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4
Epidemiologic Evidence
The panel's effort to evaluate the scientific basis for a relationship between work factors and musculoskeletal disorders of the back and upper extremities required comprehensive reviews of the epidemiologic literature. For each of the two anatomical regions, reviews of the physical and the psychosocial factors were undertaken. Referring back to Figure 1.2, the review of the epidemiologic evidence addresses several components. The workplace factors considered include all three main elements and their relationship to the person. The person is considered in terms of the several outcomes reported in these studies, while adjusting or stratifying for the individual factors that are relevant.
METHODS
Criteria for Selection and Review of Articles
In planning for this process, the panel set a number of criteria specific to the task of selecting articles for the epidemiology review:
-
Both the exposed and the nonexposed (or comparison) populations are clearly defined with explicit inclusion and exclusion criteria. It is evident why subjects who were studied were eligible and why those not studied were ineligible.
-
The participation rate was 70 percent or more.
-
Health outcomes relate to musculoskeletal disorders of the low back, neck, and upper extremities and were measured by well-defined criteria determined before the study. The health outcomes studied are carefully defined so that it is evident how an independent investigator
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-
The exposure measures are well defined. Self-report of exposure is acceptable so long as the method of collecting self-reports was well specified and there was evidence that the self-reports were reliable reflections of exposures. Job titles as surrogates for exposure were acceptable when the exposure of interest was inherent in the job (e.g., vibration exposure for those operating pneumatic chipping hammers).
-
The article was published in English.
-
The article was peer reviewed.
-
The study was done within the last 20 years (preferably).
could identify the same outcome in a different study population. Outcomes are measured either by objective means or by self-report. For self-reported outcomes, however, there are explicit criteria for how the data were collected and evidence that the collection method would permit another investigator to repeat the study in another population.
No specific limitations were placed on study designs acceptable for consideration. The advantages of prospective studies, however, were recognized. For example, there were sufficient prospective studies of low back pain to examine these separately among the studies of physical factors and exclusively among the studies of psychosocial factors.
Literature Search Methods
The literature reviews were conducted using computer-based bibliographic databases, with MEDLINE (National Library of Medicine, United States of America) a component of all searches. Additional databases included: NIOSHTIC (National Institute for Occupational Safety and Health, United States of America), HSELINE (Health and Safety Executive, United Kingdom), CISDOC (International Labour Organization, Switzerland), Ergoweb (Internet site of the University of Utah), Psychinfo, Oshrom, Ergonomics Abstracts, and ArbLine (National Institute for Working Life, Sweden).
The bibliographies of articles (particularly review articles) and the NIOSH comprehensive review (Bernard, 1997b) were examined to identify additional relevant articles.
Using these sources, a candidate list of articles was established and then systematically screened to determine which ones met the strict criteria, described above, for inclusion in the review. Each process reduced the list substantially. For physical work factors studied in association with back disorders, 255 studies were initially identified as relevant and 41 met the selection criteria and were reviewed. For psychophysical factors and back disorders, the search resulted in 975 references, which were then reduced to 21 work-related risk factor studies and 29 individual risk factor studies. For work-related physical factors and upper extremity disor-
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ders, the initial list of 265 references was reduced to 13 that provided direct and 29 that provided indirect measures of exposure. For psychophysical factors and upper extremity disorders, the initial 120 references were reduced to 28.
Analysis of Study Results
Definition of Measures: Relative Risks
In epidemiology, the relative risk is a measure of the strength of an association, here meaning the relationship between the frequency of an exposure and the occurrence of an outcome (e.g., amount of vibration and incidence of back pain). Because human populations typically have a variety of exposures occurring in near proximity, relative risk is typically measured as the incidence of disease in the exposed (e.g., helicopter pilots who experience vibration) and the incidence of disease in the unexposed (similar people, like ground crews, who are considered to share nearly the same other exposures as the exposed, such as recreational activities, diet, and living conditions). The ratio of incidence provides a measure of association, and the higher this ratio of incidences (the relative risk), the stronger the association, the more confidence we can place in a conclusion that the association is meaningful.
Because incidence is a rate calculated by following people over time, and many studies are cross-sectional or retrospective (case-control), other measures, such as the prevalence ratio and the odds ratio, have been developed to summarize the association between exposure and outcomes for these other study designs. Our analysis focused on associations expressed by such risk estimates as the odds ratio and the relative risk. These estimates were retrieved from the original article or calculated when sufficient raw data were presented.
Definition of Measure: Attributable Risk
The attributable risk is another measure used to help generate inferences. In its simplest form, it is the difference between the incidence in those exposed and those unexposed—a risk difference. This risk difference is thought of as the attributable risk in that, in theory, removing this exposure entirely would reduce the frequency of the outcome to the level of those who are unexposed. Rotham and Greenland (1998a, 1998b) discuss some of the limitations of this simple assumption. Attributable risk is often calculated as a ratio rather than a difference: risk in the exposed is divided by risk in the unexposed, producing an attributable fraction. The attributable fraction is the proportion by which the rate of the outcome
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among the exposed would be reduced if the exposure were eliminated. This fraction is calculated as the ratio of (RR − 1)/RR, where RR is the relative risk or the prevalence ratio of risk in the exposed compared with the unexposed:
AF e = (RR − 1)/RR
The attributable fraction helps scientists and policy makers recognize that in many cases a variety of factors contribute to the total incidence of a disease or other outcome, so that removal of an exposure typically does not reduce the outcome rate to zero. However, in its simplest form, the attributable risk is a measure that suggests that if the offending exposure were removed (by intervention or regulation), then the amount of disease outcomes would be estimated to be reduced by the calculated amount. As is noted below, this simple summary is enmeshed in caveats.
It is important to recognize in this calculation that the result depends on what is included. That is, if one considers a calculation of one factor as it relates to an outcome and then performs a separate calculation for another factor for the same outcome, there is overlapping (correlation) between factors that could make the sum of the two separate factors sum to more than 100 percent. Attributable fraction, then, represents a crude but important estimation of the impact of control of risk factors. An estimate of the attributable fraction for a multifactorial disease such as a musculoskeletal disorder provides only an estimate of the relative importance of the various factors studied. It is not, and cannot be, considered a direct estimate of the proportion of the disease in the population that would be eliminated if only this single factor were removed (Rotham and Greenland, 1998a). Rather it provides guidance to the relative importance of exposure reduction in those settings in which the exposure under study is prevalent. Consequently, we have not attempted to rank or further interpret the findings for attributable fractions and have chosen only to report them as a rough guide to the relative importance of the factors in the study settings in which they have been examined.
In this review, the relative risk in longitudinal studies and the prevalence or odds ratio in cross-sectional surveys were used to calculate the attributable fraction for the risk factors studied. For example, if workers exposed to frequent bending and twisting have a prevalence of low back pain that is 3 times that of those not exposed, then among the exposed the attributable fraction will be:
AF e = (3 − 1)/3 = 0.67
By this hypothetical calculation, 67 percent of low back pain in the exposed group could be prevented by eliminating work that requires bending and twisting.
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Confounding
None of the musculoskeletal disorders examined in this report is uniquely caused by work exposures. They are what the World Health Organization calls work-related conditions. “Work-related diseases may be partially caused by adverse working conditions. They may be aggravated, accelerated, or exacerbated by workplace exposures, and they may impair working capacity. Personal characteristics and other environmental and socio-cultural factors usually play a role as risk factors in work-related diseases, which are often more common than occupational diseases” (World Health Organization, 1985).
In Chapter 3 we note that the epidemiologic study of causes related to health outcomes such as musculoskeletal disorders requires careful attention to the several factors associated with the outcome. The objective of a study will determine which factor or factors are the focus and which factors might “confound” the association. In the case of musculoskeletal disorders, a study may have as its objective the investigation of individual risk factors. Such a study, however, cannot evaluate individual risk factors effectively if it does not also consider relevant work exposures; the work exposures are potential confounders of the association with individual risk factors. Conversely, a study that evaluates work exposures cannot effectively evaluate these factors if it does not also consider relevant individual risk factors; the individual risk factors are potential confounders of the association with work exposures.
Therefore, when studying the relationship of musculoskeletal disorders to work, it is necessary to consider the other known factors that cause or modify the likelihood that the disorder will occur, such as individual factors and nonwork exposures. For example, the frequency of many musculoskeletal disorders is a function of age, so age has to be taken into account before attributing a musculoskeletal disorder to a work exposure. Another common concern is whether a recreational exposure accounts for an outcome that otherwise might be attributed to work.
In every epidemiologic study, confounders need to be measured and, when relevant, included in the data analysis. The confounders selected for consideration in the analysis of data from a specific study depend on the types of exposures studied, the types of outcomes measured, and the detail on potential confounders that can be accurately collected on a sufficient number of the study subjects. As a consequence, our approach to reviewing epidemiologic studies of work and musculoskeletal disorders documented the attention given to a wide range of potential confounders (see the panel's abstract form in Box 4.1). No study can measure every possible confounder; however, the papers included by the panel were judged to have given adequate attention to the primary individual factors
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BOX 4.1 Individual Factors Considered in Analyses Form Used in Describing Studies Included in the Review
|
that might have confounded the work exposures under study. These include in particular age and gender, as well as, when necessary and possible, such factors as obesity, cigarette smoking, and comorbid states.
The role of potential confounders in epidemiologic studies and their proper management is often confusing to the nonepidemiologist. The difficulty stems from the fact that the potential confounder is often known to be associated with the disease, in this case musculoskeletal disorders. The association of a risk factor such as age with the disease, however, does not make it a true confounder of the study's examination of a separate risk
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factor such as work exposures. True confounding occurs only when, for example, both the risk factors being studied (age and work exposures) are associated with the outcome (musculoskeletal disorders) and the two risk factors are also correlated (for example, those with more work exposure are also older). Fortunately, as noted in Chapter 3, there are statistical methods available to manage confounding that provide a way to “separate,” in this example, the effects of the work exposure from the effects of age.
The panel recognizes that a number of nonwork factors are associated with or also cause the musculoskeletal disorders under study. These were not separately studied, but they were considered, as necessary, to evaluate the significance of the work factors that were studied. In our judgment, it is evident that confounding alone is highly unlikely to explain the associations of musculoskeletal disorders with work that are noted. More detailed consideration of confounding in future studies, however, should further improve the precision and accuracy of risk estimates.
Measures of Workplace Exposures
Physical Exposures
The measures of physical exposures investigated include force, repetition, posture, vibration, and temperature. Available approaches to estimating exposure to these physical stressors include worker self-report, bioinstrumentation, and direct observation. The optimal choice among methods depends on characteristics of the methods as well as of the jobs under study. Job exposure can be considered a weighted sum of the different task-specific exposures that make up the job, with weights coming from task distributions (Winkel and Mathiassen, 1994). Each of two components—exposures in each task and the relative frequency of each task—must be estimated. Workers with the same job title may have different exposure levels because of between-worker variability in either the duration and distribution of tasks within jobs or the exposures within tasks. Furthermore, job title may indicate homogenous exposure groups for some stressors, such as repetitiveness and force demands, while other features such as posture may vary widely among workers in the same job (e.g., Punnett and Keyserling, 1987; Silverstein, Fine, and Armstrong, 1987). In highly routinized or cyclical work, such as that at a machine-paced assembly line, without job rotation there is only one task, the short duration and regularity of which make the exposure determination a relatively simple problem. In contrast, in nonroutinized work, such as construction and maintenance, determination of task distributions over an extended period of time may be a more difficult undertaking. As jobs
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become less routinized, i.e., less predictably structured, valid estimation of both task distributions and task-specific exposures becomes increasingly challenging.
Typically, both observational and direct measurement techniques generate highly detailed, accurate exposure analyses for a relatively short period of elapsed time in each job. Most protocols for these methods assume that the work is cyclical, with little variability over time, so that it is reasonable to measure exposures for a short period and extrapolate them to the long term. But many jobs do not fit this model: they are not comprised of work cycles, or the cycles are highly variable in their total duration or content (the number or sequence of steps that comprise each cycle) and do not account for all of the work performed by an individual with any given job title. For these jobs, it would be infeasible to undertake continuous measurements for entire cycles as an exposure assessment strategy, because either there are no cycles, or a very large number of (long) cycles would have to be recorded in order to quantify accurately the total and average duration of exposures. With short measuring times, the data collected are of uncertain representativeness because these time periods do not match the duration of exposures that are thought to be relevant to musculoskeletal disorder development.
A versatile alternative for estimating physical exposures is the use of data collected directly from workers. Such reports may address both task-specific exposures within jobs and the distributions of tasks performed by each worker. In addition to being time-efficient, self-reports permit assessment of exposures in the past as well as the present and may be structured with task-specific questions or organized to cover the job as a whole. Some researchers have explicitly recommended a composite approach to the analysis of nonroutine jobs, in which task-specific exposures are measured directly and the temporal distribution (frequency and duration) of each task is obtained from self-report. Self-reported data can take various forms, including duration, frequency, and intensity of exposure. In some studies, absolute ratings have agreed well with observations or direct measurements of the corresponding exposures, while others have diverged significantly, especially with use of continuous estimates or responses that required choices among a large number of categories (e.g., Burdorf and Laan, 1991; Faucett and Rempel, 1996; Lindström, Öhlund, and Nachemson, 1994; Rossignol and Baetz, 1987; Torgén et al., 1999; Viikari-Juntura, 1996; Wiktorin et al., 1993).
Retrospective recall of occupational exposures has been frequently employed in studies of musculoskeletal disorders, but there are few data on the reproducibility of such information. Three studies have examined the potential for differential error (i.e., information bias) in self-reported exposure with respect to musculoskeletal disorders with mixed results;
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some risk estimates were biased away from the null value, some toward it, and others not at all (Torgén et al., 1999; Viikari-Juntura, 1996; Wiktorin et al., 1993). In the REBUS1 study follow-up population, Toomingas et al. (1997a) found no evidence that individual subjects systematically over-rated or underrated either exposures or symptoms in the same direction. Self-reported exposures have promise, but their validity depends on the specific design of the questions and response categories.
A variety of instrumentation methods exist for direct measurement of such dimensions as muscle force exertion (electromyography), joint angles and motion frequency (e.g., electrogoniometry), and vibration (accelerometers). For example, the goniometer has been used in a variety of studies of wrist posture, including field assessments of ergonomic risk factors (Moore, Wells, and Ranney, 1991; Wells et al., 1994), comparisons of keyboard designs (Smutz, Serina, and Rempel, 1994), and clinical trials (Ojima et al., 1991). Hansson et al. (1996) evaluated the goniometer for use in epidemiologic studies, and Marras developed a device for measuring the complex motion of the spine (Marras, 1992). While many consider these methods to represent collectively the standard for specific exposures, each instrument measures only one exposure, and usually only at one body part. When multiple exposures are present simultaneously and must be assessed at multiple body parts, the time required to perform instrumented analyses on each subject may limit their applicability to epidemiologic research (Kilbom, 1994). Another practical concern is the potential invasiveness that may interfere with job performance, alter work practices, or reduce worker cooperation. Thus, there is a trade-off between the precision of bioinstrumentation and the time efficiency and flexibility of visual observation and worker self-report. As discussed in Chapter 6, gross categorical exposure measures (e.g., >10 kg versus < 10 kg) used in epidemiologic studies may limit the possibility of observing an exposure-risk relationship; a continuous measure based on bioinstrumentation might make such a relationship more apparent. Thus, their high accuracy (for the period of measurement) gives these methods utility for validating other methods on population subsets and added value when they can be applied in epidemiologic studies.
A large number of observational methods for ergonomic job analysis have been proposed in the last two decades (see Kilbom, 1994). These
1In the original REBUS study conducted in 1969, participants were asked to complete a questionnaire regarding health status—all selected were given a medical examination. A diagnosis of musculoskeletal disorder required signs and symptoms. The follow-up study, conducted in 1993, asked the younger participants in the original REBUS study to participate in a reexamination.
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include checklists and similar qualitative approaches to identify peak stressors (e.g., Keyserling et al., 1993; Stetson et al., 1991). The limitation with checklists is that they provide little information beyond the presence or absence of an exposure, with a possibly crude estimate of the exposure duration. The qualitative approaches are not likely to provide sufficient detail to effectively assess exposure for epidemiologic studies.
The most common observational techniques used to characterize ergonomic exposures are based on either time study or work sampling. Both of these techniques require a trained observer to characterize the ergonomic stressors. Methods based on time study (e.g., Armstrong et al., 1982; Keyserling, 1986) are usually used to create a continuous or semicontinuous description of posture and, occasionally, force level. Therefore, changes in the exposure level, as well as the proportion of time a worker is at a given level, may be estimated. Because methods based on time study tend to be very time intensive, they are better suited to work with fairly short and easily definable work cycles. A different approach, work sampling, involves observation of worker(s) at either random or fixed, usually infrequent, time intervals and is more appropriate for nonrepetitive work (e.g., Karhu, Hansi, and Kuorinka, 1977; Buchholz et al., 1996). Observations during work sampling provide estimates of the proportion of time that workers are exposed to various stressors, although the sequence of events is lost. Though less time intensive than time study, work sampling still requires too much time for use in an epidemiologic study, especially one that employs individual measures of exposure.
There are also a few highly detailed, easily used observational analyses for use as an exposure assessment tool in an epidemiologic study. These methods employ subjective ratings made by expert observers. For example, Rodgers (1988, 1992) has developed methods based on physiological limits of exposure that rate effort level, duration, and frequency. The method developed by Moore and Garg (1995) employs ratings similar to those of Rodgers and adds posture and speed of work ratings. Moore and Garg's strain index is designed to estimate strain for the distal upper extremity. It is the weighted product of six factors placed on a common five-point scale (subjective ratings of force, hand/wrist posture, and speed of work and measurement of duration of exertion, frequency of exertion, and duration of task per day). The strain index is a single priority score designed to represent risk for upper extremity musculoskeletal disorders and is conceptually similar to the lift index for low back disorders. The lift index was developed as part of the revised NIOSH lifting equation (Waters et al., 1993) and is the ratio of the load lifted and the recommended weight limit.
Recently, Latko et al. (1997) developed a method employing visual analog scales for expert rating of hand activity level (called HAL). The
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method has also been generalized to assessment of other physical stressors, including force, posture, and contact stress (Latko et al., 1997, 1999). The HAL employs five verbal anchors, so that observers can rate the stressors reliably. In an evaluation, a team of expert observers comes to a consensus on ratings for individual jobs. These ratings correlated well with two quantitative measures, recovery time/cycle and exertions/second, and are found to be reliable when compared with ratings of the same jobs 1.5 to 2 years later (Latko et al., 1997).
