Whole-body vibration and musculoskeletal diseases in professional truck drivers

Background: Most occupational diseases do not fit the paradigm of medical interpretation of the health-disease process based on linear causality, in which it would be possible to find a single cause for each type of disease. Objectives: to conduct a systematic review in order to investigate the association between wholebody vibration (WBV) and musculoskeletal disorders (MSD) in professional truck drivers (PTD). Methods: The scientific databases of PubMed, Cochrane, Lilacs and Scielo were used to collect articles published from 2000 until the present time. Two independent reviewers adopted inclusion and quality criteria to evaluate the selected articles. Results: From adopted inclusion and quality criteria, nine articles were chosen to identify the association between MSD and WBV in PTD. The results showed that MSD seems to be closely associated to exposure to WBV in these workers, mainly due to high prevalence and symptoms of low back pain. Two cohort studies showed exposure to WBV as risk for MSD. Only one, with case-control design, did not show WBV as a * GFSM: PhD, e-mail: geraldomoraes@unifei.edu.br RFS: PhD, e-mail: sampaioufmg@gmail.com LFS: PhD, e-mail: Llfelipe.unifei@gmail.com MAPS: MSc, e-mail: nanapsouza@yahoo.com.br


Background
The labor world has undergone major changes in its organization and dynamics, creating new challenges and preserving unresolved problems on the health-labor relationship (1,2).
Musculoskeletal disorders (MSD) are among those occupational diseases that currently demand attention in the health and labor area.These MSD have been highlighted in the agenda for discussion due to their high prevalence in all countries, regardless of the degree of industrialization (3)(4)(5).The MSD are followed by suffering and disability for workers and their families, and also result in social and financial losses, resulting from the decrease of productivity and deprivation of earnings, volume of granted benefits, medical expenses and integration of the individual in the production context (6,7).
Epidemiological studies have shown that back pain accounts for approximately 50% of all MSD that cause temporary or permanent disability in workers in agricultural and industrial areas, and in service production.In addition, approximately 80% of the population have had, or will present with, an episode of pain back during his/her lifetime (7)(8)(9).Multiple risk factors are associated with the development of MSD in different sectors and occupations (2)(3)(4)(5)8).Individuals who perform work activities with a high demand of physical, cognitive and psychological features -as portrayed in the case of professional truck drivers (PTD) -are more susceptible to triggers of MSD.Physical demands, awkward postures and repetitive operations, as well as psychosocial loads, showed strong association with MSD in the lower back and even with involvement of the upper limbs, in some cases (9)(10)(11).In addition, personal attributes and characteristics of the productive context have also been identified as factors related to worsening of MSD, and therefore should be investigated in order to identify the correct ratio of its occurrence in PTD in their workplace (6,7,12,13).
In recent years, studies conducted in the cargo transport sector have analyzed the exposure to whole-body vibration (WBV) and MSD occurrence, especially in the onset of low back pain in PTD and other machinery and vehicle operators, with direct harm to the development of these professionals' activities (11,14).The impact of vibration on physical and technical capacity of the drivers may be related to the exposure time, intensity and frequency, as well as the operational and environmental conditions in which the activity is developed (11,15).Evidence suggests that WBV exposure time triggers micro and macro impacts in the spine, and presents a clear relationship between the driver's position and the impact of transmission to important areas in the musculoskeletal system that directly compromises the absorption and dissipation of forces (11, 16 -18).
Despite advances in research in this area, there is no consensus when it comes to evidence that predicts the health risk to PTD on micro and macro impacts due to WBV exposure associated with the operation of cargo transport vehicles.In the same way, measures capable of minimizing the harmful effects of the MSD on the health of drivers remain uncertain.Given the above, this study aimed to conduct a systematic review to identify evidence that explores the significance of WBV exposure in the generation of MSD in PTD.We also aimed to summarize the evidence found regarding the theme, by assessing the methodological quality of these studies in order to clarify the involved factors in this relationship and to assist with proposals for prevention and health promotion of these workers.

Methods
A systematic review was conducted based on surveys of studies published between 2000 and 2014, in the databases of PubMed1 , Cochrane2 , LILACS3 e SciELO 4 .This study period is justified due to the fact that the previous two systematic reviews on the subject were published in 1999 and 2000 with literature published from 1986 to 1997, (19) and from 1992 to 1999 (20), respectively.In this study, the last survey was performed in July of 2014.The keywords followed the description of the medical terms in English: 'Vibration' (MeSH), 'Whole Body Vibration', 'Musculoskeletal Disorder', 'Low Back Pain' (MeSH), 'Work' (MeSH), 'Workload' (MeSH), 'Occupational risk', 'Occupational Disease' (MeSH), 'Occupational Health' (MeSH), 'Occupational Accident' (MeSH), 'Occupational Hazard' and 'Truck Drivers'.Also, a search with the same keywords in Portuguese and Spanish was performed.Initially, keywords were crossed by using the Boolean operators "OR" and "AND", and then the active search for articles was performed.
In the present study, we included full-text articles with cross-sectional, case-control and cohort designs, as identified by the search strategy.Reviews and case reports were excluded.The studies should have presented an association between WBV and MSD in PTD.
We excluded studies that described the relationship between WBV and lower back pain in other occupations, and also studies with measurements that were performed in laboratories, studies using animals, experimental studies focused on interventions in the workplace, rehabilitation treatments and professional reintegration.Studies were selected by title, abstract and full text.
The summary of the identified articles after the application of the search strategy was evaluated by two independent examiners according to the following eligibility criteria: i) published in English, Portuguese or Spanish; ii) describe WBV assessment procedures with the use of a validated questionnaire/ scale; iii) consider MSD in PTD as an outcome; and iv) measure of WBV exposure in real work situations.
A standardized list of pre-defined criteria was used for evaluation of internal and external validity Based on this final score, each item was classified as being of high or low quality.High quality studies were considered those in which at least 51% of applicable items were evaluated as positive (23).

