Study and design subjects
The study was divided into two stages. In the first stage, the original English version of the SMFA was translated into Chinese. The second stage was a multi-center study, where the reliability and validity of the translated version was evaluated in a cross-sectional study. Patients with skeletal muscle injury of the upper or lower extremities were enrolled from 4 large hospitals between March and September 2014. Inclusion criteria were: upper or lower extremity skeletal muscle injury, age between 20 and 75, fluency in Chinese, and capacity to self-report. Exclusion criteria for this study were: head trauma, spinal injury or fracture with neurological dysfunction, neuromuscular disease, amputation of a limb, cardiovascular disease with an active episode three months prior to the start of this study, cancer, and serious psychiatric or cognitive disorder. Patients with reading or writing disabilities were also excluded.
The study had been filed by Institutional Ethics Committee of Guangdong Provincial Hospital of Traditional Chinese Medicine obtained Ethics review Exemption. Patients provided informed consent prior to their enrollment into the study. The participants were asked to answer the questionnaires according to their own feelings and opinions about limb function, mental states, and daily activities related to their musculoskeletal disorders. After completion, the questionnaires were collected as soon as possible.
Measurement tools
The measurement tools consisted of a demographic information questionnaire, two QOL ⁄ health status scales (Chinese versions): SMFA, Health Survey Short Form (SF-36), and a region-specific questionnaire (Chinese versions) including the disabilities of the arm, shoulder, and hand questionnaire (DASH), the hip disability and osteoarthritis outcome score (HOOS), the knee injury and osteoarthritis outcome score (KOOS) and the foot function index (FFI), depending on the region of the injury.
The demographic questionnaire gathered socio-demographic information such as age, gender, marital status, height, weight, education level, co-existing chronic diseases, and the clinical type of the musculoskeletal injuries.
The region-specific questionnaires were frequently used for assessment of the local function of the musculoskeletal injuries or disorders, whereas the SF-36 was used to evaluate the convergence validity of the SMFA. The demographic questionnaire was used to evaluate the known-groups comparison of the SMFA.
SMFA
The SMFA questionnaire was developed by Swiontkowski et al.[3], and concerns the functional and lifestyle disabilities caused by musculoskeletal disorders or injuries. It contains 46 items with 2 subscales, the dysfunction index which has 34 items for the assessment of patient functional performance, and the bother index which has 12 items for the assessment of how much the patients are bothered by their functional problems. The dysfunction index is presented in four categories: the daily activities, emotional status, arm/hand function, and mobility. All items are rated on a 5-point scale with responses of “not at all”, “a little”, “a lot”, “very much” and “impossible” scored as 1, 2, 3, 4, and 5, respectively. The scores for the two parts and the four categories are calculated by summing the responses for the individual items and transforming the scores ranging from zero to 100; higher scores indicate poorer function.
SF-36
The SF-36 is a generic health status questionnaire that can be used for the evaluation of disease, health status, economic evaluation of population, as well as assessment of the clinical curative effect of the treatment options [9]. The SF-36 Chinese version has been tested for reliability, validity and applicability [10]. It includes 36 items and provides eight scales: physical function (PF), role-physical (RP), bodily pain (BP), general health (GH), vitality (VT), social functioning (SF), role-emotional (RE), and mental health (MH). The scores are calculated according to the scoring algorithm on the SF-36 user manual. The higher the score, the better was the perceived health level.
Region-specific questionnaires
DASH
DASH is a self-administered outcome questionnaire designed to evaluate physical disability and symptoms in people with musculoskeletal disorders of the upper extremity [11, 12]. Its Chinese version has been tested for psychometric properties and is available at http://www.dash.iwh.on.ca. DASH contains 30 items concerning the patient’s health status during the preceding week, including 21 physical function items, 6 symptom items, and 3 social roles/function items. In addition, DASH contains two four-item optional modules: one for the patient’s ability to perform certain motion and/or to play a musical instrument, and the other module for the patient’s ability to work. We only used the 30-item scale in this study.
HOOS
HOOS is a simple self-administered questionnaire developed to assess patient opinions regarding hip and related problems, from patients with hip disability with or without osteoarthritis. The Chinese version has been validated for use in China [13]. HOOS consists of 40 items divided into five subscales: pain, other symptoms, functions in activities of daily living (ADL), function in sports and recreation, and hip-related quality of life.