In sum, there are many methods for assessment of ergonomic exposures. The challenge for ergonomists and epidemiologists is to determine a method of characterizing level of exposure that is efficient enough to permit analysis of intersubject and intrasubject variability across hundreds of subjects and that can also produce exposure data at the level of detail needed to examine etiologic relationships with musculoskeletal disease. The HAL, as developed by Latko, is easy to apply and has proven to be predictive of the prevalence of upper extremity musculoskeletal disorders in cross-sectional studies.
Psychosocial Exposures
Measures of psychosocial exposures reported in the literature are obtained through the use of various self-report surveys. These surveys are typically presented to subjects in a paper format in which the subject is requested to complete a series of questions. These survey tools typically comprise multiple scales used to assess psychosocial risk factors. Many of these measures assess the construct of interest using a continuous scale of measurement, by which it is possible to provide a measure of exposure in terms of degree, and not simply whether it was present or absent. Response items vary depending on the scale and typically range from 0-5, 0-7, or 0-10, with options anchored so that the respondent has a frame of reference for various responses.
Some measures are standardized, well-developed, self-report tools whose psychometric properties (reliability and validity) have been established based on past research, while other items or scales were developed for the purposes of a single study. Currently, all scales used are self-report. Depending on the length of the survey, the time to completion can range from 10 minutes to several hours. It is rare that the perceptions reported by the respondent are corroborated by an independent assessment tool or process (e.g., supervisor or coworker evaluations or direct observation of a workplace). Although it can be helpful to assess such independently collected information to support workers' reports of their sense or opinions of their environments, perceptions are, by their nature, best collected through self-report.
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The most common work-related psychosocial constructs measured in the epidemiologic literature include: job satisfaction, mentally demanding work, monotony, relationships at work that include coworker and supervisor support, daily problems at work, job pressure, hours under deadline per week, limited control over work, job insecurity, and psychological workload (a composite of a number of subitems that include stress at work, workload, extent of feeling tired, feeling exhausted after work, rest break opportunities, and mental strain).
The Job Content Questionnaire (JCQ) is an example of a workplace psychosocial measure whose measurement properties are well defined; it has been used frequently in the psychosocial epidemiology literature. The JCQ comprises three key measures of job characteristics: mental workload (psychological job demands), decision latitude, and social support (Karasek, 1985). Decision latitude is based on the worker's decision authority and the worker's discretion over skill use—that is, the worker's ability to control the work process and to decide which skills to utilize to accomplish the job. Psychological job demands reflect both physical pace of work and time pressure in processing or responding to information. In the Karasek and Theorell model (1990), high psychological job demands in combination with low decision latitude result in residual job strain and, over time, chronic adverse health effects. The JCQ, as an instrument for measuring such strain, has been shown to be highly reliable and has been validated as a predictor, in numerous countries and industrial sectors, of increased risk of cardiovascular morbidity (Karasek and Theorell, 1990; Karasek et al., 1998; Kawakami et al., 1995; Kawakami and Fujigaki, 1996; Kristensen, 1996; Schwartz, Pickering, and Landsbergis, 1996; Theorell, 1996).
Measures of Musculoskeletal Disorder Outcomes
The epidemiologic literature on the relationship between exposure to physical and psychosocial risk factors and the development of musculoskeletal disorders in the workplace focuses on four major types of outcome. Two outcomes rely on patient self-report (symptoms and work status), and two rely on sources independent of the patient (evaluation by a clinician and review of workplace or insurance records). Table 4.1 summarizes the outcomes assessed in 132 epidemiologic studies. These do not include the 29 upper extremity studies that provided indirect measures of exposure.
Self-report symptom measures were the most common outcome, with 61 studies assessing presence of symptoms (usually nonstandardized ques-
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Self-Report Symptoms |
Self-Report Work Status |
Clinical Evaluationa |
Records |
||||||||||
Risk Factor and Body Region |
Number of Studies |
Present |
Severityb |
Disability |
Sick Days |
Return to Work |
Visit Only |
Physical Exam |
Tests |
Claim |
Sick Days |
Return to Work |
|
Psychosocial—back |
|||||||||||||
• Work-related factors (longitudinal) |
21 |
6 |
5 |
2 |
2 |
4 |
2 |
3 |
4 |
1 |
|||
• Individual factors (longitudinal; not including studies above) |
29 |
9 |
8 |
6 |
2 |
6 |
1 |
1 |
1 |
||||
Psychosocial—upper extremities |
|||||||||||||
• All factors (cross-sectional) |
25 |
13 |
6 |
1 |
8 |
||||||||
• All factors (longitudinal) |
3 |
1 |
2 |
||||||||||
Physical—back |
|||||||||||||
• Workers only (cross-sectional) |
21 |
21 |
|||||||||||
• Community (cross-sectional) |
9 |
7 |
1 |
1 |
|||||||||
• Workers (longitudinal) |
7 |
2 |
4 |
1 |
|||||||||
• Workers (case-control) |
4 |
1 |
1 |
2 |
|||||||||
Physical—upper extremities |
|||||||||||||
• Workers (cross-sectional) |
13 |
2 |
7 |
4 |
|||||||||
Totalc |
132 |
61 |
19 |
9 |
4 |
10 |
3 |
22 |
4 |
9 |
5 |
2 |
aStudies are counted only once regarding clinical evaluation; some studies simply noted that a clinical visit occurred; some further specified that a physical examination was performed; and some also noted that diagnostic tests were done.
bSeverity usually measured with standardized pain or symptom severity measure.
cThe total number of specific outcomes exceeds the number of studies (i.e., 132), since some studies assessed multiple outcomes.
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tionnaires asking about prevalence or incidence), 19 studies assessing symptom severity (often with standardized pain and symptom questionnaires), and 9 studies assessing symptom-related disability. A total of 14 studies assessed the self-reported effect of the musculoskeletal disorder on work status, either as number of sick days (n = 4) or return (or nonreturn) to work (n = 14). Formal clinical evaluation constituted an outcome in 29 studies, most of which relied on a physical examination by a physician or other health care professional (e.g., physical therapist). Diagnostic tests such as X-rays or nerve conduction studies were a standard outcome in only a few studies. Information obtained from records constituted an outcome in 16 studies, including claims data, sick days, or return to work. The predominance of symptoms as an outcome is inherent in the nature of musculoskeletal disorders, which are primarily defined by pain or other symptoms. Indeed, the results of physical examination and diagnostic tests may be normal in a large proportion of individuals with musculoskeletal disorders.
There were a greater number of high-quality studies related to back pain than to upper extremity musculoskeletal disorders. More of the back pain studies were longitudinal rather than cross-sectional, providing stronger evidence for a potentially causal relationship between particular risk factors and back disorders. A greater proportion of upper extremity musculoskeletal disorder studies used clinical evaluation as an outcome.
RESULTS
Work-Related Physical Factors
Back Disorders
The scientific literature on work-related back disorders was reviewed to identify those risk factors of physical load that are consistently shown to be associated with back disorders and to determine the strength of their associations. A total of 43 publications were selected that provided quantitative information on associations between physical load at work and the occurrence of back disorders. These risk factors were found significant in almost all of the studies: lifting and/or carrying of loads in 24 of the 28 in which it was studied, whole-body vibration in 16 of the 17, frequent bending and twisting in 15 of the 17, and heavy physical work in all 8 in which this factor was studied. The following significant findings are summarized from these studies: for lifting and/or carrying of loads, risk estimates varied from 1.1 to 3.5, and attributable fractions were between 11 and 66 percent; for whole-body vibration, risk estimates varied from 1.3 to 9.0, with attributable fractions between 18 and 80 percent; for frequent bending and twisting, risk estimates ranged from 1.3 to 8.1, with attributable fractions between 19 and 57 percent; and for heavy physical
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work, risk estimates varied from 1.5 to 3.7, with attributable fractions between 31 and 58 percent. Appendix Table 4.1, Appendix Table 4.2, Appendix Table 4.3 to Appendix Table 4.4 provide the detailed findings in the 43 publications selected in this review. Three publications are not included in these tables because they did not present any significant association (Hansen, 1982; Lau et al., 1995; Riihimäki et al., 1994).
The evidence on static work postures and repetitive movements is not consistent. The characteristics of the studies have some impact on the magnitude of the risk estimate, but these characteristics do not explain the presence or absence of an association. Table 4.2 provides a compilation of results from all studies in terms of the importance of each general type of exposure.
Study designs affect these findings. Studies with small samples tend to have higher risk estimates, which may be an indication of publication bias. Due to power considerations, in smaller studies the effect of a risk factor needs to be larger in order to reach the level of statistical significance. Hence, the evaluation of the magnitude of a particular risk factor should take into account the sample size.
Case-control studies (Appendix Table 4.4) reported higher risk estimates than cross-sectional studies (Appendix Table 4.1 and Appendix Table 4.2) for manual material handling and frequent bending and twisting. An expla-
Risk Estimate |
||||||
Null Associationa |
Positive Association |
Attributable Fraction (%) |
||||
Work-Related Risk Factor |
n |
Range |
n |
Range |
n |
Range |
Manual material handling |
4 |
0.90-1.45 |
24 |
1.12-3.54 |
17 |
11-66 |
Frequent bending and twisting |
2 |
1.08-1.30 |
15 |
1.29-8.09 |
8 |
19-57 |
Heavy physical load |
0 |
8 |
1.54-3.71 |
5 |
31-58 |
|
Static work posture |
3 |
0.80-0.97 |
3 |
1.30-3.29 |
3 |
14-32 |
Repetitive movements |
2 |
0.98-1.20 |
1 |
1.97 |
1 |
41 |
Whole-body vibration |
1 |
1.10 |
16 |
1.26-9.00 |
11 |
18-80 |
aConfidence intervals of the risk estimates included the null estimate (1.0). In only 12 of 16 null associations was the magnitude of the risk estimate presented.
NOTES: n = number of associations presented in epidemiologic studies. Details on studies are presented in Appendix Table 4.1, Appendix Table 4.2, Appendix Table 4.3 through Appendix Table 4.4.
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nation may be that in case-control study design, recall bias (by subjects of exposure) is stronger than in cross-sectional studies, since there was usually a long period between exposure and recall. However, the case-control study with the highest risk estimate was based on observations at the workplace.
In general, risk estimates in community-based surveys ( Appendix Table 4.2) were smaller than those in cross-sectional studies in occupational populations ( Appendix Table 4.1). A reasonable explanation is that contrast in exposure is less in community-based studies that survey a large variety of jobs. In various cross-sectional studies, contrast in exposure has played a role in the selection of subjects.
Multivariate analyses with more than two confounders showed smaller risk estimates (see, for example, the longitudinal study by Smedley et al., 1997) than statistical analyses with just one or two confounders (see, for example, the longitudinal studies by Gardner, Landsittel, and Nelson, 1999; Kraus et al., 1997; Strobbe et al., 1988; and Venning, Walter, and Stitt, 1987). For lifting as a risk factor, this difference was statistically significant, with average risks of 1.42 and 2.14. Most studies have adjusted only for a limited number of potential confounders.
In addition to study design issues, some of the differences in findings appear related to the different ways exposure was measured. For manual material handling, the 7 studies with observations and direct measurements showed a significantly higher risk estimate than the 21 studies based on questionnaires, with average risk estimates of 2.42 and 1.86, respectively. This finding may be explained by larger misclassification of exposure in questionnaire studies, or by larger contrast in exposure in studies that used actual workplace surveys to determine exposure levels. In general, questionnaire studies showed associations between physical load and back disorders similar to those shown in studies that represented much more detailed exposure characterization. Therefore, the information from these questionnaire studies provides useful corroborating evidence.
The magnitude of the risk estimate could not be evaluated in relation to the contrast in exposure, since exposure parameters were not very comparable. Some studies have used reference groups (low exposure) that may nonetheless have had measurable exposures to physical load in other studies.
This review concludes that there is a clear relationship between back disorders and physical load imposed by manual material handling, frequent bending and twisting, physically heavy work, and whole-body vibration. Although much remains to be learned about exposure-outcome relationships (see Chapter 3), the epidemiologic evidence presented sug-
Page 101
gests that preventive measures may reduce the exposure to these risk factors and decrease the occurrence of back disorders (see Chapter 6). However, the epidemiologic evidence itself is not specific enough to provide detailed, quantitative guidelines for design of the workplace, job, or task. This lack of specificity results from the absence of exposure measurements on a continuous scale, as opposed to the more commonly used dichotomous (yes/no) approach. Without continuous measures, it is not possible to state the “levels” of exposure associated with increased risk of low back pain.
Upper Extremity Disorders
A variety of disorders of the upper extremity were studied in the selected literature. Primary among these was carpal tunnel syndrome, identified by symptoms and physical examination alone or in combination with nerve conduction testing. A second important outcome was hand-arm vibration syndrome (Raynaud's disease or other vibration-related conditions of the hand). There were also a number of operationally defined but less well-specified outcomes (defined for epidemiologic, not clinical, purposes) such as musculoskeletal disorders of the wrist, tendinitis, and bone- or joint-related abnormalities. Studies that met the most stringent criteria were not based on self-report alone. The anatomical areas with the greatest number of studies were the hand and the wrist, although a number of studies focused more generally on the upper extremities. Although a number of studies of the neck/shoulder region were considered, only two were included. The neck, shoulders, and upper arms operate as a functional unit, which makes it difficult to estimate specific exposure factors for the neck/shoulder region at a level beyond that of job or job tasks. Further complicating study of the region is the fact that most of the reported musculoskeletal problems of this region are nonspecific, without well-defined clinical diagnoses.
Table 4.3 provides a compilation of point estimates of risk from all studies across the major types of work-related physical exposure that were studied. Appendix Table 4.5 presents the risk ratios for various exposures; these ratios cover a very wide range (2 to 84), depending on how specifically the exposure and the outcome were defined. With the exception of the few studies of bone- and joint-related abnormalities, most of the results demonstrate a significant positive association between upper extremity musculoskeletal disorders and exposure to repetitive tasks, forceful tasks, the combination of repetition and force, and the combination of repetition and cold. A number of good studies demonstrated that there is also an important role for vibration.
There were 9 studies in which carpal tunnel syndrome was defined
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Risk Estimate |
||||||
Null Associationa |
Positive Association |
Attributable Fraction (%) |
||||
Work-Related Risk Factor |
n |
Range |
n |
Range |
n |
Range |
Manual material handling |
4 |
0.90-1.45 |
24 |
1.12-3.54 |
17 |
11-66 |
Repetition |
4 |
2.7-3.3 |
4 |
2.3-8.8 |
3 |
53-71 |
Force |
1 |
1.8 |
2 |
5.2-9.0 |
1 |
78 |
Repetition and force |
0 |
- |
2 |
15.5-29.1 |
2 |
88-93 |
Repetition and cold |
0 |
- |
1 |
9.4 |
1 |
89 |
Vibration |
6 |
0.4-2.7 |
26 |
2.6-84.5 |
15 |
44-95 |
aConfidence intervals of the risk estimates included the null estimate (1.0).
NOTES: n = number of associations presented in epidemiologic studies. Details on studies are presented in Appendix Table 4.5.
by a combination of a history of symptoms and physical examination or nerve conduction testing ( Appendix Table 4.5 and Appendix Table 4.6). In these studies, there were 18 estimates of risk based on various specificities of carpal tunnel syndrome diagnosis and varying degrees of work exposure. Of these, 12 showed significant odds ratios greater than 2.0 (range 2.3 to 39.8), 4 showed non-significant odds ratios of greater than 2.0 and 2 showed non-significant odds ratios between 1.7 and 2.0. These findings were supported when less specific outcomes were examined. In most instances (8 out of 10), conditions classified as “wrist cumulative trauma disorders” or “nonspecific upper extremity musculoskeletal disorders” were found to be significantly associated with work-related physical risk factors with a similar range of elevated risk. Hand-arm vibration syndrome and other vibration disorders were significantly associated with vibration exposures in 12 of 13 studies, with risk elevated 2.6 to 84.5 times that of nonexposed or low-exposed comparison workers.
It should be noted that the majority of studies were cross-sectional. Therefore, it is important to consider the temporal direction of the findings. It is likely that the occurrence of upper extremity symptoms or disorders contributes to increased work-related and nonwork-related stress. If this is the case and a reciprocal relationship exists, it does not preclude the need to reduce the impact of stress (as either cause or consequence) on
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these disorders, given the potential health effects of repeated or prolonged stress. A second limitation in cross-sectional studies is the healthy-worker effect. This effect refers to the observation that healthy workers tend to stay in the workforce, and unhealthy workers tend to leave it. Those who may have left the workforce due to the health condition being studied will be absent from the study group, resulting in an underestimation of an effect if one is present.
The findings from the studies reviewed indicate that repetition, force, and vibration are particularly important work-related factors associated with the occurrence of symptoms and disorders in the upper extremities. Although these findings are limited by the cross-sectional nature of the research designs, the role of these physical factors is well supported by a number of other studies in which exposure assessment was less specific ( Appendix Table 4.6). Despite indirect objective exposure information, the jobs studied appeared to represent conspicuously contrasting ergonomic exposures. These articles were not used to estimate exposure-response relationships for specific physical hazards (e.g., repetition, force, and posture), but they do provide a foundation for demonstrating a hazard ( Appendix Table 4.6). Only three studies included in the review examined the effects of computer keyboard work (Bernard et al., 1994; Murata et al., 1996; Sauter, Schleiffer, and Knutson, 1991). In two, significant associations were found with pain or discomfort in the upper extremity, and the third found association with slowed median nerve velocity in subclinical carpal tunnel syndrome.
The attributable fractions related to the physical risk factors that were found to be important provide additional useful information. They suggest that, when present, each of the physical factors listed in Table 4.3 is an important contributor to upper extremity disorders. The studies for which attributable fractions are reported explored associations primarily with hand/wrist disorders such as carpal tunnel syndrome and hand-arm vibration syndrome. Study of these physical factors in each of the other upper extremity disorders is indicated to further explore how strong an influence these same factors might have specifically on the other disorders. Even given the limitations on generalizing from specific studies, the estimates suggest that substantial benefit could result from reducing the most severe of these physical risk factors ( Table 4.3 and Appendix Table 4.5).
As with other epidemiology study reviews, there are limitations in the available literature. Characterization of exposure with sufficient specification to segregate and adequately describe exposure to the different physical factors for such regions as the neck/shoulder area provides an important example. Literature reviews by Anderson (1984), Hagberg and Wegman (1987), Sommerich, McGlothlin, and Marras (1993), Bernard
Page 104
(1997a), and Ariens et al. (2000) provide support for the view that physical work factors are associated with neck and shoulder musculoskeletal disorders. Had the review of the literature presented in this chapter been less restrictive regarding study specifications of exposure, it is likely that much stronger conclusions would have been drawn for each of the upper extremity musculoskeletal disorders. Our review, along with the substantial literature that has used less well-specified exposures, demonstrates the high priority to be placed on developing better exposure measures for study of the neck/shoulder as well as the other upper extremity disorders.
