The Foot Function Index (FFI) is a validated, patient‑reported questionnaire designed to quantify how foot problems affect pain, disability, and activity in everyday life. It is widely used in rheumatology, podiatry, and orthopaedic research and practice to measure treatment outcomes and the functional impact of foot and ankle disorders.
Origin and purpose
The FFI was developed in 1991 as one of the first foot‑specific outcome measures focused explicitly on the patient’s experience of pain and functional limitation. Its creators aimed to provide a brief, self‑administered tool that could sensitively capture the impact of foot pathology on daily activities in people with significant impairment, especially those with rheumatoid arthritis.
From the outset, the index was grounded in patient‑centred values, reflecting situations that patients themselves identified as problematic, such as walking on different surfaces or standing for prolonged periods. Over time it has become a reference standard for assessing foot‑related quality of life, influencing how clinicians and researchers conceptualize and measure foot function.
Structure and content
The original FFI contains 23 items divided into three subscales: Pain, Disability, and Activity Limitation. The Pain subscale includes questions about foot pain in various contexts, such as walking barefoot, wearing shoes, or at different times of day.
The Disability subscale focuses on difficulty performing functional tasks, for example walking indoors and outdoors, climbing stairs, or standing for long periods. The Activity Limitation subscale asks about the extent to which foot problems restrict participation, including how often a person must stay in bed, use assistive devices, or reduce activity because of foot pain.
All items are self‑rated on a numerical scale from 0 to 10, where 0 represents no pain or difficulty and 10 represents worst pain or maximal difficulty. Responses are usually converted into percentage scores for each subscale and for the total index, with higher scores indicating worse foot health and poorer function.
Administration and scoring
The FFI is designed as a brief, self‑administered questionnaire, generally taking around 5–10 minutes to complete. Patients are asked to rate each item according to their experience over the previous week, which balances recall feasibility with clinical relevance.
Scoring can be done at the subscale level or by calculating a total score that reflects overall foot‑related impact. Clinicians and researchers often express scores as a percentage of the maximum possible score, allowing easy interpretation and comparison between individuals or time points. Lower scores indicate better function and less pain, so improvements after treatment are seen as reductions in FFI scores.
Because it is patient‑reported, the FFI captures subjective aspects of foot health that may not be apparent on physical examination alone, such as the perceived burden of pain or the personal importance of certain activities. This makes it especially useful as an outcome measure when evaluating interventions like orthoses, surgery, pharmacological treatment, or rehabilitation programmes.
Psychometric properties and clinical utility
Extensive research has demonstrated that the FFI has good reliability, validity, and responsiveness. Test–retest reliability for total and subscale scores has been reported in the moderate‑to‑excellent range, with coefficients typically between 0.69 and 0.87, indicating stable measurement when patients’ conditions are unchanged.
Internal consistency is high, with Cronbach’s alpha values often reported between 0.73 and 0.96 across subscales, suggesting that items within each domain measure related constructs. Construct validity has been supported by factor analyses that largely confirm the three‑subscale structure and by strong correlations between FFI scores and clinical indicators of foot pathology or other disability measures.
The FFI has been used across a wide range of populations, including people with rheumatoid arthritis, non‑traumatic foot and ankle disorders, and other orthopaedic conditions. It is particularly suited to individuals with low to moderate functional levels, where foot pathology substantially interferes with daily activities; it may be less sensitive for highly active individuals who function at or above normal independence.
Revisions and limitations
Despite its strengths, the original FFI attracted some criticism, which led to development of a revised version, the FFI‑R. Concerns included limited coverage of broader aspects of functioning, ceiling effects in higher‑functioning patients, and the need for a more comprehensive theoretical framework.
The FFI‑R expanded the number of items and subscales, drawing on the World Health Organization’s International Classification of Functioning model to better capture participation and contextual factors. Even so, the original 23‑item FFI remains popular due to its brevity, ease of use, and extensive historical data, which facilitate comparison with earlier studies.
Some limitations should be considered when interpreting FFI scores. As a self‑report measure, it is influenced by patient perception, mood, and expectations, and it does not directly measure objective biomechanical variables such as joint range of motion or plantar pressures. It is also primarily a static snapshot over a one‑week period and does not automatically distinguish between acute and chronic symptom patterns.
Nonetheless, the Foot Function Index has played a pivotal role in shifting foot and ankle assessment towards patient‑reported outcomes, providing a robust, practical instrument for quantifying the lived impact of foot disorders. When used alongside clinical examination and imaging, it offers a rich, patient‑centred view of pain, disability, and activity limitation that supports both evidence‑based practice and high‑quality research.