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Foot Function Index

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Purpose

The Foot Function Index measures the effect of foot pathology on an individual’s function by measuring pain, disability and activity restriction.

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Instrument Details

Acronym FFI

Area of Assessment

Functional Mobility
Pain

Assessment Type

Patient Reported Outcomes

Cost

Not Free

Actual Cost

$0.00

Populations

Rheumatic Disease
Neuromuscular Conditions
Mixed Populations
Joint Pain and Fractures

Key Descriptions

  • 23 self-report items with 3 subscales: pain (9 items), disability (9 items) and activity limitation (5 items)
  • Each item is rated on a 0 – 10 Likert scale. Zero represents no pain/disability, and 10 represents the worst pain imaginable/severe disability for each item.
  • The original version used a visual analog scale ranging from 0 – 9 with the same anchors used for the current 10 point Likert scale.
  • For the Likert scale, the total score is reported as the sum of the scores of answers provided on the self- report instrument divided by a maximum score of 230 and multiplied by 100. The calculation is: (total score/ 230) x 100 =___%.
  • For the original visual analog scale, the total score is reported as the sum of the scores of answers provided on the self- report instrument divided by a maximum score of 207 and multiplied by 100.
    The calculation is: (total score/ 207) x 100 =___%.
  • For the total score, the minimum score is 0% (no pain or difficulty), and maximum score is 100% (worst pain and extreme difficulty requiring assistance).
  • Subscale scores are calculated by adding the item scores and dividing by the maximum total score for the items that the patient indicated were applicable. Subscale scores are multiplied by 100. (Budiman-Mak, Conrad, & Roach, 1991)
  • Alternative scoring method: The total FFI equals the average of the 3 subscale scores. Pain, disability, and activity limitation subscale scores range from 0 to 100.The total FFI equals the average of the 3 subscale scores. Pain, disability, and activity limitation subscale scores range from 0 to 100 (Rogers, & Irrgang, 2003).

Number of Items

23

Equipment Required

  • Paper version of the instrument

Time to Administer

5-10 minutes minutes

Required Training

No Training

Instrument Reviewers

Michelle Schneider PT, DPT, OCS

Considerations

There is a revised version of the FFI (Budiman-Mak, , 2006; Budiman-Mak,  2013). Caution should be used when interpreting scores and ensuring that interpretation of the results is based on the correct version.

Statistics presented that were based on non-English language versions have been noted in this instrument review.

The FFI was originally developed in English and valid versions have been translated and adapted for following languages:

Danish (Jorgensen et al., 2015),

Italian (Martinelli et al., 2014; Vetrano et al., 2014),

Brazilian-Portuguese (Martinez et al., 2016),

German (Naal et al., 2008),

Spanish (Paez-Moguer et al.,, 2014),

French (Pourtier-Piotte et al., 2015),

Chinese (González-Sánchez et al., 2017).

Joint Pain and Fractures

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Standard Error of Measurement (SEM)

Plantar fasciitis, metatarsalgia, chronic ankle sprain: (Martinez et al., 2016; n = 50, 76% female, mean age 32.9 ± 14.13 years (range 18-60), symptoms at least 6 months in duration; FFI translated to Brazilian-Portuguese)

  • SEM = 1.32 for inter-rater and 1.08 for intrarater reliability

Minimal Detectable Change (MDC)

Plantar fasciitis, metatarsalgia, chronic ankle sprain: (Martinez et al., 2016; FFI translated to Brazilian-Portuguese)

  • MDC = 2.42

Minimally Clinically Important Difference (MCID)

Plantar Fasciitis (Landorf & Radford, 2008; n = 175, symptom duration of at least 4 weeks, no further demographic information given)

  • MCID for pain subscale: 12.3 points
  • MCID for the disability subscale: 6.7 points
  • MCID for the activity limitation subscale: 0.5 points
  • MCID for the total score: 6.5 points

Test/Retest Reliability

Plantar Fasciitis; (Vetrano, 2014; n = 50; mean age 53.4(5.7) years; symptom duration 6.7 ±1.8 weeks; FFI translated and cross-culturally adapted to Italian)