KOOS
KOOS is a self-reported joint-specific measure that was developed as an extension of the WOMAC for young and/or active patients with knee osteoarthritis or knee injury [14, 15]. KOOS comprises of 42 items with five subscales: pain, other symptoms, function in ADL, function in sports and recreation, and knee-related quality of life. Its Chinese version has been adapted and tested for the psychometric properties [16].
FFI
FFI was developed in 1991 as a patient-reported instrument to measure the impact of foot problems on function in terms of pain and disability [17]. FFI consists of 23 visual analogue scales divided into three subscales: 9 related to pain, 9 related to difficulties, and 5 related to patient limitation. Its Chinese version has been evaluated and has shown good psychometric properties [18].
Translation process
The process of translation and adaptation into Chinese followed the guidelines recommended by American Academy of Orthopedic Surgeons (AAOS) and the guidelines for cross-cultural adaptation of health-related quality of life measures. Two independent translators with Chinese as their mother tongue (one aware of the concept) translated the American version into Chinese. The two translations were combined into a synthesis and the differences resolved by consensus. Two independent translators with English as their mother tongue then translated this Chinese version of the SMFA back into English. Both translators were blinded to the concepts being investigated and had no medical background. Then, we sent the back translation of SMFA to the original author aiming to test whether it conflicted with the original version. We revised according to the response from the original author, prepared the pre-final version, and tested it on 30 orthopedic outpatients with skeletal muscle injury of the upper or lower extremities before making a few minor adjustments to obtain the final version. The final version of the Chinese SMFA was then used to evaluate its validity and reliability.
Participants
Initially 352 patients were recruited in this study. Out of these, 3 patients were less than 20 years old. Additional 10 patients were excluded because they had missing answers on the SMFA. Finally, the analysis was carried out on a total of 339 patients (96 %). All participants were asked to complete three questionnaires: the SMFA, the SF-36, and a region-specific questionnaire specific to the region of their injury. Of these 339 patients, 76 and 65 patients were asked to complete the DASH and HOOS, respectively, 127 patients filled out the KOOS, and 60 patients filled out the FFI. Other patients with multiple disorders completed the region-specific scales according to their corresponding sites of injury. The flow diagram of the inclusion of respondents is presented in Fig. 1.
Statistical analysis
For each subscale of the SMFA, the floor and ceiling effects were assessed. These floor and ceiling effects were considered to be present if more than 20 % of respondents achieved the lowest or the highest possible scores [19]. The internal consistency was estimated using Cronbach’s α coefficient. A Cronbach’s α value of more than 0.70 was considered as satisfactory. A known-groups comparison was used to test how well the dysfunction index and bother index of the SMFA discriminated between subgroups of the study sample that differed in their health condition, including age, gender, body mass index (BMI), injury location and operation status. Comparisons were performed by t-test or one-way analysis of variance (ANOVA).
The convergence validity of the SMFA was evaluated by assessing the Spearman’s rank correlation coefficients between the SMFA and the SF-36, HOOS, KOOS and FFI, which are the potential measures that assess similar underlying phenomenon as the SMFA. Correlations ranging from 0.25 to 0.50 suggest a fair degree of relationship, those from 0.50 to 0.75 suggest moderate to good relationship, and values greater than 0.75 are considered good to excellent relationships. The construct validity of the SMFA was evaluated by extracting its factor structure using exploratory factor analysis (EFA) with the principal components method. Promax was performed according to the supposed correlations between the factors.
If patients had fewer than 50 % of the answers missing in any category of the dysfunction index, the mean value of that category for the missing item(s) was substituted. When one item of the SMFA from the 35 to 46 items was left unanswered, the questionnaire was excluded from the analysis. Patients who did not complete the demographic questionnaire were excluded.
All statistical analysis was performed using the software SPSS 17.0 for Windows. (SPSS Inc., Chicago, IL, USA).
Qualitative characteristics
The translation back into English revealed some minor discrepancies that were considered to be related to cultural rather than language differences. The original author approved of the back translation except the question 33 option “You feel emotionally powerless” because the original was “disabled”, which tends to be more about physical function; we revised that item. Furthermore, when testing the revision, many patients reported difficulties understanding the items on the SMFA questionnaire that were specific to American lifestyles. For example, questions that included “Mowing the lawn”, an activity not frequently performed in Chinese families as most families do not have a lawn, needed slight revision. We replaced this activity with the term "moving furniture or heavy items". Additionally, a bathtub is not widely used in China. This limitation was addressed by replacing bathtub with the term “shower” in the Chinese version of the questionnaire.