Abstract
Objective
French validation of the Foot Function Index (FFI), self-questionnaire designed to evaluate rheumatoid foot according to 3 domains: pain, disability and activity restriction.
Methods
The first step consisted of translation/back translation and cultural adaptation according to the validated methodology. The second stage was a prospective validation on 53 patients with rheumatoid arthritis who filled out the FFI. The following data were collected: pain (Visual Analog Scale), disability (Health Assessment Questionnaire) and activity restrictions (McMaster Toronto Arthritis questionnaire). A test/retest procedure was performed 15 days later. The statistical analyses focused on acceptability, internal consistency (Cronbach’s alpha and Principal Component Analysis), test-retest reproducibility (concordance coefficients), external validity (correlation coefficients) and responsiveness to change.
Results
The FFI-F is a culturally acceptable version for French patients with rheumatoid arthritis. The Cronbach’s alpha ranged from 0.85 to 0.97. Reproducibility was correct (correlation coefficients > 0.56). External validity and responsiveness to change were good.
Conclusion
The use of a rigorous methodology allowed the validation of the FFI in the French language (FFI-F). This tool can be used in routine practice and clinical research for evaluating the rheumatoid foot. The FFI-F could be used in other pathologies with foot-related functional impairments.
1
Introduction
According to a 2010 epidemiological study focusing on the prevalence of foot pain in rheumatoid arthritis (RA) and its care management, 35.4% of patients indicated that their feet was the first symptomatic site of RA. In all, 90.3% of responders reported foot pain for more than one day since the beginning of their pathology and 69.2% of them experienced foot pain during one day in the past month. In responders, 64% of patients had previously seen a podiatrist and only 54.2 of patients had plantar orthosis.
The French High Health Authority (HAS) published recommendations regarding the non-pharmacologic care management of patients with RA. Podiatric follow-up and the prescription of adapted footwear and plantar orthosis are recommended. In order to be able to evaluate the impact of the various therapeutic modalities, it is necessary to have a validated assessment tool.
Several tools have been described in the literature to evaluate the rheumatoid foot. We focused mainly on the Foot Function Index (FFI) published by Budiman-Mak et al. in 1991 . This questionnaire includes 23 items, scored from 1 to 10 using the Visual Analog Scale (VAS) and divided into three subscales: “pain” (score up to 90), “function” (score up to 90) and “activity limitation” (score up to 50). The total maximum score is 230. The FFI is designed to measure both current state, defined as the past week before taking the test, and change in status.
The FFI psychometric properties confirmed the relevance of validating it in the French language. In the original article , internal consistency evaluated by Cronbach’s alpha was reported at 0.9556 for the total score. Test-retest reliability evaluated by an Intraclass Correlation Coefficient (ICC) was also good at 0.87 (0.79–0.92) for the total score. A literature review dating from 2008 allowed the confrontation of several tools to assess the rheumatoid foot and compare their psychometric properties. Among the different questionnaires evaluated, the FFI emerged as one of the best questionnaires and the only one where responsiveness to change was correct. A revised version of the FFI was also validated .
The use of FFI in clinical practice makes it a reference tool. It is most often used as an evaluation tool for the rheumatoid foot and it is the questionnaire most used by AOFAS members . Helliwell used the FFI as a reference to develop a new evaluation scale to assess foot function in RA.
Furthermore, several validated translated versions of the FFI are now available in the Netherlands , Germany and China .
Overall, we choose the FFI because of its validated use in assessing the rheumatoid foot, its solid psychometric properties and its simple administration, with the objective to provide physicians with a reference tool for French patients.
The objective of this work is the validation of the FFI in the French language.
2
Methods
2.1
Translation of the FFI and cultural adaptation
The translation of the FFI in French abided by the literature guidelines . Step 1: translations of the FFI into French performed by two independent French native translators. Step 2: synthesis by both translators and an observer based on the two previous translations. Step 3: double translation/back translation in English of the French version of the FFI by two native English speakers, without any medical background and blinded from the original English version. Step 4: elaboration by a committee of three experts of a pre-final version. Step 5: validation test of the pre-final version on 10 patients.
