A review of the foot function index and the foot function index – revised

  • Elly Budiman-Mak1, 2Email author,

    Affiliated with

    • Kendon J Conrad3,

      Affiliated with

      • Jessica Mazza4 and

        Affiliated with

        • Rodney M Stuck5, 6

          Affiliated with

          Journal of Foot and Ankle Research20136:5

          DOI: 10.1186/1757-1146-6-5

          Received: 2 November 2012

          Accepted: 11 January 2013

          Published: 1 February 2013

          Abstract

          Background

          The Foot Function Index (FFI) is a self-report, foot-specific instrument measuring pain and disability and has been widely used to measure foot health for over twenty years. A revised FFI (FFI-R) was developed in response to criticism of the FFI. The purpose of this review was to assess the uses of FFI and FFI-R as were reported in medical and surgical literature and address the suggestions found in the literature to improve the metrics of FFI-R.

          Methods

          A systematic literature search of PubMed/Medline and Embase databases from October 1991 through December 2010 comprised the main sources of literature. To enrich the bibliography, the search was extended to BioMedLib and Scopus search engines and manual search methods. Search terms included FFI, FFI scores, FFI-R. Requirements included abstracts/full length articles, English-language publications, and articles containing the term "foot complaints/problems." Articles selected were scrutinized; EBM abstracted data from literature and collected into tables designed for this review. EBM analyzed tables, KJC, JM, RMS reviewed and confirmed table contents. KJC and JM reanalyzed the original database of FFI-R to improve metrics.

          Results

          Seventy-eight articles qualified for this review, abstracts were compiled into 12 tables. FFI and FFI-R were used in studies of foot and ankle disorders in 4700 people worldwide. FFI Full scale or the Subscales and FFI-R were used as outcome measures in various studies; new instruments were developed based on FFI subscales. FFI Full scale was adapted/translated into other cultures. FFI and FFI-R psychometric properties are reported in this review. Reanalysis of FFI-R subscales' confirmed unidimensionality, and the FFI-R questionnaires' response categories were edited into four responses for ease of use.

          Conclusion

          This review was limited to articles published in English in the past twenty years. FFI is used extensively worldwide; this instrument pioneered a quantifiable measure of foot health, and thus has shifted the paradigm of outcome measure to subjective, patient-centered, valid, reliable and responsive hard data endpoints. Edited FFI-R into four response categories will enhance its user friendliness for measuring foot health.

          Keywords

          FFI FFI-R FFI adaptation/translation FFI scores Foot health measures

          Background

          Foot problems commonly arise during our daily living activities [1, 2]. The prevalence of foot problems in general ranges between 10% and 24% [3]. Their prevalence is higher among older individuals and in chronic rheumatoid arthritis (RA), gout, and diabetes mellitus with peripheral neuropathy [4]. Foot pain and disability can affect workers’ productivity, work absenteeism, and other issues [5, 6]. Because pain and disability are subjective complaints, they are difficult to quantify without a valid patient report of the degree to which an individual is experiencing foot pain. Without a valid measure, problems arise in documenting foot health status, tracking the progression of diseases, and establishing the efficacy of treatment, including assessment of treatment satisfaction and of health related quality of life from a personal perspective.

          In 1991, the Foot Function Index (FFI) was developed as a self-reporting measure that assesses multiple dimensions of foot function on the basis of patient-centered values. The FFI consists of 23 items divided into 3 subscales that quantify the impact of foot pathology on pain, disability, and activity limitation in patients with RA [7]. The FFI was developed using the classical test theory (CTT) [8] method. It has been found to have good reliability and validity and has had wide appeal to clinicians and research scientists alike [3, 9, 10]. In the past 20 years, the FFI has been widely used by clinicians and investigators to measure pain and disability in various foot and ankle disorders and its use has expanded to involve children, adults, and older individuals. Furthermore, the FFI has been widely used in the study of various pathologies and treatments pertaining to foot and ankle problems such as congenital, acute and chronic diseases, injuries, and surgical corrections.

          In 2006, the FFI was revised (the FFI-R) on the basis of criticisms from researchers and clinicians; items were added, including a scale to measure psychosocial activities and quality of life related to foot health [11].

          A literature review was conducted to develop a theoretical model of foot functioning [12], 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. The results were the FFI-R long form (FFI-R L; 4 subscales and 68 items) and the FFI-R short form (FFI-R S; 34 items) as total foot function assessment instruments. Both the 68-item and 34-item measures demonstrated good psychometric properties.

          The FFI-R in its current form is one of the most comprehensive instruments available. However, in a review article [13], questions were raised about the unidimensionality and independence of FFI-R subscales, and we did not include such reports in our previous article about the FFI-R [11]. We carefully reviewed the comments about the FFI-R and assessed the unidimensionality of the subscales by use of the Rasch model. On the basis of these critiques, the FFI-R required a periodic revision of its metrics to ensure it represented patient-centered health values and state-of-the-art methodology.

          Our aim is to assess the contribution of the FFI and FFI-R to the measurement of foot health in the fields of rheumatology, podiatry, and orthopedic medicine. This assessment should enable us to reflect on and improve the quality of the measure. Therefore, we conducted a systematic review of literature pertaining to the FFI and FFI-R that has been published in the English language from October 1991 through December 2010. The objectives were to: (i), Assess the prevalence of uses of the FFI and FFI-R in clinical studies of foot and ankle disorders; (ii), Describe the utility and clinimetric properties of the FFI and FFI-R as they have been applied in various clinical and research settings; (iii), Enumerate the strengths and weaknesses of the FFI and FFI-R as reported in the literature; (iv), Address the suggestions found in the literature for improving the FFI-R metrics.

          Methods for systematic search of the literature

          This study was about a systematic review of articles in which the FFI and/or FFI-R were used as measures of a variety of foot and ankle problems. Relevant studies were identified by English language publication searches of the electronic bibliographic databases Pub Med/MEDLINE, EMBASE, BioMedLib and Scopus from October 1991 through December 2010.

          Search terms and eligibility criteria

          The key words: foot function index, FFI scores, foot function index scores, and foot function index revised (FFI-R).were used as search terms and was applied to all databases. FFI instruments/measure and/or FFI-R instruments/measure had to be mentioned in the abstracts and in the full articles to be collected for in-depth scrutiny. Articles fulfilling the inclusion criteria were selected for the review. The article criteria included: (i) the words foot function index/FFI or revised foot function index/FFI-R in its reports/measures; (ii) full-length articles; (iii) written in English and published from October 1991 through December 2010; (iv) the study population described needed to have foot complaint(s)/problems; and (v) regardless of the country conducting the study, the full-length article must have been published in English or in a foreign language with the abstract in English.

          Objectives with method of data collection and organization of tables

          Selected articles that fulfilled the criteria were independently reviewed and collected by the authors to address the objectives and organize collected data into several tables.

          Objective 1. Uses of the FFI and FFI-R

          We created four tables to address the first objective of describing the measurement’s uses (Tables 1, 2, 3, and 4).
          Table 1

          Study type, sample size and sample characteristics

          Study type

          Number

          Sample size (N)

          N Male

          N Female

          Age (SD)

          Measurement

          17

          1236

          458

          763

          54.9 (6.4)

          Surgery

          30

          1512

          648

          857

          45.1 (15.7)

          Orthoses

          19

          1101

          493

          521

          43.0 (15)

          Other intervention

          4

          170

          55

          115

          47.6 (6.1)

          Observational

          8

          695

          260

          432

          52.2 (27.9)

          Total

          78

          4714

          1914* (41%)

          2688* (57%)

          48.58 (4.9)

          *Gender not reported in 3 studies: Slattery, M [82] (2001), Clark, H [85] (2010) and Kulig, K [88] (2009).

          Table 2

          FFI uses across studies in foot and ankle disorders including diagnoses

          Diagnosis

          Measure

          Surgery

          Orthosis

          Observational

          Other

          Total

          Rheumatoid arthritis

          6

          5

          7

          3

           

          21

          Osteoarthritis

          2

          1

           

          1

           

          4

          Juvenile arthritis

            

          1

            

          1

          Hallux valgus

          2

          2

          1

            

          5

          Hallux rigidus

           

          3

             

          3

          Plantar fasciitis/heel pain

          2

          2

          4

           

          3

          11

          Metatarso phalangeal arthritis

           

          2

          2

            

          4

          Chronic foot pain

          3

          2

           

          1

           

          6

          Foot and ankle fracture

          1

          5

          1**

          1

           

          8

          Posterior tibial tendon pain

            

          1

           

          1

          2

          Bone graft

           

          1

             

          1

          Ankle deformity

           

          2

             

          2

          Flat foot

           

          1

             

          1

          Cavovarus Charcot-Marie-Tooth

           

          2

             

          2

          Osteo-chondral lesion of talus-tibia

           

          1

             

          1

          Failed total ankle arthrodesis

           

          1

             

          1

          Club foot

           

          1

             

          1

          Diabetic neuropathy

             

          1

           

          1

          Mid foot pain

          1

           

          2

            

          3

          Paget disease

             

          1

           

          1

          Total

          17

          31*

          19

          8

          4

          79*

          *Two different diagnoses occurred in one study, **Hemophilic ankle arthropathy.

          Table 3

          FFI Uses across studies conducted internationally

          Country

          Measure

          Surgery

          Orthosis

          Observational

          Other

          Total

          Australia

          2

          1

          1

            

          4

          Austria

           

          2

             

          2

          Brazil

            

          2

            

          2

          Canada

           

          2

           

          1

           

          3

          Czech Rep.

           

          2

             

          2

          France

           

          1

             

          1

          Germany

          1

          1

           

          2

          1

          5

          Japan

           

          1

             

          1

          So. Korea

            

          1

            

          1

          Netherlands

          2

          7

             

          9

          New Zealand

            

          1

            

          1

          Slovenia

            

          1

          1

           

          2

          Sweden

           

          1

             

          1

          Taiwan

          1

              

          1

          Turkey

          1

            

          2

           

          3

          UK

          2

          1

          3

          2

           

          8

          USA

          8

          12

          9

           

          3

          32

          Total

          17

          31

          18

          8

          4

          78

          Table 4

          FFI Full scale and subscale used across studies

          FFI

          Measure

          Surgery

          Orthosis

          Observational

          Other

          Total

          FFI Full scale (3 domains)

          10

          21

          14

          6

           

          51

          FFI Pain scale

          2

          1

          2

          2

          3

          10

          FFI Disability scale

           

          1

             

          1

          FFI Pain and Disability scale

          3

          3

          1

           

          1

          8

          FFI - 5pts

          1

          4

             

          5

          FFI-R Long form

          1

           

          2

            

          3

          FFI Used in studies

          17

          30

          19

          8

          4

          78

          Objective 2. Utility and clinimetric properties

          We designed a data-collection form to address the second objective. This form was assessed in a pilot study by collecting data from ten articles out of the collection of qualified articles; it was revised before being used in its current format. The variables used in this data-collection form were: (i) the instrument and year the article was published; (ii) the first author’s name; (iii) the objectives of the study; (iv) the population characteristics, sample size, and diagnosis; (v) psychometric analysis (reliability and validity, etc.); (vi) items/domains/subscales of the FFI or FFI-R used in the study; (vii) response type; and, (viii) a short summary evaluation of each study. Therefore, this data form recorded the analytic statements extracted from each article, and 6 tables were created (Tables 5, 6, 7, 8, 9, and 10). Data were arranged in each table in chronological order.
          Table 5

          Studies of foot function measures

          Instrument

          1stAuthor

          Objective

          Population (N, Sex, Age, Dx, location)

          Psychometric analysis

          Items/domains/subscales/item sources

          Response type

          Summary evaluation

          Foot Function Index, 1991

          Budiman-Mak, E [7]

          Instrument Development

          N: 87 (78 male)

          Classical Test Theory

          23 items

          Visual Analog Scale

          Good clinimetrics, applicable to various age groups and varieties of foot and ankle pathologies.

          Mean age: 61

          3 domains

           

          Conclusion: Positive

          (Range: 24–79)

          Pain, difficulty and activity limitation subscales clinician

            

          Dx: RA foot

             

          Location: USA

             

          Foot Function Index Pain (left/right), 1996

          Saag, KG [23]

          Foot Function Index pain scale; Compare right/left foot

          N: 63 (13 male)

          Classical Test Theory

          9 items

          Visual Analog Scale

          This measure of right vs. left side of the foot showed good clinimetric properties

          Mean age: 57.5 (SD=11.6)

           

          FFI pain subscale

           

          Conclusion: Positive.

          Dx: RA

           

          clinician

            

          Location: USA

              

          Foot Function Index/Foot Health Status Questionnaires (FHSQ), 1998

          Bennet PJ [9]

          Development of FHSQ, a new measure

          N: 111 (25 male)

          Classical Test Theory

          13 items

          Likert

          FHSQ has good clinimetrics.

          Mean age: 54 (SD=20)

           

          4 domains clinician

           

          Conclusion: Positive.

          Dx: Osteoarthritis hallux valgus

              

          Location: Australia

              

          Foot Function Index/Ankle Osteoartitis Score (AOS), 1998

          Domsic, RT [24]

          AOS consisted of Foot Function Index pain and disability scales

          N: 36 (12 male)

          Classical Test Theory

          18 items

          Visual Analog Scale

          AOS had good clinimetrics.

          Mean age: 52.7 (Range: 16–79)

          2 Domains clinician

          Conclusion: Positive.

          Dx: Ankle osteo-arthritis

            

          Location: USA

            

          Foot Function Index/Foot Function Index- 5pts in Dutch, 2002

          Kuyvenhoven, MM [3]

          Foot Function Index in Dutch

          N: 206 (78 male)

          Classical Test Theory

          15 items

          5-point Likert

          Adaptation of Foot Function Index to 5 point Likert, used as a generic measure in foot and ankle problems.

          Mean age: 61 (SD=10)

          2 domains: pain & disability clinician

          Conclusion: Positive.

          Dx: OA with limited mobility and pain

            

          Location: Netherlands

            

          Foot Function Index/Foot Health Status Questionnaire (FHSQ), 2002

          Landorf, KB [10]

          Validation of FHSQ to Foot Function Index

          N: 17 (4 male)

          Non-parametric statistics

          FHSQ

          5-point Likert

          FHSQ has less items than FFI and was printed in larger font for ease of use.

          Mean age: 44.6 (SD=10.5) (Range 24–72)

          13 items

          Conclusion: Positive.

          Dx: Painful plantar fasciitis

          4 domains; clinician

           

          Location: Australia

            

          Foot Function Index/Foot Impact Scale (FIS), 2005

          Helliwell, P [29]

          Validation with Health Assessment Questionnaire (HAQ), FFI, and Manchester Foot Disability Questionnaires (MFDQ)

          N: 148 (34 male)

          Item Response Theory

          FIS

          Visual Analog Scale

          FIS items were derived from RA patients (consisted of impairment/shoes and activities/participation subscales), with good clinimetric properties.

          Mean age: 61.7 (Range 28–89)

          51 items

          Conclusion: Positive.

          Dx: RA Foot Pain

          2 domains

           

          Location: UK

          Patient

           

          Foot Function Index, 2005

          Agel, J [25]

          Reliability and validity tests in specific population with moderate to high physical function

          N: 54 (22 male, 6 unknown)

          Correlation statistics

          Foot Function Index

          Likert Scale

          Use of Foot Function Index in non-systemic foot and ankle problems requires removal of 2 items each from pain and disability, judged not applicable for this condition.

