KOOS: The Knee Questionnaire Your Surgeon Uses

What is the KOOS?

The KOOS is a patient-reported outcome measure for the knee — a questionnaire you complete yourself that turns how the knee feels into numbers a clinician can track 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 is a validated self-administered patient-reported outcome with five subscales (pain, symptoms, ADL, sport/recreation, knee-related quality of life) for knee injury and osteoarthritis, developed from the WOMAC with added sport and quality-of-life items.. Unlike a scan, which shows structure, the KOOS captures function and symptoms: what the knee stops you doing, and how much it hurts while you do it. It works for knee injuries and for knee arthritis alike 2Ref 2American Academy of Orthopaedic Surgeons (OrthoInfo) (2024).Arthritis of the Knee.Knee arthritis has both nonsurgical and surgical treatment options and is a common reason knee function is followed over time..

The KOOS was created in the late 1990s by adapting the WOMAC index — a well-established arthritis questionnaire — and adding questions about sport, recreation, and quality of life that the WOMAC left out 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 is a validated self-administered patient-reported outcome with five subscales (pain, symptoms, ADL, sport/recreation, knee-related quality of life) for knee injury and osteoarthritis, developed from the WOMAC with added sport and quality-of-life items.. That addition is the whole point. The WOMAC was built for older adults with osteoarthritis, and its questions miss what a twenty-five-year-old with a reconstructed knee actually struggles with: cutting, landing, kneeling, trusting the joint. Osteoarthritis, the slow loss of joint cartilage, remains the single most common condition the KOOS is used to follow 3Ref 3National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) (2023).Osteoarthritis.Osteoarthritis, the loss of joint cartilage, is the most common form of arthritis., but the tool deliberately reaches well beyond it.

Who the KOOS was built for

The KOOS was designed to span an unusually wide range of ages and injuries, which is why it turns up in so many knee clinics. It is used to follow anterior cruciate ligament injuries, meniscus tears, cartilage damage, and osteoarthritis — conditions that can put a teenager and a retiree in the same waiting room. Meniscus tears alone are among the most common knee injuries treated 4Ref 4American Academy of Orthopaedic Surgeons (OrthoInfo) (2024).Meniscus Tears.Meniscus tears are among the most common knee injuries and can be treated nonsurgically or surgically..

That breadth is what sets the KOOS apart from older arthritis-only questionnaires. A physical therapist can hand the same form to someone rehabbing a new ACL reconstruction, someone recovering from meniscus surgery, and someone with decades-old knee arthritis, then compare each person against their own baseline. The KOOS was made to measure the young athlete and the older arthritis patient with one instrument, which is exactly why it added the questions about sport and pivoting that arthritis tools skip. For younger, active people, the sport and recreation subscale often moves long after pain has settled, capturing readiness the pain score alone would miss.

In practice, that makes the KOOS a natural fit for rehabilitation after an ACL reconstruction, a meniscus repair, or cartilage surgery, where the whole arc runs from a swollen, painful knee through months of graded loading back to sport. A therapist can hand it out every few weeks and watch the pain and daily-function scores recover first, then lean on the slower-moving sport subscale to judge whether the knee is ready for cutting and pivoting rather than guessing from feel alone. The same breadth is why the KOOS also works for people who will never run again but want to climb stairs without dreading them.

What do the five KOOS subscales measure?

The KOOS is made of five subscales, each scored separately: Pain, Symptoms, Function in daily living, Function in sport and recreation, and knee-related Quality of life 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 is a validated self-administered patient-reported outcome with five subscales (pain, symptoms, ADL, sport/recreation, knee-related quality of life) for knee injury and osteoarthritis, developed from the WOMAC with added sport and quality-of-life items.. Keeping them apart matters, because a knee can feel fine walking to the kitchen and still fail on a squat or a pivot — two facts a single combined score would flatten into one.

• Pain — how often the knee hurts and which movements provoke it, from twisting to climbing stairs.
• Symptoms — swelling, grinding, catching, stiffness, and how far the knee bends and straightens.
• Function in daily living (ADL) — stairs, getting in and out of a car, rising from sitting, the ordinary demands the WOMAC also covers.
• Sport and recreation — squatting, running, jumping, kneeling, and pivoting, the higher-load tasks that matter most to active people.
• Quality of life — awareness of the knee, loss of confidence in it, and how much it shapes daily choices.

A companion guide to the KOOS subscales walks through each one in more detail, but the shape above is enough to read most scores.

How KOOS scoring works

Each subscale is transformed to a 0-to-100 score, where 100 means no problems and 0 means extreme problems 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 is a validated self-administered patient-reported outcome with five subscales (pain, symptoms, ADL, sport/recreation, knee-related quality of life) for knee injury and osteoarthritis, developed from the WOMAC with added sport and quality-of-life items.. Higher is better, which surprises people used to a pain scale where a high number is worse. On the KOOS, the goal is to watch each subscale climb over weeks and months.

