Muscle, joint & pain

WOMAC: The Arthritis Score for Knees and Hips

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The Western Ontario and McMaster Universities Osteoarthritis Index has been the standard knee and hip arthritis questionnaire since 1988. It is worth knowing what its three subscales cover, why it was designed inside a drug trial, and why the first question to ask about any WOMAC number is which direction the scale runs.

Last updated: July 2026

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What is the WOMAC osteoarthritis index?

WOMAC — the Western Ontario and McMaster Universities Osteoarthritis Index — is a disease-specific, multidimensional, self-administered health status instrument for people with osteoarthritis of the hip or knee, introduced and validated by Bellamy and colleagues in 1988 1. It is organised into three subscales: pain, stiffness, and physical function 1. You complete it yourself; nobody examines you to produce the number.

That places it among patient-reported outcome measures, the family of questionnaires that record what a condition is doing to a person's life rather than what it looks like on an image. For osteoarthritis, that distinction matters more than usual. Osteoarthritis is the most common form of arthritis, a degenerative joint disease involving breakdown of cartilage, more common with age and more common in women after about age 50 2. The amount of cartilage loss visible on a radiograph and the amount of trouble a person is having are famously imperfect partners, and WOMAC measures the second of those.

Self-administered is not a small detail either. It means the score is your account of your joint, not a clinician's estimate of it, and that cuts both ways. It removes the observer's assumptions about what an arthritic knee should feel like. It also means the number moves with mood, sleep, the weather, and how the week has gone — which is one reason a single reading is weaker evidence than a series.

"Disease-specific" is the other load-bearing word. General health questionnaires ask about everything and therefore respond weakly to a change in one joint. WOMAC asks only about the arthritic hip or knee, which makes it blunt about the rest of your life and sharp about that joint. Instruments are usually built to be one or the other, and knowing which you are holding prevents most misreadings.

The three subscales: pain, stiffness, physical function

The three subscales are reported separately as well as combined, and they answer genuinely different questions 1. Pain covers how much the joint hurts during ordinary activities. Stiffness covers the quality most people describe as the joint needing to warm up. Physical function covers the tasks that stiffness and pain make hard — the largest of the three sections, and the one that usually moves most when something works.

Reading the subscales separately is where the instrument earns its keep. A knee that has become much less painful but no more usable tells a different story from one where both moved together, and a total score hides that entirely. It is reasonable to ask for the subscale breakdown rather than the single number, and any clinic administering WOMAC has it.

The three also tend to move on different schedules, which is the argument for keeping them apart. Stiffness often shifts first with movement and warmth. Pain follows. Function is usually the slowest, because it depends not only on the joint but on confidence, strength that was lost while the joint was sore, and habits built around avoiding the movement. A course of treatment that has changed only the first two is not a failure — it is an incomplete one, and the subscale breakdown is what makes that visible.

Stiffness is the smallest section and the most misunderstood. It is not asking about pain and it is not asking about weakness. It is asking about the specific experience of a joint that resists movement after rest, which behaves differently across the day from pain and often responds differently to treatment.

WOMAC describes the joint's behaviour in your life. It says nothing about the structure inside it. A person with severe changes on imaging can report modest WOMAC scores, and the reverse happens just as often. Neither result is an error in the questionnaire.

How to read a WOMAC score without being misled

Here is the honest state of the sourcing, because it changes how a printout should be read. The 1988 paper establishes what WOMAC measures and that it was validated as an evaluative instrument 1. It does not set out the item count, the total score range, or which end of the scale is the good end. Those scoring rules travel with the licensed instrument and its user guide rather than with the validation paper.

So the two questions worth asking about any WOMAC figure on a report are what the maximum is and which direction the scale runs. Both have definite answers, held by whoever administered it, and neither should be guessed from the number.

