Introduction
Musculoskeletal upper extremity symptoms and complaints of neck, shoulder and arms are common in the general population and among computer users in many industrialized countries [
1,
2]. In recent years, computer-related office work has intensified in western developed countries. In Germany for example the 2004 census revealed that computer related work constituted a large part of the daily working routine for approximately 21 million people (59% of all those with paid work) [
2]. The etiology of neck, shoulder and forearm/hands complaints in computer workers is still not completely understood. Several risk factors related to different physical exposures at work and psychosocial conditions have been identified as potential causes for neck, shoulder and forearm/hands complaints. These exposures can be physical exposures related to static neck and arm postures, repetitive tasks, workplace design [
3,
4] and also psychosocial factors related to job characteristics, high quantitative job demands, having little influence on one’s work situation, and limited support from coworkers or supervisors [
5‐
7]. Fewer studies have investigated the interaction between psychical/ergonomic and psychosocial factors for example the concept of work style [
8,
9]. Furthermore, individual factors (e.g. age, previous symptoms, etc.) have also been discussed in the literature as potential risk factors for these complaints. Hence, an etiological model explaining shoulder and neck and forearm complaints should consist of both physical and psychosocial factors at work [
10].
We conducted a longitudinal cohort study among Dutch computer office workers. The psychosocial risks factors measured in this study were derived from the Karasek model [
11‐
14]. The main thrust of this model, the Job Demand-Control-Model, is that psychological strain does not result not from a single aspect of the work environment (such as a heavy workload or other job stressors), but from a joint effect of the level of job demands and the degree of autonomy or control that employees are able to exercise over their work. The job demands construct is the measure of stressors, such as work load demands which are present in the work environment [
14]. The construct of control refers to the amount of influence that workers have over when and how they perform their work. In the Job Demand-Control-Model, these two constructs interact with each other to create job strain [
14]. The theory was expanded further by adding a third construct: the social support which buffers against the negative impact of high strain [
15,
16]. Bongers et al. [
6] have identified an association between the decision latitude and upper extremity complaints. The current study will test the main constructs in the Karasek model: i.e. job demands, job control and social support, and also job strain.
In addition to previous studies, the current prospective study aims to analyze the presence of neck, shoulder and forearm/hands complaints in relation to effects of both exposures to physical factors (i.e. work station and body posture) and to psychological factors (job demands, job control, social support and strain).
Accordingly, this study attempts to test the following research questions:
1.
To what extent are job demands, job control, social support and job strain in the workplace, associated with the occurrence of symptoms in the neck, shoulder and forearm/hands?
2.
To what extent are physical body posture and the design of the workplace associated with the occurrence of symptoms in the neck, shoulder and forearm/hands?
Discussion
In this longitudinal study among computer office workers, we found that the report of complaints in the neck region was similar to shoulder complaints, however, much higher than forearms/hands complaints, which corresponds with the results of previous studies. Boet et al. found in a Dutch cohort of general practice patients incidence rates of 23.1 cases per 1,000 person-years for neck symptoms, followed by 19.0 cases per 1,000 person-years for shoulder symptoms [
19]. Furthermore, a survey in the Netherlands showed that in 2002 and 2004, 28% of the working population reported neck/shoulder or elbow/wrist/hand symptoms in the previous 12 months [
10] and that these symptoms were at least partly caused by work. Another study in the USA [
4] indicated that among 416 employees 63% reported neck shoulder pain compared to 34% reporting arm or hand pain.
