Foot Function Index (FFI)

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Original Editors - Xiomara Hernandez

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Objective

A Foot Function Index (FFI) was developed to measure the impact of foot pathology on function in terms of pain, disability and activity restriction.

Intended Population

The FFI should prove useful for both clinical and research purposes. It has been shown to be a reasonable tool for use with low functioning individuals with foot disorders and patients with rheumatoid arthritis and non-traumatic foot or ankle problems. It may not be appropriate for individuals who function at or above the level of independent activities of daily living.

Method of Use

The FFI (questionnaire) consists of 23 self-reported items divided into 3 subcategories, namely: pain, disability and activity limitation. The patient has to score each question on a scale from 0 (no pain or difficulty) to 10 (worst pain imaginable or so difficult it requires help), that best describes their foot over the past WEEK. The pain subcategory consists of 9 items and measures foot pain in different situations, such as walking barefoot versus walking with shoes. The disability subcategory consists of 9 items and measures difficulty performing various functional activities because of foot problems, such as difficulty climbing stairs. The activity limitation subcategory consists of 5 items and measures limitations in activities because of foot problems, such as staying in bed all day. Recorded on a visual analogue scale (VAS), scores range from 0 to 100 mm, with higher scores indicating worse pain. Both total and subcategory scores are calculated.

Evidence

Reliability

The FFI was examined for test-retest reliability and internal consistency. Test-retest reliability of the FFI total and subscale scores ranged from 0.87 to 0.69. Internal consistency ranged from 0.96 to 0.73. It is proved that the FFI is a reliable instrument for patients with rheumatoid arthritis and it is also recommended as a reliable measurement scale for use in other foot orthopaedic interventions trials. For the purposes of orthopaedic studies in which one foot serves as an internal control, a study assessed the side-to-side reliability of the seven-question Foot Function Index pain subscale. Internal reliability of the scale was high, with Cronbach's alphas ranging from 0.94 to 0.96, suggesting good left versus right discriminatory abilities. Intraclass correlation coefficients were examined for test-retest reliability (separated by side) and for side-to-side reliability (separated by the day of test). The resultant intraclass correlation coefficients were nearly equivalent, ranging from 0.79 to 0.89. Generalizability analysis yielded similar results. Intraclass correlation coefficients and generalizability analysis demonstrate that the majority of variation is best explained by the differences within subjects or between subjects rather than by test-retest or side-to-side differences.

Validity

The FFI has been validated and determined to be a reliable instrument for patients with rheumatoid arthritis and non-traumatic foot or ankle problems. In the study to examine the construct validity of the FFI were a total of 87 patients, with rheumatoid arthritis, used. With the exception of two items, factor analysis supported the construct validity of the total index and the subscales. Strong correlation between the FFI total and subscale scores and clinical measures of foot pathology supported the criterion validity of the index.

Responsiveness

FFI is an instrument that was rated positively (level 3) for responsiveness.

Miscellaneous

FFI-5pt versus original FFI

The clinimetric value of the Dutch version of the Foot Function Index (FFI) was assessed by Kuyvenhoven et al. in comparison with the original FFI using verbal rating scales (FFI-5pt) rather than visual analogue scales (VAS). The FFI-5pt is a suitable generic measure. Its clinimetric properties are comparable with those of the original FFI. Its administration and data entry are less time consuming. However, responsiveness has to be more exactly assessed in an intervention study.

References

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