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.

Is occupational low back pain on the rise?

STUDY DESIGN

A retrospective analysis of back pain claim data from two sources, a workers' compensation provider and Washington State Department of Labor and Industries. The Workers' Compensation Provider claim data were examined over a 9-year period, 1987-1995, and the Washington claim data were examined over a 5-year period, 1991-1995. In addition, a third source of data, reports of back pain from the the Bureau of Labor Statistics, was examined over a 4-year period, 1992-1995.

OBJECTIVES

To characterize occupational low back pain trends in the United States. More specifically, trends in back pain rates and costs as well as back injury rates from the Bureau of Labor Statistics were discerned.

SUMMARY OF BACKGROUND DATA

The literature often refers to a recent rise in occupational low back pain. However, the question is: Do empirical data support this notion?

METHODS

Retrospective analysis of workers' compensation provider, Washington State, and Bureau of Labor Statistics data.

RESULTS

The U.S. estimate of the annual low back pain claim rate decreased 34% between 1987 and 1995, although the trend was not monotonic. There was a sharper decrease in the U.S. estimate of the annual low back pain claim costs during this time (58%). In 1995, however, occupational low back pain remained a major problem in the U.S.: an estimated $8.8 billion was spent on low back pain claims, and the rate of filing low back pain claims was 1.8 per 100 workers.

CONCLUSIONS

Evidence of a rise in occupational low back pain was not discerned for the 8-year period studied. Data from three sources support this finding. However, occupational back pain remains a major problem in the U.S.

Do workplace interventions prevent low-back disorders? If so, why?: a methodologic commentary

The demand for workplace interventions to prevent low-back disorders has increased in recent years. At the same time, a crisis in the literature has become apparent: there are conflicting reports on whether or not these interventions work. With the aim of understanding the reason for the dissension in the literature, six studies were selected for close examination. These were studies of interventions based on differing principles, i.e. a change in organizational ethos to promote back safety, back belt use, the introduction of ergonomic devices, and back-strengthening exercises. If the studies are taken at face value, any of the interventions, regardless of type, has a tremendous effect. Methodological problems inherent in these studies may provide a clue to why essentially different interventions were found to be consistently successful. Study design quality has long been noted to exert a particular influence on the evaluation of outcomes: the quality of the study design is often inversely related to reported outcomes. Of the six studies selected for examination, four did not include a contemporaneous control group, five did not randomly assign subjects to test and control groups, and none included a placebo group. Given these research designs, variables other than those tested by the studies may have produced the reported results. These variables include 'beliefs of the intervention providers' and 'coalescence of the work group', both of which are discussed. Two approaches, the pragmatic and the explanatory, may be used to study workplace interventions to prevent low-back disorders. Most of the examined studies are pragmatically oriented. Having dealt with study design problems expeditiously, these studies may be characterized as more immediately responsive to the demand to evaluate workplace interventions than explanatory studies. On the other hand, explanatory studies, most notably associated with randomized clinical trials in medicine, are more rigorous. Enough pragmatically oriented studies have been conducted to suggest that workplace interventions may have an effect on low-back disorders. More conclusive explanatory studies may now be conducted.

Classics from the spine literature revisited: a randomized trial of 2 versus 7 days of recommended bed rest for acute low back pain

STUDY DESIGN

Review of a trial of bed rest for patients with acute low back pain.

OBJECTIVES

To assess the validity and results of the study, and their applicability to and influence on current clinical practice and recommendations.

SUMMARY OF BACKGROUND DATA

Although bed rest has been a cornerstone of treatment for acute low back pain, historically this recommendation was largely based on "expert opinion." In 1986, Deyo et al. published a randomized study of 2 versus 7 days of recommended bed rest for acute low back pain. Despite results from this and other studies, current clinical practice and treatment recommendations continue to overemphasize bed rest.

METHODS

The study was reviewed using structured criteria adopted from the medical literature that focus on the validity of the study design, the results of the treatment, and the relevance of the findings to clinical practice.

RESULTS

Two hundred and three patients were randomized to 2 versus 7 days of recommended bed rest. Groups were similar at baseline evaluation. Outcomes assessed at 3 and 12 weeks were similar between groups, except that patients receiving a recommendation for 2 days of bed rest had significantly fewer days of work absence than those recommended 7 days. Limitations of the study included poor compliance with recommended bed rest, especially in the 7-day group, a marginal sample size without information on relevant confidence intervals, and patient characteristics that may have affected the generalizability of these findings to others with acute low back pain.

