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Abstract

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. Acknowledgements
  9. REFERENCES
  10. Supporting Information

Objective

To compose an inventory of instruments that have been described to measure foot function (i.e., pressure and/or gait parameters), foot pain, and foot-related disability in rheumatoid arthritis (RA), and to investigate the clinimetric quality of these measures.

Methods

A systematic search was conducted in Medline, CINAHL, EMBase, and Sportdiscus. Standardized criteria, extended with levels of evidence, were applied to assess the quality of the clinimetric studies and the properties (i.e., reliability, validity, and responsiveness) of the described instruments.

Results

A variety of measurement instruments were identified. Only 16 instruments have been studied for their measurement properties in RA patients: 7 for assessing foot function, 3 for measuring foot-related disability, and 6 for measuring both foot pain and foot-related disability. Thirteen instruments were rated for reliability, of which 10 were rated positively on different levels of evidence. No positive rating for absolute measurement error was applicable for any of the tests. Internal consistency was reported for 7 instruments; 3 assigned a positive rating. For 2 instruments, Rasch analysis was used to assess the methodologic quality. A positive rating was reported for goodness-of-fit only, not for item calibration. Seven instruments were rated for construct validity, and 3 assigned a positive rating. Only 2 instruments were rated positively for responsiveness.

Conclusion

This review offers a basis for choosing the most appropriate instruments for measuring foot function, foot pain, and foot-related disability in RA patients, both for clinical practice and for research. Further research on the quality of these measures is urgently needed.


INTRODUCTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. Acknowledgements
  9. REFERENCES
  10. Supporting Information

Rheumatoid arthritis (RA) is a systemic disease with widespread synovial joint involvement. More than 90% of patients with RA report foot symptoms at some time during the course of their disease (1, 2). The presence of foot symptoms, in both the early and chronic stages of RA, has been shown to severely affect patients' daily activities, especially ambulation and other weight-bearing tasks (3).

In conjunction with systemic drug therapy, interventions specifically targeting the foot in RA include conservative treatment (e.g., insoles and orthopedic footwear) and surgery (e.g., reconstruction and arthroplasties of foot joints). Reduction in pain and disability is the main focus of treatment. To optimize the effect of interventions, there is also a need for objective evaluation of foot function with quantitative gait and/or pressure assessments. Therefore, foot function during weight bearing, foot pain, and foot-related disability are believed to be important outcome domains when studying the foot in RA. These domains were also recommended in a review of podiatry interventions in patients with RA (4).

A broad variety of instruments have been used in the literature to assess foot function, foot pain, and foot-related disability. A lack of uniformity in measures hampers the comparison of results from different studies. Recently, a review describing different measures for foot and ankle problems was published (5). However, this review did not contain a systematic literature search and evaluation of all available instruments, and was not focused on RA-specific instruments. A systematic review of the most appropriate instruments for measuring foot and ankle problems in RA has not been undertaken before.

The purpose of the present systematic review was 2-fold. The first goal was to make an inventory of instruments reported in the literature that measure foot function (pressure and/or gait parameters), foot pain, and foot-related disability in patients with RA. The second goal was to investigate the clinimetric quality of these measures in RA.

MATERIALS AND METHODS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. Acknowledgements
  9. REFERENCES
  10. Supporting Information

Literature search.

Studies were identified by searches of the computerized bibliographic database Medline (1966 to July 2007). Subsequently, other databases (CINAHL [1982 to July 2007], EMBase [1966 to July 2007], and Sportdiscus [to July 2007]) were searched. Additional articles were identified by manually searching references of the retrieved articles and the authors' own literature database. A combination of different variations of the following text words was used: rheumatoid arthritis, and foot and pressure and/or gait analysis and pain and disability. The full search is listed in Appendix A (available at the Arthritis Care & Research Web site at http://www.interscience.wiley.com/jpages/0004-3591:1/suppmat/index.html).

Inclusion and exclusion criteria.

To create an inventory of instruments that are used to measure foot function, foot pain, and foot-related disability in RA, we used the following inclusion criteria: 1) the study population comprised adult RA patients, or the majority of the study population consisted of RA patients, or a defined subgroup of RA patients existed in the study population, for whom data were presented separately; 2) foot and/or ankle-related problems were the main topic of the article; 3) measurements of foot function (pressure and gait parameters, or other as foot function–described parameters) and/or foot pain and/or foot-related disability (functional ability) were performed; 4) the article was an original research report; 5) the article was published in English, German, French, or Dutch; and 6) the article was a full-text article (abstracts, books, theses, and conference proceedings were excluded). No restrictions concerning the year of publication were used. References of retrieved articles were screened for additional relevant studies.

