Knee Injury And Osteoarthritis Outcome Score (KOOS)

Assesses level of physical and functional impairment after knee and leg injury.

Find out more about the 5 territories analysed in the score and read instructions on how to interpret the result in the text below the calculator.

The knee injury and osteoarthritis outcome score evaluates 5 domains referring to symptoms, pain assessment, function and daily living, extreme function and overall quality of life.

This is aimed at providing an insight into the level of physical and functional impairment linked to knee and leg injury.

This is a score recommended in the assessment of patients suffering from: post traumatic osteoarthritis (OA), ACL (anterior cruciate ligament) or meniscus injury.

Each of the 42 items in the KOOS (divided in the 5 functional territories) are assessed on a variety of Likert based scales awarded a number of points from 0 to 4 (from no to severe impact).

The final score is correlated on a 0 to 100 scale (as percentage of total possible score achievable), where 0 means perceived extreme knee problems and 100 means no knee problems.


S1Do you have swelling in your knee?
S2Do you feel grinding, hear clicking or any other type of noise when your knee moves?
S3Does your knee catch or hang up when moving?
S4Can you straighten your knee fully?
S5Can you bend your knee fully?
S6How severe is your knee joint stiffness after first wakening in the morning?
S7How severe is your knee stiffness after sitting, lying or resting later in the day?

Pain while ...

P1How often do you experience knee pain?
P2Twisting/pivoting on your knee
P3Straightening knee fully
P4Bending knee fully
P5Walking on flat surface
P6Going up or down stairs
P7At night while in bed
P8Sitting or lying
P9Standing upright

Function, daily living (ADL)

A1Descending stairs
A2Ascending stairs
A3Rising from sitting
A5Bending to floor/pick up an object
A6Walking on flat surface
A7Getting in/out of car
A8Going shopping
A9Putting on socks/stockings
A10Rising from bed
A11Taking off socks/stockings
A12Lying in bed (turning over, maintaining knee position)
A13Getting in/out of bath
A15Getting on/off toilet
A16Heavy domestic duties (moving heavy boxes, scrubbing floors, etc)
A17Light domestic duties (cooking, dusting, etc)

Extreme function difficulty (sport/rec)

SP4Twisting/pivoting on your injured knee

Quality of life (QOL)

Q1How often are you aware of your knee problem?
Q2Have you modified your life style to avoid potentially damaging activities to your knee?
Q3How much are you troubled with lack of confidence in your knee?
Q4In general, how much difficulty do you have with your knee?
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Evaluation parameters

In order to assess the perceived physical and functional impairment caused by knee injury, a self-administered questionnaire consisting in 5 domains of function is applied.

■ The Symptoms domain refers to signs during the week before the assessment. Some items refer to joint stiffness which is a sensation of restriction or slowness in the ease with which the knee joint can be moved.

■ The Pain domain refer to the amount of knee pain experienced during the past week, while performing certain activities.

■ The Function, daily living domain contains questions referring to the ability to move around or look after one self.

■ The Extreme function domain refers to active or highly active physical function during sport and recreational activities.

■ Quality of Life domain refers to the perceived disruption caused by knee symptoms and impairment.

The KOOS is often employed in clinical studies, to assess the result of treatment or surgery or to monitor patient short or long term recovery. It has been successfully used in a range of knee injuries such as:

■ ACL (anterior cruciate ligament) injury;

■ Post traumatic osteoarthritis (OA);

■ Meniscus injury;

■ Chondral injury.


KOOS score interpretation

Each of the 6 functional domains consist of a different number of questions. Each question is assessed on a Likert scale (from 0 to 4):

■ Symptoms - 7 (S1 to S7);

■ Pain assessment - 9 (P1 to P9);

■ Function, daily living - 17 (A1 to A17);

■ Extreme function - 5 (SP1 to SP5);

■ Quality of life - 4 (Q1 to Q4).

Scores are calculated for each domain and then transformed into a percentage (score out of possible total score). This results in 5 answers from 0 to 100.

There are no specific interpretations and the general rule is that the lower the score, the greater the functional impairment caused by knee problems. Scores closer to 100 indicate very little to no knee problems.

An overall KOOS score is not calculated because its reliability has not been validated to this point.


About the study

KOOS is a self-administered questionnaire created by Roos et al. based on a study that started from the WOMAC Osteoarthritis Index. It has so far been used in patients of 13 to 79 years to assess short- and long-term patient-relevant outcomes after knee injury.

The study recorded a high test–retest reliability ranging from 0.6 to 0.97 across each of the six scales. The Minimal Detectable Change varies between 5 in Symptoms and 21.2 in Quality of Life. The overall Minimal Important Change was found to be around 8 to 10 points.

KOOS was found reliable in the evaluation of response to surgery and physical therapy of patients who underwent anterior cruciate ligament reconstruction.


Original reference

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. J Orthop Sports Phys Ther. 1998; 28(2):88-96.

Other references

1. Roos EM, Lohmander LS. The Knee injury and Osteoarthritis Outcome Score (KOOS): from joint injury to osteoarthritis. Health Qual Life Outcomes. 2003; 1: 64.

2. Kessler S, Lang S, Puhl W, Stove J. [The knee injury and osteoarthritis outcome score - a multifunctional questionnaire to measure outcome in knee arthroplasty] Z Orthop Ihre Grenzgeb. 2003;141:277–282.

Specialty: Rheumatology

System: Musculoskeletal

Objective: Evaluation

Type: Score

No. Of Items: 42

Year Of Study: 1998

Abbreviation: KOOS

Article By: Denise Nedea

Published On: May 22, 2017

Last Checked: May 22, 2017

Next Review: May 22, 2023