Western Ontario and McMaster Universities Osteoarthritis Index

Abstract

The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) is a globally recognized, self-administered questionnaire designed to assess the symptoms and functional limitations associated with osteoarthritis, particularly of the knee (gonarthrosis) and hip (coxarthrosis). The instrument consists of 24 items distributed across three core domains: Pain, Stiffness, and Physical Function. Responses relate to the patient’s experience over the preceding 48 hours. Depending on the version utilized, scoring relies either on a 5-point Likert scale (ranging from None to Extreme) or a 100 mm Visual Analogue Scale (VAS).

Keywords

Osteoarthritis, WOMAC, Patient-Reported Outcome, Pain, Stiffness, Physical Function, Lower Extremity, Gonarthrosis, Coxarthrosis, Rheumatology, Joint assessment.

Authors

Bellamy N (Original version, 1982), Roorda LD, et al. (Dutch version, 2004).

Purpose

The primary purpose of the WOMAC is to provide a standardized, quantifiable measure of the severity of pain, stiffness, and physical disability experienced by patients with hip or knee osteoarthritis. It serves as a vital tool in clinical practice for monitoring disease progression and evaluating the effectiveness of interventions, including pharmaceutical treatments, physical therapy, and surgical procedures.

It is widely utilized in large-scale clinical trials due to its established psychometric properties and responsiveness to clinically significant changes. The scale focuses specifically on the limitations imposed by the disease on daily activities and mobility, making it highly relevant to the patient’s quality of life.

Construct

The WOMAC measures the health status of individuals suffering from lower extremity osteoarthritis by operationalizing three distinct constructs, which are treated as separate subscales. These constructs encapsulate the patient’s subjective experience of the disease.

• Pain Subscale: Comprises 5 items assessing pain intensity during various activities such as walking on a flat surface, going up or down stairs, and nocturnal rest.
• Stiffness Subscale: Contains 2 items measuring the duration and severity of joint stiffness experienced after waking up and later in the day following periods of rest.
• Physical Function Subscale: Includes 17 items focused on the difficulty encountered when performing routine daily activities, such as standing, sitting, bending, and using stairs. The scale is classified as a Patient-Reported Outcome (PRO) measure, emphasizing the patient’s self-assessment of functional capacity.

Validity

The WOMAC possesses strong evidence of content and construct validity. Content validity is ensured by the instrument’s comprehensive coverage of symptoms critical to osteoarthritis management (pain, stiffness, and function).

Construct validity has been established through demonstrating high correlations between WOMAC subscale scores and scores on other validated measures of pain and physical function, such as the physical component summary of the SF-36. Furthermore, its discriminant validity allows clinicians and researchers to effectively distinguish between patient groups based on different levels of disease severity and joint involvement.

Reliability

The reliability of the WOMAC is consistently reported as excellent across multiple language translations and patient cohorts. The instrument typically demonstrates high internal consistency, particularly for the Pain and Physical Function subscales, where Cronbach’s alpha often exceeds 0.80, confirming the homogeneity of items within each domain.

Test-retest reliability is also robust, with intra-class correlation coefficients (ICCs) frequently reported above 0.90 for the total score and individual subscales, indicating that the measure produces stable results over time, provided the patient’s clinical status remains unchanged.

Factor Analysis

Confirmatory factor analysis (CFA) studies consistently support the hypothesized, three-factor structure of the WOMAC: Pain, Stiffness, and Physical Function. This established structure validates the clinical utility of interpreting scores across these three separate dimensions rather than relying solely on a single total score.

While some research has explored alternative factor models, the original three-factor model remains the most prevalent and clinically accepted framework. This structure ensures that the scale accurately captures the multidimensional burden of osteoarthritis on the patient’s lower extremity function.

Instrument

Test Type: Patient-Reported Outcome Measure (PROM), Questionnaire

Format: Self-administered 24-item questionnaire. Scoring can use either a 5-point Likert scale (0=None, 4=Extreme) or a 100 mm Visual Analogue Scale (VAS) (0=No pain/difficulty, 100=Extreme pain/difficulty).

Language Available: English (Original), Dutch, and numerous other validated international translations.

Population Group: Adults, Elderly.

Age Group: Adult patients suffering from gonarthrosis (knee osteoarthritis) or coxarthrosis (hip osteoarthritis).

Population Details: Individuals with musculoskeletal disorders, specifically bone, joint, and cartilage disorders affecting the lower extremity. The scale assesses functions related to activities, the musculoskeletal system, mobility, and sensory functions (pain).

Test Methodology: Retrospective self-report covering symptoms experienced over the preceding 48 hours.

Keywords

PROM, Self-report, Rheumatology, Assessment, Knee pain, Hip pain, Joint stiffness, Functional limitation, Clinical trial endpoint, Lower extremity.

Authors

Author ORCID Identifier: N/A (Specific identifiers not provided in source material)

Affiliation Email addresses: N/A (Specific contact information not provided)

Correspondence Address: N/A (Specific address information not provided)

Permissions & Fee and Test Year

The original version of the WOMAC was first published in 1982 by Nicholas Bellamy. The Dutch version was validated by Roorda LD, et al. in 2004. The scale is widely used in academic research and clinical settings. Researchers should confirm current licensing requirements, as specific versions or commercial use may require formal permission from the copyright holders, typically associated with McMaster University and the University of Western Ontario.

Reference’s

• Bellamy N, Buchanan WW, Goldsmith CH, Campbell J, Stitt LW. (1988). Validation study of the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC): a health status instrument for measuring clinically important outcomes in rheumatic drug trials. Journal of Rheumatology, 15(12): 1833-1840.
• Bellamy N. (1982). The WOMAC Osteoarthritis Index: a user’s guide. Faculty of Health Sciences, University of Western Ontario.
• Roorda LD, Peter WF, Roebroeck ME, Bierma-Zeinstra SM, Harlaar J, Lankhorst GJ. (2004). The Dutch version of the WOMAC Osteoarthritis Index: a validation study in patients with hip or knee osteoarthritis. Osteoarthritis and Cartilage, 12(11): 915-921.

Items of the Western Ontario and McMaster Universities Osteoarthritis Index

IMPORTANT: The following scale items must be preserved in their original language and must not be changed in any way. The original source provided links to the scale instrument and explanatory form, which contain the specific items.

The original explanatory form (Toelichtingsformulier) can be downloaded here: WOMAC Explanatory Form PDF.

The original instrument (Meetinstrument) containing the 24 items can be downloaded here: WOMAC Instrument PDF.