In the present study, measurement of foot function was defined as a quantitative analysis of pressure and/or gait parameters. Measurement of foot pain was defined as a score for pain in the foot and/or ankle as reported by the patient. Measurement of foot-related disability was defined as a score for the patients' limitation to perform daily, weight-bearing activities, such as walking and stair climbing.

For the second goal of this study, to investigate the clinimetric quality of the instruments in patients with RA, the results of the first search were used. Studies were included when information on the measurement properties of the identified measures was provided. Furthermore, we searched for studies on the measurement properties of these instruments in a general population of RA patients. We included full-text articles in which the clinimetric quality of the instruments was the aim of the study.

Selection of articles.

Article selection, data extraction, and quality assessment were performed by 2 independent reviewers (MvdL and MPMS). Disagreements were discussed and resolved. All abstracts were scanned against the inclusion criteria. Full-text articles were retrieved for all abstracts that fulfilled the inclusion criteria and for abstracts that indicated that relevant measurements were present in the full-text article. The retrieved articles were again reviewed against the inclusion criteria.

Data extraction.

For the first aim of the study, a list of measures was made. For the second aim of the study, the description of the measures was extracted from the included articles. The measurement properties of the instruments were evaluated using the methods described below.

Quality assessment of the clinimetric studies and measurement properties.

To evaluate the methodologic quality and results of the clinimetric studies, a checklist was composed that was based on the checklist for questionnaires by Bot et al (6) and the checklist for performance-based methods by Terwee et al (7, 8). We extended the checklist by defining different levels of evidence for reliability, validity, and responsiveness, depending on the quality of the methods of the clinimetric studies (see below). Once the applicable level of evidence had been identified, a positive or negative rating was assigned corresponding to the results of the study. If the methods were not appropriate, the measurement property was rated as indeterminate. If no information was available, a zero was recorded.

The following measurement properties were evaluated.

Reproducibility.

A distinction was made between reliability and absolute measurement error (agreement).

Reliability.

Reliability refers to the ability to differentiate among patients, despite measurement errors (9). The intraclass correlation coefficient (ICC), or kappa value for dichotomous or ordinal data, was considered an adequate measure of reliability (9). An ICC or kappa value and a sample size of at least 50 patients were needed for evidence to be considered level 1. A positive rating was assigned if the ICC or kappa was >0.70, with the lower limit of the confidence interval >0.60 (7). Evidence was designated as level 2 evidence if a Pearson's correlation coefficient and a sample size of at least 50 patients were used. An r > 0.80 was rated positively. For level 3 evidence, an ICC, kappa, or Pearson's correlation coefficient with a sample size <50 was needed. A positive rating was assigned if the ICC or kappa was >0.80, with the lower limit of the confidence interval >0.60, or if a Pearson's correlation coefficient >0.90 was present. If confidence intervals were not reported, they were calculated based on the ICC and the sample size (10).

Measurement error.

Measurement error, or agreement (9), refers to the precision of the instrument and is expressed in the units of measurement of the instrument. The limits of agreement (11), the standard error of measurement, and the smallest detectable change (SDC) (9) were regarded as adequate measures of measurement error to receive a level 1 evidence rating. The rating of the measurement error depends on what is considered a minimal important difference (MID) in scores within persons over time. Measurement error was rated positively if the limits of agreement or SDC was smaller than the MID. If the MID was not known, a level 2 evidence rating was assigned. A value of 0.5 SD was considered a general guideline for the MID (12).

Internal consistency.

Internal consistency is a measure of homogeneity of a (sub)scale. Evidence was designated as level 1 if factor analysis was applied to determine if summarized scores measured the same concept. In addition, a Cronbach's alpha was required for each set of summarized scores (13). A sample size of at least 7 times the number of items and a minimum of 100 patients were considered necessary. A level 2 evidence rating was assigned if the sample size was too small for factor analysis. A minimum of 4 patients per item and 50 patients in total was necessary. A level 3 evidence rating was designated if a minimum of 4 patients per item was included and the sample size was <50. A Cronbach's alpha >0.70 was needed for a positive rating on all levels of evidence (7).

