2.1 Translation and cross-cultural adaptation
The original version of the IdFAI questionnaire was translated according to the principles reported in previous studies [6,23]. In brief, the translation included the following several steps. (1) For the forward translation step, two native Chinese speakers highly familiar with the English language (one translator was an orthopedist in the hospital, while the other was a professional translator without a medical background) were asked to translate the IdFAI questionnaire into a simplified Chinese version. (2) For the discussion I step, all the investigators discussed the two independently translated versions, and finally, the two versions were merged into a preliminary version of the SC-IdFAI questionnaire. (3) For the backward translation step, two native English speakers independently translated the preliminary version of the SC-IdFAI questionnaire into the English language. (4) For the discussion II step, the versions were discussed by the investigators again to address any discrepancies, ambiguities, or other language expression issues in the preliminary version of the SC-IdFAI questionnaire. Then, the prefinal version of the SC-IdFAI questionnaire was obtained. (5) In the pretesting step, twenty patients with CAI were asked to complete the prefinal version of the SC-IdFAI questionnaire. The questions asked by the 20 patients during the completion of the scale were also recorded. If a CAI patient had difficulty understanding a certain item, then the item was specifically modified in the third discussion. After the above standard steps were completed, the final version of the SC-IdFAI questionnaire was obtained.
2.2 Patients and data acquisition
The consecutive native Chinese-speaking patients with CAI who were treated in our hospital (the General Hospital of Western Theater Command) between February 2016 and March 2018 were consecutively recruited. The inclusion criteria were as follows: (1) patients aged >18 years who were capable of independently providing consent; (2) Chinese native speakers who could independently read and complete the questionnaire; and (3) those with at least two cases of severe ankle sprains, feelings of ankle instability that have been reported on multiple occasions, chronic pain in the ankle and/or “giving way” in sports activities or daily life. The exclusion criteria were as follows: 1) previous surgeries in musculoskeletal structures or fractures in the lower extremities, 2) acute injuries to the musculoskeletal structures of the other lower limb joints in the previous three months, and (3) other chronic inflammatory diseases in the lower limbs that might affect ankle function. Patients who met all the eligibility criteria and volunteered to participate were included in the study. In addition, the number of included participants also met the sample size criteria of PROMs, as recommended by Terwee et al. . In brief, the sample size for internal consistency analysis should be ≥100, and the sample sizes for floor or ceiling effect, reliability, and validity analyses should be ≥50. All the participants carefully read and signed the informed consent form. The study was approved by the Ethics Committee of the General Hospital of Western Theater Command.
On the first day of admission to the hospital, the patients were required to provide demographic information and, in a quiet meeting room, to complete 3 scales independently, including the SF-36, SC-IdFAI and FAAM. One day before the beginning of physiotherapy, that is, one week after the questionnaire was completed for the first time, the patients completed the SC-IdFAI for the second time so that the test-retest reliability of the scale could be assessed. Patients undergoing related treatment in the previous week were excluded. Finally, the patients who volunteered to undergo an 8-week physiotherapy program in the hospital were asked to complete the SC-IdFAI questionnaire for the third time so that the responsiveness could be assessed.
The IdFAI is a scale specifically designed to assess patients with CAI. It was developed by Matthew Donahue et al. based on the CAIT and AII . It has the advantages of both the CAIT and AII scales and thus has the following specific advantages: (1) the IdFAI questionnaire contains 10 questions, which are easily understood and can be completed by patients in a very short time; and (2) the questionnaire has very high accuracy in assessing patients. The IdFAI questionnaire alone can yield higher accuracy than the CAIT or AII . The IdFAI questionnaire consists of the following three subscales: (1) factor 1, concerning the patient’s history of ankle sprains (items 5, 6, 7, and 10); factor 2, concerning the presence and severity of ankle instability (items 1, 2, 3, and 4); and factor 3, concerning the patient’s functional performance in daily living and other physical activities (items 8 and 9). Because the first question is a nonchoice question, the answer is not included in the total score, while the scores of the other nine questions are summed to obtain the final score. The total score ranges from 0 to 37, with higher scores indicating poorer ankle function. Generally, if the total score is >10, the patient is considered to have CAI .
The FAAM is a region-specific scale designed specifically for the assessment of foot and ankle functions . The FAAM contains two subscales, namely, the activities of daily living (ADL) and sports subscales. The ADL subscale contains 21 questions, while the sports subscale contains 8 questions. The score for each question ranges from 0 to 4. Thus, the ranges of the total scores of the ADL subscale and sport subscale are 0–84 and 0–32, respectively, with higher scores indicating better functions. Although the FAAM is a region-specific rather than a disease-specific scale, previous studies have demonstrated that the FAAM has high validity when used in patients with CAI . The SF-36 is a versatile scale for assessing quality of life, and it contains 35 questions in 8 subscales. The first four subscales can be categorized as “physical subscales,” which mainly assess the physiological functions of patients, while the remaining four subscales can be categorized as “mental subscales,” as they mainly assess the mental status of patients. Each subscale of the SF-36 scale has a specific scoring method, while the final score is converted into a centesimal score. A higher score on the SF-36 scale indicates a better mental status and physical function . The abovementioned two scales have been translated into Chinese, and it has been proven that these versions have excellent responsiveness, reliability and validity [28,29].
2.4 Psychometric assessments and statistical analysis
The validity, reliability, and responsiveness of the SC-IdFAI questionnaire were assessed to evaluate whether the questionnaire can be applied in native Chinese-speaking patients with CAI.
