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KOOS - Knee injury and Osteoarthritis Outcome Score

The Knee injury and Osteoarthritis Outcome Score (KOOS) is a patient-reported outcome measure designed to assess the patient's opinion about their knee and associated problems. It evaluates five dimensions: Pain, Symptoms, Activities of Daily Living, Sport and Recreation Function, and Quality of Life.

What is the KOOS - Knee injury and Osteoarthritis Outcome Score?

The Knee injury and Osteoarthritis Outcome Score (KOOS) is a comprehensive, patient-reported outcome measure that evaluates your opinion about your knee and associated problems. It assesses five important areas: pain, other symptoms (like swelling and stiffness), function in daily living, function in sport and recreation, and knee-related quality of life. The KOOS has been validated in numerous languages and is widely used by clinicians and researchers to track knee health over time.

Scoring System

The KOOS uses a 5-point Likert scale (0-4) for each question: 0 = No problems, 1 = Mild, 2 = Moderate, 3 = Severe, 4 = Extreme problems. Each subscale score is calculated independently using the formula: Score = 100 - ((sum of items / number of items) × 100 / 4). This results in a 0-100 scale where 100 represents no problems and 0 represents extreme problems. Higher scores indicate better knee function. No total KOOS score is calculated; subscales remain independent for clinical interpretation.

General Information

Importance:
Common
Scoring:
Higher is Better
Time to Complete:
10 minutes
Pages:
5
Questions:
41
Licensed:
Yes

Clinical Information

Medical Specialties:
orthopaedics sports medicine rheumatology
Anatomic Areas:
knee
Indications:
knee osteoarthritis knee injury ACL injury meniscal injury post-knee surgery

Instructions

The KOOS takes approximately 10 minutes to complete and should be self-administered. Patients should answer based on their experiences over the past week. The questionnaire can be completed on paper, electronically, or via interview. All 42 items should be completed for valid subscale scoring, though missing data can be handled if >50% of items in a subscale are answered. Patients should be instructed to give their best answer even if they did not perform certain activities in the past week.

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KOOS - Knee injury and Osteoarthritis Outcome Score

The Knee injury and Osteoarthritis Outcome Score (KOOS) is a patient-reported outcome measure designed to assess the patient's opinion about their knee and associated problems. It evaluates five dimensions: Pain, Symptoms, Activities of Daily Living, Sport and Recreation Function, and Quality of Life.

Instructions:

The KOOS takes approximately 10 minutes to complete and should be self-administered. Patients should answer based on their experiences over the past week. The questionnaire can be completed on paper, electronically, or via interview. All 42 items should be completed for valid subscale scoring, though missing data can be handled if >50% of items in a subscale are answered. Patients should be instructed to give their best answer even if they did not perform certain activities in the past week.

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Pain

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Function, Daily Living

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Function, Sports and Recreational Activities

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Patient Watch Form - 10/31/2025

Detailed Scoring Methodology

The KOOS uses a 5-point Likert scale (0-4) for each question: 0 = No problems, 1 = Mild, 2 = Moderate, 3 = Severe, 4 = Extreme problems. Each subscale score is calculated independently using the formula: Score = 100 - ((sum of items / number of items) × 100 / 4). This results in a 0-100 scale where 100 represents no problems and 0 represents extreme problems. Higher scores indicate better knee function. No total KOOS score is calculated; subscales remain independent for clinical interpretation.

Assessment Subscales

Activities of Daily Living

Measures difficulty with daily activities including stairs, sitting/rising, walking, domestic duties, personal care, and mobility

Questions: 17
Score Range: 0-100
Quality of Life

Evaluates awareness of knee problem, lifestyle modifications, confidence in knee, and overall difficulty

Questions: 4
Score Range: 0-100
Pain

Assesses knee pain frequency and severity during various activities including walking, stairs, sitting, lying, and standing

Questions: 9
Score Range: 0-100
Symptoms

Evaluates swelling, stiffness (morning and later), mechanical symptoms (catching, clicking, grinding), and range of motion limitations

Questions: 7
Score Range: 0-100
Sport and Recreation Function

Assesses difficulties in sporting activities including squatting, running, jumping, twisting/pivoting, and kneeling

Questions: 5
Score Range: 0-100

Meaningful Change Threshold

A change of 8-10 points in any subscale score is considered clinically significant. Minimal clinically important difference (MCID) varies by subscale: Pain MCID ≈ 8-10 points, Symptoms MCID ≈ 7-10 points, ADL MCID ≈ 8-10 points, Sport/Rec MCID ≈ 9-11 points, QoL MCID ≈ 8-12 points.

About the Developers

The KOOS was developed by Dr. Ewa Roos, Dr. HP Roos, Dr. L Stefan Lohmander, Dr. Christina Ekdahl, and Dr. Bruce Beynnon between 1995-1998. Originally created at Lund University in Sweden and University of Vermont in the USA, the KOOS was designed as an extension of the WOMAC Osteoarthritis Index to evaluate short-term and long-term consequences of knee injury, particularly relevant for younger and more active patients.

Copyright Information

The KOOS is protected by international copyright. Permission for use must be obtained from the KOOS Development Group or through Mapi Research Trust. The questionnaire is freely available for clinical and research use with proper citation, but requires permission for commercial applications or electronic implementations. Contact: www.koos.nu or ePROVIDE™ platform.

Administration Instructions

The KOOS takes approximately 10 minutes to complete and should be self-administered. Patients should answer based on their experiences over the past week. The questionnaire can be completed on paper, electronically, or via interview. All 42 items should be completed for valid subscale scoring, though missing data can be handled if >50% of items in a subscale are answered. Patients should be instructed to give their best answer even if they did not perform certain activities in the past week.

Limitations & Considerations

The KOOS is self-reported and subject to patient perception and mood. It may not capture all aspects of knee function in highly active or athletic populations. The Sport/Recreation subscale may have ceiling effects in very active patients. Cultural and linguistic adaptations require validation. The questionnaire focuses on subjective symptoms and may not correlate directly with objective clinical measures or imaging findings.

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