2.2
French version of the Foot Function Index (FFI-F)
The validated FFI-F is a self-questionnaire made of 23 items scored from 0 to 10 on a numeric scale and spread out in three subscales: pain (out of 90), function (out of 90) and activity limitation (out of 50).
Looking at all the various published translations of the FFI , we noticed that most of these questionnaires included 18 items and not 23 as in the original questionnaire. This is due to the fact that the third domain related to activity limitations was taken off in several versions, because its reproducibility was deemed too low. We chose not to change the initial questionnaire by keeping the 23 items in order to be consistent in comparing our statistical results with those of the original questionnaire.
2.3
Patient cohort and validation procedure
The prospective validation was conducted on patients with RA who filled out the FFI-F questionnaire. These patients came from the Physical Medicine and Rehabilitation (PM&R) and rheumatology consultations as well as rheumatology hospitalization. Patients had validated RA according to the American College of Rheumatology (ACR) criteria with or without foot affections and were able to understand and read French. The number of patients to be included was set to a minimum of 50, following the recommendations published by Terween et al. and in accordance with our recruitment abilities. Furthermore, the following data were collected: foot-related history and recent disease activity score (DAS) 28-C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR). For each patient, the maximum walking perimeter was collected. During the consultation, the time needed to walk 10 m and 200 m was recorded. Each foot was examined: collecting deformations, painful joints, range of motion, and testing of ankle and foot muscles.
In order to evaluate the external validity of the questionnaire for each of the successive domains, each patient, aside from the FFI-F, also filled out a VAS for the pain on the day of the consultation and the previous week, the Health Assessment Questionnaire (HAQ) and the main foot disability using the McMaster Toronto Arthritis (MACTAR) questionnaire .
The latter is also used to compensate for the limited evaluation of activity limitation in the third subscale of the FFI-F. This tool was initially validated and used to assess RA-related activity limitations. In our case, the question asked was: which is the main disability related to your rheumatoid feet?
The retest was performed at D15.
2.4
Statistical considerations
In addition to the usual descriptive statistical analyses, the following psychometric properties of the scale were explored:
- •
acceptability: data quality was deemed acceptable if less than 5% of data were missing. The range (minimum and maximum), mean (and associated standard deviation SD) and median, floor and ceiling thresholds (for both, the maximum accepted as 15%), and asymmetry in scores’ distribution (skewness and kurtosis measures, limits: from -1 to +1) were analyzed;
- •
internal consistency was evaluated with the Cronbach α coefficient (accepted minimal value: 0.70), the inter-item correlation coefficient (≥ 0.30) and the overlap (correlation between an item and its dimension, ≥ 0.30) (data not shown here). Internal consistency was also determined by the correlation between the domains making up the scale (standard, 0.30 to 0.70) . Construct validity of the FFI-F was explored using a principal component analysis (PCA). A factorial analysis (principal component analysis and varimax rotation) was conducted in order to determine the multi-dimension structure of the scale. PCA consists in replacing a family of variables by new variables with maximum variation, not correlated two by two and which are linear combinations of the original variables. These new variables, called principal. These new variables, called principal components, define factorial planes serving as a base for a graph representation of the initial variables. Thus, it is an approach designed to synthesize the data to study and visualize the correlations between variables (in this case FFI items) in order to explore the links between items and study their potential redundancy. The final number of factors selected, the part of data to be kept and the screen plot of eigenvalues were determined according to the eigenvalue-one criterion (Kaiser criterion);
- •
reproducibility: the intraclass correlation coefficient (random-effects model ICC) and the Lin’s Concordance Correlation Coefficient (CCC) were computed to determine the test-retest reliability. ICC and CCC values ≥ 0.70 were deemed satisfactory;
- •
regarding external consistency, relationships between the questionnaire score and the other measures (HAQ, MACTAR and VAS) were evaluated via the correlation coefficient (Pearson’s or Spearman’s according to the distribution of the parameters studied, P > 0.50);
- •
accuracy: for each domain, the standard error of the mean (SEM) was computed as such SEM = SD × √ (1-ICC test-retest ). It is admitted that good accuracy is equivalent to SEM ≤ 1/2 (SD). Furthermore, the valued associated to the SDD (smallest detectable difference) for each domain was calculated from the reproducibility study allowing to evidence, for the 3 subscales of the FFI, an estimation of the variability of the measure and thus of the error;
- •
following the exhaustive analysis of the published studies , it seems that no method, related to the sensitivity of a measure, has been validated in the scientific world. In this study, the responsiveness to change was evaluated by paired samples’ tests (Student’s t -test or Wilcoxon signed-rank test, if the conditions of the t -test were not respected) in order to study the evolution of the parameters associated to the HAG, and VAS (day and week) and the FFI domains on the study population.