  • Excellent test–retest reliability for the:
    • total score ( ICC = 0.97)
    • pain subscale  ( ICC = 0.98)
    • disability subscale ( ICC = 0.98)
    • activity limitation subscale (ICC = 0.86)

Mixed foot pain: (Jorgensen et al., 2015; n=35; mean age = 43.3(11.7) years; n = 2 post-operative rehabilitation to the ankle; n = 5 sprained, ankles; n = 3 RA; n = 11 undefined rear foot complaints; n = 8 undefined forefoot complaints, n = 4 fasciitis plantaris; n = 2 osteoarthritis verified radiographically; FFI translated and culturally adapted to Danish (FFI-DK)

  • Excellent test-retest reliability for the:
    • total score (ICC = 0.95)
    • pain subscale (ICC = 0.98)
    • disability subscale (ICC = 0.97)
    • activity limitation subscale (ICC = 0.95)

Interrater/Intrarater Reliability

Plantar fasciitis, metatarsalgia, chronic ankle sprains: (Martinez et al., 2016; FFI translated to Brazilian-Portuguese)

  • Excellent inter and intrarater reliability (ICC = 0.97-0.99)

Internal Consistency

Plantar Fasciitis; (Vetrano, Vulpiani, Erroi, Vadalà, Ferretti, & Saraceni, 2014; FFI translated and cross-culturally adapted to Italian)

  • Excellent internal consistency for the:
    • total score (Cronbach’s alpha = 0.98)
    • pain subscale (Cronbach’s alpha = 0.99)
    • disability subscale (Cronbach’s alpha = 0.99)
    • activity limitation subscale (Cronbach’s alpha = 0.93)

Plantar fasciitis, metatarsalgia, chronic ankle sprains: (Martinez et al., 2016; FFI translated to Brazilian-Portuguese)

  • Poor to Adequate (Cronbach’s alpha = 0.61-0.80)

Mixed foot pain:

(Budiman-Mak, et al., 2006; n = 92; mean age = 69 years; average duration of foot problems = 19 years; FFI-Revised (FFI-R)

  • Excellent internal consistency (Chronbach’s alpha = 0.95)
  • Excellent internal consistency, FFI-R Short Form (Chronbach’s alpha = 0.95)
  • Excellent person reliability (analogous to Chronbach’s alpha = 0.96)
  • Excellent item reliability (0.93)

(Jorgensen et al., 2015; FFI translated and culturally adapted to Danish (FFI-DK)

  • Excellent internal consistency for the:
    • Total score (Chronbach’s alpha = 0.97)
    • Pain subscale (Chronbach’s alpha = 0.99)
    • Disability subscale (Chronbach’s alpha = 0.98)
    • Activity limitation subscale (Chronbach’s alpha = 0.98)

(Paez-Moguer et al., 2014; n = 80, mean age = 36(16) years; participants with some foot pathology; n=17 hyperkeratosis; FFI translated and culturally adapted to Spanish (FFI-Sp)

  • Poor to excellent internal consistency for the:
    • Pain subscale (Chronbach’s alpha = 0.95)
    • Disability subscale (Chronbach’s alpha = 0.96)
    • Activity limitation subscale (Chronbach’s alpha = 0.69)

Construct Validity

Mixed foot pain:

(Budiman-Mak et al., 2006)

  • Adequate relationship between 50-ft walking time and FFI-R total = 0.306, p=0.018, n=59

(Paez-Moguer et al., 2014; FFI translated and culturally adapted to Spanish (FFI-Sp)

  • Excellent correlation of the FFI-Sp and the FHSQ (r = -0.62 to -0.79)
  • Adequate correlation of the FF-Sp and the EuroQoL 5D (r = -0.57)
  • Adequate correlation of the FF-Sp and the SF-12 physical (r = -0.49)
  • Excellent correlation of the FF-Sp and the VAS foot pain (r = 0.63)

Floor/Ceiling Effects

Plantar Fasciitis (Vetrano, 2014; FFI translated and cross-culturally adapted to Italian)

  • Floor effects noted in some aspects of the disability and activity limitation subscale

Mixed foot pain: (Jorgensen et al., 2015; FFI translated and culturally adapted to Danish (FFI-DK)

  • No floor or ceiling effect was present in subscale pain or disability or the total score. However, 22/35 scored the lowest score (0) in the activity limitation subscale.

