Identification of Functional Ankle Instability (IdFAI)
- Fysiobasen
- Sep 18
- 3 min read
The Identification of Functional Ankle Instability (IdFAI) is a simple 10-item questionnaire developed to assess ankle stability in individuals with a history of ankle sprains.
The IdFAI combines elements from the Cumberland Ankle Instability Tool (CAIT) and the Ankle Instability Instrument (AII), providing clinicians and researchers with an effective tool to identify functional ankle instability (FAI)【1】【2】.
Advantages and Limitations
Advantages
High reliability: ICC2,1 = 0.92 for the total score; subscales also show strong consistency【2】.
Quick administration: Takes only a few minutes to complete.
Cross-cultural adaptability: Validated in Chinese, French, Korean, Persian, Spanish, and more【6–14】.
Limitations
Relies on self-report, which may introduce subjective variation.
Limited validation in older adults and pediatric populations.
Method of Use
The IdFAI is divided into three domains:
History of Ankle Instability
Questions assess perceived instability, frequency of “giving way” episodes, and the ability to control ankle movement (items 5, 6, 7, 10).
Previous Ankle Sprains
Covers number of sprains, severity, time since the most recent injury, need for support, and diagnosis (items 1–4).
Instability in Daily Activities
Focuses on recovery time and instability during everyday tasks (items 8–9).
Scoring System
≤10 points: Low probability of functional ankle instability (FAI).
≥11 points: High probability of FAI.
Psychometric Properties
Reliability
Total score: ICC2,1 = 0.92 (excellent).
History of instability: ICC2,1 = 0.81 (good).
Previous sprains: ICC2,1 = 0.94 (excellent).
Daily activities: ICC2,1 = 0.83 (good).
Validity
Significant negative correlations with the Lower Extremity Functional Scale (LEFS):
Total: r = –0.38
History of instability: r = –0.29
Previous sprains: r = –0.24
Daily activities: r = –0.41【2】
A higher IdFAI score indicates greater instability, while a lower LEFS score reflects poorer functional capacity.
Conclusion
The IdFAI is a reliable, efficient, and practical tool for assessing functional ankle instability.
Provides clinicians with strong diagnostic and monitoring support.
Suitable for both research and clinical practice.
Further validation is needed in specific populations such as older adults and children.
Sources:
1. Simon J, Donahue M, Docherty C. Development of the identification of functional ankle instability (IdFAI). Foot & Ankle International. 2012 Sep;33(9):755-63.
2. Donahue M, Simon J, Docherty CL. Reliability and validity of a new questionnaire created to establish the presence of functional ankle instability: the IdFAI. Athletic Training & Sports Health Care. 2013 Jan 1;5(1):38-43.
3. Gerber JP, Williams GN, Scoville CR, Arciero RA, Taylor DC. Persistent disability associated with ankle sprains: a prospective examination of an athletic population. Foot & ankle international. 1998 Oct;19(10):653-60.
4. Cameron KL, Owens BD, DeBerardino TM. Incidence of ankle sprains among active-duty members of the United States Armed Services from 1998 through 2006. Journal of athletic training. 2010 Jan;45(1):29-38.
5. Donahue M, Simon J, Docherty CL. Critical review of self-reported functional ankle instability measures. Foot & Ankle International. 2011 Dec;32(12):1140-6.
6. Martinez BR, Sauers AD, Ferreira CL, de Castro Lugli L, Turchetto PC, Docherty CL, Yi LC. Translation, cross-cultural adaptation, and measurement properties of the Brazilian version of the Identification of Functional Ankle Instability (IdFAI) questionnaire. Physical Therapy in Sport. 2018 Jan 1;29:1-8.
7. Wang W, Sheng J, Tang Y, Xie Q, Wei M, Li Z, Zheng W. Adaptation and psychometric evaluation of the simplified Chinese version of the identification of functional ankle instability questionnaire in Chinese-speaking patients with chronic ankle instability disorders. BMC Musculoskeletal Disorders. 2020 Dec;21(1):1-1.
8. Beaudart C, Demoulin C, Mehmeti K, Bornheim S, Van Beveren J, Kaux JF. Validity and reliability of the French translation of the Identification of Functional Ankle Instability (IdFAI). Foot and Ankle Surgery. 2022 Aug 1;28(6):756-62.
9. Tsekoura M, Billis E, Samada EK, Savvidou I, Fousekis K, Xergia S, Lampropoulou S, Tsepis E. Cross cultural adaptation, reliability and validity of the Greek version of Identification of Functional Ankle Instability (IdFAI) questionnaire. Foot and Ankle Surgery. 2021 Dec 1;27(8):906-10.
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11. Ko J, Rosen AB, Brown CN. Cross-cultural adaptation, reliability, and validation of the Korean version of the identification functional ankle instability (IdFAI). Disability and Rehabilitation. 2018 Dec 18;40(26):3185-90.
12. Mohamadi S, Dadgoo M, Ebrahimi I, Salavati M, Saeedi A, Valiollahi B. Translation, cross-cultural adaptation, reliability, and validity of the Identification of Functional Ankle Instability questionnaire in Persian speaking participants with a history of ankle sprain. Disability and Rehabilitation. 2019 Jul 31;41(16):1931-6.
13. Cervera-Garvi P, Ortega-Avila AB, Marchena-Rodriguez A, Gijon-Nogueron G. Transcultural adaptation and validation of the Spanish version of the Identification of Functional Ankle Instability questionnaire (IdFAI-Sp). Disability and Rehabilitation. 2022 Jun 19;44(13):3221-7.
14. Tayfur A, Şendil A, Karakaya J, Ergun N. Cross-cultural adaptation, validity, and reliability of Turkish version of Identification of Functional Ankle Instability (IdFAI) scale. Acta orthopaedica et traumatologica turcica. 2020 May;54(3):300.
