Elsevier

The Spine Journal

Volume 5, Issue 1, January–February 2005, Pages 24-35
The Spine Journal

2004 Outstanding Paper Award: Nonoperative Science
Discographic, MRI and psychosocial determinants of low back pain disability and remission: a prospective study in subjects with benign persistent back pain

https://doi.org/10.1016/j.spinee.2004.05.250Get rights and content

Abstract

Background context

A range of morphologic and psychosocial variables has been suggested as risk factors for serious low back pain (LBP) illness. Although the relative contributions of structural and psychosocial variables are intensely debated, the validity of differing hypotheses has proven difficult to test because the incidence of serious disabling LBP illness is low in healthy subjects. These factors dictate the requirement for large sample sizes, extensive structural imaging and extended longitudinal study. Previous studies included either small cohorts with intensive imaging testing or large population studies that do not establish a detailed morphologic baseline.

Purpose

To establish, using a strict patient sample design, the relative contribution of structural and psychosocial determinants of serious LBP illness among subjects with no previous LBP disability or clinical LBP illness.

Study design/setting

A prospective, longitudinal study of subjects with high risk factors for serious LBP as determined by structural and psychosocial characteristics.

Patient sample

One hundred subjects with known mild persistent low back pain and a 2:1 ratio of chronic (non-lumbar) pain syndrome were recruited from a study population with a predisposition to disc degenerative disease, to undergo baseline examination, testing and 5-year follow-up.

Outcome measures

Observations were made at 6-month intervals over 4 to 6 years (mean, 5.3) for the after primary outcomes measures: episodes of serious back pain (visual analogue scale [VAS]≥6), episodes of occupational disability less than 1 week, episodes of occupational disability for 1 week, remission episodes of all back pain symptoms at least 6 months and medical visits primarily for LBP evaluation and treatment.

Methods

Lumbar magnetic resonance imaging (MRI), lumbar provocative discography (in psychometrically normal subjects), physical examinations, medical and work histories and psychometric testing were performed at baseline. Imaging and psychometric testing were graded by blinded examiners. A scripted interview was conducted every 6 months during follow-up by independent research assistants who also were blinded to patient baseline data. The interview covered interval medical, occupational and accident or injury histories.

Results

Psychosocial variables strongly predicted both long- and short-term disability events, duration and health-care visits for LBP problems (p<0.0001–0.004). The likelihood of a sustained remission from the baseline persistent (subclinical) LBP appeared to be linked to occupation factors (leaving a heavy labor occupation; p=0.0001), neurophysiologic variables (chronic nonlumbar pain; p=0.0002) and psychometric profiles at baseline (DRAM and FABQ-PA; p=0.003–0.002). Of the structural findings measured only moderate or severe Modic changes of the vertebral end plate were weakly associated with an adverse outcome. A positive provocative discogram at baseline did not predict any future adverse event.

Conclusion

The development of serious LBP disability in a cohort of subjects with both structural and psychosocial risk factors was strongly predicted by baseline psychosocial variables. Structural variables on both MRI and discography testing at baseline had only weak association with back pain episodes and no association with disability or future medical care.

Introduction

Low back pain (LBP) associated with functional decline or disability is a common and costly medical and social problem [1], [2], [3], [4], [5]. Previous large and well-designed studies suggested that a history of LBP could be the most powerful predictor of future, serious LBP [6], [7]. Other risk factors suggested to correlate with the development of significant LBP illness have included structural factors, exposure to mechanical stressors, psychological factors and social circumstances [1], [2], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19]. The relative contribution of psychosocial versus structural factors has been the subject of controversy and debate.

Some investigators suggested that it is the morphologic status of the intervertebral disc complex, specifically the annulus or end plates, that primarily determines the presence and degree of low back problems [8], [15], [20], [21], [22]. Others suggested that disabling LBP illness is determined in large part by psychosocial or neurophysiologic factors (somatic distress, pain amplification, depression, secondary gain, etc.) [4], [6], [11], [12]. Which of these hypotheses could in fact be most valid has proven difficult to test using standard epidemiologic methods. Because the incidence of serious disabling LBP illness is low, resources have not allowed a sufficient number of subjects with defined degenerative changes (magnetic resonance imaging [MRI] or other imagining) and “at risk” psychosocial variables to be followed in a prospective fashion.