Neuromuscular Conditions

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Standard Error of Measurement (SEM)

Foot and ankle neuromusculoskeletal diseases: (Gonzalez et al., 2018); n = 306; mean age = 43.94(12.33) years; FFI translated and culturally adapted to Chinese (FFI-Ch) 

  • SEM = 0.973

Minimal Detectable Change (MDC)

Foot and ankle neuromusculoskeletal diseases: (Gonzalez et al., 2018; FFI translated and culturally adapted to Chinese (FFI-Ch) 

  • MDC = 2.270

Internal Consistency

Foot and ankle neuromusculoskeletal diseases: (Gonzalez et al., 2018; FFI translated and culturally adapted to Chinese (FFI-Ch)  

  • Excellent internal consistency for the:
    • Total score (Chronbach’s alpha = 0.998)
    • Pain subscale (Chronbach’s alpha = 0.997)
    • Disability subscale (Chronbach’s alpha = 0.998)
    • Limit activity subscale  (Chronbach’s alpha = 0.996)

Construct Validity

Foot and ankle neuromusculoskeletal diseases: (Gonzalez et al., 2018; FFI translated and culturally adapted to Chinese (FFI-Ch) 

  • Poor to excellent correlation of the FFI-Ch with the FFI-Taiwan
    • r = 0.619 to 0.886 (Factor 1)
    • r = 0.381 to 0.727 (Factor 2)
    • r = 0.099 to 0.249 (Factor 3)
  • Poor to excellent correlation of the FFI-Ch with the Chinese versions of SF12-V2
    • r = 0.116 to 0.856 (Factor 1)
    • r = 0.206 to 0.518 (Factor 2)
    • r = 0.121 to 0.270 (Factor 3)
  • Poor to excellent correlation of the FFI-Ch with the Chinese versions of EuroQoI5D
    • r = 0.855 to 0.858 (Factor 1)
    • r = 0.530 to 0.542 (Factor 2)
    • r = 0.138 to 0.150 (Factor 3)

Rheumatic Disease

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Standard Error of Measurement (SEM)

 

Test/Retest Reliability

Rheumatoid Arthritis:

(Budiman-Mak, 1991; n = 87; mMean age = 61 years, range 24-79 years; American Rheumatism Association (ARA) Functional Classification level I or II)

  • Excellent test- retest reliability (ICC = . 87)

(Pourtier-Piotte et al., 2015; n = 53; mean age = 60(12) years; FFI translated and cross-culturally adapted to French (FFI-F)

  • Excellent test-retest reliability for the:
    • Total score (ICC = 0.90)
    • Pain subscale (ICC = 0.87)
    • Function subscale (ICC = 0.89)
  • Adequate test-retest reliability for the:
    • Activity limitation subscale (ICC = 0.56)

(Saag, Saltzman, Brown, & Budiman-Mak, 1996; n = 30; mean age 57.5 + 11.6 years; Disease duration 17.5 + 12.8 years)

  • Excellent test-retest reliability (ICC = .79-.89)

Internal Consistency

Rheumatoid Arthritis:

(Budiman-Mak, 1991)

  • Excellent internal consistency (Cronbach’s alpha = .96) (Budiman-Mak, 1991)

(Pourtier-Piotte et al., 2015; FFI translated and cross-culturally adapted to French (FFI-F)

  • Excellent internal consistency for the:
    • Pain subscale (Chronbach’s alpha = 0.97)
    • Function subscale (Chronbach’s alpha = 0.97)
    • Activity limitation subscale (Chronbach’s alpha = 0.85)

(Saag, Saltzman, Brown, & Budiman-Mak, 1996)

  • Excellent internal consistency (Cronbach’s alpha  ranging from 0.942 – 0.96 measured as a combination for each lower extremity and each test session) (Saag, Saltzman, Brown, & Budiman-Mak, 1996)

Criterion Validity (Predictive/Concurrent)

Concurrent Validity

Rheumatoid Arthritis: (Budiman-Mak, 1991)

  • Adequate correlations with the foot joint count  (r = 0.53) and the 50 meter walking time ( r = 0.48)

