Background
An important debate is still ongoing on the relationships between workplace factors and chronic low back pain (CLBP). According to Waddells’ biopsychosocial model of pain [
1] chronic pain represents a clinical syndrome that fundamentally differs from acute pain. This distinction applies not only to the duration of the symptoms but also to the presumed causing and maintaining factors of chronic pain, which are supposed to be diverse and include physical, psychological, and social variables. According to this, the model postulates that sensory inputs, cognitive factors, and emotional mechanisms modulate and drive pain development. Empirical findings support the biopsychosocial model: Different social and psychological factors seem to exert considerable influence on the development of chronic back pain [
2,
3]. For instance, occupational factors such as employment status, job dissatisfaction, work attitudes, and social support at the workplace have been found to be associated with CLBP [
4*,
5‐
7]. However, information on the consistency of findings and the size of effects is still missing. Data synthesis with systematic reviews or meta-analyses provides the means to shed light on evidence about the antecedents of CLBP.
With a world-wide prevalence of about 23% [
8,
9], CLBP is the most prevalent chronic pain condition and severe musculoskeletal disorder. It is associated with high social and economic costs, especially in high-income countries [
10]. For instance, CLBP is the leading cause for a premature retirement of employees [
11,
12]. Furthermore, CLBP adversely affects the everyday life activities of individuals, their self-perception, and their contact to others [
13]. In addition, CLBP is associated with increasing emotional distress and adoption of the sick role [
14,
15]. Although there is a great number of studies on the factors driving chronic back pain, a final summary and conclusion of results is difficult as chronic manifestation of pain was not defined consistently throughout these studies [
16‐
18]. Therefore, this work aims to define the outcome more carefully (chronic low back pain) in order to increase comparability between the study results and their validity. We use a specific definition for CLBP that is pain in the lumbar region lasting 3 months or longer. This definition seems to be the most common approach and was used in several studies [
19].
In addition to define CLBP precisely, investigating linkages between psychosocial workplace factors and CLBP needs a stronger conceptual and theoretical underpinning in order to increase validity of results. Psychosocial workplace stressors are consistently associated with signs and symptoms of musculoskeletal problems in central body regions and the back [
20]. So far, most research on work-related psychosocial risk factors was conducted within the Job-Demands-Control (JDC) framework [
21,
22] assuming that high job strain (i.e., jobs characterized by a combination of high job demands and low job control) increases risks for developing low back pain (LBP; e.g. [
23,
24]). The review and meta-analysis of Lang, Ochsmann [
25] supported this by showing that high job demands (OR = 1.32), low job control (OR = 1.30), high job strain (OR = 1.38), and, in addition, low social support (ORs = 1.19 to 1.42) are associated with increased risks for lower back symptoms. Similarly, Elfering and colleagues [
26] found in a longitudinal study that low support from the supervisor increases the risk for LBP. In addition, in the study of Bernal and colleagues [
27] effort-reward imbalance was associated with more prevalent musculoskeletal disorders (OR = 6.13) and low social support was related to incidents of back pain (OR = 1.83). In sum, these findings support that LBP in general is related to psychosocial work factors such as high work demands, low job control, low levels of social support and, in addition, low reward. However, whether psychosocial work factors also promote the development of
chronic pain is still debated [
28]. Following this, there is an urgent need to review the literature on CLBP in more detail. Additionally, we consider it necessary to shed light on how the heterogeneous approaches of these studies might impact the findings.
Such a review is also necessary as the working world in western industrialized countries is currently undergoing many changes shaping the workplaces of employees. For instance, digitalization processes might lead to new work tasks and different kinds of work organization [
29]. This leads to other work factors related to the health of employees becoming more and more important, for instance, procedural justice and work values [
30]. It is therefore the aim of this review to synthesize findings on the associations between these ‘new’ work factors and CLBP, in addition to the “traditional” psychosocial risk factors in occupational health research (demand, control and social support; see [
31]). A theoretical approach that integrates such new as well as established psychosocial work factors into a core framework is the Areas of Worklife (AW) model [
32]. Based upon an extensive theory and study review, Leiter and Maslach [
33] propose that fairness and work values have to be added to workload, job control, social support, and reward [
21,
22,
34] when explaining antecedents of job stress, burnout, and work-related strain symptoms more comprehensively [
32]. More specifically, fairness refers to how fair and equitable decisions are made within the organization and values concern the fit or conflict between individual and organizational values.