          Mean age: 52.8 (SD=12.3) (Range 19–74)

          23 items

          Conclusion: Positive.

          Dx: Non-traumatic foot/ankle complaints

          3 domains

           

          Location: USA

            

          Foot Function Index, 2005

          Shrader, JA [28]

          Reliability and validity measures of navicular joint deformity vs. clinical findings

          N: 20 (0 male)

           

          Foot Function Index

          Visual Analog Scale

          Foot Function Index was used to measure the foot health status associated with joint deformities.

          Mean age: 55.4 (SD=11.4 years); Dx: RA 12.7 years (SD=10.4)

          Index 23 items

          Conclusion: Positive.

          Dx: Navicular joint dropped and foot pain

          3 domains

           

          Location: USA

            

          Foot Function Index-R with Foot Function Index, 2006

          Budiman-Mak, E [11]

          Instrument Development

          N: 97 (90 male)

          Item Response Theory

          Foot Function Index

          Likert scale (replaced Visual Analog Scale)

          Foot Function Index-R had 3 domains, plus 4th psychosocial domain added to assess quality of life.

          Mean age: 69 (range: 38–88)

          68 items (long)

          Conclusion: Positive

          Dx: Chronic foot and ankle complain

          34 items (short)

           

          Location: USA

          Clinicians and patients

           

          Foot Function Index, 2006

          Bal, A [26]

          Comparing Foot Function Index with Health Assessment Questionnaires (HAQ) & SFC

          N: 78 (11 male)

          Correlation statistics

          Foot Function Index

          Visual Analog Scale

          Strong correlations of HAQ and Foot Function Index scores, HR and CV also reflected in Foot Function Index scores and were highly correlated with Rand 36 items Short Form Health Survey (SF36).

          Mean age: 50.65 (SD=10.7); RA duration 13.96 (SD=8.09)

          23 items

          Conclusion: Positive

          Location: Turkey

          3 Domains

           

          Foot Function Index & SF36, 2006

          SooHoo, N [27]

          Validity test in foot health and general physical health

          N:69 (25 male)

          Correlation statistics

          Foot Function Index

          Visual Analog Scale

          The 3 domains of Foot Function Index demonstrated moderate-high correlation with SF36, thus it was reasonable to use Foot Function Index to monitor outcomes.

          Mean Age: 46 (Range 16–82)

          23 items

          Conclusion: Positive.

          Dx: Foot & Ankle disorder

          3 domains

           

          Location: USA

            

          Foot Function Index & American Orthopedic Foot and Ankle Society (AOFAS) hallux module, 2006

          Baumhauer, JF [32]

          Reliability and validity of test, compared with Foot Function Index

          N:11 (1 male)

          Correlation statistics

          AOFAS hallux & lesser toes module

          Numeric rating scale

          Only AOFAS hallux for pain correlated with Foot Function Index pain scale.

          Mean age: 54 (Range: 40–72)

          Conclusion: Positive.

          Dx: RA without foot complaints

           

          Location: USA

           

          Foot Function Index, 2006

          Van der Leeden, M [30]

          Measure forefoot damage

          N:62 (15 male)

          Correlation Statistics

          Validation with Western Ontario Mac Masters Universities Osteoarthritis Index (WOMAC) and Disease Activity in 44 RA joints (DAS-44)

          Numeric rating scale

          Foot Function Index function subscale correlated with WOMAC and DAS-44. Foot Function Index pain score correlated with forefoot pain. Foot Function Index function score correlated with hind foot problem.

          Mean age: 55.7 (SD=13.11)

          Conclusion: Positive.

          Dx: RA forefoot complaints, duration of 96 months

           

          Location: Netherlands

           

          Foot Function Index, American Orthopedic Foot and Ankle Society (AOFAS) clinical rating component, 2007

          Ibrahim, T [33]

          Testing the criterion validity of clinical rating components of AOFAS with Foot Function Index

          N:45 (11 male)

          Correlation Statistics

          Validity of AOFAS scale

          Numeric rating scale

          The scores of AOFAS clinical ratings and Foot Function Index were moderately correlated based on 41% response rate.

          Mean age: 55 years (range=15-81)

          Conclusion: Positive.

          Dx: Hallux deformities

           

          Location: UK

           

          Foot Function Index,/Foot Function Index Chinese (Taiwan), 2008

          WU, SH [36]

          Reliability and validity measure of PCS of SF-26, Taiwan version;

          N:50 (planta fasciitis); mean age 46.9 (SD=10.6)

          Cross-cultural adaptation

          Foot Function Index

          Visual Analog Scale

          Foot Function Index Taiwan Chinese consisted of 21 items. Could measure non-traumatic and traumatic foot and ankle problems. The floor score was 10%, in sample with fractures.

          N:29 (ankle/foot fracture); mean age 37.2 (SD=14.8) 25 male

          21 items

          Conclusion: Positive.

          Location: Taiwan

          3 domains

           

          The order of items was changed.

           

          Clinician and patient

           

          Foot Function Index, Foot Function Index-D, 2008

          Naal, FD [34]

          Foot Function Index-D,

          N:53 (14 male)

          Cross-cultural adaptation

          Foot Function Index-D

          Numeric rating scale

          Foot Function Index underwent German translation. Foot Function Index-D added 3 new items and revised 8 items of the Foot Function Index and had demonstrated good clinimetrics.

          Age: 57.2 (SD=13.7) Range (18=77)

          Index-D 18 items (pain & disability subscales)

          Conclusion: Positive.

          Dx: Foot complaints

          2 domains

           
             

          Location: Germany

           

          Clinician and patient

            
          Table 6

          Clinimetric properties of patient-reported foot function measures

          Instrument; author year

          Reliability e.g., IRT, CTT ICC, kappa, test-retest

          Cronbach’s alpha

          Instrument /Domain N items/ Item generated sources

          Validity (Face, content, criterion or construct) and other measures

          Response to change

          Completion time

          Sample N diagnoses conclusion

          FFI; Budiman Mak, E [7] 1991

          CTT

          Total: 0.96

          FFI

          Face: yes

          Yes

          10 minutes

          N=87

          ICC total: 0.87

          Pain: 0.70

          23 items

          Criterion: r=0.52 FFI total scores vs 50 ft walked

          Early rheumatoid arthritis

          ICC (pain): 0.70

          Disability: 0.93 Activity

          Clinician and patient

          Construct: Yes

          Conclusion: Positive

          ICC (disability): 0.84

          Limitation 0.73

             

          ICC (activity limitation): 0.81

              

          FFI pain subscale (R/L foot); Saag, KG [23] 1996

          CTT

          0.94-0.96

          FFI side-to-side; Clinician and patient

          Face: Yes

            

          N=63 Rheumatoid foot pain

          ICC: 0.79-0.89

            

          Content: Yes

            

          Conclusion: Positive

          FFI and AOS; Domsic, RT [24]1998

          CTT

           

          AOS

          Criterion: AOS vs WOMAC disability

            

          N=562

          ICC: 0.97

           

          18 items; Clinician

          r=0.65 pain r=0.79

            

          Dx: Ankle Osteoarthritis

          Pain: 0.95

            

          Construct: Yes

            

          Conclusion: Positive

          Disability: 0.94

                

          FFI & FHSQ. Bennet, PJ [9]1998

          CTT

          0.85-0.88

          FHSQ

          Criterion: Yes

           

          3-5 minutes

          N=255 Dx: Hallux valgus osteoarthritis

          ICC

          Pain: 0.88

          13 items

          Construct: Yes, discriminant validity; Goodness of Fit

            

          Conclusion: Positive

          0.74-0.92

          Function: 0.85

          Clinician and Patient

              

          pain 0.86

          Footwear: 0.85

               

          function 0.92

          Foothealth: 0.87

               

          footwear 0.74

                

          foothealth 0.78

                

          FFI (5 pt); Kuyvenhoven, MM [3] 2002

          CTT

          0.88-0.94

          FFI (5 pt)

          Concurrent validity: Yes

          Yes

           

          N=206

          ICC 0.64-0.79

          Total: 0.93

          15 items

             

          Dx: Non-traumatic foot complaint

          Total: 0.76

          Pain: 0.88

          Clinician

             

          Conclusion: Positive

          Pain: 0.64

          Disability: 0.92

               

          Disability: 0.79

                

          FFI & FIS; Helliwell,P [29] 2005

          IRT

          Not performed

          FIS

          Face: Yes

            

          N=192

          ICC

           

          51 items

          Content: Yes

            

          Rheumatoid arthritis

          Impairment/shoes: 0.84 Activities/participation: 0/96

           

          2 subscales

          Construct: Yes

            

          Conclusion: Positive

            

          clinician and patient

          Goodness of Fit

             

          FFI; Agel, J [25] 2005

          ICC

           

          FFI

             

          N =54 FFI was tested in non-systemic or traumatic foot problems.

          Total: 0.68

           

          19 items items each from pain and difficulty subscales were deleted

             

          FFI was good for individuals with low level functioning.

          All subscale values were significant at .01 level

           

          Clinician

             

          Conclusion: Positive

          FFI-R; Budiman-Mak, E [11] 2006

          IRT

          Total: 0.95

          FFI-R

          Criterion: Yes

           

          15 minutes

          N=92

          Person reliability: 0.96

          Pain: 0.93

          Long form (68 items); Short form (34 items) Clinician and patient

          Construct: Yes

            

          Dx: Chronic foot and ankle problems

          Item reliability:0.93

          Disability: 0.93

           

          Minimal floor effect (4.5%)

            

          Conclusion: Positive

           

          Activity limitation: 0.88

           

          Goodness of Fit

             
           

          Psychosocial: 0.86

               

          FFI & SF 36: SooHoo, NF [27] 2006

          Pearson Correlation of FFI to SF-36: Pain: -0.10 to −0.61;

           

          FFI

          Construct: Yes

            

          N=69

          Disability: -0.23 to −0.69

           

          23 items

             

          Forefoot and hindfoot complaints

          Activity limitation: -0.23 to −0.61

           

          3 domains

             

          Moderate correlation between FFI and SF-36

                

          Conclusion: Positive

          FFI AOFAS; Baumhaur, JF [32] 2006

          ICC AOFAS Summary Scores: Hallux 0.95 Lesser toes: 0.8 Pearson’s correlations mean value AOFAS Hallux vs. FFI: r=0.80, AOFAS lesser toes vs FFI: r=0.69; Pain subscale AOFAS Hallux vs. FFI summary score: r=0.31

           

          FFI

          Content: Yes

            

          N=11

            

          23 items

          Criterion: Yes

            

          Rheumatoid Hallux and lesser toes

            

          3 domains

          Ceiling effect noted in lesser toe activity subscale

            

          Conclusion: Positive

          FFI FHSQ ; Landorf, KB [101] 2007

          ICC measures were reported; Minimal important difference (MID) was the focus of this clinical measure

           

          MID

             

          N=175

            

          FHSQ Pain 14, Function 7, General health 9

             

          Plantar fasciitis

            

          FFI Pain 12, Function 7, Total 7

             

          Conclusion: Positive

            

          VAS

              

          Pain 9

          FFI, AOFAS; Ibrahim, T [33] 2007

          Test-retest AOFAS; pre and post operation was no different; 41% response rate. Pearson correlation with FFI was −0.68 for all the subjective components of AOFAS. Hallux module subjective component was −0.46

           

          AOFAS subjective component; Items dependent on modules

          Criterion: yes

          Yes

           

          N=45 Foot and ankle problems

            

          Clinician

          Construct: Yes

            

          AOFAS reliability and validity was tested.

             

          Discriminant and predictive validity

            

          Conclusion: positive with caution due to several limitations as mentioned in the paper.

          FFI, FFI Taiwan Chinese; Wu, SH [36] 2008

          ICC

          CA

           

          Criterion: Yes Floor effect 10%

            

          N=79

          Total 0.82

          Total 0.94

              

          Traumatic (fracture) non-traumatic plantar fasciitis foot problems

          Pain 0.74

          Pain 0.91

              

          Conclusion: positive with caution, due to limitations (see article)

          Disability 0.76 activity limitation 0.88

          Disability 0.95

               
           

          Activity limitation 0.75

          Clinician and patients

              

          Pearson’s correlations

           

          FFI total with SF 36 r=−0.59 plan- tar fasciitis r=−0.61 ankle fracture

               

          FFI, FFI- German Naal FD [34] 2008

          ICC

          CA total 0.97

          FFI German 18 items pain and disability subscales 3 items were added to the instrument by patients

          Construct yes Convergent validity FFI-G vs PCS of SF-36, VAS pain, disability UCLA activity scale

          Yes

          8.3 min

          N= 53

          Total 0.98

          pain 0.90

          Clinician and patients

             

          Various foot problems required surgery

          Pain 0.97

          disability 0.95

          Patient related difficulty 2.4 of rating scale 1-10

              

          Disability 0.99

          Cross cultural adaptation English to German with forward and backward protocol

              

          Conclusion: positive

          FFI-R; Rao S [75] 2009

          This report is about minimal detectible change (MDC90) a measure of clinical importance.

           

          FFI-R long 68 items

          MDC Total 5 Pain 5

            

          N=22 Orthoses treatment in mid foot pain

          A result of orthoses intervention in midfoot arthritis

            

          Activity limitation 7

            

          Conclusion positive

             

          Effect Size (ES) Total 0.4 Pain 0.6 Activity limitation 0.4

            

          MDC and ES findings are significant

          FFI-R; Rao, S [76] 2010

          A measure of clinical importance of orthoses intervention

           

          FFI-R long 68 items

          MDC Total 5, Pain 5 Stiffness 6, Disanility 7, Activity limitation 7 Psychosocial 7 ES: Total 0.7, Pain 0.84, Stiffness 0.31, Disability 0.6, Limitation 0.57, Psycho social 0.32

            

          N 30 Mid foot pain

                 

          Conclusion positive

          Table 7

          Studies using foot function measures in surgical interventions

          Instrument

          1stAuthor

          Objective

          Population (N, Sex, Age, Dx, location)

          Analysis

          Items/Domains/Subscales

          Response type

          Summary evaluation

          Foot Function Index (FFI), 2000

          Lin, S [39]

          Validation of AOFAS forefoot outcomes of arthrodesis surgery

          N: 16 Mean age: 44 (SD=13.96) 8 male

          Pre-post surgery

          FFI

          VAS

          Both FFI and AOFAS scores were improved at post surgery.

             

          Dx: Tarsometatarso injury/degenerative arthritis

          Follow-up 36 months (24–65 months)

          23 items

           

          Conclusion: useful

             

          Location: USA

          FFI and AOFAS were applied at pre-surgery and at follow up

          3 domains

            

          FFI, 2002

          Watson, TS [61]

          Validation with VAS pain scale with SF-36 short form in plantar fasciotomy

          Group I N (control): 75 Mean age: 46 (range: 20–78) 14 male

          Retrospective observational Follow up duration 26.4 months

          FFI

          VAS

          FFI scores were improved.

             

          Group II N (surgery): 46 Mean age: 46 (Range: 25–78) 9 male

          Group II filled out FFI and SF-26 at post-surgery only

          23 items

           

          FFI scores reflected activities of daily living. SF-36 s cores reflection satisfaction of physical and role model.

             

          Dx: Sub-Calcaneal pain syndrome

          Validation with VAS pain scale SF-36 short form

          3 domains

           

          Conclusion: useful.

