Disabling musculoskeletal pain in working populations: Is it the job, the person, or the culture?
aMedical Research Council Lifecourse Epidemiology Unit, University of Southampton, UK
bSchool of Nursing, University of São Paulo, São Paulo, Brazil
cCorporación para el Desarrollo de la Producción y el Medio Ambiente Laboral – IFA (Institute for the Development of Production and the Work Environment), Quito, Ecuador
dDepartment of Industrial Engineering, School of Engineering, Pontificia Universidad Javeriana, Bogotá, Colombia
eSouthwest Center for Occupational and Environmental Health, The University of Texas Health Science Center at Houston School of Public Health, Houston, Texas, USA
fCenter for Disease Control and Prevention/National Institute for Occupational Safety and Health, Atlanta, GA, USA
gMedical Research Council Social, Genetic and Developmental Psychiatry Centre, Institute of Psychiatry, Kings College, London, UK
hCenter for Research in Occupational Health (CiSAL), Universitat Pompeu Fabra, Barcelona, Spain
iCIBER of Epidemiology and Public Health, Barcelona, Spain
jOccupational Health Service, Parc de Salut MAR, Barcelona, Spain
kEpidemiology and Preventive Medicine Research Center, University of Insubria, Varese, Italy
lDepartment of Social Medicine, Medical School, University of Crete, Heraklion, Greece
mDepartment of Public Health, University of Tartu, Estonia
nDepartment of Environmental Health, Faculty of Health Sciences, American University of Beirut, Beirut, Lebanon
oDepartment of Occupational Health, Faculty of Health, Shahroud University of Medical Sciences, Shahroud, Iran
pDepartment of Community Health Sciences, Aga Khan University, Karachi, Pakistan
qDepartment of Medical Education and Health Sciences, Faculty of Medical Sciences, University of Sri Jayewardenepura, Gangodawila, Nugegoda, Sri Lanka
rClinical Research Centre for Occupational Musculoskeletal Disorders, Kanto Rosai Hospital, Kawasaki, Japan
sNational Institute for Occupational Health, National Health Laboratory Service, Johannesburg, South Africa
tFaculty of Health Sciences, University of Witwatersrand, Johannesburg, South Africa
uDepartment of Epidemiology and Preventive Medicine, School of Public Health and Preventive Medicine, Monash University, Melbourne, Victoria, Australia
vDepartment of Preventive and Social Medicine, University of Otago, Dunedin, New Zealand
wSchool of Nursing of Ribeirão Preto, University of São Paulo, São Paulo, Brazil
xFederal University of Paraná, Curitiba-PR, Brazil
yInstitute for Studies on Toxic Substances (IRET), National University of Costa Rica, Heredia, Costa Rica
zDepartment of Clinical Sciences and Community Health, Università degli Studi di Milano, Milan, Italy
aaFondazione Ca’ Granda Ospedale Maggiore Policlinico, Milan, Italy
abDepartment of Psychiatry, Medical School, University of Crete, Heraklion, Greece
acCentre for Research in Environmental Epidemiology (CREAL), Barcelona, Spain
adIMIM (Hospital del Mar Research Institute), Barcelona, Spain
aeNational School of Public Health, Athens, Greece
afNorth Estonia Medical Centre, Tallinn, Estonia
agPõlva Hospital, Põlva, Estonia
ahKlinikum Leverkusen, Leverkusen, Germany
aiDepartment of Physiology, Faculty of Medical Sciences, University of Sri Jayewardenepura, Gangodawila, Nugegoda, Sri Lanka
ajSection of Epidemiology and Biostatistics, School of Population Health, Faculty of Medical and Health Sciences, University of Auckland, New Zealand
akDepartment of Epidemiology, School of Public Health, University of Alabama at Birmingham, USA
alFaculty of Medicine, University of Kelaniya, Kelaniya, Sri Lanka
amDepartment of Joint Disease Research, University of Tokyo, Tokyo, Japan
anCentre for Occupational and Environmental Health, Department of Social and Preventive Medicine, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia
aoInjury Prevention Research Unit, Department of Preventive and Social Medicine, University of Otago, Dunedin, New Zealand
Received December 14, 2012; Revised February 11, 2013; Accepted February 19, 2013.
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Our study has demonstrated large variation among occupational groups internationally in the occurrence of disabling musculoskeletal illness. The variation applied even to groups carrying out similar occupational activities, and was only partially explained by the personal demographic, physical, and psychosocial risk factors examined. After allowance for personal risk factors, associations were found also with group awareness of others outside work with musculoskeletal pain, and for DWHP, with access to an occupational health service and adverse beliefs in the group about the prognosis of arm pain. However, even after these had been taken into account, there were still 8-fold differences in the prevalence of DWHP among occupational groups.
In comparisons of illness among countries, and particularly of subjective complaints, there is a possibility of bias because symptoms are understood differently in different languages and cultures. Thus, even with the care that we took in translation, the term “pain” may not have meant the same to all participants in our study. To reduce the potential for misinterpretation and bias, we focused on pain that made everyday activities difficult or impossible. Moreover, in some cases, large differences in prevalence were observed even among occupational groups from the same country who were questioned in the same language. For example, rates of DWHP in Brazilian office workers and nurses were some 15 times higher than those in other workers (sugar cane cutters) from Brazil. Thus, we do not think that the variation in reported pain prevalence can be explained simply by differences in the understanding of pain. The anatomical sites of interest were illustrated by diagrams, and are unlikely to have been misinterpreted systematically.
For practical reasons, it was necessary to administer the questionnaire by interview in some occupational groups (e.g., those with low literacy) and by self-completion in others (e.g., where they were geographically dispersed or their employers would not allow time for them to be interviewed). However, adjustment for the method by which questionnaires were answered did not materially alter our findings.