Construct Validity

Convergent Validity

Rheumatoid Arthritis:

(Budiman-Mak, 1991)

  • Adequate correlation with:
    • foot joint count (r = 0.53)
    • walking time (r = 0.48)
    • pain, disability, and activity limitation subscales scores with foot joint count (r = 0.54, r = 0.43, r = 0.43 respectively)
    • pain, disability, and activity limitation with walking time (r = 0.34, r = 0.51, r = 0.42 respectively)

(Pourtier-Piotte et al., 2015; FFI translated and cross-culturally adapted to French (FFI-F)

  • Excellent correlation of the total FFI-F score to the VAS, HAQ, and MACTAR (r = 0.69 to 0.73)
  • Adequate correlation with FFI-F activity limitation scale and VAS (r = 0.57) and HAQ (0.59)
  • Poor correlation with FFI-F activity limitation scale and MACTAR (r = 0.39)
  • Walking speed (10 m and 200 m tests) was not correlated to FFI-F. There was a reverse correlation between gait perimeter and FFI-F (r = -0.48).

Divergent Validity

Rheumatoid Arthritis: (Budiman-Mak, 1991)

  • Adequate correlation of the total score with hand joint count and a non-foot function measure (r = 0.33)
  • Adequate correlation of the pain subscale score with hand joint count and a non-foot function measure (r = 0.30)
  • Adequate correlation of the disability subscale with hand joint count and a non-foot function measure (r = 0.31)
  • Poor correlation of the and activity limitation subscale score with hand joint count and a non-foot function measure (r = 0.25)

Content Validity

Rheumatoid Arthritis: (Budiman-Mak, 1991)

  • Supported by factor analysis for all except 2 items on the activity limitation subscale

Floor/Ceiling Effects

Rheumatoid Arthritis: (Muradin & Van der Heide, 2016)

  • Excellent with no floor or ceiling effect noted

Responsiveness

Rheumatoid Arthritis

(Budiman-Mak, 1991) Responsiveness was reported as an association between changes in the number of painful foot joints, as an objective measure of disease activity, and changes in the FFI total and sub-scale scores over a 6 month period of time)

  • Adequate correlation between painful foot joint count and the total FFI score after 6 months (r = 0.45)
  • Adequate correlation between painful foot joint count and the pain subscale after  6 months (r = 0.47)
  • Adequate correlation between painful foot joint count and the activity limitation subscale after  6 months (r = 0.34)
  • Poor correlation  between the painful foot joint count and the disability subscale ( r = 0.11)

(Muradin & Van der Heide, 2016)

  • Large change in RA patients pre -surgery and 36 months after surgery (ES = -0.8)

(van der Leeden, 2008) *Levels of evidence were defined by the authors. Evidence was designated as level 3 for a sample size < 50. A positive rating was assigned if the ICC or kappa was >0.80, with the lower limit of the confidence interval >0.60, or if a Pearson’s correlation coefficient >0.90 was present.

  • A positive level 3 rating indicating that a change was detected in a subgroup of at least 20 patients

Mixed Populations

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Cut-Off Scores

 

Test/Retest Reliability

Referred for surgical intervention:

(Martinelli et al., 2014; n = 89; mean age = 51.8(13.9) years; FFI translated and cross-culturally adapted to Italian

  • Excellent test-retest reliability for the:
    • pain subscale (ICC = 0.94)
    • disability subscale (ICC = 0.91)

(Naal et al., 2008; n = 53; mean age = 57.2 (13.7) years; undergoing surgery at the department; FFI translated and cross-culturally adapted to German FFI (FFI-D)

  • Excellent test-retest reliability for the:
    • total score (ICC = 0.98)
    • pain subscale (ICC = 0.97)
    • disability subscale (ICC = 0.99)

Internal Consistency

Referred for surgical intervention:

(Martinelli et al., 2014; FFI translated and cross-culturally adapted to Italian)

  • Excellent internal consistency for the:
    • Pain subscale (Chronbach’s alpha = 0.95)
    • Disability subscale (Chronbach’s alpha = 0.95)

(Naal et al., 2008; German version, FFI-D)