CONCLUSIONS

Despite limitations, this study provided strong evidence that less bed rest was associated with similar outcomes for acute low back pain along with quicker return to work. Results from this and other studies support a shift away from bed rest as a primary recommendation in the initial management of low back pain. In spite of this, bed rest recommendations for episodes of low back pain remain common. Additional efforts are needed to change clinical practice.

Length of disability and cost of workers' compensation low back pain claims

Although information exists on the cost of workers' compensation low back pain (LBP), there is limited information on the duration of lost work time as well as the association between cost and duration. For this study, cost and duration of lost work time information were derived from a large workers' compensation company's database for 1992 LBP claims (n = 106,961). The distribution of cost was skewed, with an average cost of a claim being 20 times higher than its median. A disproportionately small percentage of the costliest LBP claims (10%) were responsible for a large percentage of the total cost (86%). The distribution of length of disability (LOD) was also skewed, with an average of 102 days and a median of zero. The average and median LOD for those claims with at least one day of compensable disability was 303 and 39 days, respectively. As a "rule of thumb," it was found that of those claimants who remain on disability at the end of n weeks, approximately 50% will be off disability at the end of 6.n weeks. Additionally, the 7% of the claims with an LOD greater than one year accounted for 75.1% of the cost and 84.2% of the total disability days. Disability days that were accrued after one year of disability accounted for 59.3% of the total number of disability days. This result suggests that other LOD estimation techniques, which may not account for disability days beyond one calendar year (e.g., the Bureau of Labor Statistics Annual Survey of Occupational Injuries and Illnesses), may result in a marked underestimation of LOD.

Design factors in epidemiologic cohort studies of work-related low back injury or pain

The connection between work-related exposures and the onset of back injury or pain is complex and not clearly understood. This paper raises design issues related to the planning and conduct of cohort studies of industrial low back pain (or injury)(LBP), with care given to definition and measurement of exposure and outcome events. These issues include sample size, outcome definition, study biases, and practical considerations when seeking and maintaining company collaboration with a research effort. Without resolving these issues, the authors conclude: (1) cohort studies of worksite-based LBP are needed to elucidate the causal associations between work tasks and LBP onset, (2) both acute and cumulative exposures should be assessed as risk factors for low back injury or pain, and (3) attention should be paid to the planning of such studies and minimization of potential biases that can limit the validity of the results. These design issues will benefit researchers and companies engaged in the planning and conduct of cohort studies of industrial LBP.

The epidemiology of low back pain in the rest of the world. A review of surveys in low- and middle-income countries

STUDY DESIGN

A criteria-based review of the literature.

SUMMARY OF BACKGROUND DATA

The literature on the epidemiology of low back pain is accumulating, but for the most part studies are restricted to high-income countries, which comprise less than 15% of the world's population. Little is known about the epidemiology of low back pain in the rest of the world.

OBJECTIVES

To address the imbalance in the literature and to review the relatively few studies on the epidemiology of low back pain in low- and middle-income countries. Rates from these studies are contrasted with rates from selected high-income countries. In reviewing the literature, a hypothesis is tested: low back pain rates are higher in low-income countries than in high-income countries, not only because hard physical labor is more prevalent in low-income countries, but also because, unlike high-income countries, hard physical labor for older workers in low-income countries often is unavoidable.

METHODS

Among other sources, articles for the review come from a search of the MEDLINE bibliographic database, with "back pain" and individual low- and middle-income countries entered as key words. To avoid recall biases, findings specifically on point prevalence are reviewed.

RESULTS

Within the categories of low-income and high-income countries, low back pain rates vary twofold or more. In comparisons between these categories of countries, rates on the whole are higher among the general populations of selected high-income countries than among rural low-income populations; specifically, rates are 2-4 times higher among Swedish, German, and Belgium general populations than among Nigerian, southern Chinese, Indonesian, and Filipino farmers. Within low income countries, rates are higher among urban populations than among rural populations and still higher among workers in particular worksites, referred to as "enclosed workshops."

CONCLUSIONS

The disparity in low back pain rates within categories of countries, high-income and low-income, calls attention to the high proportion of studies on the epidemiology of low back pain that are methodologically questionable. Recommendations are offered to improve the methodologic quality of this type of study. Conclusions may be drawn from comparisons between studies, although, in the absence of set methodologic standards, they are tentative. The considerably lower rates among populations of low-income farmers compared with rates of the affluent populations of selected northern European countries indicate that, contrary to the hypothesis proposed here, hard physical labor itself is not necessarily related to low back pain. The higher rates in urban low-income populations as compared with rates in rural low-income populations and the sharply higher rates among workers in enclosed workshops of low-income countries suggest a disturbing trend: low back pain prevalence may be on the rise among vast numbers of workers as urbanization and rapid industrialization proceed.

