What Each Part of the KOOS Measures About Your Knee

What are the five KOOS subscales?

The KOOS asks 42 questions and sorts them into five groups, each scored on its own from 0 to 100 1Ref 1Roos EM, Roos HP, Lohmander LS, Ekdahl C, Beynnon BD (1998).Knee Injury and Osteoarthritis Outcome Score (KOOS)—Development of a Self-Administered Outcome Measure.The KOOS's design and structure: a self-administered questionnaire for knee injury and osteoarthritis with five separately scored subscales — pain, other symptoms, function in daily living, function in sport and recreation, and knee-related quality of life — each reported on its own rather than summed, with the WOMAC contained within it.. One hundred means no problems in that area; zero means extreme problems. The groups are pain, other symptoms, function in daily living, function in sport and recreation, and knee-related quality of life, and every question asks about the past week rather than your worst day.

The five are reported side by side as a profile. There is no sixth number underneath them, and the absence is deliberate.

Why the five scores are never added into one

Because they move independently, and a total would erase exactly the information the instrument exists to show. The KOOS was built to be scored subscale by subscale, not summed 1Ref 1Roos EM, Roos HP, Lohmander LS, Ekdahl C, Beynnon BD (1998).Knee Injury and Osteoarthritis Outcome Score (KOOS)—Development of a Self-Administered Outcome Measure.The KOOS's design and structure: a self-administered questionnaire for knee injury and osteoarthritis with five separately scored subscales — pain, other symptoms, function in daily living, function in sport and recreation, and knee-related quality of life — each reported on its own rather than summed, with the WOMAC contained within it.. A knee that has stopped hurting can still swell and catch. A knee that manages stairs can still have taken over your week. Blending those into one figure destroys both facts and buys nothing but tidiness.

The temptation is real, because one number is easier to chart and easier to compare. That trade does get made on purpose: koos jr. exists to give exactly one number for one narrow question — did a knee replacement help this person — and it pays for it by discarding the profile.

The second reason is weighting. The five subscales do not deserve equal importance for any given person, and no fixed formula could be right for everyone. For a 68-year-old with knee osteoarthritis — the most common form of arthritis, in which joint cartilage breaks down, and more likely with age 2Ref 2National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) (2023).Osteoarthritis.That osteoarthritis is the most common form of arthritis, a degenerative joint disease involving breakdown of cartilage, and that it becomes more common with age. — the sport subscale may be beside the point entirely. For a 22-year-old six months out from a ligament reconstruction, it may be the only one that matters. A total would quietly impose one answer on both.

Pain and symptoms sound like the same thing. They are not.

Pain, on the KOOS, is nine questions about how often the knee hurts and how much during named movements: twisting, straightening, bending, walking on the flat, stairs, night-time in bed, sitting, and standing upright 1Ref 1Roos EM, Roos HP, Lohmander LS, Ekdahl C, Beynnon BD (1998).Knee Injury and Osteoarthritis Outcome Score (KOOS)—Development of a Self-Administered Outcome Measure.The KOOS's design and structure: a self-administered questionnaire for knee injury and osteoarthritis with five separately scored subscales — pain, other symptoms, function in daily living, function in sport and recreation, and knee-related quality of life — each reported on its own rather than summed, with the WOMAC contained within it.. Symptoms is seven questions about what the knee does mechanically — swelling, grinding, catching, stiffness first thing in the morning, stiffness later in the day, and whether the joint fully straightens and bends.

The split has a nice piece of texture in it. The KOOS asks about straightening your knee twice: once in the pain subscale, where the question is how much it hurts, and once in the symptoms subscale, where the question is whether you can do it at all. Those are different facts about a knee, and they come apart often.

An effusion is fluid inside the joint itself — swelling felt as tightness and a knee that will not fully bend, rather than puffiness you can see on the surface.

So the symptoms subscale is worth reading closely even when the pain number is the one everybody discusses. Mechanical trouble tends to be structural, and it is the sort of knee pain people fail to report because it does not hurt enough to complain about. Most people do not notice their range going until it has gone.

Why daily living is the biggest subscale, and what it borrows

Seventeen of the KOOS's 42 questions ask about ordinary daily function, making it the largest of the five by a wide margin 1Ref 1Roos EM, Roos HP, Lohmander LS, Ekdahl C, Beynnon BD (1998).Knee Injury and Osteoarthritis Outcome Score (KOOS)—Development of a Self-Administered Outcome Measure.The KOOS's design and structure: a self-administered questionnaire for knee injury and osteoarthritis with five separately scored subscales — pain, other symptoms, function in daily living, function in sport and recreation, and knee-related quality of life — each reported on its own rather than summed, with the WOMAC contained within it.. It covers going down and up stairs, rising from sitting, standing, bending to the floor, walking on flat ground, getting in and out of a car, shopping, putting socks on and taking them off, lying down and rising in bed, sitting, getting on and off the toilet, and heavy and light household duties.

The size is inherited rather than chosen. Those items are the WOMAC's function questions, carried into the KOOS whole: the KOOS was designed to contain the older WOMAC inside it, so a clinic using the KOOS can still produce a WOMAC score and compare against decades of prior work 1Ref 1Roos EM, Roos HP, Lohmander LS, Ekdahl C, Beynnon BD (1998).Knee Injury and Osteoarthritis Outcome Score (KOOS)—Development of a Self-Administered Outcome Measure.The KOOS's design and structure: a self-administered questionnaire for knee injury and osteoarthritis with five separately scored subscales — pain, other symptoms, function in daily living, function in sport and recreation, and knee-related quality of life — each reported on its own rather than summed, with the WOMAC contained within it..

