Open Access

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

  • Elly Budiman-Mak1, 2Email author,
  • Kendon J Conrad3,
  • Jessica Mazza4 and
  • Rodney M Stuck5, 6
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,
https://static-content.springer.com/image/art%3A10.1186%2F1757-1146-6-5/MediaObjects/13047_2012_Article_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. 10.1093/aje/148.7.657.PubMed
  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. 10.1080/16501970410029816.PubMed
  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. 10.1111/j.1532-5415.2001.49275.x.PubMed
  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. 10.1016/0895-4356(91)90220-4.PubMed
  8. Nunally J, Bernstein I: Psychometric Theory. 1994, New York: McGraw-Hill
  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: 12-10.1186/1757-1146-3-12.PubMed CentralPubMed
  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: 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. 2000, Mahwah, NJ:Lawrence Erlbaum Associates Inc,
  20. Bond TG, Fox CM: Applying the Rasch model: fundamental measurement in the human sciences. 2007, Mahwah, NJ: Lawrence Erlbaum Associates
  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. 10.1007/s10067-005-0115-z.PubMed
  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, 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. 10.1002/art.21176.PubMed
  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. 10.1093/rheumatology/kei186.
  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. 10.1053/j.jfas.2006.12.002.PubMed
  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.
  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. 10.1016/j.apmr.2008.11.002.PubMed
  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. 10.1016/S0929-6646(08)60124-2.PubMed
  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. 10.1080/17453670610045858.PubMed
  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. 10.3109/17453671003628764.PubMed CentralPubMed
  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. 10.3113/FAI.2007.0482.PubMed
  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. 10.3113/FAI.2010.0670.PubMed
  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. 10.1302/0301-620X.92B3.23186.PubMed
  48. Ibrahim T, Taylor G: The new press-fit ceramic Moje metatarsophalangeal joint replacement; short-term outcomes. The Foot. 2004, 14: 124-128. 10.1016/j.foot.2004.01.002.
  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. 10.1016/j.fcl.2005.06.011.
  50. Schutte BG, Louwerens JW: Short-term results of our first 49 Scandanavian total ankle replacements (STAR). Foot Ankle Int. 2008, 29: 124-127. 10.3113/FAI.2008.0124.PubMed
  51. Bonnin MP, Laurent JR, Casillas M: Ankle function and sports activity after total ankle arthroplasty. Foot Ankle Int. 2009, 30: 933-944. 10.3113/FAI.2009.0933.PubMed
  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. 10.2106/JBJS.H.01475.PubMed
  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. 10.2106/JBJS.J.00089.PubMed
  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. 10.2106/JBJS.G.01356.PubMed CentralPubMed
  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. 10.1007/s00402-009-0948-z.PubMed
  59. van der Heide HJ, Louwerens JW: Reconstructing the rheumatoid forefoot. Foot Ankle Surg. 2010, 16: 117-121. 10.1016/j.fas.2009.07.001.PubMed
  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. 10.3113/FAI.2010.0024.PubMed
  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. 10.1097/TA.0b013e31818866fd.PubMed
  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. 10.1177/0363546510381575.PubMed
  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. 10.1097/TA.0b013e3181a74667.PubMed
  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. 10.1093/rheumatology/kei163.
  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. 10.1016/0895-4356(96)00534-3.PubMed
  71. Williams AE, Rome K, Nester CJ: A clinical trial of specialist footwear for patients with rheumatoid arthritis. Rheumatology (Oxford). 2007, 46: 302-307.
  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. 10.1177/0269215508101737.PubMed
  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: 17-10.1186/1757-1146-3-17.PubMed CentralPubMed
  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. 10.1097/00124743-199512000-00001.PubMed
  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. 10.1016/j.apmr.2009.11.027.PubMed
  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. 10.3113/FAI.2008.0781.PubMed
  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. 10.1080/09638280802239441.PubMed
  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-
  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. 10.2106/JBJS.E.01281.PubMed
  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. 10.3113/FAI.2009.0877.PubMed
  89. Rompe JD, Cacchio A, Weil L, 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. 10.2106/JBJS.I.01651.PubMed
  90. Williams AE, Bowden AP: Meeting the challenge for foot health in rheumatic diseases. The Foot. 2004, 14: 154-158. 10.1016/j.foot.2004.03.006.
  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. 10.5152/tjr.2010.02.
  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. 10.3113/FAI.2010.1075.PubMed
  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.
  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. 10.1016/j.gaitpost.2007.02.008.PubMed
  97. Trevethan R: Evaluation of two self-referent foot health instruments. Foot (Edinb). 2010, 20 (4): 101-108.
  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. 10.2519/jospt.2007.2403.PubMed
  99. Landorf KB, Burns J: Health Outcome Assessment. Merriman's Assessment of the Lower Limb. Edited by: Ben Y, Merriman LM. 2009, Philadelphia,PA 19103–2899: Churchill Livingstone, Elsevier Limited, 33-3,
  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. 10.1016/j.foot.2007.06.006.
  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. 10.1002/art.24016.
  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. 10.1080/16501970410033569.PubMed
  104. Rogers JC, Irrgang JJ: Measures of Adult Lower Extremity Function. Arthritis Rheum. 2003, 49: S67-S84. 10.1002/art.11401.

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