In this study, the responsiveness to change was evaluated by paired samples’ tests (Student’s t -test or Wilcoxon signed-rank test, if the conditions of the t -test were not respected) in order to study the evolution of the parameters associated to the HAG, and VAS (day and week) and the FFI domains on the study population.
2.5
Ethics
The protocol, the information sheet as well as the case report form were submitted to the Ethics Committee of the Clinical Investigation Centers of the Inner region Rhône Alpes Auvergne. The Ethics Committee gave its approval on 12/15/2011. A signed written consent form was collected from patients before study inclusion. The study was conducted according to good clinical practices and the declaration of Helsinki.
2
Methods
2.1
Translation of the FFI and cultural adaptation
The translation of the FFI in French abided by the literature guidelines . Step 1: translations of the FFI into French performed by two independent French native translators. Step 2: synthesis by both translators and an observer based on the two previous translations. Step 3: double translation/back translation in English of the French version of the FFI by two native English speakers, without any medical background and blinded from the original English version. Step 4: elaboration by a committee of three experts of a pre-final version. Step 5: validation test of the pre-final version on 10 patients.
2.2
French version of the Foot Function Index (FFI-F)
The validated FFI-F is a self-questionnaire made of 23 items scored from 0 to 10 on a numeric scale and spread out in three subscales: pain (out of 90), function (out of 90) and activity limitation (out of 50).
Looking at all the various published translations of the FFI , we noticed that most of these questionnaires included 18 items and not 23 as in the original questionnaire. This is due to the fact that the third domain related to activity limitations was taken off in several versions, because its reproducibility was deemed too low. We chose not to change the initial questionnaire by keeping the 23 items in order to be consistent in comparing our statistical results with those of the original questionnaire.
2.3
Patient cohort and validation procedure
The prospective validation was conducted on patients with RA who filled out the FFI-F questionnaire. These patients came from the Physical Medicine and Rehabilitation (PM&R) and rheumatology consultations as well as rheumatology hospitalization. Patients had validated RA according to the American College of Rheumatology (ACR) criteria with or without foot affections and were able to understand and read French. The number of patients to be included was set to a minimum of 50, following the recommendations published by Terween et al. and in accordance with our recruitment abilities. Furthermore, the following data were collected: foot-related history and recent disease activity score (DAS) 28-C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR). For each patient, the maximum walking perimeter was collected. During the consultation, the time needed to walk 10 m and 200 m was recorded. Each foot was examined: collecting deformations, painful joints, range of motion, and testing of ankle and foot muscles.
In order to evaluate the external validity of the questionnaire for each of the successive domains, each patient, aside from the FFI-F, also filled out a VAS for the pain on the day of the consultation and the previous week, the Health Assessment Questionnaire (HAQ) and the main foot disability using the McMaster Toronto Arthritis (MACTAR) questionnaire .
The latter is also used to compensate for the limited evaluation of activity limitation in the third subscale of the FFI-F. This tool was initially validated and used to assess RA-related activity limitations. In our case, the question asked was: which is the main disability related to your rheumatoid feet?
The retest was performed at D15.
