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Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
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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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
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    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.

  • 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).

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-

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
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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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
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among the exposed would be reduced if the exposure were eliminated. This fraction is calculated as the ratio of (RR1)/RR, where RR is the relative risk or the prevalence ratio of risk in the exposed compared with the unexposed:

AF e = (RR1)/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.

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
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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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
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BOX 4.1 Individual Factors Considered in Analyses Form Used in Describing Studies Included in the Review

Described

Used in Analysis

Does Not Vary

Age

Gender

Body mass index

Weight

Height

Smoking

Marital status

Income

Educational status

Comorbid states

Hormone-related conditions (e.g., pregnancy)

Strength or capacity

Race

Workers' compensation policies

Nonoccupational exposure factors

Methods used to control confounding:

Matching

Stratification

Standardization

None

Regression

Other: ——

Consideration of interactions:

Interaction between different types of work exposures

Interaction between work exposures and nonwork exposures/cofactors



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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
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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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
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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;

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
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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.

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
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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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
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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.

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
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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-

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
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TABLE 4.1 Outcome Measures in Epidemiologic Studies of Work and Back and Upper Extremity Musculoskeletal Disorders

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.

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
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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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
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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-

TABLE 4.2 Summary of Epidemiologic Studies with Risk Estimates of Null and Positive Associations of Work-Related Risk Factors and the Occurrence of Back Disorders

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.

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
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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-

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
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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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
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TABLE 4.3 Summary of Epidemiologic Studies with Risk Estimates of Null and Positive Associations of Specific Work-Related Physical Exposures and the Occurrence of Upper Extremity Disorders

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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
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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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
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(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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
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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

TABLE 4.4 Summary of Work-Related Psychosocial Factors and Back Pain: 21 Prospective Studies

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.

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
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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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
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TABLE 4.5 Summary of Individual Psychosocial Factors and Back Pain: 38 Prospective Studies

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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
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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-

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
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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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
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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.

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
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TABLE 4.6 Summary of Epidemiologic Studies: Psychosocial Risk Factors and Work-Related Upper Extremity Disorders

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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
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TABLE 4.6 Continued

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.

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
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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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
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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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
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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.

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
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Page 116

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
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Appendix

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

Page 118

APPENDIX TABLE 4.1 Significant Associations Between Work-Related Risk Factors and the Occurrence of Back Disorders, Expressed as Odds Ratio, in Cross-Sectional Epidemiologic Studies Among Occupational Populations

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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
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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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
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APPENDIX TABLE 4.1 Continued

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.

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
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APPENDIX TABLE 4.2 Significant Associations Between Work-Related Risk Factors and the Occurrence of Back Disorders, Expressed as Odds Ratio, in Cross-Sectional Community, Based on Epidemiologic Studies

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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
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Page 122

APPENDIX TABLE 4.2 Continued

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.

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

Page 123

APPENDIX TABLE 4.3 Significant Associations Between Work-Related Risk Factors and the Occurrence of Back Disorders, Expressed as Relative Risk, in Longitudinal Epidemiologic Studies Among Occupational Populations

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.

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

Page 124

APPENDIX TABLE 4.4 Significant Associations Between Work-Related Risk Factors and the Occurrence of Back Disorders, Expressed as Odds Ratio, in Case-Control Epidemiologic Studies Among Occupational Populations

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.

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

Page 125

APPENDIX TABLE 4.5 Associations Between Work-Related Risk Factors and the Occurrence of Upper Extremity Disorders, Expressed as Odds Ratio, in Epidemiologic Studies Among Occupational Populations

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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

Page 126

APPENDIX TABLE 4.5 Continued

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%

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

Page 127

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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

Page 128

APPENDIX TABLE 4.5 Continued

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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

Page 130

APPENDIX TABLE 4.5 Continued

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%

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

Page 132

APPENDIX TABLE 4.5 Continued

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.