That is not pedantry, because closely related knee and hip measures genuinely run in opposite directions from one another. The KOOS, JR is scored on an interval scale from 0 to 100 in which 0 represents complete knee disability and 100 represents perfect knee health — higher is better 3. The HOOS, JR uses the same convention for the hip, with 0 as total hip disability and 100 as perfect hip health 4. A score of 78 on one of those is a good result. A score of 78 on a scale where the number counts trouble is not.

A practical consequence. If a clinic switches instruments between visits, or if a summary letter reports one number from a physiotherapy record and another from a surgical clinic, the two are not comparable and should not be subtracted from one another. Comparing a WOMAC to a WOMAC, collected the same way, is the only arithmetic the instrument supports.

Why WOMAC was built inside a drug trial

WOMAC was developed and tested within a double-blind randomised controlled parallel trial of two anti-inflammatory drugs, and its intended role was as an evaluative instrument for osteoarthritis clinical trials 1. The paper reports its face, content and construct validity, its reliability, its responsiveness, and its relative efficiency — that last term meaning how economically it detects a change compared with the alternatives available at the time 1.

That origin explains most of the instrument's personality. A trial measure has one job: notice when a group of people gets better or worse, and notice it with as few patients as possible. It does not need to diagnose anyone, it does not need to decide anyone's treatment, and it does not need to be interpretable for a single individual on a single day.

WOMAC has since been carried into ordinary clinical use, joint registries, and pre- and post-surgical follow-up, which is a promotion it was not designed for. Mostly it copes. The places where it strains are exactly the places you would predict from its origins: interpreting one person's single score, and saying how much change in that person is enough to matter.

Despite the phrase "clinically important" in its title, the 1988 validation paper reports no minimal clinically important difference and no minimal detectable change 1. Those thresholds came later, from separate responder-criteria and psychometric work, and a change threshold quoted for WOMAC belongs to whichever of those papers produced it — not to the instrument's founding study.

WOMAC, KOOS and HOOS: how the family fits together

WOMAC's three subscales cover pain, stiffness and function, which is most of what matters to an older adult with an arthritic joint and not all of what matters to a younger one. Two later instruments extended the idea outward, and both are now as commonly used as the original in their respective joints.

The koos questionnaire — the Knee Injury and Osteoarthritis Outcome Score — is a validated patient-reported measure with five subscales: pain, symptoms, activities of daily living, sport and recreation, and knee-related quality of life 5. The two additions are the point. Sport and recreation asks about demands that a pain-stiffness-function questionnaire never reaches, and knee-related quality of life asks how much mental space the knee is occupying.

The hoos hip score does the same for the hip, with the same five subscales, and it was validated in total hip replacement 6. One finding from that validation is worth stating directly, because it is a head-to-head comparison rather than an opinion: the HOOS proved more responsive than WOMAC on the pain and symptom subscales in that population 6.

Responsiveness is an instrument's ability to register change that has genuinely occurred. A less responsive measure does not report a false result; it reports a smaller one, and real improvement can end up buried inside its measurement error. That is why responsiveness, rather than accuracy, is the property outcome researchers argue about most, and why the choice of questionnaire can change what a study appears to find.

Which one you are handed usually reflects the setting, not a judgement about you. Rheumatology and osteoarthritis drug research have long defaulted to WOMAC. Sports medicine and younger post-injury populations tend toward the KOOS. Hip and knee replacement services increasingly use the short forms built specifically for them.

The short forms built for joint replacement

Two abbreviated instruments now dominate joint-replacement follow-up, and both were derived by statistically stripping the longer questionnaires down to the items that still carried the signal. They are short enough to be collected at every visit without anyone resenting them, which is the whole design goal.

The KOOS, JR is a seven-item instrument measuring a single dimension its developers call knee health, collapsing pain, symptom severity and daily-activity items relevant to advanced knee osteoarthritis; its interval score runs 0 to 100 with higher meaning better 3. It was derived by Rasch analysis on 2,291 patients undergoing primary unilateral knee replacement, then externally validated against a national joint replacement registry, with internal consistency of 0.84 to 0.85 and standardised response means of 1.70 to 1.79 3.