             

          Location: USA

              

          FFI, 2003

          Mulcahy, D [56]

          Surgery-Reconstruction of the forefoot; FFI scores were used to test if there was correlation with WOMAC, AOFAS HMIP, and AOFAS LMIP.

          N: 79 14 male Mean age: 59 (Range: 24–80)

          Retrospective observational; Follow up 6yrs.+3 mo (6mo-19 years)

          FFI; 23 items; 3 domains

          VAS

          FFI pain subscale was used to monitor pain in both groups.

             

          Dx: RA forefoot deformity

             

          Conclusion: useful

             

          Mean age of surgery: 52 years (range: 23–79)

              
             

          Group 1 stable 1st ray. (no surgery)

              
             

          Group 2: 1st ray surgery

              
             

          Location: Canada

              

          FFI, 2004

          Ibrahim T [48]

          Surgery- MTP joint replacement; Validation of AOFAS Hallux scale scores with FFI scores from those who did not have surgery and those who had surgery

          N: 8, 1 male

          Retrospective observational; Follow up for 17 months

          FFI

          VAS

          Correlation observed between the scores of AOFAS and FFI

             

          Mean age: 58 (Range: 51–80)

           

          23 items

           

          Note: AOFAS Hallux scale had not been validated.

             

          Dx. Hallux rigidus

           

          3 domains

           

          Conclusion: useful

             

          Location: UK

              

          FFI, 2004

          Vallier, HA [52]

          Surgery-Open reduction internal fixation; Correlation of FFI and musculoskeletal function assessment (MFA)

          N: 100 60 male

          Retrospective observational

          FFI

          VAS

          Scores of FFI and MFA were correlated

             

          Mean age: 32.6 (Range: 13–77)

          Follow up 36 months (12–74 months)

          23 items

           

          Conclusion: useful

             

          Dx: Talar neck fracture

          FFI was applied to N=59 at follow-up

          3 domains

            
             

          Location: USA

              

          FFI, 2005

          Taranow, WS [49]

          Surgery- metalic hemiarthroplasty: Do FFI scores improve at post-operation

          N: 28 17 male

          Retrospective observational case review

          FFI

          VAS

          FFI scores from pre to post operation showed significant improvement.

             

          Mean age: 52.9 (Range: 38–71)

          Follow 33.4 months

          23 items

           

          Conclusion: useful

          (3–mo-111mo)

             

          Dx: Hallux rigidus

           

          3 domains

            
             

          Location: USA

              

          FFI, 2005

          Grondal, L [40]

          Surgery-Athrodesis vs. Mayo resection of MTP; FFI scores as outcomes

          N: 31; 26 male

          RCT not-blinded, ANOVA and multiple comparisons

          FFI

          VAS

          FFI scores at post-surgery within groups were improved and there no significant differences between the groups.

             

          Mean age: 54 yrs

           

          23 items

           

          Conclusion: useful

          (Range: 33–77)

             

          Resection N=: 16

           

          3 domains

            
             

          Fusion N=: 15

              
             

          Dx: RA painful forefoot deformity

              
             

          Location: Sweden

              

          FFI, 2005

          Daniels, TR [62]

          Surgery -Free tibular graft; FFI scores were validated with MODEMS and SF-36 short form

          N: 28, 13 male

          Observational

          FFI 21 items (2 items about orthoses were not applicable) 3 domains

          Likert

          The scores of FFI, SF-36 and MODEMS were demonstrating similar improved outcomes at post-surgery

             

          Mean age: 52 (Range: 22–76)

          Follow-up: 36 months (26–52 months)

            

          Conclusion: useful

             

          Dx: Vascularized fibular bone graft

          FFI was applied at pre-surgery and at 6 and between 26–54 month post surgery

             
             

          Location: Canada

              

          FFI, 2005

          Lee, S [63]

          Surgery -Isolated sesamoidectomy; FFI disability sub-scale validated with VAS pain scale and SF-36 short form

          N; 32; 8 male

          Retrospective observational

          FFI 9 items

          VAS

          The scores of FFI disability and VAS pain sub-scales were correlated.Conclusion: useful

             

          Mean age: 37.2 (Range: 18–65)

          62 month

          1 domain: disability scale

            

          Post-op N=: 20

             

          Dx: Hallux alignment

              
             

          Location: USA

              

          FFI, 2006

          SooHoo, NF [64]

          Surgery- Any type of foot and ankle surgery; Validating AOFAS, SF-36 and measuring Standard Response Mean (SRM) and effect size (ES)

          N: 25; 6 Male

          Pre-post surgery FFI was applied at pre-surgery and 6 months post-surgery

          FFI

          VAS

          Of the instruments used, scores of the pain subscale was the only measure reflecting high SRM (−0.83) and ES (−0.86). Therefore, pain is the most important outcome in studies regarding chronic foot and ankle pain.

             

          Mean age: 40 (Range: 21–69)

           

          23 items

           

          Conclusion: useful

             

          Dx: Chronic foot and ankle conditions requiring surgery

           

          3 domains

            
             

          Location: USA

              

          FFI, 2006

          Van der Krans, A [41]

          Surgery- Calcaneal Cuboid arthrodesis; Correlation with AOFAS clinical rating index (CRI) of the hind foot

          N: 20; 4 Male

          Pre-post surgery

          FFI-Dutch 15 items

          5-point verbal scale

          FFI and CRI scores showed significant improvements

             

          Mean age: 55 (Range: 30–66)

          Follow-up 25 months (13–39 months)

          Pain and function subscales

           

          Conclusion: useful

             

          Dx: Flat foot

          FFI was applied at pre-surgery and ad follow-up

             
             

          Location: Netherlands

              

          FFI, 2006

          Harris, M [53]

          Surgery- High impact fracture repair; Correlation with Musculoskeletal function assessment (MFA)

          N: 76; 45 Male

          Pre-post surgery follow up 26 months (24–38 months). FFI was applied at pre-surgery, 6 and 12 weeks and at 6 months by mail, telephone, and was self-administered.

          FFI

          VAS

          High FFI score occurred in those with the worse fractures and external fixation. This is also reflected in MFA scores.

             

          Mean age: 45 (Range: 17–81)

           

          23 items

           

          Conclusion: useful

             

          Dx: distal tibial plafond fracture

           

          3 domains

            
             

          Location: USA

              

          FFI, 2006

          Stegman M [42]

          Surgery-Triple arthrodesis; Correlation with AOFAS hind foot scores

          N: 81; 38 Male

          Pre-post surgery

          FFI Dutch

          Likert

          FFI-5pt and AOFAS hind foot scores improved 89%. However, patient did not perceive the benefit of the procedure.

             

          Mean age: 40.5 (Range: 14–79)

          FFI applied at pre-surgery and 1 yr (1–4) post surgery

          15 items

           

          Conclusion: useful

             

          Dx: Hind foot disorders

           

          2 domains

            
             

          Location: Netherlands

              

          FFI, 2007

          Jung, HG [45]

          Surgery-Fusion of tarso metatarso-joint; Correlation with SF-36, AOFAS

          N: 67; 12 Male

          Retrospective observational

          FFI

          VAS

          Scores of the FFI, SF-36 AOFAS and VAS pain scale were markedly improved at post-surgery

             

          Mean age: 60.2 (Range: 35–84)

          Follow for 40.6 months

          23 items

           

          Conclusion: useful

             

          Dx: Non-traumatic osteoarthritis of the tarso-meta-tarso joints

          FFI applied at post-surgery

          3 domains

            
             

          Location: USA

              

          FFI, 2008

          Vesely, R [43]

          Surgery – Tibio Calcaneal arthrodesis; Correlation with ankle-hind foot score

          N: 20; 16 Male

          Retrospective observational

          FFI

          VAS

          The scores of FFI and ankle hind foot were improved.

             

          Mean age: 58.7 (Range: 23–72)

          FFI applied at post-surgery, time unknown

          23 items

           

          Conclusion: useful

             

          Dx: Traumatic arthritis of the ankles

          Article in Czech with English abstract.

          3 domains

            
             

          Location: Czech Republic

              

          FFI, 2008

          Stropek, S [37]

          Surgery- arthroscopy

          N: 26; 6 Male

          Pre-post surgery observational

          FFI

          VAS

          FFI pain scale scores were markedly improved at post surgery in 79% of the patients

             

          Age: male: 45; female: 49

          FFI applied at pre-surgery and at 3 month follow-up

          Pain scale

           

          Conclusion: useful

             

          Dx: Calcaneal spur

           

          9 items

            
             

          Location: Czech Republic

              

          FFI, 2008

          Schutte, BG [50]

          Surgery-Total ankle replacement; pain and function outcome measure

          N: 47; 16 Males

          Pre-post surgery

          FFI-Dutch

          Likert

          Total scores improved at post–surgery

             

          Mean age: 57.1 (range 37–81)

          FFI applied at pre-surgery and at follow up

          18 items

           

          Conclusion: useful

             

          Dx: Ankle joint deformity

          Duration of follow up 28 months (range 12–67)

          Pain and difficulty subscales

            
             

          Location: Netherlands

              

          FFI, 2008

          Ward, CM [57]

          Surgery-Reconstruction; Validation of SF 26 with FFI

          N: 25; 14 Male

          Pre-post surgery

          FFI

          VAS

          At follow up the FFI scores were in the mid-range. The scores for smokers were worse than non-smokers, females were worse than males. FFI activity limitation and disability scores were correlated with SF-36 physical component scores.

             

          Mean age: 15 (Range: 8.7-25)

          FFI applied at mean age of 41.5 years after 26.1 yrs follow-up

          23 items

           

          Conclusion: useful

             

          Dx: Flexible Cavovarus Charcot Marie-Tooth

           

          3 domains

            
             

          Location: USA

              

          FFI, 2009

          Castellani, C [65]

          Surgery-Fixation with cannulation osteosynthesis; Outcomes of an intervention

          N: 21; 11 Male

          Retrospective observational

          FFI

          VAS

          At follow-up 3 of the 21 (14%) had poor FFI disability scores

             

          Dx: Transitional fracture of distal tibia

          FFI was applied at 3.8 yrs after implants removal

          23 items

           

          Conclusion: useful

             

          Age 13.7 (1.4)

           

          3 domains

            
             

          Location: Austria

              

          FFI, 2009

          Bonnin, MP [51]

          Surgery – Total ankle arthoplasty; Correlations of FAAM (foot and ankle ability measure)

          N: 140; 50 Male

          Pre-post surgery pre at pre-surgery FAAM and FFI was applied, and also at 53.8 ±29 months (12–125) post- surgery

          FFI

          VAS

          FFI pain scores were no different between OA and RA groups. The FFI scores were improved and were similar to that of FAAM.

             

          Mean age: 60.9 (Range: 26–90)

           

          23 items

           

          Conclusion: useful

             

          Dx: OA: 100 RA: 40

           

          3 domains

            
             

          Location: France

              

          FFI, 2009

          Potter, MQ [54]

          Surgery- Intraarticular fracture of the Calcaneus; Correlation with AOFAS hind foot scores

          N: 73; 52 Male

          Retrospective observational FFI applied at follow up of 12.8 years (5–18.5)

          FFI

          VAS

          Scored of FFI, AOFAS hind foot and Calcaneal scores were correlated.

             

          Dx: Calcaneal fracture

           

          23 items

           

          Conclusion: useful

             

          Location: USA

           

          3 domains

            

          FFI, 2010

          Aurich, M [66]

          Surgery-Arthroscopic chondrocyte implant; Correlation with AOFAS hind foot scores and Core Scale of the foot and ankle module of the Academy of Orthopedic Surgeon (AAOS)

          N: 18; 13 Male

          Retrospective observational FFI was applied at pre-arthroscopy and at follow-up, with mean duration of 19 months

          FFI 18 items; Pain and function subscales

          Likert

          FFI scores improved comparable with those of AOFAS results and Core Scale scores

             

          Mean age: 29.2 (SD 10.2 years)

             

          Limitation: Use of FFI measures with caution in individual whose. functional level is better than the level of activities of daily living.

             

          Dx: Osteochondral lesion of talus/tibia

             

          Conclusion: useful

             

          Location:Australia

              

          FFI, 2010

          Van der Heide, HJL [59]

          Surgery-Correction pes cavo varus; Validation AOFAS lesser toe module

          N: 39; 6 Male

          Pre-post surgery; FFI applied at pre-surgery and 40 month post-surgery

          FFI-Dutch

          VAS

          FFI pain and function scores improved post-surgery

             

          Mean age: 59 (Range: 29–81)

             

          Conclusion: useful

             

          Dx: RA lesser MTP

           

          23 items

            
             

          Location: Netherlands

           

          3domains

            

          FFI- Dutch, 2010

          Kroon, M [60]

          Surgery-Correction pes cavo varus; Validation AOFAS hind foot scale

          N: 15; 8 Male

          Pre-post surgery FFI applied at pre and 50 month post surgery

          FFI-Dutch

          Likert

          Pain and function scores improved post surgery

             

          Mean age:40 (SD 14)

           

          18 items

           

          Conclusion: useful

             

          Dx: Cavo varus foot deformity

           

          Pain and function subscales

            
             

          Location: The Netherlands

              

          FFI, 2010

          Van Doeselaar, DJ [46]

          Surgery-Fusion of MTP; Correlation with VAS pain and satisfaction

          N: 62

          Pre-post surgery; FFI applied at pre-surgery and 12 month post-surgery

          FFI Dutch; 18 items

          Likert

          FFI-5 pts scores were improved.

          2 groups

             

          Dx: H rigidus; N: 27; 9 Male

             

          Conclusion: useful

             

          Mean age: 58 (Range: 42–72)

              
             

          Dx: H valgus; N: 35; 6 Male

              
             

          Mean age: 61 (Range: 37–76)

              
             

          Location: Netherlands

              

          FFI, 2010

          Doets, HC [44]

          Surgery-Salvage arthrodesis for failed TAA; Correlating with AOFAS and VAS pain scale

          N: 18; 4 Male

          Retrospective observational FFI applied at follow up, 3–12 years

          FFI-Dutch

          5 point rating scale

          FFI scores improved similar to that of AOFAS, VAS pain, disability and satisfaction measure

             

          Mean age: 55 (Range: 27–76)

           

          15 items

           

          Conclusion: useful

             

          Dx: Failed TAA

           

          Pain and function subscales

            
             

          Location: Netherlands

              

          FFI, 2010

          Niki, H [47]

          Surgery-TMT fusion and osteotomy; Concurrent assessment of FFI and SF-36 and Japanese Society for Surgery of the Foot and Ankle Score

          N: 30; 1 Male

          Pre-post surgery FFI was applied at pre-surgery and at 36 mos follow-up

          FFI

          VAS

          The scores of all instruments were improved at post-surgery.

             

          Mean age: 53.6 (Range: 45–67)

           

          23 items

           

          Conclusion: useful

             

          Dx: RA fore-foot deformity

           

          3 domains

            
             

          Location: Japan

              

          FFI, 2010

          Schlegel, UJ [58]

          Surgery-Club foot correctional; Post-surgery foot health assessment

          N: 98; 72 Male

          Retrospective observational FFI was applied at 8.2 years (0–11.2); Post surgery N: 46 (50%)

          FFI

          VAS

          FFI scores indicated good foot health.

