The Knee Injury and Osteoarthritis Outcome Score, or KOOS, is a 42-item patient-reported outcome measure used to assess knee pain, symptoms, daily function, sport and recreation function, and knee-related quality of life. It can support monitoring and progress tracking for knee injury and osteoarthritis presentations, but it does not diagnose a condition, confirm pathology or clear someone for sport on its own.
Knee problems can affect walking, stairs, squatting, running, jumping, sport participation, work demands and confidence with movement.
The Knee Injury and Osteoarthritis Outcome Score, commonly called the KOOS, is a patient-reported outcome measure designed to capture the client’s own view of their knee symptoms, function and quality of life.
It is commonly used for:
knee injury monitoring
anterior cruciate ligament injury or reconstruction follow-up
meniscal injury monitoring
knee osteoarthritis
total knee replacement or knee arthroplasty follow-up
sport and recreation limitations
long-term progress tracking
research and clinical outcome reporting
The KOOS is a 42-item questionnaire with five separately scored subscales: Pain, Symptoms, Activities of Daily Living, Sport/Recreation and Knee-Related Quality of Life. Scores range from 0 to 100, where 100 represents no knee problems and 0 represents extreme knee problems.
Outcome measure: Knee Injury and Osteoarthritis Outcome Score
Abbreviation: KOOS
Body region: Knee
Type: Patient-reported outcome measure
Number of items: 42
Subscales: Pain, Symptoms, Activities of Daily Living, Sport/Recreation, Quality of Life
Score range: 0–100 for each subscale
Higher score means: Better perceived knee status
Lower score means: More pain, symptoms, limitation or quality-of-life impact
Related versions: KOOS-12, KOOS-PS, KOOS-Child
Best used for: Baseline assessment, reassessment, progress tracking and outcome reporting
Key limitation: KOOS does not diagnose a condition or determine clearance on its own
The KOOS is a knee-specific patient-reported outcome measure.
It was designed to assess short-term and long-term consequences of knee injury and knee osteoarthritis from the client’s perspective.
The five KOOS subscales are:
Pain
Other Symptoms
Activities of Daily Living
Sport and Recreation Function
Knee-Related Quality of Life
The KOOS is an extension of the WOMAC Osteoarthritis Index and was developed for use across knee injury and knee osteoarthritis contexts. Official KOOS resources also identify related versions including KOOS-12, KOOS Physical Function Short Form and KOOS-Child.
The KOOS is used because physical testing alone does not always show how a knee problem affects the client’s daily life, sport or confidence.
A client may show improving strength or range of motion but still report:
pain with stairs
difficulty squatting
swelling or stiffness after activity
poor confidence with running
reduced sport participation
fear around pivoting or landing
poor quality of life because of the knee
The KOOS can help professionals:
establish a baseline
identify which domains are most affected
monitor change over time
support client education
guide goal-setting conversations
compare symptoms and function across reassessments
combine client-reported outcomes with physical testing
improve reporting quality in Measurz
The KOOS should support assessment reasoning and progress tracking. It should not be used as a stand-alone diagnostic, treatment or clearance tool.
The Pain subscale captures knee pain during different activities and situations.
It may provide insight into pain during:
walking
stairs
sitting or lying
standing
twisting or pivoting
knee bending
The Symptoms subscale captures knee-related symptoms such as:
swelling
stiffness
restricted movement
grinding or clicking
mechanical symptoms
general symptom severity
The ADL subscale captures day-to-day function.
This may include:
walking
stairs
rising from sitting
bending to the floor
getting in and out of positions
routine daily tasks
The Sport/Recreation subscale captures higher-demand function.
This may include:
squatting
running
jumping
twisting
kneeling
sport participation
The Quality of Life subscale captures the broader impact of the knee problem.
