Rheumatology, Vol 38, 355-361, Copyright © 1999 by British Society for Rheumatology
F Wolfe
OBJECTIVES: The Western Ontario MacMaster (WOMAC) is a validated instrument
designed specifically for the assessment of lower extremity pain and
function in osteoarthritis (OA) of the knee or hip. In the clinic, however,
we have noted that OA patients frequently have other musculoskeletal and
non-musculoskeletal problems that might contribute to the total level of
pain and functional abnormality that is measured by the WOMAC. In this
report, we investigated back pain and non- articular factors that might
explain WOMAC scores in patients with OA, rheumatoid arthritis (RA) and
fibromyalgia (FM) in order to understand the specificity of this
instrument. METHODS: RA, OA and FM patients participating in long-term
outcomes studies completed the WOMAC and were assessed for low back pain,
fatigue, depression and rheumatic disease symptoms by mailed
questionnaires. RESULTS: Regardless of diagnosis, WOMAC functional and pain
scores were very much higher (abnormal) among those complaining of back
pain. On average, WOMAC scores for back pain (+) patients exceeded those of
back pain (-) patients by approximately 65%,, and 52% of OA patients
reported back pain. In regression analyses, study symptom variables
explained 42, 44 and 38% of the variance in WOMAC function, pain and
stiffness scores, respectively. In the subset of OA patients, radiographic
scores added little to the explained variance. The strongest predictor of
WOMAC abnormality in bivariate and multivariate analyses was the fatigue
score, with correlations of 0.58, 0.60 and 0.53 with WOMAC function, pain
and stiffness, respectively. The WOMAC performed well in RA and FM, and
correlated strongly with the Health Assessment Questionnaire (HAQ)
disability scale and a visual analogue scale (VAS) pain scale. CONCLUSION:
The WOMAC captures more than just knee or hip pain and dysfunction, and is
clearly influenced by the presence of fatigue, symptom counts, depression
and low back pain. WOMAC scores also appear to reflect psychological and
constitutional status. These observations suggest the need for care in
interpreting WOMAC scores as just a measure of function, pain or stiffness,
and indicate the considerable importance of psychological factors in
rheumatic disease and rheumatic disease assessments.
ORIGINAL PAPERS
Determinants of WOMAC function, pain and stiffness scores: evidence for the role of low back pain, symptom counts, fatigue and depression in osteoarthritis, rheumatoid arthritis and fibromyalgia
Arthritis Research Center and University of Kansas School of Medicine, Wichita 67214, USA.
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