has become a global standard of measurement for clinical trials in hip and knee OA in rheumatology, is widely used in clinical research, and has been incorporated into several major regulatory and guidelines documents. The WOMAC Index has been important to the development of global harmonisation in outcome measurement, in formulating response and state attainment criteria, and in adjudicating the clinical benefit of new treatments for knee OA.