Foot Function Index is a widely-used patient-reported measure of foot health. It has strong clinimetrics and is applicable across a variety of age groups and pathologies.
It is one of the shortest questionnaires that has been developed to measure foot health and has good psychometric properties. However, its validity has not been independently assessed.
Reliability
The Foot Function Index (FFI) is a self-reporting measure that evaluates the impact of foot pain and disability on a patient’s quality of life. It is composed of 23 questions divided into three subscales: pain, disability, and activity limitation. Each question is scored on a visual analog scale and the total score can be expressed as a percentage. The FFI is an important tool to use in clinical practice because it can provide useful information on a patients’ overall functioning.
The FFI is a reliable and valid outcome measure, and has been used in many studies of foot and ankle disorders. The FFI is also frequently used as a validation criterion for other foot health measures. This review identifies 17 articles that report the results of studies using the original FFI or its revised version (FFI-R). The FFI is also often used as a basis for developing new instruments.
To identify studies that used the original FFI or its revision (FFI-R), a systematic literature search was conducted in the PubMed/Medline and Embase databases for full-length articles published from October 1991 through December 2010. Articles were selected if they had an abstract, full-length article, and the words “foot function index” or “FFI” or “FFI-R” in their title. The analyzed articles were scrutinized, and data were collected into tables designed for this review.
Construct Validity
The Foot Function Index was first published in 1991 and is a self-report measure of foot pain, disability and activity limitation. It contains 23 questions divided into three sub-scales and scored on a visual analog scale with 10 intervals. The total score is reported as a percentage and may be presented as either a raw or a standardized number. The FFI has shown good clinimetric properties in terms of internal consistency, exploratory factor analysis and construct validity. It has also been used as a validation criterion for other measures of foot health and well-being and has demonstrated strong correlations with these instruments.
The FFI has been adapted for use in different patient populations, including individuals with rheumatoid arthritis, and in other languages. For example, the Dutch FFI has good clinimetric properties and is applicable to patients with both traumatic and non-traumatic foot problems. The German adaptation, the FFI-D, adds 3 items and has shown good clinimetric properties in a sample with a variety of foot disorders. The FFI was also adapted to Arabic and has shown good clinimetric properties, with low floor and ceiling effects.
The FFI has been compared with other PROMs, and the FFI has been found to have greater sensitivity to change than other measures of foot pain. This reflects the fact that the FFI includes questions on a range of aspects of foot and ankle function and therefore is more comprehensive than other measures.
Cross-Sectional Validity
The Foot Function Index asks patients 23 short questions that evaluate foot-related quality of life. It is user-friendly and has good psychometric properties. The questionnaire has been translated into several languages. It can be used to measure patient-reported outcomes in many different clinical settings. It is also an excellent tool for analyzing the effect of treatment on patient-reported outcomes.
Originally developed by Elly Budiman-Mak and Kendon J Conrad at VA’s Center of Innovation for Complex Chronic Health Care, the FFI was created to address the lack of an outcome measure specifically for the treatment of foot pain and disability. The index measures three aspects of foot function: pain, activity limitation, and disability. The instrument uses a 10-point Likert scale where zero means no pain/disability and 10 is the worst pain/disability imaginable.
A number of studies have validated the FFI. For example, a study by SooHoo and colleagues found that the FFI had good cross-sectional validity for people with plantar fasciitis, metatarsalgia, and chronic ankle sprain. The test-retest reliability was also high.
In addition, the FFI has been shown to have criterion validity. A recent study by Bal and colleagues found that the Foot Function Index was correlated with other health measures, including the Health Assessment Questionnaire (HAQ) and Steinbrocker functional class. This supports the criterion validity of the FFI as an outcome measure in RA.
Long-Term Validity
The Foot Function Index is the most widely used self-report measure to assess foot pain and disability. It asks patients 23 short questions about how their feet have been over the past week. The questionnaire is scored on a scale of 0 to 10 where zero means no pain or disability and ten indicates the worst pain and disability possible. It is easy to understand and is used by a variety of patients worldwide.
The Foot Function Index was developed to evaluate the impact of foot pathology on patient function by measuring disability, activity limitation and pain. It consists of 23 items that are grouped into three categories. Patients are asked to rate each question on a scale from 0 (no problem) to 10 (the worst pain you can imagine). The Foot Function Index has good construct validity and internal consistency. It is also well-tested for test-retest reliability and responsiveness.
It was pioneered by researchers in the VA system who wanted to be able to measure their patients’ outcomes. It has been adapted over the years for use in different populations and disease conditions, including rheumatoid arthritis. The instrument has helped shift the focus from reliance on clinical and biochemical findings to using patient-centered hard data endpoints.
The Foot Function Index is a useful tool for clinicians and researchers. However, it has some limitations. First, clinicians created the questions without the help of patients, and they may not have fully understood patients’ needs. In addition, the index does not contain psychosocial questions about quality of life or satisfaction with care.