If Rasch analysis was used to assess the methodologic quality, a level 1 evidence rating was assigned if the following information was described: item-response theory model, software package, and method of estimation used. In addition, goodness-of-fit should have been assessed (e.g., overall goodness-of-fit [χ2] or person separation on the level of the subscale, or InFit/OutFit statistics on item level). In addition, item calibration was judged (e.g., item separation). A positive rating was assigned for goodness-of-fit if the fit was good on the scale level or for 80% of the items (i.e., χ2 not significant, person separation at least 0.70, InFit statistics between 0.7 and 1.3). A positive rating for item calibration was assigned if at least 80% of the interitem differences were at least 0.15 logits. Evidence was designated as level 2 if the descriptive information was incomplete.

Content validity.

Validity refers to the ability of an instrument to measure the concept that it is intended to measure (14). Content validity examines the extent to which the domain of interest is comprehensively sampled by the items in a questionnaire or parts of a performance test (15). Items on the instrument must reflect areas that are important to RA patients with foot problems. Therefore, a positive rating was assigned when patients were involved during item selection (6).

Criterion validity.

Criterion validity refers to the extent to which scores on a particular instrument relate to a gold standard. A positive rating was assigned if convincing arguments were presented that the used standard really is “gold” and if the correlation with the gold standard was at least 0.70 (8) or if no significant differences between the instrument and the gold standard were found.

Construct validity.

Construct validity was assigned a level 1 evidence rating if specific hypotheses were defined concerning expected relationships with other measures or expected differences in scores between specific subgroups. A positive level 1 rating was assigned if at least 75% of these hypotheses were confirmed in (sub)groups of at least 50 patients (8). Level 2 evidence was considered if no hypothesis about expected relationships with other measures was defined beforehand. A positive level 2 rating was designated if plausible relationships with other measures were found in a (sub)group of at least 50 patients. A positive level 3 rating was designated if plausible relationships with other measures were found in a (sub)group of at least 20 patients.

Floor and ceiling effects were considered present if >15% of respondents achieved the highest and lowest possible score, respectively (16). A positive rating was achieved if there was no floor or ceiling effect.

Responsiveness.

Responsiveness refers to an instrument's ability to detect important change over time in the concept being measured (17). It should be considered an aspect of validity in a longitudinal setting. Responsiveness was therefore rated similarly to construct validity (7).

Reproducibility, validity, and responsiveness depend on the setting and the population in which they are assessed. Therefore, a clear description of the design of each individual clinimetric study (including characteristics of the study population [diagnosis and clinical features], measurements, testing conditions, and data analysis) was required to receive a positive rating. Furthermore, if any methodologic weakness in the design or execution of the clinimetric study was found, the evaluated measurement property was rated as indeterminate (7).

Interpretability.

Interpretability was defined as the degree to which one can assign qualitative meaning to quantitative scores (14). Investigators should provide information about what (change in) score would be clinically meaningful. To enable interpretation of change scores over time and sample size calculations, an MID should be defined. A sample size of 50 patients is considered adequate to determine the MID (8).

Practical issues.

The time needed to complete the test was recorded as a measure of patient burden. In addition, the requirements to perform the test were recorded in terms of apparatus and space required. These practical issues were not rated because their importance depends on the application of the test, e.g., in clinical practice or in a large study (7).

RESULTS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. Acknowledgements
  9. REFERENCES
  10. Supporting Information

For the first aim of the study, we obtained the following number of abstracts from the searches: 1,170 in Medline, 584 in EMBase, 81 in CINAHL, and 10 in SportDiscus. For further inspection of the full-text articles, 240 abstracts were selected. In addition, 7 articles were considered from our own literature databases or by reference tracking of the retrieved articles. Finally, we included 194 studies, referring to 36 different types of instruments (Table 1; and Appendix B, available at the Arthritis Care & Research Web site at http://www.interscience.wiley.com/jpages/0004-3591:1/suppmat/index.html).

Table 1. List of measurement instruments
DomainMeasurement instrumentsReferences
  • * VAS = visual analog scale; TADL = Toronto Activities of Daily Living; SIP = Sickness Impact Profile; RBFA = Robinson Bashall Functional Assessment; AOFAS = American Orthopaedic Foot and Ankle Society clinical rating scale; WOMAC = Western Ontario and McMaster Universities Osteoarthritis Index; FFI = Foot Function Index; LFIS = Leeds Foot Impact Scale; MFPDQ = Manchester Foot Pain and Disability Questionnaire; FHSQ = Foot Health Status Questionnaire.

  • References are listed in Appendix B (available at the Arthritis Care & Research Web site at http://www.interscience.wiley.com/jpages/ 0004-3591:1/suppmat/index.html).

