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OrthoMeasure

Patient-reported outcome measure

FAOS Calculator

Foot and Ankle Outcome Score

The FAOS is a 42-item patient-reported questionnaire adapted from the KOOS that scores foot and ankle problems as five separate subscales — Symptoms, Pain, Activities of Daily Living, Sport and Recreation, and Quality of Life — each from 0 (extreme problems) to 100 (no problems).

Free to use42 items~10 min0–100, higher is better

Symptoms

These questions should be answered thinking of your foot/ankle symptoms during the last week.

1Do you have swelling in your foot/ankle?
2Do you feel grinding, hear clicking or any other type of noise when your foot/ankle moves?
3Does your foot/ankle catch or hang up when moving?
4Can you straighten your foot/ankle fully?
5Can you bend your foot/ankle fully?

Stiffness

The following questions concern the amount of joint stiffness you have experienced during the last week in your foot/ankle. Stiffness is a sensation of restriction or slowness in the ease with which you move your foot/ankle joint.

6How severe is your foot/ankle joint stiffness after first wakening in the morning?
7How severe is your foot/ankle stiffness after sitting, lying or resting later in the day?

Pain

What amount of foot/ankle pain have you experienced the last week during the following activities?

8How often do you experience foot/ankle pain?
9Twisting/pivoting on your foot/ankle
10Straightening foot/ankle fully
11Bending foot/ankle fully
12Walking on flat surface
13Going up or down stairs
14At night while in bed
15Sitting or lying
16Standing upright

Function, daily living

The following questions concern your physical function. By this we mean your ability to move around and to look after yourself. For each of the following activities please indicate the degree of difficulty you have experienced in the last week due to your foot/ankle.

17Descending stairs
18Ascending stairs
19Rising from sitting
20Standing
21Bending to floor/pick up an object
22Walking on flat surface
23Getting in/out of car
24Going shopping
25Putting on socks/stockings
26Rising from bed
27Taking off socks/stockings
28Lying in bed (turning over, maintaining foot/ankle position)
29Getting in/out of bath
30Sitting
31Getting on/off toilet
32Heavy domestic duties (moving heavy boxes, scrubbing floors, etc.)
33Light domestic duties (cooking, dusting, etc.)

Function, sports and recreational activities

The following questions concern your physical function when being active on a higher level. Please answer each question indicating the degree of difficulty you have experienced in the last week due to your foot/ankle.

34Squatting
35Running
36Jumping
37Twisting/pivoting on your injured foot/ankle
38Kneeling

Quality of Life

39How often are you aware of your foot/ankle problem?
40Have you modified your life style to avoid potentially damaging activities to your foot/ankle?
41How much are you troubled with lack of confidence in your foot/ankle?
42In general, how much difficulty do you have with your foot/ankle?

What the FAOS score means

FAOS scores run from 0 to 100, where a higher score is better. The bands below are conventional reporting categories, not diagnostic cut-offs.

  • Extreme problems0–24
  • Severe problems25–49
  • Moderate problems50–74
  • Mild problems75–89
  • No to minimal problems90–100

Clinically important thresholds

A change in score only matters if it exceeds the smallest difference patients actually notice. Every threshold below is reported with the population it was derived in — a threshold quoted without its population is not usable.

TypeValueSubscalePopulationFollow-upSource
MCID10 pointsAll subscalesAnkle disorders, by analogy with the KOOS—Roos EM 2001
MDC10–20 points depending on subscale—Chronic ankle instability—Sierevelt IN 2018

MCID is the smallest change a patient perceives as meaningful. PASS is the score above which patients consider their state acceptable. SCB is a substantial rather than minimal benefit. MDC is the smallest change exceeding measurement error.

How the score is calculated

Stated in full so the calculation can be independently checked, and reproduced by hand if needed.

Each item is scored 0 to 4, where a higher raw score means worse symptoms. For each of the five subscales the mean of that subscale’s item scores is calculated, then transformed to a 0–100 scale with the formula: score = 100 − (mean item score × 100 ÷ 4). A score of 100 indicates no problems and 0 indicates extreme problems. The five subscale scores are reported separately and are not averaged into a single total.

Missing data

If no more than two items in a subscale are missing, the mean of the observed items in that subscale is substituted for the missing values. If more than two items in a subscale are missing, that subscale score is not calculated; the remaining subscales stay valid and are still reported.

