The Foot Function Index (FFI) is a self-reported questionnaire designed to measure the impact of foot pathology on a person’s daily life, focusing on pain, disability, and activity limitation. It is widely used in clinical and research settings to assess foot-related health outcomes, especially in individuals with conditions like rheumatoid arthritis or non-traumatic foot disorders.

Foot health plays a crucial role in maintaining mobility, independence, and overall quality of life. When foot problems arise—whether due to injury, chronic conditions, or degenerative diseases—they can significantly impair a person’s ability to perform everyday activities. To quantify and monitor these effects, healthcare professionals rely on standardized tools like the Foot Function Index (FFI).

Developed in 1991 by Budiman-Mak and colleagues, the FFI was designed to evaluate the functional limitations caused by foot disorders. It provides a structured way to assess how foot pain and disability affect a patient’s life, making it an essential instrument in both clinical practice and research.

Purpose and Development

The primary goal of the Foot Function Index is to measure the impact of foot pathology on function. It was initially created for patients with rheumatoid arthritis, but its use has expanded to include individuals with various foot and ankle conditions. The FFI is particularly useful for patients with low functional capacity, as it captures the nuances of how foot issues interfere with daily living.

The original version of the FFI includes 23 items divided into three subscales:

• Pain (9 items): Assesses the intensity and frequency of foot pain.
• Disability (9 items): Evaluates the difficulty in performing tasks due to foot problems.
• Activity Limitation (5 items): Measures restrictions in participation in daily activities.

Each item is rated on a 0–10 Likert scale, where 0 indicates no pain or difficulty and 10 represents the worst imaginable pain or severe disability.

Structure and Scoring

The FFI is a self-administered questionnaire, meaning patients complete it independently, reflecting their own perceptions of their foot health. This approach ensures that the data collected is patient-centered and relevant to their lived experience.

Scoring involves calculating the average score for each subscale and then combining them to produce a total score. Higher scores indicate greater impairment. The simplicity of the scoring system makes it easy for clinicians to interpret and track changes over time.

There are also revised versions of the FFI, such as the FFI-R, which aim to improve reliability and validity by refining question wording and scaling methods.

Applications in Clinical and Research Settings

The Foot Function Index is used in a variety of contexts:

1. Clinical Assessment

• Helps clinicians understand the severity of a patient’s foot problems.
• Guides treatment decisions and rehabilitation planning.
• Monitors progress over time, especially after interventions like surgery or physical therapy.

2. Research

• Used in studies evaluating the effectiveness of treatments for foot disorders.
• Provides standardized data for comparing patient outcomes across different populations.
• Supports the development of new therapies and interventions.

Because the FFI is sensitive to changes in foot function, it is particularly valuable in longitudinal studies where researchers track patient outcomes over months or years.

Target Population

The FFI is best suited for individuals who experience functional limitations due to foot pathology. This includes:

• Patients with rheumatoid arthritis.
• Individuals with non-traumatic foot or ankle problems.
• People recovering from foot surgery or injury.

However, it may not be appropriate for individuals who function at or above the level of independence in activities of daily living, as the questionnaire focuses on limitations and impairments.

Strengths of the Foot Function Index

• Patient-Centered: Captures the patient’s own experience of foot pain and disability.
• Easy to Administer: Requires minimal time and no special equipment.
• Quantitative: Provides numerical scores that can be tracked over time.
• Versatile: Applicable in both clinical and research environments.
• Validated: Proven reliability and validity across multiple studies and populations.

Limitations and Considerations

While the FFI is a valuable tool, it has some limitations:

• Subjectivity: As a self-reported measure, responses may be influenced by mood, memory, or misunderstanding of questions.
• Not Ideal for High-Functioning Individuals: May not capture subtle impairments in people with mild or no functional limitations.
• Cultural Sensitivity: The questionnaire may need adaptation for use in different cultural or linguistic contexts.

To address these issues, researchers have developed modified versions of the FFI and translated it into multiple languages, ensuring broader applicability.

Evolution and Variants

Since its inception, the Foot Function Index has undergone several revisions:

• FFI-R (Revised): Improves clarity and psychometric properties.
• FFI-D (Dutch version) and other localized adaptations.
• FFI-5pts: Uses a 5-point scale instead of the original 10-point scale for easier scoring.

These variants aim to enhance usability, reliability, and cultural relevance, making the Foot Function Index a more robust tool for diverse populations.

The Foot Function Index is a cornerstone in the assessment of foot-related health issues. By quantifying pain, disability, and activity limitation, it empowers clinicians and researchers to make informed decisions and track patient progress. Its simplicity, reliability, and patient-centered design make it a widely adopted tool in the management of foot disorders.

As healthcare continues to emphasize personalized and outcome-based care, instruments like the Foot Function Index will remain essential in bridging the gap between clinical observations and patient experiences.