Foot functionBarefoot plantar pressure measurements1–31
 In-shoe plantar pressure measurements16,25,32–41
 Gait analysis (instrumented walkway)2,16,42–51
 Forceplate14,28,42,52–57
 3-dimensional movement analysis system14,16,31,52–63
Foot painOne-item questions 
  Pain during ambulation/in certain part of foot (dichotomous or multiple grading)1,5,9,18–22,25,48,50,54,58,64–120
  VAS (10 cm/100 mm)2,34,36,44,46,47,49,52–54,58
 Questionnaire 
  Brief Pain Inventory33
Foot-related disabilitySelf-report 
  One-item questions 
   Ambulation/activity (dichotomous and multiple grading)19,22,36,65,66,69,70,73,74,77,80–84, 86–88,94,95,99,101,103,104,106, 107,110–112,114–116,119,120,124, 127,130
   VAS mobility128
  Questionnaires 
   TADL walking/stair climbing subscales121
   SIP ambulation subscale34,52,131
 Performance based 
  Quantitative outcome 
   50-foot walking time121,132,133
   10-meter walking test8,15
   Walking speed/gait timing device27,34,38
   RBFA ambulation subscale121
  Qualitative outcome 
   Assessment of walking ability (9 classes)134
   Assessment of different postures and gait68,74,100,106,135
Foot-related pain/disabilityAnkle/hindfoot scoring systems 
  AOFAS ankle/hindfoot scoring system53,135–147
  Scoring system by Mazur136,137,139,148–150
  Scoring system by Moran/rheumatoid ankle grading system141,150,151
  Scoring system by Koefoed128,152
  Scoring system by Evanski and Waugh135,153,154
  Scoring system by Figgie et al155
  Scoring system by Wang and Simmonds156
 Forefoot scoring systems 
  AOFAS forefoot scoring systems3,60,109,125,157–162
  Scoring system by McGarvey and Johnsson37
  Scoring system by Miehlke160,163–165
  Scoring system by Moeckel et al166
  Scoring system by Gainor37,167–169
  Scoring systems according to Bonney and MacNab170,171
 Questionnaires 
  WOMAC3,8,15,172
  FFI3,5,8,12,15,31,32,38,62,63,132,133,159, 161,173–181
  LFIS14,176
  MFPDQ16,176,182–184
  FHSQ181

For the second aim of this study, 14 full-text articles referring to 13 different instruments were included from the initial search. These were studies describing 1 or more measurement properties of the identified instruments. The additional search, in which measurement properties of the identified instruments in a general RA population were searched, produced 5 full-text articles in which 3 additional instruments were studied for their measurement properties. In total, 19 articles describing 16 instruments were included.

Inventory of measurement instruments per domain.

Foot function was measured with 5 different methods (Table 1). For each method, different systems were used in the literature, e.g., for barefoot plantar pressure measurements, the EMED system (Novel GmbH, München, Germany) was the most frequently used (in 16 articles). Foot pain was frequently measured with 1-item questions with great diversity in the type of question and response options. Foot-related disability was measured with self-report instruments (i.e., 1-item questions and a subscale of a questionnaire measuring functional ability) and performance tests (with a quantitative or a qualitative outcome). Time to perform a test is an example of a quantitative outcome, whereas gait inspection with a rating scale score for the ability to walk is an example of a qualitative outcome. Furthermore, measures with multiple domains, including subscales of both pain and disability, were reported in the literature.

Measurement properties of the identified instruments.

A description of the instruments concerning which properties were described in RA patients is shown in Table 2. Sixteen instruments were identified: 7 instruments for assessing foot function, 3 instruments for measuring foot-related disability (1 questionnaire and 2 performance tests), and 6 instruments for measuring both foot pain and foot-related disability (2 scoring systems and 4 questionnaires).

Table 2. Description of measurement instruments*
DomainInstrumentMeasurement conceptMeasuresTarget populationStudy populationNo. of scales/ scoresNo. of itemsNo. of response optionsTime to administerRequirements
  1. a

    RA = rheumatoid arthritis; 3-D = 3-dimensional; ROM = range of motion; OA = osteoarthritis; see Table 1 for additional definitions.