Instrument profile

Developer
Ewa M. Roos and colleagues
Institution
Lund University, Sweden
First published
2001
Custodian
koos.nu
Items
42
Response format
5-point Likert, scored 0–4
Score range
0 to 100
Direction
Higher score = better
Recall period
The last week
Completion time
About 10 minutes
Age range
Adults
Regions
Foot & Ankle
Conditions
Ankle instability, Ankle osteoarthritis, Ankle sprain, Achilles tendinopathy, Hallux valgus, Ankle fracture
Procedures
Ankle ligament reconstruction, Ankle arthrodesis, Total ankle arthroplasty, Ankle fracture fixation
Languages
English, Swedish, Dutch, German, Persian, Turkish, Chinese
Test–retest (ICC)
0.86–0.92 across subscales
Internal consistency
Cronbach's alpha 0.78–0.96
Validity
Adapted directly from the KOOS with the same structure and scoring. Content validity for forefoot problems is weaker than for the ankle, because several items are knee-derived.
Responsiveness
Responsive after ankle ligament reconstruction and ankle fracture. The Sport/Rec and QOL subscales carry most of the signal in active patients.
Ceiling effect
Ceiling effect in the ADL subscale in patients with isolated forefoot pathology, many of whom have no difficulty with the listed activities.

Normative values

Reference values from published cohorts, for comparison against the score you calculated.

PopulationAgeMeanSD
Healthy reference, no foot or ankle complaint—90–100 across subscales—
Chronic ankle instability—Sport/Rec 45–60—

When to use the FAOS

Well suited to

  • Ankle instability, ankle osteoarthritis and ankle fracture follow-up, where the five-subscale structure separates pain from function from quality of life.
  • Studies wanting direct structural comparability with KOOS and HOOS data.

Limitations and poor fits

  • Isolated forefoot pathology such as hallux valgus, where several items are irrelevant and the FAAM or a forefoot-specific measure fits better.
  • When a single summary score is required — the FAOS has no validated total.
  • Where completion burden matters; the FAAM is 29 items and the CAIT is 9.

FAOS compared with other instruments

Instruments measuring a related construct, with the practical difference between them.

InstrumentItemsRangeWhat it adds
FAAM290–100The FAAM is a 29-item patient-reported questionnaire for musculoskeletal disorders of the leg, foot and ankle that produces two separate subscale scores — Activities of Daily Living from 21 items and Sports from 8 items — each expressed from 0% (unable to perform the listed activities) to 100% (no limitation).
FADI340–100The Foot and Ankle Disability Index is a patient-reported questionnaire of 26 scored items — 22 activities and 4 pain items, each rated 0 to 4 for a maximum of 104 — with an optional 8-item sports subscale out of 32, where a higher score means less disability.
LEFS200–80The LEFS is a 20-item patient-reported questionnaire that measures difficulty with everyday lower limb activities on a single 0 to 80 scale, where 80 indicates no difficulty and a change of 9 points is the smallest difference patients reliably notice.
KOOS420–100The KOOS is a 42-item patient-reported questionnaire that scores knee function as five separate subscales — Symptoms, Pain, Activities of Daily Living, Sport and Recreation, and Quality of Life — each from 0 (extreme problems) to 100 (no problems).

Copyright and permitted use

Published openly because it is the question every clinician and researcher asks before using an instrument, and almost nobody answers it.

Free to useRights holder: Ewa M. Roos

The FAOS is distributed free of charge by its developer for clinical and research use, alongside the KOOS and HOOS, with the questionnaire and scoring instructions published openly at koos.nu.

Rights holder’s own page

References

  1. Roos EM, Brandsson S, Karlsson J. Validation of the foot and ankle outcome score for ankle ligament reconstruction. Foot & Ankle International. 2001.PMID 11669161
  2. Sierevelt IN, Beimers L, van Bergen CJA, Haverkamp D, Terwee CB, Kerkhoffs GMMJ. Validation of the Dutch language version of the Foot and Ankle Outcome Score. Knee Surgery, Sports Traumatology, Arthroscopy. 2015.PMID 25655383
  3. Sierevelt IN, Zwiers R, Schats W, et al.. Measurement properties of the most commonly used Foot- and Ankle-Specific Questionnaires: the FFI, FAOS and FAAM — a systematic review. Knee Surgery, Sports Traumatology, Arthroscopy. 2018.PMID 29138918

Editorial status

Not yet reviewedQueued for clinical review by Sam Tuffun, PT, DPT. Sign-off has not taken place — this is a placeholder assignment, not a completed review.