In previous studies risk factors were assessed in chronic LBP treatment groups and prospectively in occupational settings or in population cohorts. Few of these studies defined the spinal degeneration status with MRI, discography, or both findings. Small cohorts of asymptomatic subjects have been followed after magnetic resonance (MR) scanning or discography of the lumbar spine, but the subject numbers were small and these studies were inconclusive because of low statistical power [11], [13], [14], [23]. Because the incidence of serious or disabling LBP problems is relatively small in healthy individuals, prospective trials performed on an asymptomatic group are likely to lack the statistical power to detect significant trends without an extremely large sample size and extended follow-up.

However, by studying a medium-sized cohort of subjects (n=100) with baseline profiles suggested in previous literature to correlate with increased incidences of serious LBP illness, the predictive power of analysis is substantially increased. That is, a cohort of subjects, for instance, with a known propensity for degenerative disc disease, psychological distress or both would be expected to have a higher (and therefore measurable) incidence of future serious LBP illness. A prospective observational study of reasonable size could analyze the rates of serious adverse LBP outcomes.

As cited above, previous investigations indicated that persons with previous or current nondisabling LBP are at a greater risk of developing serious LBP problems and disability [6], [7], [9]. We selected such a group with a history of LBP as the primary group for this study to increase the statistical power of the sample. Then, systematically recruiting a cohort of subjects with chronic mild LBP, a propensity to degenerative disk disease (DDD), chronic pain and psychological distress at baseline would allow their relative predictive effects to be studied within a manageable cohort size. To our knowledge, a group with ongoing benign back pain but no serious LBP problems has never been studied for the above-mentioned factors in a prospective manner to determine the natural history or predictive factors determining eventual outcomes.

Therefore, to define the predictive factors for serious LBP problems we selected a cohort of subjects with ongoing mild LBP pain, without current or past LBP disability but a known propensity to DDD. This study examined such a cohort at baseline for radiographic, MRI and discographic evidence of structural changes, as well as demographic, occupational and psychometric features. We then followed this group over 5 years with interval assessments for LBP problems and reported on the subsequent values of baseline variables to predict future significant LBP variables.

Section snippets

Study design

This study was a prospective, longitudinal, observational study designed according to statistical power analysis (see “Power analysis”) to investigate the effect of spinal degenerative factors and nonspinal factors on the subsequent development of LBP episodes. All subjects recruited had known risk factors for degenerative lumbar disc disease and a history of mild, persistent but nondisabling LBP. Subject selection was biased (2:1) to subjects with a history of chronic nonlumbar pain, because

Baseline demographics and imaging studies

As previously discussed, the recruitment process was intended to produce a population with relatively high risk of future LBP illness on the basis of baseline disc degeneration, neurophysiologic factors or psychosocial factors. The demographic data of the study population are presented in Table 2. The resulting population of 100 subjects included 78 subjects with degenerated discs, types 3, 4 and 5 according to the Boos criteria (DDD); 64 subjects with chronic nonlumbar pain syndromes; and 45

Discussion

The cause of serious LBP illness in cases without clear and serious anatomic pathology is not known, yet two hypotheses have emerged to explain the development of LBP illness and associated disability. Some researchers have sought to define specific degenerative pathology in the spine that may, as an independent finding, cause the observed LBP illness [8], [11], [15], [18], [19], [20], [21], [25], [37], [38], [39]. In contrast, others have pointed to psychosocial issues as the main determinant

Conclusion

The development of serious LBP disability in a cohort of subjects with both structural and psychosocial risk factors was strongly predicted by baseline psychosocial variables. Structural variables on both MRI and discography testing at baseline had only weak association with back pain episodes and no association with disability or future medical care.

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    Funding to complete this study was received from the AO Foundation and Department research funding at Stanford University. Nothing of value received from a commercial entity related to this research.

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