One warning about this subscale: it is the one most likely to look better than the person feels. Daily life adapts silently. People take the stairs less, buy shoes they can step into, park closer to the door. A year later they answer honestly that stairs give them only moderate difficulty — because they now take four a day instead of forty. The score has held. The life has not.

The sport and recreation subscale, and its floor

Five questions, and the most physically demanding on the instrument: squatting, running, jumping, twisting or pivoting on the affected knee, and kneeling 1Ref 1Roos EM, Roos HP, Lohmander LS, Ekdahl C, Beynnon BD (1998).Knee Injury and Osteoarthritis Outcome Score (KOOS)—Development of a Self-Administered Outcome Measure.The KOOS's design and structure: a self-administered questionnaire for knee injury and osteoarthritis with five separately scored subscales — pain, other symptoms, function in daily living, function in sport and recreation, and knee-related quality of life — each reported on its own rather than summed, with the WOMAC contained within it.. It is the shortest subscale and the most volatile. In a young, athletic knee it is the most sensitive of the five — first to fall when something goes wrong, last to recover. In an older, less active knee it is frequently close to meaningless.

A floor effect is what happens when nearly everyone scores at the bottom, so the number stops telling one person apart from another.

Ask a 70-year-old with knee osteoarthritis 2Ref 2National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) (2023).Osteoarthritis.That osteoarthritis is the most common form of arthritis, a degenerative joint disease involving breakdown of cartilage, and that it becomes more common with age. how much trouble jumping gives them and the answer is extreme difficulty — but so it is for almost everyone in that group, including the ones doing well. The subscale is not measuring their knee. It is measuring the fact that they were not going to jump this week regardless.

So a sport score of zero is not automatically alarming; both ends depend on what the person was doing before. That is why activity level is recorded separately. The tegner activity scale exists to write down what someone actually does, from sedentary through competitive, so a function score can be read against the life it belongs to.

The subscale most people skip: knee-related quality of life

Four questions, and they are the least like the rest of the instrument 1Ref 1Roos EM, Roos HP, Lohmander LS, Ekdahl C, Beynnon BD (1998).Knee Injury and Osteoarthritis Outcome Score (KOOS)—Development of a Self-Administered Outcome Measure.The KOOS's design and structure: a self-administered questionnaire for knee injury and osteoarthritis with five separately scored subscales — pain, other symptoms, function in daily living, function in sport and recreation, and knee-related quality of life — each reported on its own rather than summed, with the WOMAC contained within it.. They ask how often you are aware of your knee problem, whether you have modified your way of life to avoid activities that might damage the knee, how much you are troubled by a lack of confidence in it, and how much difficulty the knee gives you in general.

Not one of them is about a movement. This is the subscale that asks what the knee costs you when you are not using it: the mental space it occupies, the trips quietly not planned. It is often the lowest of the five and often the one nobody raises in the appointment, because the appointment runs on pain.

If one subscale should not be skimmed, it is quality of life. It is the closest the KOOS comes to asking about your life rather than your knee.

The confidence question catches something no physical examination does. A knee that has buckled twice produces a person who avoids uneven ground and keeps a hand near the rail, and that person can keep all of it long after the knee has been repaired and pronounced stable. A surgeon reading only the pain and daily-living numbers would see a good result.

How to read the shape across the five

A KOOS profile is read as a pattern rather than a total: which subscales are low, which are high, and which ones move when something changes. The five come apart routinely, and the divergence is itself the finding. Treatments do not act evenly across them, and the trial evidence is full of interventions that shifted one subscale and left another untouched.

Pooled trials of arthroscopic surgery for a degenerative knee are the clearest example: a small and short-lived benefit for pain, no benefit at all for function, alongside real harms 3Ref 3Thorlund JB, Juhl CB, Roos EM, Lohmander LS (2015).Arthroscopic surgery for degenerative knee: systematic review and meta-analysis of benefits and harms.That arthroscopic surgery for degenerative knee disease produced at most a small, short-lived benefit for pain and no benefit for function, with associated harms — an example of an intervention whose effect on pain and on function diverge.. One blended number could have shown a faint improvement while hiding the fact that its two halves were doing different things. Movement in the other direction is just as informative. Land-based exercise for knee osteoarthritis reduces pain and improves function together, and the gain holds for months after the sessions stop 4Ref 4Fransen M, McConnell S, Harmer AR, et al. (2015).Exercise for osteoarthritis of the knee.That land-based therapeutic exercise reduces knee pain and improves physical function in knee osteoarthritis, with benefit sustained for months after formal treatment ends — an effect appearing across more than one domain.. Adding intensive weight loss to exercise, in overweight and obese adults with knee osteoarthritis, produced more pain relief, less inflammation, and better function than exercise alone 5Ref 5Messier SP, Mihalko SL, Legault C, et al. (IDEA) (2013).Effects of Intensive Diet and Exercise on Knee Joint Loads, Inflammation, and Clinical Outcomes Among Overweight and Obese Adults With Knee Osteoarthritis: The IDEA Randomized Clinical Trial.That in overweight and obese adults with knee osteoarthritis, intensive diet-induced weight loss combined with exercise produced greater reductions in pain and inflammation and better function than exercise alone.. An effect appearing across several subscales at once is a different quality of result from one that moves pain alone.

Patterns worth recognising:

• Pain low, daily living high. Common early. The knee hurts and life has not yet reorganised around it.
• Daily living low, quality of life lower still. The reorganising has happened — often the profile of someone who has stopped mentioning the knee because there is nothing new to say.
• Sport low, the other four high. A young knee, and the case for the sport subscale existing at all: it is the only one with room left to detect the problem.

After surgery the five recover on different clocks — pain often before symptoms, symptoms before confidence — which is part of why a knee replacement recovery timeline is described in months rather than weeks.