This may include:
confidence
awareness of the knee
lifestyle impact
frustration
participation restriction
perceived long-term impact
The KOOS may be useful for:
exercise professionals
rehabilitation practitioners
strength and conditioning coaches
allied health support teams
performance professionals
movement assessment professionals
students learning outcome measures
professionals using Measurz or MAT for structured progress tracking
It may be relevant for clients with:
knee injury
ACL injury or reconstruction
meniscal injury
knee osteoarthritis
patellofemoral pain or symptoms
cartilage-related knee symptoms
post-operative knee recovery
persistent swelling, stiffness or pain
sport-related knee limitations
Use the KOOS when you want to understand how a knee problem affects the client’s pain, symptoms, function and quality of life.
It may be useful at:
initial assessment
onboarding
reassessment
post-injury monitoring
post-operative milestones
return-to-running planning
return-to-sport planning
knee osteoarthritis monitoring
discharge or progress review
The KOOS is most useful when repeated over time using the same version and scoring method.
Use caution when:
the client cannot complete the questionnaire independently
literacy, language or cognitive factors affect responses
the wrong language version is being used
the client has multiple body regions contributing to limitation
the client has not attempted the activities being scored
many items are missing
the score is being used as a pass/fail decision
the result is interpreted without physical assessment context
The KOOS should not be used to:
diagnose a condition
confirm injury
determine tissue healing
identify the exact cause of symptoms
clear someone for sport
replace professional judgement
replace medical assessment when needed
KOOS questionnaire
Official KOOS user guide or validated scoring resource
Measurz recording workflow
Client-reported symptom and function notes
Baseline and retest dates
Optional related physical tests, such as:
knee range of motion
knee swelling assessment
quadriceps strength testing
hamstring strength testing
single-leg squat
hop testing
balance testing
gait, running or sport assessment
Explain the purpose of the questionnaire before the client completes it.
Example wording:
“This questionnaire helps us understand how your knee is affecting your pain, symptoms, daily function, sport and quality of life. It does not diagnose the problem on its own, but it helps us monitor change over time.”
The KOOS can be completed:
on paper
digitally
independently
with assistance
before a session
during reassessment
as part of a Measurz workflow
Ask the client to:
answer based on their current knee problem
choose the response that best matches their experience
answer every item where possible
avoid overthinking each question
ask for clarification if they do not understand the wording
complete the same version at each retest
Record whether the KOOS was completed:
independently
digitally
on paper
verbally
with assistance
This matters because assistance, wording clarification or completion format may influence responses.
If help is required:
explain the instructions without leading the answer
avoid telling the client which response to choose
record that assistance was provided
use the same assistance approach at retest where possible
Do not guess missing responses.
Use the official KOOS scoring guidance for the version being used. If too many items are missing for a subscale, record that subscale as incomplete rather than creating an unreliable score. Official KOOS user guides are available through the KOOS website.
Each KOOS item is scored from 0 to 4.
Each subscale is transformed to a 0–100 score.
General scoring direction:
100: no knee problems
0: extreme knee problems
The five subscales should be interpreted separately rather than combined into one unsupported total score.
Retest at meaningful time points, such as:
baseline
after a training block
after a rehabilitation phase
pre-return to running
pre-return to sport
after a flare-up
after post-operative milestones
discharge or progress review
For consistency, record:
date
current activity level
recent flare-ups
recent training load
whether the client has returned to the activities being scored
any major changes in sport, work or daily demands
The KOOS is a self-report questionnaire, so it does not create physical testing risk.
However, a major worsening in score may support further assessment if the client reports:
severe deterioration
major quality-of-life impact
worsening function
severe swelling or pain
unexpected decline
new mechanical symptoms
The KOOS has five separate subscale scores.
Each subscale ranges from 0 to 100.
Higher scores indicate better perceived knee status.
Lower scores indicate more reported problems.
Pain: 0–100
Symptoms: 0–100
Activities of Daily Living: 0–100
Sport/Recreation: 0–100
Quality of Life: 0–100
A higher score may suggest:
less knee pain
fewer symptoms
better daily function
better sport or recreation function
better knee-related quality of life
improved confidence with knee-related activity
A lower score may suggest:
more pain
more symptoms
reduced daily function
reduced sport or recreation capacity
reduced confidence
greater knee-related quality-of-life impact
A KOOS score does not prove:
the diagnosis
the tissue source of symptoms
the severity of structural injury
readiness to return to sport
whether imaging is required
whether a specific intervention caused the change
Example wording:
“Your KOOS results suggest your daily function is improving, but your sport and quality-of-life scores are still more affected. This does not tell us exactly what structure is causing symptoms, but it helps us understand how your knee is affecting the activities that matter to you.”