An equally important need is for more prospective studies to address individual physical risk factors and their combination as these relate to each of the upper extremity musculoskeletal disorders. The cross-sectional findings demonstrating a strong interaction between repetition and force and between repetition and cold indicate combinations that should be priorities for future study. Given the findings on work-related psychosocial risk factors and upper extremity disorders (see below), it will be particularly important to carry out studies that examine the combined effects of physical and psychosocial factors.
Psychosocial Factors
Psychosocial risk factors for work-related musculoskeletal disorders can be separated into two major categories: those that are truly specific to the workplace (job satisfaction, poor social support at work, work pace, etc.) and those that are individual psychosocial factors (such as depression). Both types of factors are important to review for several reasons. First, there is an abundance of literature regarding the relationship between both types, particularly for back pain. Second, individual psychosocial factors such as depression are typically present both at work and outside it, making it nearly impossible to distinguish which aspects of depression are work-related and which nonwork-related. As a result, we summarize the literature on both types of risk factors, describing each separately. For research on back pain, separate tables are provided. For upper extremity disorders, fewer studies examining individual psychosocial factors were identified. Therefore, the two types of risk factors are distinguished but included in the same table.
Back Disorders
Work-Related Psychosocial Factors
A relatively large number of work-related psychosocial factors have been suggested as related to back pain and the resultant disability. These
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range from general conceptualizations, such as “job satisfaction,” to more specific variables, such as “decision latitude” or “work pace.” A great many measurement techniques and research designs have been employed, making direct comparison among studies difficult.
The robustness of the association between work-related psychosocial factors and back pain is suggested by two facts. First, the findings are relatively consistent in this literature despite vastly different methodologies. Second, the relationship remains and sometimes becomes stronger when possible biasing factors are controlled.
When discrepancies are found, it may be necessary to call on several factors to help explain them. These include the sample composition and size, severity of the injury/disease, measures of predictors, time of outcome, outcome criteria, study design, and possible treatment received between initial assessment and outcome. It is difficult to calculate the exact size of the effects observed, even though many of the psychosocial variables prove to be better predictors than biomedical or biomechanical factors.
Taken as a whole, the body of research provides solid evidence that work-related psychosocial factors are important determinants of subsequent back pain problems ( Table 4.4 and Appendix Table 4.7). The studies produced strong evidence (i.e., at least three studies showing a positive association) for six factors, including low job satisfaction, monotonous work, poor social support at work, high perceived stress, high perceived job demands (work pace), and perceived ability to return to work. In
Null Association |
Positive Association |
Attributable Fraction (%) |
||
Work-Related Psychosocial Factor |
n |
n |
n |
Range |
High job demands |
1 |
5 |
2 |
21-48 |
Low decision latitude/control |
0 |
2 |
||
Low stimulus from work (monotony) |
2 |
4 |
1 |
23 |
Low social support at work |
0 |
7 |
3 |
28-48 |
Low job satisfaction |
1 |
13 |
6 |
17-69 |
High perceived stress |
0 |
3 |
1 |
17 |
High perceived emotional effort |
0 |
3 |
||
Perceived ability to return to work |
0 |
3 |
||
Perceived work dangerous to back |
0 |
2 |
NOTE: Details on studies are presented in Appendix Table 4.7.
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addition, moderate evidence was found for linking low back pain to low job control, an emotionally demanding job, and the perception that the work could be dangerous for the back. General measures, such as job satisfaction and stress, showed a very distinct relationship. However, such general measures may reflect other aspects of the psychological work environment, such as relationships at work or job demands. Therefore, the studies provide relatively little information about the mechanisms or processes involved. Despite huge differences in study design and some problems outlined below, the general methodological quality of these studies is relatively high, and participation rates are good. Few studies employed a theoretical framework, and a consequence has been difficulty in specifying which predictor variables should be measured.
The relationships examined involve a large number of parameters that may influence the strength of the association. A given risk factor may, for instance, interact with the outcome variable employed. The belief that work is dangerous would seem to be relevant for the outcome variable of return to work, but possibly not for the onset of back pain. Similarly, some risk factors may be relevant only for certain types of work. As an illustration, for assembly line employment, work pace may be strongly related to future back pain complaints, but for professionals, such as nurses, it may have a weaker relationship.
The general quality of the studies was high. By selecting prospective investigations, a minimum standard was set. Nevertheless, there is great diversity in the methodology and this causes several prominent problems. One concern is that the same concept has been measured in many different ways. Since reliability and validity are generally not specified, it is possible that two studies claiming to measure the same entity may in fact be measuring quite different ones. There was also substantial variation from study to study in the definition and measurement of the outcome variable, and this may have had considerable consequences on the results obtained. There is, for example, a difference between a simple report of having had back pain during the past year with dysfunction, with health care visits, or with sick leave.
Individual Psychosocial Factors
The results demonstrate that individual psychosocial factors are related to back pain from its inception to the chronic stage (Table 4.5 and Appendix Table 4.8). Indeed, these variables were shown to be important in the development of pain and disability. Nonetheless, since psychosocial factors account for only a portion of the variance, and since other factors are known to be of importance, the present findings may underscore the necessity of a multidimensional view in which psychological
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Null Association |
Positive Association |
Attributable Fraction (%) |
||
Individual Psychosocial Factor |
n |
n |
n |
Range |
Depression or anxietya |
5 |
17 |
6 |
14-53 |
Psychological distressb |
0 |
11 |
4 |
23-63 |
Personality factors |
3 |
4 |
4 |
33-49 |
Fear-avoidance-coping |
1 |
8 |
1 |
35 |
Pain behavior/functionc |
1 |
6 |
1 |
38 |
a17 studies assessed depression only, 2 studies anxiety only, and 3 studies both depression and anxiety.
b9 studies assessed psychological distress, and 2 assessed stress.
c4 studies assessed pain behavior, and 3 assessed pain-related functioning.
NOTE: Details on studies are presented in Appendix Table 4.8.
factors interact with other variables. Although psychological factors are considered to be of particular importance in chronic pain, the data reviewed show distinctly that psychosocial factors are also pivotal in the transition from acute to chronic pain as well as being influential at onset. Moreover, the results suggest that psychosocial factors are not simply an overlay, but rather an integral part of a developmental process that includes emotional, cognitive, and behavioral aspects.
Considerable research has examined the relationship between psychosocial variables and back pain, but few have penetrated the reasons why these variables may be important. A challenge for future research is therefore to devise studies that include a theoretical perspective. Too often, studies have simply employed a convenience measure of a “psychological” variable, without considering why or how the variable might work. With a theoretical model, stronger designs could be used that would provide answers to specific questions.
Few investigations have amply treated the temporal aspects of the problem. The data reviewed suggest that certain factors are important very early, while others may be important at first consultation or a recurrence. Moreover, the reciprocal nature of pain and psychological variables was almost always treated as unidirectional, such as depression causing pain rather than pain affecting depression.
Even though all studies were prospective, methodological shortcomings ranged from selection bias and inappropriate use of statistical tests to
Page 108
failure to account for the intercorrelation of measures. The use of self-ratings as both the dependent and independent variable is a particular problem that may inflate risk estimates. It is difficult to summarize some results, because different terminology and measurement methods have been used to assess similar concepts (e.g., reluctance to participate in activities being “fear-avoidance,” “disability,” or “somatic anxiety”). There is a need to improve the quality of prospective studies in this area and to foster the use of a more structured terminology.
Some prominent psychological factors do emerge, however. First, a cognitive component represented by attitudes, beliefs, and thoughts concerning pain, disability, and perceived health seems to be a central theme. A second theme is an emotional dimension in which distress, anxiety, and depression are central. Third, a social aspect appears, in which family and work issues seem to be relevant, even if the data are less convincing. Finally, a behavioral domain emerges, in which coping, pain behaviors, and activity patterns are consequential elements.
It is tempting to conclude that since the studies included in Appendix Table 4.7 and Appendix Table 4.8 have prospective designs, the observed relationships are causal; however, this may be incorrect. Although the relationships may be temporal, they need not be causal in nature. Caution in drawing conclusions concerning causality does not lessen the value of the reviewed findings, but points to the need for experimental or other designs to advance understanding.
An important implication is how this knowledge may be incorporated into clinical practice. First, considerable psychosocial information that could be of the utmost importance in conjunction with medical examinations may be overlooked if proper assessment of these variables is not conducted. Second, if psychosocial elements play a central role in back pain, then better interventions could be designed to deal with these factors to provide better care and prevention.
Summary of Work-Related and Individual Psychosocial Factors
Based on the studies reviewed here, there is ample evidence that both work-related and individual psychosocial factors are related to subsequent episodes of back pain (Table 4.4 and Table 4.5; Appendix Table 4.7 and Appendix Table 4.8). Strong evidence for a risk factor was defined as at least 3 studies demonstrating a positive association and a distinct majority (i.e., at least 75 percent) of the studies examining that risk factor showing a positive association. Moderate evidence for a risk factor was defined as two studies showing a positive association and none showing a negative association. Inconclusive evidence for a risk factor meant neither strong nor moderate evidence was demonstrated. Of the nine types of work-related psychoso-
Page 109
cial risk factors, six had strong evidence for an association with back pain (low job satisfaction, monotonous work, poor social support at work, high perceived stress, high perceived job demands, and perceived ability to return to work), and 3 had moderate evidence (low job control, emotionally demanding job, and perception that work could be dangerous). Of the 5 types of individual psychosocial risk factors, 4 had strong evidence, while 1 was inconclusive. Conclusions regarding psychosocial risk factors are further strengthened by the fact that a main criterion for selection of back pain studies for review was a prospective design, thus ensuring that the psychosocial factor was measured before the outcome. Nonetheless, the studies do not elucidate the mechanisms or the developmental process whereby “normal” acute back pain becomes chronic.
The attributable fractions related to work-related psychosocial risk factors suggest that improvement in job satisfaction may reduce risk for back disorders by 17 to 69 percent, while improved social support at work might reduce risk by 28 to 48 percent. Acknowledging the limitations associated with the interpretation of attributable fractions (as discussed earlier in the chapter) we conclude that these results point to the potential for structural changes in job supervision, teamwork structures, and the ways in which work may be organized to reduce risk. The most consistent evidence related to individual psychosocial risk factors suggests that reduction in depression and anxiety symptoms could reduce the risk for back disorders by 14 to 53 percent, and reduction in psychological distress could reduce risk by 23 to 63 percent. This is important because a number of effective treatments are available for depression, anxiety, and psychological distress. In a number of studies, the attributable risk associated with a particular psychosocial factor could not be estimated, because although the factor was significantly associated with back disorders in multivariate models, the exact data sufficient to calculate relative risk were not provided.
Upper Extremity Disorders
Exposure measures investigated among the 28 reviewed studies of the impact of psychosocial factors on upper extremity disorders included specific work demands (e.g., number of hours on deadline), perceptions of the degree of support from supervisors and coworkers; perceived control over high work demands; and reports of symptoms that may be stress-related (e.g., stress-related abdominal distress), which is a measure of response to stressors rather than a stressor itself. Such a measure is used as a proxy to stress exposure (assuming the response is indicative of exposure to stress) and is not therefore a direct measure of exposure to a
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stressor. This type of measure was found only in studies of nonwork-related psychosocial exposures. Table 4.6 provides a compilation of results from all studies across all anatomic areas, as well as for each specific anatomic location. Detailed summaries can be found in Appendix Table 4.9 and Appendix Table 4.10.
The most frequently studied outcome was the report of symptoms (pain, numbness, tingling, aching, stiffness, or burning) in a specific anatomical area over the past week, month, or year, measured by self-report survey. Of 28 studies, 7 included confirmation of symptoms by physical examination. The anatomical areas with the greatest number of studies were the shoulder and the neck, although a number of studies focused on the hand and the elbow.
The tables indicate that the risk ratios for work-related exposures ranged from 1.4 to 4.4. The majority of the findings were below 2.0. Considering all upper extremity sites, this table indicates that the number of studies reporting a positive association for high job demands, high perceived stress, and nonwork-related worry and distress was greater than those reporting no significant effect for these exposures. This table also indicates that a number of potential psychosocial risk factors were not shown to be associated with the onset of work-related upper extremity symptoms or disorders. Specifically, the majority of studies that met the methodological criteria for inclusion did not report a significant effect for low decision latitude, work-related and nonwork-related (friends and family) social support, or few rest break opportunities. A similar pattern of results was observed for each of the specific anatomical locations. It should be noted that the majority of studies were cross-sectional; therefore, it is difficult to determine the direction of the findings.
The findings from the review of psychosocial work factors indicate that high job stress and high job demands are work-related factors that are consistently associated with the occurrence of symptoms and disorders in the upper extremities. The review also indicated that nonwork-related worry, tension, and psychological distress were consistently associated with work-related upper extremity symptoms and disorders. Although these findings are limited by the cross-sectional nature of the research designs, the role of job stress as a risk for upper extremity disorders was also supported by one large-scale prospective study (Bergqvist, 1995). These findings are also consistent with a prospective study in a community sample of recently diagnosed workers with a number of work-related upper extremity diagnoses (Feuerstein et al., 2000). This study indicated that level of perceived job stress predicted a composite index of outcomes (symptoms, function, lost time from work, mental health) at 3 months after diagnosis.
Page 111
Risk Estimate |
||||||||
Null Associationa |
Positive Association |
Attributable Fraction (%) |
||||||
Work-Related Risk Factor |
n |
Range |
n |
Range |
n |
Range |
||
A. |
Wrist/Forearm |
|||||||
High job demands |
4 |
1.2-1.4 |
5 |
1.6-2.3 |
4 |
37-56 |
||
Low decision latitude; low control and low stimulus from work |
8 |
1.0-1.7 |
3 |
1.6-6.3 |
3 |
37-84 |
||
Low social support |
4 |
- |
3 |
1.4-2.1 |
3 |
28-52 |
||
Low job satisfaction |
4 |
1.4 |
0 |
- |
- |
- |
||
High perceived stress |
1 |
1.5 |
3 |
- |
- |
- |
||
Few rest break opportunities |
5 |
2.7 |
2 |
1.5 |
1 |
33 |
||
Low support nonwork-related |
4 |
- |
0 |
- |
- |
- |
||
Worry, tension, psychological distress, nonwork-related |
0 |
- |
2 |
2.3-3.4 |
2 |
56-71 |
||
B. |
Shoulder/Upper Arm |
|||||||
High job demands |
6 |
1.1 |
6 |
1.5-1.9 |
3 |
33-47 |
||
Low decision latitude; low control and low stimulus from work |
8 |
1.1 |
6 |
1.6-1.9 |
3 |
37-47 |
||
Low social support |
7 |
1.2 |
5 |
- |
- |
- |
||
Low job satisfaction |
2 |
- |
0 |
- |
- |
- |
||
High perceived job stress |
3 |
1.5 |
3 |
- |
- |
- |
||
Few rest break opportunities |
3 |
- |
1 |
3.3 |
1 |
70 |
||
Low support nonwork-related |
3 |
- |
0 |
- |
- |
- |
||
Worry, tension, psychological distress, nonwork-related |
1 |
- |
1 |
4.8 |
- |
79 |
||
C. |
Elbow/Arm |
|||||||
High job demands |
3 |
1.1 |
6 |
2.0-2.4 |
2 |
50-58 |
||
Low decision latitude; low control and low stimulus from work |
5 |
1.0-3.0 |
1 |
2.8 |
1 |
64 |
||
Low social support |
5 |
1.2-1.7 |
0 |
- |
- |
- |
||
Low job satisfaction |
2 |
- |
0 |
- |
- |
- |
||
High perceived job stress |
1 |
1.4 |
2 |
2.0 |
1 |
50 |
||
Few rest break opportunities |
1 |
- |
1 |
3.1 |
1 |
67 |
||
Low support nonwork-related |
1 |
- |
0 |
- |
- |
- |
||
Worry, tension, psychological distress, nonwork-related |
0 |
- |
1 |
1.4-1.8 |
1 |
28-44 |
||
continues |
Page 112
Risk Estimate |
||||||||
Null Associationa |
Positive Association |
Attributable Fraction (%) |
||||||
Work-Related Risk Factor |
n |
Range |
n |
Range |
n |
Range |
||
D. |
All Upper Extremity |
|||||||
High job demands |
6 |
1.1-1.4 |
10 |
1.5-2.4 |
6 |
33-58 |
||
Low decision latitude; low control and low stimulus from work |
10 |
1.1-1.7 |
6 |
1.6-2.8 |
4 |
37-64 |
||
Low social support |
7 |
1.2 |
7 |
1.4-2.1 |
3 |
28-52 |
||
Low job satisfaction |
4 |
1.1-1.4 |
0 |
- |
- |
- |
||
High perceived job stress |
2 |
1.4 |
5 |
2.0 |
1 |
50 |
||
Few rest break opportunities |
3 |
1.4-1.5 |
3 |
1.5-3.3 |
2 |
33-70 |
||
Low support nonwork-related |
3 |
- |
0 |
- |
- |
- |
||
Worry, tension, psychological distress, nonwork-related |
1 |
- |
3 |
1.4-4.8 |
3 |
28-79 |
aConfidence intervals of the risk estimates included the null estimate (1.0). The magnitude of the risk estimate often was not presented.
NOTES: n = number of associations presented in epidemiologic studies. Details on studies are found in Appendix Table 4.9.
The attributable fractions related to these risk factors suggest that modification of the high job demands could potentially reduce the risk for upper extremity disorders and symptoms by 33 to 58 percent. Reduction in perceived levels of job stress could reduce the risk for upper extremity disorders and symptoms by 50 percent, and reduction in nonwork-related worry, tension, and distress has the potential to reduce risk by 28 to 79 percent. These findings highlight the potential impact of modifying both work-related and nonwork-related sources of stress; however, they must be considered within the limitations presented earlier in this chapter on the interpretation of attributable fractions. The observation that no study that considered both psychosocial and physical risk factors met review inclusion criteria is important, since many models assume a complex interaction among medical, physical/ergonomic, and workplace and individual psychosocial factors (e.g., Armstrong et al., 1994).
There is a need for more prospective studies. Unlike the area of back pain, there are very few prospective studies of psychosocial risk factors in work-related upper extremity disorders. There is also a need for more consistent use of measures that assess specific psychosocial exposures.
