Importance of measuring the burden of back pain

Nonspecific low back pain continues to be a common and costly condition worldwide. Although only a small proportion of individuals experiencing low back pain seek medical care, in high-income countries it is still one of the most common reasons to see a health professional and it remains a common cause of disability and work absence. A recent population-based study in the US found that the prevalence of chronic low back pain had more than doubled in the 14-year period between 1992 and 2006– from 3.9% to 10.2% in adults 21 years of age and over . Data from methodologically acceptable studies show that the prevalence of low back pain in middle- and low-income countries is also substantial , suggesting that it is a significant challenge in these countries as well. While it imposes the greatest burden during middle age, important from a societal work productivity perspective, back pain is not inconsequential in youth or old age. Its prevalence rises to approach adult levels during adolescence , and, in contrast to ‘benign’ back pain which decreases around the middle of the sixth decade, severe back pain increases into old age .

Yet, despite these epidemiological data, low back pain is often seen as a trivial problem possibly because, unlike cardiovascular disease, malignancy and infectious diseases, it is rarely lethal. For example, a 2004 update of the Global Burden of Disease (GBD) study, a World Health Organisation initiative, ranked back pain 101st compared with other conditions in terms of disability-adjusted life years, representing only 0.09% of the overall GBD . Importantly, these rankings are often used by governments and charitable organisations to determine health priorities and allocation of resources and the low ranking means that back pain has likely been relatively under-prioritised and under-funded compared with other conditions.

In the first article of this issue, ‘The burden of back pain’, Hoy and colleagues describe the GBD studies, which have provided a common metric of disease rankings for the world and its major regions since 1990 when the first GBD study was performed. The third GBD study (2005) is currently underway and is using a broader perspective on measurement than previous studies. This provides an opportunity to ensure that low back pain will now be more appropriately ranked relative to other conditions. Hoy et al. present an overview of the methods that are being undertaken to estimate the global burden of low back pain for this study, results of which are expected to be available at the end of 2010. They highlight the difficulties they have encountered in obtaining clear prevalence estimates for low back pain due to the lack of a uniform case definition, marked methodological heterogeneity across studies and the paucity of true population-based estimates. If back pain is to be more appropriately prioritised going forwards, it will be important to ensure that these issues are addressed in future population-based epidemiological studies of low back pain.

Prognosis of low back pain

In most instances, it is unclear what precipitates an episode of low back pain. Most cases are of unknown cause and uncertain mechanism and are therefore labelled as ‘nonspecific’. While there is modest evidence that certain lifestyle factors such as smoking, obesity and physical inactivity are associated with low back pain , it is unlikely that we will be able to completely prevent nonspecific low back pain incidence . This has led to an increasing emphasis on studies of prognosis of low back pain in recent years.

In the article, ‘Prognosis of non-specific low back pain’, Hayden and colleagues discuss the state of the art on prognosis of low back pain, including description of the course, evidence on important prognostic factors and identifying risk groups of populations who are likely to have different outcomes. The article includes a novel and comprehensive presentation of different types of prognostic research and discussion of the strength of low back pain prognosis evidence. Although many prognosis studies (and reviews of prognosis studies) are now available, researchers have had only moderate success identifying independent modifiable causal factors that can inform effective treatment strategies, and inform the development of valid, reproducible and practice-friendly tools to identify groups of low back pain patients who are at high or low risk of poor outcome. Hayden and colleagues’ explicit discussion of ‘phases of investigation’ is a helpful framework to interpret the strength of prognosis evidence. The fact that most evidence about low back pain prognosis is at an early exploratory stage of development explains the lack of consistency across the literature and can help inform future research. Advanced phases of investigation, including confirmation studies for prognostic factors, and validation and impact studies for prediction models will help advance the field.

Despite the limitations of the available research evidence, some conclusions can be garnered from the field. Studies show that most low back pain episodes are mild and rarely disabling, with only a small proportion of individuals seeking health care. Among patients presenting for care, there tends to be variations in outcome according to their characteristics: most new episodes recover within a few weeks, however, recurrences are common and individuals with long-standing low back pain tend to show a more persistent course. In general, approximately 60% of health-care consulters with low back pain will continue to have pain after a year, although not necessarily severe or incapacitating. Important low back pain prognostic factors come from multiple domains: they are related to the individual’s back-pain episode, the demographic and psychological characteristics, and the individual work and social environment.