Another possible source of bias was the loss of subjects who declined to take part in the study. Although rates of participation were generally high, response rates in a few occupational groups were notably lower. However, exclusion of the 5 groups with response rates <50% did not significantly change the pattern of results.
Bias might also have arisen through differential healthy worker selection. If individuals with musculoskeletal disorders had been selected out of employment in some occupational groups because of their illness (or in some occupational groups were absent from work at the time when the study sample was recruited), spuriously low prevalence rates could have resulted. However, it seems highly unlikely that such selection would have occurred on a scale sufficient to explain the large differences in prevalence that were observed.
A further limitation was the relatively crude information that we obtained about occupational activities. Because of limited resources, we were unable to make detailed ergonomic assessments of working practices. If there were nondifferential errors in the ascertainment and characterisation of exposures, this would have tended to bias risk estimates towards the null, causing us to underestimate the contribution of physical activities to variations in prevalence among occupational groups. That said, observed differences in pain prevalence between nurses (who carried out more heavy lifting) and office workers (who carried out more work with computer keyboards) were much smaller than the differences among occupational groups carrying out similar activities in different countries (). Moreover, the variation in prevalence of DWHP that was unexplained after adjustment for measured risk factors did not appear to be related to occupational category. Thus, it seems unlikely that a more detailed and accurate assessment of individual activities would have accounted for substantially more of the variation among occupational groups.
Previous studies have also indicated major international variation in the prevalence of musculoskeletal pain [3,17]
. However, findings cannot be compared directly with ours because they do not relate to specific occupational groups, the countries studied were largely different from those in our investigation, and the definition of pain outcomes differed from that which we used. Moreover, these studies did not explore risk factors that might explain the variation.
The associations that were found with personal risk factors, both physical and psychosocial, were much as would have been expected from previous research, including some analyses based on data from individual countries in the CUPID study [2,10,16,21]
. Most notable was the elevated risk in people who tended to somatise, a finding that has been reported before, both for low back and wrist/hand pain, including in longitudinal studies in which somatising tendency predicted the future incidence and persistence of pain [12,19]
. It would not be surprising if people who tended to worry about other common somatic symptoms were also more aware of, and more likely to report, musculoskeletal complaints. Associations were also observed with adverse beliefs about the work-relatedness and prognosis of musculoskeletal pain, and in the case of DWHP, with awareness of RSI or equivalent terms (). However, these were weaker. The patterns of association with psychosocial risk factors were similar for DLBP and DWHP, suggesting that similar psychological mechanisms contribute to both forms of illness.
A cross-sectional survey such as ours cannot establish the extent to which observed associations are causal. It may be, for example, that part of the association between disabling pain and low mood occurred because living with pain is depressing (although longitudinal studies indicate that if this does occur then it is not the full explanation 
). Also, the presence of pain may make people more aware of, and more likely to report, occupational activities that are made difficult by the symptom. However, even with the assumption that all associations with personal risk factors were causal, those risk factors did not explain the major variation in pain prevalence among occupational groups. Furthermore, the persisting correlation between DWHP and DLBP after adjustment for personal risk factors () suggests that whatever was responsible for the variation applied similarly to both health outcomes.
A particular strength of our study was its capacity to examine group-level, cultural, and socioeconomic influences on disabling pain while adjusting for personal risk factors at an individual level. However, with a total of only 47 occupational groups, we were concerned not to use too many degrees of freedom when analysing group-level risk factors. Thus, we first examined each group-level risk factor separately, and in our final model, retained only those that showed statistically significant associations when examined independently. As well as socioeconomic variables such as unemployment rate and social security support for the unemployed, we defined some group-level risk factors according to the prevalence of individual characteristics within each occupational group. In one case (knowing someone outside work with back or arm pain) there was a danger that the responses of individuals with pain might be biased by their illness (i.e., the occurrence of similar pain in other people would be brought to their attention because of their own symptoms). Thus, the group prevalence would be a more reliable measure. In other cases, we speculated that the group prevalence might reflect an environment that had an influence over and above that of the same characteristic in the individual.
The association of disabling pain with group awareness of people outside work with musculoskeletal symptoms may have occurred because nonoccupational risk factors increased the prevalence of such symptoms both in the occupational group and in the wider community from which it was drawn. Another possibility is that greater awareness of musculoskeletal pain in a community predisposed workers to develop symptoms through a nocebo effect, similar to that which has been proposed for chronic whiplash injury 
. Against this, however, once account had been taken of the individual worker’s knowledge, DWHP was not related to group awareness of terms such as RSI.
The higher risk of DWHP where workers had access to an occupational health service may reflect a greater tendency to medicalise symptoms in these circumstances, especially if occupational health practitioners overstate the risks of musculoskeletal injury through work. However, it is also possible that in some cases occupational health services are engaged because of a high frequency of musculoskeletal disorders in a workforce.
Adjustment for significant group-level risk factors did reduce the differences in prevalence of DWHP among occupational groups, but fell a long way short of explaining the variation, which remained 8-fold. This indicates that there are other important determinants of common musculoskeletal complaints that were not adequately captured by the variables that we analysed.
Overall, our findings are consistent with the hypothesis that widespread awareness of musculoskeletal pain and adverse beliefs about it predispose to its occurrence in a workforce, but any such effect appears to be relatively small and did not account for major differences in prevalence that we observed. Nor could the variation be explained by well-established personal risk factors or by socioeconomic influences such as systems of compensation for work-related illness and injuries, and financial support for health-related incapacity for work.