Foot Function Index (FFI)

Objective

A Foot Function Index (FFI) was developed in 1991 to measure the impact of foot pathology on function in terms of pain, disability and activity restriction. [1] It is a self-administered index consisting of 23 items divided into 3 sub-scales. Both total and sub-scale scores are produced.

Intended Population

The FFI has been shown to be a reasonable tool for use with low functioning individuals with foot disorders[2] ,patients with rheumatoid arthritis[1] and non-traumatic foot or ankle problems.[3] It can be used in both clinical and research settings.

However, it may not be appropriate for individuals who function at or above the level of independence in activities of daily living. [2]

Method of Use

The FFI (questionnaire) consists of 23 self-reported items divided into 3 subcategories on the basis of patient values: pain, disability and activity limitation.[4] 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.[4]

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. [1]

Scale Questions Scoring
Pain Scale
  • Pain in the morning upon taking your first step
  • Pain standing barefoot
  • Pain walking barefoot
  • Pain standing with shoes
  • Pain walking with shoes
  • Pain standing with orthotics
  • Pain walking with orthotics
  • How is your pain at the end of the day
  • How severe is your pain at its worst
0/90
Disability Scale
  • Difficulty when walking in the house
  • Difficulty when walking outside
  • Difficulty when walking four blocks
  • Difficulty when climbing stairs
  • Difficulty when descending stairs
  • Difficulty when getting out of chair
  • Difficulty when standing tip toe
  • Difficulty when climbing curbs
  • Difficulty when running or fast walking
0/90
Activity Limitation
  • Stay indoors all day due to feet
  • Stay in bed all day due to feet
  • Use an assistive device (stick, walker, crutches, frame) indoors
  • Use an assistive device outdoors
  • Limit physical activity
0/50

Evidence

Reliability

Test-retest reliability of the FFI total and subscale scores range from 0.87 to 0.69, while internal consistency ranged from 0.96 to 0.73.[1]

It is reported that the FFI is a reliable instrument for patients with rheumatoid arthritis[1] and it has also been recommended as a reliable measurement scale for use in other foot orthopaedic intervention trials. [5]

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. Generalisability analysis yielded similar results. Intraclass correlation coefficients and generalisability 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. [5]

Validity

The FFI has been validated and determined to be a reliable instrument for patients with rheumatoid arthritis [1]and non-traumatic foot or ankle problems.[3] In the study to examine the construct validity of the FFI there were a total of 87 patients, with rheumatoid arthritis were used. With the exception of two items, factor analysis supported the construct validity of the total index and the sub-scales. Strong correlation between the FFI total and sub-scale scores and clinical measures of foot pathology supported the criterion validity of the index. [1]

Responsiveness

FFI is an instrument that was rated positively (level 3) for responsiveness. [6]

Miscellaneous

FFI-5pt versus original FFI

The clinimetric value of the Dutch version of the Foot Function Index (FFI) was assessed 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. [7]

Revision of the FFI

In 2006, the FFI was revised (known as the FFI-R) on the basis of criticisms from researchers and clinicians.[8]

Some areas were identified for potential improvement, including:

  1. FFI’s theoretical basis
  2. Use of a visual analog scale
  3. Limited sample on which the FFI was evaluated
  4. Limitations of the Classical Test Theory measurement model that was used in its development in 1996, as there have been advances in psychometrics since

A literature review was conducted to develop a theoretical model of foot functioning, based on the World Health Organization International Classification of Functioning (ICF) model. The FFI-R items were developed from the original 23 FFI items, and more items were added as a result of the literature review. As a result of clinicians and patients’ input, the final draft of the FFI-R, which consisted of 4 subscales and 68 items, was completed.

There are two versions of the FFI-R: a FFI-R long form (FFI-R L; 4 subscales and 68 items) and the FFI-R short form (FFI-R S; 34 items). Both the FFI short and long from demonstrated good psychometric properties.