The five scores are reported side by side, not added into a single total. That is deliberate: averaging the sport subscale into the pain subscale would erase the very gap between them that tells a therapist what to work on next. A perfect 100 on the sport and recreation subscale describes a knee that handles running, jumping, and pivoting without symptoms — a demanding bar many recovered but not fully athletic knees never reach. The questionnaire takes about ten minutes and tolerates a few skipped items, so an occasional blank does not ruin the result.

A worked example: a KOOS after ACL surgery

Picture a runner nine months after an ACL reconstruction whose KOOS reads: Pain 95, Symptoms 90, daily function 96, Sport and recreation 65, and Quality of life 72. The everyday knee is essentially recovered, but the sport subscale and the quality-of-life score reveal what a pain rating alone would miss — the knee is not yet trusted at full athletic load.

At the start of rehabilitation, all five subscales might have sat far lower, so the real story is in how far each has climbed. The sport score of 65 is not a warning sign here; that subscale is the last to return after a knee injury and the one that separates a knee that walks well from a knee ready to cut and pivot. A physical therapist reads that gap as the remaining work, not as a failure.

Two knees can share the same pain score and be worlds apart on sport — which is precisely the difference the KOOS was designed to catch and a single number would erase. For a competitive athlete, the sport and quality-of-life subscales often drive the return-to-play conversation long after pain has gone quiet. Tracking them month by month shows readiness building in a way memory cannot, and it keeps a knee that merely feels good from being mistaken for a knee that is actually ready.

The KOOS, the KOOS JR, and the hip's HOOS

The full KOOS is thorough but long, so a shortened version exists for high-volume settings. The KOOS JR condenses the questionnaire into seven items that produce a single combined score, built specifically for tracking knee replacement and osteoarthritis outcomes across large registries. When a hospital reports a KOOS JR knee replacement score, it is using that streamlined form rather than the full five-subscale version.

The KOOS also has a mirror image one joint up: the HOOS questionnaire measures the hip using the same five subscales and the same 0-to-100 scoring 5Ref 5Nilsdotter AK, Lohmander LS, Klässbo M, Roos EM (2003).Hip disability and osteoarthritis outcome score (HOOS)—validity and responsiveness in total hip replacement.The HOOS is the hip counterpart of the KOOS, using the same five subscales and 0-to-100 scoring.. Someone with an arthritic hip and an injured knee might complete a HOOS for one and a KOOS for the other, and both are read identically. If you are handed a KOOS at one visit and a KOOS JR at the next, that is a change in form length, not a sign your knee is being assessed differently.

Where the KOOS fits into knee care

The KOOS does not treat anything; it measures whether treatment is working. For knee osteoarthritis, guidelines rank exercise, physical therapy, and weight management as strongly supported first-line care, with surgery reserved for knees that no longer respond 6Ref 6American Academy of Orthopaedic Surgeons (AAOS) (2021).Management of Osteoarthritis of the Knee (Non-Arthroplasty), Third Edition — Clinical Practice Guideline.Strong evidence supports exercise, physical therapy, and weight loss as first-line management for knee osteoarthritis.. Tracking your KOOS subscales through a course of physical therapy is one of the clearest ways to see whether that conservative sequence is paying off.

The same score carries into surgical decisions and recovery. Filled out before an operation and again months after, the KOOS lets you and your surgeon set a measured before against a measured after, instead of trading on a hazy memory of how the knee used to feel. The KOOS is not there to push you toward or away from surgery — it exists to make the effect of whatever you choose visible over time. Once conservative care no longer keeps pain and function in check, procedures such as knee replacement or a meniscus repair are well-established options, and the KOOS is one of the tools used to confirm they delivered.

None of that makes the KOOS a decision-maker. It does not know your goals, your other joints, or how you weigh a longer recovery against a faster one; it only reports what the knee is doing. The number belongs in a conversation with a clinician who can set it beside your exam, your imaging, and what you actually want to get back to. Walking the dog without a limp is a different target than returning to competitive sport, and the same score can read as success for one and unfinished work for the other.

What a KOOS score can and cannot tell you

A KOOS score answers "how much," never "why." It can show that the knee is holding you back, but it cannot name the culprit — a ligament, a meniscus, worn cartilage, or pain traveling down from the hip all look identical to the questionnaire. Pinning down the cause takes a history, hands-on testing, and sometimes a scan. Treat the KOOS as a measuring tape, not a verdict; it sizes the problem without ever identifying it.

The knee is only one entry in a whole catalogue of these tools. For the low back there is the Oswestry Disability Index, for the neck the Neck Disability Index, and for the arm and shoulder the DASH questionnaire — each one a patient's own tally of function, and none a diagnosis. What makes any of them trustworthy is repetition: completed over and over and lined up against your earlier numbers, the KOOS reveals real recovery instead of a lucky day.

How carefully the form is completed shapes how much it is worth. Basing each answer on an average recent stretch instead of a standout good or bad day, and actually reading every item rather than pattern-filling, is what keeps the tally honest. The KOOS deliberately asks about a recent, defined window to fence in the drift of memory, and hurried or rose-tinted answers quietly warp the very trend it is there to surface.