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Medical Disclaimer: This guide provides technical information for researchers and clinical staff. It does not provide medical advice or treatment recommendations.
Short Answer
The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) is a 24-item patient-reported outcome measure evaluating pain, stiffness, and physical disability in hip or knee osteoarthritis. Validated by Nicholas Bellamy and colleagues in 1988, it uses a 5-point Likert scale (0–96 total) or 100 mm Visual Analogue Scale. WOMAC is proprietary intellectual property requiring formal licensing prior to clinical or research administration.
Definition and Scope
The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) is a standardized health status instrument developed by Dr. Nicholas Bellamy and collaborators (1988) at the University of Western Ontario and McMaster University. Designed for osteoarthritis clinical trials, it provides an evaluative measure sensitive to medical and surgical interventions.
What is the Western Ontario and McMaster University Osteoarthritis Index (WOMAC)?
In clinical trials governed by Good Clinical Practice, patient-reported outcome measures serve as essential evaluative endpoints. WOMAC isolates lower-extremity symptoms and functional limitations rather than general quality of life. Translated into more than 110 languages, WOMAC is recognized by global regulatory authorities as an established primary and secondary efficacy endpoint in osteoarthritis cohorts.
How It Works and How It Is Used in Practice
WOMAC captures patient-reported joint impairment through a structured 24-item self-administered questionnaire divided into three core dimensions.
WOMAC Questionnaire Items and Structure
The instrument covers three subscales reflecting daily joint function:
- Pain (5 items): Walking, using stairs, in bed at night, sitting or lying, and standing upright.
- Stiffness (2 items): Morning stiffness upon waking, and stiffness after sitting or resting later in the day.
- Physical Function (17 items): Stairs, rising from sitting, standing, bending, walking, car transfers, shopping, dressing, rising from bed, bathing, sitting, toilet transfers, and domestic duties.
How is the WOMAC Questionnaire Scored?
WOMAC is scored using either an ordinal 5-point Likert scale (WOMAC LK) or a 100 mm Visual Analogue Scale (WOMAC VA):
- Likert Scale (0–4 per item): 0 (None) to 4 (Extreme). Subscales: Pain 0–20, Stiffness 0–8, Physical Function 0–68. Total score: 0 to 96 points. Higher scores indicate worse symptoms and impairment.
- Visual Analogue Scale (0–100 mm per item): Subscales: Pain 0–500 mm, Stiffness 0–200 mm, Function 0–1,700 mm (total 0–2,400 mm).
- Normalized 0–100 Scale: Protocols frequently calculate
Normalized Score = (Raw Score / Maximum Subscale Score) × 100, where 0 represents no impairment and 100 represents maximum disability. - Missing Data Rules: Under CONSORT-PRO and SPIRIT-PRO standards, mean item substitution is allowed if missing items do not exceed 1 in Pain, 1 in Stiffness, and 3 in Function. Otherwise, the subscale is invalid.
What is the MCID for WOMAC?
The Minimal Clinically Important Difference (MCID)—or Minimal Clinically Important Improvement (MCII)—identifies the threshold at which score reductions reflect perceptible clinical benefit:
- Empirical MCII Benchmarks: In a prospective cohort of 1,362 osteoarthritis patients (Tubach et al., 2005, Annals of the Rheumatic Diseases), patient-anchored MCII thresholds on a 0–100 normalized scale were -9.1 points (-26.0%) for knee osteoarthritis and -7.9 points (-21.1%) for hip osteoarthritis. Pain VAS MCII was -19.9 mm (-40.8%) for knee and -15.3 mm (-32.0%) for hip.
- Intervention Context: In conservative therapy, a 10% to 15% reduction (8–12 normalized points) represents a clinically meaningful difference (Angst et al., 2001). In total joint arthroplasty (TKA/THA), recovery typically exceeds 20 to 35 normalized points.
Is WOMAC Free to Use? Copyright and Licensing Requirements
WOMAC is not free to use or in the public domain. The questionnaire is copyrighted intellectual property owned by Professor Nicholas Bellamy. Distributing, copying, or integrating WOMAC items into electronic systems without an executed agreement constitutes copyright infringement.
- Licensing Channels: Permissions are managed through womac.com and the Mapi Research Trust / ePROVIDE platform.
- Commercial and Academic Trials: Industry sponsors pay per-administration licensing fees; academic investigators must also apply for formal user agreements.
- Digital Migrations: Incorporating WOMAC into ePRO platforms requires formatting review from the licensor to preserve psychometric validity.