  • Excellent internal consistency for the:
    • Total score (Chronbach’s alpha = 0.97)
    • Pain subscale (Chronbach’s alpha = 0.90)
    • Disability subscale (Chronbach’s alpha = 0.95)

Construct Validity

Referred for surgical intervention:

(Martinelli et al., 2014; FFI translated and cross-culturally adapted to Italian)

  • Adequate to excellent correlation of the FFI-Italian version pain and disability subscales with the SF-36 subscales (r = -0.31 to -0.69)
  • Adequate to excellent correlation of the FFI-Italian version pain and disability subscales with the visual analogue scale assessing pain (r = 0.55 to 0.64)

(Naal et al., 2008; German version, FFI-D)

  • Adequate to excellent correlation of the FFI-D with the physical related SF-36 domains (r = -0.43 to -0.80)
  • Excellent correlation of the FFI-D with the visual analogue scale (VAS) assessing pain (r = 0.81)
  • Excellent correlation of the FFI-D with the VAS assessing function (r = 0.77)
  • Adequate correlation of the FFI-D with the UCLA activity scale (r = -0.52)

 

Chronic Foot and Ankle Conditions (SooHoo, 2006; n = 69; mean age 46 years with a range of 16-82 years) * SF subscales: Physical Component Summary Scale (PCS); Mental Component Summary Scale (MCS); Physical Functioning (PF); Role-Physical (RP); Bodily Pain (BP); General Health (GH); Vitality (VT); Social Functioning (SF); Role-Emotional (RE); Mental Health Sub-Scales (MH).

 

  • Poor to Adequate correlation of the Disability subscale with the SF-36  subscales: (PCS r = -0.67, MCS r = -0.23, PF r  = -0 .69, RP r  = -0.62, BP r = -0.64, GH r = -0.23, VT r = -0.32, SF r = -0.39, RE r = -0.44, and MH r =  -0.34)
  • Poor to Adequate correlation of the Activity Limitation subscale with the SF-36 (PCS r = -0.53, MCS r = -0.40, PF r  = -0 .55, RP r  = -0.64, BP r = -0.41, GH r = -0.28, VT r = -0.43, SF r = -0.57, RE r = -0.47, and MH r =  -0.47)
  • Poor to Adequate correlation of the Pain subscale with the SF-36 (PCS r = -0.45, MCS r = -0.10, PF r  = -0 .32, RP r  = -0.37, BP r = -0.61, GH r = -0.14, VT r = -0.22, SF r = -0.12, RE r = -0.25, and MH r =  -0.18)

Floor/Ceiling Effects

Non-systemic Foot Disorders: (Agel, J, 2005; n = 54; mean age 52.8 (12.3) years)

  • Poor: large number of ceiling effects noted for participants who function at or above the level of independent activities of daily living (those with active lifestyles and/or participation in physical recreation).

Responsiveness

Ankle/ Foot Disorders and post-surgical (SooHoo, 2016; n = 25; mean age 40 years with a range of 21-69 years; initial data collection occurred at preoperative clinic visit, second data collection occurred at 6 months postoperatively)

  • Moderate change in the activity Limitation subscale ( ES = -0.55, standardized response means (SRM) = 0.039)
  • Moderate change in the pain subscale (ES = -0.86, SRM = -0.83)
  • Moderate change in the Disability subscale (ES = -0.75, SRM = -0.68)

Referred for surgical intervention: (Martinelli et al., 2014; average follow-up from surgery was 6.4 months ± 0.8;  FFI translated and cross-culturally adapted to Italian)

  • The responsiveness was high with an ES of 0.95 and 0.83, for pain and disability subscales, respectively, and SRM of 0.74 and 0.72.

Bibliography

Agel, J., Beskin, J. L., Brage, M., Guyton, G. P., Kadel, N. J., Saltzman, C. L., ... & Thordarson, D. B. (2005). “Reliability of the Foot Function Index: a report of the AOFAS Outcomes Committee.” Foot & ankle international, 26(11), 962-967.

Budiman-Mak, E., Conrad, K., & Roach, K. (1991). “The foot function index: A measure of foot pain and disability.” Journal of Clinical Epidemiology, 44(6), 561-570.

