Association between Upper Extremity Musculoskeletal Disorders and Psychosocial Factors at Work: A Review on the Job DCS Model's Perspective.

Over years it has been increasingly concerned with how upper extremity musculoskeletal disorders (UEMSDs) are attributed to psychosocial job stressors. A review study was conducted to examine associations between UEMSDs and psychosocial work factors, and to recommend what to consider for the associations. For studies in which the job demand-control-support (DCS) model or its variables were specifically employed, published papers were selected and reviewed. A number of studies have reported relationships between UEMSDs symptoms and psychosocial exposure variables. For example, the findings are: higher numbness in the upper extremity was significantly attributed to by less decision latitude at work; work demands were significantly associated with neck and shoulder symptoms while control over time was associated with neck symptoms; and the combination of high psychosocial demands and low decision latitude was a significant predictor for shoulder and neck pain in a female working population. Sources of bias, such as interaction or study design, were discussed. UEMSDs were shown to be associated with psychosocial work factors in various studies where the job DCS model was addressed. Nonetheless, this review suggests that further studies should be conducted to much more clarify the association between UEMSDs and psychosocial factors.

Introduction

Upper extremity musculoskeletal disorders (UEMSDs) have been frequently reported for elevated risks in workers exposed to psychosocial work factors in different countries. Disorders or economic cost issues due to MSDs have been increasing, making work-related musculoskeletal problems one of the most serious health problems over past decades [1-7].

According to a report presented by an International Labor Office (ILO) researcher [1], musculoskeletal complaints are a major cause of absence due to sickness in developed countries. The researcher reported that the cost of work-related MSDs, based on a National Institute of Occupational Safety and Health (NIOSH) report in 1996, was estimated at about US$ 13 billion in the United States, and it ranged from 2.7% to 5.2% of the gross national product in Nordic countries in 1991. Up to 60% of people on early retirement or long-term sick leave claimed MSDs as a reason in Sweden. In Korea, MSD cases accounted for 68%, 74% and 77%, respectively, of non-fatal occupational illness cases approved in workers' compensation claims for the years of 2006, 2007 and 2008 [2,8].

During recent decades, the contribution of psychosocial stressors to the occurrence of UEMSDs has become increasingly clear. Fig. 1 shows possible associations between UEMSDs and psychosocial factors. Researchers stated that the psychosocial factors, particularly low work content and poor social support, increased the risk for UEMSDs and that a combination of poor psychosocial work environment and exposure to ergonomic variables (e.g., monotonous work with awkward posture) became a highest risk factor [4,9,10].

Fig. 1

Interaction between upper ex tremity musculoskeletal disorder symp toms and psychosocial load, physi cal load, or individual factors (From Bongers PM, et al. Am J Ind Med 2002;41:315-42 [4]).

The job demand-control-support (DCS) model is a well-known job strain model which consists of three psychosocial factors (i.e., job demand, job decision latitude, and social support) as basic dimensions [11-13]. Information including overview or criticisms of the job DCS model is provided in a study [14] although the model has been documented in a large number of studies. Using the job DCS model, numerous studies have been reported how psychosocial work factors are associated with musculoskeletal symptoms [15-19].

However, in epidemiologic research on musculoskeletal injuries or disorders, individual capacity has mainly been interpreted as physical capacity (e.g., muscle strength, range of movement), whereas little attention has been given to psychological coping capacity or relationships between UEMSDs and psychosocial factors at work. Compared to the studies on low back pain, there are still few research studies that provide for clear understanding of the role of psychosocial stressors in the development of UEMSDs. Thus, there is a need to review how psychosocial work factors contribute to the occurrence of UEMSDs.

This study, focused on studies with respect to the job DCS model, was to examine associations between UEMSDs and psychosocial work factors, and to recommend what to consider for the corresponding associations in the future.

Methods

Since this study was primarily concerned with the association between UEMSDs and occupational psychosocial factors, it was necessary to examine information on how UEMSDs were associated with psychosocial variables and what relationships between UEMSDs and psychosocial factors were documented in published studies.