Although the importance of the AW model as six organizational factors was mainly investigated for the development of burnout symptoms [
35] there is some initial support for their association with (chronic) low back pain. First, Pohling, Buruck, Jungbauer, and Leiter [
36] found that the factors workload, control, reward, and values are related to musculoskeletal complaints. Second, burnout as a unique affective response to chronic exposures of work stress [
37] predicts the subsequent development of LBP [
38] as well as musculoskeletal pain in several occupational groups [
39]. In a large Finnish study [
40] burnout was also an important correlate of musculoskeletal disorders among women even after adjusting for other contributing factors.
Therefore, the purpose of our study is to review and quantify the associations between employees’ exposure to the six psychosocial work-related AW factors [
32] and CLBP. Our review and meta-analysis adds the following contributions to the literature. In contrast to other reviews [
25,
27,
41], we consider the
long-lasting and
chronic states of lower back pain as outcome and define CLBP as pain in the lumbar region lasting for 3 months or longer [
19]. While the previous reviews investigated associations between LBP and task-related as well as interpersonal work stressors, for instance, job demands, job control, job strain, social support, job security, and monotonous work, we extend this view and add fairness and values as predicting organizational variables.
Discussion
Using data from 18 studies with 19,572 employees in total, this systematic review and meta-analysis examined relationships between psychosocial work factors from the AW model [
32] and CLBP lasting 3 months and longer [
19]. Our results suggest an overlap between psychosocial workplace factors associated with low back pain in general [
25,
27] and those associated with CLBP: Workload, job control, and social support. Therefore, the proposed yellow flags for CLBP should be re-assessed. However, psychosocial factors that Leiter and Maslach [
32] suggested as job resources against work stress developing from current changes in the working world, for instance, high fairness and a fit between personal and organizational values, have been widely neglected in relation to CLBP. Future research should strengthen research in these areas to get a more comprehensive and complementary view on how different work-related psychosocial risk factors affect the long-term development of musculoskeletal problems.
AW factors and CLBP
The results of our review and meta-analysis supported that well-known psychosocial work factors such as workload, job control, and social support significantly relate to CLBP. More specifically, high workload increases the risk whereas high job control reduces the risk for developing CLBP. However, the latter association was supported only for the combined measure of job control and for decision authority alone, but not for skill discretion. High social support from colleagues and supervisors also proved to be a resource that prevents or reduces the risks for CLBP. Our findings contribute to the literature in at least two ways. First, our results extend findings from other meta-analyses in this field of research revealing that high work-related psychosocial risk factors such as high workload, low job control, and low social support not only increase the risk for current musculoskeletal symptoms [
25,
27] but also drive the development of CLBP in a long run. Second, our results also bolster theoretical assumptions from the Job-Demands-Control-Support model (JDCS [
21];) that these three central work factors not only affect employees’ well-being (see [
31] for a review) but also relate to physical strain symptoms. Theoretical models on how psychosocial work stressors affect the development of musculoskeletal strain reactions assume two paths (see [
41] for an integration of study results): (a) a physical one via increased load at work and (b) a psychophysiological one via increased muscle tension, prolonged activation of motor units, and changes in blood supply and anabolic activity. Our purpose was not to uncover the exact mechanisms of CLPB. However, this is an important task for future reviews because such information might be helpful in developing preventive measures at the worksite.
The purpose of the AW model [
32] was to extend the traditional JDCS model by including new and theoretically-based work factors with a further potential to reduce upcoming strain-reactions from work. One of those, reward, was considered in two studies but the pooled effect size for relationships to CLBP was not significant here. The results of the sensitivity analysis also showed inconsistent associations. We note that such small sized and heterogeneous effects might also be due to ignoring potential moderators such as the level of workload and the individuals’ tendency to work more than expected [
34]. These moderators could strengthen the risks of low reward for CLBP. However, such moderating effects were not investigated in our selected sample of studies calling for more research efforts in future. This also concerns the impact of psychosocial risk factor patterns. For instance, Lang et al. [
25] and Hauke et al. [
41] found some initial support that the risks for back symptoms are significantly increased under high strain jobs, which means a combination of low control and high demands.