The HOOS, JR is six items — two from the pain domain and four from activities of daily living — converted through a crosswalk table to a 0-to-100 interval measure 4. Its reported responsiveness is high, with standardised response means of 2.38 and 2.03 in its two cohorts 4.

One number in that paper deserves reading carefully, because it is the honest limit of every short form. The HOOS, JR showed ceiling effects of 37% to 46% 4. A ceiling effect of 37% to 46% means that between roughly a third and a half of patients scored at the very top of the scale 4. Once someone is at the ceiling, the instrument cannot tell whether they are doing well or extremely well, and it cannot register further improvement. For a measure used after hip replacement — where most people do well — that is a substantial blind spot, and it is why registry scores flatten out in the second year after surgery.

What a WOMAC score cannot tell you

It cannot diagnose osteoarthritis, which is a clinical diagnosis made from history, examination and sometimes imaging 2. It cannot grade cartilage. It cannot tell you whether you need a joint replacement, and it cannot predict how a replacement will turn out. It is a record of what you reported about pain, stiffness and function on the day you filled it in, and its value is almost entirely in the comparison with the last time you filled in the same form.

A few specific misreadings are worth naming, because they recur:

  • Treating one score as a severity grade. WOMAC has no published severity bands in its founding paper, and a single number in isolation is not a stage of disease 1.
  • Subtracting scores from different instruments. A WOMAC and a KOOS, JR are not the same scale, do not run in the same direction, and cannot be differenced.
  • Reading a flat score as no progress. Near the top of any of these scales, a ceiling effect can hide real improvement — the effect that runs to 37% to 46% on the HOOS, JR 4.
  • Expecting it to reflect a scan. The questionnaire and the radiograph are measuring different things, and disagreement between them is ordinary rather than alarming.

Every body region has its own version of this family — the oswestry disability index for the low back, the neck disability index for the neck, the dash questionnaire for the arm, shoulder and hand. They share the same logic and the same limits: they measure a life, in a specific region, on a specific day, and they are most useful when the same one is repeated over time and read alongside someone who can examine the joint.

Common questions

It depends entirely on which version and which reporting convention the clinic uses, so it is a question to ask rather than assume. Some knee and hip measures are scored so that higher is better — the KOOS, JR and HOOS, JR both put 100 at perfect joint health — and others count trouble upward. Whoever administered the form knows which one you have.

No. It measures pain, stiffness and physical function in people already known or suspected to have hip or knee osteoarthritis. The diagnosis comes from history and examination, sometimes supported by imaging. Filling in a WOMAC before anyone has assessed the joint produces a number without a context to interpret it in.

WOMAC has three subscales: pain, stiffness and physical function. The KOOS has five, adding sport and recreation and knee-related quality of life. The extra two matter most for younger or more active people, whose limitations often show up in sport long before they show up in walking or stair climbing.

Because a single reading says little and a pair says a great deal. Joint replacement services and registries collect these questionnaires before the operation and again afterwards so that the change can be measured, both for the individual and to track how the service as a whole is performing over thousands of patients.

Possibly it is just insensitive at your end of the scale. Short arthritis measures show pronounced ceiling effects — on the HOOS, JR, between 37% and 46% of patients scored at the very top — and once someone is at the ceiling, further improvement has nowhere to register. Say so; it is useful information.

The 1988 validation paper does not answer that. It reports no minimal clinically important difference and no minimal detectable change, despite the phrase in its title. The thresholds people quote come from later work, and a number offered as the meaningful change on WOMAC should be attributed to whichever study produced it.

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Joint symptoms a questionnaire is not designed to catch

  • —A single joint that becomes hot, swollen and red over hours, especially with fever or shaking chills
  • —Sudden inability to put weight through a hip or knee after a fall, or a leg that looks shortened or turned outward
  • —A knee that locks in one position or repeatedly gives way and causes falls
  • —New numbness, pins and needles, or weakness in the leg alongside the joint pain

A hot, swollen, red joint with fever needs to be seen the same day in an emergency department — an infected joint is assessed urgently, not at the next routine appointment. Call 911 if you cannot bear weight at all after a fall.

