Neck and shoulder pain : Prevalence, incidence and risk factors The IKCo cohort study
Abstract: p>This thesis presents the results of the prevalence and the incidence of neck/shoulder pain (NSP) and its risk factors in an industrial population based cohort study. The project was completed between 2003 and 2007 in Iran Khodro Car Manufacturing Company (IKCo), the largest car company in Iran and the Middle East. At the beginning of the study, the company employed more than 18,000 people. The four papers are the results of a project that began with a baseline survey of self-reported NSP prevalence and risk factors (Study I) and continued with a one-year and a four-year follow up for sick leave cases due to NSP (Studies II and III). In addition, a Persian-language version of a well-known questionnaire on musculoskeletal disorders and risk factors (the MUSIC- Norrtälje questionnaire) was validated during the project (Study IV). Study I: The study population comprises all full-time employees of the company (n=18,031). The measurement tool was the Nordic Questionnaire. A total of 14,384 (79.8%) of all employees completed the questionnaire. Depending on the questions used to measure neck and shoulder symptoms, the results show that the prevalence varied widely (from 20.5% to 3.9%). In the multiple logistic regression model, limited to employees with at least one year of work experience, the indicators of risks that remained for disabling pain of the neck/shoulder for males were: duration of employment, high visual demands, repetitive work, sitting position at work, awkward working position, no regular exercise, monotonous work, lack of an encouraging organizational culture and anxiety concerning change. In females repetitive work, sitting position at work and no support if there is trouble at work were the only factors that remained. The results show similarities between prevalence and risk factors for NSP between industries in middleincome countries and former studies, although a young population of workers and job security can affect the results, especially for disabling pain. Studies II and III: The study population comprises all participants in Study I. One- year incidence of sick leave due to NSP was extremely low (0.1%). This incidence occurred only in unskilled and office workers. Results indicate that although the prevalence of NSP and LBP was similar in the baseline study, a small number of NSP cases were detected, compared to low back pain during the one-year follow-up. The study shows that a simultaneous investigation of prevalence, incidence and recurrence could be a good way to better understand the natural pattern of NSP. In Study III, all the population was followed for four years. The four-year incidence was also very low (0.8%), and only 98 cases of all employees (n=12,184) had one episode of sick leave. Having the same prevalence for NSP in baseline compared to other studies, but a low number of cases based on sick leave and low recurrence, suggests the hypothesis that perhaps most workers continue to work regardless of pain, although the population of young workers, insurance systems, health behaviour and job insecurity are other factors that may affect the results. In the final regression model, the remaining factors for potential physical risk were repetitive work and sitting positions at work; in the case of psychosocial factors, unattractive work was the only significant remaining factor. These results indicate that risk factors for sick leave were different from risk factors for self-reported NSP prevalence in Study I. Study IV: For a better understanding of NSP at work, repeated measurements with a more elaborate questionnaire are needed. The MUSIC-Norrtälje Questionnaire was chosen and tested for future studies. In the first step of the validity and reliability testing of the questionnaire, two expert panel groups were established in Iran and Sweden. The Focus Group Discussion (FGD) method was used to detect questionnaire face and content validity. To detect questionnaire reliability, we used the test-retest method. Except for two items, all other questions that respondents had problems with in the focus group (20 of 297), had unclear translations; the ambiguity was related to the stem of the questions and the predicted answers were clear for the participants. In the test-retest study, the reliability coefficient was relatively high in most items (only 5 items out of 297 had an ICC or kappa below 0.7). The final results of study indicate that the Persian-language version of the MUSIC Questionnaire is a reliable and valid instrument. Most studies of NSP are cross-sectional and related to high-income and industrialized countries. There is little information on NSP in low-/middle-income countries. The results of this research into NSP from different aspects (self-reported prevalence of NSP and risk factors, sick leave due to NSP and risk factors and comparison of NSP to LBP) in the same population can help to increase our knowledge in relation to NSP.
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