Workshop report

Abstract

Low-back pain is a common health condition in working populations. Considering the lifetime prevalence of 60–85%, nonspecific low-back pain will eventually affect almost everyone during worklife, men and women equally (1). Low-back pain is a frequent reason for seeking medical care, with 42% of the adult population annually consulting a health professional for their complaints (2). In The Netherlands, around 24% of those with low-back pain take sick leave; 6% do no return to work within 4 weeks (2). In the past two decades, it has been well documented that physical load caused by frequent lifting, awkward back postures, and whole-body vibration are risk factors for the occurrence of low-back pain (3–5) and consequent sickness (6, 7). These occupational risk factors have been incorporated into several national and international guidelines aimed at reducing the occurrence of work-related low-back pain (8–10). Despite this evidence on occupational risk factors for low-back pain, many physicians are faced with the problem of whether an episode of nonspecific low-back pain in a particular worker may be the result of his or her work conditions. In practice, it is difficult to determine to what extent the individual episode can be attributed to a specific (combination of) exposure at work according to specified criteria (eg, exceeding the advised occupational exposure limits). Most occupational health guidelines for the management of low-back pain do not determine the work-relatedness of low-back pain when considering an individual worker who presents him- or herself with low-back pain (10). A more accurate assessment of the work-relatedness of nonspecific low-back pain might enable practitioners to intervene in a more effective way in the relationship between the worker and the work environment, for example, by recommending specific modifications to the patient’s job. Moreover, it may improve the quality of notification of nonspecific low-back pain as an occupational disorder. Because of the difficulty in providing proof for the work-related origin of low-back pain, hardly any evidence-based criteria exist to support the recognition of nonspecific low-back pain as an occupational disorder. Recently, a practical tool was developed to evaluate the magnitude of work-relatedness of nonspecific low-back pain. The basis of this tool is a structured meta-analysis of established risk factors for nonspecific low-back pain and an assessment of the overall strength of the exposure relationship between these risk factors and the occurrence of low-back pain in various occupational populations (11). With the use of methods from the clinical decision theory, this information was incorporated into a decision model that estimates the relative contribution of specific risk factors at work to the occurrence of nonspecific low-back pain in an individual worker. This model translates the population-based attributable fraction of (a combination of) work-related risk factors into individual attributable risk, interpreted as the best estimate for the etiologic fraction. In order to stimulate the further development of clinical tools for evaluating the contribution of workload to nonspecific low-back pain, an international workshop was held under the auspices of SALTSA (Joint Program for Working Life Research in Europe) in Amsterdam in November of 2003. Experts in health care and research on musculoskeletal disorders from nine countries (see the list of participants in the acknowledgments) participated and discussed critical issues regarding the development of a practical tool based on the decision model. The discussions addressed the following three main topics: (i) the basic assumptions of the decision model to assess the work-relatedness of an episode of nonspecific low-back pain in an individual worker, (ii) the appropriate assessment of exposure to risk factors at work when the model is applied in practice, and (iii) the applicability of the model in occupational health care. In order to guide the discussions in the workshop, statements were formulated on the critical features of each of these topics. This workshop report summarizes these critical features and the discussions among the participants. It does not represent a consensus statement. Some discussions resulted in suggestions for improving the model or in recommendations for the further development and application of decision tools in occupational health care. Whenever possible, these suggestions were followed, and the subsequent changes in the published decision model are outlined in this report. Basic assumptions of the decision model The decision model for the work-relatedness of nonspecific low-back pain is based on the baseline probability of having nonspecific low-back pain among workers without any relevant occupational exposure and the increase in probability due to the personal exposure profile for well-established risk factors. The calculated overall probability presents the likelihood for the occurrence of nonspecific low-back pain, given a specific combination of risk factors present. The difference between the baseline probability and the overall probability is used to estimate the attributable risk, interpreted as the best estimate for the etiologic fraction at the individual level (11). This method has several critical features; among them are the definition of the work-related risk factors, the assessment of their effect on the occurrence of nonspecific low-back pain, the estimation of the baseline prevalence of nonspecific low-back pain among unexposed workers, and the conversion of population-based attributable risk into an etiologic fraction at the individual level. The basic assumptions regarding these critical issues were worded into the four statements that follow. Statement concerning the definition of work-related risk factors: “The guidelines used internationally to define relevant exposure provide reasonable cut-off points to distinguish those exposed from those unexposed.” The definition of work-related risk factors in the model was based on a review of relevant epidemiologic literature and national and international guidelines that distinguish manual materials handling, bending and twisting of the trunk, whole-body vibration, and job dissatisfaction (1, 8–10). After a consideration of the lack of scientifically sound information on