We sought studies in which the above study questions were primarily dealt with in the literature. Study papers were gathered using an automatic search from online data bases such as PubMed and Science Direct. Some papers were collected the library of Korea Occupational Safety and Health Agency. When searched through the online data bases, a combination of 'musculoskeletal disorders' and 'psychosocial factors'/'job stress factors' was used as keywords. Once paper lists were obtained, we selected study papers in which the job DCS model or its variables were specifically employed in a cross sectional or longitudinal study. The study papers were reviewed to achieve the objectives of this study while three (2 cross sectional and 1 prospective) of them were exemplified in the section of 'UEMSDs and psychosocial factors at work.' It was assumed this approach could reflect characteristics of associations between UEMSDs and psychosocial work factors on a basis of the job DCS model's perspective. When a study didn't address either MSDs for upper extremity body parts or psychosocial exposure variables, it was excluded.

We intended to describe the findings, such as risk estimates or descriptive statements, on associations between UEMSDs and psychosocial work factors. Definitions of UEMSDs and psychosocial variables were somewhat closely examined. If a term, for instance, was specified in peer-reviewed literature, it was assumed to be objectively used. Information on interaction or bias among study variables was also documented and extensively discussed, expecting that this could lead to better understanding or recommendations for future research.

Musculoskeletal Disorders of the Upper Extremities

UEMSDs refer to soft tissue disorders in the neck, shoulders, arms, wrists, hands and fingers. The soft tissues include nerves, tendons, ligaments, muscle and fascia. Frequently, the disorders are documented as carpal tunnel syndrome, epicondylitis, neck tension syndrome, tendinitis, tenosynovitis, thoracic outlet syndrome, or white finger [4,20,21]. The symptoms of UEMSDs, depending on the type of disorders, are generally characterized by pain, aches, discomfort, numbness, stiffness, and/or weakness.

UEMSDs are prevalent in jobs such as video display terminal (VDT) operators, food processors, automobile and electronics assemblers, carpenters, garment workers, and grocery store cashiers. For example, VDT operators have often reported musculoskeletal symptoms primarily in the upper extremities, neck and shoulders [15]. Moreover, highest incidence rates of UEMSDs have occurred in industries where a substantial amount of repetitive, monotonous, and forceful exertion exists at work [20].

UEMSDs affect the soft tissues of the upper extremity in different ways. UEMSDs can be temporary if a rate of work vs. rest is appropriately provided. They, however, can become permanently disabling when exposures to ergonomic risk factors or poor work conditions are prolonged. Repetitive exertions, awkward posture, and mechanical pressure have been recognized as important etiological factors for chronic UEMSDs. For example, long hours of sitting in a static posture and repetitiously keying are considered to influence the development of musculoskeletal symptoms among VDT operators [15]. In particular, the etiologic significance of psychosocial factors impacting musculoskeletal problems has been reported [8,15-19].

Psychosocial Work Factors

Psychosocial work factors generally describe the subjective aspects of work conditions or work organization, and how they are perceived by workers [22]. With the job DCS model, psychosocial exposure variables have been differently classified and addressed, depending on the studies' objectives (Table 1). Still, classification or terminology regarding psychosocial factors is incompletely established. For example, Bongers et al. [5] classified those factors into two categories in one study whereas Bongers et al. [4] classified them in dif ferent way in another study. Skov et al. [16] divided them into four categories when they assessed the psychosocial job charac teristics.

Table 1

Psychosocial factors reportedly associated with musculoskeletal symptoms

In this study, job demand, job decision latitude and social support are regarded as primarily psychosocial factors although other psychosocial variables are addressed as well.

UEMSDs and Psychosocial Factors at Work

Different papers showed a variety of findings on associations between UEMSDs and psychosocial factors. Associations between UEMSDs and psychosocial factors were assessed by researchers who conducted a cross sectional study for VDT operators in a large newspaper [15]. Karasek's Job Content Instrument (JCI) was used for self-reported measures of psychosocial stress factors. The JCI variable like decision latitude was a significant risk factor for potential UEMSDs. For example, higher numbness in the upper extremity was significantly attributed to by less decision latitude (Table 2). There were also interaction effects, showing that associations between symptom severity and work posture variables were modified by psychosocial factors. Higher numbness in the upper extremity was shown to be associated with keyboard heights above the elbow. For employees reporting high decision latitude, the association between numbness and keyboard heights was quite small.

Table 2

Multiple regression analyses of upper extremity symptom severity among newsroom employees

*Job Content Instrument (JCI) subscales used at step 3.

†DecLat × Relkybd = Decision latitude × Relative keyboard height.

‡JobInsc × Relkybd = Job insecurity × Relative keyboard height.

§p < 0.05.

∥p < 0.01.