2.4
Statistical considerations
In addition to the usual descriptive statistical analyses, the following psychometric properties of the scale were explored:
- •
acceptability: data quality was deemed acceptable if less than 5% of data were missing. The range (minimum and maximum), mean (and associated standard deviation SD) and median, floor and ceiling thresholds (for both, the maximum accepted as 15%), and asymmetry in scores’ distribution (skewness and kurtosis measures, limits: from -1 to +1) were analyzed;
- •
internal consistency was evaluated with the Cronbach α coefficient (accepted minimal value: 0.70), the inter-item correlation coefficient (≥ 0.30) and the overlap (correlation between an item and its dimension, ≥ 0.30) (data not shown here). Internal consistency was also determined by the correlation between the domains making up the scale (standard, 0.30 to 0.70) . Construct validity of the FFI-F was explored using a principal component analysis (PCA). A factorial analysis (principal component analysis and varimax rotation) was conducted in order to determine the multi-dimension structure of the scale. PCA consists in replacing a family of variables by new variables with maximum variation, not correlated two by two and which are linear combinations of the original variables. These new variables, called principal. These new variables, called principal components, define factorial planes serving as a base for a graph representation of the initial variables. Thus, it is an approach designed to synthesize the data to study and visualize the correlations between variables (in this case FFI items) in order to explore the links between items and study their potential redundancy. The final number of factors selected, the part of data to be kept and the screen plot of eigenvalues were determined according to the eigenvalue-one criterion (Kaiser criterion);
- •
reproducibility: the intraclass correlation coefficient (random-effects model ICC) and the Lin’s Concordance Correlation Coefficient (CCC) were computed to determine the test-retest reliability. ICC and CCC values ≥ 0.70 were deemed satisfactory;
- •
regarding external consistency, relationships between the questionnaire score and the other measures (HAQ, MACTAR and VAS) were evaluated via the correlation coefficient (Pearson’s or Spearman’s according to the distribution of the parameters studied, P > 0.50);
- •
accuracy: for each domain, the standard error of the mean (SEM) was computed as such SEM = SD × √ (1-ICC test-retest ). It is admitted that good accuracy is equivalent to SEM ≤ 1/2 (SD). Furthermore, the valued associated to the SDD (smallest detectable difference) for each domain was calculated from the reproducibility study allowing to evidence, for the 3 subscales of the FFI, an estimation of the variability of the measure and thus of the error;
- •
following the exhaustive analysis of the published studies , it seems that no method, related to the sensitivity of a measure, has been validated in the scientific world. In this study, the responsiveness to change was evaluated by paired samples’ tests (Student’s t -test or Wilcoxon signed-rank test, if the conditions of the t -test were not respected) in order to study the evolution of the parameters associated to the HAG, and VAS (day and week) and the FFI domains on the study population.
In this study, the responsiveness to change was evaluated by paired samples’ tests (Student’s t -test or Wilcoxon signed-rank test, if the conditions of the t -test were not respected) in order to study the evolution of the parameters associated to the HAG, and VAS (day and week) and the FFI domains on the study population.
2.5
Ethics
The protocol, the information sheet as well as the case report form were submitted to the Ethics Committee of the Clinical Investigation Centers of the Inner region Rhône Alpes Auvergne. The Ethics Committee gave its approval on 12/15/2011. A signed written consent form was collected from patients before study inclusion. The study was conducted according to good clinical practices and the declaration of Helsinki.
3
Results
3.1
Translation and cultural adaptation
Cultural adaptations were necessary. The main one concerned the evaluation of the gait perimeter. The notion of “blocks” was not used in France to evaluate distance. After research, 200 m was equivalent to one block thus we adapted the translation “four blocks” by using 800m. FFI-F was read by 10 patients who did not find it necessary to change that version.
3.2
Descriptive analysis
Prospective validation was conducted on 53 patients with RA who filled out the FFI-F. The cohort included 39 women and 14 men aged 17 to 78 years. Median disease progression time was 14 years (interquartile range IQR 5–23). Thirty-four patients were unemployed. Only 14 patients had seen a podiatrist before the beginning of the disease. Thirty-four had foot orthosis and 7 had custom-made therapeutic footwear. Two patients had previous foot surgery. The total of the scores obtained for each questionnaire is listed in Table 1 .
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