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OrthoMeasure

Patient-reported outcome measure

KOOS Calculator

Knee injury and Osteoarthritis Outcome Score

The KOOS is a 42-item patient-reported questionnaire that scores knee function as five separate subscales — Symptoms, Pain, Activities of Daily Living, Sport and Recreation, and Quality of Life — each from 0 (extreme problems) to 100 (no problems).

Free to use42 items~10 min0–100, higher is better

Symptoms

Answer these questions thinking of your knee symptoms during the last week.

1Do you have swelling in your knee?
2Do you feel grinding, hear clicking, or any other type of noise when your knee moves?
3Does your knee catch or hang up when moving?
4Can you straighten your knee fully?
5Can you bend your knee fully?

Stiffness

The following questions concern the amount of joint stiffness you have experienced during the last week in your knee. Stiffness is a sensation of restriction or slowness in the ease with which you move your knee joint.

6How severe is your knee joint stiffness after first wakening in the morning?
7How severe is your knee joint stiffness after sitting, lying, or resting later in the day?

Pain

What amount of knee pain have you experienced the last week during the following activities?

8How often do you experience knee pain?
9Twisting/pivoting on your knee
10Straightening knee fully
11Bending knee fully
12Walking on a flat surface
13Going up or down stairs
14At night while in bed
15Sitting or lying
16Standing upright

Function, daily living

This section describes your ability to move around and to look after yourself. For each of the following activities, please indicate the degree of difficulty you have experienced in the last week due to your knee.

17Descending stairs
18Ascending stairs
19Rising from sitting
20Standing
21Bending to the floor/pick up an object
22Walking on a flat surface
23Getting in/out of a car
24Going shopping
25Putting on socks/stockings
26Rising from bed
27Taking off socks/stockings
28Lying in bed (turning over, maintaining knee position)
29Getting in/out of bath
30Sitting
31Getting on/off toilet
32Heavy domestic duties (moving heavy boxes, scrubbing floors, etc)
33Light domestic duties (cooking, dusting, etc)

Function, sports and recreational activities

This section describes your ability to be active on a higher level. For each of the following activities, please indicate the degree of difficulty you have experienced in the last week due to your knee.

34Squatting
35Running
36Jumping
37Twisting/pivoting on your injured knee
38Kneeling

Quality of Life

39How often are you aware of your knee problem?
40Have you modified your life style to avoid activities potentially damaging to your knee?
41How much are you troubled with lack of confidence in your knee?
42In general, how much difficulty do you have with your knee?

What the KOOS score means

KOOS scores run from 0 to 100, where a higher score is better. The bands below are conventional reporting categories, not diagnostic cut-offs.

  • Extreme problems0–24
  • Severe problems25–49
  • Moderate problems50–74
  • Mild problems75–89
  • No to minimal problems90–100

Clinically important thresholds

A change in score only matters if it exceeds the smallest difference patients actually notice. Every threshold below is reported with the population it was derived in — a threshold quoted without its population is not usable.

TypeValueSubscalePopulationFollow-upSource
MCID8–10 pointsPainTotal knee arthroplasty6–12 monthsRoos EM 2003
MCID8–10 pointsADLTotal knee arthroplasty6–12 monthsRoos EM 2003
MCID10 pointsAll subscalesACL reconstruction12 monthsRoos EM 2003
PASS~78 pointsPainKnee arthroplasty12 monthsConnelly JW 2019
PASS~63 pointsQOLKnee arthroplasty12 monthsConnelly JW 2019
MDC6–12 pointsVaries by subscaleKnee osteoarthritis—Collins NJ 2011

MCID is the smallest change a patient perceives as meaningful. PASS is the score above which patients consider their state acceptable. SCB is a substantial rather than minimal benefit. MDC is the smallest change exceeding measurement error.

How the score is calculated

Stated in full so the calculation can be independently checked, and reproduced by hand if needed.

Each item is scored 0 to 4, where a higher raw score means worse symptoms. For each of the five subscales, the mean of that subscale's item scores is calculated, then transformed to a 0–100 scale with the formula: score = 100 − (mean item score × 100 ÷ 4). A score of 100 indicates no problems and 0 indicates extreme problems. The five subscale scores are reported separately and are not averaged into a single total.

Missing data

If no more than two items in a subscale are missing, the mean of the observed items in that subscale is substituted for the missing values. If more than two items in a subscale are missing, that subscale score is not calculated. Other subscales remain valid and are still reported.