FFI-R

Scale Questions Scoring
Pain and stiffness
  • Before you get up in the morning
  • First pain standing without shoes
  • First pain walking without shoes
  • First pain standing with shoes
  • First pain walking with shoes
  • Pain standing with custom shoe inserts
  • Pain walking with custom shoe inserts
  • How is your pain at the end of the day
  • Pain with foot cramps
  • Pain before sleep
  • How severe is your pain at its worst
  • Stiffness before getting up in the morning
  • Stiffness standing without shoes
  • Stiffness walking without shoes
  • Stiffness standing with shoes
  • Stiffness walking with shoes
  • Stiffness walking with custom shoe inserts
  • Stiffness before sleep
  • Stiffness at worse
Rated 0-6 per item, ranging from
  1. No pain
  2. Mild pain
  3. Moderate pain
  4. Severe pain
  5. Very severe pain
  6. Worst pain imaginable
Difficulty
  • Walking around the house
  • Walking outside on uneven ground
  • Walking four or more blocks
  • Climbing stairs
  • Descending stairs
  • Getting out of chair
  • Standing normally
  • Standing tip toe
  • Carrying or lifting more than 5 pounds
  • Running
  • Fast walking
  • Walking downhill
  • Keeping regular walking pace
  • Walking regular distance
  • Keeping balance
  • Keeping foot clean
  • Walking with assistive devices
  • Because of hazards at home
  • Operating vehicle requiring foot to maneuver
  • Performing daily activities
Rated 0-6 per item, ranging from
  1. No difficulty
  2. Mild difficulty
  3. Moderate difficulty
  4. Severe difficulty
  5. Very severe difficulty
  6. So difficult unable
Activity limitation
  • Stay indoors all day due to feet
  • Stay in bed all day due to feet
  • Use an assistive device (stick, walker, crutches, frame) indoors
  • Use an assistive device outdoors
  • Take extra precautions when walking in crowds for fear of foot injury
  • Limit outdoor activity
  • Choose not to use public transportation
  • Choose not to drive
Rated 0-6 per item, ranging from
  1. None of the time
  2. A little of the time
  3. Some of the time
  4. Much of the time
  5. Most of the time
  6. All of the time
Social issues
  • Fear of falling
  • Embarrassment due to limp
  • Difficulty finding fashionable footwear
  • Difficulty finding dress shoes
  • Embarrassment due to footwear
  • Depression from foot problems
  • Difficulty finding suitable footwear
  • Feeling awful because of foot problem
  • Limit social activities due to foot problems
  • Constant aggravation due to managing foot pain
  • Difficulty participating in social activities due to footwear
  • Aggravation in performing daily activities
  • Poor sleep because of foot pain
  • Burden of taking medication to control pain
  • Difficulty finding comfortable footwear
  • Difficulty finding employment
  • Concern with appearance of feet
  • Concern about limited work around house
  • Concern about possible amputation of foot, leg or toes
Rated 0-6 per item, ranging from
  1. None of the time
  2. A little of the time
  3. Some of the time
  4. Much of the time
  5. Most of the time
  6. All of the time

References

  1. 1.0 1.1 1.2 1.3 1.4 1.5 1.6 Budiman-Mak E, Conrad KJ, Roach KE. The Foot Function Index: a measure of foot pain and disability. J Clin Epidemiol. 1991;44:561–570. (level of evidence B)
  2. 2.0 2.1 Agel J, Beskin JL, Brage M, Guyton GP, Kadel NJ, Saltzman CL, Sands AK, Sangeorzan BJ, SooHoo NF, Stroud CC, Thordarson DB: Reliability of the foot function index: a report of the AOFAS outcomes committee. Foot Ankle Int 2005, 26:962-967. (level of evidence C)
  3. 3.0 3.1 Martin RL, Irrgang JJ. A survey of selfreported outcome instruments for the foot and ankle. J Orthop Sports Phys Ther.2007;37:72–84. (level of evidence A)
  4. 4.0 4.1 Kornelia Kulig, Stephen F Reisch I. Nonsurgical Management of Posterior Tibial Tendon Dysfunction With Orthoses and Resistive Exercise: A Randomized Controlled Trial. Physical Therapy, 2009 Jan; 89 (1): 26-37. (Level of evidence 1B)
  5. 5.0 5.1 Saag KG, Saltzman CL, Brown CK, Budiman-Mak E: The Foot Function Index for measuring rheumatoid arthritis pain: evaluating side-to-side reliability. Foot Ankle Int 1996, 17:506-510. (level of evidence C)
  6. Marike Van Der Leeden, Martijn P.M. Steultjens, Caroline B. Terwee, Dieter Rosenbaum, Debbie Turner, Jim Woodburn and Joost Dekkera. Systematic review of instruments measuring foot function, foot pain, and foot-related disability in patients with rheumatoid arthritis. Arthritis & Rheumatism (Arthritis Care & Research) Vol. 59, No. 9, September 15, 2008, pp 1257–1269. (level of evidence 1A)
  7. 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. (level of evidence C)
  8. Budiman-Mak E, Conrad K, Stuck R, Matters M. Theoretical Model and Rasch Analysis to Develop a Revised Foot Function Index. 2006. Foot and Ankle International. (27) 7, 519-527