Page 113
These measures should have sound psychometric properties (e.g., reliability and validity) that justify their use. The inclusion of various measures should also be based on well-conceived hypotheses based on working models of how these factors may affect the occurrence of these symptoms and disorders (Chapter 7 discusses such models). The case definitions used in studies should be carefully delineated, and a more consistent use of outcome measures of symptoms, disorders, and/or functional limitations should be implemented. The criteria used to select studies for review may have been too restrictive, given the relative level of sophistication of the psychosocial literature in this area. Nevertheless, despite this rigor, an association among perceived job stress, high job demands, nonwork-related distress, and upper extremity disorders was noted. These findings highlight the importance of conducting additional studies to identify specific factors that contribute to the identified risk factors and to explain how these interact to influence the development, exacerbation, or maintenance of work-related upper extremity disorders. It is also important to determine how these psychosocial factors interact with medical and ergonomic risk factors to modify risk. It is possible that the psychosocial factors that were not found to be consistently associated with the occurrence of work-related upper extremity symptoms and disorders may influence the recovery process following onset. It is also possible that these factors may impact other outcomes, such as functional limitation or the ability to sustain a full day's work. The role of psychosocial factors in the exacerbation and maintenance of these disorders requires further investigation.
This review highlights the potential utility of increased efforts directed at understanding the mechanisms by which job stress may impact work-related upper extremity disorders and the biological basis for such an association. The review also supports the need to investigate approaches that eliminate or reduce work- and nonwork-related sources of stress in prevention efforts.
CONCLUSION
A number of general and specific reviews were identified in which physical and psychosocial factors were examined in relation to musculoskeletal disorders of the upper extremities and back [see review references]. These reviews served as a resource to supplement the panel's efforts to identify relevant epidemiologic studies. They also were examined to determine whether conclusions drawn from the panel's review were consistent with previous review efforts. The objectives of the reviews differed; some focused on specific industries, jobs, or exposures, but others were more general. As a whole, the findings from these other
Page 114
reviews are consistent with those arrived at in the panel's review and provide additional support for the conclusions.
The approach for considering causal inferences described in Chapter 3 is useful for summarizing our review of the data from epidemiologic studies. As the tables in this chapter show, a number of studies were judged to be of sufficient quality for inclusion in this review, and these vary in terms of the types of designs and measurement approaches. While this variety complicates the generalization of causal inferences, the summary tables indicate meaningful associations between work-related physical and psychosocial exposures and musculoskeletal disorders. The tables show not only a preponderance of evidence for some exposures (e.g., 26 of 32 studies found a significant association between vibration and upper extremity musculoskeletal disorders), but also a consistency of association for many of the exposures and outcomes. Although the literature contains mostly cross-sectional surveys, some work to establish temporality; combined with the available prospective studies, evidence for temporal association has been included in this chapter.
Most studies reviewed here also show a meaningful strength of association measured by both estimates of the relative risk and calculation of attributable risk. The attributable risk provides an estimate of the proportion of musculoskeletal disorders that might be prevented if effective interventions were implemented; the calculations are appreciable for most for the exposures summarized here.
While the measure of attributable risk is meaningful for conceptualizing public health impact, the calculations are presented for one factor at a time and do not account for other factors. As noted in this chapter, many studies did account for potential confounders that could provide alternative explanations for the observed findings, but the number of confounders examined in each study tends to be limited. While this is due to multiple factors (including expense associated with satisfying sample size requirements), the fact that the associations persist after accounting for the confounders measured to date supports the fundamental association, but it also justifies more detailed investigation.
The joint effect of exposures is another element of the risk estimation suggested in Chapter 3 and illustrated in this chapter. The attributable fraction summarizes the impact of a single exposure. However, scant attention has been paid to the joint effect, or interaction, of two (or more) exposures, increasing risk beyond the level of either alone. As noted in Chapter 3, some combinations of exposures might work jointly, although their individual actions may or may not be significant. The studies by Silverstein (e.g., Silverstein, Fine, and Armstrong, 1987) showed an interaction between high force and high repetition for upper extremity disorders among industrial workers. Further investigation for joint effects of
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exposures is indicated from the current review. The effect of joint exposures can be investigated within physical (vibration, force, load, etc.), and psychosocial (job strain, job demand, etc.) domains. This review indicated the utter lack of studies that were found to be of sufficient quality and that examine both physical and psychosocial factors together. Because evaluation of each has shown important effects on the development of musculoskeletal disorders, and some of the current evidence (although modest) suggests that one does not explain the other, it is unlikely that more detailed investigation will demonstrate that the association of either with musculoskeletal disorders is due to confounding with the other. However, additional studies are needed to understand the degree to which each contributes to the overall incidence of musculoskeletal disorders, and the extent to which both work synergistically in selected work settings.
While the results presented in this chapter are consistent with one another, it is important to examine the degree to which they are consistent with the results from the basic science and the biomechanics studies ( Chapter 5 and Chapter 6). Some of these studies have been mentioned in this chapter; their results are generally consistent, providing here some suggestion of biological plausibility for the association between physical forces and musculoskeletal disorders. The degree of consistency across different levels of study will be discussed in more detail in the integration chapter.
Most epidemiologic studies have been summarized as having exposure and/or outcome measures dichotomized. The ability to make inferences about dose-response relationship is limited in this context. While there are step-wise differences in dichotomous measures across studies (e.g., see Boshuizen, Bongers, and Hulshof, 1992, and Bovenzi and Zadini, 1992) that make cross-comparisons tantalizing, the differences in comparison groups and other design features hinder the combining of results for generating inferences on dose-response relationships. Future studies can help generate strong inferences by paying greater attention to more refined levels of measurement. While this is a challenge, the strength of the current studies justifies this effort.
In conclusion, the epidemiologic evidence provides support for associations between workplace physical and psychosocial exposures and both back and upper extremity musculoskeletal disorders.
Page 118
Author |
Study Population |
Outcomes |
Work-Related Risk Factor |
Risk |
95% Confidence Interval |
Attributable Fraction Exposed |
Alcouffe et al., 1999 |
7,010 workers (M&F) |
LBP in past 12 months (56%) |
Lifting (every day > 10kg) |
1.4 |
1.2-1.6 |
NA |
Whole-body vibration (> 4 h/day vs. never) |
1.3 |
1.0-1.6 |
NA |
|||
Awkward postures (yes/no) |
2.0 |
1.7-2.2 |
NA |
|||
Arad and Ryan, 1986 |
831 nurses (F) |
LBP in past month (42%) |
Lifts per shift (> 6 vs. less) |
2.5 |
1.8-3.4 |
41% |
Bongers et al., 1990 |
133 helicopter pilots and 228 non-flying officers (M) |
Regularly experienced LBP (55% and 11%) |
WBV (az > 0.5 m/s2) |
9.0 |
4.9-16.4 |
80% |
Boshuizen, Bongers, and Hulshof, 1990 |
450 tractor drivers and 110 agriculture workers (M) |
Regularly experienced LBP (31% and 19%) |
WBV (az > 0.3 m/s2) |
1.9 |
1.1-3.4 |
39% |
Boshuizen, Bongers, and Hulshof, 1992 |
242 drivers and 210 operators (M) |
LBP in past 12 months (51% and 42%) |
WBV (az > 0.5 m/s2) |
1.7 |
1.1-2.8 |
18% |
Bovenzi and Zadini, 1992 |
234 bus drivers and 125 maintenance workers (M) |
LBP in past 12 months (83% and 66%) |
WBV (az > 0.6 m/s2) |
3.6 |
1.6-8.2 |
NA |
Awkward posture (frequent) |
2.3 |
1.2-4.3 |
NA |
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Bovenzi and Betta, 1994 |
1,155 tractor drivers and 220 office workers (M) |
LBP in past 12 months (67% and 35%) |
WBV (az > 0.5 m/s2) |
2.4 |
1.5-3.8 |
NA |
|
Awkward posture (hard) |
2.2 |
1.3-3.8 |
NA |
||||
Burdorf, Govaert, and Elders, 1991 |
114 concrete workers and 52 maintenance workers (M) |
LBP in past 12 months (59% and 31%) |
Bends and twists (37% and 27%) |
2.8 |
1.3-6.0 |
30% |
|
WBV (yes/no) |
3.1 |
1.3-7.5 |
NA |
||||
Burdorf, Naaktgeboren, and de Groot, 1993 |
94 crane operators and 86 office workers (M) |
LBP in past 12 months (50% and 34%) |
Static sedentary posture (yes/no) |
3.3 |
1.5-7.1 |
32% |
|
Burdorf et al., 1997 |
161 tank terminal workers |
LBP in past 12 months (35%) |
Lack of social support (yes/no) |
3.8 |
1.6-9.1 |
47% |
|
Estryn-Behar et al., 1990 |
1,505 nurses (F) |
LBP in past 12 months |
Postural load (high vs. low) |
2.1 |
NA |
19% |
|
MMH (high vs. low) |
MMH |
2.0 |
NA |
21% |
|||
Gilad and Kirschenbaum, 1986 |
250 production workers (M) |
BP in past 12 Lifting months (59%) |
Lifting (frequent vs. never) |
3.1 |
1.1-8.7 |
35% |
|
Holmström, Lindell, and Moritz, 1992a, 1992b |
1,772 construction workers (M) |
LBP in past 12 months (54%) |
MMH (every 5 min vs. less) |
1.1 |
1.0-1.3 |
11% |
|
Daily stooping (> 4 h vs. <1h) |
1.3 |
1.1-1.5 |
22% |
||||
Magnusson et al., 1996 |
228 drivers and 137 sedentary workers (M) |
LBP in past 12 months (58% and 42%) |
WBV (yes/no) |
1.8 |
1.2-2.8 |
27% |
|
Lifting (frequent vs. none) |
1.6 |
1.0-2.4 |
NA |
||||
Lifting > 10 kg (frequent vs. none) |
1.9 |
1.2-2.8 |
NA |
||||
continues |
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Author |
Study Population |
Outcomes |
Work-Related Risk Factor |
Risk |
95% Confidence Interval |
Attributable Fraction Exposed |
Ory et al., 1997 |
418 tannery workers (M) |
LBP in past 12 months (61%) |
Lifting (regular over 20 kg vs. seldom) |
3.5 |
1.4-8.8 |
NA |
Pietri et al., 1992 |
1,709 commercial travellers (M & F) |
LBP in past 12 months (27%) |
WBV (> 20 h vs. < 10 h) |
2.0 |
1.3-3.1 |
39% |
Frequent load carrying |
1.3 |
1.0-1.7 |
22% |
|||
Prolonged standing (yes/no) |
1.3 |
1.0-1.6 |
14% |
|||
Riihimäki et al., 1989a |
852 machine operators, 696 carpenters, 674 office clerks |
Sciatica in past 12 months (34%, 29% and 19%) |
Bending and twisting (rather much vs. rather little) |
1.5 |
1.2-1.9 |
NA |
Smedley et al., 1995 |
1,616 nurses (F) |
LBP in past 12 months (45%) |
Lifting (> 1 patient/day) |
1.3 |
1.1-1.6 |
13% |
Suadicani et al., 1994 |
469 steel workers (M&F) |
LBP in past 12 months (50%) |
Lifting (> 1 year heavy objects vs. 0) |
2.4 |
1.5-3.6 |
28% |
Awkward posture (> 1 year vs. 0) |
2.4 |
1.6-3.7 |
28% |
|||
Waters et al., 1999 |
284 industrial workers (M) |
LBP in past 12 months (30%) |
Lifting (lifting index > 1) |
2.1 |
1.1-4.0 |
43% |
Wells et al., 1983 |
196 letter carriers, 76 meter readers, 127 clerks (M) |
Significant BP (28%, 21% and 11%) |
Carrying weight (yes/no) |
2.2 |
1.3-3.7 |
46% |
NOTE: M = male; F = female; BP = back pain; LBP = low-back pain; WBV = whole-body vibration; MMH = manual material handling; NA = not available.
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Author |
Study Population |
Outcomes |
Work-Related Risk Factor |
Risk |
95% Confidence Interval |
Attributable Fraction Exposed |
Heliovaara et al., 1991 |
2,946 Finnish women and 2,727 Finnish men |
Medically diagnosed LBP (12% and 12%) |
Physical load (yes/no) |
2.6 |
2.1-3.2 |
56% |
Medically diagnosed) sciatica (5% and 6%) |
Physical load (yes/no) |
2.5 |
1.8-3.4 |
58% |
||
Houtman et al., 1994 |
5,865 Dutch workers (M&F) |
Back complaints (25%) |
Heavy physical load (yes/no) |
1.6 |
1.4-1.9 |
NA |
Leigh and Sheetz, 1989 |
1,414 U.S.A workers (M&F) |
BP in past 12 months (20%) |
Heavy physical load (yes/no) |
1.7 |
1.1-2.9 |
37% |
Liira et al., 1996 |
8,020 Canadian blue-collar workers (M&F) |
Long-term back problems (8.4%) |
Bends & lifts (> 50x/day) |
1.7 |
1.3-2.2 |
39% |
Frequent lifts < 50 lb |
1.5 |
1.1-1.9 |
32% |
|||
WBV (yes/no) |
1.8 |
1.3-2.7 |
46% |
|||
Awkward back posture |
2.3 |
1.7-3.2 |
57% |
|||
Linton, 1990 |
22,180 Swedish workers (M&F) |
LBP in past 12 months with medical consultation (16%) |
Lifting heavy loads (yes/no) |
1.8 |
1.5-2.1 |
NA |
Awkward postures (yes/no) |
2.2 |
1.8-2.6 |
NA |
|||
Vibration (yes/no) |
1.8 |
1.5-2.2 |
NA |
|||
Saraste and Hultman, 1987 |
2,872 Swedish women and men |
LBP (36%) |
Bends & twists (always/no) |
2.6 |
2.1-3.3 |
56% |
Daily heavy lifting (yes/no) |
1.9 |
1.6-2.3 |
40% |
|||
WBV (yes/no) |
2.1 |
1.3-3.5 |
52% |
|||
Repetitive work (always/no) |
2.0 |
1.6-2.4 |
41% |
|||
continues |
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Author |
Study Population |
Outcomes |
Work-Related Risk Factor |
Risk |
95% Confidence Interval |
Attributable Fraction Exposed |
Svensson and Andersson, 1983 |
940 Swedish men ages 40-47 |
LBP in past month (31%) |
Frequent lifting (yes/no) |
1.7 |
1.1-2.6 |
36% |
Heavy physical load (yes/no) |
1.5 |
1.0-2.4 |
31% |
|||
Svensson and Andersson, 1989 |
1,410 Swedish women |
LBP in past month (35%) |
Regularly bending (yes/no) |
1.4 |
1.1-1.8 |
21% |
Xu, Bach, and Orhede, 1997 |
5,940 workers (M&F) |
LBP in past 12 months (43%) |
Bending and (all the time vs. seldom) twisting |
2.0 |
1.7-2.4 |
32% |
Heavy physical load (all the time vs. seldom) |
2.5 |
1.6-3.9 |
35% |
|||
Whole-body vibration (all the time vs. seldom) |
1.8 |
1.2-2.7 |
23% |
|||
Standing (all the time vs. seldom) |
1.6 |
1.3-1.8 |
22% |
NOTE: M = male; F = female; BP = back pain; LBP = low-back pain; WBV = whole-body vibration; NA = not available.
Page 123
Author |
Study Population |
Outcomes |
Work-Related Risk Factor |
Risk |
95% Confidence Interval |
Attributable Fraction Exposed |
Boshuizen, Bongers, and Hulshof, 1990 |
789 tractor drivers (M) |
Sickness absence > 28 days due to back disorders |
WBV (az > 0.4 m/s2) |
1.5 |
1.0-2.1 |
32% |
Due to intervertebral disc |
WBV (az > 0.4 m/s2) |
73.1 |
1.2-8.3 |
68% |
||
Gardner, Landsittel, and Nelson, 1999 |
31,076 material handlers in retail merchandise stores |
BP claim due to material handling (2.8%/year) |
Material handling (lifting jobs versus light lifting jobs) |
1.6 |
1.2-1.9 |
38% |
Kraus et al., 1997 |
31,000 employees (M&F) in retail stores |
BP claim (± 3.4%/year) |
Lifting (frequently lifting or carrying loads > 11.35 kg) |
2.9 |
2.6-3.3 |
66% |
Pietri, 1992 |
601 commercial travellers |
LBP incidence (13%/year) |
WBV (> 20 h vs. < 10 h) |
3.3 |
1.0-10.5 |
70% |
Smedley et al., 1997 |
838 female nurses (no LBP in past month) |
LBP incidence (47% cumulative incidence / 2 year) |
Lifting (≥ 1 patient vs. 0) |
1.4 |
1.0-1.9 |
19% |
Transfer (≥ 5 patients vs. less) |
1.6 |
1.1-2.3 |
18% |
|||
Stobbe et al., 1988 |
415 nurses (F) |
BP claim (5.2%/year) |
Lifting (> 5 patients vs. < 2) |
2.2 |
1.1-4.2 |
54% |
Venning, Walter, and Stitt, 1987 |
4,306 nurses (M&F) |
BP claim (2.8%/year) |
Lifting (≥ 1 patient vs. 0) |
2.2 |
NA |
54% |
NOTE: M = male; F = female; BP = back pain; LBP = low-back pain; WBV = whole-body vibration; NA = not available.
Page 124
Author |
Study Population |
Outcomes |
Work-Related Risk Factor |
Risk |
95% Confidence Interval |
Attributable Fraction Exposed |
Josephson and Vingard, 1998 |
81 female nurses (referents: 188 female nurses) |
LBP medical care |
Severe trunk flexion (at least 1 hour/day) |
4.3 |
1.6-12 |
NA |
High perceived exertion (PPE - Borg ≥ 14) |
2.3 |
1.2-4.5 |
NA |
|||
Kelsey et al., 1984 |
325 medical patients (referents: 241 care seekers in same clinics) |
Acute prolapsed lumbar intervertebral disc |
Lifting loads > 11.3 kg (25lb)(> 25 times/day) |
3.5 |
1.5-8.5 |
NA |
Carrying loads > 11.3 kg (25lb)(> 25 times/day) |
2.7 |
1.2-5.8 |
NA |
|||
Nuwayhid, Stewart, and Johnson, 1993 |
115 fire fighters (referents: 109 fire fighters) |
LBP claim |
Physical exertion on job |
3.7 |
1.9-7.1 |
NA |
Lifting (> 18 kg vs. less) |
3.1 |
1.3-7.9 |
NA |
|||
Climbing (> 100 steps/day vs. less) |
2.3 |
1.2-4.4 |
NA |
|||
Punnett et al., 1991 |
95 assembly workers (referents: 124 assembly workers) |
LBP claim |
Bends & twists (100% vs. 0%) |
8.1 |
1.5-44.0 |
NA |
Lifting (> 44.5 N/minute) |
2.2 |
1.0-4.7 |
NA |
NOTE: LBP = low-back pain; PPE = perceived physical exertion; NA = not available.