exposure–response and exposure–effect relationships, it was posed that any cut-off point is to some extent arbitrary. Although the preventive effects of the occupational exposure limits proposed in these guidelines still have to be corroborated, it was concluded that these guidelines present a suitable, but crude, starting point for distinguishing between hazardous and harmless work situations. A certain disadvantage of these predefined cut-off points of exposure is that the procedure may obscure the presence of high risk among people with much higher exposure than the occupational exposure limit. In addition, exposures below these cut-off points may still be associated with an increased risk of developing low-back pain. With regard to manual materials handling, a further definition of frequent lifting was advocated to enable a consistent application of the decision model. Furthermore, regarding the risk factor frequent bending and twisting of the trunk, the issue was raised of whether it was possible and meaningful to distinguish between high and low exposure on the basis of the defined cut-off points. The inclusion of job dissatisfaction as an independent risk factor was not supported because an objective measurement is not possible since job dissatisfaction is a result of interaction between work and the worker and thus partly reflects individual characteristics that are hard to measure objectively. Thus it can be concluded that, in the absence of better data on exposure–response relationships, the cut–off points to distinguish exposed workers from those unexposed are acceptable, even though arbitrary. The users of the model should be advised to also consider actual exposure levels and be attentive when these levels are much higher than the occupational exposure limits used in the current model. Following the results of this discussion, three concrete changes were made in the original model. First, the exposure definition of manual materials handling was made more explicit; “frequent lifting of more than 5 kilograms” was changed to “handling objects of more than 5 kg more than 2 times a minute for a total of more than 2 hours per workday”. Second, the definition of high exposure to frequent bending or twisting of the trunk was changed from “more than 30 degrees more than 10% of the worktime” to “more than 40 degrees more than 30 minutes per workday”. And, third, while annotating that job dissatisfaction may be a relevant factor to investigate when a worker with nonspecific low-back pain is under consideration, this psychosocial factor was excluded from the model. These changes in the exposure definitions will not greatly affect the decision model due to the large overlap between the old and new characterization of risk factors. Statement concerning the assessment of the effect of risk factors on nonspecific low-back pain: “The overall adjusted risk estimates provide the best available evidence of the independent effect of risk factors for nonspecific low-back pain.” In the model, the assessment of the effect of risk factors on nonspecific low-back pain is based on adjusted pooled risk estimates. Thus assessing the work-relatedness of nonspecific low-back pain depends heavily on the procedures in the meta-analysis to arrive at unbiased estimates for each risk factor. Since very few epidemiologic studies have included all relevant risk factors, the adjustment of a particular risk factor is conditional on the presence or absence of other relevant risk factors. Although a procedure for a correction factor in the pooled estimates was introduced into the published model (11), the meta-analysis is sensitive to the number and quality of the epidemiologic studies included. The participants suggested that a sensitivity analysis be conducted to evaluate the changes in the assessment of work-relatedness relative to the effect of statistical uncertainty of the pooled risk estimates derived from the meta-analysis. The decision model is constrained to the specific end point used in most studies (ie, the presence of nonspecific low-back pain in the past 12 months) and the array of occupational groups involved [ie, mainly nurses, (tractor) drivers, construction workers, and industrial workers] (11). This definition of nonspecific low-back pain incorporates cases with a short acute episode, as well as those with chronic complaints, and the assigned risks to specific work-related factors may differ with the severity of nonspecific low-back pain (12). Following the suggestion of the participants with respect to the sensitivity of the model, additional analyses were performed to evaluate the effect of the statistical uncertainty of the adjusted pooled risk estimates on the resulting attributable risk. These analyses demonstrated that a departure from the baseline prevalence of 30% (on the assumption of a range of 10% to 50%) in combination with observed 95% confidence intervals around the risk estimates resulted in etiologic fractions varying from 13% to 40% for manual materials handling relative to the 23% in the original model. For frequent bending or twisting of the trunk these figures were 13% and 45% (relative to 28% in the model), and for whole-body vibration the values were 9% and 30% (relative to 18% in the model). It was concluded that the validity of the model depends on the use of the model. Therefore, when the model is implemented, users need to receive information on the scope of the applicability of the model and the limitations of the model for use outside its current context, such as the definition of nonspecific low-back pain. Statement concerning the estimation of the baseline prevalence of nonspecific low-back pain: “The age-dependent prevalence of nonspecific low-back pain among unexposed persons should be considered the probability of having nonspecific low-back pain due to nonwork-related factors.” In the decision model, the probability of nonspecific low-back pain among people not exposed to any of the distinguished risk factors was derived from the prevalence of nonspecific low-back pain among unexposed groups in the epidemiologic studies included in the meta-analysis. In these selective groups, an age-dependent prevalence was observed, and this prevalence may partly reflect exposure to factors not accounted for in the analysis and exposure to included risk factors at levels below the applied limit values. Individual