Foot functionPressure measurement 1 (18)Quantitative plantar pressure measurement (barefoot)Peak pressure, contact timePatients with foot/ankle symptomsChronic arthritis patients (majority RA) with foot symptoms2?Pressure platform and software (EMED; Novel)
 Pressure measurement 2 (19)Semiquantitative plantar pressure measurement (barefoot)Peak pressure in 6 foot regionsPatients with foot/ankle symptomsRA patients with foot deformities6?PressureStat footprint mat
 Gait analysis 1 (20)Measurement of gait parametersWalking speed, cadence, stride length, step length, base of support, gait cycle timePatients with gait limitationsRA patients with foot symptoms6?Instrumented walkway (GaitRite): 3.66-meter walkway with 48 sensors, and footswitches
 Gait analysis 2 (21)Measurement of gait parametersWalking speed, cadence, and stride length at a self-selected pace and fast speedPatients with gait limitationsRA patients with off-the-shelf orthopedic footwear3?8-meter electric footswitch walkway
 Gait analysis 3 (35)Measurement of gait parametersWalking speed, step length, stance phase duration, time to peak thrusting force, ground reaction forcePatients with gait limitationsRA patients with forefoot pain5?Contact sensitive walkmat system, Kistler forceplate
 3-D movement analysis 1 (22)Analysis of foot motionRearfoot motion, forefoot motion, navicular height, hallux flexion/ extensionPatients with foot/ankle symptomsRA patients with established disease and foot symptoms4?6-camera 60-Hz video-based motion analysis system (Vicon)
 3-D movement analysis 2 (23)Quantifying 3-D kinematics at the ankle joint complexAngular rotation position, ROM, and motion curve shapePatients with foot/ankle symptomsRA patients with ankle/hindfoot deformity3?6-D research system (electromagnetic tracking)
Foot-related disabilitySIP ambulation (30)Restrictions in ambulationQuestions (self-reportGeneric (36)RA patients (female)1?2 (y/n)30 minutes for SIP 136Pencil, questionnaire
 RBFA ambulation (31)Ambulation performance testTimed test of standing, walking, and managing stairsRA patientsArthritis patients13??
 50-foot walking time (32–34)Walking timeTime to walk 50 feet as fast as possiblePatients with gait limitationsRA patientsShort50-foot walkway, stopwatch
Foot-related pain/disabilityMoeckel forefoot scoring system (37)Pain, function, and objective findingsQuestions and physical examinationRA patients with orthopedic intervention of forefootRA patients after forefoot operation33–5 per scale?Pencil, scoring system
 AOFAS forefoot (26)Pain, function, footwear, joint motion, joint stability, callus, and alignmentQuestions and physical examinationPatients with forefoot symptoms (38)RA patients without active foot/ankle problems82–4 per scale?Pencil, scoring system
 FFI (27, 28)Pain, disability, and activity restrictionQuestions (self-report)RA patients with foot symptomsRA patients with an indication of orthoses (27), RA patients with at least 1 tender foot joint (28)323 (subscale pain: 7 items)VAS5–10 minutesPencil, questionnaire
 LFIS (29)Impairments/shoes and activities/participationQuestions (self-report)RA patients with foot symptomsRA patients with foot symptoms251Dichotomous: true/not true?Pencil, questionnaire
 WOMAC (39)Pain, function, and joint stiffnessQuestions (self-report)Knee/hip OA patients (40)RA patients324VAS?Pencil, questionnaire
 MFPDQ (41)Pain, function, and personal appearanceQuestions (self-report)Patients with foot symptomsPatients of a rheumatology clinic3193?Pencil, questionnaire

The measurement properties of the included instruments are shown in Tables 3 and 4. The quality assessment of the 16 measures is summarized in Table 5. For none of the instruments was there complete reporting of all measurement properties in RA patients. Reliability was the most commonly studied measurement property (13 instruments had a score for reliability). Absolute measurement error was not assessed for the identified instruments, with the exception of the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), for which limits of agreement were given. However, the WOMAC was rated indeterminate on measurement error because the MID could not be extracted from the data. Internal consistency was not applicable for the foot function instruments. It was assessed for 5 instruments measuring pain and/or disability. No level 1 evidence could be assigned because the identified studies did not include 100 patients. Content validity was rated positively for the Leeds Foot Impact Scale (LFIS) and Manchester Foot Pain and Disability Questionnaire (MFPDQ). Construct validity was assessed for 7 instruments. Only 3 were rated positively, whereas the other instruments were rated as indeterminate as a result of the study design. Responsiveness was assessed for 5 instruments, with a positive level 3 rating for the 50-foot walking time and the Foot Function Index (FFI). A zero for interpretability was recorded for all instruments because no MIDs were calculated.