We found no studies investigating the relationships between CLBP and fairness and values. Associations between workplace injustice, which means a lack of fairness, and backaches have been reported [
66,
67]. However, fairness and values are the motivating connection between the worker and the workplace, which goes beyond the utilitarian exchange of time for money or career. Due to globalization and digitalization those psychosocial work factors become increasingly important [
30] and on their relation to physical well-being should be more concentrated in the future.
In sum, we found that research on work-related factors and CLBP has mainly stressed on the role of task characteristics (workload, control) and interpersonal characteristics (support). However, in line with the AW model it might be valuable to extend this view in future research to the role of organizational variables (i.e., reward, values, fairness).
Moderator analysis
For most of the reported relationships between psychosocial risk factors and CLBP heterogeneity of effect sizes between studies was indicated. Therefore, average relationships should be interpreted with caution. In turn, we conducted a series of moderator analyses to get more insights on factors explaining such between-study variance.
We found a moderating role of samples’ mean age for the relationship between job control and CLBP. Similarly, Zacher and Schmitt [
68] point to interaction effects of work related factors and age on occupational well-being. One explanation could be that older workers in contrast to younger ones have higher emotional competencies that are helpful in dealing with such workplace stressors. This concerns, for instance, the regulation of own emotions and understanding others’ emotions which was as supported by a recent systematic review [
52].
Skill discretion did not significantly correlate with CLBP. However, we found exposure duration and sex distribution as potential moderator variables affecting this relationship. First, it is possible that employees actively shape their working conditions in sense of job crafting which, in turn, reduces CLBP. Job crafting goes beyond the more traditional ‘top-down’ concepts of work design and describes the active redesign of one’s own work by the employees themselves as a bottom-up process [
69,
70]. Through job crafting employees regain control and influence at work [
70]. Second, these results further suggest that it is necessary to keep such demographic variables as sex and age (as we discussed above) not only as confounders of CLBP but also as potential moderating variables. Therefore, future studies should compare adjusted models with moderator models (e.g., stratified models) when investigating relationships between psychosocial risk factors and CLBP.
Limitations
Our review is not without limitations. First, we conducted an extensive literature research of studies. However, the number of available studies for data aggregation was limited. Although the number of studies is similar to other reviews in this research [
25,
27,
41], the small number of cases affects the precision of effect size estimates and also the possibility to conduct moderator analyses because of low statistical power. In addition, we note that we were not able to adjust pooled effect size estimates for unreliability and ‘artificial’ dichotomization of variables as information was missing in the studies [
46]. Consequently, our results most likely represent rather conservative estimates of true effects. Future research in this domain should report reliability estimates of measures and should use the full-scale range instead of dichotomizing variables.
Second, we included articles from published peer-reviewed journals and only articles in German or English language. By chance, these studies primarily examined Caucasian populations from Europe. Therefore, pooled effect size estimates and heterogeneity of effect sizes might change when including samples from other countries and, in addition, when integrating data from unpublished studies. However, with the relationship between skill discretion and CLBP as an exception, we found only weak evidence for a possible publication bias [
46]. In addition, simulation analyses revealed only a minor impact of such a bias for the presented average effects. Thus, the reported pooled effect size estimates seem to be relatively robust. Nevertheless, future meta-analyses might extend the scope of literature search.
Finally, the low to medium quality of included studies might have biased our results. The most common problem involves an unspecific assessment of the outcome. Although CLPB was clearly defined according to our inclusion criteria (pain in the lumbar region lasting for 3 month or longer), many studies did not apply such a measure (see e.g. [
60*,
61,
71*]). One reason might be a lack of agreement about the definition of CLBP [
16,
17] and, in turn, no consistent use of measures. In addition, some studies did not report the reliability of the instruments to measure psychosocial stressors or main characteristics of the study population. Also, adjustment of confounders varied across the studies. However, we always used effect sizes for pooling that were at least adjusted for demographic variables, also to strengthen their comparability. Moreover, reported pooled effect size estimates were comparable in studies using prospective designs with higher quality and, in addition, we found no evidence that methodological quality of studies was a moderator affecting the reported effect size estimates. In sum, we conclude that although our review of literature calls for more high quality studies in this research, study quality is not a variable explaining the results reported here.