Adapted from Faucett J et al. Am J Ind Med 1994;26:597-612. [15]

Various factors including the job DCS model variables were shown to be related to UEMSDs in another cross sectional study (Table 3) [16]. In multivariate analysis of the study, work demands were significantly associated with neck and shoulder symptoms (odds ratio [OR], 1.43 to 1.47). Control over time at work was also significantly associated with neck symptoms (OR, 1.44). These findings are consistent with those of other researchers [5,19]. On the other hand, an interaction between perceived competition and control over time was found in the study, showing that only the combination of high demands and low control was associated with an increased risk of neck symptoms.

Table 3

Significant factors in final models of a multivariate analysis for neck and shoulder body region

*p < 0.0.

Adapted from Skov T et al. Occup Environ Med 1996;53:351-6. [16]

In a prospective study [19], the combination of high job demands and low decision latitude (i.e., job strain) was statistically significant (OR, 1.73; 95% confidence interval [CI], 1.29 to 2.31) for shoulder and neck pain in female workers. However, the job strain was not significant in male workers (OR, 1.22; 95% CI, 0.84 to 1.79). High job demands, low decision latitude, and low support were not associated with elevated risk for developing neck and shoulder pain during follow up in male or female working populations. Additionally, in an analysis examining effect modification between job strain factor and mechanical exposure factor, the study found evidence which increased the risk of shoulder and neck pain among female but not male workers.

Discussion and Recommendations

A variety of information on associations between UEMSDs and psychosocial factors at work was found in studies where the job DCS model was addressed. Those studies have commonly shown that UEMSDs, independently or in a combined manner, were associated with psychosocial factors at work. In addition, there were shown to be interactions between different sets of variables for UEMSDs and psychosocial factors.

Since it has been received attention to understand relationships between UEMSDs and psychosocial stressors, it is desirable to review, on the basis of the job DCS model's perspective, the extent to which or how UEMSDs are associated with psychosocial work factors. While the three psychosocial variables in the job DCS model are related to musculoskeletal symptoms, they, together with physical factors, are reported to increase work-related stress [15,16,18,19,23]. Also, it has been documented that musculoskeletal symptoms are affected by other psychosocial work factors such as time pressure, low job satisfaction, monotonous work, and job insecurity [5,19,24].

Furthermore, a study has comprehensively reviewed associations between UEMSDs and psychosocial work factors [5]. For psychosocial factors regarding job demand and control, a number of the cross-sectional studies reported there were relationships between psychosocial variables and symptoms of the neck or shoulders. Longitudinal studies also provided a positive relationship between neck pain and time pressure. Yet, there is evidence that high work demands increased the prevalence of neck or shoulder symptoms.

There still seem, however, to be contradictions in findings among studies. It was recognized that researchers didn't present conclusive evidence due to complex correlations between UEMSDs and psychosocial factors, and difficulties in measuring work/nonwork factor variables [4,5,21]. Westgaard [9] also stated difficulty obtaining consistent results on association between psychosocial strain and musculoskeletal pain for both the conceptual and operational variables.

MSDs are predicted to be the most prevalent of the major diseases among United Kingdom workers over the coming 20 years [25]. Researchers document that pain appears to occur more frequently from the shoulder and neck although low back pain has been the dominant problem for a long time [19]. Thus, it is necessary to more sufficiently assess the association between UEMSDs and psychosocial stressors since UEMSDs increasingly account for the economic costs as well as occupational illness cases. For a study on relationships between UEMSDs and psychosocial work factors, it is necessary to assess both musculoskeletal symptom duration/type from self-reports and musculoskeletal signs from physical examinations [5,17]. Moreover, a clear distinction between sets of UEMSD physical risk factors, symptom persistence, or disability prediction appears to be important.

This study restrictively dealt with questions on association between UEMSDs and psychosocial work factors. In fact, there are other aspects of questions related to UEMSDs or psychosocial work factors. Many researchers have reported that workers with jobs characterized by psychosocial factors have a high risk of other endpoints such as cardiovascular diseases or burnout syndrome [13,14,26], which adversely affect musculoskeletal symptoms. The present study may encompass sources of bias in that the reviewed studies include the crosssectional study design. Longitudinal studies can provide clearer relationships between UEMSDs and psychosocial work factors [14]. Thus, future studies on UEMSDs and psychosocial factors should be longitudinal, directed towards the analysis of symptom development or persistence. Such studies may provide further useful information on correlations or interactions between biomechanical load, psychosocial factors, and stress symptoms at work. At least, those studies would pro vide stakeholders with better insight to set priorities in the prevention of UEMSDs and psychosocial stress at work.