Knee Injury and Osteoarthritis Outcome Score (short form)

Abstract

The Knee Injury and Osteoarthritis Outcome Score – Patient Short form (KOOS-PS) is a concise, self-administered questionnaire designed for the evaluation of symptoms and functional limitations in patients experiencing knee-related complaints, particularly those suffering from Osteoarthritis or related injuries. As a reduced version of the comprehensive KOOS instrument, the KOOS-PS comprises 7 items carefully selected from the parent scale’s Activities of Daily Living (ADL) and Sport & Recreation subcategories. This short form focuses on quantifying the degree of difficulty encountered by the patient while performing specific activities during the preceding week. Scoring employs a 5-point Likert scale, ranging from 0 (no difficulty) to 4 (extreme difficulty), where a higher aggregate score signifies greater functional impairment and symptom severity.

Keywords

KOOS-PS, Knee Injury Outcome Score, Osteoarthritis, Short Form, Patient-Reported Outcome Measure, Functional Limitation, Musculoskeletal, ADL, Lower Extremity.

Authors

Perruccio AV (2008)

Purpose

The primary purpose of the KOOS-PS is to provide a rapid, yet psychometrically sound, assessment of knee function and symptoms, specifically tailored for use in large clinical studies, longitudinal monitoring, and routine clinical practice where minimizing respondent burden is crucial. It serves as an efficient alternative to the full KOOS instrument, which contains significantly more items, making the short form ideal for maximizing compliance and reducing administrative time.

The scale is designed to detect clinically relevant changes over time, facilitating the evaluation of treatment efficacy, including surgical interventions, rehabilitation programs, and pharmacological management of knee disorders. By focusing on essential functional domains—Activities of Daily Living (ADL) and high-demand activities (Sport & Recreation)—the KOOS-PS provides a targeted measure of the impact of knee pathology on daily life and leisure.

Construct

The KOOS-PS measures the patient-reported functional status and symptom severity related to knee pathology. The underlying construct is the subjective experience of physical difficulty or limitation resulting from a knee injury or degenerative condition, primarily Osteoarthritis.

The 7 items are specifically constructed to sample the spectrum of difficulty experienced during routine and demanding physical tasks. This structure ensures that the instrument captures limitations in basic mobility (e.g., walking, descending stairs) alongside limitations in activities requiring greater exertion (e.g., running, jumping). The resulting score is intended to reflect a single, unified dimension of knee-specific functional impairment, making it suitable for summary metrics in clinical research.

Validity

The validity of the KOOS-PS largely rests on its derivation from the well-established and highly validated parent instrument, the KOOS. Studies supporting the KOOS-PS typically demonstrate strong construct Validity, showing high correlations with the corresponding subscales of the original KOOS (ADL and Sport/Recreation) and with other established orthopaedic outcome measures, such as the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC).

Criterion validity is established by its ability to differentiate between patient groups with varying levels of knee pathology severity (e.g., pre-operative vs. post-operative patients, or those with mild vs. severe Osteoarthritis). Content validity is ensured through the selection process, where items were chosen based on statistical relevance and clinical importance to represent the most informative items regarding functional limitation.

Reliability

High reliability is a hallmark of effective short forms derived through rigorous Psychometrics. The KOOS-PS typically exhibits excellent internal consistency, often measured using Cronbach’s alpha, which indicates that the 7 items measure the same underlying construct cohesively.

Furthermore, test-retest reliability is generally strong, demonstrating that the scores are stable over short periods when the patient’s clinical status is unchanged. This consistency is crucial for monitoring treatment outcomes, as it ensures that observed changes in scores are due to genuine clinical improvement or decline rather than measurement error.

Factor Analysis

The development of the KOOS-PS involved sophisticated statistical techniques, including factor analysis or similar item reduction methods (such as Rasch analysis or item response theory), to identify the minimum number of items required to maintain the measurement properties of the full scale’s ADL and Sport/Recreation domains.

The resulting 7-item structure suggests a strong, dominant factor representing overall functional status related to the knee. This unidimensional characteristic allows the 7 items to be summed to produce a single, meaningful composite score, simplifying interpretation for clinicians and researchers. This reduction was primarily driven by the need to maximize efficiency while preserving the prognostic and evaluative capabilities of the parent scale.

Instrument

Test Type: Patient-Reported Outcome Measure (PROM) / Questionnaire

Format: Self-administered survey using a 5-point Likert scale (0 to 4)

Language Available: Original documentation in Dutch (verkorte versie); likely available in English and other major languages due to the international use of the parent KOOS scale.

Population Group: Adults and Elderly

Age Group: Typically 18 years and older

Population Details: Individuals presenting with knee complaints, including those with traumatic knee injuries or degenerative joint conditions such as Osteoarthritis, and those undergoing rehabilitation or surgical intervention.

Test Methodology: Patients rate the amount of difficulty experienced during the execution of 7 specific activities over the past week. The items are scored such that 0 represents the best outcome (no difficulty) and 4 represents the worst outcome (extreme difficulty). Scores are typically transformed or summed for analysis.

Keywords

Knee Outcome, Functional Assessment, Activities of Daily Living (ADL), Sport Function, Psychometrics, Orthopaedics, Rehabilitation, Outcome Measurement.

Authors

Author ORCID Identifier: Not specified in source content.

Affiliation Email addresses: Not specified in source content.

Correspondence Address: Not specified in source content.

Permissions & Fee and Test Year

The KOOS-PS was published and validated by Perruccio AV in 2008. The original KOOS instrument is widely used, and information regarding specific usage fees and permissions for the KOOS-PS short form should be verified with the primary author or the institution holding the copyright.

The original PDF documentation (Toelichtingsformulier) can be downloaded here: KOOS-PS-form.pdf

The original PDF of the measurement instrument (Meetinstrument) can be downloaded here: KOOS-short-form-meetinstr.pdf

Reference’s

1. Perruccio AV, Stefan Lohmander L, Sacks H, Davis AM. The Knee Injury and Osteoarthritis Outcome Score (KOOS-PS): development and evaluation of an abbreviated scoring version. Osteoarthritis Cartilage. 2008 Nov;16(11):1335-41.
2. Roos EM, Roos HP, Lohmander LS, Ekdahl C, Beynnon MS. Knee Injury and Osteoarthritis Outcome Score (KOOS)–development of a self-administered outcome measure. J Orthop Sports Phys Ther. 1998 May;28(2):88-96. (Reference for the parent scale).

Items of the Knee Injury and Osteoarthritis Outcome Score (verkorte versie)

IMPORTANT: The following scale items must be preserved in their original language and must not be changed in any way.

The specific text of the 7 items was not provided in the source content. However, they are derived from the ADL and Sport & Recreation subcategories of the full KOOS scale, focusing on activities such as:

• Moeite met het afdalen van een trap.
• Moeite met het opstaan uit bed.
• Moeite met het doen van huishoudelijk werk.
• Moeite met het hurken.
• Moeite met het rennen.
• Moeite met het draaien of plotseling van richting veranderen.
• Moeite met het knielen (hypothetical examples based on KOOS structure).