Results
The search criteria used in this review initially identified a total of 351 articles.After screening by the titles and abstracts, 283 articles were excluded, as they did not fit the theme addressed.In addition, 31 were discarded due to design (literature review), duplication in two or more databases, or because they did not meet the proposed inclusion criteria.Thus, 37 works were reviewed by two researchers through a complete reading followed by the application of the pre-defined eligibility criteria for the systematization of evidence.The final result of the search and selection phase included nine articles (9,10,11,17,24,25,26,27,28): six cross-sectional, two prospective cohort, and one case-control studies, all of which were classified as high quality by the identification of the association between WBV and MSD in PTD (Figure 1). of the studies.The list was adapted from van der Windt et al. (21) and Hayden, Bombardier and Côté (22) (Table 1).Two independent reviewers applied the criteria, and their results were compared to select the potential articles for inclusion in this review.Discrepancies in the evaluation of the reviewers were discussed collectively to reach a consensus for a final decision about the inclusion or exclusion of the article.
The items of the assessment tool received the following classification: positive (no bias); negative (potential bias); undefined (when the information in the article was insufficient) and, lastly, do not apply.Disagreements between reviewers in certain items were identified and resolved during a consensus meeting.After reading the articles selected, the references cited therein were checked, and those judged relevant were also reviewed.Articles that met the study eligibility criteria were classified as ACCEPTED for this review and a full reading was performed.
For each study, a total quality index was calculated by counting the number of items classified as positive, divided by the total number of applicable study items.Selected articles for full-reading n = 37 Articles included in the review n = 9 Studies excluded based on the eligibility criteria (Table 1) n = 28

Figure 1-Flow diagram of systematic review inclusion criteria
Table 2 presents the results of the methodological quality assessment of the selected studies.
The selected articles showed a population of 2173 PTD [2160 were men (99.4%) and 13 women (0.6%)], and samples that ranged from 14 to 598 participants.All studies defined the participants' occupation as PTD.Two studies compared results with a one-year and a two-year follow-up (11,17).
Table 3 describes, in detail, the features of the articles selected for this systematic review.(To be continued) (To be continued) (To be continued)

Discussion
This study aimed to conduct a literature review and investigate the association between exposure to WBV and MSD.The finding of this systematization of evidence suggests an association between exposure to WBV in PTD in the event of MSD, especially due to the observation of high prevalence of low back pain and symptoms resulting from this condition.
The PTD are exposed to injuries in the cervical and lumbar spine, pressure points and poor circulation in the legs and buttocks, resulting from long periods in the sitting position.Furthermore, they may increase their risk of injury when handling objects, in addition to their usual occupation activities (30).
These professionals have a higher prevalence of low back pain, which presents greater intensity when compared to the other drivers (10).The age of the vehicle, the driver's body mass and other organizational factors appear as significant variables in the negative impact caused by the exposure to the WBV (24).The posture assumed during the driving operation, along with the WBV exposure is another variable that may be identified as associated with back pain (33).
The physiological effects of this condition can be explained by the posture taken by the employee during his/her working hours, associated with the organic-structural conditions of the individual who is subjected to adverse environmental conditions (33).As a result of this issue, one can highlight the capacity ratio of that person to deal and interact with these exposure factors that trigger MSD and manifest themselves in the form of a disease.That person builds this capacity through strategies during his working life.(11,30,33).
According to Dejours (34) the "work organization is defined as the division of labor and of men."The prescription precedes the task execution, and composes a record that meets the need for guidance, bureaucratization and inspection, being a source for both recognition and punishment.The real work is one that happens at the very moment of its execution.Time of weekly exposure to WBV and the distance driven were variables that have been observed and associated with the occurrence of MSD (26).The intensity of pain and the incapacity for work are manifested directly with increasing exposure gradients (17,27).