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

Page 133

APPENDIX TABLE 4.6 Epidemiologic Studies Providing Supportive Evidence on Associations of Physical Factors with Upper Extremity Musculoskeletal Disorders

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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

Page 134

APPENDIX TABLE 4.6 Continued

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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

Page 136

APPENDIX TABLE 4.6 Continued

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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

Page 138

APPENDIX TABLE 4.6 Continued

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)

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

Page 140

APPENDIX TABLE 4.6 Continued

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.

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

Page 141

APPENDIX TABLE 4.7 Prospective Studies of Work-Related Psychosocial Factors and Back Pain

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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

Page 142

APPENDIX TABLE 4.7 Continued

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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

Page 144

APPENDIX TABLE 4.7 Continued

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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

Page 146

APPENDIX TABLE 4.7 Continued

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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

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.

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

Page 148

APPENDIX TABLE 4.8 Prospective/Longitudinal Studies of Individual Psychological Risk Factors

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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

Page 150

APPENDIX TABLE 4.8 Continued

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.

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

Page 152

APPENDIX TABLE 4.8 Continued

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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

Page 154

APPENDIX TABLE 4.8 Continued

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.

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

Page 156

APPENDIX TABLE 4.8 Continued

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)

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

Page 158

APPENDIX TABLE 4.8 Continued

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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

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.

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

Page 160

APPENDIX TABLE 4.9 Summary Tables of Psychosocial Factors and Work-Related Upper Extremity Disorders: Cross-Sectional Studies

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%

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

Page 162

APPENDIX TABLE 4.9 Continued

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%

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

Page 164

APPENDIX TABLE 4.9 Continued

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

-

-

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

Page 166

APPENDIX TABLE 4.9 Continued

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%

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

Page 168

APPENDIX TABLE 4.9 Continued

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

-

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

Page 170

APPENDIX TABLE 4.9 Continued

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

-

-

-

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

Page 172

APPENDIX TABLE 4.9 Continued

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)

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

Page 174

APPENDIX TABLE 4.9 Continued

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

-

-

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

Page 176

APPENDIX TABLE 4.9 Continued

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

-

-

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

Page 178

APPENDIX TABLE 4.9 Continued

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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

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

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

Page 180

APPENDIX TABLE 4.9 Continued

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

-

-

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

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.

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

Page 182

APPENDIX TABLE 4.10 Summary Table of Psychosocial Factors and Work-Related Upper Extremity Disorders: Longitudinal Studies

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%

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×

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).

Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×
Page 85
Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×
Page 86
Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×
Page 87
Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×
Page 88
Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×
Page 89
Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×
Page 90
Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×
Page 91
Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×
Page 92
Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×
Page 93
Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×
Page 94
Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×
Page 95
Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
×
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Suggested Citation:"Epidemiological Evidence." National Research Council and Institute of Medicine. 2001. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press. doi: 10.17226/10032.
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Every year workers' low-back, hand, and arm problems lead to time away from jobs and reduce the nation's economic productivity. The connection of these problems to workplace activities-from carrying boxes to lifting patients to pounding computer keyboards-is the subject of major disagreements among workers, employers, advocacy groups, and researchers.

Musculoskeletal Disorders and the Workplace examines the scientific basis for connecting musculoskeletal disorders with the workplace, considering people, job tasks, and work environments. A multidisciplinary panel draws conclusions about the likelihood of causal links and the effectiveness of various intervention strategies. The panel also offers recommendations for what actions can be considered on the basis of current information and for closing information gaps.

This book presents the latest information on the prevalence, incidence, and costs of musculoskeletal disorders and identifies factors that influence injury reporting. It reviews the broad scope of evidence: epidemiological studies of physical and psychosocial variables, basic biology, biomechanics, and physical and behavioral responses to stress. Given the magnitude of the problem-approximately 1 million people miss some work each year-and the current trends in workplace practices, this volume will be a must for advocates for workplace health, policy makers, employers, employees, medical professionals, engineers, lawyers, and labor officials.

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