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Ann Rehabil Med > Volume 47(6); 2023 > Article
Kim: Patient-Reported Outcome Measure of Knee Function: Knee Injury and Osteoarthritis Outcome Score (KOOS)
A plethora of instruments have been developed to assess function in patients with knee problems. These measurements have focused on patient-reported measures from the patient’s perspective rather than clinician-based measures because of superior validity [1]. Grounded in the psychometric properties such as reliability, validity, and responsiveness, recommended patient-reported measures include the International Knee Documentation Committee (IKDC) Subjective Knee Form, Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), Knee Injury and Osteoarthritis Outcome Score (KOOS), Lysholm Knee Scoring Scale, Cincinnati Knee Rating System, Activity Rating Scale, Knee Outcome Survey Activities of Daily Living Scale, and Oxford Knee Score [1,2]. The IKDC Subjective Knee Form, in particular, was instituted to standardize international documentation of the evaluation after knee surgery or treatment and has strengths in being responsive to change in surgical interventions [2,3]. The WOMAC, initially developed in 1982, was designed to evaluate the progression of disease or efficacy of treatments in patients with knee or hip osteoarthritis (OA). It comprises three domains: pain severity during various positions or movements, severity of joint stiffness, and difficulty performing daily functional activities, with 5, 2, and 17 items, respectively. The Likert version is rated on 5 levels, with scores ranging from 0 (“none”) to 4 (“extreme”). Cumulative scores for each domain range from 0–20 for pain, 0–8 for stiffness, and 0–68 for physical function, with higher scores indicating a more severe condition. Self-administered or interview-administered questionnaire takes 5–10 minutes [4,5]. Its psychometric evidence is sufficiently reliable and valid for use in clinical and research setting [1,2,4]. A Korean version of the WOMAC has been authenticated for reliability, validity, and responsiveness [6]. Notably, items from the three WOMAC sub-types are incorporated into the KOOS.
The KOOS, developed based on the WOMAC, offers patient-reported outcome measures to evaluate both short and long-term outcomes. Suitable for assessing knee injuries and/or OA across various age groups, it also gauges the course of the disease and the effect of treatments, interventions, and surgeries [7]. The self-administered KOOS evaluates 5 domains: Pain (9 items); other Symptoms (7 items); Activities of Daily Living (ADL) (17 items); Sport and Recreation function (5 items); and knee-related Quality of Life (4 items) [8]. The KOOS, added to Domains from WOMAC, has been shown in previous studies to be more responsive and sensitive than WOMAC in younger or more active elderly [9,10]. Subsequently, through Rasch analysis, the KOOS Physical Function Short Form (KOOS-PS) was derived from Sport and Recreation function and knee-related Quality of Life subscales of the KOOS, and could quickly evaluates the difficulty level of seven physical functions (rising from bed, putting on socks/stockings, rising from sitting, bending to the floor, twisting/pivoting on injured knee, kneeling, and squatting) over recent weeks due to knee pain. All items of KOOS and KOOS-PS are rated on 5-point Likert scale scored from 0–4. The raw score is the sum of 7 items, and is converted to a score of 0 to 100 using a conversion chart or program. The lower the score, the worse. The KOOS takes 8–10 minutes to complete, while the KOOS-PS takes about 2 minutes [2,8,11]. Although the Sport and Recreation function is more valid for younger patients and ADL subscale for elderly, KOOS has adequate internal consistency, test-retest reliability and construct validity for young and old patients with knee injuries and OA [2,8]. The Korean version of KOOS, as a patient-centric clinical measure for knee injury treatments, has also been verified for validity, reliability and responsiveness [12]. National record-based reference values for KOOS subscale were pain 85.3 (95% confidence interval [95% CI], 84.6–85.9), symptoms 85.1 (95% CI, 84.5–85.8), ADL 86.7 (95% CI, 86.0–87.3), Sport and Recreation function 70.9 (95% CI, 69.8–72.0), and QOL 74.9 (95% CI, 73.9–75.8) [13]. In previous study that confirmed changes in KOOS and WOMAC scores according to patients’ age, sex, and BMI in 714 healthy populations, older subjects had a worse score on the ADL and Sport and Recreation function, especially “Sport and Recreation function subscale” [14]. The minimal detectable change for KOOS subscales ranges from 6–12 for knee injuries and from 13.4–21.1 for knee OA, 14.3–19.6 for younger individuals, and >20 for older individuals [2,8]. The minimal important changes in KOOS after rehabilitation after total knee arthroplasty in 148 patients were 16.7 for Pain (sensitivity, 83%; specificity, 82%), 10.7 for Symptoms (sensitivity, 80%; specificity, 80%), and 18.4 for ADL (sensitivity, 82%; specificity, 82%), 12.5 for Sport and Recreation function (sensitivity, 96%; specificity, 78%), and 15.6 for Quality of Life (sensitivity, 88%; specificity, 67%) [15].
In summary, the KOOS was developed based on WOMAC to measure not only knee OA but also various age groups and knee injury. Both KOOS and WOMAC possess robust psychometric evidence, making them suitable for clinical and research outcomes. While the KOOS is more time-consuming than the WOMAC, the burden on respondents is minimal. The KOOS, which integrates the three WOMAC sub-scales, offers comparability with prior WOMAC-based research and may be more advantageous for younger demographics, those with high physical activity levels, or interventions primarily focused on physical function (Table 1). However, missing data might arise in the high level of ADL and Sport and Recreation function subscales for older or less physically active individuals. When selecting an appropriate patient-reported outcome measure of knee function in clinical and research settings, factors like the patient’s age, physical activity level, disease characteristics, and intervention types should be considered.