This page explains what an arthritis questionnaire measures and how its scores are structured. It is general education, not medical advice, and no score can diagnose a condition, stage it, or decide whether a procedure is appropriate for you.

References

  1. 1.Bellamy N, Buchanan WW, Goldsmith CH, et al. (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. J Rheumatol. PMID 3068365 ✓That WOMAC is a disease-specific, multidimensional, self-administered health status instrument for osteoarthritis of the hip or knee, organised into three subscales (pain, stiffness, physical function); that it was introduced and validated within a double-blind randomised controlled parallel trial of two antirheumatic drugs as an evaluative instrument for OA clinical trials; and its reported face, content and construct validity, reliability, responsiveness and relative efficiency. Also cited for what the paper does NOT establish: it reports no minimal clinically important difference, no minimal detectable change, and no item count, score range, scoring direction or severity bands.
  2. 2.National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) (2023). Osteoarthritis. NIAMS, National Institutes of Health. link ✓That osteoarthritis is the most common form of arthritis, a degenerative joint disease involving cartilage breakdown, more common with age and more common in women after age 50; and that it is identified clinically rather than by a questionnaire.
  3. 3.Lyman S, Lee YY, Franklin PD, Li W, Cross MB, Padgett DE (2016). Validation of the KOOS, JR: A Short-form Knee Arthroplasty Outcomes Survey. Clinical Orthopaedics and Related Research, 474(6):1461-1471. doi:10.1007/s11999-016-4719-1 ✓That the KOOS, JR is a seven-item instrument measuring a single 'knee health' dimension, scored on an interval scale of 0-100 in which higher is better (0 = complete knee disability, 100 = perfect knee health); that it was derived by Rasch analysis on 2,291 patients undergoing primary unilateral total knee arthroplasty and externally validated against the FORCE-TJR registry; and its internal consistency (Person Separation Index 0.84-0.85) and responsiveness (standardised response means 1.70-1.79).
  4. 4.Lyman S, Lee YY, Franklin PD, et al. (2016). Validation of the HOOS, JR: A Short-form Hip Replacement Survey. Clinical Orthopaedics and Related Research, 474(6):1472-1482. doi:10.1007/s11999-016-4718-2 ✓That the HOOS, JR is a six-item short form drawn from the pain domain (2 items) and activities-of-daily-living domain (4 items) of the HOOS, converted by a crosswalk table to an interval measure scaled 0-100 where 0 is total hip disability and 100 is perfect hip health; its responsiveness (standardised response means 2.38 and 2.03); and its reported ceiling effects of 37% to 46%.
  5. 5.Roos EM, Roos HP, Lohmander LS, Ekdahl C, Beynnon BD (1998). Knee Injury and Osteoarthritis Outcome Score (KOOS)—Development of a Self-Administered Outcome Measure. Journal of Orthopaedic & Sports Physical Therapy. doi:10.2519/jospt.1998.28.2.88That the KOOS is a validated self-administered patient-reported outcome measure for knee injury and osteoarthritis with five subscales: pain, symptoms, activities of daily living, sport and recreation, and knee-related quality of life.
  6. 6.Nilsdotter AK, Lohmander LS, Klässbo M, Roos EM (2003). Hip disability and osteoarthritis outcome score (HOOS)—validity and responsiveness in total hip replacement. BMC Musculoskeletal Disorders. PMID 12777182 ✓That the HOOS is a validated patient-reported outcome for hip osteoarthritis with five subscales (pain, symptoms, activities of daily living, sport and recreation, hip-related quality of life), validated in total hip replacement, and that it proved more responsive than WOMAC on the pain and symptom subscales in that population.

6 sources, numbered by first appearance. General health information, not medical advice. AI-assisted editorial content — citations link their sources. Editorial policy

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