Page 125
Author |
Study Population |
Outcomes |
Work-Related Risk Factor |
Riska |
95% Confidence Interval |
Attributable Fraction Exposedb |
Silverstein, Fine, and Armstrong, 1986 |
574 industrial workers |
Hand/wrist CTDs (Sx & PE) |
High force/low repetition |
OR = 5.2 |
1.1-25.0 |
78% |
Hand/wrist CTDs (Sx & PE) |
Low force/high repetition |
OR=3.3 |
0.7-15.9 |
78% |
||
Hand/wrist CTDs (Sx & PE) |
High force/high repetition |
OR=29.1 |
5.9-142.7 |
93% |
||
Bovenzi, Fiorito, and Volpe, 1987 |
67 foundry workers and 46 manual laborers |
Olecranon spurs (X-ray) |
Hand-held vibrating tools: frequency-weighted energy-equivalent acceleration for 4 hours |
OR=2.6 |
1.2-5.8 |
44% |
Osteoarthritis in elbow (X-ray) |
Hand-held vibrating tools: frequency-weighted energy-equivalent acceleration for 4 hours |
OR=2.1 |
0.6-6.9 |
47% |
||
Calcification in elbows (X-ray) |
Hand-held vibrating tools: frequency-weighted energy-equivalent acceleration for 4 hours |
OR=1.7 |
0.4-6.8 |
38% |
||
continues |
Page 126
Author |
Study Population |
Outcomes |
Work-Related Risk Factor |
Riska |
95% Confidence Interval |
Attributable Fraction Exposedb |
Bone cysts in wrist (X-ray) |
Hand-held vibrating tools: frequency-weighted energy-equivalent acceleration for 4 hours |
OR=1.0 |
0.4-2.3 |
0 |
||
Osteoarthritis in wrist (X-ray) |
Hand-held vibrating tools: frequency-weighted energy-equivalent acceleration for 4 hours |
OR=5.3 |
1.1-24.7 |
78% |
||
Osteoarthritis in shoulder (X-ray) |
Hand-held vibrating tools: frequency-weighted energy-equivalent acceleration for 4 hours |
OR=0.4 |
0.1-1.6 |
NA |
||
Silverstein, Fine, and Armstrong, 1987 |
652 industrial workers |
CTS (Sx & PE) |
High force/low repetition |
OR=1.8 |
0.2-20.6 |
38% |
CTS (Sx & PE) |
Low force/high repetition |
OR=2.7 |
0.3-28.4 |
70% |
||
CTS (Sx & PE) |
High force/high repetition |
OR=15.5 |
1.7-141.5 |
88% |
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Bovenzi, Franzinelli, and Strambi, 1988 |
76 stonedrillers and stonecutters and 60 controls |
Raynaud's/VWF |
Hand-held vibrating tools: frequency-weighted energy-equivalent acceleration for 4 hours |
OR=6.1 |
2.2-17.0 |
77% |
Nilsson, Burstrom, and Hagberg, 1989 |
89 platers (n=89) and 61 office workers |
Raynaud's/VWF |
Hand-held vibrating tools |
OR=13.9 |
5.1-38.0 |
NA |
105 any vibration exposure and 45 no vibration exposure |
Raynaud's/VWF |
Hand-held vibrating tools |
OR=56.0 |
11.6-269 |
NA |
|
71 current vibration exposure and 45 no vibration exposure |
Raynaud's/VWF |
Hand-held vibrating tools |
OR=84.5 |
14.7-486 |
NA |
|
Chiang et al., 1990 |
207 frozen food factory workers |
CTS (Sx, PE, & NCV) |
repetition and/or cold exposure |
OR=7.4 |
2.0-27.5 |
89% |
86 frozen food factory workers |
CTS (Sx, PE, & NCV) |
repetition, but no cold exposure |
OR=2.2 |
0.2-21.2 |
90% |
|
170 frozen food factory workers |
CTS (Sx, PE, & NCV) |
repetition and cold exposure |
OR=9.4 |
2.4-37.2 |
89% |
|
Bovenzi et al., 1991 |
34 forestry workers and 31 hospital maintenance workers |
Persistent pain in any upper extremity site |
<7.5 m/s2 (vibration exposure expressed in energy-equivalent frequency-weighted acceleration) |
OR=2.7 |
Not significant |
NA |
continues |
Page 128
Author |
Study Population |
Outcomes |
Work-Related Risk Factor |
Riska |
95% Confidence Interval |
Attributable Fraction Exposedb |
31 forestry workers and 31 hospital maintenance workers |
Persistent pain in any upper extremity site |
>7.5 m/s2 (vibration exposure expressed in energy-equivalent frequency-weighted acceleration) |
OR=14.1 |
P<0.005 |
NA |
|
34 forestry workers and 31 hospital maintenance workers |
At least one muscle-tendon syndrome (Sx & PE) |
<7.5 m/s2 (vibration exposure expressed in energy-equivalent frequency-weighted acceleration) |
OR=6.0 |
P<0.005 |
NA |
|
31 forestry workers and 31 hospital maintenance workers |
At least one muscle-tendon syndrome (Sx & PE) |
>7.5 m/s2 (vibration exposure expressed in energy-equivalent frequency-weighted acceleration) |
OR=11.9 |
P<0.0001 |
NA |
|
34 forestry workers and 31 hospital maintenance workers |
Carpal tunnel syndrome (Sx & PE) |
<7.5 m/s2 (vibration exposure expressed in energy-equivalent frequency-weighted acceleration) |
OR=13.6 |
P<0.03 |
NA |
Page 129
31 forestry workers and 31 hospital maintenance workers |
Carpal tunnel syndrome (Sx & PE) |
>7.5 m/s2 (vibration exposure expressed in energy-equivalent frequency-weighted acceleration) |
OR=39.8 |
P<0.0001 |
NA |
|
Bovenzi, 1994 |
137 vibration-exposed stone workers and 258 unexposed controls |
HAV—sensorineural disturbances (Sx) |
Hand-held vibrating tools: ln (lifetime vibration dose) > 24 m2-h3/s4 |
OR=27.3 |
2.81-7.82 |
73% |
137 vibration-exposed stone workers and 258 unexposed controls |
Symptoms of VWF |
Hand-held vibrating tools: ln (lifetime vibration dose) > 24 m2-h3/s4 |
OR=4.69 |
13.1-56.6 |
93% |
|
137 vibration-exposed stone workers and 258 unexposed controls |
CTS (Sx & PE) |
Hand-held vibrating tools: ln (lifetime vibration dose) > 24 m2-h3/s4 |
OR=3.24 |
1.21-8.69 |
83% |
|
137 vibration-exposed stone workers and 258 unexposed controls |
Dupuytren's contracture |
Hand-held vibrating tools: ln (lifetime vibration dose) > 24 m2-h3/s4 |
OR=3.20 |
1.39-7.37 |
82% |
|
137 vibration-exposed stone workers and 258 unexposed controls |
Muscular weakness |
Hand-held vibrating tools: ln (lifetime vibration dose) > 24 m2-h3/s4 |
OR=14.7 |
3.25-66.6 |
95% |
|
137 vibration-exposed stone workers and 258 unexposed controls |
Pain in the upper limbs |
Hand-held vibrating tools: ln (lifetime vibration dose) > 24 m2-h3/s4 |
OR=3.15 |
1.91-5.20 |
69% |
|
continues |
Page 130
Author |
Study Population |
Outcomes |
Work-Related Risk Factor |
Riska |
95% Confidence Interval |
Attributable Fraction Exposedb |
Moore and Garg, 1994 |
Pork processing workers |
Total UEMSDs |
“Hazardous” vs. “safe” (dichotomized on Strain Index) |
RR=11.7 |
P<0.001 |
NA |
Pork processing workers |
Total UEMSDs excluding CTS |
“Hazardous” vs. “safe” (dichotomized on Strain Index) |
RR=38.9 |
P<0.001 |
NA |
|
Pork processing workers |
Total “specific disorders” |
“Hazardous” vs. “safe” (dichotomized on Strain Index) |
RR=6.9 |
P≤0.02 |
NA |
|
Pork processing workers |
Specific disorders excluding CTS |
“Hazardous” vs. “safe” (dichotomized on Strain Index) |
RR=19.4 |
P≤0.02 |
NA |
|
Pork processing workers |
CTS (Sx and NCV) |
“Hazardous” vs. “safe” (dichotomized on Strain Index) |
RR=2.8 |
P=0.44 |
NA |
|
Bovenzi et al., 1995 |
56 forestry workers and 194 controls |
VWF (Sx and abnormal digital artery response to cold provocation) |
Hand-held vibrating tools: ln (lifetime vibration dose) < 19 m2s−4hd |
OR=4.06 |
1.06-16.4 |
65% |
Page 131
56 forestry workers and 194 controls |
VWF (Sx and abnormal digital artery response to cold provocation) |
Hand-held vibrating tools: ln (lifetime vibration dose) = 19-20 m2s−4hd |
OR=4.65 |
1.34-16.1 |
76% |
|
56 forestry workers and 194 controls |
VWF (Sx and abnormal digital artery response to cold provocation) |
Hand-held vibrating tools: ln (lifetime vibration dose) = 20-21 m2s−4hd |
OR=9.37 |
3.10-28.4 |
88% |
|
56 forestry workers and 194 controls |
VWF (Sx and abnormal digital artery response to cold provocation) |
Hand-held vibrating tools: ln (lifetime vibration dose) > 21 m2s−4hd |
OR=34.3 |
11.9-99.2 |
95% |
|
Roquelaure et al., 1997 |
65 factory workers and 65 case controls |
CTS (Sx, PE, NCV, and/or surgery for CTS) |
Force greater than 1 kg |
OR=9.0 |
2.4-33.4 |
NA |
65 factory workers and 65 case controls |
CTS (Sx, PE, NCV, and/or surgery for CTS) |
Elementary operation (cycle time) ≤ 10 sec |
OR=8.8 |
1.8-44.4 |
NA |
|
Latko et al., 1999 |
352 manufacturing workers |
Nonspecific upper extremity discomfort |
Hand repetition (“low” vs. “high”) |
OR=2.45 |
1.42-4.24 |
53% |
352 manufacturing workers |
Tendinitis |
Hand repetition (“low” vs. “high”) |
OR=3.23 |
1.27-8.26 |
71% |
|
352 manufacturing workers |
CTS (hand diagram) |
Hand repetition (“low” vs. “high”) |
OR=2.32 |
1.07-4.99 |
61% |
|
352 manufacturing workers |
CTS (hand diagram & NCV) |
Hand repetition (“low” vs. “high”) |
OR=3.11 |
0.89-10.87 |
66% |
|
Lundström et al., 1999 |
125 vibration-exposed and 45 nonexposed |
Impaired multifrequency vibrotactile sensation (both hands) |
Cumulative vibration exposure (nonexposed vs. CVE up to 24,000 meters-hours/sec2) |
OR=1.3 |
0.25-7.03 |
NA |
Page 132
Author |
Study Population |
Outcomes |
Work-Related Risk Factor |
Riska |
95% Confidence Interval |
Attributable Fraction Exposedb |
125 vibration-exposed and 45 nonexposed |
Impaired multifrequency vibrotactile sensation (both hands) |
Cumulative vibration exposure (nonexposed vs. CVE greater than 24,000 meters-hours/sec2) |
OR=3.3 |
1.41-7.57 |
NA |
|
125 vibration-exposed and 45 nonexposed |
Impaired multifrequency vibrotactile sensation (both hands) |
Cumulative vibration exposure (CVE greater than 24,000 meters-hours/sec2 vs. CVE up to 24,000 meters-hours/sec2) |
OR=2.6 |
1.32-4.98 |
NA |
aOdds ratios adjusted for age and other factors, if available.
bAttributable fractions were not presented by the article authors and, therefore, were calculated using results available from the data presented in the published studies.
NOTE: CTD = cumulative trauma disorder; CTS = carpal tunnel syndrome; CVE = cumulative vibration exposure ; HAV = hand-arm vibration; NA = not available; NCV = nerve conduction velocity; OR = odds ratio; PE = physical examination; Sx = symptoms; RR = relative risk; UEMSD = upper extremity musculoskeletal disorder; VWF = vibration white finger.
Page 133
Author |
Study Population |
Outcomes |
Work-Related Risk Factor |
Risk |
95% Confidence Interval |
Comments |
Load or Force |
||||||
Gorsche et al., 1998 |
665 meat packing workers |
Incidence of trigger finger ~1-yr follow-up |
Hand tool use (yes/no) |
OR = 4.7 |
Knife use Digits 3 & 4 most frequently affected |
|
Kurppa et al., 1991 |
Meat packing plant employees—377 strenuous and 338 nonstrenuous |
Tenosynovitis, peritendinitis, epicondylitis (clinical diagnosis) |
Level of physical work (cutters, sausage makers, packers) |
Tenosynovitis (OR = 18) |
Physical work not measured—repetition and force; Incidence per 100 hour reported |
|
Epicondylitis (OR = 7.8) |
||||||
Luoparjärvi et al., 1979 |
152 assembly line packers and 133 shop assistants |
Muscle-tendon syndrome (clinical diagnosis) |
Repetition and/or static load by job group (yes/no) |
OR = 4 crude ratio |
Grasping and forceful movements in addition |
|
continues |
Page 134
Author |
Study Population |
Outcomes |
Work-Related Risk Factor |
Risk |
95% Confidence Interval |
Comments |
Ohlsson et al., 1995 |
82 female industrial workers and 64 controls |
Neck, shoulder, hand-wrist, elbow pain, tendinitis, neck tension, etc. (Sx, physical exam, blood and urine) |
Repetition (yes/no) pressing and assembling fuses |
POR = 4.6 |
1.9-12 |
Job category used as index of exposure; workers taped, controls not taped |
Roto and Kivi, 1984 |
90 meatcutters and 77 construction foremen |
Epicondylitis, tenosynovitis (PE and Sx) |
Meatcutting (yes/no) |
Epicondylitis Tenosynovitis |
−6.4 |
0.99-40.9 |
Stetson et al., 1993 |
Industrial workers in high exposure jobs—103 with hand/wrist symptoms, 137 asymptomatic, and 105 controls |
Median and ulnar nerve dysfunction (Sx-questionnaire, electrophysiological measures) |
Repetition, force, hand grip, posture, etc. (low, medium, high) |
Distal conduction significantly lower for those with symptoms |
Gripping and carrying loads associated with reduced NCV |
|
Vibration |
||||||
Bovenzi, Petronio, and Di Marino, 1980 |
169 caulkers, 50 welders, and 10 electricians |
Raynaud's (Sx), temperature differences |
Vibration (yes/no) |
OR = 4.7 |
All caulkers exposed regularly, others rarely if ever |
Page 135
Brubaker et al., 1983 |
147 tree fellers and 142 controls |
VWF, Raynaud's (Sx, delayed finger rewarming) |
Vibration (yes/no); over 11 years |
OR = 53.0 |
70% occurrence with 11-15 years exposure; 75% with 20 years |
|
Burdorf and Monster, 1991 |
101 riveters and bucketers and 76 controls |
VWF (Sx) self reports, questionnaire |
Vibration (yes/no); work samples, self reports |
OR = 3.0 |
Analysis based on job titles—no quantitative data used |
|
Härkönen et al., 1984 |
279 lumberjacks and 279 peat bog workers |
VWF (Sx) self reports, questionnaire |
Vibration (yes/no) |
OR = 6 crude ratio |
Mean 10 yrs exposure-dose response demonstrated |
|
Iwata, Makimo, and Miyashita, 1987 |
Student nurses and examinees at health care center—635 males and 835 females |
Raynaud's, stiffness, numbness (self report) |
No exposure to vibration—females with higher incidence |
OR = 1.69 |
||
Kaji et al., 1993 |
384 carpentry, forestry, and mining |
Bracial arteriography (hyopthenar hammer syndrome) |
Vibration |
7.2% occurrence (HHS) |
No control |
|
Kiveka et al., 1994 |
213 lumberjacks and 140 controls (camp workers) |
VWF (Sx, clinical exam, radiographs) |
Vibration |
Risk Ratio = 8.9 |
2.5-28.9 |
Risk ratio for lumberjacks (25 years exposure) |
continues |
Page 136
Author |
Study Population |
Outcomes |
Work-Related Risk Factor |
Risk |
95% Confidence Interval |
Comments |
Koskimies et al., 1992 |
Forest workers (1972-1990; n varies between 118 and 205) |
VWF numbness (Sx, self report, clinical exam) |
Vibration (1,500 hours of chainsaw operation); chainsaw redesign over time |
Prevalence rate reduced from 40% to 5% |
||
Letz et al., |
271 shipyard workers—53 no vibration, 115 part-time vibration, and 103 full-time vibration |
HAV (questionnaire responses, vascular scale, VWF, numbness) |
Vibration (3 levels) |
Prevalence—Numbness: High = 84%; Med = 50% None = 17% White finger: High = 71% Med = 33% None = 6% |
OR = 2.9 when vascular stage was polychotomous outcome variable (CI = 1.7-5.0) for each log unit increase in total hours of vibration tool use; OR = 1.8 (CI = 1.2-2.9) when sensorineural stage was the outcome |
|
McKenna et al., 1993 |
Riveters (46 matched with 46 controls |
Systolic blood pressure (after cold |
Vibration (riveter—non riveter); |
OR = 7.7 Incidence C |
Page 137
on age and smoking status) |
immersion, after work; 3 circulating markers of vascular activity) |
Counter pressure group, gun holder group, both |
pressure = 45% Gun holder = 10% Both = 27% |
|||
Nagata et al., 1993 |
179 forestry workers and chainsaw operators, and 205 controls |
Raynaud's, sclerodactyly hand edema (clinical exam, interviews) |
Vibration (yes/no) |
Raynaud's: OR = 7.06 |
2.51-19.87 |
|
Scelerodactyly: OR = 6.54 (long term) |
3.30-13.36 |
|||||
OR = 7.05 (short term) |
3.41-14.60 |
|||||
Taylor et al., 1984 |
30 stone cutters |
VWF (PE) |
Vibration (yes) |
80% VFW |
No controls |
|
Virokannas, 1995 |
31 railway workers and 32 lumberjacks |
Sensory disturbances in peripheral nerves (VPT, clinical exam, ENMG) |
Vibration (hand held tamping machines vs. chainsaws) |
Exposure duration & VPT (log scale) |
||
Rail workers: r = .55-.47 |
p=.017-.001 |
|||||
Lumberjacks: r = .77-.59 |
p=.003-.0001 |
|||||
Posture and Vibration |
||||||
Dimberg et al., 1989 |
2,814 industrial workers in aircraft engine division |
Cervobracial (Sx, self report, quest, clinical exam) |
Physical work (low, medium, high based on amount of body rotation); vibration (yes/no) |
Vibration (OR = 2.0) Prevalence significantly higher for shoulder, neck, and hand symptoms in high work condition |
||
continues |
Page 138
Author |
Study Population |
Outcomes |
Work-Related Risk Factor |
Risk |
95% Confidence Interval |
Comments |
Posture and Motion |
||||||
Bernard et al., 1994 |
973 newspaper workers |
Neck, shoulder, hand-wrist pain (Sx) self report |
Hours of keyboard use (work sample, self-report) |
Hand-wrist OR = 2.5 |
1.6 - 3.9 |
|
Murata et al., 1996 |
23 VDT workers and 19 students |
NCV median nerve |
VDT use > 6 hrs/day |
Mean differences wrist-finger, wrist-palm |
p<0.001 |
Students: very minor VDT use |
Sauter, Schleiffer, and Knutson, 1991 |
539 VDT workers in two state agencies—detailed analysis for 40 |
Upper extremity discomfort (self report by body region) |
Workstation layout (e.g., keyboard height) |
Significant r2 for upper arm angle, relative keyboard height, relative document distance, righth and extended; Overall adjusted r2 modest |
No epidemiologic measures, no psychosocial measures |
|
All Exposures (and Load) |
||||||
Franklin et al., 1991 |
Workers in Washington State reporting CTS |
CTS based on workers' compensation claims |
Analysis by industry |
Rate ratio: 13.8 (meat packing); 1.1 (Clerical NOC) |
Meat packing (11.6-16.4) Cler NOC (0.1-0.1) |
Page 139
Schierhout, Meyers, and Bridger, 1995 |
401 workers from 7 sectors of manufacturing industry (11 factories, 46 jobs with ergonomic stressors) |
Musculoskeletal pain (self-report body diagnosis) |
Posture, repetition, force, vibration, and other workplace environment factors |
Neck/shoulder (repetition) OR = 5.38 |
1.16-25 |
|
Forearm, wrist, hand (wrist posture) OR = 10.2 |
1.39-75.6 |
|||||
Stenlund, 1993 |
Construction workers—54 bricklayers, 55 rock blasters, and 98 foremen |
Shoulder tendinitis (PE, medical history) |
Load, vibration, hours of exposure |
Rockblasters vs. foremen: OR = 3.3 left shoulder |
1.21-9.15 |
|
OR = 1.71 right shoulder |
0.71-4.17 |
|||||
Vibration: OR = 1.84 left shoulder |
1.10-3.07 |
|||||
OR = 1.66 right shoulder |
1.06-2.61 |
|||||
Stenlund et al., 1992 |
Construction workers—54 bricklayers, 55 rock blasters, and 98 foremen |
Osteoarthrosis acromioclavicular joints (radiograph) |
Load, years of lifting, vibration |
Right side: |
Exposure based on job title (all subjective) |
|
Load: OR = 3.18 |
1.09-0.24 |
|||||
Vibration: OR = 2.18 |
1.04-4.56 |
|||||
Left side: |
||||||
Load: OR = 10.34 |
3.10-34.46 |
|||||
Vibration: OR = 3.13 |
1.40-6.99 |
|||||
continues |
Page 140
Author |
Study Population |
Outcomes |
Work-Related Risk Factor |
Risk |
95% Confidence Interval |
Comments |
Wells et al., 1983 |
Letter carriers—104 with weight increase and 92 without weight increase; 76 meter readers; and 127 postal clerks |
Significant joint problems (questionnaire and point scale) |
Carrying weight (increased, standard, none), walking (yes/no) |
Increased weight: 23% shoulder, 31% back Standard weight: 13% shoulder, 24% back Meter readers: 7% shoulder, 21% back Postal clerks: 5% shoulder, 11% back |
25-35 lbs vs. none |
|
Wieslander et al., 1989 |
38 men who underwent surgery for CTS, 69 hospital controls, and 74 general population controls |
CTS (hospital records, telephone interviews) |
Repetition, load, vibration, etc. (obtained by interview) |
Number of risk factors: 1: OR = 1.7 2: OR = 3.3 >2: OR = 7.1 |
0.6-4.4 1.2-9.1 2.2-5.2 |
NOTE: CTD = cumulative trauma disorder; CTS = carpal tunnel syndrome; CVE = cumulative vibration exposure; ENMG = electoneuromyography; HAV = hand-arm vibration; HHS = hypothenar hammer syndrome; NA = not available; NOC = not otherwise classified; NCV = nerve conduction velocity; OR = odds ratio; PE = physical examination; POR = prevalence odds ratio; Sx = symptoms; VPT = vibration perception threshold; VDT = video display terminal; VWF = vibration white finger.