Budiman-Mak E, Conrad K, Stuck R, Matters M. (2006). “Theoretical model and Rasch analysis to develop a revised foot function index.” Foot & Ankle International, 27(7), 519-527.

Budiman-Mak, E., Conrad, K., Mazza, J., & Stuck, R. (2013). “A review of the foot function index and the foot function index - revised.” Journal of Foot & Ankle Research, 6(1), 1-37.

González-Sánchez, M., Ruiz-Muñoz, M., Li, G. Z., & Cuesta-Vargas, A. I. (2017). “Chinese cross-cultural adaptation and validation of the Foot Function Index as tool to measure patients with foot and ankle functional limitations.” Disability and Rehabilitation, 1-6.

Jorgensen, J. E., Andreasen, J., & Rathleff, M. S. (2015). “Translation and validation of the Danish Foot Function Index (FFI-DK).” Scandinavian Journal Of Medicine & Science In Sports, 25(4), e408-e413

Landorf, K., & Radford, J. (2008). “Minimal important difference: Values for the foot health status questionnaire, foot function index and visual analogue scale.” The Foot, 18(1), 15-19.

Martinelli, N., Scotto, G. M., Sartorelli, E., Bonifacini, C., Bianchi, A., & Malerba, F. (2014). “Reliability, validity and responsiveness of the Italian version of the Foot Function Index in patients with foot and ankle diseases.” Quality Of Life Research: An International Journal Of Quality Of Life Aspects Of Treatment, Care And Rehabilitation, 23(1), 277-284.

Martinez, B.R., Staboli, I.M., Kamonseki, D.H., Budiman-Mak, E., & Yi, L.C. (2016). “Validity and reliability of the foot function index (FFI) questionnaire Brazilian-Portuguese version.” SpringerPlus; 5(1):1810.

Muradin, I., & Van der Heide, H. (2016). “The foot function index is more sensitive to change than the Leeds Foot Impact scale for evaluating Rheumatoid Arthritis patients after forefoot or hindfoot reconstruction.” International Orthopaedics, 40(4), 745-749.

Naal, F. D., Impellizzeri, F. M., Huber, M., Rippstein, P. F. (2008). “Cross-cultural adaptation and validation of the foot function index for use in German-speaking patients with foot complaints.” Foot & Ankle International, 29(12), 1222-1228.

Paez-Moguer, J., Budiman-Mak, E., & Cuesta-Vargas, A. I. (2014). “Cross-cultural adaptation and validation of the Foot Function Index to Spanish.” Foot And Ankle Surgery, 2034-39.

Pourtier-Piotte, C., Pereira, B., Soubrier, M., Thomas, E., & Gerbaud, L. (2015). “French validation of the Foot Function Index (FFI).” Annals of Physical and Rehabilitation Medicine, 58(5), 276-282.

Saag, K. G., Saltzman, C. L., Brown, C. K., Budiman-Mak, E. (2016). “The Foot Function Index for Measuring Rheumatoid Arthritis Pain: Evaluating Side-to-Side Reliability.” Foot & Ankle International, 17(8), 506 – 510.

SooHoo, N. F., Samimi, D. B., Vyas, R. M., & Botzler, T. (2006). “Evaluation of the validity of the Foot Function Index in measuring outcomes in patients with foot and ankle disorders.” Foot & Ankle International, 27(1), 38-42.

SooHoo, N. F., & Vyas, R. & Samini, D. (2016). “Responsiveness of the Foot Function Index, AOFAS Clinical Rating Systems, and SF-36 after Foot and Ankle Surgery.” Foot & Ankle International, 27(11), 930 – 934.

van der Leeden, M., Steultjens, M. P., Terwee, C. B., Rosenbaum, D., Turner, D., Woodburn, J., & Dekker, J. (2008). “A systematic review of instruments measuring foot function, foot pain, and foot-related disability in patients with rheumatoid arthritis.” Arthritis and Rheumatism, 59(9), 1257-1269.

Vetrano M, Vulpiani MC, Erroi D, Vadalà A, Ferretti A, Saraceni VM. (2014). “Cross-cultural adaptation and reliability of the Italian version of the foot function index (FFI-I) for patients with plantar fasciitis.” The Journal of Sports Medicine and Physical Fitness, 54(5), 636-43. 

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