Neck, shoulder and forearms/hand complaints were associated with both work-related psychosocial and physical factors. Different studies have taken physical and psychosocial work related factors into account when studying upper extremity complaints with mixed results [
1,
10,
20‐
24]. The current study showed that among the work related physical factors significant associations were found between irregular head and body posture and neck, shoulder and forearms/hands complaints. The irregularity was identified as either sitting with a twisted trunk or in a symmetrical position or with the neck held in a bent position. In the scientific literature their seems to be some consensus on poor ergonomic conditions at workstations contributing to musculoskeletal symptoms or disorders [
22,
25]. Ariens et al. indicated that holding the neck in a forward bent posture for a prolonged period of time, and repeatedly working in the same position for a prolonged period of time were both significantly associated with neck pain. Other studies showed [
26,
27] that the odds ratios for neck pain increased with the time spent working in a sitting position, suggesting a dose-response relation between sitting posture and neck pain. According to Ortiz-Hernandez et al. [
28], remaining seated for long periods, usually accompanied by a bent curvature of the spine, increases pressure on vertebral discs, stresses ligaments, and provokes muscle pain. The association found with both neck, shoulder and forearm complaints indicates that whatever irregularity exists (i.e. either a twisted, bended or asymmetrical position) it predicted the presence of complaints in this study population.
Furthermore, previous history of complaints was significantly associated with the presence of current complaints. This result corresponds with findings from Smedley et al. [
29] and Bongers et al. [
10] who found in a longitudinal study that the strongest predictor of incident neck/shoulder pain was previous history of the symptoms.
Psychosocial factors have been discussed as predictors in previous studies [
6,
13,
30]. In a systematic review it has been found that, high job demands, low decision latitude, time pressure, mental stress, job dissatisfaction, high workload, and lack of social support from colleagues and superiors were suggested as risk factors for upper extremity musculoskeletal disorders [
6,
13]. In the current study seven variables adapted from the Karasek model were tested (i.e. job demands (task difficulty and work pressure), job control (decision authority and skill discretion), social support (support between coworkers and supervisors and work flow) and job strain. The results found support for the association between task difficulties and complaints in the neck and shoulder. This finding is consistent with other prospective studies of neck pain which also found that job demands were a risk factor [
13,
31].
The multivariable model indicated that a significant association was found between upper extremity musculoskeletal complaints and both the job demands and head and body posture. These findings are in line with recent studies examining the combined and/or interactive effects of both biomechanical/physical factors and occupational psychosocial factors [
32‐
34]. The interaction among psychosocial stressors, work demands, ergonomic exposures, and the complex individual response to these workplace factors refer to someone’s work style. This work style model is based upon the hypothesis that how an individual performs his/her work tasks in reaction to increased work demands may either increase the likelihood of developing upper extremity symptoms or exacerbate and maintain preexisting symptoms [
8,
33]. Although the current study did not test the work style construct, work style is, however, very much related to many of the findings in the current study in terms of the role of work demands and the biobehavioral response to these demands that can expose these workers to both biomechanical and psychosocial factors.
Generally, this study confirms the main findings of the literature [
10,
17,
22,
24,
35]. Neck and shoulder complaints occurred significantly more often than complaints in the other parts of the upper extremities. Neck, and shoulder and forearm/hands complaints were positively associated with irregular head and body posture and job demands (i.e. task difficulty). The findings of the current study are based on the simultaneous consideration of various regions of the upper extremities and various risk factors.
However, there are some limitations that merit discussion. First, the report of complaints may have been biased due to the fact that subjects had to report neck or shoulder complaints that occurred in the past 12 months which might have introduced recall bias. Second, the measurement of ergonomic risk factors was subjective, and not based on actual measuring of the degree/level on neck position, distance from monitor by means of for example video recordings.
The study results suggest that intervention strategies aiming at reducing the occurrence of neck, shoulder and forearms complaints most likely have to take into account both ergonomic improvements and psychosocial aspects and the interaction between these two risk factors. Based on the results of this study, interventions should be aimed to reduce computer exposure and also toward improving ergonomic conditions. Further, one can cautiously postulate that the negative impact of work demands should be viewed not only from the perspective of autonomy (i.e. control on how and when tasks are performed) but also from the perspective of task difficulty and complexity such as perceived by the worker.
Acknowledgments
We would like to thank the management, doctors and employees of the GAK (national unemployment insurance office) in Maastricht and Heerlen, The Netherlands, for their willingness to participate in this study.