Page 141
Author |
Study Population |
Outcomes |
Psychosocial Risk Factors |
Significancea |
Attributable Fractionb |
Design Comments |
Other Comments |
Bergenuud and Nilsson, 1988 |
1,542 general population, 55-year-olds (575 at follow-up) |
Back pain report (yes/no) |
Job satisfaction (self-report, nonstandardized item) |
S |
NA |
Prospective 45 years |
69% participation |
Mentally demanding work (self-report, nonstandardized) |
S |
||||||
Biering-Sörensen, Thomsen, and Hilden, 1989 |
928 general population |
LBP report past 12 months (yes/no) |
Work speed |
NS |
NA |
Prospective 12 months |
99% participation |
Monotony |
NS |
||||||
Job satisfaction (measures were self-reports, nonstandardized) |
S |
||||||
Bigos et al., 1991 |
1,223 ages 21-67 in aircraft industry, 22% female |
Reported injury (injury claim or treatment at occupational health service) |
Enjoy work |
S |
41% (satisfaction) |
Longitudinal, 12-month follow-up |
Study controlled for other factors. MMPI also significant predictor |
Work relations (both measured by Modified Work APGAR) |
S |
||||||
Cats-Baril and Frymoyer, 1991 |
252 patients with new episode of LBP, % female not stated |
Reported return to work (not employed and attributed to LBP) |
Job satisfaction (self-report) |
S |
NA |
Prognostic 3 and 6 months |
Psychosocial factors correctly classify 89% |
continues |
Page 142
Author |
Study Population |
Outcomes |
Psychosocial Risk Factors |
Significancea |
Attributable Fractionb |
Design Comments |
Other Comments |
Coste et al., 1994 |
103 primary care patients, pain < 72 hours |
Recovery and return to work (no reported pain,VAS, or disability, not on sick leave, Roland & Morris Disability Questionnaire) |
Job satisfaction (self-report, not stated how measured) |
S |
NA |
Prospective 5 assessments during 3 months |
Low job satisfaction one of significant factors (others = pain, previous disability, compensation, male) |
Fishbain et al., 1997 |
128 patients with back pain > 6 months, 57% female |
Work status (insurance and medical records = normal employment) |
Intent to work |
S |
NA |
Prospective 30 months |
54% participation rate 75% correctly classified |
Job stress |
S |
||||||
Belief work is dangerous (self-reports, nonstandardized items) |
S |
||||||
Hasenbring et al., 1994 |
111 acute disc prolapse, 38% female |
Pain intensity (self-rated, numerical scale) Recurrence (surgeon's rating yes/no) Early retirement (application made) |
Daily hassles at work (self-reports, standardized) |
S |
NA |
Prognostic 6 months |
Hassles was one of two best predictors (other = depression) for early retirement |
Page 143
Hazard et al., 1996 |
166 LBP injury report, % female not stated |
Return to work (self-report, not working due to LBP) |
Perceived job demands |
S |
NA |
Prospective 3 months follow-up |
11 items were good predictors producing 94% sensitivity, 84% specificity. Poor participation rate (37%) |
Relations at work |
S |
||||||
Perceived chance to work |
S |
||||||
Perceived blame (Vermont Disability Prediction Questionnaire) |
S |
||||||
Hellsing, Linton, and Kälvemark, 1994 |
121 acute back pain, 48% female |
Sick leave (number of sick days, National Insurance Authority) |
Monotonous work (self-report, nonstandardized) |
S |
NA |
Prospective 12 months |
Found function and pain intensity not to be related |
Hemingway et al., 1997 |
6,894 male and 3,414 female office workers |
Sick leave < = 7 days Sick leave > 7 days (workplace records) |
Work control |
S |
<7 days sick: control: 55%m/32%f Satisfaction: 49%m/25%f Pace: 52%m/44%f Support: 31%m/7%f Conflict: 1%m/38%f >7 days sick: Control: 38%m/48%f |
Prospective |
Controlled for other variables, All psychosocial factors significant before adjustment. Job satisfaction significant only in age-adjusted models |
Job satisfaction |
S |
||||||
Pace (self-report, nonstandardized) |
S |
||||||
continues |
Page 144
Author |
Study Population |
Outcomes |
Psychosocial Risk Factors |
Significancea |
Attributable Fractionb |
Design Comments |
Other Comments |
Satisfaction: 33%m/20%f Pace: 32%m/0%f Support: 33%m/17%f Conflict: 28%m/31%f |
|||||||
Hurri, 1989 |
188 female patients with back pain < 1 year |
Return to work (self-report) Spontaneous recovery (Oswestry LBP Questionnaire) |
Job satisfaction (self-report, standardized) |
S |
NA |
Prospective not clear, 6 months |
92% participation, Included guidance, influence, learning new, feedback, communication, etc. |
Lancourt and Kettelhut, 1992 |
134 patients on workers' compensation |
Return to work (not stated how measured) |
Stress |
S |
NA |
Prospective 6 months |
|
Job satisfaction |
NS |
||||||
Perceived load (self-reports, nonstandardized) |
S |
||||||
Leino and Hänninen, 1995 |
902 workers, 32% female |
LBP (rated frequency, examination) |
Work content |
S |
NA |
Prospective 10-year follow-up |
men = all women = S For white collar, blue collar only work control S |
Work control |
S |
||||||
Social relations (self-report, standardized) |
S |
Page 145
Linton and Halldén, 1998 |
142 acute spinal pain, 65% female |
Sick leave (reported number of days) |
Monotonous work |
S |
NA |
Prospective 6 months |
Adjusted for confounders. Five best predictors were fear-avoidance beliefs, perceived future pain, perceived work function, stress, and previous sick leave. |
Perceived work function |
S |
||||||
Job satisfaction |
S |
||||||
Belief should not work with pain (self-report, standardized) |
S |
||||||
Papageorgiou et al., 1997 |
4,501 general population, 55% female |
New episode of back pain (LBP>1 day, yes/no) |
Job satisfaction |
S |
Satisfaction: 41% Social relations: 29% |
Prospective 12 months |
Dissatisfied twice as likely to experience a new episode |
Social relations |
S |
||||||
Sufficient money (self-report, nonstandardized) |
S |
||||||
Ready et al., 1993 |
131 nurses |
Back injury (claims at work) |
Job satisfaction (RR = 2.29, 1.08 - 4.85) (self-report, nonstandardized) |
S |
56% |
Prospective 18 months |
91% participation rate |
Riihimäki et al., 1989b |
167 concrete workers and 161 house painters |
Sciatic pain (self-report, pain radiating to a leg) |
Job stress (self-report, nonstandardized) |
S |
17% |
Longitudinal 5 years |
The effect was relatively small |
continues |
Page 146
Author |
Study Population |
Outcomes |
Psychosocial Risk Factors |
Significancea |
Attributable Fractionb |
Design Comments |
Other Comments |
Riihimäki et al., 1994 |
From 2,222 male longshoremen, construction, carpenters, and office workers selected 1,149 without pain |
Cumulative incidence (3 yrs) of sciatic pain (self-report, pain radiating to a leg) |
Work pace |
S |
48% (relations with work mates) |
Prospective |
36 months |
Monotonous work |
S |
||||||
Problems in relations with workmates/supervisors (self-report, nonstandardized) |
S |
||||||
Rossignol, Lortie, and Ledoux, 1993 |
269 aircraft assembly workers |
Compensation past year (workers' compensation) Absenteeism past year (company records) Work limitation past wk. (rating) Back symptom past wk. (duration, quality, frequency) |
Boredom |
NS |
66% |
Longitudinal 12 months |
76% participation |
Job satisfaction: Compensation |
NS |
||||||
Other outcomes (OR>=3.0) (self-report, nonstandardized) |
S |
Page 147
van der Weide et al., 1999 |
142 workers on sickleave >10 days for LBP; Participation = 85% |
Functional disability (Roland & Morris Disability Questionnaire) Time to return to work (computerized records, days to return) |
12 months for function: |
Lack of variation: 23% per 10 units (0-100 scale) Satisfaction: 69% Social isolation: 88% |
Prospective 3 and 12 months |
The main factors found were radiating pain, functional disability at pretest, relations with colleagues, and high work tempo/quantity |
|
Lack of work variation |
S |
||||||
Emotional (work) effort |
S |
||||||
Lack of energy at work |
S |
||||||
Social isolation at work |
S |
||||||
Job satisfaction |
S |
||||||
For time to work: |
|||||||
Relations with colleagues |
S |
||||||
Work tempo |
S |
||||||
Work quantity (self-report, nonstandardized) |
S |
||||||
van Poppel et al., 1998 |
238 males with heavy work |
New episode LBP (self- report, yes/no) Sick leave, LBP (self-report, number of days) |
Job satisfaction (self-report, standardized) |
S |
New episode: 17% Sick leave: 17% |
Longitudinal |
Controlled for earlier back pain, age, etc. |
aResults of the relationship are denoted as S for a significant finding and NS for not significant.
bAttributable fractions were not presented by the article authors and, therefore, were calculated using results available from the data presented in the published studies.
NOTE: m = male; f = female; LBP = low back pain; NA = not available; NCV = nerve conduction velocity; PE = physical examination; Sx =symptoms; VAS = visual analog scale; VWF = vibration white finger.