             

          Mean follow-up: 4.5M (Range: 1–68)

           

          23 items

           

          Conclusion: useful

             

          Dx: Club foot

           

          3 domains

            
             

          Location: Germany

              

          FFI, 2010

          Gaskill, T [55]

          Surgery- Internal fixation of the instraarticular Calcaneal fracture; Concurrent evaluation with OAFAS hind foot

          N: 146; 99 Male

          Retrospective observational FFI was applied at post-surgery 8.98 years

          FFI

          VAS

          FFI scores of Group 1 were better than Group 2 at post surgery.

             

          Group 1 <50 yrs; N: 99; 65 male

           

          23 items

           

          Conclusion: useful

             

          Mean age: 36 (Age range)

           

          3 domains

            
             

          Group 2 >50 years; N: 47; 33 male

              
             

          Mean age: 58 (Range: 50–84)

              
             

          Dx: Calcaneal fracture

              
             

          Location: USA

              

          FFI, 2010

          Eberl, R [67]

          Surgery- Various surgical techniques were applied; Post surgery outcomes

          N: 24; 18 Male

          Retrospective observational

          FFI

          VAS

          FFI scores improved in both groups. Group 1 scored better than Group 2.

             

          Mean age: 13.2 (Range: 5–17 yrs)

          Follow-up 3.2 years (7 months-8.2 years)

          23 items

           

          Limitation: The author stated that use of self-report in instrument in children may result in spurious outcomes, due to their pronounced potential for compensation.

             

          Group 1 <12 years; N: 9; Age : 9.2

          FFI applied at follow up

          3 domains

           

          Conclusion: useful

             

          Group 2 >12 years; N: 15; Age: 14.6

              
             

          Dx: Complex ankle injuries

              
             

          Location: Australia

              
          Table 8

          Studies using foot function measures in orthotic intervention

          Instrument

          1stAuthor

          Study and objective

          Population (N, Sex, Age, Dx, location)

          Methods & Analyses

          Items/Domains/ Subscales

          Measurement scale

          Summary evaluation

          FFI,1995

          Budiman-Mak, E [74]

          Outcome measure of orthotic intervention in hallux valgus deformity

          N=102

          RCT double blind Intent to Treat Analysis FFI applied at baseline and each follow up visit

          FFI

          VAS

          This study suggest that foot orthosis can prevent or slowed the progression of hallux valgus deformity

             

          Treatment group (N: 52)

           

          23 items

            
             

          Mean age: 60.2 (SD 10.6)

           

          3 domains

            
             

          Male: 46 (88.5%)

              
             

          Control group (N:50)

              
             

          Mean age: 58.8 (SD 11.9)

              
             

          Male: 43 (86%)

              
             

          DX:RA

              
             

          Location: USA

              

          FFI, 1996

          Conrad, KJ [70]

          Outcome measure-Pain and function measures

          N:102

          RCT double blind Post –test Random effect model for longitudinal data

          FFI

          VAS

          This study showed no benefit on pain and disability measures between treatment group and placebo group

             

          Treatment group (N: 52)Mean age: 60.2 (SD 10) 46 male

          FFI applied at baseline and at each follow up visit

          23 items

           

          Conclusion: useful

             

          Control group (N:50) Mean age: 58.8 (SD11.9) 43 male

           

          3 domains

            
             

          Dx: RA

              
             

          Location: USA

              

          FFI, 1997

          Caselli, MA [77]

          Outcome measure - Effectiveness of the intervention

          N: 34; Mean age: 43 (28–59) 12 male

          RCT, not-blinded FFI was applied at baseline and at 4 weeks

          FFI

          Categorical rating scale

          58% (11/19) of participants showed improvement in pain scores Conclusion: useful

             

          Group 1: Group with magnet (N: 19)

           

          23 items

            
             

          Group 2: Group with no magnet (N: 15)

           

          3 domains

            
             

          Dx: Heel pain

              
             

          Location: USA

              

          FFI, 1997

          Caselli, MA [68]

          Outcome measure -Effectiveness of the intervention

          N: 35; Mean age: 42 (23–65); 18 male

          RCT not blinded FFI was applied at baseline and at 4 weeks

          FFI

          Categorical rating scale

          FFI scores improved at 4 weeks reported as the following:

             

          Group 1: Viscoped (N: 16)

           

          23 items

           

          60% (Group1)

             

          Group 2: Poron (N: 12)

           

          3 domains

           

          43% (Group 2)

             

          Group 3: Control(N: 7)

             

          10% (Group 3)

             

          Dx: Painful submetatarsal hyperkeratosis

             

          Conclusion: useful

             

          Location: USA

              

          FFI, 1999

          Pfeffer, G [78]

          Outcome measure – primary interest is in pain subscale outcome at 8 weeks

          N: 236; Mean age: 47 (23–81); 160 male

          RCT not blinded 6 months interventions multi-centers. FFI was applied at baseline and at 8 week intervals At 8 weeks the group response rate was 88.2%

          FFI

          VAS rating scale

          Pain subscale scores improved at 8 weeks

             

          Group 1: Stretching only (N: 39) Mean age: 47 (25–81) 11 male

           

          23 items

           

          Pain change scores controlled for covariates. Results are reported as the following:

             

          Group 2: Custom orthoses & stretch (N: 34) Mean age: 48.5 (23–69) 11 male

           

          3 domains

           

          Group 1: -17.2

             

          Group 3: Silicon & stretch (N: 51) Mean age: 49.5 (30–75) 17 male

             

          Group 2: -16.9

             

          Group 4: Rubber & stretch (N: 43) Mean age: 44 (27–69) 11 male

             

          Group 3: -23.9

             

          Group 5: Felt & stretch (N:42) Mean age: 48 (26–76) 13 male

             

          Group 4: -24.5

             

          Dx: Proximal plantar fasciitis

             

          Group 5: -20.2

             

          Location: USA

             

          Conclusion: useful

          FFI, 2001

          Slattery, M [82]

          Outcome measure – effectiveness of the intervention

          N: 46; Mean age: 24 (6.2) Sex not reported

          Observational 6 weeks FFI applied at baseline

          FFI

          VAS rating scale

          FFI scores of pain and disability subscales markedly improved at 6 weeks

             

          Dx: Hemophilic foot and ankle arthropathy at level 1–5 joint damange

           

          23items

           

          Conclusion: useful

             

          Location: Australia

           

          3 domains

            

          FFI, 2002

          Gross, MT [79]

          Outcome measure – Effectiveness of the intervention correlation with 100 meter walk and VAS pain scale

          N: 15; 8 male

          Pre-post test design FFI was applied at baseline and post orthosis at 12–17 days

          FFI 18 items Pain and disability scales

          VAS rating scale

          Pain and disability improved. The author suggested to modify FFI items if FFI will be used for plantar fasciitis.

             

          Mean age male: 43.8 (SD=6.3)

             

          Conclusion: useful

             

          Mean age female: 45.9 (SD=11.9)

              
             

          Dx: Plantar fasciitis

              
             

          Location: USA

              

          FFI, 2002

          Woodburn, J [80]

          Outcome measure – effectiveness of the intervention

          N: 98; Orthosis/vsControl

          RCT double blind; 30 months study. FFI was applied at 3, 6, 12, 18, 24, and 30 months

          FFI

          VAS rating scale

          FFI scores improved at the completion of the RCT

             

          Orthosis (N: 50) Mean age: 54 (SD=11.8) 16 male

           

          23 items

           

          Conclusion: useful

             

          Control (N: 48) Mean age: 53 (SD=11.1) 17 male

           

          3 domains

            
             

          Dx: RA rear foot valgus deformity

              
             

          Location: UK

              

          FFI, 2005

          Powell, M [83]

          Outcome measure – Validation of The Pediatric Pain VAS Questionnaires, Pediatric quality of life (PedQOL) inventory physical function scale

          N: 40; Custom orthoses: N: 15; 2 Male Mean age: 12.14

          RCT 3 arms, Single blinded

          FFI

          VAS rating scale

          The largest improvement of FFI scores was in the custom orthoses. VAS scoring appears applicable in children

             

          Insert N: 12; 4 Male Mean age: 12.7

          Intent to Treat Analysis; ANOVA

          23 items

           

          Conclusion: useful

             

          Athletic shoes N: 13; 4 Male Mean age: 13.77

          FFI was applied at baseline and at 3 months

          3 domains

            
             

          Dx: JRA and foot pain

              
             

          Location: USA

              

          FFI, 2006

          Magalahaes, E [69]

          Outcome measure – Concurrent measure with Health Assessment Questionnaires (HAQ)

          N: 36; 5 Male

          Prospective observational

          FFI

          VAS rating scale

          FFI scores in pain, disability, activity limitation improved; no correlations with HAQ scores

             

          Orthosis N: 28

          2 treatment groups; 6 months trial

          23 items

           

          Conclusion: useful

             

          Sham N: 8

          FFI was applied at baseline, 30, 90, and 180 days

          3 domains

            
             

          Mean age: 46 (32–68) RA years 11 (1–34)

              
             

          Location: Brazil

              

          FFI, 2007

          Williams, AE [71]

          Outcome measure – Concurrent measure with FHSQ for designed shoes intervention

          N: 80; 35 male

          Age: N/A

          RCT single blinded; 12 weeks trial. FFI was applied at baseline and 12 weeks N:34 completed the study

          FFI

          VAS rating scale

          Both scores of FFI and FHSQ were improved at 12 weeks

             

          Group 1: Designed shoes (N: 40); 11 male

           

          23 items

           

          Between groups general health was unchanged

             

          Group 2: Traditional shoes (N: 40) 19 male

           

          3 domains

           

          Conclusion: useful

             

          RA 17 years (14.4 yrs)

              
             

          Dx: Hallux valgus

              
             

          Location: UK

              

          FFI, 2008

          Lin, JL [81]

          Outcome measure – Validation with AOFAS VAS pain scale SF-36

          N: 32; 6 male

          Observational 7–10 years (mean 8.8 years); FFI was applied at the end of the observation

            

          FFI scores for pain and disability were improved and well correlated with AOFAS scores

             

          Dx: Stage II posterior tibialis tendon dysfunction (PTTD)

             

          Conclusion: useful

             

          Location: USA

              

          FFI, 2009

          Cho, NS [72]

          Outcome measure – Validation with VAS pain scale

          N: 42; Semi-rigid insole: N: 22

          RCT single blinded 6 month trial FFI was applied at baseline and 6 month At 6 months N34 completed the study

          FFI

          VAS rating scale

          Semi-rigid insole group showed markedly improved FFI scores

          0 male

             

          11fore foot/11 hind foot

           

          23 items

           

          Conclusion: useful

             

          Mean age: 48.7 (SD=11.6)

           

          3 domains

            
             

          Soft insole: N: 20; 0 male 11 fore/10 hind foot

              

          Mean age: 48.7 (SD=11.7)

             

          Dx: RA foot deformity, hind or forefoot

              
             

          Location: Korea

              

          FFI, 2009

          Novak, P [84]

          Outcome measure – Correlation with 6 minute walk time

          N: 40; Mean age: 56.23; 2 male

          RCT double blinded 6 months trial FFI was applied at baseline visits 1, 2, and 3 at 6 months

          FFI

          VAS rating scale

          Pain improved correlation with 6 minute walk time was moderate

             

          Orthosis (N: 20) Mean age: 55.7 (SD=9.31) RA: 10.5 yrs (SD=8.17)

           

          9 items

           

          Conclusion: useful

             

          Control (N: 20) Mean age: 56.75 (SD=11.1) RA: 11.5 yrs (SD=6.86)

           

          Pain scale

            
             

          Dx: RA

              
             

          Location: Slovenia

              

          FFI, 2009

          Baldassin, V [35]

          Outcome measure – pain relief

          N: 142; Custom Orthosis: N=72

          RCT double blind; 8 weeks trial. FFI was applied at 4 and 8 weeks

          FFI

          VAS rating scale

          Less pain was observed in both groups but no significant differences between groups

             

          Mean age: 55.7 (SD=12.4)

           

          23 items

           

          Conclusion: useful

             

          RA: 47.2 yrs (SD=8.17) 51 male

           

          3 domains

            
             

          Prefabricated orthosis: N=70

           

          Pain subscales 9 items (modified)

            
             

          Mean age: 47.5 (SD=11.5)

              
             

          Dx: Plantar fasciitis

              
             

          Location: Brazil

              

          FFI-R, 2009

          Rao, S [75]

          Outcome measure – FFI-R scores translated to clinical measure MDC90, Correlation with medial mid-foot pressure loading

          N: 20; 0 male

          Intervention 4 weeks FFI-R was applied at pre and post intervention Statistician was blinded from data sources

          FFI-R

          Likert

          Total FFI-R scores improved correlated with significant reduction in pressure loading of the medial aspect of the midfoot

             

          Mean age: 63 (55–78)

           

          68 items

           

          Conclusion: useful

             

          Full length orthosis

           

          Long form

            
             

          Dx: Midfoot arthritis

              
             

          Location: USA

              

          FFI-R, 2010

          Rao, S [76]

          Outcome measure – Clinical measure MDC 90 validation with segmental foot kinematic values

          N: 30; 2 male

          Intervention 4 weeks FFI-R was applied at pre and post intervention

          FFI-R

          Likert

          Full length foot orthoses reduced motion of the 1st metatarsophalangeal and was significantly correlated with FFI-R scores

             

          Mean age: 62 (47–78)

           

          68 items

           

          Conclusion: useful

             

          Full length carbon graphite orthosis

           

          Long form

            
             

          Dx: Midfoot arthritis

              
             

          Location: USA

              

          FFI, 2010

          Welsh, BJ [73]

          Outcome measure – validation with foot kinematic values VAS pain scale

          N: 32; 6 male

          Case series 24 weeks Pre-post test design

          FFI

          VAS rating scale

          FFI pain subscale significantly improved and met the criteria of equivalence to analgesic response. This pain reduction was not correlated with that of the biomechanical changes of the 1st metatarsophalangeal joint.

             

          Mean age: 42 (SD=11.5)

           

          9 items

           

          Conclusion: useful

             

          Pre-fabricated vs. custom orthosis

           

          Pain subscale

            
             

          Dx: MTP joint pain

              
             

          Location: UK

              

          FFI, 2010

          Clark H [85]

          Outcome measure – Orthosis reduced pain and disability and correlated with gait parameter

          N: 41; Gender not reported

          RCT single blind 16 weeks trial. FFI was applied at baseline, 8 and 16 weeks

          FFI

          VAS rating scale

          FFI scores were improved in orthoses and simple insole groups but the intervention did not improve gait parameter.

             

          Orthosis: N: 20; Simple insole: N: 21

           

          23 items

           

          Conclusion: useful

             

          Age>18 years; RA>3 years

           

          3 domains

            
             

          Location: New Zealand

              
          Table 9

          Studies using foot function measures in various interventions

          Instrument

          1stAuthor

          Objective

          Population (N, Sex, Age, Dx, location)

          Analysis

          Items/domains/subscales

          Response type

          Summary evaluation

          Foot Function Index, 2005

          Cui, Q [86]

          Improvement in pain and function

          N: 5; Mean age: 40 (range: 25–54); 3 male

          Retrospective study; Follow-up 24 months (16–30 months). FFI was applied at pre and at post treatment

          FFI

          VAS

          FFI scores improved on 3 out of 5 patients post surgery.

