Abstract
Introduction
The term Musculoskeletal Disorders (MSDs) refers to a large group of inflammatory and degenerative diseases that involve the muscles, ligaments, tendons, joints, inter vertebral disc, peripheral nerves and blood vessels [1, 2]. Work-related Musculoskeletal Disorders (WMSDs) are subcategories of MSDs which are caused or exacerbated by the work environment [2]. WMSDs are widespread in the industrialized and developing countries and are one of the most important problems in disabilities and injuries merging in these countries [1–3].
Some of the important biomechanics and physical risk factors which led to WMSDs are awkward posture for long period of time, static posture [4–6], repeated movements [4, 7], local or whole-body vibration [5, 8], lifting and forceful movements, environmental low temperature, and incompetent brightness (which leads to awkward posture) [5, 6, 8]. Posture and job situations are of the most important risk factors [5, 9–11]. Poor working condition leads to exerting static strength on soft tissues and therefore gathering of the metabolic materials. This state is a reason for damaging start point and serious injuries to the disc [11] and is one of the main causes of the musculoskeletal complaints including pain [12].
Due to the study of MSDs and its relation to job factors, many countries have increased their attention to creating methods which estimate and record the signs of MSDs; for example developing instruments and questionnaires [10]. It is necessary to standardizethe recording and analysis of the MSDs prepared by these questionnaires. In the case of absence of the standard methods, it is difficult to compare the results of various studies [13]. Methods based on self-administrated questionnaire for gathering the information are reliable, low in price, and valid in regard to discernment [14].
Nordic musculoskeletal questionnaire is one of the most popular questionnaires for evaluating WMSDs [7]. The Specific Nordic questionnaire probes more deeply into analysis of these disorders than general Nordic questionnaire [13]. To date, three validated versions of this questionnaire have been reported in Brazilian [15], Portuguese [12] and Greek [16] populations. However, no studies, to our knowledge, have been reported on the reliability and validity of this questionnaire in Iran. It is distinctly clear to use the instrument in different cultures; not only should the items of the criteria be well-translated but the criterion validity, concept, and cross-cultural adaptations should also be preserved [12]. Translation and cross-cultural adaptation procedures create a version of the original scale in a target language that is conceptually equivalent to the source instrument and psychometrically valid to allow for data pooling and cross-national and cross-cultural comparisons. For this purpose to be achieved, a standardized methodology is required. The process is usually completed by a team of people with different skills.
In our country, Iran, there are many half–mechanized industries in which workers are directed to involve in productivity process. WMSDs (in knee and lumbar areas) in these industries are most common [4, 17]. Therefore, the aim of this study was to translate, cross-culturally adapt, and validate to Persian the SNQ for the assessment of WMSDs in Iranian industrial workers.
Materials and methods
Translation and cross-cultural adaptation
In our study, this process was performed following the guidelines recommended by the International Quality of Life Assessment (IQOLA) project [18] for the specific Nordic questionnaire.
The questionnaire in the source (original) language, English, was forward translated to the target language, Persian, by two independent translators, preferably certified, whose mother language was Persian. The translators were bilingual (fluent in English and Persian). In addition, the two translators were thoroughly proficient in translation of questionnaires but unfamiliar with Nordic questionnaire. This approach generated two translated versions (TL1 and TL2) that contain words and sentences covering both the medical and the usual spoken languages with their cultural nuances.
In this step, a consensus was achieved in a meeting with the investigator of the research team, the two translators from Step 1 and the third translator who was a native Persian speaker with extensive knowledge of the English language. The quality of the forwarded translation was rated in terms of clarity, the use of the same language, concept, and adaptation equivalency. The third translator compared the F-TL1 and F-TL2, to both the TL1 and TL2 in comparison to the source language version of the questionnaire. Any ambiguities and discrepancies were discussed and resolved using a committee approach. Finally, this process generated the preliminary initial translated version of the questionnaire in Persian (F-TL).
In this step, the F-TL was translated back into the source language by an independent native English speaker translator with the same qualifications and characteristics described above in Step 1 who had never seen the original version of the questionnaire. This process resulted in a back-translated version of the questionnaire in its original language (B-TL). This step allowed for clarification of words and sentences used in the translations. Similar to step 2, a consensus was achieved in a meeting with all 3 translators and the investigator of the research team, and ambiguities and discrepancies were solved.
In this step, the pilot testing of the Persian-version was performed on 10 Persian language participants who suffered from the MSDs to evaluate the instructions, response formats, and the items of the questionnaire for clarity. This step was used to further support the conceptual, semantic, and content equivalency of the translated questionnaire and to further improve the structure of sentences used in the instructions and items of the pre-final version of the questionnaire to be easily understood by the target population prior to psychometric testing. At the end of this step, none of the items was omitted [18].