Page 148
Author |
Study Population |
Outcomes |
Psychosocial Risk Factorsa |
Attributable Fractionb |
Design Comments |
Other Comments |
Adams, Mannion, and Dolan, 1999 |
403 health care workers with no serious back pain, 92% female |
“Serious” back pain (medical attention or time off work) |
Distress: + Depression: + Health locus of control: 0 (3 standardized questionnaires) |
Distress and depression: 23% |
Prospective 3 years |
90% participation rate. Included medical factors. Lateral bending, long back, lumbar lordosis, and previous back pain also predictors. |
Bigos et al., 1991 |
3,020 (1,223 participated) aircraft workers, 22% female |
Reported injury (injury claim or treatment at occupational health service) |
Enjoy work: − MMPI (hysteria): + Work relation: − (enjoy work, MMPI best predictors) (Standardized: Work APGAR) |
Enjoy work: 41% |
Prospective 3 years |
Study controlled for other factors |
Burton et al., 1995 |
252 LBP, primary care, 48% female |
Disability (Roland & Morris questionnaire) |
Distress: + Catastrophize: + Pain intensity: + Pray/hoping: + Dysfunction: + (5 standardized questionnaires) |
NA |
Prospective 1 year |
Strong design. 76% correctly classified, psychosocial factors better predictors than standard medical/history variables |
Page 149
Cats-Baril and Frymoyer, 1991 |
250 patients, new episode LBP, % female not stated |
Reported return to work (not employed and attributed to LBP) |
Work satisfaction, Status: − Perceived injury as compensatable: − Education level: − (self-reports, nonstandardized) |
NA |
Prognostic 3 and 6 months |
Predictive model with psychosocial factors correctly predicts 89% |
Croft et al., 1996 |
4,501 general population, % female not stated |
New episodes of pain (either a consultation or self−reported symptoms in postal survey) |
Distress: − (standardized; General Health Questionnaire) |
44% |
Prospective 12 months |
1.8 increase even when bias factors controlled |
Cherkin et al., 1996a |
219 primary care patients LBP, 47% female |
Symptom satisfaction (self-report, standardized) |
Depression: + (standardized, Symptom Checklist-90 Depression Scale) |
52% |
Prospective 12 months |
Depression (OR=2.3), Pain below knee (OR=2.2) |
Dionne et al., 1997 |
1,213 primary care, acute LBP, 53% female |
Disability |
Somatization: + Depression: + |
NA |
Prospective 24 months |
85% correctly classified with depression and somatization |
continues |
Page 150
Author |
Study Population |
Outcomes |
Psychosocial Risk Factors a |
Attributable Fraction b |
Design Comments |
Other Comments |
Engel, von Korff, and Katon, 1996 |
1,059 primary care, LBP, 53% female |
Costs (computerized records, back pain, and total) |
Depression: + (Standardized; Symptom Checklist 90-Depression Scale) Pain: + (1. standardized; Graded Chronic Pain Scale; 2.0 number ofdays/6 months) |
Depression: 38% Pain: 70% |
Prospective 12 months |
Pain status and disc disorders strong predictors, depression also predicted high costs. |
Estlander, Takala, and Viikari-Juntura, 1998 |
452 forestry-industry workers with neck, shoulder or back pain |
Change in pain status (standardized ratings) |
Distress: 0 Depression: 0 Self-efficacy: 0 Work Prognosis: 0 Disability: + Work characteristics: 0 (3 standardized, 3 nonstandardized questionnaires) |
NA |
Prospective 24 months |
Distress, self-efficacy, depression, and work prognosis were significant in univariate analyses, All had pain at baseline. |
Page 151
Feyer et al., 2000 |
694 nursing students (61% participation at 1 year), 85% female |
New episode(s) of back pain (self-report, yes/no) |
During training: |
During training: |
Prospective Every 6 months up to 3 years |
Relatively low participation rate (61%). Controlled for previous back pain and other confounders. |
Distress: + |
Distress: 30% |
|||||
Life events: + |
Life events: 5% |
|||||
Job satisfaction: + |
Satisfaction: 2% |
|||||
At 1 year: |
At 1 year: |
|||||
Distress: + |
Distress: 63% |
|||||
Life events: 0 |
Life events: NA |
|||||
Job satisfaction: 0 |
Satisfaction: NA |
|||||
(3 standardized questionnaires) |
||||||
Fishbain et al., 1997 |
128 patients with back pain > 6 months, 57% female |
Work status (insurance and medical records = normal employment) |
Gender: + Intent to work: + Job stress: + Age: + Education: + Belief work dangerous: + (nonstandardized questionnaire) |
NA |
Prospective 30 months (work assessed retrospectively) |
75% correctly classified at 30 months |
Gatchel et al., 1994 |
152 chronic LBP, 36% female |
Return to work (self-report; yes/no) |
Psychopathology: 0 (standardized; SCID) |
NA |
Prospective Prognosis 12 months |
If psychopathology is addressed, it does not affect outcome |
Page 152
Author |
Study Population |
Outcomes |
Psychosocial Risk Factorsa |
Attributable Fractionb |
Design Comments |
Other Comments |
Gatchel, Polatin, and Kinney, 1995 |
324 acute LBP, 36% female |
Return to work (self-report; yes/no) |
Pain and disability score: + Axis I depression, anxiety, substance abuse disorders: 0 Axis II personality disorder: + MMPI Hysteria: + (Standardized questionnaires and interview) |
Pain and disability: 38% Axis II personality: 49% |
Prospective 6 months |
Pain and disability are important predictors even when injury severity and work controlled for. 87% correctly classified. |
Gatchel, Polatin, and Mayer, 1995 |
421 patients with acute back pain, 38% female |
Job status (self- report and insurance data) |
Pain and disability: − Psychopathology: 0 MMPI: − (Standardized; MMPI, SCID) |
Pain and disability: 38% MMPI: 33% |
Prospective 3, 6, 9, 12 months |
91% correctly classified robust psychological factor; psychopathology does not predispose |
Hansen, Biering-Sörensen, and Schroll, 1995 |
673 general population, 43% female |
Back pain (10 prevalence; yes/no) |
MMPI: 0 (standardized; MMPI) |
NA |
Prospective 10 and 20 years |
MMPI not related to a new episode |
Page 153
Hasenbring et al., 1994 |
111 acute disc prolapse, 38% female |
Pain intensity (numerical scale) Recurrence (surgeon's rating) Early retirement (application made) |
Depression: + Avoidance: + Nonverbal pain behavior: + Search social support: + (4 standardized questionnaires) |
NA |
Prognostic 6 months |
Psychosocial variables correctly classified 70%, while all variables classified = 86% Psychosocial variables are most important |
Hazard et al., 1996 |
166 LBP injury report, % female not stated |
Working (not working = self-report not working due to LBP) |
Pain intensity: + Job demands: + Perceived future problem: + Relations at work: + Perceived chance to work/6 months: + Blame: + (Standardized; Vermont Disability Prediction Questionnaire) |
NA |
Prospective measure within 15 days, 3 months outcome |
11 questions were good predictors. 94% sensitivity, 84% specificity |
Hellsing, Linton, and Kälvemark, 1994 |
121 acute neck/back pain, 48% female |
Sick leave (Insurance Authority, number of days) |
ADL function: 0 Pain intensity: 0 Monotonous work: + (ADL and pain = standardized; monotonous = nonstandardized) |
NA |
Prospective 1 year |
|
continues |
Page 154
Author |
Study Population |
Outcomes |
Psychosocial Risk Factors a |
Attributable Fraction b |
Design Comments |
Other Comments |
Junge, Dvorak, and Ahern, 1995 |
164 secondary care, chronic LBP, 40% female |
Response to surgery (Good = pain <6 VAS; sick leave <6 months; no regular visits to doctor or hospitalization during past year) |
Depression + (Standardized; Beck's Depression Inventory) |
NA |
Prospective 6-12 months |
Outcome correctly classified by pain (73%), psychological variables (63%), and overall score (80%) |
Klenerman et al., 1995 |
300 acute LBP, 50% female |
Pain and disability (rated pain, Roland & Morris Disability Questionnaire) Sick leave (self-report) |
Fear avoidance beliefs: + Psychosocial variables (distress, experienced disability, depression, pain intensity): + (7 standardized questionnaires) |
NA |
Prospective measures at 1 and 8 weeks to predict 12 months |
66% correctly classified with only fear-avoidance variables, 88% with all variables. |
Page 155
Lancourt and Kettelhut, 1992 |
134 patients receiving workers' compensation, acute to chronic, % female not stated |
Return to work (not stated how measured) |
Stress: + Family factors: + Coping: + Job satisfaction: 0 Nonorganic signs: + (self-reports, nonstandardized) |
NA |
Prospective 6 months |
Combination of physical and psychological factors showed good predictive ability |
Lehmann, Spratt, and Lehmann, 1993 |
55 acute LBP, 33% female |
Time to return to work (self-report; <1 month to not returned) |
Pain: 0 Job satisfaction/work: 0 History: 0 Function: 0 (Standardized and some nonstandardized) |
NA |
Prospective 6 months |
Small n provides limited power |
Leino and Magni, 1993 |
607 employees, 36% female |
Musculoskeletal pain (self-report, rated frequency) |
Depressive symptoms: + Distress: + (nonstandardized questionnaire) |
NA |
Prospective 3-, 5-year periods |
Effects of depression were general as they predicted pain at various sites |
Linton et al., 1999 |
449 pain free general population, 49% female |
New episode spinal pain (self-report, yes/no) Activity hindered (standardized exam) |
Fear-avoidance: + (modified Fear-Avoidance Behavior Questionnaire) Catastrophizing: + (Pain and Catastrophizing: Scale) |
Fear-avoidance: 51% pain 41% activity Catastrophizing 35% pain 33% activity |
Prospective 1 year |
Fear-avoidance produced an OR=2.04 for pain, while catastrophizing was 1.5. |
continues |
Page 156
Author |
Study Population |
Outcomes |
Psychosocial Risk Factors a |
Attributable Fraction b |
Design Comments |
Other Comments |
Linton and Halldén, 1998 |
142 acute spinal pain, 65% female |
Pain (rated) Function (ADL) Sick leave (days) (self-report on standardized items) |
Work: − Pain: + Fear-avoidance: + ADL: − Coping: 0 Job satisfaction: − Perceived future: − Stress/anxiety: + Mood: − (standardized) |
NA |
Prospective 6 months |
The best predictors for sick leave were fear-avoidance, perceived future pain, perceived work function, stress, and earlier sick leave. |
Magni et al., 1993 |
2,341 general population (representative 25- to 74-year-olds) 57% female |
Chronic pain (pain > 1 month during past year) |
Depression: + (Center for Epidemiologic Studies Depression Scale) |
NA |
Prospective 8 years |
Depression increased the risk for MSP by 2- to 3-fold. |
Magni et al., 1994 |
2,324, 57% female |
Chronic pain (pain > 1 month during past year) |
Depression: + (Center for Epidemiologic Studies Depression Scale) |
53% |
Prospective 8 years |
Depression related to pain (OR=2.14) and pain related to depression (OR=2.85) |
Page 157
Main et al., 1992 |
567 patients LBP referred to orthopedic clinic (107 included in follow-up), 51% female |
Disability (Roland and Morris Disability Questionnaire) |
Depression (Zung): + Distress (MSPQ): + DRAM (distress and depression): + |
Mild depression: 48% DRAM: 81% |
Prognosis 1 to 4 years |
Scores on DRAM highly related to future disability |
Mannion, Dolan, and Adams, 1996 |
403 volunteers, no pain, 92% female |
Back pain (yes/no) Pain-absenteeism (yes/no) Consultation (yes/no) |
Distress: + (MSPQ) Depression: + (Zung) Health locus of control: 0 (Multidimensional Health Locus of Control) |
NA |
Prospective 6,12,18 months |
Distress and depression were good predictors, but present at beginning so not causal |
Papageorgiou et al., 1997 |
4,501 general population, 55% females |
New episode of back pain (LBP >1 day, yes/no) |
3 questions: 1. job satisfaction: − 2. relations at work: 0 3. sufficient money: − (nonstandardized) |
Satisfaction: 41% Social relations: 29% |
Prospective 12 months |
Dissatisfied were twice as likely to experience a new episode |
continues |
Page 158
Author |
Study Population |
Outcomes |
Psychosocial Risk Factors a |
Attributable Fraction b |
Design Comments |
Other Comments |
Philips and Grant, 1991 |
117 acute back, 57% female |
Pain status (pain/no pain) |
Pain intensity: + Pain quality: + Negative cognitions: + Anxiety: + Impact (SIP): + (6 standardized questionnaires) |
NA |
Measures at pre−3 and −6 months |
80% were correctly classified |
Pietri-Taleb et al., 1994 |
1,015 men < 7 day neck pain |
Severe neck pain (> 30 days neck pain preceding year) |
Hysteria: + Neuroticism: + Depression: + (Middlesex Hospital Questionnaire, Maudsley Personality Inventory) |
Hysteria: 44% Neuroticism: 21% Depression: 14% |
3 years |
Complex interaction between occupation and results. Other parts of Maudsley and Middlesex not significant |
Potter and Jones, 1992 |
45 patient at 4 weeks pain, % female not stated |
Pain (persistent pain for 26 weeks) |
Pain intensity: + Depression: + Passive coping: + (Standardized) |
NA |
Prospective followed 26 weeks |
|
Radanov et al., 1994 |
117 whiplash |
Symptoms (self-reported symptoms, yes/no) |
Personality: 0 Cognitive failure: 0 (Standardized) |
NA |
Longitudinal 3, 6, 12 months |
Neither personality nor psychoneurological variables predicted |
Page 159
Werneke, Harris, and Lichter, 1993 |
183 LBP patients off work, 33% female |
Return to work (self-report, yes/no) |
Behavioral signs test: − (standardized) |
NA |
Prognostic 3 months |
All 8 behavioral signs significantly higher for the“failed” group at discharge |
Viikari-Juntura et al., 1991 |
154 general population, 47% female |
Neck or back pain as adult (> 7 days sick leave, high disability rating = severe) |
Intelligence: 0 Alexithymia: 0 Social confidence: 0 (mostly standardized) |
NA |
Prospective measures taken in adolescence |
Personality, etc.. in childhood did not predict future problem |
Von Korff, Le Resche, and Dworkin, 1993 |
803 HMO enrollees, 59% female |
Back pain onset (self-report) |
Depression: 0 (Symptom Checklist 90 Depression) Number of pain conditions: + (self-report, yes/no) |
Depression: NA Number of pain: 52% |
Prospective 3 years |
Depression related to chest and headache pain, but not directly to back pain onset. Number of pain sites was predictive |
Öhlund et al., 1996 |
103 patients LBP, subacute |
Return to work (working >50%) |
Pain drawing: + (standardized) |
NA |
Prospective prognosis |
aA positive relationship is denoted with a plus (+), a negative relationship with a minus (−) and no relationship with a zero (0).
bAttributable fractions were not presented by the article authors and, therefore, were calculated using results available from the data presented in the published studies.
NOTE: ADL = activities of daily living; LBP = low back pain; MMPI = Minnesota Multiphasic Personality Inventory; NA = not available; OR = odds ratio; SCID = Structured Clinical Interview for DSM Disorders; SIP = Sickness Impact Profile.
Page 160
Author |
Study Population |
Outcomes |
Psychosocial Risk Factors |
Risk |
95% Confidence Interval |
Attributable Fractiona |
Ahlberg Hultén, Theorell, and Sigala, 1995 |
90 female health care personnel |
Symptoms of the shoulder: Pain during the last month (self reported questionnaire alternatives from no to almost daily) Prevalence total population: 26 % Prevalence unexposed not presented |
Poor support—Low positive factors index: 5-item factor on relationships at work, which was the result of a factor analysis of a 16-item index of relationships at work; Items: calm and pleasant atmosphere, good sense of fellowship, support of workmates, ba |
Positive association, ordinal logistic regression estimate (0.18) |
- |
|
High job strain (JCQ)—sum score for skill utilization (4 items) and authority over decisions (2 items) (combined often called control) divided by job demands scale (5 items) |
No association—ordinal logistic regression estimate (0.94) |
- |
||||
Bergqvist et al., 1995b |
260 VDU workers, Prevalence unexposed not presented |
Shoulder/neck discomfort during the last 12 months (self reported Nordic Questionnaire) Prevalence total population: 61.5% |
Limited rest break opportunities |
2.7 |
1.2-5.9 |
63% |
High perceived stress: Stomach related stress reaction |
3.5 |
1.5-8.2 |
71% |
Page 161
Worry/distress; negative affectivity: sum score containing items on anger, disgust, scorn, guilt, fearfulness, depression |
2.0 |
1.0-4.2 |
50% |
|||
Shoulder/neck symptoms during the last 7 days that interfered with work activities (self report questionnaire) Prevalence total population: 7.3% |
High perceived stress: Stomach related stress reaction |
5.4 |
1.6-7.6 |
81% |
||
Any diagnosis in the shoulder region established in a physiotherapy examination based on tests and anamneses over the previous 12 months Prevalence total population: 11.9% |
Limited work task flexibility |
3.2 |
1.2-8.5 |
69% |
||
Limited rest break opportunities |
3.3 |
1.4-7.9 |
70% |
|||
High perceived stress: Stomach related stress reaction |
4.8 |
2.1-10.7 |
79% |
|||
Arm/hand discomfort during the last 12 months (self reported Nordic Questionnaire) Prevalence total population:29.9% |
Poor social support: Limited or excessive peer contacts |
2.1 |
1.1-4.1 |
52% |
||
High demands: Frequent overtime |
2.2 |
1.2-4.1 |
55% |
|||
High perceived stress: Stomach related stress reaction |
3.8 |
2.0-7.3 |
74% |
|||
continues |
Page 162
Author |
Study Population |
Outcomes |
Psychosocial Risk Factors |
Risk |
95% Confidence Interval |
Attributable Fraction a |
Any diagnosis in the arm/hand region established in a physiotherapy examination; examination based on tests and anamneses over the previous 12 months Prevalence total population: 8.7% |
Poor support: Limited or excessive peer contacts |
4.5 |
1.3-15.5 |
78% |
||
Limited rest break opportunities |
2.7 |
0.8-9.1 |
63% |
|||
High perceived stress Stress reaction |
3.4 |
1.3-8.4 |
70% |
|||
Bernard et al., 1994 |
973 newspaper workers |
NIOSH case-definition (self-reported questionnaire): Pain, numbness, tingling, aching, stiffness, or burning in the shoulder area within the preceding year and no previous non-work-related accident/injury Symptoms began after current job Lasted > 1 week or at least once a week Intensity > moderate (midpoint 5-point scale) Prevalence total population: 17% |
Poor control: Perceived lack of participation in job-decision making (very little versus moderate: upper quartile versus lower quartile); NIOSH general job stress instrument (multi-item scale with adequate internal consistency) |
1.6 |
1.2-2.1 |
37% |
High demands: Perceived increased job pressure (moderately disagree versus moderately agree, upper quartile versus lower quartile); NIOSH general job stress instrument (multi-item scale with adequate internal consistency) |
1.5 |
1.0-2.2 |
33% |
Page 163
Same case-definition in the elbow-region; prevalence total population: 10% Same case-definition in hand or wrist region Prevalence total population: 22% |
||||||
High demands: Number of hours spent under a deadline per week (30-39 hours versus 0-10 hours) |
1.6 |
1.2-2.3 |
37% |
|||
Poor support: Perceived lack of support from an immediate supervisor (very much vs. a little, upper quartile versus lower quartile) |
1.4 |
1.2-2.5 |
28% |
|||
Bru and Mykletun, 1996 |
492 female hospital staff No prevalence presented (only average symptoms scores) |
Pain in the shoulder in the last 12 months; self reported, Nordic Questionnaire with adjusted answering categories on a 5-point scale developed by Westgaard Janssen, 1992a, combined with intensity score (mild to severe, 3- point scale of the Ursin Health |
Poor support: Social relations; multi-item factor based on Cooper stress check (relations with colleagues, relations with subordinates, relations with boss) |
Positive association (multiple linear regression) |
Change in T score |
- |
Low skill discretion/monotony: Work content multi-item factor based on self-designed questionnaire: Distribution, cooperation, variation, new competence, and challenge in tasks |
Positive association (multiple linear regression) |
Change in T score |
- |
|||
continues |
Page 164
Author |
Study Population |
Outcomes |
Psychosocial Risk Factors |
Risk |
95% Confidence Interval |
Attributable Fractiona |
High demands: Work overload multi-item factor based on Cooper stress check (mistakes, time pressure, overwork, work—home, feeling undervalued, managing people) |
Positive association (multiple linear regression) |
Change in T score |
- |
|||
Burdorf, van Riel, and Brand, 1997 |
144 tank terminal workers; no musculo—skeletal complaints before current job |
Self-reported pain that lasted at least a few hours during the past 12 months in the shoulder (adapted Nordic Questionnaire) Prevalence 14% |
High demands: Working under pressure (self report, one question yes/no) |
NS |
- |
- |
Poor support: Lack of social support (self report, one question yes/no) |
NS |
- |
- |
|||
Self-reported pain that lasted at least a few hours during the past 12 months in the elbow (adapted Nordic Questionnaire) Prevalence 11% |
High demands: Working under pressure (self report, one question yes/no) |
NS |
- |
- |
||
Poor support: Lack of social support (self report, one question yes/no) |
NS |
- |
- |
|||
Self-reported pain that lasted at least a few hours during the past 12 months in the wrist (adapted Nordic Questionnaire) Prevalence 9% |
High demands: Working under pressure (self report, one question yes/no) |
NS |
- |
- |
||
Poor support: Lack of social support (self report, one question yes/no) |
NS |
- |
- |
Page 165
Dimberg et al., 1989 |
2,814 industrial workers |
Many signs and symptoms established during physical examination |
High perceived job stress: Mental stress at the time symptoms started (0 to 10 indication of level) |
Correlation with trapeziums myalgia, lateral epicondylitis |