          Cortisone injection and arthroscopic surgery

          Dx: Post traumatic ankle adhesive capsulitis

          Pain and disability subscales

          Conclusion: useful

           

          Location: USA

          18 items

           

          Foot Function Index, 2005

          Di Giovanni, BF [87]

          Reduction of foot pain Stretching exercise and wearing foot insert

          N: 101; 33 male

          Randomized clinical Trial Longitudinal mixed-model analysis of covariance FFI was applied at baseline and at 8 weeks (N=:82, A=46, B=36). At 2 years (N:=66, A=39,B=27)

          FFI

          VAS

          FFI pain scores improved at 2 weeks and much improved at 2 years

          Mean age: 45 (range 23–60)

          Pain subscale

          Group A had a better scores than B

          Group A: Plantar fascia stretching

          9 items

          Conclusion: useful

          Group B: Achillus tendon stretching

            

          DX: Plantar fasciitis

            

          Location: USA

            

          Foot Function Index, 2009

          Kulig,K [88]

          Validation of physical activity scale (PAS) and 5 minutes walk test, and simple heel raise test.

          N=: 10; Gender: NA

          Exercise intervention: 10 weeks Follow up: 6 months. FFI was applied at baseline, 10 weeks and 6 months

          FFI

          VAS

          FFI pain and function subscales were used to monitor pre- and post-intervention outcomes.

          Mean age:52.1 (SD6.5)

          23 items

          Conclusion: useful

          DX: Posterior tibial tendon dysfunction

          3 domains

           

          Location: USA

            

          Foot Function Index, 2010

          Rompe, JD [89]

          Outcomes: Change scores between observations. Stretching and shock wave therapy

          N=54; 18 male

          Randomized parallel treatment 15 months trial. Intend to treat analysis FFI was applied at baseline, 4 and 15 months

          FFI

          VAS

          FFI pain scores were better in stretching exercise group

          Mean age: 53.1 (SD =27.7)

          Pain subscale

          Conclusion: useful

          Dx: Plantar Fasciotomy

          9 items

           
             

          Location: Germany

              
          Table 10

          Studies using foot function measures in observational studies

          Instrument

          1stAuthor

          Study and objective

          Population (N, Sex, Age, Dx, location)

          methods & analyses

          Items/domains/subscales

          Response type

          Summary evaluation

          FFI, 2004

          Novak, P [4]

          Epidemiology of Type II Diabetes Mellitus

               
            

          Correlation of pain score with 6 minute walk time; Comparing intergroup pain score

          Total N: 90; 3 groups;

          Cross-Sectional study

          FFI

          VAS scale

          High pain score correlated with shorter distance walk, group with Type II diabetes neuropathy with symptoms showed the highest pain scores

          Descriptive & correlation statistics

             

          Neuropathy with symptoms N: 30 Mean age 64.87 (SD=11)

           

          9 items

           

          Conclusion: useful

             

          20 male

           

          Pain scale

            
             

          Neuropathy, no symptoms N:30; Mean age: 64.87 (SD=11)

              
             

          20 male;

              
             

          Healthy volunteers N: 30; Mean age: 64.87 (SD=11)

              
             

          20 male;

              
             

          Slovenia

              

          FFI, 2004

          Williams, AE [90]

          Epidemiology Rheumatic diseases

          N: 139; 39 male

          Cross sectional study

          FFI

          VAS scale

          FFI scores showed a high prevalence of foot and ankle pathologies, which indicated the need of podiatry care

          Descriptive statistics

            

          To assess foot health status

          Age: NA

           

          23 items

           

          Conclusion: useful

             

          Inflammatory and degenerative joint diseases

           

          3 domains

            
             

          UK

              

          FFI, 2006

          Williams, AE [91]

          Epidemiology of Paget diseases of the foot Concurrent measures of FSI and quality of Life 12-items short form

          N: 134; 64 male

          Cross sectional study Descriptive statistics

          FFI

          VAS scale

          Correlations of scores were not found between instruments

             

          Mean age: 74.5 (46–91)

           

          23 items

           

          Conclusion: not useful

             

          UK

           

          3 domains

            

          FFI, 2006

          Rosenbaum, D [95]

          Plantar sensitivity assesstment

          N:25; 2 male

          Observational study

          FFI 23 items 3 domains

          VAS scale

          FFI was to evaluate foot sensation related to RA

            

          Rheumatoid arthritis foot

          Mean age: 55 (SD=9.9) RA; 9.6 (SD=7)

             

          Conclusion: useful

            

          Evaluate the correlation of painful walking and loss of sensitivity of the plantar surface of the foot

          Germany

              

          FFI, 2008

          Schmeigel, A [96]

          Pedobarography in rheumatoid arthritis

          N: 112; Mean age: 55 (SD=11)

          Observational

          FFI

          VAS scale

          Higher FFI scores correlated with pedograph scores

            

          To evaluate the function and pedographic impairment

          RA1; N: 36; HAQ scores 0–1

           

          23 items; 3 domains

           

          Conclusion: useful

            

          Correlation of foot pain and pedograph

          3 male; Mean age: 50.6 (SD=10.5)

           

          RA1: FFI total score: 20.7 (SD=12.9)

            
             

          RA2; N: 38 HAQ scores 1.1-2

           

          RA2: FFI total score: 28.8 (SD=12.1)

            
             

          1 male; Mean age: 55.2 (SD=10.4)

           

          RA3: FFI total score: 48.7 (SD=15.9)

            

          RA3 N: 38 HAQ scores 2.1-3

             

          2 male; Mean age: 58.5 (SD=11.3)

           

          Control NA

            
             

          Control N:20 Mean age: 53.2 (SD=12.3)

              
             

          Germany

              

          FFI, 2010

          Kamanli, A [92]

          Foot Bone Mineral Density

          RA: N: 50; RA<3 yrs

          1 male, 5 female

          Cross sectional study

          FFI

          VAS

          Moderate-strong correlation of FFI scores with disease duration, VAS pain scale, Stoke index, HAQ, femur bone mineral density (BMD). No correlation with foot BMD.

          To assess the correlation of FFI scores with VAS pain scale, HAQ Ritchie articular index, and stoke index

          Descriptive statistics

          Pain scale 9 items

             

          RA>3 yrs

             

          Conclusion: useful.

             

          4 male, 40 female

              
             

          Mean age: 52 (SD=10.9)

              
             

          OA: N:40; 3 male

              
             

          Mean age: 52.4 (SD=11.8)

              
             

          Healthy volunteers; N: 14

              
             

          Turkey

              

          FFI, 2010

          Goldstein, CL [94]

          Foot and ankle trauma

          N: 52; 31 male

          Cross sectional study the mean duration post trauma 15.5 months (1 month-10 years)

          FFI

          VAS

          There was a high correlation among FFI scores and the 5 listed instruments.

            

          Correlation of FFI, SF-12, SMFA, FAAM, AAOS, AOFAS

          Mean age: 43.3 (18–85)

           

          9 items

           

          Conclusion: useful

             

          OA; Foot and ankle trauma

           

          Pain scale

            
             

          Canada

              

          FFI, 2010

          Kavlak, Y [93]

          Elderly men Concurrent measure with VAS pain scale, foot problem score, hind foot function scale

          N: 53; 53 male

          Cross sectional study

          FFI

          VAS scale

          FFI was simple and comprehensive and was significantly correlated with hind foot function scale, and scores of timed up and go.

             

          Mean age: 73.8 (7.08)

           

          23 items

           

          Conclusion: useful

             

          Foot problems

           

          3 domains

            
             

          Turkey

              

          Objective 3. Enumerate the strengths and weaknesses of the FFI and FFI-R as reported in the literature

          This was a qualitative summary of the results as found in Table 5 and Table 6.

          Objective 4. Improving the FFI-R metrics

          Table 11 summarizes results of the Rasch analysis. This was a reanalysis of the FFI-R database collected in 2002 with the aim of improving FFI-R metrics.
          Table 11

          Reliability and unidimensionality of the full scale, short form, and subscales

           

          Full scale

          Short form

          1-11

          12-19

          20-39

          40-49

          50-68

           

          (68 items)

          (34 items)

          (Pain)

          (Stiffness)

          (Difficulty)

          (Limitation)

          (Social issues)

          Person Reliability

          .96

          .95

          .89

          .89

          .94

          .78

          .84

          Cronbach’s Alpha

          .98

          .97

          .93

          .95

          .97

          .87

          .94

          Unidimensionality Criteria (Ratio of the raw variance explained by measures: Unexplained variance in 1st contrast ≥ 3)

          56.8/10.6=

          60.2/15.8=

          66.7/22.1=

          67.5/34.7=

          72.7/15.5=

          63.4/19.2=

          53.6/18.1=

          5.4

          3.8

          3.0

          1.941

          4.69

          3.32

          2.963

           

          Yes

          Yes

          Yes

          No

          Yes

          Yes

          No

          1 Further inspection of the data revealed that the two-factor solution was associated with the severity of the items, where the two factors were actually low and high severity stiffness, i.e. opposite poles of the same factor. Therefore, the scale is useful as a measure of stiffness. 2 These were the results after removing item 41 (ASSISTO).

          3 Approximately unidimensional.

          Descriptive analysis methods

          Quantitative data were reported using simple statistics expressed as the sum, means, and standard deviations for continuous variables and as frequencies for categorical data. (Tables 1, 2, 3, and 4) Analytic statements and evaluations/comments for each article collected are summarized in Table 12. This depicts the summary of FFI and FFI-R uses as illustrated in Objective 2, and in six tables (Tables 5, 6, 7, 8, 9 and 10).
          Table 12

          Summary of FFI and FFI-R uses as provided in detail in Tables 5-10

          FFI/FFI-R instrument usage

          Category

          Name of instrument

          First Author’s name [reference number]

          Measurement

             

          (Details in Tables 5 & 6)

          A) New Instrument

          FFI

          Budiman- Mak E [7]

           

          FFI-R

          Budiman-Mak E [11]

            

          FFI-site to site

          Saag KG [23]

            

          AOS

          Domsic RT [24]

            

          FFI Likert Scale

          Agel J [25]

           

          B) FFI as Criterion Validity

          HAQ and SFC

          Bal A [26]

            

          SF-36

          SooHoo NF [27]

            

          Navicular joint alignment

          Shrader JA [28]

            

          FIS

          Helliwell P [29]

            

          WOMAC and DAS 44

          Van der Linden M [30]

            

          AOFAS

          Lau JT [31]

            

          AOFAS Hallux

          Baumhauer JF [32]

            

          AOFAS

          Ibrahim T [33]

           

          C) Cultural adaptation/Translation

          Dutch-FFI-5pts

          Kuyvenhoven MM [3]

            

          FFI-G

          Naal FD [34]

            

          FFI-Taiwan Chinese

          Wu SH [36]

            

          FFI- Spanish

          MAPI Institute [38]

          Surgeries

             

          (Details in Table 7)

          a) Arthrodeses and Fusions

          FFI, FFI-Dutch,

          Lin SS [39], Grondal L [40],van der Krans A [41], Stegman M [42], Vesely R [43], Doets HC [44], Jung HG [45], van Doeselaar DJ [46], Niki H [47]

           

          b) Arthroplasty

          FFI, FFI pain and difficulty subscales,

          Ibrahim T [48], Taranow WS [49], Schutte BG [50], Bonnin MP [51]

           

          c) Fracture Care

          FFI

          Vallier HA [52], Harris AM [53], Potter MQ [54], Gaskill T [55]

           

          d) Reconstruction Surgery

          FFI, FFI-Dutch

          Mulcahy D [56], Ward CM [57], Schlegel UJ [58], van der Heide HJ [59], Kroon M [60]

           

          e) Other surgery

          FFI, FFI disability subscale, FFI pain subscale, FFI pain and disability subscales

          Watson TS [61], Daniels TR [62], Lee S [63], SooHoo NF [64], Stropek S [37], Castellani C [65], Aurich M [66], Eberl R [67].

          Orthoses

             

          (Details in Table 8)

          a) Forefoot

          FFI

          Caselli MA [68], de P Magalahaes [69], Conrad KJ [70], William AE [71], Cho NS [72], Welsh BJ [73], Budiman-Mak E [74].

           

          b) Mid foot

          FFI-R

          Rao S [75], Rao S [76]

           

          c) Hind foot

          FFI, FFI, Brazil (pain subscale modified),

          Caselli MA [77], Baldassin V [35], Pfeffer G [78], Gross MT [79], Woodburn J [80],Lin JL [81], Slattery M [82], Powell M [83], Novak P [84], Clark H [85]

          Other interventions

             

          (Details in Table 9)

          Injection

          FFI pain and disability subscales

          Cui Q [86]

           

          Stretching exercise

          FFI, FFI pain subscale

          DiGiovani BF [87], Kulig K [88], Rompe JD [89].

          Observational studies

             

          (Details in Table 10)

          Foot morbidities

            
           

          In diabetes mellitus

          FFI pain subscale

          Novak P [4]

           

          In rheumatic diseases

          FFI

          Williams AE [90], Williams AE [91]

           

          In bone mineral density

          FFI pain subscale

          Kamanli A [92]

           

          In elderly

          FFI

          Kavlak Y [93]

           

          In foot post-injury

          FFI pain subscale

          Goldstein CL [94]

           

          In rheumatoid arthritis

          FFI

          Rosenbaum D [95], Schmeigel A [96]

          Rasch analysis method

          To address specific critiques of the FFI-R found in the literature, the unidimensionality of the FFI-R and its subscales were evaluated against the Rasch model. The statistical package Winsteps version 3.72.3 [14] was used to conduct a principal components analysis (PCA) of the standardized residuals to determine whether substantial subdimensions existed within the items [1517] and whether the FFI-R L, the FFI-R S, and the 5 subscales were unidimensional. The criterion used to define unidimensionality was a large variance (> 40%) explained by the measurement dimension [18]. Unexplained variance in the first contrast of the data should be small and fall under the criterion of 15% for a rival factor. We chose a ratio of variance of at least 3 to 1 in the first principal component [19], compared to the variance of the first component of residuals.

          Rasch reliability statistics

          Reliability was estimated with Cronbach’s Alpha and Rasch person reliability statistics. Both indices reflect the proportion of variance of the person scores or measures to total variance (i.e., including measurement error). Unlike Cronbach’s Alpha, Rasch person reliability is based on the estimated locations of persons along the measurement continuum, excluding those with measures reflecting extreme (zero or perfect) scores and including cases with missing data. For both indices, our criterion for acceptability was .80.

          Response category analysis

          One requirement of the Rasch model is monotonicity: the requirement that, as person ability increases, the item step response function increases monotonically [20]. This means that choosing one categorical response over the prior—for example, moving from selecting “2 = A little of the time,” to selecting, “3 = Most of the time,”—increases with person ability. The proper functioning of the rating scale is examined using fit statistics, where: (i) outfit mean squares should be less than 2.0, (ii) average measures advance monotonically with each category, and (iii) step calibrations increase monotonically [21, 22].

          Results

          Review of the literature

          Articles were obtained by using the search method defined in the Methods section; the search results included 752 articles from PubMed/MEDLINE and 640 articles from Embase. Further screening and selection procedures, as detailed in Figure 1, yielded 182 full-text articles. Of these, 53 articles were qualified for review. Twenty-five more articles were obtained from the search engine BioMedLib and from manual searches. A total of 78 articles qualified for this review, summarized and categorized into several tables,
          http://static-content.springer.com/image/art%3A10.1186%2F1757-1146-6-5/MediaObjects/13047_2012_487_Fig1_HTML.jpg
          Figure 1

          Algorithm of searched and screened for qualified paper.