Subjects
During a one-year period, a convenient sample of 122 native Persian speaking industrial workers who had at least the basic literacy and 2 years of job tenure within the ages of 20 to 68 years old with knee or back MSDs in the last one year were recruited. All of them worked in operating parts of the National Iranian Oil and Gas Company in Ahvaz, Iran. In this study, subjects over 61 years old, whose lumbar and knee problems maybe the result of the effect of age and not be directly associated with work-related injuries, have been excluded.
In the first session, all subjects completed the basic information form for details of demographic and clinical characteristics (Table 1). Subjects who suffered from lumbar MSDs (n = 62) completed the lumbar specific Nordic questionnaire (LSNQ) and the ones who suffered from knee MSDs (n = 60) completed the knee specific Nordic questionnaire (KSNQ). To evaluate the construct validity of KSNQ, subjects completed the Knee injury and Osteoarthritis Outcome Score(KOOS) questionnaire and for evaluating the construct validity of LSNQ, they completed the Oswestry Disability Index (ODI). The LSNQ and KSNQ were re-administrated to a random sample of 60 subjects, seven days after the first session of the evaluation of test-retest reliability.
All subjects signed an informed consent form approved by the Ethics Committee at Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran.
Instruments
One of the most popular questionnaires in relation to WMSDs is Nordic questionnaire. This questionnaire which was designed in 1987 by Kuorinka et al., is formed of two different parts, specific and general. The general part records the signs of disorders in nine areas of the body (neck, shoulders, upper back, lower back, hands/ wrists, thighs, knees, foot/ankles) in the last 12 months [13]. This questionnaire is also able to recognize the periodic prevalence of the musculoskeletal disorders and the relation between the individual work and daily activities [4, 19, 20]. More specifically, it has a deep analysis of these factors and gives information in relation to individual accidents, at work or home environment, physical injuries, period of injuries, and the effects of pain on work and daily activities and recreations, etc. [13].
The KOOS is a knee-specific questionnaire, developed to assess the patients’ opinion about their knee and associated problems. This questionnaire evaluates both short-term and long-term consequences of knee injury. It holds 42 items in 5 separately scored subscales: Pain, other symptoms, function in daily living (ADL), function in sport and recreation (Sport/Rec.), and knee-related quality of life (QOL). All items were scored from zero (no problem) to four (extreme problem). The Persian version of KOOS has been validated for use in Iran [21].
The Oswestry Disability Index (ODI) is an important questionnaire that researchers and disability evaluators use to measure a patient’s permanent functional disability. This questionnaire is a golden standard for low back functional outcomes. It consists of 10 questions: Pain intensity, personal care, lifting, walking, sitting, standing, sleeping, sex life, social life and traveling. For each question, the possible score is 0 to 5 (minimal to maximum disability). The Persian version of ODI has been validated for use in Iran [22].
Analysis
Descriptive techniques were used to analyze and characterize the subjects. The test-retest reliability was assessed with the Kappa agreement correlation coefficient. Internal consistency was assessed with the Cronbach’s alpha. To evaluate the construct validity between SNQ and KOOS/ODI, Pearson correlation coefficient was computed. All the statistical analysis was done by SPSS 15.0.
Assessment of the psychometric properties of the questionnaire
Validity
In this study, because of the absence of an ultimate standard for the concept of musculoskeletal disorder, validity was reported in terms of construct validity. Construct validity is a type of validity which shows the ability of an instrument to reflect the construct [23]. Because of the normal distribution of data, the Pearson correlation coefficient was used to assess the association between the Persian KSNQ and KOOS. Also the Pearson correlation coefficient was used to assess the association between the Persian LSNQ an ODI. The Pearson correlation coefficient range is from +1 to –1 in which the scores between 0.5 and 1 indicate high correlation, 0.3 to 0.5 indicate medium correlation, and 0.1 to 0.3 indicate low correlation. It was hypothesized a priori that the correlation between the Persian KSNQ and the KOOS (Pain and QOL subscales) should be higher than the correlation between Persian KSNQ and other subscales of KOOS. Regarding construct validity with ODI, it was hypothesized a priori that the correlation between Persian LSNQ and ODI would be high.
Reliability
Reliability is the ability of an instrument to measure something the same way twice [24]. In the present study, reliability was assessed through test-retest reliability and internal consistency. The test-retest reliability is the ability of an instrument to produce similar results on repeated administration when no real change in health status has occurred within this period [25].
As questionnaire’s variables were nominal, in this study, we calculated test-retest reliability using the Kappa correlation coefficient. Values of kappa greater than 0.75 are considered excellent, values between 0.4–0.75 are fair to good, and values of less than 0.4 represent poor agreement beyond chance alone [25]. In this study, the test-retest procedure was assessed by a 7-day time interval because too short a period might allow subjects to recall their earlier responses and too long a period might allow changes in the symptoms during the time interval [17].