A descriptive study of recurrent low back pain claims

This is the first large-scale study of US workers that describes the demographic and cost differences between recurrent and nonrecurrent low back pain (LBP) disability claimants, using data from a large workers' compensation insurer. Persons with at least one LBP claim in 1990 and one or more additional claims in 1990 to 1996 were defined as recurrent. Persons with at least one LBP claim in 1990 but no subsequent claims were defined as nonrecurrent. Fourteen percent of claimants were recurrent. The percentage of recurrent claimants who were male (77.2%) was higher than the percentage that were female (22.8%). This difference was more pronounced in the younger age groups. The median total cost for recurrent LBP claims in 1990 was 4% greater than for nonrecurrent 1990 LBP claims, whereas the mean cost was 48% less. Most studies of LBP recurrence among US workers have followed single-corporation employees. Our rate of recurrence was lower than these previously reported rates. However, analysis of independent workers' compensation insurance company data may provide a more accurate assessment of LBP claim recurrence among US workers.

Why does geographic variation in health care practices matter? (And seven questions to ask in evaluating studies on geographic variation)

One of the most active fields in health services research is the study of "geographic variation," or disparities in rates of certain types of health care practices among large areas (such as countries or regions of a country) or small areas (such as countries or hospital market areas); "small area analysis" in particular has received much attention in journals and the popular press. Increasingly, data upon which to base studies of geographic variation are becoming available. This article poses questions to ask in applying studies on geographic variation to health care settings. Because findings from these studies may ultimately affect patient care, the questions are important for physicians as well as health services researchers. The questions are: 1) What events are to be analyzed? 2) What geographic units are to be analyzed? 3) How good are the data? 4) Are differences in rates due to chance alone? 5) Are high rates too high? 6) How is geographic variation to be explained? 7) What is the role of "presentation style" in explaining geographic variation?

Patterns in low back pain hospitalizations: implications for the treatment of low back pain in an era of health care reform

OBJECTIVE

To examine patterns in both surgical and nonsurgical low back pain (LBP) hospitalizations through time and among geographic regions and to explore the practical implications of these patterns for health care reform.

SETTING

For time trends, the U.S. (1979-1987); for geographic variations, major regions of the U.S. (1987). DATE SOURCE: The National Hospital Discharge Survey.

RESULTS

Rates of both surgical and nonsurgical LBP hospitalization varied twofold among regions of the U.S., and average lengths of stay for these types of hospitalization varied considerably as well. The U.S. rate of LBP surgery increased sharply during the period covered by the study. Over the same time, the U.S. rate of nonsurgical LBP hospitalization declined, as did average lengths of stay for both types of LBP hospitalization.

CONCLUSION

Wide variations in LBP hospitalization practices raise the issue of which practices are most appropriate. Outcomes research addresses this issue, as does research on patient preferences for certain types of treatment. As indicated by the increasing rate of LBP surgery, more research also needs to be done on changing physician practice style. If such research were to result in a reduction in LBP hospitalization, savings in health care costs would be considerable.

Small area analysis of lumbar spine surgery in South Australia

The hospital separation records for 1987 in the health planning regions of South Australia were reviewed using a selection algorithm to identify all hospitalizations involving a lumbar spine surgery (LSS) for low back or leg pain. Among 16 health planning regions (two additional regions were excluded from the analysis because of the low number of observations) the LSS rate varied almost four-fold, from 25 to 92/100,000, with a mean of 55/100,000. The effect of 24 socioeconomic and health care supply characteristic variables upon observed differences in rates were tested. The unemployment rate was the only significant variable in the analysis, explaining 11% of the variation in the surgery rates for the 16 regions. This finding is in agreement with studies from other countries that suggest that characteristics of small areas do not substantially predict the rates of elective surgical procedures. The decision-making processes of surgeons and their patients remain poorly defined; the contributions to the rate of lumbar spine surgery by the health care delivery system, physician behaviours or patient expectations are not yet identified.

Use of the International Classification of Diseases (ICD-9-CM) to identify hospitalizations for mechanical low back problems in administrative databases

Large administrative databases are increasingly valuable tools for health care research. Although increased access to these databases provides valuable opportunities to study health care utilization, costs and outcomes and valid and comparable results require explicit and consistent analytic methods. Algorithms for identifying surgical and nonsurgical hospitalizations for "mechanical" low back problems in automated databases are described. Sixty-six ICD-9-CM diagnosis and 15 procedure codes that could be applied to patients with mechanical low back problems were identified. Twenty-seven diagnosis and two procedure codes identify hospitalizations for problems definitely in the lumbar or lumbosacral region. Exclusion criteria were developed to eliminate nonmechanical causes of low back pain, such as malignancies, infections, and major trauma. The use of the algorithms is illustrated using national hospital discharge data.