Table 3. Reproducibility, absolute measurement error, and internal consistency*
Instrument              Reproducibility               Absolute measurement error          Internal consistency         
ReliabilityDesignTime intervalStudy sizeAbsolute measurement errorStudy sizeMIDDimensions studiedAlphaGoodness- of-fitItem calibrationStudy size
  • *

    MID = minimal important difference; ICC = intraclass correlation coefficient; NA = not applicable; 95% CI = 95% confidence interval; 3-D = 3-dimensional; see Table 1 for additional definitions.

Pressure measurement 1 (18)ICC 0.86–0.91Intrasession (2-step protocol, 3 trials)Consecutive13NA    
Pressure measurementκ = 0.21–0.59Interrater (4 raters)NA10NA    
 2 (19)κ = 0.33–0.57IntraraterAt least 1 week         
Gait analysis 1 (20)ICC 0.75–0.87 (0.65–0.91)Intersession (3 trials each session)Same day: before and after clinical appointment50NA    
Gait analysis 2 (21)ICC 0.95–0.99 (0.79–0.99)Intrasession (5 trials)Consecutive30NA    
 95% CI 0.86–0.99Intersession3× with 1-week interval         
Gait analysis 3 (35)NA    
3-D movement analysis 1 (22)r = 0.830–0.956Intrasession (5 trials)Consecutive11NA    
3-D movement analysis 2 (23)r = 0.809–0.927Intrasession (5 trials)Consecutive10NA    
SIP ambulation (30)   
RBFA ambulationr = 0.98InterraterSimultaneously13No0.82  98
 (31)r = 0.99Intersession4–9 days10        
50-foot walkingICC 0.907Intrarater15 minutes44NA    
 time (32)ICC 0.901InterraterSimultaneously         
50-foot walking time (33)NA    
50-foot walking time (34)NA  
Moeckel forefoot scoring system (37)Kendall coefficient of concordance = 0.94; 0.90Interrater??  
  Intrarater?         
AOFAS forefoot (26)ICC 0.72–0.95Intersession1 week11  
FFI (27)ICC 0.70–0.87 (0.53–0.92)Intersession1 week39Yes0.73–0.96  86
FFI pain (28)ICC 0.79/0.80 (0.61–0.90)Intersession8 days30Yes0.92–0.96  30
LFIS (29)ICC 0.84 (0.75–0.90), 0.96 (0.93–0.98)Intersession2 weeks85Yes YesNo85
WOMAC (39)  YesNo1,013
MFPDQ (41)Yes0.99  31
Table 4. Content validity, criterion validity, construct validity, and responsiveness*
InstrumentContent validityCriterion validityConstruct validityResponsiveness
Hyp.Main resultsStudy sizeHyp.Main resultsStudy sizeHyp.TreatmentFollowup timeMain resultsStudy size
  • *

    Hyp. = hypotheses;– = no data presented; HAQ = Health Assessment Questionnaire; 3-D = 3-dimensional; RA = rheumatoid arthritis; GP = general practitioner; see Table 1 for additional definitions.

Pressure measurement 1 (18)
Pressure measurement 2 (19)YesSignificant different pressure values for PressureStat compared with EMED system10   
Gait analysis 1 (20)
Gait analysis 2 (21)Nor = −0.62 to −0.68 with HAQ30
Gait analysis 3 (35)NoSecond-line drugs6 monthsNo significant correlations in change of gait parameters with change in clinical assessment22
3-D movement analysis 1 (22)
3-D movement analysis 2 (23)
SIP ambulation (30)Nor = 0.65 and r = 0.51 with Keitel index and Lansbury Articular Index99
RBFA ambulation (31)Therapists were asked to judge the scale, no patients were involvedNor = 0.44 with range of motion hip98NoIntensive rehabilitation program?No relevant results98
50-foot walking time (32)
50-foot walking time (33)Nor = −0.53 to −0.68 with functional scales92NoShort hospitalization in rheumatology rehabilitation unit12 monthsNo relevant results92
50-foot walking time (34)  24NoNo treatment: time was used as “treatment”2–4 weeksr = 0.54–0.68 with clinical measures; standardized response mean 0.4624
Moeckel forefoot scoring system (37)
AOFAS forefoot (26)Yesr = −0.31 to −0.94 with FFI11
FFI (27)Experts selected the items, no patients were involvedYesFoot disability: r = 0.51 with 50-foot walking time; foot pain: r = 0.54 with foot joint count57–87YesFunctional foot orthoses6 months0.45 (FFI-total) and 0.47 (FFI-pain) with changes in foot joint count42
FFI pain (28)
LFIS (29)Patients and experts were involved in selection of itemsNoNo quantitative results presented85
WOMAC (39)
MFPDQ (41)Patients were involved in selection of itemsYesκ = 0.48 and 0.50 with 2 questions of the of Functional Limitation Profile YesSignificant difference on 11 of 19 items between RA patients with current foot pain and GP consulters and community subjects17     
Table 5. Summary of the evaluation of the quality and outcomes of the clinimetric studies*
DomainMethodReliabilityAbsolute measurement errorInternal consistencyGoodness-of-fitItem calibrationMIDContent validityCriterion validityConstruct validityFloor/ ceiling effectResponsivenessInterpretability
  • *