For general fitness clients, KOOS can help show how knee symptoms affect:
walking
stairs
squatting
gym training
daily activity
recreational exercise
Interpretation cautions:
scores may change with recent activity
symptoms from other body regions may affect answers
sport items may be less relevant if the client does not participate in sport
For athletes, the Sport/Recreation and Quality of Life subscales are often especially important.
A client may score well on daily activities but still report limitations with:
running
jumping
cutting
landing
pivoting
confidence in competition
Interpretation should include sport-specific testing. A high KOOS score should not be treated as return-to-sport clearance on its own.
For older adults and people with knee osteoarthritis, KOOS may help monitor pain, stiffness, walking, stairs and knee-related quality of life.
Interpretation cautions:
other health conditions may affect scores
general strength and balance may influence function
sport subscales may be less relevant for some clients
broad reference values should be used cautiously
Standard KOOS is designed for adults. For children or adolescents, a specific child version, KOOS-Child, is available through official KOOS resources.
Consider:
age
reading level
comprehension
parent or guardian assistance
sport exposure
whether the questionnaire version is appropriate
KOOS is often used after ACL injury and reconstruction to monitor symptoms, function and knee-related quality of life.
Interpretation should include:
strength testing
hop testing
confidence measures
sport exposure
graft or surgical timeline where relevant
movement quality and workload progression
Meaningful thresholds may differ after ACL injury or meniscal injury, and systematic review evidence suggests thresholds should be selected based on the specific intervention and population.
For meniscal presentations, KOOS can help track pain, symptoms, function and sport limitation.
Interpretation should consider:
mechanical symptoms
swelling
range of motion
squat and kneeling tolerance
sport-specific pivoting demands
whether surgery has occurred
For knee osteoarthritis, KOOS can provide a broader view than pain alone by capturing symptoms, daily function, sport/recreation and quality of life.
Interpretation should consider:
flare-ups
comorbidities
body mass
physical activity exposure
medication changes
functional goals
For post-operative clients, KOOS can help track perceived recovery over time.
Interpretation should consider:
surgery type
healing stage
weight-bearing restrictions
expected post-operative symptoms
rehabilitation stage
medical or surgical guidance where relevant
Meaningful change values help interpret whether a score change is likely to matter.
Key terms:
MCID / MIC: the smallest change that may be meaningful to clients or professionals, depending on the method used
MDC: the amount of change likely needed to exceed measurement error
SEM: the estimated measurement error around a score
Responsiveness: the ability of the measure to detect change over time
PASS: a score threshold sometimes used to describe a patient acceptable symptom state
SCB: substantial clinical benefit, used in some surgical outcome studies
Meaningful change values vary by population, condition, subscale, intervention and method.
For ACL tear and traumatic meniscal injury, the OPTIKNEE systematic review identified meaningful thresholds for patient-reported outcomes after interventions, including KOOS-related thresholds. This supports using population-specific values rather than applying one universal KOOS change score to all clients.
For knee arthroplasty, post-2000 studies have examined MCID, PASS and substantial clinical benefit thresholds for KOOS-based scores, including KOOS Pain, KOOS-PS and KOOS Joint Replacement. These thresholds are useful only when the client population and outcome version match the study context.
When interpreting KOOS change:
compare each subscale to baseline
use population-specific MCID, MIC, MDC or SEM where available
avoid applying one universal threshold to every knee presentation
look for consistent improvement across relevant subscales
compare score change with client goals
check whether activity exposure has increased
consider pain, swelling, strength, range of motion and functional tests
Reported meaningful change values may vary by:
condition
age
surgery type
non-surgical versus surgical care
subscale
language version
follow-up timeframe
anchor method
baseline severity
When no matching value exists, interpretation should rely more heavily on:
baseline comparison
repeated measurement
client-reported change
physical assessment findings
training or activity exposure
professional judgement
Published KOOS reference values are available, but they should be applied carefully.