Internal consistency is a measure based on the correlation between different items on the same test. It measures whether several items that propose to measure the same general construct produce similar scores [23]. In this study, we used Cronbach’s alpha coefficient to evaluate internal consistency of the KSNQ and LSNQ. The Cronbach’s alpha coefficient level ≥0.70 was considered acceptable [19].
Results
Cross-cultural adaptation process
In terms of cultural and linguistic appropriateness for Iranian industrial workers, the results showed that no major modifications were made by the translators. In a pilot study, no item was found problematic by the subjects. Table 1 shows the demographic and personal characteristics of the general group participating in this study.
Validity
As shown in Table 2, there was significant positive correlation between KSNQ and KOOS pain (r = 0.71, p < 0.05) and the KSNQ and KOOS QOL (r = 0.72, p < 0.05).
The results of Pearson correlation demonstrated the existence of high correlation between LSNQ and ODI (r = 0.77, p < 0.05).
Reliability
The KSNQ test-retest reliability was assessed using the kappa agreement correlation coefficient with an internal of 1 week. Table 3 showed the kappa agreement correlation coefficient (values are between 0.83 and 1).
According to Table 4, LSNQ test-retest reliability showed values between (0.63 –1).
For some variables, it was not possible to compute the test because all the individuals gave the same answer for the two applications of the questionnaire.
The internal consistency of the KSNQ and LSNQ was assessed using the Cronbach’s alpha coefficient, which showed a correlation coefficient of 0.67.
Discussion
Because WMSDs represent one of the most important public health problems, researchers have developed instruments and questionnaires to evaluate the functional capability, location and severity of pain, quality of life and social aspects of patients with such symptoms [17]. One of the most practical questionnaires in the study of work-related musculoskeletal disorders is the Nordic questionnaire, designed for the assessment of musculoskeletal disorders in various jobs [17, 18]. But there is very little information regarding psychometric properties of this questionnaire. Because the English version of this questionnaire is not usable in populations with other languages (such as Persian–speakers), this study concentrated on the cross-cultural adaptation and validation of the SNQ.
With regard to construct validity, the KSNQ had higher correlation with those subscales of KOOS that are supposed to measure similar concepts (i.e. Pain and QOL) than those subscales of KOOS that measure dissimilar concepts (i.e. Symptom and Sport/Rec). This may imply that patients with high level of MSDs in knee region would probably have high scores in Pain and QOL. These results suggest that the KSNQ and KOOS assess the similar concepts.
In the study of construct validity of LSNQ, there was an acceptable positive correlation between LSNQ and ODI (r = 0.77, P < 0.001). This correlation may reflect that these two questionnaires assess the similar concepts. As a result, those patients with higher scores in the LSNQ also had high scores in the ODI. These results were predictable because the ODI is a lumbar specific questionnaire and the LSNQ questions are about the pain of back and decrease of patients’ activities because of the lumbar disorders. Similar findings were reported for the Portuguese version. These findings showed that correlation between back region of General Nordic questionnaire and ODI was higher than the correlations between other regions of General Nordic questionnaire and ODI [12].
The results of the test-retest reliability showed an excellent level of reliability as per the high values of correlation obtained in the majority of variables (Table 3 and Table 4). These results are in agreement with the original version of Nordic questionnaire in which percentage of disagreeing answers were measured (0 to 4 percentage disagreement responses) [13]. Good test-retest reliability of this questionnaire shows the capability of this questionnaire for the assessment of musculoskeletal disorders in repeated measurements over time. These results are well fit with the results of Portuguese version (Kappa = 0.67–1) [12] and Brazilian version (Kappa = 0.64–1) [15].
High internal consistency in Persian version of the Nordic questionnaire demonstrates the relation among all questions in this questionnaire. This represents that all the items of the Persian version of the questionnaire are in relation to each other and they measure a similar construct. Since internal consistency had not been assessed in the other versions of Nordic questionnaire, we have not chance to compare the results with them.
In this research there is a limitation. The responsiveness of the Persian specific Nordic questionnaire was not assessed in our study. Thus, we recommend sensitivity measurement of this questionnaire for future studies.
Conclusion
The major conclusion of this study is that the Persian version of specific Nordic questionnaire is a valid and reliable questionnaire for assessing musculoskeletal disorders in Iranian industrial workers.
Appendix 1
Lumbar Specific Nordic Questionnaire (LSNQ)
Footnotes
Acknowledgments
This study is part of M.Sc thesis of Mrs. Namnik. Special thanks to Ahvaz Jundishapur University of Medical Sciences for the financial support (Master thesis grant no: PHT-9103).