The authors noted that future studies should more closely investigate broader social environment characteristics, such as societal beliefs, social support, benefits systems, family influences and availability of health care, as potentially important modifiable causal factors. Although numerous studies have developed prediction models to identify high-/low-risk groups in the field, most models/tools typically explain less than 50% of outcome variability and few have been tested in independent samples. The Örebro Musculoskeletal Pain Screening Questionnaire was noted as one outcome prediction tool that has shown moderate predictive ability and has been tested in multiple settings, and the STarTBack Tool appears to be a promising new outcome prediction instrument.

Prognosis of low back pain

In most instances, it is unclear what precipitates an episode of low back pain. Most cases are of unknown cause and uncertain mechanism and are therefore labelled as ‘nonspecific’. While there is modest evidence that certain lifestyle factors such as smoking, obesity and physical inactivity are associated with low back pain , it is unlikely that we will be able to completely prevent nonspecific low back pain incidence . This has led to an increasing emphasis on studies of prognosis of low back pain in recent years.

In the article, ‘Prognosis of non-specific low back pain’, Hayden and colleagues discuss the state of the art on prognosis of low back pain, including description of the course, evidence on important prognostic factors and identifying risk groups of populations who are likely to have different outcomes. The article includes a novel and comprehensive presentation of different types of prognostic research and discussion of the strength of low back pain prognosis evidence. Although many prognosis studies (and reviews of prognosis studies) are now available, researchers have had only moderate success identifying independent modifiable causal factors that can inform effective treatment strategies, and inform the development of valid, reproducible and practice-friendly tools to identify groups of low back pain patients who are at high or low risk of poor outcome. Hayden and colleagues’ explicit discussion of ‘phases of investigation’ is a helpful framework to interpret the strength of prognosis evidence. The fact that most evidence about low back pain prognosis is at an early exploratory stage of development explains the lack of consistency across the literature and can help inform future research. Advanced phases of investigation, including confirmation studies for prognostic factors, and validation and impact studies for prediction models will help advance the field.

Despite the limitations of the available research evidence, some conclusions can be garnered from the field. Studies show that most low back pain episodes are mild and rarely disabling, with only a small proportion of individuals seeking health care. Among patients presenting for care, there tends to be variations in outcome according to their characteristics: most new episodes recover within a few weeks, however, recurrences are common and individuals with long-standing low back pain tend to show a more persistent course. In general, approximately 60% of health-care consulters with low back pain will continue to have pain after a year, although not necessarily severe or incapacitating. Important low back pain prognostic factors come from multiple domains: they are related to the individual’s back-pain episode, the demographic and psychological characteristics, and the individual work and social environment.

The authors noted that future studies should more closely investigate broader social environment characteristics, such as societal beliefs, social support, benefits systems, family influences and availability of health care, as potentially important modifiable causal factors. Although numerous studies have developed prediction models to identify high-/low-risk groups in the field, most models/tools typically explain less than 50% of outcome variability and few have been tested in independent samples. The Örebro Musculoskeletal Pain Screening Questionnaire was noted as one outcome prediction tool that has shown moderate predictive ability and has been tested in multiple settings, and the STarTBack Tool appears to be a promising new outcome prediction instrument.

Identifying subgroups

While it is still not possible to identify the specific cause of low back pain for the majority of symptomatic people who present for care, much recent research effort has been directed towards trying to identify clinical characteristics that identify subgroups of patients who may respond better to particular forms of therapy. In contrast to prognostic factors that identify characteristics that might confer a better (or worse) outcome or recovery rate, these characteristics, called treatment effect modifiers, provide information about which patients are likely to respond best to a specific intervention .

In Chapter 3, ‘Treatment-based upon subgroups’, Kamper et al. discuss methods for defining subgroups of low back pain patients based on treatment response, and presents a guide to assist readers in the interpretation of published studies in this area. Most studies, to date, have focussed upon identifying factors that identify preferential response to physical therapies such as manipulative treatment. Recent studies have begun to address response to other types of interventions, such as increasing exposure to physical activities designed to address fear-avoidance beliefs . Kamper and colleagues conclude that only a minority of studies has evaluated treatment effect modification in a rigorous fashion. Understanding the methodological traps that can lead to biased and misleading results is essential to properly interpret the results of these investigations, and these issues must be addressed if future studies are to reliably identify valid treatment-based subgroups.

A related issue is whether there are subgroups of patients who have a good prognosis regardless of treatment, and thus would ideally avoid any interaction with the health-care system. Recent studies in Norway and in the US suggest that these groups exist, but accurate methods of explicitly identifying these persons early on have not yet been widely validated.