No potential conflict of interest relevant to this article was reported.



Table 1.
Domains in the WOMAC and KOOS and their respective scoring
Domains (items) Pain (5) Pain (9)
Joint stiffness (2) Other Symptoms (7)
Daily functional activities (17) Activities of Daily Living (17)
Sport and Recreation (5)
Knee-related Quality of Life (4)
Score range 5-Point Likert scale (0–4)
Cumulative scores Cumulative scores,
Pain (0–20) then converted to 0%–100%
Stiffness (0–8)
Physical function (0–68)
The higher the score, the worse The lower the score, the worse
Time (min) 5–10 8–10

WOMAC, Western Ontario and McMaster Universities Osteoarthritis Index; KOOS, Knee Injury and Osteoarthritis Outcome Score.


1. Wang D, Jones MH, Khair MM, Miniaci A. Patient-reported outcome measures for the knee. J Knee Surg 2010;23:137-51.
crossref pmid
2. Collins NJ, Misra D, Felson DT, Crossley KM, Roos EM. Measures of knee function: International Knee Documentation Committee (IKDC) Subjective Knee Evaluation Form, Knee Injury and Osteoarthritis Outcome Score (KOOS), Knee Injury and Osteoarthritis Outcome Score Physical Function Short Form (KOOS-PS), Knee Outcome Survey Activities of Daily Living Scale (KOS-ADL), Lysholm Knee Scoring Scale, Oxford Knee Score (OKS), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), Activity Rating Scale (ARS), and Tegner Activity Score (TAS). Arthritis Care Res (Hoboken) 2011;63(Suppl 11): S208-28.
crossref pmid pmc
3. Higgins LD, Taylor MK, Park D, Ghodadra N, Marchant M, Pietrobon R, et al. Reliability and validity of the International Knee Documentation Committee (IKDC) subjective knee form. Joint Bone Spine 2007;74:594-9.
crossref pmid
4. McConnell S, Kolopack P, Davis AM. The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC): a review of its utility and measurement properties. Arthritis Rheum 2001;45:453-61.
crossref pmid
5. Bellamy N, Buchanan WW, Goldsmith CH, Campbell J, Stitt LW. Validation study of WOMAC: a health status instrument for measuring clinically important patient relevant outcomes to antirheumatic drug therapy in patients with osteoarthritis of the hip or knee. J. Rheumatol 1988;15:1833-40.
6. Bae SC, Lee HS, Yun HR, Kim TH, Yoo DH, Kim SY. Cross-cultural adaptation and validation of Korean Western Ontario and McMaster Universities (WOMAC) and Lequesne osteoarthritis indices for clinical research. Osteoarthritis Cartilage 2001;9:746-50.
crossref pmid
7. Roos EM, Roos HP, Lohmander LS, Ekdahl C, Beynnon BD. Knee Injury and Osteoarthritis Outcome Score (KOOS)--development of a self-administered outcome measure. J Orthop Sports Phys Ther 1998;28:88-96.
crossref pmid
8. Collins NJ, Prinsen CA, Christensen R, Bartels EM, Terwee CB, Roos EM. Knee Injury and Osteoarthritis Outcome Score (KOOS): systematic review and meta-analysis of measurement properties. Osteoarthritis Cartilage 2016;24:1317-29.
crossref pmid
9. Roos EM, Roos HP, Lohmander LS. WOMAC Osteoarthritis Index--additional dimensions for use in subjects with post-traumatic osteoarthritis of the knee. Western Ontario and MacMaster Universities. Osteoarthritis Cartilage 1999;7:216-21.
10. Roos EM, Toksvig-Larsen S. Knee injury and Osteoarthritis Outcome Score (KOOS) - validation and comparison to the WOMAC in total knee replacement. Health Qual Life Outcomes 2003;1:17.
pmid pmc
11. Perruccio AV, Stefan Lohmander L, Canizares M, Tennant A, Hawker GA, Conaghan PG, et al. The development of a short measure of physical function for knee OA KOOS-Physical Function Shortform (KOOS-PS) - an OARSI/OMERACT initiative. Osteoarthritis Cartilage 2008;16:542-50.
crossref pmid
12. Seo SS, Chung KC, Kim YB. Assessment of validity, reliatility and responsiveness of Korean Knee injury and Osteoarthritis Outcome Score (KOOS) for the knee injury. J Korean Orthop Assoc 2006;41:441-53.
crossref pdf
13. Larsen P, Rathleff MS, Roos EM, Elsoe R. Knee injury and osteoarthritis outcome score (KOOS) - national record-based reference values. Knee 2023;43:144-52.
crossref pmid
14. Marot V, Murgier J, Carrozzo A, Reina N, Monaco E, Chiron P, et al. Determination of normal KOOS and WOMAC values in a healthy population. Knee Surg Sports Traumatol Arthrosc 2019;27:541-8.
crossref pmid pdf
15. Monticone M, Ferrante S, Salvaderi S, Motta L, Cerri C. Responsiveness and minimal important changes for the Knee Injury and Osteoarthritis Outcome Score in subjects undergoing rehabilitation after total knee arthroplasty. Am J Phys Med Rehabil 2013;92:864-70.
crossref pmid
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