The reliability tests of SC-IdFAI chiefly address measurement error, internal consistency and test-retest reliability. The degree of internal consistency is described to be the degree of interaction among scale questions , which is chiefly assessed by the Cronbach's α value of the scale. When α > 0.9, 0.8, and 0.7, the scale has acceptable, good, and excellent internal consistency . However, high Cronbach’s α values do not always indicate good validity. For instance, Cronbach’s α values >0.95 generally indicate question redundancy in the scale . In addition, the Cronbach’s α value was also calculated after the questions in the SC-IdFAI questionnaire were omitted one by one to assess the influence of each question on the α value, which is also a method used to assess internal consistency [24,32]. To assess the test–retest reliability of the SC-IdFAI questionnaire, the patients were asked to answer the questions twice, with an interval of 1 week, and the answers were compared. The intraclass correlation coefficient (ICC), which was calculated for two-way analysis of the variance with a random effects model, was the assessment indicator used for the test-retest reliability, and an ICC of > 0.9 and 0.8 suggested that the scale had excellent and good reliability, respectively . Measurement errors include random and systematic errors, not the patient score, and is not indicative of the real changes in the scale to be tested . The error was calculated in accordance with the formula and analyzed using the standard error of measurement (SEM): SD × √ (1 – ICC). In the first evaluation, the standard deviation of all patients was expressed as SD . The minimal detectable change (MDC) reflected the minimal individual change in the score that could be interpreted as a real change. It was calculated as SEM × 1.96 × √2 at an individual level and SEM × 1.96 ×√2/√n at the group level . To determine the systematic errors between the first two surveys, we generated the Bland-Altman diagram .
We can evaluate the validity of the CAIT-C by its construct validity and content validity. The relevance and comprehensiveness of the questions were evaluated to assess content validity . The three indexes of the question comprehensiveness evaluation are patients’ feedback, the response rate, and ceiling/floor effects. Assuming that the ceiling/floor effects are lower than 15%, the response rate of the scale is more than 95%, and the patients who completed the questionnaire had no difficulty in understanding the questions, then the scale being assess has excellent comprehensiveness [24,38]. In addition, we invited one rehabilitation specialist as well as two orthopedic specialists to help determine whether the items were relevant for the construct to be measured and for patients with CAI . Since a gold standard for the assessment of SC-IdFAI criterion validity does not exist, the hypothesis test was used to assess the construct validity of SC-IdFAI. Construct validity is the extent to which the scores on a scale are consistent with hypotheses based on the assumption that the scale validly measures a specific construct . In this study, FAAM and SF-36 were selected as the control scales for SC-IdFAI. Most of the questions included in the SC-IdFAI questionnaire addressed the physical conditions but not mental conditions of patients with CAI. Therefore, it was hypothesized that the results of the SC-IdFAI questionnaire highly correlated with those of the physical subscales of the SF-36 (physical functioning, role physical, bodily pain, and general health), as well as those of the FAAM, but poorly correlated with the results of the metal subscales of the SF-36 (vitality, social functioning, role emotional, and mental health). In addition, the FAAM is a region-specific scale specifically designed for patients with ankle injuries, while the SF-36 is a generic scale with wide applicability. Therefore, although the FAAM is not a disease-specific scale that was designed specifically for patients with CAI, the contents of the FAAM should be more similar to those of the IdFAI than to those of the SF-36. Thus, it was further hypothesized that the correlation between the SC-IdFAI and FAAM should be stronger than those with the subscales of the SF-36. More details on the hypotheses for the scales are shown in Table 4. Based on these hypotheses, the Spearman’s correlation coefficients (rs) of the SC-IdFAI with the SF-36 and FAAM were analyzed using the first responses from the patients for the scales. Then, the construct validity of the SC-IdFAI questionnaire was assessed on the basis of the consistency between the data and the hypotheses. Good construct validity was considered to exist when at least 75% (30/40 or more) of the predetermined a priori hypotheses were met . The correlations were determined to be excellent (rs = 0.8-1.0), good (rs = 0.6-0.8), moderate (rs = 0.4-0.6), fair (rs = 0.2-0.4) or poor (rs = 0-0.2) .
Responsiveness is a metric used to determine the capability of a parameter to be measured over time . In this study, the responsiveness of the SC-IdFAI was evaluated by comparing the scale results before (the first time the questionnaire was completed) and 9 weeks after physiotherapeutics were administered (the third time the questionnaire was completed). The physical therapy programs included strength training (isokinetic muscle strength training and home strength training) [40,41], balance training (star excursion balance training; SEBT) , and proprioceptive training (multitask training) .
The two indicators of responsiveness are the standardized response mean (SRM) and effect size (ES). We calculated the SRM by dividing the average change between each time point by the SD of this change. The ES was calculated as the average change in the treatment outcome within the 9 weeks before and after the physiotherapeutics divided by the SD of the SC-IdFAI score before treatment . When the SRM and ES values exceeded 0.80, the effect size was considered large; when the values were between 0.51 and 0.80, the effect size was considered medium; and when the values were less than 0.50, the effect size was considered small .
Statistical Package for the Social Sciences, version 20.0 (SPSS, Chicago, IL, USA), was used to perform the statistical analyses. The mean value is expressed with the standard deviation (SD). The ICC values are reported with the 95%confidence intervals (CIs). A P value less than or equal to 0.05 is considered statistically significant.