    MID = minimal important difference; + = positive rating; 0 = no information available; NA = not applicable; − = negative rating; ? = indeterminate rating; 3-D = 3-dimensional; see Table 1 for additional definitions.

  • + for navicular height, − for rearfoot and forefoot motions.

  • + for AOFAS hallux scale, − for AOFAS lesser toes scale.

  • §

    Ceiling effect for AOFAS lesser toe scale (activity subscale).

  • + for disability subscale, activity limitation subscale, and total score; − for pain subscale.

  • #

    + for subscales, ? for total score.

  • **

    No ceiling or floor effect for function scale, no information available for pain scale.

Foot functionPressure measurement 1 (18)3+0NA  0NA00NA00
 Pressure measurement 2 (19)3−0NA  0NA0NA00
 Gait analysis 1 (20)1+0NA  0NA00NA00
 Gait analysis 2 (21)3+0NA  0NA?0NA00
 Gait analysis 3 (35)00NA  0NA00NA3−0
 3-D movement analysis 1 (22)3+/3−0NA  0NA00NA00
 3-D movement analysis 2 (23)3−0NA  0NA00NA00
Foot-relatedSIP ambulation (30)000  0002+000
 disabilityRBFA ambulation (31)3+02+  0?0?NA?0
 50-foot walking time (32)3+0NA  0NA00NA00
 50-foot walking time (33)00NA  0NA02+NA?0
 50-foot walking time (34)00NA  0NA00NA3+0
Foot-related pain/ disabilityMoeckel forefoot scoring system (37)?0NA  0000000
 AOFAS forefoot (26)3+/3−0NA  000?§00
 FFI (27)3+/3−02+/?#  0?01+03+0
 FFI pain (28)3+03+  0000000
 LFIS (29)1+0 +00+0?000
 WOMAC (39)0? +0000+/0**00
 MFPDQ (41)00?  0+??000

DISCUSSION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. Acknowledgements
  9. REFERENCES
  10. Supporting Information

In the present study, we identified a variety of instruments that aim to measure foot function, foot pain, and foot-related disability in RA. We recorded 36 different instruments. Of these instruments, only 16 were studied for 1 or more measurement properties in patients with RA: 7 for foot function, 3 for foot-related disability, and 6 for both foot pain and foot-related disability. For each measurement property, we developed different levels of evidence to assess the methodologic quality of the included studies. Reliability was the most commonly studied property. Validity and responsiveness were studied less frequently. Based on the limited information available on measurement properties, some cautious recommendations for instrument use can be made.

For foot function, peak pressure and contact time appear to be reliably measured with the EMED system. Barefoot plantar pressure measurements using EMED were evaluated for their intrasession reliability, and rated with a 3+ (18). Besides the EMED system, a more simple, semiquantitative system for measuring plantar pressure, PressureStat (Bailey Instruments, Manchester, UK), was studied for reliability and construct validity, but was rated negatively for both properties (19). Therefore, use of the PressureStat system could not be recommended. There were no studies investigating measurement properties for in-shoe plantar pressure measurements. Currently, the EMED system is the only plantar pressure system for which some information about its clinimetric quality is available. Reliability of gait parameters measured with the GaitRite system (CIR Systems, Havertown, PA) (20) scored positively as level 1 evidence, while gait parameters measured with an 8-meter footswitch system (21) scored a 3+. Reliability of 3-dimensional movements of the foot and ankle measured with the Vicon system (Vicon, Oxford, UK) (22) and a system for electromagnetic tracking (23) were rated positively (level 3 evidence). The choice of a certain instrument to measure foot function is dependent on the research aim or the aim of the clinical application, ranging from easy to use, affordable measurements of gait (e.g., a plantar pressure system or a walkmat system) to more advanced measurements of gait (e.g., 3-dimensional movement analysis). Based on the evidence presented here, both options can be cautiously recommended.