          Objective 1: Assessment of the prevalence of the FFI or FFI-R usage, population characteristics, and study locations

          Among the 78 studies, we identified 4714 study participants for whom the FFI or FFI-R instrument had been used to measure foot health. This sample consisted of 1914 (41%) male participants and 2688 (57%) female participants, with a mean age of 48.58 years (SD, 4.9 years). There was a discrepancy of 2% between the sums of male and female participants, because gender was not reported in three studies (Table 1). Most of the participants were individuals and young adults, and a few studies involved juvenile participants. The types of studies included measurement practice studies (n=17), surgery studies (n=30), studies of orthotics (n=19) or other clinical interventions (n=4), and observational studies (n=8). We identified 20 different diagnoses of foot and ankle pathology that were measured by FFI and FFI-R (Table 2). Among them, RA and plantar fasciitis were the two most common diagnoses and were also noted to be the most painful and disabling foot conditions. These studies were conducted by investigators in 17 countries; the United States, the Netherlands, and the United Kingdom were the three most frequent users of the FFI and FFI-R in studies involving foot and ankle problems (Table 3).

          Table 4 displays the versatility of the FFI with all 3 domains and FFI Subscales and FFI-R uses across the studies. This shows that clinicians and researchers were choosing the FFI scales depending on the nature of their studies. Among the various scales of the FFI, we found the FFI with all 3 domains (full scale), the FFI pain subscale only, and a combination of the pain and disability subscales to be the most frequently used, whereas the FFI-R was the least frequently used. The Dutch adaptation of the FFI, the FFI-5pts, was mostly used in the Netherlands as an outcome measure in studies of many surgical interventions.

          In summary, the FFI with all 3 domains, or as subscales, was frequently chosen as a measurement instrument across various studies and countries and among various age groups and sexes, for the assessment of acute and chronic foot and ankle conditions.

          Objective 2: Uses of the FFI and FFI-R in the field of foot health research

          The uses of the FFI and FFI-R are provided in detail in Tables 5, 6, 7, 8, 9, and 10. Table 12 describes the study types, the name of the instruments, and the first author’s name and the reference number. The studies are grouped by how the instruments were used and ordered chronologically within group.

          Measurement, validation and cultural adaptation

          Table 12 describes the utility of the FFI and FFI-R in studies of foot function measures and includes 17 articles. Category A New Instruments. Includes four articles in which foot health measures are described including the original FFI [7], the FFI-R [11]. The FFI Side to Side was derived from pain and disability subscales of the FFI [23]. The Ankle Osteoarthritis Scale (AOS) [24]; measured foot problems related to foot and ankle osteoarthritis. Agel et al. [25] modified the rating scale of the FFI pain and function subscales from the visual analog rating scale (VAS) to the Likert categorical scale; this modification was tested in a sample of individuals with non-traumatic foot complaints, and the metric of the Likert scale was valid. Category B FFI as Criterion Validity. Articles in this category describe several health measures and use the FFI full scale or subscales to validate these measures. Bal et al. [26] found a strong correlation of FFI scores and scores of RA functional measures: the Health Assessment Questionnaire (HAQ) and Steinbrocker Functional Class (SFC). SooHoo et al. [27] found that the Rand 36-Item Short Form Health Survey (SF-36) scores of a sample of individuals with foot and ankle disorders were moderately correlated with FFI scores and concluded that FFI scores can be used to monitor the quality of life of these patients. Shrader et al. [28] measured the stability of navicular joint alignment and found that this measure correlated well with the FFI scores of the sample. Helliwell et al. [29] developed a new measure, the Foot Impact Scale (FIS), to measure the impact of foot problems on foot health in a sample of individuals with RA; the metric of FIS was validated with the FFI and HAQ. In an RA study, van der Leeden et al. [30] reported that Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and Disease Activity Scores in 44 joints (DAS 44) were correlated with FFI scores; furthermore, this author discerns the correlations that the FFI pain subscale scores correlated with forefoot pain while the FFI function subscale scores correlated with hindfoot problems. The FFI scores were also used as validation measures of the American Orthopedic Foot and Ankle Society (AOFAS) clinical rating scales, an instrument that was widely used by foot and ankle surgeons [31]. These validation studies were reported by Baumhauer et al. [32] for the AOFAS hallux clinical rating scale and by Ibrahim et al. [33] for the AOFAS clinical rating scale, which was well to moderately correlated with FFI scores. The latter finding was based on his study with a 41% response rate in a sample consisting of 45 individuals. Category C Cultural Adaptation or Translation. The first translation of the FFI was the Dutch-language instrument known as Dutch FFI-5pts [3]. The German-language translation of the instrument is the FFI-G [34]; the FFI was also translated into Brazilian Portuguese [35], Taiwan Chinese [36], Turkish [26], and Czech [37]. There was also a Spanish translation conducted by the MAPI Institute in Lyon, France [38]. These translations complied with rigorous language translation procedures; occasionally, some item adjustments of the scales were needed. In summary, the FFI was developed with good reliability and validity; it also inspired and served as criterion validity for newer foot health measures and attracted the attention of researchers around the world, who conducted translations and adaptations of the tool into their native languages and cultures.

          Table 6 is a supplement to Table 5 and displays the clinimetrics of the instruments listed in Table 5; measures were metrically good, with reliability and validity values greater than 0.7 with one exception where the pain subscale had a reliability of 0.64 [3].

          Surgical intervention

          The FFI is one of the outcome measures most frequently used by AOFAS members [31]. It was first used to measure surgical outcomes. The surgical interventions and outcomes are summarized in Table 7. There are 30 articles, categorized generally according to type and location of surgical procedure. Five distinct procedural categories were identified as follows: (a) arthrodeses within the foot or ankle [3947], (b) arthroplasty within the foot or ankle [4851], (c) fracture care of the foot or ankle [5255], (d) deformity reconstruction surgery of the foot or ankle [5660], and (e) various surgical interventions for chronic conditions [6164]. The FFI was also used to assess outcomes of less invasive procedures, such as calcaneal spur treatment by arthroscopy [37], distal tibia repair using fixation with cannulation osteosyntheses [65], arthroscopic chondrocyte implant of the tibia and fibula [66], and surgical interventions for complex ankle injuries [67]. In summary, the FFI and the Dutch FFI-5pts appeared to be useful in measuring outcomes of various surgical procedures in children, adults, and individuals with acute, chronic, and congenital foot and ankle problems.

          Orthotic interventions

          Table 8 lists studies using foot function outcome measures in orthotic interventions in the foot and ankle. The studies assessed the impact of orthotic treatment on forefoot, midfoot, and hindfoot/ankle pathology. Orthotic treatment on the forefoot in patients with RA improved the scores for pain, disability and activities [68, 69], however the scores were unchanged in the study by Conrad et al. [70]. Other studies using special shoes and shoe inserts showed symptoms of relief in hallux valgus pain [71] hindfoot and forefoot problems [72, 73]; and slowing the progression of hallux valgus in early RA [74]. Midfoot studies assessing the treatment of full length orthoses on pain relief [75], and mobility were performed using the FFI-R as an outcome measures [76]. For hindfoot conditions treatment with orthoses included studies of heel pain [77], plantar fasciitis [35, 78, 79], stabilizing hindfoot valgus [80], correction of posterior tibialis tendon dysfunction [81], destructive hemophilic arthropathy of the foot and ankle [82] and juvenile idiopathic arthritis of the foot and ankle [83]. Shoes/shoe inserts have also been found to relieve foot and ankle pain from arthritides [84, 85]. In summary, the FFI and FFI-R clearly provided useful outcome measures for orthotic management of a wide range of foot and ankle disorders.

          Medical intervention

          The FFI also was used to measure foot health outcomes associated with medical interventions (Table 9), such as cortisone injection of the ankle adhesive capsulitis [86]; the injection resulted in improved FFI pain and disability subscale scores. Di Giovanni et al. [87] measured the outcome of stretching exercises for plantar fasciitis versus Achilles tendonitis; both groups showed improvement in FFI pain subscale scores. Kulig et al. [88] used the FFI pain and disability subscales to measure the outcomes of exercise intervention in posterior tibial tendon dysfunction. Rompe et al. [89] reported the FFI pain score improved in the stretching treatment group of a randomized clinical trial using stretching and shockwave therapy to treat patients with plantar fasciopathy. Overall, the FFI was useful in measuring the outcomes of conservative interventions in chronic foot and ankle conditions.

          Observational studies

          Investigators had chosen the FFI scores or the subscale scores to determine the prevalence and disease burden of foot and ankle conditions in the general population (Table 10). Novak et al. [4] used FFI scores to evaluate type 2 diabetes with and without neuropathy and identified that group with neuropathy had worse FFI scores. Williams and Bowden [90] correlated high FFI scores to foot morbidity in rheumatic diseases, and estimated cost of care/staffing concerns for that patient subset. Williams [91] also used the FFI scores in patients with Paget’s disease and noted the impacts on plantar foot pressures, gaits, and ambulation abilities. Kamanli et al. [92] correlated the scores of the FFI and foot bone mineral density, then extrapolated these scores to that individual’s skeletal bone density. Kavlak and Demitras [93] reported a strong correlation of FFI scores with the scores of VAS pain scale, foot pain scale (FPS), and hindfoot function scale (HFS) in patients with foot problems. Goldstein et al. [94] noted that FFI scores of individuals with previous foot injuries had a high correlation with 6 other foot function instruments. Rosenbaum et al. [95] found that plantar sensory impairment of the foot in patients with RA was correlated with poor FFI scores. Schmiegel et al. [96] found that pedobarograph scores of patients with RA with foot pain were correlated with poor FFI and HAQ scores. In summary, FFI scores were useful in detecting the prevalence of foot and ankle problems and as a measure of concurrent validity for other foot health measures in various chronic foot conditions.

          In all, we found the FFI instrument was frequently chosen as an outcome measure of surgical, orthotic, and medical treatments, but its application was wider than we originally imagined. It was not limited to outcome measures; FFI scores were also applied in the promotion of foot health as a common public health issue and in increasing the awareness of health system administrators. The FFI was also used in the validation of newly developed foot health measures.

          Objective 3: The strengths and weaknesses of the FFI and FFI-R as reported in the literature

          FFI: The FFI questionnaire had good psychometric properties [97100], and the pain subscale was sensitive to change during instrument development [13]. In a study about treatment of plantar fasciitis in individuals with chronic foot pain, SooHoo et al. [64] reported that the pain subscale of the FFI had high standard response mean (SRM) and high effect size (ES) as outcome measures of surgery in chronic foot and ankle problems. While Landorf and Radford measured the clinical ability to detect a change as minimal important difference (MID) in plantar fasciitis [101]. All these clinical measures add to the credibility of the FFI as a self-reporting measure, the FFI reflects patients’ assessment of their symptoms/health status, which directs providers about proper care planning and progress toward treatment goals. FFI is one of the most cited measures of its kind [102].

          There are weaknesses of the FFI. During the development of the index, clinicians generated the questionnaire items without patient participation [13, 97]; therefore, items might not fully reflect patients’ needs, might be sex biased [7], and might not be applicable to high-functioning individuals. A theoretical model was not part of the design, nor were the items related to footwear [13, 103], which are essential to support the construct of this instrument. It is also lacking items for measuring quality of health and satisfaction with care; however, these items can be appended as a global statement in the questionnaire. In all, the FFI has been the most studied and widely used foot-specific self-reporting measure; however, further testing by gender, age, race, language, etc. would provide assurance of its generalizability.

          FFI-R : The FFI-R was developed in response to criticism of the FFI and to address issues of contemporary interest. Most original items from the FFI were selected in the development of FFI-R, and new items about footwear and psychosocial factors were added, which improved its construct coverage. Patients and clinicians were involved in the generation of items. Its design closely followed the ICF theoretical model [13]; its psychometric properties are strong and are based on the IRT 1-parameter or the Rasch measurement model. It was designed to be a comprehensive measure of foot health–related quality of life, with both long and short forms [99], allowing clinicians and researchers to choose the measures they need for the intended study. Although the FFI-R did not include information on clinical ability to measure change in its development, Rao et al. [75, 76] did measure the minimal detectible change (MDC) and the effect size, in individuals with midfoot arthritis, which also added to the credibility of its metrics.

          Objective 4: The newly analyzed FFI-R with improved psychometric values

          The full scale and short form

          For the FFI-R L (68 items) [11], person reliability was high: 0.96, respectively. In the PCA, 56.8% of the variance was explained by the measure, with only 10.6% of the variance explained by the first factor of residuals. These findings support that the full FFI-R meets the unidimensionality requirement of the Rasch model. Further, the criterion for unidimensionality was a ratio of the raw variance in the first contrast of residuals that was 5.4 (i.e., greater than 3). For the FFI-R S (34 items) [11], person reliability was 0.95, similar to the reliability estimates of the FFI-R L. The PCA of the FFI-R S revealed that unidimensionality criteria were also satisfied. This supports the use of a short form of the measure, because the item response burden on patients is lower, at 34 questions. Because this measure is as reliable as the full measure, its use is supported for clinical settings.

          Subscales

          All subscales of the FFI-R had strong person reliability estimates (Table 11), ranging from 0.78 to 0.94 for person reliability. The PCA indicated that unidimensionality held for each subscale, with the exception of the stiffness subscale. Further inspection of the data revealed that the two-factor solution reflected groups of the low-severity and high-severity items and was not the result of a competing factor. Unidimensionality for the limitation subscale was met after dropping item 41 (ASSISTO), an item listed in the FFI-R database. Overall, the subscales of the FFI-R satisfied unidimensionality criteria and were reliable measures of the latent traits (Table 11).

          Response category analysis

          The response category analyses for each of the subscales (done after collapsing Categories 5 and 6) revealed that, for the first three subscales (pain, stiffness, and difficulty), the response categories behaved as required by the Rasch model. However, for the subscales of limitation and social issues (both of which are time scales), there was some indication that respondents had difficulty distinguishing between, “2 = A little of the time,” and, “3 = Some of the time.” We considered, then, collapsing these categories and making all FFI-R subscales have four possible response categories. This would ensure uniformity of the measure and decrease the burden on patient response. Therefore, the first three subscales, which measure severity, “3 = Severe pain,” “4 = Very severe pain,” and “5 = Worst pain imaginable,” were collapsed. This was justified because all three captured the notion of severe pain. Overall, the analyses showed that the response to each item functioned well with the four-item response categories.

