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Appraisal Clinimetrics
Western Ontario and McMaster Universities
Osteoarthritis Index (WOMAC)
Description
The WOMAC was developed in the early 1980s as a ‘moderate’ as 2, ‘severe’ as 3, and ‘extreme’ as 4. Scores
disease-specific measure for hip and knee osteoarthritis for each section are summed to produce pain, stiffness, and
(Bellamy 2009). It was designed to provide a standardised physical function subscale scores. The WOMAC is scored on
assessment of self-reported health status while incorporating a best to worst scale, so that lower subscale scores represent
activities relevant to patients. The instrument has since less pain, less stiffness, or better physical function. A total
been used extensively in lower limb osteoarthritis and joint WOMAC score can also be produced and is commonly
replacement research. The WOMAC consists of 24 items: 5 transformed to a 0–100 scale for ease of interpretation and
pain, 2 stiffness, and 17 physical function items. It produces comparison with other studies.
three subscale scores (pain, stiffness, and physical function)
and a total score. The WOMAC has been translated into Reliability, validity and sensitivity to change: Many
80 languages and the Australian version (3.1) is available studies have reported the psychometric properties of the
in 5-point Likert, 11-point numerical rating, and 100 mm WOMAC (Bellamy 2009), including a comprehensive
visual analogue scale formats. Clinicians and researchers literature review (McConnell et al 2001). Each subscale
interested in obtaining a copy of the instrument and User has been shown to be internally consistent and test-retest
Guide should visit the WOMAC website for information reliability has been reported for the pain and physical
about licensing and applicable fees. function subscales (McConnell et al 2001). The WOMAC
has also demonstrated construct validity when compared
Instructions to the client and scoring: The WOMAC can with other measures including joint range of motion, gait
be self-administered and takes approximately 5 minutes to tests, and the Medical Outcomes Study 36-Item Short Form
complete. Patients are asked to answer each question with (SF-36). The responsiveness of the WOMAC has been
regard to the pain, stiffness, or difficulty experienced in the documented across a number of research settings, including
previous 48 hours. In particular, the Likert version is simple an Australian study which showed the measure was highly
to use and offers 5 response options ranging from ‘none’ to efficient in detecting short-term improvements after joint
‘extreme’. A response of ‘none’ is scored as 0, ‘mild’ as 1, replacement (Ackerman et al 2006).
Commentary
The WOMAC is an easily-administered instrument that by examining the concordance between WOMAC scores
is used widely to evaluate outcomes of osteoarthritis and clinical examination and X-ray findings. Clinically
interventions, both conservative and surgical. From a important differences for improvement and deterioration
physiotherapy perspective, the measure has been used in have also been published; however, these vary substantially
acute and rehabilitation settings and has provided valuable depending on the setting and statistical approach used
information about the efficacy of land-based exercise for (Chesworth et al 2008). Clinicians may also be interested in
osteoarthritis (including pre- and post-operative programs), international research showing that preoperative WOMAC
aquatic physiotherapy, and patellar taping. In research scores predict pain and physical function up to 2 years after
settings, the disease-specific WOMAC is often concurrently joint replacement (Fortin et al 2002, Lingard et al 2004).
administered with a generic (non-disease-specific) measure
of health status or Health-Related Quality of Life to obtain In summary, the WOMAC is a valid, reliable and responsive
a more holistic assessment and enable comparison with data measure for evaluating outcomes of interventions for people
from other patient groups. with osteoarthritis. The clear wording of the items together
with the simple scoring algorithm enhances the applicability
The WOMAC covers a range of home-based and community- of this instrument in both clinical and research settings.
based functional activities that are important for many Ilana Ackerman
people with osteoarthritis. In our experience, the WOMAC The University of Melbourne
is straightforward for patients to complete, although we
have encountered missing data for activities which are not References
commonly performed in the early post-operative period after
Ackerman IN et al (2006) Arthritis Care Res 55: 583–590.
joint replacement, eg, ‘bending to the floor’ (Question 12)
and ‘getting in or out of the bath’ (Question 20). However, Bellamy N (2009) WOMAC Osteoarthritis Index User Guide IX.
the User Guide provides information on score substitution (Available through WOMAC website.)
for missing data (Bellamy 2009). Chesworth B et al (2008) J Clin Epidemiol 61: 907–918.
Fortin PR et al (2002) Arthritis Rheum 46: 3327–3330.
Although there are no formal criteria for the classification
of WOMAC scores, a cut-off score of 39 and above (on Hawker GA et al (2000): New Engl J Med 342: 1016–1022.
a 0–100 scale) has been used by Canadian researchers Lingard EA et al (2004): J Bone Joint Surg 86A: 2179–2186.
to denote severe arthritis potentially requiring joint McConnell S et al (2001): Arthritis Care Res 45: 453–461.
replacement (Hawker et al 2000). Based on scores reported
by joint replacement patients in Ontario, Canada, the Website
positive predictive value of this cut-off score was verified www.womac.com
Australian Journal of Physiotherapy 2009 Vol. 55 – © Australian Physiotherapy Association 2009 213