The visual analog scale (VAS) global pain has been reported to be valid, reliable, and responsive in patients with RA and is included in the core set of outcome measures for rheumatology (24, 25). However, measurement properties of a standardized VAS foot pain were not found. Furthermore, foot pain was measured as part of a scoring system or a multiple-domain questionnaire. Only the American Orthopaedic Foot and Ankle Society (AOFAS) clinical rating scale forefoot scales were studied for their clinimetric quality in RA, with a positive rating for reliability (level 3) for the AOFAS hallux scale (26). Construct validity was rated as indeterminate. More research on the clinimetric quality of the AOFAS scales is needed to rate their usefulness as outcome instruments in RA. Multidomain questionnaires that have been studied for 1 or more measurement properties include the FFI, LFIS, WOMAC, and MFPDQ. The FFI and LFIS were most extensively studied and generally received positive ratings (27–29). For the purpose of evaluation of an intervention, the FFI is the only instrument that was rated positively (level 3) for responsiveness.

For foot-related disability, self-report and performance-based instruments have been used. We recommend considering both self-report and performance-based instruments when studying foot problems in patients with RA because they can provide complementary information concerning patients' level of functional ability. Positive ratings were assigned to the self-report Sickness Impact Profile ambulation subscale (construct validity) (30) and 2 performance tests: the Robinson Bashall Functional Assessment ambulation subscale (internal consistency and reliability) (31) and the 50-foot walking time (reliability, construct validity, and responsiveness) (32–34).

In the present study, we investigated the measurement properties of disease-specific instruments. Disease-specific instruments, in contrast to generic instruments, are designed to be sensitive to the unique characteristics of one distinct disease state or population. Generic instruments involve broad questions that are appropriate for a wide range of musculoskeletal and nonmusculoskeletal conditions (5). Authors can decide to add a generic instrument to the outcome measures to be able to compare their study group with other studies with different patient populations.

In addition, general disability and quality of life measures can be used to evaluate outcome in studies concerning the foot in patients with RA. The American College of Rheumatology and Outcome Measures in Rheumatology Clinical Trials recommend the use of the Health Assessment Questionnaire and Arthritis Impact Measurement Scales as outcome measures of general disability in the RA literature (24, 25).

Other outcome domains, such as joint damage, deformity, shoe wear, participation restriction, and patient and physician global assessment, can be used depending on the aim of the study. These outcomes were not within the focus of this review.

There might be more instruments in the literature that are suitable for measuring foot function, foot pain, and foot-related disability. However, our strategy was to search for the instruments that are currently being used in studies concerning the foot in patients with RA.

Only studies containing information on measurement properties that was intentionally calculated to assess a measurement property were included in the present study. More evidence is probably available in the literature that could be used to determine validity and responsiveness of the measurement instruments, e.g., identified measurement instruments that were compared with other measures. We did not include these studies because the results are difficult to interpret without specified hypotheses about expected relationships between the measures (7).

Arbitrary choices have been made to define the different levels of evidence. However, no standardized criteria to evaluate measurement properties exist.

In conclusion, a variety of measurement instruments have been identified in studies concerning foot problems in patients with RA. Although based on a limited number of clinimetric studies currently available, this review offers a basis for choosing the most appropriate measurement instruments for assessing foot function, foot pain, and foot-related disability in patients with RA for both clinical practice and research.

AUTHOR CONTRIBUTIONS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. Acknowledgements
  9. REFERENCES
  10. Supporting Information

Mr. Steultjens had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Study design. Van der Leeden, Steultjens, Terwee, Rosenbaum, Dekker.

Acquisition of data. Van der Leeden, Steultjens.

Analysis and interpretation of data. Van der Leeden, Steultjens, Terwee, Turner, Woodburn, Dekker.

Manuscript preparation. Van der Leeden, Steultjens, Terwee, Rosenbaum, Turner, Woodburn, Dekker.

Statistical analysis. Van der Leeden, Steultjens.

Acknowledgements

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. Acknowledgements
  9. REFERENCES
  10. Supporting Information

We thank Ingrid Riphagen and Remke Albers for their help with the searches in the electronic databases.

REFERENCES

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  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. Acknowledgements
  9. REFERENCES
  10. Supporting Information
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Supporting Information

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. Acknowledgements
  9. REFERENCES
  10. Supporting Information
FilenameFormatSizeDescription
ART_24016_sm_OnlineAPPENDIX.doc60KAPPENDIX A. FULL SEARCH STRATEGY, APPENDIX B: REFERENCES INCLUDED IN TABLE 1

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