          Discussion

          This review evaluated 78 eligible articles (Figure 1). In the past 20 years, it appears that the FFI and FFI-R were widely used across national and international clinical and research communities. The instruments were administered to over 4700 study participants of males and females worldwide, across age groups, with 20 different diagnoses consisting of congenital, inflammatory/degenerative, acute and chronic foot and ankle problems. The FFI was also incorporated into other newer foot health measures [23, 24], and also underwent changes in the measurement scale from VAS to Likert scale such as the one conducted by Agel et al. [25]. The scale changes also occurred in FFI adaptation to the Dutch [3], German [34], and Taiwanese Chinese [36] including our revised FFI-R [11] to give a few examples. The strong metrics of FFI subscales and full scale (Table 12, Category A), facilitated the investigator’s choice to use its subscale(s) or full scale in clinical or research applications as appropriate. The FFI was also frequently used as validation criterion for other foot health measures (Table 12, Category B); this validation usage has elevated the credibility of the FFI as an outcome measure for foot and ankle problems. Since the FFI was developed using CTT procedures, it is sample and content dependent, therefore its metrics were tested in many different samples, where its metrics were proven to be consistently strong. The exception was in the study of Baumhauer et al. [32] where high foot functioning was evident in the sample; therefore, investigators should exercise caution in the interpretation of this result. While the FFI was developed initially as disease specific for early RA, in later years, it was used in many non-RA foot and ankle problems and was proven to be a valid measure as well. The FFI and FFI-R were frequently used as outcome measures in surgical and clinical interventions with positive results (Tables 7, 8, 9, and 10). The FFI scores were also used in many observational studies (Table 10) and those reports might be helpful for researchers and the health system administrators in establishing a health policy. Although the FFI was extensively studied and generally received positive ratings [23, 29, 102], we realized the need for improvement in the measures of FFI and FFI-R and have discussed this issues comprehensively under Objective 3 in this paper. We conducted a re-analysis and made improvements to the metrics and scales of FFI-R as presented in Table 11 and questionnaires FFI-R Long Form (See Additional file 1), and Short Form (See Additional file 2).

          In recent articles about FFI used as outcome measures, the authors have included the clinical measures; the effect size, and standard response mean [64], and minimal important difference [101], while Rao et al. reports minimal detectible change and effect size of the FFI-R [75], all these have increased the credibility of the clinical use of the FFI to help in power analysis and sample size estimation for future studies.

          Limitations of this review

          Our literature search was limited to publications written in the English language and covered only publications until 2010; therefore, this might exclude the FFI- and FFI-R–related published articles not written in English, as well as those more recent articles published in English.

          Conclusions

          The FFI pioneered measuring outcomes in foot health. This instrument has been tested through time and adapted in its measures as it was frequently used in full scales or subscales to measure outcomes in various clinical practice or research studies. The FFI has also had a role in shifting the paradigm from a reliance on physical and biochemical findings as outcomes to the use of outcomes that are relevant to patients. Thus, the measure established patient-centered, valid, reliable, and responsive hard data endpoints. The rating scales also underwent changes; for practicality and user-friendliness in clinical and research settings. The FFI was recognized as a valid instrument and used as a validation criterion of other measures. It was adapted and translated into multiple languages. It was applied to all age groups, across genders and was useful in measuring varied medical and surgical conditions.

          In realizing the scope of FFI applications, we acknowledge the contributions of friends and colleagues around the world who not only used the FFI in their studies but also made adaptations and translations to make the FFI a versatile instrument in promoting and maintaining foot health. The FFI-R has good psychometric properties and is available in long and short forms for ease of clinical use. In response to findings in this review, we conducted a rigorous analysis to strengthen the metrics of the FFI-R and changed the rating scales to be more user-friendly and practical.

          Both the FFI and FFI-R are in the public domain and permission to use them is free of charge. They are available from the developers of these instruments and from the AOFAS web site. These instruments are self-administered and are written at an eighth-grade reading level. The FFI scores are interpreted as 0%-100% for each subscale and the overall score. Higher FFI and FFI-R scores indicate poor foot health and poor foot health-related quality of life. The FFI and FFI-R put minimal burden on respondents and the questionnaires are not emotionally sensitive. The administrative burden is also minimal and it does not require formal training to score or to interpret [104]. Translations and adaptations are available in Dutch [3], Taiwan Chinese [36], German [34], Turkish [26], Brazilian Portuguese [35], and Spanish [38].

          This review attests to the widespread use of foot health measures, and we have noticed the advancement of foot health in general across diagnoses. It has been a privilege for us to serve patients, clinicians, and researchers to fulfill the mission in improving foot health through the use of the FFI and FFI-R. These instruments are available for users, and can be downloaded as they are presented as electronic files.

          Abbreviations

          AOFAS: 

          American Orthopedic Foot and Ankle Society

          CTT: 

          Classical test theory

          EMBASE: 

          Excerpta Medica Database

          FFI: 

          Foot Function Index

          FFI-R: 

          Foot Function Index Revised

          EBM: 

          Elly Budiman-Mak

          FFI-R L: 

          Foot Function Index Revised Long Form

          FFI-R S: 

          Foot Function Index Revised Short Form

          HAQ: 

          Health Assessment Questionnaire

          IRT: 

          item response theory

          JM: 

          Jessica Massa

          KJC: 

          Kendon J Conrad

          Medline: 

          Medical Literature Analysis and Retrieval System

          PUBMED: 

          public Medline

          RA: 

          rheumatoid arthritis

          RMS: 

          Rodney M. Stuck

          VAS: 

          visual analog rating scale

          AAOS: 

          American Academy of Orthopedic Surgeon

          ANOVA: 

          Analysis of Variance

          AOS: 

          Ankle Osteoarthritis Index

          BMD: 

          Bone Mineral Density

          CA: 

          Crohnbach’s Alpha

          CRI: 

          Clinical Rating Index

          CV: 

          Calcaneal Varus

          DAS 44: 

          Disease Activity Score in 44 joints of patient with rheumatoid arthritis (RA)

          DX: 

          Diagnosis

          EF: 

          External Fixation Procedure

          ES: 

          Effect Size

          FAAM: 

          Foot and Ankle Ability Measure

          FFI-5pts: 

          Dutch Foot Function Index with 5 point Likert Scale

          FFI-G: 

          Foot Function Index - German Language

          FHSQ: 

          Foot Health Status Questionnaire

          FIS: 

          Foot Impact Scale

          FPS: 

          Foot Problem Score

          FSI: 

          Foot Structure Index

          FX: 

          Fracture

          HFS: 

          Hind Foot Function Scale

          HMIP: 

          Hallux Metatarso-interphalangeal Joint

          HR: 

          Hallux Rigidus

          ICC: 

          Interclass Correlation Coefficient

          JIA: 

          Juvenile Idiopathic Arthritis

          JRA: 

          Juvenile Rheumatoid Arthritis

          LMIP: 

          Lesser Metatarso-interphalangeal Joint

          MCS: 

          Mental Component Score of SF-36

          MDC: 

          Minimal Detectible Change

          MFA: 

          Musculoskeletal Function Assessment

          MFDQ: 

          Manchester Foot Disability Questionnaires

          MID: 

          Minimal Important Difference

          MODEMS: 

          Musculo-skeletal Outcome Data Evaluation and Management System

          MTP: 

          Metatarsophalangeal Joint

          NA: 

          Not Applicable

          OA: 

          Osteoarthritis

          PAS: 

          Physical Activity Scale

          PCS: 

          Physical Component Score of SF-36

          PedQL: 

          Pediatric Quality of Life Scale

          PF: 

          Plantar Fasciitis

          PTTD: 

          Posterior Tibialis Tendon Dysfunction

          QOL -12: 

          Quality of Life 12 items short form

          RAI: 

          Ritchie Articular Index

          RCT: 

          Randomized Control Trial

          SD: 

          Standard Deviation

          SF-36: 

          Rand 36 items health survey form

          SF-36 MCS: 

          Mental Component Score of SF-36

          SF-36 PCS: 

          Physical Component Score of SF-36

          SF-12: 

          Rand 12 items short form health survey

          SFC: 

          Steinbrocker Functional Class

          SMFA: 

          Musculoskeletal Function Assessment

          SRM: 

          Standard Response Mean

          SI: 

          Stroke Index

          TAA: 

          Total Ankle Arthroplasty

          TMT: 

          Tarso Meta-metatarso Joint

          UCLA: 

          University of California - Los Angeles

          WOMAC: 

          Western Ontario MacMaster University Osteo Arthritis Index.

          Declarations

          Acknowledgements

          The authors gratefully acknowledge the support from the Center for Management of Complex Chronic Care, Hines VA Hospital, Hines, IL, USA. The paper presents the findings and conclusions of the authors; it does not necessarily represent the Department of Veterans Affairs or Health Services Research and Development Service. We are also grateful to Cindi Fiandaca and the Hines VA medical library staff for assisting in the literature search, Madeline Thornton for assisting in designing the tables, Leahanne Sarlo and Mary Reidy for editing the manuscript.

          Authors’ Affiliations

          (1)
          Center for Management of Complex Chronic Care, Staff Physician, Medical Service, Hines, VA Hospital
          (2)
          Department of Medicine Loyola University Stritch School of Medicine, Loyola University of Chicago
          (3)
          Health Policy and Administration (MC 923) School of Public Health University of Illinois at Chicago
          (4)
          University of Illinois at Chicago School of Public Health (MC923)
          (5)
          Department of Orthopaedic Surgery, Loyola University Stritch School of Medicine, Loyola University of Chicago
          (6)
          Surgical Service, Hines VA Hospital