assessment can be improved if individual characteristics such as gender, psychological traits, and history of back complaints, as expressed by severity, chronicity, and recurrence, are taken into account. However, we lack sufficient data on the contribution of these nonwork-related factors relative to different levels of exposure at the workplace to expand the decision model with these individual and disorder characteristics. The weighted pooled prevalence was based upon various studies across different occupational populations in different countries. Hence the decision model can be adjusted for populations with a lower “baseline” prevalence than that incorporated in the current model (ie, 30%). It was advised to present the decision model for a variety of baseline prevalences in order to tailor its application to the specific characteristics of the population from which the person with nonspecific low-back pain originates. It was concluded that the statement should be reworded to: “The age-dependent prevalence of nonspecific low-back pain among unexposed persons should be considered the probability of having nonspecific low-back pain due to individual characteristics, possible exposure to risk factors not accounted for in the model, or exposure to risk factors of physical load included in the model at levels below the applied limits.” In compliance with the advice of the participants, a table has been constructed with attributable fractions for a range of baseline prevalences (10%, 20%, 30%, 40%, 50%). Statement concerning the conversion from population-based attributable risk to the individual attributable fraction: “The attributable fraction at the group level can be interpreted as the average attribution of work to nonspecific low-back pain at the individual level.” An important assumption is, although common in medicine, that the attributable fraction at the group level can be interpreted as the best estimate for the attributable fraction at the individual level, given a specific definition of a health effect. Hence the application of the decision model is limited to a worker with an episode of nonspecific low-back pain. It may not be applicable right away to a worker seeking health care or a worker on sick leave since the decision to seek care or to take sick leave depends on several factors not included in the model (13). Additional analyses are required to evaluate whether the decision model can be used for health outcomes more than the presence of nonspecific low-back pain. the assumptions in the model, it to be that the attributable fraction is an of the probability that the episode of nonspecific low-back pain is due to work-related risk factors. Hence the model does not present an etiologic that the nonspecific low-back pain is caused by This difference in between probability and etiologic is in the application of the decision model in occupational health Thus the current model to workers with nonspecific low-back pain. The attributable fraction calculated by the model should be interpreted as an of the probability that the episode of nonspecific low-back pain in the person is due to work-related risk factors. of occupational exposure to the risk factors The definitions of occupational exposure to the risk factors in the model are based on exposure exposure can be by or from methods (on or from or measurement methods work or in These methods have been in the and their and have been in the decision on what methods of exposure assessment are to be when work-relatedness of nonspecific low-back pain is is the between the required level of the of exposure information on and applicability or in on the The discussions on this issue were by two Statement of an is not accurate to assess the level of exposure to the risk factors in the an individual worker with nonspecific low-back pain a exposure information is by the worker because it is the and However, the and of are limited into the presence and of and provide the information to determine exposure according to the definitions of the model. In the workshop, it was that, in information can be important since it may be to the work but it is not accurate for risk can be used to support an on the presence or absence of risk factors. determine whether or not nonspecific low-back pain is an occupational disorder for a specific objective exposure data are Statement to the risk factors in the model should be by an by of of specific work and to such relevant information as actual of the objects results of studies on work in different and the magnitude of vibration in of This is in with of the on the health and regarding the exposure of workers to whole-body vibration the participants the that is not the as that objective of as worded in the are in cases of for or these discussions it was concluded that the required level of for exposure assessment and depends on the specific application of the model. a users of the model need to be of the of the of their data on the validity of the of the model. of the model should for objective exposure by people with relevant and objective data are required in or in occupational health care the lack of evidence-based methods that can be used by practitioners to evaluate the work-relatedness of nonspecific low-back pain, the model can provide a basis for a practical tool in occupational health care. However, the discussions made it that are several to its applicability in the scope of the applicability of the model, four statements considering possible to the model in occupational health care on an individual level and on a group level were discussed during the Statement “The decision model can be used as a tool in occupational health The most application of the model is to use it as a tool to the work-relatedness of nonspecific low-back pain in an individual worker. It was that the model is for this that it is applied by people with relevant and The participants the that the of the model in the of support it can to practitioners in their by providing a for relevant exposure data and its relative contribution to the occurrence of nonspecific low-back pain. for to an practitioners need to the of the model with additional information on the worker and the work Statement “The attributable fraction of a can be used to the individual an it was discussed whether the probability of work-relatedness for a worker can be used to the individual The