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What it measures:

The Knee Injury and Osteoarthritis Outcome Score (KOOS) is a self-reported outcome measure assessing the patient's opinion about the health, symptoms, and functionality of their knee. It is a 42-item questionnaire, including 5 subscales: symptoms, pain, ADLs, sports/recreation, and quality of life. The maximum score a patient can achieve is 100, indicating no knee problems. The minimum score is zero, indicating severe knee problems. KOOS is used for any knee pathology and was found to be useful in assessing patients of various age populations, ranging from young to elderly adults.(1)

KOOS is an extension of the Western Ontario and McMaster Universities Arthritis Index (WOMAC).(2,3) WOMAC primarily focuses on hip and knee osteoarthritis, while KOOS is centered on the knee, which makes it better suited for the younger and more active population.(4)

KOOS subscales of sports/recreation and quality of life make it a more responsive measure than WOMAC or SF-36 in the younger and/or more active populations.(5)

KOOS has been used with a variety of pathologies and populations. Variations of KOOS listed below were developed to create an outcome measure that is specific for a population or condition. A short version of KOOS was developed as well. In addition to the variations listed below, KOOS has been translated and validated in many languages (ie, Spanish, Persian, Dutch).(1) Variations of KOOS and similar versions were also developed for the hip, neck, and foot/ankle areas.

Variations/revisions of KOOS:

KOOS-12: 12-item short form(6)

KOOS-PF: specific to patellofemoral syndrome(6)

KOOS-PS: physical function short form(6)

KOOS-Child: specific for children with knee injuries(6)

KOOS-JR: specific for joint replacement(6)

Similar outcome measures for other joints:

HOOS: Hip disability and Osteoarthritis Outcome Score(6)

NOOS: Neck OutcOme Score(6)

FAOS: Foot and Ankle Outcome Score(6)

ICF Domain(s):       

  • Body Structure and Function
  • Activity
  • Participation                                                    

ICF Categories:

  • Mobility: Walking & Moving Around
  • Changing & Maintaining Body Position
  • Carrying, Moving, & Handling Objects
  • Self-Care
  • Recreation and Leisure

Conditions and Test Variations Included in This Summary:

  • ACL tear/reconstruction( 1,7,8,9)
  • Meniscus injury(10)
  • Knee osteoarthritis(1,4,11,12)
  • Knee ligament injury(2,13)
  • Focal cartilage lesion(1,14-17)
  • Total knee arthroplasty(18-20 )
  • Joint replacement for osteoarthritis(4,11,7)
  • Normative data for healthy individuals(2)

The following is a review of KOOS. The summary includes psychometric properties of the original KOOS and its translated and validated versions in the following languages: Spanish,(13,19) Dutch,(8,11,18,21) French,(2) Persian,(7,10) and Swedish.(4)

Access Test:

Original KOOS Questionnaire

KOOS User Guide

KOOS Scoring

Clinical Insights

  • KOOS scores will have significant variation in individuals who are considered obese with BMI ranging from 35-66. (26) These individuals will have worse outcome scores in subscales regarding pain, activities of daily living, sport, and quality of life. (26 )
  • For patients with recent and ACL ruptures and reconstruction (within 1 year), the International Knee Documentation Committee Subjective Knee Form is considered to be more useful than KOOS. (8)
  • In patients with OA awaiting TKA, mean age of 71.3 years, KOOS may have better ability to predict improvement in the subscales of pain and sports/recreation than WOMAC. (4)
  • In patients with OA who had TKA, mean age of 71.3 years, KOOS is better in detecting improvements over time than WOMAC. (4)
  • Compared with WOMAC, KOOS is better adapted for younger, more active populations and is better in detecting smaller effect size from interventions, detecting changeover a longer period of time, and detecting change in physical function. (4)
  • KOOS is a validated and reliable outcome measure for elderly individuals with advanced osteoarthritis. (4)
  • KOOS is a validated and reliable outcome measure for people undergoing ACL reconstruction, with a mean age of 32 years. (5)
  • In patients with knee injuries and/or OA, age range from 18 to 84 years, age and gender matched reference values of KOOS are recommended to be used in evaluating the effects of interventions. (25)
  • A further evaluation of the clinimetric proper, ties in subgroups, such as age and gender, would be of great value to provide self-administered questionnaires for patient-specific subpopulations. (16)
  • The findings will have to be confirmed by further studies evaluating other subpopulations (eg, men and women, young and elderly) before generalizations are applicable. Comparison of the baseline data obtained in the 2 samples suggests that the instrument allows discrimination between patients with different levels of knee OA severity. (12)
  • A limitation of KOOS is it doesn't account for history of knee injury, disease, or general health, and it does not account for age, sex, and activity level. (2)
  • KOOS is sensitive in detecting clinical changes. (20)

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