WOMAC Osteoarthritis Index
Original Editor - Oyemi Sillo
The Western Ontario and McMaster Universities Arthritis Index (WOMAC) is widely used in the evaluation of Hip and Knee Osteoarthritis. It is a self-administered questionnaire consisting of 24 items divided into 3 subscales:
- Pain (5 items): during walking, using stairs, in bed, sitting or lying, and standing upright
- Stiffness (2 items): after first waking and later in the day
- Physical Function (17 items): using stairs, rising from sitting, standing, bending, walking, getting in / out of a car, shopping, putting on / taking off socks, rising from bed, lying in bed, getting in / out of bath, sitting, getting on / off toilet, heavy domestic duties, light domestic duties
Area of Assessment
WOMAC Index was developed for hip and knee osteoarthritis, however it has been used with other rheumatic conditions such as: rheumatoid arthritis, juvenile rheumatoid arthritis, fibromyalgia, systemic lupus erythematosus and low back pain.
Method of Use
The WOMAC takes approximately 12 minutes to complete, and can be taken on paper, over the telephone or computer. Both the computerized and the mobile versions of the test have been found to be comparable to the paper form, with no significant difference.
The test questions are scored on a scale of 0-4, which correspond to: None (0), Mild (1), Moderate (2), Severe (3), and Extreme (4).
The scores for each subscale are summed up, with a possible score range of 0-20 for Pain, 0-8 for Stiffness, and 0-68 for Physical Function. Usually a sum of the scores for all three subscales gives a total WOMAC score, however there are other methods that have been used to combine scores.
Higher scores on the WOMAC indicate worse pain, stiffness, and functional limitations.
The test-retest reliability of the WOMAC varies for the different subscales. The pain subscale has not been consistent across studies, but it generally meets the minimum standard. The physical function subscale is more consistent and has a stronger test-retest reliability. The stiffness subscale has shown low test-retest reliability.
The WOMAC Index has been used extensively in clinical trials, and has generally been shown to exhibit greater or comparable responsiveness to change than other tests. This varies, however, for different subscales and types of interventions.
Two potential weaknesses of the WOMAC are:
1. the stiffness subscale has low test-retest reliability, and there is little evidence for its measurement properties.
2. Some studies report inadequate factorial validity in the pain and physical function subscales of the WOMAC. Thus, the physical function subscale might be limited in its ability to detect change if the association between pain and function is weak.
- American College of Rheumatology. Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). http://www.rheumatology.org/practice/clinical/clinicianresearchers/outcomes-instrumentation/WOMAC.asp. (accessed 12 July 2013).
- WOMAC Osteoarthritis Index. http://www.womac.org/womac/index.htm. (accessed 12 July 2013).
- Theiler R, Spielberger J, Bischoff H.A., Bellamy N, Huber J, Kroesen S. Clinical evaluation of the WOMAC 3.0 OA Index in numeric rating scale format using a computerized touch screen version [abstract]. OSTEOARTHR CARTILAGE 2002;10(6):479-481
- Bellamy N, Wilson C, Hendrikz J, Whitehouse S.L., Patel B, Dennison S, Davis T. Osteoarthritis Index delivered by mobile phone (m-WOMAC) is valid, reliable, and responsive [abstract]. J CLIN EPIDEMIOL 2011;64(2):182-190