A 2023 national record-based study established reference values for KOOS and KOOS-12 because the measures were commonly used but lacked national record-based reference values to support interpretation.
A 2020 Dutch population study developed percentile curves for KOOS in a middle-aged population. The study reported that scores were generally good but were worse in women and with higher BMI, and concluded that percentile curves may be useful as benchmarks in research and clinical practice.
Reference values provide context, but interpretation should consider whether the reference population matches the client’s:
age
sex
country
health status
knee injury history
osteoarthritis status
BMI
activity level
sport or work demands
surgical history
Practical guidance:
Scores closer to 100 generally suggest fewer reported knee problems.
Lower scores suggest greater pain, symptoms, limitation or quality-of-life impact.
Sport/Recreation and Quality of Life may remain limited after ADL improves.
Population reference values provide context, not strict pass/fail thresholds.
The client’s own baseline is often the most useful comparison.
The KOOS has extensive post-2000 evidence supporting its use across knee injury, osteoarthritis and surgical populations.
A 2003 validation study comparing KOOS with WOMAC in total knee replacement concluded that KOOS was valid, reliable and responsive in that population, and that KOOS may provide improved validity compared with WOMAC while being at least as responsive.
A 2016 systematic review and meta-analysis synthesised evidence on KOOS measurement properties across knee injury and osteoarthritis populations, identifying 37 eligible studies and using COSMIN methods to assess methodological quality.
A 2024 clinimetric appraisal describes KOOS as a patient-completed questionnaire for young, middle-aged and older adults with knee injuries and/or osteoarthritis, and notes that KOOS is available in many languages and recommended in Australian knee osteoarthritis clinical practice guidance.
Reliability and validity are stronger when:
the correct KOOS version is used
the same scoring method is repeated
all relevant items are completed
subscales are interpreted separately
the correct language version is used
retesting occurs at meaningful time points
results are interpreted alongside physical and functional assessment
Interpret cautiously when:
many items are missing
the client has not attempted sport or work tasks yet
only one subscale changes slightly
the change is smaller than known measurement error or meaningful change
symptoms are strongly influenced by a recent flare-up
the score is being used without objective assessment context
Common errors include:
treating KOOS as a diagnosis
using KOOS as a return-to-sport clearance tool
combining subscales into one unsupported total score
ignoring missing items
using inconsistent scoring methods
not recording the version used
not recording the completion date
comparing scores without considering activity exposure
over-interpreting small changes
using reference values as strict pass/fail cut-offs
Limitations include:
self-report can be influenced by mood, expectations and recent activity
sport items may be less meaningful if the client has not returned to sport
scores do not identify the exact physical cause of symptoms
meaningful change values vary by condition and population
reference values may not match the client’s age, activity level or condition
KOOS should be paired with physical tests and client goals
The KOOS may help professionals:
document baseline knee status
identify whether pain, symptoms, sport or quality of life are most affected
track change over time
monitor post-injury or post-surgical recovery
support knee osteoarthritis monitoring
support goal setting
improve client education
communicate progress with a broader team
strengthen Measurz reports
For athletes, KOOS can help identify whether sport and quality-of-life concerns remain despite improvement in daily function.
For general population clients, KOOS can help track walking, stairs, squatting, swelling, pain and participation.
For knee osteoarthritis, it can help monitor how symptoms affect function and quality of life over time.