          References

          1. Benvenuti F, Ferrucci L, Guralnik JM, Gangemi S, Baroni A: Foot pain and disability in older persons: an epidemiologic survey. J Am Geriatr Soc 1995, 43:479–484.PubMed
          2. Leveille SG, Guralnik JM, Ferrucci L, Hirsch R, Simonsick E, Hochberg MC: Foot pain and disability in older women. Am J Epidemiol 1998, 148:657–665.PubMedView Article
          3. 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, 29:1023–1028.PubMed
          4. Novak P, Burger H, Marincek C, Meh D: Influence of foot pain on walking ability of diabetic patients. J Rehabil Med 2004, 36:249–252.PubMedView Article
          5. Menz HB, Lord SR: The contribution of foot problems to mobility impairment and falls in community-dwelling older people. J Am Geriatr Soc 2001, 49:1651–1656.PubMedView Article
          6. Menz HB, Lord SR: Foot pain impairs balance and functional ability in community-dwelling older people. J Am Podiatr Med Assoc 2001, 91:222–229.PubMed
          7. 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.PubMedView Article
          8. Nunally J, Bernstein I: Psychometric Theory. New York: McGraw-Hill; 1994.
          9. Bennett PJ, Patterson C, Wearing S, Baglioni T: Development and validation of a questionnaire designed to measure foot-health status. J Am Podiatr Med Assoc 1998, 88:419–428.PubMed
          10. Landorf KB, Keenan AM: An evaluation of two foot-specific, health-related quality-of-life measuring instruments. Foot Ankle Int 2002, 23:538–546.PubMed
          11. Budiman-Mak E, Conrad K, Stuck R, Matters M: Theoretical model and Rasch analysis to develop a revised Foot Function Index. Foot Ankle Int 2006, 27:519–527.PubMed
          12. International Classification of Impairments, Disabilities and Handicaps. [http://​www.​who.​int/​entity/​classification/​icf/​en] []
          13. Walmsley S, Williams AE, Ravey M, Graham A: The rheumatoid foot: a systematic literature review of patient-reported outcome measures. J Foot Ankle Res 2010, 3:12.PubMedView ArticlePubMed Central
          14. Linacre JM: Winsteps Rasch Measurement (Version 3.72.0). 2011.
          15. Linacre JM: Structure in Rasch residuals:Why principal components analysis (PCA)? Rasch Measurement Transactions 1998, 1:636.
          16. Linacre JM: Detecting multidimensionality: which residuals data-type works best? J Outcome Meas 1998, 2:266–283.PubMed
          17. Smith EW Jr: Detecting and evaluating the impact of multidimensionality using item fit statistics and principal component analysis of residuals. J Appl Meas 2002, 3:205–231.PubMed
          18. Reckase M: Unifactor latent trait model applied to multifactor tests: results and implications. J Educ and Behav Stat 1979, 4:207–230.
          19. Embretson SE, Reise SP: Item response theory for psychologists. Mahwah, NJ: Lawrence Erlbaum Associates Inc; 2000.
          20. Bond TG, Fox CM: Applying the Rasch model: fundamental measurement in the human sciences. Mahwah, NJ: Lawrence Erlbaum Associates; 2007.
          21. Linacre JM: Investigating rating scale category utility. J Outcome Meas 1999, 3:103–122.PubMed
          22. Linacre JM: Optimizing rating scale category effectiveness. J Appl Meas 2002, 3:85–106.PubMed
          23. 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.PubMed
          24. Domsic RT, Saltzman CL: Ankle osteoarthritis scale. Foot Ankle Int 1998, 19:466–471.PubMed
          25. Agel J, Beskin JL, Brage M, Guyton GP, Kadel NJ, Saltzman CL, Sands AK, Sangeorzan BJ, Soohoo NF, Stroud CC, et al.: Reliability of the Foot Function Index: a report of the AOFAS Outcomes Committee. Foot Ankle Int 2005, 26:962–967.PubMed
          26. Bal A, Aydog E, Aydog ST, Cakci A: Foot deformities in rheumatoid arthritis and relevance of foot function index. Clin Rheumatol 2006, 25:671–675.PubMedView Article
          27. Soohoo NF, Samimi DB, Vyas RM, Botzler T: Evaluation of the validity of the Foot Function Index in measuring outcomes in patients with foot and ankle disorders. Foot Ankle Int 2006, 27:38–42.PubMed
          28. Shrader JA, Popovich JM Jr, Gracey GC, Danoff JV: Navicular drop measurement in people with rheumatoid arthritis: interrater and intrarater reliability. Phys Ther 2005, 85:656–664.PubMed
          29. Helliwell P, Reay N, Gilworth G, Redmond A, Slade A, Tennant A, Woodburn J: Development of a foot impact scale for rheumatoid arthritis. Arthritis Rheum 2005, 53:418–422.PubMedView Article
          30. VanderLeeden M, Steultjens M, Dekker JH, Prins AP, Dekker J: Forefoot joint damage, pain and disability in rheumatoid arthritis patients with foot complaints: the role of plantar pressure and gait characteristics. Rheumatology (Oxford) 2006, 45:465–469.View Article
          31. Lau JT, Mahomed NM, Schon LC: Results of an Internet survey determining the most frequently used ankle scores by AOFAS members. Foot Ankle Int 2005, 26:479–482.PubMed
          32. Baumhauer JF, Nawoczenski DA, DiGiovanni BF, Wilding GE: Reliability and validity of the American Orthopaedic Foot and Ankle Society Clinical Rating Scale: a pilot study for the hallux and lesser toes. Foot Ankle Int 2006, 27:1014–1019.PubMed
          33. Ibrahim T, Beiri A, Azzabi M, Best AJ, Taylor GJ, Menon DK: Reliability and validity of the subjective component of the American Orthopaedic Foot and Ankle Society clinical rating scales. J Foot Ankle Surg 2007, 46:65–74.PubMedView Article
          34. Naal FD, Impellizzeri FM, Huber M, Rippstein PF: Cross -culteral adaptation and validation of the Foot function Index for use in German -speaking patients with foot complaints. Foot Ankle Int 2008, 12:1222–1228.View Article
          35. Baldassin V, Gomes CR, Beraldo PS: Effectiveness of prefabricated and customized foot orthoses made from low-cost foam for noncomplicated plantar fasciitis: a randomized controlled trial. Arch Phys Med Rehabil 2009, 90:701–706.PubMedView Article
          36. Wu SH, Liang HW, Hou WH: Reliability and validity of the Taiwan Chinese version of the Foot Function Index. J Formos Med Assoc 2008, 107:111–118.PubMedView Article
          37. Stropek S, Dvorak M: Arthroscopic treatment for calcaneal spur syndrome. Acta Chir Orthop Traumatol Cech 2008, 75:363–368.PubMed
          38. Foot Function Index Spanish Translation. [http://​www.​proqolid.​org] []
          39. Lin SS, Bono CM, Treuting R, Shereff MJ: Limited intertarsal arthrodesis using bone grafting and pin fixation. Foot Ankle Int 2000, 21:742–748.PubMed
          40. Grondal L, Hedstrom M, Stark A: Arthrodesis compared to Mayo resection of the first metatarsophalangeal joint in total rheumatoid forefoot reconstruction. Foot Ankle Int 2005, 26:135–139.PubMed
          41. van der Krans A, Louwerens JW, Anderson P: Adult acquired flexible flatfoot, treated by calcaneocuboid distraction arthrodesis, posterior tibial tendon augmentation, and percutaneous Achilles tendon lengthening: a prospective outcome study of 20 patients. Acta Orthop 2006, 77:156–163.PubMedView Article
          42. Stegman M, Anderson PG, Lowerens JWK: Triple arthrodesis of the hindfoot, a short term prospective outcome study. Foot Ankle Surg 2006, 71–77.
          43. Vesely R, Prochazka V, Visna P, Valentova J, Savolt J: Tibiotalocalcaneal arthrodesis using a retrograde nail locked in the sagittal plane. Acta Chir Orthop Traumatol Cech 2008, 75:129–133.PubMed
          44. Doets HC, Zurcher AW: Salvage arthrodesis for failed total ankle arthroplasty. Acta Orthop 2010, 81:142–147.PubMedView ArticlePubMed Central
          45. Jung HG, Myerson MS, Schon LC: Spectrum of operative treatments and clinical outcomes for atraumatic osteoarthritis of the tarsometatarsal joints. Foot Ankle Int 2007, 28:482–489.PubMedView Article
          46. van Doeselaar DJ, Heesterbeek PJC, Louwerens JWK, Swierstra BA: Foot Function After Fusion of the First Metatarsophalangeal Joint. Foot Ankle Int 2010, 31:670–675.PubMedView Article
          47. Niki H, Hirano T, Okada H, Beppu M: Combination joint-preserving surgery for forefoot deformity in patients with rheumatoid arthritis. J Bone Joint Surg Br 2010, 92:380–386.PubMedView Article
          48. Ibrahim T, Taylor G: The new press-fit ceramic Moje metatarsophalangeal joint replacement; short-term outcomes. The Foot 2004, 14:124–128.View Article
          49. Taranow WS, Moutsatson MJ, Cooper JM: Contemporary Approaches to stage II and III Hallux Rigidus: The role of Metalic Hemiarthroplasty of the Proximal Phalanx. Foot Ankle Clinic N Am 2005, 10:713–728.View Article
          50. Schutte BG, Louwerens JW: Short-term results of our first 49 Scandanavian total ankle replacements (STAR). Foot Ankle Int 2008, 29:124–127.PubMedView Article
          51. Bonnin MP, Laurent JR, Casillas M: Ankle function and sports activity after total ankle arthroplasty. Foot Ankle Int 2009, 30:933–944.PubMedView Article
          52. Vallier HA, Nork SE, Barei DP, Benirschke SK, Sangeorzan BJ: Talar neck fractures: results and outcomes. J Bone Joint Surg Am 2004, 86-A:1616–1624.PubMed
          53. Harris AM, Patterson BM, Sontich JK, Vallier HA: Results and outcomes after operative treatment of high-energy tibial plafond fractures. Foot Ankle Int 2006, 27:256–265.PubMed
          54. Potter MQ, Nunley JA: Long-term functional outcomes after operative treatment for intra-articular fractures of the calcaneus. J Bone Joint Surg Am 2009, 91:1854–1860.PubMedView Article
          55. Gaskill T, Schweitzer K, Nunley J: Comparison of surgical outcomes of intra-articular calcaneal fractures by age. J Bone Joint Surg Am 2010, 92:2884–2889.PubMedView Article
          56. Mulcahy D, Daniels TR, Lau JT, Boyle E, Bogoch E: Rheumatoid forefoot deformity: a comparison study of 2 functional methods of reconstruction. J Rheumatol 2003, 30:1440–1450.PubMed
          57. Ward CM, Dolan LA, Bennett DL, Morcuende JA, Cooper RR: Long-term results of reconstruction for treatment of a flexible cavovarus foot in Charcot-Marie-Tooth disease. J Bone Joint Surg Am 2008, 90:2631–2642.PubMedView ArticlePubMed Central
          58. Schlegel UJ, Batal A, Pritsch M, Sobottke R, Roellinghoff M, Eysel P, Michael JW: Functional midterm outcome in 131 consecutive cases of surgical clubfoot treatment. Arch Orthop Trauma Surg 2010, 130:1077–1081.PubMedView Article
          59. van der Heide HJ, Louwerens JW: Reconstructing the rheumatoid forefoot. Foot Ankle Surg 2010, 16:117–121.PubMedView Article
          60. Kroon M, Faber FW, van derLinden M: Joint preservation surgery for correction of flexible pes cavovarus in adults. Foot Ankle Int 2010, 31:24–29.PubMedView Article
          61. Watson TS, Anderson RB, Davis WH, Kiebzak GM: Distal tarsal tunnel release with partial plantar fasciotomy for chronic heel pain: an outcome analysis. Foot Ankle Int 2002, 23:530–537.PubMed
          62. Daniels TR, Thomas R, Bell TH, Neligan PC: Functional outcome of the foot and ankle after free fibular graft. Foot Ankle Int 2005, 26:597–601.PubMed
          63. Lee S, James WC, Cohen BE, Davis WH, Anderson RB: Evaluation of hallux alignment and functional outcome after isolated tibial sesamoidectomy. Foot Ankle Int 2005, 26:803–809.PubMed
          64. Soohoo NF, Vyas R, Samimi D: Responsiveness of the foot function index, AOFAS clinical rating systems, and SF-36 after foot and ankle surgery. Foot Ankle Int 2006, 27:930–934.PubMed
          65. Castellani C, Riedl G, Eberl R, Grechenig S, Weinberg AM: Transitional fractures of the distal tibia: a minimal access approach for osteosynthesis. J Trauma 2009, 67:1371–1375.PubMedView Article
          66. Aurich M, Bedi HS, Smith PJ, Rolauffs B, Muckley T, Clayton J, Blackney M: Arthroscopic treatment of osteochondral lesions of the ankle with matrix-associated chondrocyte implantation: early clinical and magnetic resonance imaging results. Am J Sports Med 2011, 39:311–319.PubMedView Article
          67. Eberl R, Singer G, Schalamon J, Hausbrandt P, Hoellwarth ME: Fractures of the talus–differences between children and adolescents. J Trauma 2010, 68:126–130.PubMedView Article
          68. Caselli MA, Levitz SJ, Clark N, Lazarus S, Velez Z, Venegas L: Comparison of Viscoped and PORON for painful submetatarsal hyperkeratotic lesions. J Am Podiatr Med Assoc 1997, 87:6–10.PubMed
          69. de PMagalhaes E, Davitt M, Filho DJ, Battistella LR, Bertolo MB: The effect of foot orthoses in rheumatoid arthritis. Rheumatology (Oxford) 2006, 45:449–453.View Article
          70. Conrad KJ, Budiman-Mak E, Roach KE, Hedeker D, Caraballada R, Burks D, Moore H: Impacts of foot orthoses on pain and disability in rheumatoid arthritics. J Clin Epidemiol 1996, 49:1–7.PubMedView Article
          71. Williams AE, Rome K, Nester CJ: A clinical trial of specialist footwear for patients with rheumatoid arthritis. Rheumatology (Oxford) 2007, 46:302–307.View Article
          72. Cho NS, Hwang JH, Chang HJ, Koh EM, Park HS: Randomized controlled trial for clinical effects of varying types of insoles combined with specialized shoes in patients with rheumatoid arthritis of the foot. Clin Rehabil 2009, 23:512–521.PubMedView Article
          73. Welsh BJ, Redmond AC, Chockalingam N, Keenan AM: A case-series study to explore the efficacy of foot orthoses in treating first metatarsophalangeal joint pain. J Foot Ankle Res 2010, 3:17.PubMedView ArticlePubMed Central
          74. Budiman-Mak E, Conrad KJ, Roach KE, Moore JW, Lertratanakul Y, Koch AE, Skosey JL, Froelich C, Joyce-Clark N: Can Foot Orthoses Prevent Hallux Valgus Deformity in Rheumatoid Arthritis? A Randomized Clinical Trial. J Clin Rheumatol 1995, 1:313–322.PubMedView Article
          75. Rao S, Baumhauer JF, Becica L, Nawoczenski DA: Shoe inserts alter plantar loading and function in patients with midfoot arthritis. J Orthop Sports Phys Ther 2009, 39:522–531.PubMed
          76. Rao S, Baumhauer JF, Tome J, Nawoczenski DA: Orthoses alter in vivo segmental foot kinematics during walking in patients with midfoot arthritis. Arch Phys Med Rehabil 2010, 91:608–614.PubMedView Article
          77. Caselli MA, Clark N, Lazarus S, Velez Z, Venegas L: Evaluation of magnetic foil and PPT Insoles in the treatment of heel pain. J Am Podiatr Med Assoc 1997, 87:11–16.PubMed
          78. Pfeffer G, Bacchetti P, Deland J, Lewis A, Anderson R, Davis W, Alvarez R, Brodsky J, Cooper P, Frey C, et al.: Comparison of custom and prefabricated orthoses in the initial treatment of proximal plantar fasciitis. Foot Ankle Int 1999, 20:214–221.PubMed
          79. Gross MT, Byers JM, Krafft JL, Lackey EJ, Melton KM: The impact of custom semirigid foot orthotics on pain and disability for individuals with plantar fasciitis. J Orthop Sports Phys Ther 2002, 32:149–157.PubMed
          80. Woodburn J, Barker S, Helliwell PS: A randomized controlled trial of foot orthoses in rheumatoid arthritis. J Rheumatol 2002, 29:1377–1383.PubMed
          81. Lin JL, Balbas J, Richardson EG: Results of non-surgical treatment of stage II posterior tibial tendon dysfunction: A 7- to 10-year followup. Foot Ankle Int 2008, 29:781–786.PubMedView Article
          82. Slattery M, Tinley P: The efficacy of functional foot orthoses in the control of pain in ankle joint disintegration in hemophilia. J Am Podiatr Med Assoc 2001, 91:240–244.PubMed
          83. Powell M, Seid M, Szer IS: Efficacy of custom foot orthotics in improving pain and functional status in children with juvenile idiopathic arthritis: a randomized trial. J Rheumatol 2005, 32:943–950.PubMed
          84. Novak P, Burger H, Tomsic M, Marincek C, Vidmar G: Influence of foot orthoses on plantar pressures, foot pain and walking ability of rheumatoid arthritis patients–a randomised controlled study. Disabil Rehabil 2009, 31:638–645.PubMedView Article
          85. Clark H, Rome K, Atkinson I, Plant M, Dixon J: The clinical effectiveness of foot orthoses in rheumatoid arthritis. Rheumatology (Oxford) 2010, 49:Suppl. 171.View Article
          86. Cui Q, Milbrandt T, Millington S, Anderson M, Hurwitz S: Treatment of posttraumatic adhesive capsulitis of the ankle: a case series. Foot Ankle Int 2005, 26:602–606.PubMed
          87. DiGiovanni BF, Nawoczenski DA, Malay DP, Graci PA, Williams TT, Wilding GE, Baumhauer JF: Plantar fascia-specific stretching exercise improves outcomes in patients with chronic plantar fasciitis. A prospective clinical trial with two-year follow-up. J Bone Joint Surg Am 2006,88(8):1775–1781.PubMedView Article
          88. Kulig K, Lederhaus ES, Reischl S, Arya S, Bashford G: Effect of eccentric exercise program for early tibialis posterior tendinopathy. Foot Ankle Int 2009, 30:877–885.PubMedView Article
          89. Rompe JD, Cacchio A, Weil L Jr, Furia JP, Haist J, Reiners V, Schmitz C, Maffulli N: Plantar fascia-specific stretching versus radial shock-wave therapy as initial treatment of plantar fasciopathy. J Bone Joint Surg Am 2010, 92:2514–2522.PubMedView Article
          90. Williams AE, Bowden AP: Meeting the challenge for foot health in rheumatic diseases. The Foot 2004, 14:154–158.View Article
          91. Williams AE, O'Neil TW, Mercer S, Toro B, Nester CJ: Foot pathology in patients with Paget's disease of bone. J Am Podiatr Med Asoc 2006, 96:226–231.
          92. Kamanli A, Suluhan O, Ozgocmen S, Kaya A, Ciftci I, Ardicoglu O: Measurement of Foot Bone Mineral Density in Rheumatoid arthritis: Its Application and Clinical Relevance. Turk J Rheumatol 2010, 25:56–62.View Article
          93. Kavlak Y, Demirtas N: Effect Of Foot Problems On Foot Function In Elderly Men. Turk J Geriatri 2010, 13:191–196.
          94. Goldstein CL, Schemitsch E, Bhandari M, Mathew G, Petrisor BA: Comparison of Different Outcome Instruments Following Foot and Ankle Trauma. Foot Ankle Int 2010, 31:1075–1080.PubMedView Article
          95. Rosenbaum D, Schmiegel A, Meermeier M, Gaubitz M: Plantar sensitivity, foot loading and walking pain in rheumatoid arthritis. Rheumatology (Oxford) 2006, 45:212–214.View Article
          96. Schmiegel A, Rosenbaum D, Schorat A, Hilker A, Gaubitz M: Assessment of foot impairment in rheumatoid arthritis patients by dynamic pedobarography. Gait Posture 2008, 27:110–114.PubMedView Article
          97. Trevethan R: Evaluation of two self-referent foot health instruments. Foot (Edinb) 2010,20(4):101–108.View Article
          98. Martin RL, Irrgang JJ: A survey of self-reported outcome instruments for the foot and ankle. J Orthop Sports Phys Ther 2007, 37:72–84.PubMedView Article
          99. Landorf KB, Burns J: Health Outcome Assessment. In Merriman's Assessment of the Lower Limb. 3rd edition. Edited by: Ben Y, Merriman LM. Philadelphia, PA 19103–2899: Churchill Livingstone, Elsevier Limited; 2009:33.
          100. Button G, Pinney S: A meta-analysis of outcome rating scales in foot and ankle surgery: is there a valid, reliable, and responsive system? Foot Ankle Int 2004, 25:521–525.PubMed
          101. Landorf KB, Radford JA: Minimal important difference: Values for the Foot Health Status Questionnaire, Foot function Index and Visual Analogue Scale. The Foot 2008, 18:15–19.View Article
          102. van der LM, Steultjens MP, Terwee CB, Rosenbaum D, Turner D, Woodburn J, Dekker J: A systematic review of instruments measuring foot function, foot pain, and foot-related disability in patients with rheumatoid arthritis. Arthritis Rheum 2008, 59:1257–1269.View Article
          103. Jannink MJ, deVries J, Stewart RE, Groothoff JW, Lankhorst GJ: Questionnaire for usability evaluation of orthopaedic shoes: construction and reliability in patients with degenerative disorders of the foot. J Rehabil Med 2004, 36:242–248.PubMedView Article
          104. Rogers JC, Irrgang JJ: Measures of Adult Lower Extremity Function. Arthritis Rheum 2003, 49:S67-S84.View Article

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