Skip to main content
main-content
Top

Tip

Swipe om te navigeren naar een ander artikel

01-12-2013 | Review | Uitgave 1/2013 Open Access

Journal of Foot and Ankle Research 1/2013

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

Tijdschrift:
Journal of Foot and Ankle Research > Uitgave 1/2013
Auteurs:
Elly Budiman-Mak, Kendon J Conrad, Jessica Mazza, Rodney M Stuck
Belangrijke opmerkingen

Electronic supplementary material

The online version of this article (doi:10.​1186/​1757-1146-6-5) contains supplementary material, which is available to authorized users.

Competing interests

The authors declare that they have no competing interests.

Authors’ contributions

EBM, KJC, have contributed in drawing the concept and design of this paper, EBM initiated the literature search, reviewed, scrutinized them, and collected the abstracts and organized into tables. KJC, RMS and JM reviewed the tables and all authors participated in drafting the manuscript. KJC and JM also reanalyzed the original FFI-R data and revised the subscales and FFI-R response categories. All authors participated in revising the manuscript and have given final approval of the version to be published.
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.

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,

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.

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.
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://​creativecommons.​org/​licenses/​by/​2.​0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Competing interests

The authors declare that they have no competing interests.

Authors’ contributions

EBM, KJC, have contributed in drawing the concept and design of this paper, EBM initiated the literature search, reviewed, scrutinized them, and collected the abstracts and organized into tables. KJC, RMS and JM reviewed the tables and all authors participated in drafting the manuscript. KJC and JM also reanalyzed the original FFI-R data and revised the subscales and FFI-R response categories. All authors participated in revising the manuscript and have given final approval of the version to be published.

Onze productaanbevelingen

BSL Podotherapeut Totaal

Binnen de bundel kunt u gebruik maken van boeken, tijdschriften, e-learnings, web-tv's en uitlegvideo's. BSL Podotherapeut Totaal is overal toegankelijk; via uw PC, tablet of smartphone.

Extra materiaal
Additional file 1: Revised FOOT FUNCTION INDEX (FFI-R).(DOCX 24 KB)
13047_2012_487_MOESM1_ESM.docx
Additional file 2: Revised FOOT FUNCTION INDEX (FFI-R) Short Form. (DOCX 22 KB)
13047_2012_487_MOESM2_ESM.docx
Authors’ original file for figure 1
13047_2012_487_MOESM3_ESM.pdf
Authors’ original file for figure 2
13047_2012_487_MOESM4_ESM.doc
Authors’ original file for figure 3
13047_2012_487_MOESM5_ESM.doc
Literatuur
Over dit artikel

Andere artikelen Uitgave 1/2013

Journal of Foot and Ankle Research 1/2013 Naar de uitgave