Research implications
In view of the changes within the current working world, job exposures that shape the exchange and interplay between organization and employee, for instance, reward, fairness, and values, are expected to become more important in maintaining health in general and preventing CLBP in particular [
72,
73]. Consequently, there is a need for future research investigating those constructs more specifically. Additionally, we recommend including all of the AW factors [
32] that are workload, control, support, reward, fairness, and values. Keeping up this rationale, it would be possible to investigate combined additive and interactive effects of these psychosocial work-related factors over and above the assumptions from the JDCS model [
31,
74] and the effort-reward imbalance model [
34].
An enormous challenge in preparing the systematic review was the identification of studies using an accurate and rigorous definition of CLBP. We defined CLBP as unspecific LBP lasting for 3 month or longer. During literature search, we noted that there is a substantial lack in studies investigating the association between psychosocial work factors and CLBP following this definition. Future research should use a more consistent and rigorous definition of CLBP, apply appropriate (valid and reliable) measures for CLBP in order to improve consistency of results and to allow a comparative analysis. Meucci and colleagues [
75] suggested a minimal definition of CLBP that includes a precise description of the anatomical area, the pain duration, and level of CLBP induced limitations in general daily activities. Moreover, to increase the validity of diagnosis the assessment of CLBP by interviews and by medical examinations should be preferred in contrast to self-report questionnaires.
Although we found a number of prospective studies that could be included in our review, future research should apply high quality randomized and longitudinal case-control studies as well as intervention studies more often. Such designs allow investigating causal interference of relationships between work exposures and CLBP more strongly. Therefore, future research should investigate psychosocial risk factors of the AW model in combination when exploring antecedents of CLBP.
Practical implications
In view of the rising burden and associated high costs of CLBP [
76‐
78] for the
individuals (e.g., reduced life activities, impaired well- being), for the
employers (e.g., lower work performance, higher absence rates from work), and for the
society (e.g., expenses of health care services and social welfare system) this meta-analysis yields important implications for public health and human resource management. In particular, the chronic state of back pain constitutes a unique clinical syndrome [
1] representing a great challenge for interventions [
79]. Our results suggest that psychosocial job exposures (workload, control and social support) are not only associated with a higher risk for lower back pain (e.g. [
25]) but also with a higher risk that this becomes chronic. Therefore, a reduction of those stressors and the design of healthy job exposures are required for CLBP prevention.
Using a stepwise approach, first, potential risk factors at work have to be assessed with valid instruments, for instance, by self-report [
35,
80] or by workplace observation [
81,
82]. Second, organizational-level interventions designed to change and to optimize those psychosocial factors (e.g. task restructuring, increasing work control or the level of participation) need to be implemented. More specifically, other research found that if the involvement of employees during interventions is high, measurements focusing on the design of ‘healthy’ workplaces are more successful [
83,
84]. For instance, involvement can be increased bottom-up if employees develop context-specific solutions in cooperation, prepare action plans targeting the improvement of their health and well-being, and, in turn, implement and evaluate these measures. There might be situations where a reduction of psychosocial stressors is hardly possible (e.g., high workload because of absence-related understaffing). Therefore, according to our results, it is necessary to strengthen potential job resources with the power to reduce adverse (physical) effects of high job demands [
85]. This concerns task-level and interpersonal-level work factors such as time and method control and opportunities for social support but also time to recover from work [
86]. For instance, a recent meta-analysis showed that even paid within-shift breaks reduce employees’ physical discomfort and increase their well-being and task-performance [
87]. Moreover, increasing employees’ psychological detachment from work seems to be a helpful recovery process for preventing physical discomfort and back pain [
86,
88]. In sum, participatory and organizational-focused interventions could serve as an important complement to the widely used individual-level measures [
89,
90] to reduce the risk of CLBP.
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