6.1 WMSDs accounted for the largest part of occupational diseases
In Taiwan, the ODIS from 2008/01/01 to 2011/12/31 had 4,781 reported cases, and WMSDs accounted for 46.8% (2,239 cases). Moreover, the WMSDs accounted for 87% of the compensation by Taiwan Labor Insurance in average from this period. Also, WMSDs constitute the most frequent diagnoses underlying sickness absence and disability pensions most Western countries [45]. Musculoskeletal problems are common amongst the general and working population and can result in serious social and economic impacts on individuals and communities [46, 47]. Therefore, the WMSDs are worth of further research and discussion.
In this study, we emphasized on CTS and HIVD. However, there were Other WMSDs should be of concern. The limitations of available diagnostic technologies for WMSDs have been discussed by others [48, 49]. The lack of standardized case definitions in part reflects the constraints of the diagnostic categories relative to the wide variety of symptoms and signs reported by affected workers. Conditions with well-defined identifiable pathology such as CTS and spinal disc herniation, account for only a small proportion of all WMSD morbidity [50].
6.2 The high risk industrial categories suffering from WMSDs
We concluded the top five risk industries of WMSDs in this study. Male who worked in the division Wood And Bamboo Products Manufacturing (120.9 cases per 106 population per year), Sand, Stone And Clay Quarrying (91.9 cases per 106 population per year), Postal And Courier Services (58.5 cases per 106 population per year), Specialized Design Services (57.2 cases per 106 population per year) and Electricity And Gas Supply (52.4 cases per 106 population per year) had higher risk with CTS. As for female, who worked in the division Non-Metallic Mineral Products Manufacturing (171.4 cases per 106 population per year), Buildings Construction (157.0 cases per 106 population per year), Residential Care Services (156.1 cases per 106 population per year), Warehousing And Storage (153.2 cases per 106 population per year) and Wood And Bamboo Products Manufacturing (150.2 cases per 106 population per year) had higher risk with CTS. While male who worked in the division Warehousing And Storage (213.4 cases per 106 population per year), Land Transportation (114.9 cases per 106 population per year), Electricity And Gas Supply (114.2 cases per 106 population per year), Air Transportation (95.2 cases per 106 population per year) and Wood And Bamboo Products Manufacturing (94.42 cases per 106 population per year) had higher risk with HIVD. As for female, there were the division Residential Care Services (114.5
cases per 106 population per year), Warehousing And Storage (36.2 cases per 106 population per year), Accommodation Services (26.3 cases per 106 population per year), Wood And Bamboo Products Manufacturing (25.2 cases per 106 population per year) and Buildings Construction (16.9 cases per 106 population per year) which had higher risk with HIVD.
To our best knowledge, this is the first study to emphasize the WMSDs on the job divisions by The Standard Industrial Classification (SIC). There were also some studies which focused on occupations and WMSDs. In a Danish study which looked at specific occupations or job titles, Jensen et al. [51] conducted a 10-year follow-up study of 2,175 long-haul truck drivers, 5,060 other truck drivers and 6,174 bus drivers. Compared with the general working population in Denmark, the standardized hospitalization ratios (SHRs) for being hospitalized for intervertebral disc disorders were increased in long-haul drivers and bus drivers (SHRs 133 and 141, respectively) compared with other types of truck drivers (SHR 109). It was concluded that professional driving was a risk factor for intervertebral disc disease. In our study, the division land transportation also had high risk with HIVD.
6.3 The risk factors of WMSDs
In addition to industry, other environmental factors, such as obesity and smoking,
have been reported to be associated with prevalent LBP, although the quantitative effect of the majority of these has been found to be small [52-55]. However, our study was an ecological design. The information we could obtained was in group level. Also, we could conduct the risk of WMSDs by industries, ergonomic and self-reported symptoms.
In 2001, the NORA MSD team published a national occupational research agenda for musculoskeletal disorders conducted that many risk factors associated with development of musculoskeletal disorders have been identified or suggested.
Biomechanical risk factors include exposures to excessive force, awkward posture, movement, and vibration. These can be characterized in terms of their magnitude and temporal factors, such as frequency, repetition, duty cycle, and duration of exposure.
Psychological and social factors included work organization arrangements (extended work hours, shift work, piecework, machine pacing), lack of training, inadequate conditioning, and cognitive or emotional stress. Personal factors included variables associated with size, strength, age, gender, cultural factors, and history of injury [56].
This article pointed to new possible way for future research in WMSDs and its risk factors.
The figure about Self-reported percentage level of workers having hands or wrists musculoskeletal discomfort or some ergonomic factors showed a trend that the increase
in exposure percentage levels with the increase of SIR in the first to third group levels.
But the trend went down in the final or the largest exposure group. This condition might explain with the “healthy worker effect”. The exposed persons who developed Work-related MSDs may have left employment disproportionately. This problem, which results from actual selection processes in the workplace, leads to an underestimate of the relationship with exposure and thus does not invalidate associations found between MSDs and workplace features [13].
6.4 Secondary self-reported questionnaire
The exposure data was from a secondary self-reported questionnaire. Our study was limited to the secondary data, and the existing questionnaire was also a limitation.
Our study emphasized on exposure factors, but the questionnaire was not designed to evaluate the workplace ergonomic factors and the musculoskeletal symptoms. The questionnaire about these parts did not exactly answer our research questions. There were also other risk factors which might cause WMSDs, including forceful grip, forceful movements of the hands and repetitious flexion and extension of the wrist for CTS [28, 57]. Also, other risk factor, such as frequent bending and twisting might cause HIVD [29]. In another example, the questionnaire about the musculoskeletal discomforts was only asked that if there was any “sore or pain” with the hands or wrist.
To the best of our knowledge, the symptom about CTS was “numbness”, i.e., the questionnaire did not ask the correct question for some situations. Thus, the correlation between SIR of CTS and self-reported hands or wrists discomforts were not as well as HIVD with self-reported back and waist discomforts.
Self-reported symptoms or functional impairments may thus often be more informative than the available physical examination maneuvers [13]. Some individuals with different symptoms, ranged from specific to non-specific, suffer severe pain and disability. Even though their findings do not conform to specific diagnostic entities such as CTS, rotator cuff tendinitis, or de Quervain’s disease. Examination techniques still do not exist that can serve as a ‘‘gold standard’’ for many of the symptoms that are frequently reported in workplace studies [49]. MSDs symptoms are often intermittent and episodic, especially in the early stages. However, even when they do not correspond to defined clinical syndromes, they may be of major public health significance [13].
6.5 Limitation
First of all, the WMSDs cases were collected from the ODIS which might underestimate the actual conditions.
Second, the independent variables were from the National Survey of Recognition of Occupational Safety and Health in employees which limited to define more detailed
conditions. Dependent and independent variables were from two separated data set. The dependent variables were from the ODIS from 2008 to 2011, but the independent variables were from the National Survey of Recognition of Occupational Safety and Health in employees in 2010. There are defects about the time sequence. Because the latency period of HIVD is up to 8 to 10 years, the relationship between HIVD and its risk factors should not be an issue. However, the latency period of CTS is less than the latency period of HIVD. Therefore, the relationship between CTS and its risk factors might not correlate as well as HIVD. Besides, this study was under the assumption that the workplace conditions did not have big change in this few years.
Finally, since the research belongs to ecological design, correlation observed is mainly at group level. Extrapolation of the observed relationship to individual level has to be cautious.