participants of the workshop to this use of the model. It was that, for this it is important to consider exposure to the risk factors in to the attributable fraction. the that the model in this respect is limited to on exposure to physical It no information on return to work However, these it was concluded that the magnitude of the probability of work-relatedness can provide when are the attributable fraction is should more on workplace when the attributable fraction is should more on personal Statement “The decision model can be used as a tool in occupational health An evidence-based estimation of the probability of work-relatedness of nonspecific low-back pain may enable the and notification of nonspecific low-back pain as an occupational disorder. do have to be made relevant cut-off points of attributable occupational disorders were considered as mainly caused by occupational risk factors, it to take an attributable fraction of as the cut-off from a point of also the and notification of cases with an attributable fraction than are of The participants of the workshop suggested that, with respect to occupational health the of the model should be considered in combination with other relevant information on the worker. Furthermore, it was that the model should not be used to assess job risk Statement “The decision model can be used to the of The model can provide a of the relative contribution of work-related risk factors to the occurrence of nonspecific low-back pain and thus in theory, provide an assessment of the For to support structured and advice for it be to be to estimate a in the of However, the participants of the workshop that this is not a application of the model. The model incorporates data on between exposure and the presence of nonspecific low-back pain. The of of it the other way and that is not without information from studies on between a in exposure and a in nonspecific low-back pain is available It be an to use the model to evaluate the of that the model is not cut-off to between the and the Thus the model a of the of in that it might be used for In in occupational health care, the model is applicable on an individual level to support in the of the work-relatedness of nonspecific low-back pain. a group level, the model can provide an of the relative contribution of work-related risk factors to the occurrence of nonspecific low-back pain. of the main discussed during the workshop Basic assumptions of the decision model. The decision model for the work-relatedness of nonspecific low-back pain is based on the baseline probability of having nonspecific low-back pain without any relevant occupational exposure and the increase in probability due to exposure to relevant occupational materials handling, bending and twisting of the trunk, and whole-body In the absence of sound information on relationships, the definitions of relevant exposure to work-related risk factors in the model are to some It is to not the presence or absence of exposure to the risk factors on the basis of the occupational exposure but also to consider the actual exposure values and be attentive when these levels are much higher than the established exposure The assessment of the effect of risk factors on nonspecific low-back pain is based on adjusted pooled risk estimates from epidemiologic some extent the quality of the model is limited due to the lack of sufficient epidemiologic The decision model is constrained to the specific end point used in most studies (ie, the presence of nonspecific low-back pain in the past 12 and the array of occupational groups The age-dependent baseline prevalence of nonspecific low-back pain should be considered to be the probability of having nonspecific low-back pain due to individual characteristics, possible exposure to risk factors not accounted for in the model, or exposure to risk factors of physical load included in the model at levels below the applied occupational exposure With respect to conversion from population-based attributable risk to individual attributable an important assumption of the decision model is that the attributable fraction at the group level can be interpreted as the best estimate of the average attributable fraction at the individual level, given a specific definition of a health effect. Thus the model to workers with an episode of nonspecific low-back pain. of occupational exposure to the risk factors A of an is not accurate for an assessment of the level of exposure to the risk factors in the model. of the model should to objective exposure by people with relevant and objective data are required for or in occupational health care The decision model is applicable in occupational health care on an individual level, as well as on a group level. the individual level, it can support in their of the work-relatedness of nonspecific low-back pain for a worker with nonspecific low-back pain and will provide for the most relevant a group level, the model can provide an of the relative contribution of work-related risk factors to the occurrence of nonspecific low-back pain. the critical features of the model, the participants expressed the that published decision model the best available structured on the work-relatedness of nonspecific low-back pain for an individual The proposed model can practitioners in occupational health care to a more evidence-based However, given the various assumptions the decision model, the attribution is not a in but is an of the probability of The model can be upon as a structured that can be adjusted according to the specific individual characteristics and work of the worker to be with respect to nonspecific low-back pain. Additional analyses are required to evaluate whether the decision model can be used for health outcomes more than the presence of nonspecific low-back pain. The contribution of nonwork-related factors relative to exposure at the workplace also further The decision model is not a tool for a given its critical assumptions and the to the a certain the quality of the decision model is limited due to a lack of sufficient epidemiologic studies on exposure–response between personal and work-related risk factors and the and severity of nonspecific low-back pain. With the of the decision model may need to be within a few In the it a for and practitioners to investigate the basic of the work-relatedness of disorders not caused by a work-related