Knee Injury and Osteoarthritis Outcome Score – Physical Function Short Form (KOOS-PS)

Description

The Knee Injury and Osteoarthritis Outcome Score – Physical Function Short Form (KOOS-PS) is a concise, scientifically validated patient-reported outcome measure (PROM) developed to provide a rapid assessment of physical knee function in individuals with knee injuries and knee osteoarthritis. Derived from the original Knee Injury and Osteoarthritis Outcome Score (KOOS), the KOOS-PS was designed to reduce respondent burden while maintaining excellent psychometric properties and clinical sensitivity for evaluating functional limitations associated with knee disorders.

Unlike the full KOOS questionnaire, which evaluates five distinct health domains, the KOOS-PS focuses specifically on physical function, providing clinicians and researchers with an efficient method for assessing difficulties encountered during everyday mobility and more demanding physical activities.

The questionnaire evaluates the impact of knee pathology on functional performance, including pain-related movement limitations, mobility restrictions, and the ability to perform routine and physically demanding activities. Because of its brevity and strong measurement properties, the KOOS-PS has become widely used in orthopedics, sports medicine, physical therapy, rehabilitation medicine, rheumatology, and clinical research involving patients undergoing conservative treatment or surgical procedures such as total knee arthroplasty, anterior cruciate ligament (ACL) reconstruction, and other orthopedic interventions.

Data Analysis and Applications

Data collected using the KOOS-PS are analyzed using advanced psychometric and statistical methods to provide an objective evaluation of functional knee performance.

Participants complete the questionnaire using a five-point Likert response scale, indicating the degree of difficulty experienced while performing specific physical activities. Responses are transformed according to the standardized KOOS-PS scoring algorithm into a normalized score ranging from 0 to 100, allowing comparisons across patient populations and longitudinal follow-up assessments.

Psychometric evaluation of the KOOS-PS typically includes:

• Internal consistency, assessed using Cronbach’s alpha coefficient.

• Test–retest reliability, evaluating measurement stability over time.

• Construct validity, investigated through Exploratory Factor Analysis (EFA) and Confirmatory Factor Analysis (CFA).

• Convergent, discriminant, and criterion validity, established through comparisons with validated instruments such as the KOOS, WOMAC, Oxford Knee Score (OKS), SF-36, EQ-5D, and other measures of knee function and health-related quality of life.

In clinical research, KOOS-PS scores are commonly analyzed using:

• Descriptive statistics, including means, standard deviations, medians, and frequency distributions.

• Comparative analyses, such as independent-samples t-tests, Analysis of Variance (ANOVA), Mann–Whitney U tests, and Kruskal–Wallis tests, to compare functional outcomes among different patient groups.

• Correlation analyses, using Pearson and Spearman correlation coefficients to investigate associations between physical function and demographic or clinical variables.

• Multivariate statistical techniques, including linear regression, logistic regression, mediation and moderation analyses, and Structural Equation Modeling (SEM) to identify predictors of functional recovery, treatment outcomes, and health-related quality of life.

Purpose

The primary purpose of the KOOS-PS is to provide a rapid, reliable, and standardized assessment of physical knee function in individuals with knee injuries or osteoarthritis.

More specifically, the instrument is designed to:

• evaluate functional limitations associated with knee disorders;

• assess the severity of mobility impairment;

• monitor patient recovery following conservative or surgical treatment;

• evaluate rehabilitation outcomes;

• support clinical decision-making through standardized functional assessment;

• facilitate epidemiological and clinical research involving knee disorders.

Because of its short administration time and excellent measurement properties, the KOOS-PS is particularly suitable for routine clinical practice, large-scale outcome studies, and longitudinal follow-up of orthopedic patients.

Scoring

The KOOS-PS consists of 7 items assessing the patient’s ability to perform activities requiring knee function.

Each item is rated using a five-point Likert response scale, and responses are converted according to the standardized KOOS-PS scoring algorithm into a normalized score ranging from 0 to 100.

• Higher scores indicate better physical knee function, fewer functional limitations, and lower symptom burden.

• Lower scores indicate greater functional impairment, increased difficulty performing daily activities, and a more substantial impact of knee pathology on physical performance.

The KOOS-PS demonstrates excellent psychometric performance, including high internal consistency, construct validity, criterion validity, responsiveness to clinical change, and test–retest reliability, making it one of the most widely recommended short-form outcome measures for evaluating knee function in both clinical practice and research.

References

• Perruccio, A. V., Stefan Lohmander, L., Canizares, M., Tennant, A., Hawker, G. A., Conaghan, P. G., Roos, E. M., & Jordan, J. M. (2008). The Development of the KOOS-Physical Function Shortform (KOOS-PS): An OARSI/OMERACT Initiative. Osteoarthritis and Cartilage, 16(5), 542–550.

• Roos, E. M., & Lohmander, L. S. (2003). The Knee Injury and Osteoarthritis Outcome Score (KOOS): From Joint Injury to Osteoarthritis. Health and Quality of Life Outcomes, 1, 64.

• Collins, N. J., Prinsen, C. A. C., Christensen, R., Bartels, E. M., Terwee, C. B., & Roos, E. M. (2016). Knee Injury and Osteoarthritis Outcome Score (KOOS): Systematic Review of Measurement Properties. Osteoarthritis and Cartilage, 24(8), 1317–1329.

• Roos, E. M., Roos, H. P., Lohmander, L. S., Ekdahl, C., & Beynnon, B. D. (1998). Knee Injury and Osteoarthritis Outcome Score (KOOS): Development of a Self-Administered Outcome Measure. Journal of Orthopaedic & Sports Physical Therapy, 28(2), 88–96.