Instrument profile

Developer
Ewa M. Roos and colleagues
Institution
Lund University, Sweden
First published
1998
Custodian
koos.nu
Items
42
Response format
5-point Likert, scored 0–4
Score range
0 to 100
Direction
Higher score = better
Recall period
The last week
Completion time
About 10 minutes
Age range
Adults and adolescents (validated from roughly 13 years upward)
Regions
Knee
Conditions
Knee osteoarthritis, ACL injury, Meniscal injury, Post-traumatic knee injury
Procedures
ACL reconstruction, Meniscectomy, Total knee arthroplasty, Cartilage repair
Languages
English, Swedish, Spanish, German, French, Dutch, Chinese, 40+ validated translations
Test–retest (ICC)
0.75–0.93 across subscales
Internal consistency
Cronbach's alpha 0.71–0.95
Validity
Strong construct validity against the WOMAC, SF-36 and Lysholm.
Responsiveness
Highly responsive after ACL reconstruction and arthroplasty; Sport/Rec and QOL are the most responsive subscales in younger, active patients.
Ceiling effect
Notable ceiling effect in the ADL subscale in young, active populations — the KOOS-Sport/Rec and QOL subscales discriminate better in that group.
Floor effect
Floor effects in Sport/Rec among older patients with advanced osteoarthritis, many of whom cannot attempt the activities at all.

Normative values

Reference values from published cohorts, for comparison against the score you calculated.

PopulationAgeMeanSD
Healthy reference, no knee complaints18–3494–99 across subscales—
Healthy reference, no knee complaints55–7485–95 across subscales—
Knee osteoarthritis, pre-arthroplasty—Pain 35–45, QOL 25–35—

When to use the KOOS

Well suited to

  • Following ACL reconstruction, meniscal surgery or cartilage repair, where the Sport/Rec and QOL subscales capture change that shorter instruments miss.
  • Longitudinal tracking of knee osteoarthritis, including before and after arthroplasty.
  • Any setting where distinguishing pain from function from quality of life changes clinical decisions.

Limitations and poor fits

  • When a single summary figure is required for a registry — use the KOOS JR, which is validated as a single score, rather than averaging KOOS subscales.
  • When completion burden matters and only a global measure is needed — the KOOS-12 covers the same constructs in 12 items.
  • In young, highly active patients where only ADL is of interest, because of the ceiling effect.

KOOS compared with other instruments

Instruments measuring a related construct, with the practical difference between them.

InstrumentItemsRangeWhat it adds
IKDC180–100The IKDC Subjective Knee Evaluation Form is an 18-item patient-reported questionnaire covering knee symptoms, sports and daily activity and current knee function, whose raw total is transformed to a 0 to 100 score where 100 means no symptoms and no activity limitation — it requires permission from the AOSSM, so the items are not reproduced here.
Lysholm80–100The Lysholm Knee Scoring Scale is an eight-domain questionnaire that rates knee symptoms and function — limp, support, locking, instability, pain, swelling, stair climbing and squatting — on a 0 to 100 scale, where 95 and above is graded excellent, 84 to 94 good, 65 to 83 fair, and below 65 poor.

Copyright and permitted use

Published openly because it is the question every clinician and researcher asks before using an instrument, and almost nobody answers it.

Free to useRights holder: Ewa M. Roos

The KOOS is distributed free of charge by its developer for clinical and research use, and the questionnaire and scoring instructions are published openly at koos.nu.

Rights holder’s own page

References

  1. Roos EM, Roos HP, Lohmander LS, Ekdahl C, Beynnon BD. Knee Injury and Osteoarthritis Outcome Score (KOOS) — development of a self-administered outcome measure. Journal of Orthopaedic & Sports Physical Therapy. 1998.PMID 9699158
  2. Roos EM, Lohmander LS. The Knee injury and Osteoarthritis Outcome Score (KOOS): from joint injury to osteoarthritis. Health and Quality of Life Outcomes. 2003.doi:10.1186/1477-7525-1-64PMID 14613558
  3. Collins NJ, Misra D, Felson DT, Crossley KM, Roos EM. Measures of knee function. Arthritis Care & Research. 2011.doi:10.1002/acr.20632PMID 22588746
  4. Paradowski PT, Bergman S, Sundén-Lundius A, Lohmander LS, Roos EM. Knee complaints vary with age and gender in the adult population. BMC Musculoskeletal Disorders. 2006.doi:10.1186/1471-2474-7-38PMID 16670005
  5. Connelly JW, Galea VP, Rojanasopondist P, et al.. Patient acceptable symptom state at 1 and 3 years after total knee arthroplasty. Journal of Bone and Joint Surgery. 2019.doi:10.2106/JBJS.18.00233PMID 30801373

Editorial status

Not yet reviewedQueued for clinical review by Sam Tuffun, PT, DPT. Sign-off has not taken place — this is a placeholder assignment, not a completed review.