For Measurz users, KOOS is most useful when combined with objective measures such as:
knee range of motion
knee swelling assessment
quadriceps strength
hamstring strength
single-leg squat
hop testing
balance testing
gait or running assessment
Record:
outcome measure name: Knee Injury and Osteoarthritis Outcome Score / KOOS
version used: KOOS, KOOS-12, KOOS-PS, KOOS-Child or other
date completed
completion method: paper, digital, interview or assisted
language/version used
condition or presentation being tracked
side involved: left, right or bilateral
Pain subscale score
Symptoms subscale score
ADL subscale score
Sport/Recreation subscale score
Quality of Life subscale score
score range: 0–100
direction of scoring: higher score indicates better status
missing items, if any
assistance provided, if any
current pain score, if relevant
current symptoms
current activity or sport exposure
key functional limitations
confidence or participation goals
baseline comparison
MCID/MDC/MIC/PASS comparison where supported
related physical assessment findings
interpretation notes
retest date
referral or further assessment notes where appropriate
Record whether the main limitation appears to be:
pain dominant
symptom or swelling dominant
daily function limitation
sport/recreation limitation
quality-of-life limitation
mixed presentation
unclear due to incomplete responses
This improves:
repeatability
communication
client education
assessment reasoning
monitoring over time
team consistency
reporting quality
The KOOS measures self-reported knee pain, symptoms, daily function, sport and recreation function, and knee-related quality of life.
The full KOOS has 42 items across five subscales.
Each subscale is converted to a 0–100 score. A higher score indicates better knee status.
KOOS is usually interpreted using five separate subscale scores rather than one combined total score.
No. KOOS does not diagnose a condition. It helps measure the client’s perceived symptoms, function and quality-of-life impact.
Meaningful change depends on the population, condition, subscale and intervention. Use MCID, MIC, MDC, SEM, PASS or SCB values only when they match the client group and KOOS version.
KOOS can support return-to-sport reasoning, especially the Sport/Recreation and Quality of Life subscales, but it should not be the only clearance measure.
It can be repeated at baseline, reassessment, after a training or rehabilitation phase, after surgery milestones and at key return-to-activity points.
KOOS is a 42-item knee-specific patient-reported outcome measure.
It includes Pain, Symptoms, ADL, Sport/Recreation and Quality of Life subscales.
Each subscale is scored from 0 to 100.
Higher scores indicate better perceived knee status.
KOOS does not diagnose a condition or clear a client for sport.
Meaningful change values should be matched to the population, subscale and context.
Published reference values are available, but they should be used as context rather than strict pass/fail standards.
Measurz should record each subscale, version, completion method, side, baseline comparison, related findings and retest plan.
Collins, N. J., & Mills, K. (2024). Clinimetrics: The Knee injury and Osteoarthritis Outcome Score (KOOS). Journal of Physiotherapy. https://doi.org/10.1016/j.jphys.2024.11.011
Macri, E. M., Young, J. J., Ingelsrud, L. H., Khan, K. M., Terluin, B., Juhl, C. B., Whittaker, J. L., Culvenor, A. G., Crossley, K. M., & Roos, E. M. (2022). Meaningful thresholds for patient-reported outcomes following interventions for anterior cruciate ligament tear or traumatic meniscus injury: A systematic review for the OPTIKNEE consensus. British Journal of Sports Medicine, 56(24), 1432–1444.
Mills, K., et al. (2023). Knee injury and Osteoarthritis Outcome Score (KOOS) and KOOS-12: National record-based reference values. The Knee. https://doi.org/10.1016/j.knee.2023.06.001
Roos, E. M., & Toksvig-Larsen, S. (2003). Knee injury and Osteoarthritis Outcome Score (KOOS): Validation and comparison to the WOMAC in total knee replacement. Health and Quality of Life Outcomes, 1, 17. https://doi.org/10.1186/1477-7525-1-17
Roos, E. M. (2023). 30 years with the Knee injury and Osteoarthritis Outcome Score (KOOS). Osteoarthritis and Cartilage. https://doi.org/10.1016/j.joca.2023.09.007
Salavati, M., et al. (2016). Knee Injury and Osteoarthritis Outcome Score (KOOS): Systematic review and meta-analysis of measurement properties. Osteoarthritis and Cartilage, 24(8), 1317–1329. https://doi.org/10.1016/j.joca.2016.03.010
Loef, M., Kroon, F. P. B., Böhringer, S., Roos, E. M., Rosendaal, F. R., & Kloppenburg, M. (2020). Percentile curves for the Knee injury and Osteoarthritis Outcome Score in the middle-aged Dutch population. Osteoarthritis and Cartilage. https://doi.org/10.1016/j.joca.2020.07.013