Types and Related Concepts
Investigators select patient-reported instruments based on anatomical focus, patient age, and licensing structure:
| Instrument | Items | Anatomical Target | Licensing Model | Primary Context |
|---|---|---|---|---|
| WOMAC | 24 items | Knee and Hip Osteoarthritis | Proprietary (Prof. Nicholas Bellamy; licensed via Mapi / ePROVIDE) | Primary outcome endpoint in osteoarthritis trials and arthroplasty registries |
| KOOS | 42 items | Knee injury and pathology | Open Access / Free (Roos et al., 1998) | Younger, active populations and post-traumatic knee injury cohorts |
| HOOS | 40 items | Hip injury and pathology | Open Access / Free (Klässbo et al., 2003) | Younger active adults and hip preservation registries |
| LEFS | 20 items | Lower extremity disorders | Open Access / Free (Binkley et al., 1999) | Outpatient physical therapy and orthopedic rehabilitation |
| Oswestry Disability Index (ODI) | 10 items | Lumbar spine (low back pain) | Proprietary (Mapi Research Trust / Fairbank & Pynsent) | Spine surgery and chronic low back pain trials |
While KOOS and HOOS incorporate athletic domains for younger cohorts, WOMAC remains the preferred standard for regulatory trials in older populations. When systemic functional domains are required, investigators frequently supplement WOMAC with generic instruments such as PROMIS measures.
Where It Matters for Labs, Clinics, and Research Decisions
Selecting WOMAC impacts protocol design and operational execution:
- Regulatory Efficacy Endpoints: In confirmatory Phase 3 clinical trials, WOMAC pain and function subscales serve as primary efficacy outcomes accepted by the FDA and EMA.
- Composite Endpoints: Protocols frequently combine WOMAC clinical criteria with radiographic joint space narrowing into a composite endpoint.
- Operational Budgeting: Licensing fees, certified language translations, and ePRO validation certificates must be integrated into study startup timelines and trial budgets.
Common Misunderstandings
- Misunderstanding: WOMAC is free to download and administer.
Reality: WOMAC is proprietary intellectual property. Unlicensed use compromises trial governance and regulatory compliance. - Misunderstanding: WOMAC measures whole-body functional status.
Reality: WOMAC evaluates only knee and hip joint symptoms, not spine or upper-extremity conditions. - Misunderstanding: A higher numerical score signifies better health.
Reality: WOMAC scores are severity-weighted: higher values indicate worse pain, greater stiffness, and higher disability. - Misunderstanding: Any numerical decrease demonstrates clinical efficacy.
Reality: Reductions must reach or exceed MCID/MCII thresholds (typically 8–12 points normalized, or 21%–26% relative improvement) to reflect meaningful patient improvement.
Frequently Asked Questions
What is the Western Ontario and McMaster University Osteoarthritis Index (WOMAC)?
WOMAC is a validated 24-item patient-reported outcome measure assessing pain, stiffness, and physical function specifically in hip and knee osteoarthritis (Bellamy et al., 1988).
How is the WOMAC questionnaire scored?
In the Likert format, 24 items are scored 0 to 4 across Pain (0–20), Stiffness (0–8), and Physical Function (0–68), totaling 0 to 96 points. In the VAS format, items are measured on a 100 mm scale. Higher scores indicate worse symptoms and impairment.
Is WOMAC free to use?
No. WOMAC is copyrighted by Professor Nicholas Bellamy and administered through authorized channels, including womac.com and the Mapi Research Trust / ePROVIDE. All users must obtain an official license prior to administration.
What is MCID for WOMAC?
The MCID for WOMAC is typically a 10% to 15% reduction (8 to 12 normalized points) in conservative care. In clinical trial cohorts (Tubach et al., 2005), physical function MCII was -9.1 points (-26.0%) for knee osteoarthritis and -7.9 points (-21.1%) for hip osteoarthritis.
How does WOMAC differ from the Oswestry Disability Index?
WOMAC evaluates osteoarthritis of the knee and hip joints across 24 items. The Oswestry Disability Index (ODI) is a 10-item instrument designed specifically to measure functional impairment caused by low back pain and lumbar spine pathology.
Sources
- Bellamy N, Buchanan WW, Goldsmith CH, Campbell J, Stitt LW. (1988). “Validation study of WOMAC: a health status instrument for measuring clinically important patient relevant outcomes to antirheumatic drug therapy in patients with osteoarthritis of the hip or knee.” The Journal of Rheumatology, 15(12):1833-1840. PMID: 3068365. https://pubmed.ncbi.nlm.nih.gov/3068365/ (Checked 2026-11-07).
- Mapi Research Trust / ePROVIDE. (2026). “Western Ontario and McMaster Universities Arthritis Index (WOMAC®)”. Instrument Record. https://eprovide.mapi-trust.org/instruments/western-ontario-and-mcmaster-universities-osteoarthritis-index (Checked 2026-11-07).
- Tubach F, Ravaud P, Baron G, et al. (2005). “Evaluation of clinically relevant changes in patient reported outcomes in knee and hip osteoarthritis: the minimal clinically important improvement.” Annals of the Rheumatic Diseases, 64(1):29–33. doi:10.1136/ard.2004.022905. PMCID: PMC1755212. PMID: 15208174. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1755212/ (Checked 2026-11-07).
- Angst F, Aeschlimann A, Stucki G. (2001). “Smallest detectable and minimal clinically important changes of rehabilitation intervention with their implications for interpretation of group results: as illustrated by the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC).” Arthritis & Rheumatism, 45(4):384-391. PMID: 11501727. https://pubmed.ncbi.nlm.nih.gov/11501727/ (Checked 2026-11-07).
