PM Bongers et al published “Psychosocial factors at work and musculoskeletal disease” in 1993. It wasn’t the first study to posit that physical hazards may not be sufficient to explain the etiology of occupational musculoskeletal disorders (MSDs), but it has the distinction of being the most cited. And it topped the list in a recent Swedish survey of the 10 most cited occupation health studies since 1949. Arguably, that top ranking is a signpost to a slippery issue.
JF Gehanno et al gave it first place in their "Citation classics in occupational medicine journals" survey in 2007. That ranking speaks to the difficulty of pinning down the exact nature of the link. It also speaks to the endurance of a widespread conviction that the link is a key to understanding MSDs.
Researchers have taken many directions to investigating the relationship between the two. Their qualifying statements and disclaimers about their results illuminate the typical problems that stand in the way of the investigations. Together, their studies paint a reasonably consistent picture of psychosocial factors as an amorphous array of characteristics of jobs, work environments and organizations that are hazardous for most work groups. The difficulty lies in the relationship, and in the mechanisms that tie these factors to MSDs.
Three major reviews of the literature represent a shortcut to looking at the directions of the investigations. One includes a comprehensive analysis of the innate difficulties of the subject.
The 1993 Bongers paper reviews the studies to that date in an attempt to establish whether the epidemiologic literature amounts to evidence of an association between psychosocial work factors and MSDs. In a hypothetical model it suggests that individual characteristics and stress symptoms can modify this relationship, but that the reviewed studies “do not present conclusive evidence due to high correlations between psychosocial factors and physical load and to difficulties in measuring dependent and independent variables.” The authors were prepared to state that “monotonous work, high perceived work load, and time pressure are related to musculoskeletal symptoms,” but backed off presenting other insights as conclusive.
The National Institute for Occupational Safety and Health (NIOSH) reviewed a vast body of literature four years later in the report, “Musculoskeletal Disorders and Workplace Factors: A Critical Review of Epidemiologic Evidence for Work-Related Musculoskeletal Disorders of the Neck, Upper Extremity, and Low Back.” In Chapter 7 the report observes that psychosocial factors “relate to aspects of organizational function and culture, participation, latitude in decision making, career development, role in organization, job content, the workload and pace of work, work schedules, interpersonal workplace relationships and the work-home interface.” It notes that each of these nine characteristics of work has proved stressful and/or harmful to health under certain conditions. “Work characteristics might not be simply additive in their effects on health, the report continues, but …might combine interactively in relation to such effects.”
Carayon et al in the United States undertook a comprehensive review of the literature in 1999 to focus on disorders of the upper extremities. They proposed several pathways for a theoretical relationship between job stress and work-related musculoskeletal disorders (WRMDs). The researchers observed that physical ergonomic and psychosocial work factors should be examined simultaneously in order to fully understand the etiology of WRMDs.
Other investigations have looked at the link in scores of occupations. Truck drivers, offshore oil and gas workers, air traffic controllers, bus drivers, assembly-line workers, call center personnel and nurses and nursing aides have all come in for a share of the scrutiny. In many cases questionnaires were followed by medical examinations.
Whatever the source, findings are generally presented with a comment or comments from the author/s about the limitations of the study.
While NIOSH is not telling readers of its 1997 report to take all the findings in the studies reviewed “with a pinch of salt,” it is saying that unqualified trust in the findings is misplaced. It devotes significant space to picking apart the reliability of research into the topic.
“There is considerable confusion regarding the contribution of psychosocial factors to musculoskeletal illness and injury,” NIOSH notes. It questions the Bongers 1993 findings, for instance, describing as unclear the “work-relatedness” of a host of psychosocial factors associated with the individual worker and back pain and disability. The list of fuzzy factors includes personality and psychological status, and the extra-work environment, such as living alone.
The report cautions that it is “necessary to be aware [in the studies reviewed] that, in general, researchers have not used standardized methods for assessing psychosocial factors in relationship to MSDs. Thus, individual psychosocial factors assessed by investigators vary from study to study. Moreover, even when work-related psychosocial factors (e.g., workload , job control, social support, job satisfaction, etc.) included by various investigators are the same or similar, they may be measured by different methods and different kinds of scales which can vary in psychometric quality. These methodological limitations complicate the process of drawing definitive conclusions regarding the literature as a whole and when comparing results between studies, one must take these differences into account.
