Foot Function Index (FFI) - 5pt

Clinical intent

The Foot Function Index (FFI) was developed to measure the effect of foot problems on function in terms of pain and disability. The FFI is a self-administered index consisting of 23 items divided into 3 scales (Limitation, Pain, and Disability). All the items are rated on a visual analog scale (VAS) and have satisfactory clinimetric properties[1].

FFI-5pt

The original FFI instrument uses VAS scales to rate the different items. However, administration, coding, and data entry of the VAS scores are time consuming. Because of this and since several studies have shown high correlation between scores using VAS and those using verbal rating scales (VRS)12-14, the items in this version are rated on a 5 point VRS, the "FFI-5pt"[1].

Calculation

The score procedure of the FFI-5pt is identical to the original version:

1. Discard the items that are "Not applicable", they should be omitted in further calculations
2. Calculate a score for each scale (limitation, disability & pain scale) by summing the item scores and divide that by the maximum possible sum of the item scores. Multiply that number with 100.
3. Calculate the total score: the mean of the scale scores.

Clinical interpretation

The scores range from 0 to 100; the higher the score, the more limitation/pain/disability is present.

References

[1] Kuyvenhoven MM, Gorter KJ, Zuithoff P, Budiman-Mak E, Conrad KJ, Post MW. The foot function index with verbal rating scales (FFI-5pt): A clinimetric evaluation and comparison with the original FFI. J Rheumatol. 2002 May;29(5):1023-8. PMID: 12022318.