Date Published: April 6, 2017
Publisher: Public Library of Science
Author(s): Romain Balaguier, Pascal Madeleine, Kévin Rose-Dulcina, Nicolas Vuillerme, Alejandro A. Espinoza Orías.
The prevalence of low back disorders is dramatically high in viticulture. Field measurements that objectively quantify work exposure can provide information on the relationship between the adopted trunk postures and low back pain. The purposes of the present study were three-fold (1) to carry out a kinematics analysis of vineyard-workers’ pruning activity by extracting the duration of bending and rotation of the trunk, (2) to question separately the relationship between the duration of forward bending or trunk rotation with low back pain intensity and pressure pain sensitivity and (3) to question the relationship between the combined duration of forward bending and trunk rotation on low back pain intensity and pressure pain sensitivity. Fifteen vineyard-workers were asked to perform pruning activity for 12 minutes with a wireless triaxial accelerometer placed on their trunk. Kinematic analysis of the trunk showed that vineyard-workers spent more than 50% of the time with the trunk flexed greater than 30° and more than 20% with the trunk rotated greater than 10°. These results show that pruning activity lead to the adoption of forward bended and rotated trunk postures that could significantly increase the risk of work related musculoskeletal disorders in the low back. However, this result was mitigated by the observation of an absence of significant association between the duration of forward bending and trunk rotation with low back pain intensity or pressure pain sensitivity. Even if prospective field measurements and studies assessing the effects of low back pain confounders are needed, this field study provides new genuine information on trunk kinematics during pruning activity.
Work related musculoskeletal disorders (WMSDs) affecting the low back are considered in numerous industrialized and developed countries as a major public health problem [1–4]. For instance, Farioli and colleagues  have recently reported a 46% one year prevalence for low back pain (LBP) among almost 35 000 European workers. The consequences of LBP include disability, early retirement, healthcare consumption, loss of productivity and sickness absences [6,7]. Among all the working sectors, the highest rate of LBP is commonly observed in agriculture . Thereby, in a recent review on the prevalence of WMSDs among farmers, Osborne and colleagues  have reported respectively a 75% lifetime and a 48% one year prevalence of LBP. In France, the viticulture sector, which employs more than 500 000 persons, is the agricultural sector with the highest prevalence of WMSDs in the low back [9,10]. Although the origin of LBP is multifactorial, biomechanical risk factors such as heavy physical workload, repetitive motions, awkward postures—especially excessive forward bending and rotation of the trunk—are known to increase the risk of new and recurrent episodes of LBP [11–17]. Interestingly, the few studies assessing WMSDs risk factors among vineyard-workers have also reported an exposure to these biomechanical risk factors especially during the winter job activities such as fixing and pruning [9,18–21]. In an epidemiological study among almost 4 000 French vineyard-workers, Bernard and colleagues  have concluded that the postural constraints during pruning activity could increase the risk of LBP. Meyers and colleagues , using an observational checklist, have reported that the risk of LBP was increased during pruning due to frequent trunk flexion up to 90°. However, biomechanical exposure in these afore-mentioned studies have been assessed using self-reported measurements or observational methods which can tend to overestimate the time of exposure to risk factors [22–24]. Kato and colleagues  have conducted an experimental study addressing the effects of different pruning trellis systems on the risk of developing WMSDs in the lower back. However, a single field study has to our knowledge assessed trunk postures among vineyard-workers during pruning . At this point, this study presents two major limitations. First, it was focused on the assessment of trunk thigh angle in the sagittal plane, while numerous studies have highlighted the effect of the duration of trunk forward bending and trunk rotation on the risk of LBP [26–28]. Second, it did not assess the association between physical exposure and risk of LBP among vineyard-workers, while numerous studies have highlighted the need to evaluate more precisely this association using objective and quantitative field measurements [16,29,30]. As mentioned in numerous studies [31,32], one valid approach to quantify the risk of LBP among workers is to assess the relationship between duration of forward bending and self-reported LBP intensity, e.g. using numeric pain rating scale (NRS). Such analysis can be complemented by measurements of pressure pain thresholds over the low back. Consequently, assessing pressure pain sensitivity over locations of the low back offers an interesting and reliable [33,34] opportunity to investigate and visualize the associations of trunk forward bending, trunk rotation and pain sensitivity.
Taken together, the present findings showed that vineyard-workers’ pruning activity is likely to lead to the adoption of bended and rotated postures for relatively long period of time. For instance, during the 12 minutes of pruning activity, vineyard-workers spent almost 60% of the time with the trunk bended >30°. Our results are comparable to those reported in a study specifically designed to assess the effects of different pruning trellis on the risk of WMSDs in the low back . In the latter, 11 vineyard workers were asked to perform a simulated pruning task during approx. five minutes showing that vineyard-workers spend between 31% and 80% with the trunk forward bended > 30°. Once extrapolated over a working day, this result suggests that vineyard-workers spend most of their working time with trunk postures which have extensively been reported to increase the risk of LBP [15,27,28]. Interestingly, Coenen and colleagues  have reported that this risk is significantly amplified when the trunk is bended >60° more than 5% of the time. In our study, pruning activity largely exceeded this threshold (i.e., 21%), consequently increasing the risk of LBP among vineyard-workers. This observation is corroborated by previous studies showing that trunk forward bending negatively affects viscoelastic tissues such as ligaments, fascia, discs [44–46] and spine stability. Indeed, prolonged trunk forward bending increases the risk of ligaments laxity and ligaments micro-damages, the risk of inflammation and, consequently, the risk of LBP [44,46].
This field study revealed that vineyard-workers adopt forward bended and rotated trunk postures that may increase the risk of WMSDs in the low back during the execution of pruning activity. Indeed, more than half of the assessed working time was spent with the trunk flexed greater than 30° and more than 20% with the trunk rotated greater than 10°. Then, our study has also pointed out a significant difference between left and right rotation of the trunk. However, our study did not reveal any relationship between duration of forward bending or trunk rotation and LBP intensity or pressure pain sensitivity. Finally, this study reinforces the necessity of further field measurements with longer time of observation and larger sample size to confirm our findings and to investigate other variables specifically the effects of potential LBP confounders such as gender, age or job seniority to accurately quantify the risk exposure.