- |
- |
Engström, Hanse, and Kadefors, 1999 |
67 assembly operators |
Symptoms (ache, pain, discomfort) experienced during the previous 12 months (self-reported Nordic Questionnaire) in the upper extremities (elbow, forearm, wrists, hands, and fingers) |
Poor control: Decision latitude (influence and control over work and stimulus from the work itself; both 5-item scales with adequate internal consistency) |
Partial correlation 21 (p< 0.10) |
- |
- |
Poor support: Social support at work (co-worker and supervisor support, both 5-item scales; with adequate internal consistency) |
NS |
- |
- |
|||
High perceived job stress: Psychological load (stress at work, work load, extent of feeling tired, exhausted after work, rest break opportunities, mental strain) |
NS |
- |
- |
|||
continues |
Page 166
Author |
Study Population |
Outcomes |
Psychosocial Risk Factors |
Risk |
95% Confidence Interval |
Attributable Fractiona |
Hales et al., 1994 |
518 telecommunication employees (VDU work) |
Very well-specified case definition: Self-reported symptoms in shoulder confirmed by physical examination, according to strict criteria |
Extensive questionnaire (job characteristics inventory and job diagnostic survey included) 21 multi-item scales (i.e. job control, work pressure, work load) |
2.7 |
1.3-5.8 |
63% |
Pain, numbness, tingling, aching, stiffness, or burning within the preceding year and No previous nonwork-related accident/injury Symptoms began after current job Lasted > 1 week or at least once a week Positive physical findings in the body region specified Prevalence 22% |
Job insecurity: Fear of being replaced by computer (single item) |
|||||
Elbow problems according to above definition |
Job insecurity: Fear of being replaced by computer (single item) |
3.0 |
1.5-6.1 |
66% |
||
Job demands: Surges in work load (multi-item scale) |
2.4 |
1.2-5.0 |
58% |
|||
Low job control: Routine work lacking decision making opportunities (full-time scale) |
2.8 |
1.4-5.7 |
64% |
Page 167
Hand/wrist problems according to above definition |
High qualitative demands: i.e. high information processing demands |
2.3 |
1.4-4.3 |
56% |
||
Hoekstra et al., 1996 |
108 teleservice representatives with telephone tasks Prevalence: shoulder: 35% elbow: 20% hand/wrist: 30% |
NIOSH case-definition (self reported Q) Pain, numbness, tingling, aching, stiffness, or burning in the neck, shoulder, elbow or hand/wrist area within the preceding year and no previous nonwork-related accident/injury Symptoms began after current job Lasted > 1 week or at least once a week Intensity > moderate (midpoint 5-point scale) |
NIOSH general job stress instrument (multi-item scale with adequate internal consistency) Perceived workload variability: (continuing changing workload during the day) Rubenowitz instrument, 5 dimensions all measured with 5-item scales with adequate internal consistency. Poor control: Influence and control over work (influence on rate, method, tasks, technical matters, rules, and regulations) |
NS in final model (applies to shoulder, elbow, and hand/wrist problems each) NS in final model |
- |
|
Johansson and Rubenowitz, 1994 |
167 white-and 241blue-collar workers of 8 metal companies |
Self-reported symptoms (discomfort, aches, pain) in the shoulder region during the last 12 months (Nordic questionnaire); Work-related: and yes to the following question: ‘the symptoms are solely related to my present work' |
Poor skill discretion: Stimulus from work itself (interesting, varied, use talents and skills, learn new things, general feeling about work) |
Blue S |
White All work-related S |
|
continues |
Page 168
Author |
Study Population |
Outcomes |
Psychosocial Risk Factors |
Risk |
95% Confidence Interval |
Attributable Fractiona |
Poor social support: Supervisor climate (can ask for advice, regards viewpoints, provides information, general communication company) |
S |
S |
- |
|||
Poor social support: Relations with fellow workers (contacts, can talk, cheerful environment, discuss work problems, friends) |
NS Work-related: S |
S |
- |
|||
High perceived job stress: Psychological load (stress at work, work load, extent of feeling tired, exhausted after work, rest break opportunities, mental strain) |
S |
S |
||||
Johansson et al., 1993 |
28 workers of a truck assembly system |
Self-reported symptoms (discomfort, aches, pain) in the shoulder region during the last 12 month (Nordic questionnaire) |
Rubenowitz instrument 5 dimensions all measured with 5-item scales with adequate internal consistency |
- |
Page 169
High perceived job stress: Psychological load (stress at work, work load, extent of feeling tired, exhausted after work, rest break opportunities, mental strain) |
0.39 S (newest workstation layout) |
- |
||||
Kamwendo, Linton, and Moritz, 1991a, 1991b |
420 medical secretaries |
Self-reported shoulder pain during the previous year (6-point scale, seldom to often, dichotomized so that the outcome is often shoulder pain). Prevalence 44% Prevalence nonexposed 34% |
Index of psychosocial work environment based on 10 items (4-point scale, never to usually) and dichotomized in good ≤ 20 or poor > 20. Individual items showing a significant association with shoulder pain: Poor social support: friendly cooperation with co-workers Poor control: Poor influence on working conditions High demands: Given too much to do Work commitment (yes very/yes rather vs. not very/not at all) Poor social support: Support and help from superiors (always/mostly versus mostly not/never) |
1.87 (prevalence rate ratio of often shoulder pain) |
P<0.05 |
46% |
continues |
Page 170
Author |
Study Population |
Outcomes |
Psychosocial Risk Factors |
Risk |
95% Confidence Interval |
Attributable Fractiona |
Lagerström et al., 1995 |
688 female nursing employees |
Self-reported symptoms of shoulder pain during the last 12 months (Nordic questionnarire) supplemented with 10-point answering scale (not at all – very much) Symptoms > 0 (prevalence: 53%) Severe symptoms > 5 (prevalence: 18%) |
High demands scale JCQ |
1.65 (S) |
1.09-2.39 |
39% |
Poor stimulation at work: Skill discretion scale JCQ |
- |
- |
- |
|||
Poor control: authority over decisions scale JCQ |
1.73 |
1.13-2.67 |
42% |
|||
Work commitment (yes very/yes rather vs. not very/not at all) |
- |
- |
- |
|||
Self-reported symptoms of hand during the last 12 months (Nordic questionnaire) supplemented with 10 point answering scale (not at all – very much) Symptoms > 0 (prevalence: 22%) Severe symptoms > 5 (prevalence: 4%) |
Poor social support: Support and help from superiors (always/mostly versus mostly not/never) |
- |
- |
- |
||
High demands scale JCQ |
- |
- |
||||
Poor stimulation at work: skill discretion scale JCQ |
1.62 |
1.05-2.59 |
38% |
|||
Poor control: authority over decisions scale JCQ |
- |
- |
- |
Page 171
Leclerc et al., 1998 |
1,006 workers with industrial repetitive work (assembly, clothing, food, and, packaging) |
Diagnosis of CTS based on positive (defined criteria) Tinel's sign or Phalen's test at a medical examination or a diagnosis based on nerve condition velocity was already established Prevalence: 11.8% workers with repetitive work (range from 7.2 in food industry to 16 in packaging) 2.4% nonexposed control group (with comparable education level in jobs such as maintenance, cleaning, or catering) |
Poor work satisfaction: Satisfaction with 7 items: work station, workload, variety of work and relations at work dichotomized (high ≥ 5 and low < 5) |
1.42 |
0.95-2.11 |
29% |
Poor job control: Score 0-5 based on influence on time of break, additional breaks, pace, quantity of work, dichotomized in low and high score |
1.43 1.59 (adjusted for organizational factors) |
0.92-2.23 1.04-2.34 |
37% |
|||
Work organization (group level): Autonomy at work station |
- 2.24 |
- 1.40-3.57 |
- 55% |
|||
Just in time production External constraints (high competitiveness, subcontractor, seasonal goods, perishable foodstuffs) |
||||||
Poor psychological and psychosomatic well being (8-item scale) |
2.32 |
1.40-3.82 |
57% |
|||
continues |
Page 172
Author |
Study Population |
Outcomes |
Psychosocial Risk Factors |
Risk |
95% Confidence Interval |
Attributable Fractiona |
Lemasters et al., 1998 |
522 union carpenters with different types of carpentry work |
Telephone interview (data on reliability and validity against physical exam): Within the past 12 months have you experienced any recurring symptoms such as pain, aching, numbness in your shoulder? |
Poor job control (reliability Q referenced): Control over amount of work, availability of materials, policies and procedures, pace, quality, and scheduled hours |
1.9 |
1.1-3.2 |
47% |
High demands: exhausted end of day |
1.5 |
0.9-2.4 |
33% (NS) |
|||
Plus: |
||||||
Onset after starting as carpenter Symptoms at least once a week or lasting 1 week No history of injury |
||||||
Same question in elbow |
High demands: Exhausted end of day |
1.4 |
0.9-2.2 |
29% (NS) |
||
Poor job control (reliability Q referenced): Control over amount of work, availability of materials, policies and procedures, pace, quality, and scheduled hours |
1.6 |
0.9-2.6 |
37% (NS) |
|||
Same question hand or wrist |
High demands: Exhausted end of day |
1.5 |
0.9-2.5 |
33% (NS) |
Page 173
Poor job control (reliability Q referenced): Control over amount of work, availability of materials, policies and procedures, pace, quality, and scheduled hours |
1.6 |
1.0-2.7 |
37% |
|||
Marcus and Gerr, 1996 |
449 female office workers of 40 years or younger |
Pain or soreness of the neck or shoulder at least once per week of at least moderate intensity during the month preceding completion of the questionnaire. Prevalence neck or shoulder symptoms 63% |
Low job security (likely to lose job) |
2.23 |
1.3-3.7 |
54% |
High perceived job stress: High job stress previous 2 weeks |
2.47 |
1.2-5.1 |
60% |
|||
Pain or soreness in the finger, hands, wrists, forearms or elbows, or numbness or tingling of the fingers of at least moderate intensity during the month preceding completion of the questionnaire |
High perceived job stress: High job stress previous 2 weeks |
2.04 |
1.0-4.0 |
43% |
||
Prevalence arm symptoms is 34% |
||||||
continues |
Page 174
Author |
Study Population |
Outcomes |
Psychosocial Risk Factors |
Risk |
95% Confidence Interval |
Attributable Fractiona |
Pickett and Lees, 1991 |
79 data entry office workers in 5 different offices of the same company |
Self-reported work-related symptoms of shoulder, arm or hand/wrist; precise question not presented; shoulder symptoms prevalence 76% |
Rest breaks in task |
Not presented |
- |
- |
Perceived stress: Occupational stress: single item, portion of time at work operators perceived themselves to be under emotional or mental stress (rarely, sometimes, almost, always) |
Not presented |
- |
- |
|||
Hand-wrist symptoms: Prevalence 52% |
Occupational stress |
Not presented |
- |
- |
||
Arm symptoms: Prevalence 53% |
Occupational stress |
Not presented |
- |
- |
Page 175
Pocekay et al., 1995 |
3,175 semi-conductor workers from 8 manufacturing companies |
Several health outcomes; relationships with risk factors not separately presented: Any distal upper-extremity symptom = physician diagnosed carpal tunnel syndrome within the past year, questionnaire (self-report) diagnosed CTS, hand/wrist pain daily for 1 week within past year; elbow/forearm pain daily for 1 week within the past year Medical diagnosed CTS in past year Hand/wrist pain daily for 1 week within past year Elbow/forearm pain daily for 1 week within the past year Epidemiologic CTS in past year Daily shoulder pain for 1 week in past year Medical diagnosed tendinitis in past year |
Perceived stress: Job stress index: job is very demanding; job is very tiring; job is very stressful |
Range 1.1-1.5 |
- |
9-33% |
Non-work stress: Somatization index (symptoms over the most recent 4 weeks: feeling tired, tingling in fingers or toes, heart palpitations, feeling irritable, light headedness, lack of muscle strength, chest tightness) |
Range 1.4-1.8 |
- |
28-44% |
|||
1.4 |
- |
28% |
||||
continues |
Page 176
Author |
Study Population |
Outcomes |
Psychosocial Risk Factors |
Risk |
95% Confidence Interval |
Attributable Fractiona |
Silverstein, Fine, and Armstrong, 1987 |
136 workers more than 4 years employed in an investment casting plant |
Carefully defined and well described (additional paper) outcome assessment of hand/wrist CTD by interview and physical examination disorders, nerve entrapment, non specific included as clear pattern shown in: Interview: Pain, numbness, tingling Lasting > 1 week or > 20 times last year No acute traumatic onset Onset not before 1983 study job Physical Examination: Characterize signs and endpoints Exclude referred symptoms Prevalence: Low exposed: 5% High exposed (repetition and force): 13% |
Poor job satisfaction, assessed by interview: How often do you find your work satisfying? Very often/fairly often/sometimes/rarely Little variation in job dissatisfaction was presented In general the workers reported to be very or fairly satisfied with their work |
No association |
- |
- |
No stimulus from work, assessed by interview with the following question: How often do you find your work interesting? Very often/fairly often/sometimes/rarely |
No association |
- |
- |
Page 177
Hoekstra, Hurrell, and Swanson, 1995 |
108 workers at 2 teleservice centers |
Any symptoms (pain, numbness, tingling, aching, stiffness, or burning) within the preceding year and all of the following: No preceding acute and non occupational injury Symptoms began after starting the current job Symptoms lasted > 1 week or occurred at least once a month within the past year Symptoms were reported as moderate (midpoint) or worse on 5-point intensity scale |
Poor job control: Job control Not presented was measured with a NS multi-item scale. |
Not presented NS |
- |
- |
Variability of workload: Not presented Perceived workload NS variability was measured with a multi-item scale; specified as continually changing workload during the day Although not explicitly stated, high-perceived workload variability is presumed to be the risk full exposure and not low |
Not presented NS |
- |
- |
|||
Shoulder: prev 35% |
||||||
Elbow prevalence: 20% |
Poor job control |
Not presented NS |
- |
- |
||
Variability of workload |
Not presented NS |
- |
- |
|||
Hand/wrist: prevalence: 30% |
Poor job control |
Not presented NS |
- |
- |
||
Variability of workload |
Not presented NS |
- |
- |
|||
continues |
Page 178
Author |
Study Population |
Outcomes |
Psychosocial Risk Factors |
Risk |
95% Confidence Interval |
Attributable Fraction a |
Toomingas et al., 1997b |
83 male furniture movers, 89 female medical secretaries, 96 men and 90 women from the working population, resulting in 358 men and women in various occupations, but with large groups of males with heavy work and females with office work |
Nordic Questionnaire and 24 signs recorded at the physical examination were included concerning neck/shoulder/elbow/hand/wrist. Signs and symptoms were combined in two relevant syndromes for the neck/upper extremities, i.e., tension neck syndrome and tendalgia of the upper extremities. Outcome-variables: Symptoms (Nordic) Signs (24 in total) Syndromes (combined signs and symptoms) |
High job demands: Multi-item scale JCQ |
- |
- |
- |
Low control: Multi-item scale: Low decision latitude (low control and little stimulus from work, learning ability, etc.) |
NS |
NS |
- |
|||
Poor social support Multi-item scale High job strain: Job demands divided by decision latitude |
Shoulder 3.2 |
1.3-7.8 |
68% PR |
|||
Hand/wrist 1.8 |
1.1-3.1 |
44% PR |
||||
Shoulder 2.2 |
1.0-5.1 |
55% PR |
||||
Hand/wrist 1.5 |
0.8-2.8 |
33%PR |
Page 179
Westgaard, Jensen, and Hansen, 1993 |
52 female production workers (chocolate plant) and 34 female office workers |
Symptom score for each region based on intensity and frequency of symptoms in the last 12 months and their whole employment period within the present function Ranged from no symptoms to daily occurrence of severe symptoms: Shoulder/neck |
Perceived stress Overall psychosocial work-related stress score based on a 14 item questionnaire with items on: Mental stress due to work task, new work tasks Stress due to reorganization Demands because of efficiency, work speed Effect of redundancies Personal development Support by colleagues and supervisor Total score dichotomized, but the way it is dichotomized is unclear |
Positive association |
- |
- |
Arms |
Perceived stress |
Positive association |
- |
- |
||
continues |
Page 180
Author |
Study Population |
Outcomes |
Psychosocial Risk Factors |
Risk |
95% Confidence Interval |
Attributable Fractiona |
Westgaard and Jansen, 1992a, 1992b |
210 production workers, mainly sewing machine operators in several plants of a garment industry and 35 office workers employed at this industry |
Symptoms score based on frequency and intensity Shoulder/neck |
Nonwork distress Scoring of psychological problems by the interviewer in low, intermediate, high after a worker interview (based on interviewer's impression) High indicates recurring depression or anxiety |
No association |
- |
- |
Arms |
Nonwork distress |
No association |
- |
- |
||
Zetterberg et al., 1997 |
564 car assembly workers (440 men and 124 women) |
Symptoms: Nordic Questionnaire Extensive physical examination; 114 signs established (76 hand/wrist), including: myalgia, impingement, epicondylitis, nerve entrapment, tendinitis, joint signs symptoms/signs shoulder |
Perceived stress Work satisfaction 5-item work APGAR but questions taken apart in support, satisfaction, and stress |
Positive association |
- |
- |
Low social support |
Positive association |
- |
- |
|||
Poor job satisfaction |
Positive association |
- |
- |
Page 181
Symptoms/signs wrist hand |
Perceived stress |
Positive association |
- |
- |
||
Low social support |
- |
- |
- |
|||
Poor job-satisfaction |
- |
- |
- |
|||
Magnavita et al., 1999 |
2,041 physician sonographers |
Self-reported question with a 21-item symptom list. Divided in syndromes by factor analysis Hand/wrist concerned 6 items. Three or more of these symptoms of the hand/wrist region is the effect studied. Prevalence: 5.3% |
Limited rest break opportunities: Long average time executing sonology activities without intermittent rest break is only a proxy for rest break opportunities. This variable measures more physical load than psychosocial load and additional measures of perceived time pressure or job demands were not included |
1.50 |
1.1-2.1 |
33% |
aThe attributable fraction is calculated with the OR as estimate for the relative risk. This approximation will be fairly accurate when the prevalence of the health effect at study is below 20-30%. With higher prevalences the OR is an overestimation of the relative risk and thus the attributable fraction is overestimated. Attributable fractions were not presented by the article authors and, therefore, were calculated using results available from the data presented in the published studies.
NOTE: CTS = carpal tunnel syndrome; JCQ = job content questionnaire; NS = not significant; S = significant; VDU = video display unit.
Page 182
Author |
Study Population |
Outcomes |
Psychosocial Risk Factors |
Risk |
95% Confidence Interval |
Attributable Fraction |
Bergqvist, 1995 |
341 visual display unit workers |
Shoulder-neck discomfort during the last 12 months (Nordic Questionnaire) Prevalence total population at end of follow up: 44% |
Increased perceived monotony |
- |
- |
- |
Prevalence unexposed not presented |
Elbow-shoulder discomfort during the last 12 months (Nordic Questionnaire) Prevalence total population at end of follow up: 27% |
Increased perceived monotony |
- |
- |
- |
|
Hand/wrist discomfort during the last 12 months (Nordic Questionnaire) Prevalence total population at end of follow up: 16% |
Increased perceived monotony |
1.7 |
0.6-4.4 |
41% |
||
3.1 |
1.2-7.8 |
68% |
Page 183
Ferreira, De Souza Conceição, and Hilário Nascimento Salvida, 1997 (retrospective cohort) |
106 bank employees (telephone tasks) |
History in medical records of one or more periods of upper extremity symptoms with time away from work confirmed by at least two medical specialists (who based the diagnosis on recurrent pain with or without clinical evidence from physical examination of tendon or tendon sheath impairment or nerve entrapment based) |
Time pressure increase (i.e., shorter processing time task) Change in management (new administrative procedures) Registered overtime work Rest break opportunities |
Limited rest breaks and relatively high time pressure were associated with WRUED |
- |
- |
Roquelaure et al., 1997 |
65 (55 women, 10 men) cases with CTS matched with 65 controls (55 women, 10 men) Cases and controls recruited from television manufacturing plant |
Case: blue-collar worker, 18-59, with medical history of carpal tunnel syndrome (CTS) between 1/1/1990 and 12/30/1992. Subjects with a history of CTS problems, diabetes, thyroid or musculoskeletal dysfunction, malignancies, rheumatic diseases before 1990 excluded. Referent: blue-collar, same gender, same year of birth, free of CTS or musculoskeletal disorders of the upper limb from 1984 to 1992. |
Work organization factors: No job rotation between different work stations No association for: Autonomy: possibility to choose the way the work is done Rest break opportunities: duration and number of breaks |
6.3 |
2.1-19.3 |
NA |
NOTE: CTS = carpal tunnel syndrome; WRUED = work-related upper extremity disorder(s).