NIOSH also points out that most of the psychosocial scales in the reviewed studies were in office settings, where physical factors may be less important than psychosocial factors in their relationship with MSDs.
NIOSH introduces its concluding statements about the role of perceptions in psychosocial factors with the caution that “the findings of the studies reviewed are not entirely consistent.”
The report remarked that the problems of arriving at more conclusive findings are in in determining the relative importance of the physical and psychosocial factors. According to the report, psychosocial factors are usually measured at the individual level, while physical factors are more often measured at the group level, and often by methods with limited precision or accuracy. It states that “objective measures" of aspects of the psychosocial work environment are difficult to develop and are rarely used, while objective methods to measure the physical environment are more readily available: “Until we can measure most workplace and individual variables with more comparable techniques, it will be hard to determine precisely their relative importance.”
The NIOSH report cited several authors to posit that “psychosocial demands may produce increased muscle tension and exacerbate task-related biomechanical strain. Psychosocial demands could also complicate the picture, affecting awareness and reporting of musculoskeletal symptoms, and/or perceptions of their cause. Within this second explanation may fall the “perverse incentive” view, according to the report, in which societies may provide workers with systems, such as workers’ compensation, that may lead to over-reporting of MSD symptoms. It also points out that initial episodes of pain based on a physical insult may trigger a chronic nervous system dysfunction, physiological as well as psychological, which perpetuates a chronic pain process.
The NIOSH report was written in 1997. It could be argued that study techniques have moved on, improving the reliability of research findings. The 2007 ranking of the Bongers paper as a classic study, as well as recent research articles, however, suggest that the investigational challenges endure.
Bongers et al allude to the problem of slippery data in a 2002 paper. They observe that since the 1993 study, research has focused on upper extremity problems (UEPs). “There was some evidence for a relationship between high job demands and UEP, although the results did not meet the pre-set criterion for consistency. … Firm conclusions on the role of these factors in the etiology of UEP are not possible due to the cross-sectional nature of most studies.”
In a study of knee MSDs, Gareth Jones, MD, is frank about the limitations of his investigation. He noted the “relatively modest effect of mechanical factors; possible underestimation of cases of knee pain; lack of data on prior knee injury; failure to measure psychosocial factors outside the workplace; and variation in the severity of reported knee pain.”
It is a scientific challenge to ascertain the relative importance between these different types of factors, writes Fadi Fathallah in his study about the relationship between psychosocial factors and MSDs in 2008. “Several researchers have emphasized that a multi-disciplinary approach to the problem may be the right vehicle to understand the relative importance of these factors.” Nine years before, Carayon et al observed that physical ergonomic and psychosocial work factors should be examined simultaneously in order to fully understand the etiology of WRMDs.
PM Bongers, CR deWinter, MAJ Kompier, and VH Hildebrandt: “Psychosocial factors at work and musculoskeletal disease: Scandinavian Journal of Work, Environment & Health, 1993; 19(5):297-312.
J-F Gehanno, K Takahashi, S Darmoni, and J Weber: “Citation classics in occupational medicine journals:” Scandinavian Journal of Work, Environment & Health, 33(4), 245-251, 2007
“Musculoskeletal Disorders and Workplace Factors: A Critical Review of Epidemiologic Evidence for Work-Related Musculoskeletal Disorders of the Neck, Upper Extremity, and Low Back.” NIOSH Publication No. 97-141
Pascale Carayon, Michael J. Smith, Maria C. Haims: “Work Organization, Job Stress, and Work-Related Musculoskeletal Disorders:” Human Factors, Vol. 41, 1999
Bongers PM, Kremer AM, ter Laak J: “Are psychosocial factors, risk factors for symptoms and signs of the shoulder, elbow, or hand/wrist?: A review of the epidemiological literature.” Am J Ind Med. 2002 May;41(5):315-42
Gareth Jones: “Psychosocial Factors May Increase Risk for Knee Pain” Ann Rheum Dis. August 25, 2006.
Fathallah, Fadi A.; Brogmus, George E.; Lim, Soo-Yee; Marras, William S.; Krawczyk, Sheila; Snook, Stover H.; Swanson, Naomi G.; Volinn, Ernest: “The Role of Psychosocial Factors in Occupational Musculoskeletal Disorders:” Human Factors and Ergonomics Society Annual Meeting Proceedings, Industrial Ergonomics , pp. 642-645(4)
This article originally appeared in The Ergonomics Report™ on 2008-11-12.