Final Considerations
In this systematic review study on the importance of WBV exposure and MSD, we identified that organizational factors and operating conditions may directly or indirectly affect WBV exposure, and they must be considered in the analysis of the physical harms associated with PTD work.There are some examples of factors that must be addressed with intervention measures at the level of prevention and health promotion, such as: long journeys and working hours that cause longer exposure times to WBV, body postures assumed while driving the vehicle, the influence of the work organization, the value of the exposure magnitude affected by the age of the vehicle, road conditions and others.This review's findings identified that the included studies presented methodological quality on the subject, which provides solid and sufficient evidence to reduce WBV exposure to the lowest possible in order to prevent the occurrence of MSD, especially low back pain among PTD.The study subject, from an epidemiological point of view, should place more value on prospective studies with more consistency and less on those, which only seek association.
The PTD who has a sedentary lifestyle and finds himself exposed to high levels of WBV associated with the density and intensity of working hours, may increase the damage to his health, once he is at the limit required for systemic functioning (30).Such factors predispose the PTD to health problems such as MSD affecting his overall physical ability, with consequent impairment in the production process and impact on the healthcare system.The consequences of this relationship are highlighted in the individual's removal as a "social being" and in the physical impairments that can lead to mental impairment.
The majority of workers, while reporting MSD, only considered those diseases as a limiting factor for work when they are unable to perform their occupational activities.They use the knowledge acquired with the working practice to put them forward in a situation in which they are exposed to risks, such as in the case of WBV exposure.
Among the studies chosen for review, after the application of the selection criteria, we did not find evidence for the relevance of WBV exposure to health issues except in the case-control study developed by Palmer et al. (28).The authors explain their findings by the conditions of the sample cases in relation to the period of WBV exposure, which was after the occurrence of low back pain; and by the diversity of activities present by the drivers.They suggest that exposure to WBV may be not the main cause of severe back pain; instead, the mental aspects and the perception of general health have a more significant contribution with stronger association with the occurrence of low back pain in the sample.However, two studies of cohort/longitudinal design, developed by Bovenzi (11,17), stressed the importance of WBV exposure in the onset of low back pain.Those studies present a greater power of risk elucidation and less vulnerability to bias.
This systematic review sought to raise current and scientifically proven evidence to assist the development of diagnostic analysis and MSD management for PTD.The quality of the selected studies was verified, as well as the control of the following possible confounding variables to the analyzed outcome: other salient exposure in the labor process, associated with the diversity of the driver's work (weight lifting, prolonged sitting, twisting of trunk, among others).However, there is no consensus in the available literature on the subject, when it comes to the establishment of a dose-response association.

Table 1 -
Standardized checklist of methodological quality of the cross-sectional (CS), case-control (CC) and cohort (CO) articles Aim of the study 1 Positive, if a particular objective is clearly described CA /CS / CC / CO 2 Positive, if the definition of the research question is well defined and contextualized CA / CS / CC / CO Population study 3 Positive, the main characteristics of the study population are described (sampling procedures and population distribution by age and sex) CA / CS / CC / CO 4 Positive, if the sample is representative of the characteristics of interest and sufficient to avoid bias in the results CS / CC / CO 5 Positive, if cases and controls are drawn from the same population and there is a clear definition of cases and controls, and those with low back pain in the last three months are excluded from controls CC 6 Positive if the participation rate is ≥ 80% or if the participation rate is 60%-80% and nonresponse is not selective (in the presented data) CS / CC / CO 7 Positive if the adherence to the follow-up is ≥ 80% or if non-response is not selective (in the presented data) CO Exposure assessment of whole-body vibration [if not included in the project, not applicable (NA)] 8 Positive, if the data are collected and presented CA / CS / CC / CO 9 Method for measuring whole-body vibration: direct measurement and observation, interview or questionnaire CA / CS / CC / CO 10 Positive, if more than one whole body vibration dimension is measured: frequency, duration or amplitude CA /CS / CC / CO 11 Positive, if the monitoring time is adequate / sufficient to avoid bias in the results CA / CS / CC / CO 12 Positive, if the data is collected and displayed on the current occupational exposure CA / CS / CC / CO (To be continued)

Table 1 -
Standardized checklist of methodological quality of the cross-sectional (CS), case-control (CC) and cohort (CO) articles 13 Positive, if the data is collected and if previous occupational exposure is considered CA / CS / CC / CO 14 Positive, if the data is collected and a history of musculoskeletal disorders is considered CA / CS / CC / CO 15 Positive, if exposure is measured in the same way for cases and controls CC 16 Positive, if the exposure assessment is masked to the disease state CS / CC 17 Positive, if exposure is assessed at a time before the occurrence of the disease CC (22)ussion and Conclusion25 Positive, if the evidence supports the conclusions described CA / CS / CC / CO Note: Subtitle: (+) = positive; (-) = negative Source: adapted from van der Windt et al(21).andHayden,Côté, Bombardier(22).

Table 2 -
Standardized checklist of methodological quality of the cross-sectional (CS), case-control (CC) and cohort (CO) articles

Table 2 -
Standardized checklist of methodological quality of the cross-sectional (CS), case-control (CC) and cohort (CO) articles

Table 3 -
Characteristics of the articles selected for systematic review

Table 3 -
Characteristics of the articles selected for systematic review

Table 3 -
Characteristics of the articles selected for systematic review

Table 3 -
Characteristics of the articles selected for systematic review

Table 3 -
Characteristics of the articles selected for systematic review