Small area analysis of surgery for low-back pain

Rates of spine surgery (discectomy, laminectomy, fusion) vary several-fold among "small areas" such as counties or hospital market areas. To ascertain why this is so, an analysis was conducted of variability in rates among counties in the State of Washington (N = 39). Since, unlike previous published reports, this study excluded patients with cancer, major trauma, and infection, as well as those with cervical and thoracic procedures, rates in this study pertain specifically to the problem of low-back pain. Six classes of variables to explain variability among county rates were defined: I) percentage of the labor force in heavy labor and transportation occupations; II) socioeconomic conditions; III) neurologic and orthopedic surgeon density; IV) occupancy rate of back surgery hospitals; V) primary payer and VI) health care availability. In all, the effect of 28 explanatory variables was tested. In doing so, the authors took into account the possibility of spurious correlation. The rate of surgery for low-back pain varied nearly 15-fold among counties. The explanatory variables that were tested, however, accounted for only a minor part of the variability. The hypothesis that "physician practice style factor" accounts for the major part is explored; potential properties of practice style factor are specified for further testing.

Theories of back pain and health care utilization

Because most people in the United States have occasional back pain, demand for the treatment of back pain is widespread. Yet, few treatments have proven to be more effective than placebo therapy. We examine patterns of treatment that have emerged in the absence of definitive treatment. We concentrate on high-cost users of back pain treatment (i.e., chronic pain patients) and high-cost treatments (i.e., surgical and non-surgical hospitalization for low back pain). The small minority of back pain patients whose disability persists into chronicity (90 days or more) accounts for a disproportionate amount of all back pain costs. Interventions have been developed to prevent back pain but, once back pain has already occurred, little is done to prevent it from becoming chronic. Drug therapy may be used to treat the symptom of chronic pain, the cause of which may not be thereby affected. Regarding high-cost treatments, surgical and nonsurgical hospitalizations for low back pain are common practices in the United States. Pain specialists for the past 15 years have advocated a conservative approach to back pain, but the rate of surgery for low back pain increased during this time. Average lengths of stay for surgical and nonsurgical low back pain hospitalizations decreased. We explore why, in the instance of low back pain surgery, change was resisted, whereas, in the instance of average lengths of stay, change was accepted. In view of why change may be resisted or accepted, we discuss interventions designed to change physicians' practice style.

Epidemiology of low back pain

The science of epidemiology is difficult to apply to the problem of low back pain. This article discusses the problems associated with the study of low back pain, population surveys, risk factors for low back pain, and disability because of low back pain.

Back sprain in industry. The role of socioeconomic factors in chronicity

A minority of industrial-back-sprain claimants account for most of the cost of industrial back sprain: those whose disability persists into "chronicity", which is defined as 90 days or more off work. The data in this study demonstrate the effects of socioeconomic factors on chronicity. This analysis is based on State of Washington industrial insurance claims for back sprain. For both men and women, three socioeconomic factors significantly affect the risk of chronicity: age, wage, and the family status of being either widowed or divorced with no children. In addition, the Nam-Powers Socioeconomic Index is significant for men. Wage compensation ratio cannot be shown to be a factor in chronicity.

What is too much variation? The null hypothesis in small-area analysis

A small-area analysis (SAA) in health services research often calculates surgery rates for several small areas, compares the largest rate to the smallest, notes that the difference is large, and attempts to explain this discrepancy as a function of service availability, physician practice styles, or other factors. SAAs are often difficult to interpret because there is little theoretical basis for determining how much variation would be expected under the null hypothesis that all of the small areas have similar underlying surgery rates and that the observed variation is due to chance. We developed a computer program to simulate the distribution of several commonly used descriptive statistics under the null hypothesis, and used it to examine the variability in rates among the counties of the state of Washington. The expected variability when the null hypothesis is true is surprisingly large, and becomes worse for procedures with low incidence, for smaller populations, when there is variability among the populations of the counties, and when readmissions are possible. The characteristics of four descriptive statistics were studied and compared. None was uniformly good, but the chi-square statistic had better performance than the others. When we reanalyzed five journal articles that presented sufficient data, the results were usually statistically significant. Since SAA research today is tending to deal with low-incidence events, smaller populations, and measures where readmissions are possible, more research is needed on the distribution of small-area statistics under the null hypothesis. New standards are proposed for the presentation of SAA results.