Changes in occupational physical loading during the lifetimes of Finnish men

The Boeing prospective study and beyond

STUDY DESIGN

The Boeing prospective study was reviewed. The Boeing prospective study, comprising two articles, was a large field study that explored why workers would or would not report occupational back pain problems.

OBJECTIVES

The most immediate objective was to determine the extent to which conclusions drawn from the Boeing prospective study withstand critical examination. The ultimate purpose of this review was to develop guidelines for field studies of back pain in industry.

SUMMARY OF BACKGROUND DATA

For more than a century, researchers have noted great variability among individuals in the reporting of back pain, but the explanations posed for this variability have been inconsistent. Because findings gain credibility roughly to the extent that they bear on the world outside the laboratory, field studies in particular hold great potential for clarifying the underlying explanation for individual variability in back pain reporting. The Boeing prospective study was a large and ambitious field study that examined this issue.

METHODS

The Boeing prospective study was examined through the lens of research conducted since it was published. The review used both the methodological and substantive literature.

RESULTS

The Boeing prospective study, based on a minority of workers originally solicited to participate in it (33-41%), accounted for 7% of the variation in why workers would or would not report a back pain problem. A number of issues that may have biased its results toward the null are examined.

CONCLUSIONS

The highlighting of the Boeing prospective study's limitations may be instructive not so much to criticize this one particular study but, rather, to anticipate problems that in general may be encountered in field studies of back pain in industry. Looking beyond the Boeing prospective study, the following guidelines for the conduct of such studies may be proposed: 1) Study designs should be based on explanations from which testable hypotheses may be derived; 2) Subgroups within the more general category of "back pain" should be delineated; 3) Both occupational exposures and psychosocial factors should be entered into the analysis; 4) Factors not apparent at the workplace should be considered; 5. Abstracts of articles should be carefully crafted.

The influence of occupation on lumbar degeneration

In many countries, back problems have been defined as occupational injuries. The belief underlying this injury model is that back symptoms are caused primarily by work-related mechanical factors that damage the structures of the spine, either through a single incident or repeated loading. Although the etiopathogenesis of degenerative findings in the disc and their relation to pain are poorly understood, changes in the disc are suspected of underlying many back symptoms. The focus of this article is on examining the relation between occupational factors and disc degeneration. Occupational factors suspected of accelerating spinal degeneration include accident-related trauma; heavy physical loading and materials handling, including lifting, bending, and twisting; prolonged sitting; and sustained nonneutral work postures and vehicular driving. There is evidence to suggest that occupational exposures have an effect on disc degeneration. However, these factors explain little of the variability in degeneration found in the adult population. Furthermore, the lack of a clear dose-response relation between time spent in various occupational loading conditions and degenerative findings adds to doubts about a strong causal link. The contribution of suspected occupational risk factors appears to be particularly modest when compared with familial influences, which reflect the combined effects of genes and early childhood environment. These findings challenge the dominant role assumed for occupational loading in disc degeneration and associated back problems, and suggest a more complex etiology.

Repeated survey on changes in musculoskeletal complaints relative to age and work demands

OBJECTIVES

To examine changes in musculoskeletal complaints over four years in groups of employees relative to age and work demands.

METHODS

Repeated questionnaire data of male employees in heavy physical work (exposed group, n = 7324) and mental work (control group, n = 4686), stratified for age (20-9, 30-9, 40-9, 50-9), were analysed. For each employee, data on the occurrence of musculoskeletal complaints from two surveys with a mean interval of around four years were available. Changes in prevalences over the follow up interval were analysed. Proportions of new, recovered, and chronic cases as well as those free of complaints at both surveys were studied.

RESULTS

For most complaints, there were significantly greater increases in prevalences in the exposed group compared with the control group over the follow up interval particularly within the group aged 40-9 for back, neck, and several sites of the upper and lower limbs. The 20-9 year age group also had significantly greater changes for several musculoskeletal complaints. Within the oldest age group (50-9) exposure to heavy physical work demands only affected changes in prevalences of neck and upper arm complaints. After four years in the cohort free of complaints at the start of the follow up the group aged 40-9 had the highest prevalence of complaints of the back, neck, and the upper and lower limbs.

CONCLUSIONS

Middle aged and younger employees develop musculoskeletal complaints as a result of exposure to heavy physical work. In the oldest age group health related selection seems to mask the occupational health risks under study. To prevent the expected increase in musculoskeletal disorders and related work disability in our aging workforce, preventive measures should be taken at all stages of a working life.

Lumbar mobility in former élite male weight-lifters, soccer players, long-distance runners and shooters

OBJECTIVE: To investigate the long-term effects of different loading conditions in sports and work on lumbar mobility. DESIGN: Factors associated with lumbar mobility were sought by examining sports experience, occupational history, back pain history, anthropometric characteristics, and lumbar magnetic resonance images in 114 former Finnish male élite athletes: 30 soccer players, 29 weight-lifters, 27 long-distance runners, and 28 shooters, aged 45-68 yr. BACKGROUND: Back pain and aging reduce spinal mobility, whereas some sports may increase it. Little is known about the effects of common loading conditions found in work and sports, that do not require extremes of spinal motion on lumbar mobility later in life. METHODS: Sports and occupational histories were obtained from a standardized interview. Lumbar mobility was measured by the flexicurve method. Disc degeneration was evaluated from lumbar magnetic resonance images. The results were analysed with analysis of variance and covariance and multiple regression models. RESULTS: The athlete groups did not differ significantly in lumbar sagittal mobility. Higher body-mass index was associated with less flexion, reduced disc height with less extension, as was a high lifetime number of low back pain episodes. Occupations characterized by varying work postures and light lifting were associated with greater mobility, and heavy work with lesser mobility. CONCLUSIONS: Participation in sports with clearly different loading patterns, that do not emphasize extremes of spinal range of motion, do not appear to lead to significant differences in back mobility in later adulthood, but occupational loading factors and disc height narrowing appear to influence spinal mobility.

"Movement" in work status after pain facility treatment

STUDY DESIGN

This was a randomized prospective follow-up study of pain facility treatment of chronic pain patients with low back pain, with return to work and work capacity as the outcome measures.

OBJECTIVES

To determine if after pain facility treatment chronic pain patients "move" in and out of work and in their work capacity; to determine the patterns of "movement;" and to determine the post-pain facility treatment follow-up sampling time points that would maximize the number of chronic pain patients correctly classified according to their final work and work capacity status.

SUMMARY OF BACKGROUND DATA

Past research and empiric observation have indicated that chronic pain patients may "move" after pain facility treatment in and out of work and in their job work capacity. Such "movement" can affect the results of outcome studies.

METHODS

Two hundred thirty-six consecutive chronic pain patients who fit study selection criteria were followed up at 1, 3, 6, 12, 18, 24, and 30 months after pain facility treatment for determination of work and work capacity status and separated according to the pattern of movement. Stepwise discriminant analysis was used to answer the study objectives. "Movement" in and out of work for these chronic pain patients also was compared with the US general population.

RESULTS

Chronic pain patients demonstrated eight work and four work capacity movement patterns. The 24- and 1-month time points predicted final work status correctly for 97.0% and 77.0% of the chronic pain patients, respectively, whereas the most significant predictor for correct work capacity status was the 24-month point. The annual percentage change in employment status for these chronic pain patients was more than in the US general population.

CONCLUSIONS

Because chronic pain patients "move" in and out of employment and for work capacity status after pain facility treatment, future outcome studies using these measures will have to consider carefully the impact of "movement" on their results.