WOMAC Osteoarthritis Index — Hip & Knee Assessment
The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) is a widely used, disease-specific patient-reported outcome measure for assessing symptoms and functional limitations in patients with hip and knee osteoarthritis.
About
The WOMAC was developed at Western Ontario and McMaster Universities (Canada) in 1982 by Bellamy et al. It is a self-administered questionnaire consisting of 24 items divided into 3 subscales: pain (5 items), stiffness (2 items), and physical function (17 items). Each item is scored on a 5-point Likert scale (0 = none, 1 = mild, 2 = moderate, 3 = severe, 4 = extreme). Total score ranges from 0 to 96. The WOMAC has excellent test-retest reliability (r = 0.87-0.91), internal consistency (Cronbach's alpha 0.81-0.95), and responsiveness to change. It is the most widely used outcome measure in osteoarthritis clinical trials and is recommended by OMERACT and Osteoarthritis Research Society International (OARSI).
Formula
24 items each scored 0-4: 0 = none, 1 = mild, 2 = moderate, 3 = severe, 4 = extreme. Pain subscale (5 items): 0-20. Stiffness subscale (2 items): 0-8. Physical function subscale (17 items): 0-68. Total WOMAC score = pain + stiffness + function = 0-96. Higher scores indicate worse symptoms.
The WOMAC is scored by summing individual item scores. Pain subscore: walking on flat surface, going up/down stairs, at night in bed, sitting or lying, standing upright. Stiffness subscore: morning stiffness, stiffness after sitting/lying/resting. Physical function subscore: descending stairs, ascending stairs, rising from sitting, standing, bending to floor, walking on flat, getting in/out of car, going shopping, putting on socks/stockings, lying in bed, getting out of bed, sitting, getting on/off toilet, heavy domestic duties, light domestic duties. A normalized score (0-100 scale) can be calculated as (total/96) × 100 for easier clinical interpretation. The minimal clinically important difference (MCID) is 12-15 points total or 8-10 points on the normalized 0-100 scale.
Score Interpretation
The WOMAC is the most widely used patient-reported outcome measure in osteoarthritis research and clinical practice. It has been validated in over 65 language versions and hundreds of clinical trials. The MCID is 12-15 points for total score. The WOMAC pain subscore correlates well with the visual analog scale (VAS) for pain (r = 0.71-0.88). It is the primary outcome measure recommended by FDA, EMA, and OARSI for osteoarthritis clinical trials. A 20% or greater improvement in WOMAC score is considered a clinically meaningful treatment response.
Mild Symptoms — 0–24
Mild pain, stiffness, and functional limitations. Likely managing well with conservative care.
Management: Exercise therapy (strengthening, aerobic, range of motion), weight management, and patient education. Consider NSAIDs as needed.
Moderate Symptoms — 25–48
Moderate pain and functional limitations affecting daily activities.
Management: Regular physical therapy. Consider intra-articular corticosteroid or hyaluronic acid injections. Activity modification.
Severe Symptoms — 49–72
Significant pain and disability limiting most daily activities.
Management: Orthopedic surgery consultation for joint replacement evaluation. Optimization of conservative therapy. Pain management referral.
Very Severe Symptoms — 73+
Extreme pain and disability. Patient likely a candidate for surgical intervention.
Management: Urgent orthopedic consultation. Total joint arthroplasty evaluation indicated. Pre-operative optimization.
Reference Ranges
| Population | Normal Range |
|---|---|
| Community adults (no OA) | Total 0-10 (asymptomatic) |
| Knee OA awaiting total knee arthroplasty | Total 40-80 (mean 55-60) |
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A 65-year-old woman with bilateral knee OA: Pain subscore 12/20 (walking flat 3, stairs 3, night 2, rest 2, standing 2), Stiffness subscore 5/8 (morning 3, later 2), Function subscore 42/68 (descend stairs 3, ascend 3, rising 3, standing 2, bending 2, walking flat 3, getting in car 3, shopping 3, socks 3, lying 2, getting out of bed 2, sitting 2, toilet 2, heavy duties 4, light duties 2). Total WOMAC: 59/96 — Severe symptoms. Recommendation: Orthopedic consultation for TKA evaluation.
Common Mistakes
Using WOMAC for conditions other than hip or knee osteoarthritis where it has not been validated.
WOMAC is validated specifically for hip and knee osteoarthritis. For other conditions (RA, low back pain, shoulder arthritis), use condition-specific outcome measures (e.g., DAS28, ODI, DASH).
Frequently Asked Questions
What is the difference between WOMAC and KOOS/HOOS?
How should WOMAC be administered?
What is the clinically meaningful change in WOMAC?
References
- Bellamy N, Buchanan WW, Goldsmith CH, Campbell J, Stitt LW. 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. J Rheumatol. 1988;15(12):1833-1840.
- McConnell S, Kolopack P, Davis AM. The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC): a review of its utility and measurement properties. Arthritis Rheum. 2001;45(5):453-461.
- OARSI Guidelines for the Non-Surgical Management of Knee OA (2024).
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