Theoretical Schemas to Guide Back Pain Consortium (BACPAC) Chronic Low Back Pain Clinical Research

Abstract

Background: Chronic low back pain (cLBP) is a complex with a heterogenous clinical presentation. A better understanding of the factors that contribute to cLBP is needed for accurate diagnosis, optimal treatment, and identification of mechanistic targets for new therapies. The Back Pain Consortium (BACPAC) Research Program provides a unique opportunity in this regard, as it will generate large clinical datasets, including a diverse set of harmonized measurements. The Theoretical Model Working Group was established to guide BACPAC research and to organize new knowledge within a mechanistic framework. This article summarizes the initial work of the Theoretical Model Working Group. It includes a three-stage integration of expert opinion and an umbrella literature review of factors that affect cLBP severity and chronicity.

Methods: During Stage 1, experts from across BACPAC established a taxonomy for risk and prognostic factors (RPFs) and preliminary graphical depictions. During Stage 2, a separate team conducted a literature review according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines to establish working definitions, associated data elements, and overall strength of evidence for identified RPFs. These were subsequently integrated with expert opinion during Stage 3.

Results: The majority (∼80%) of RPFs had little strength-of-evidence confidence, whereas seven factors had substantial confidence for either a positive association with cLBP (pain-related anxiety, serum C-reactive protein, diabetes, and anticipatory/compensatory postural adjustments) or no association with cLBP (serum interleukin 1-beta / interleukin 6, transversus muscle morphology/activity, and quantitative sensory testing).

Conclusion: This theoretical perspective will evolve over time as BACPAC investigators link empirical results to theory, challenge current ideas of the biopsychosocial model, and use a systems approach to develop tools and algorithms that disentangle the dynamic interactions among cLBP factors.

Keywords: Chronic Pain; Low Back Pain; Measurement; Research; Spine; Theoretical Model.

Figure 1.

Two exemplary working sub-models developed to support focused TMWG discussions. (A) This scheme illustrates features and activities contributing to loads generated in the spine during daily-living activities. Tissue stresses triggering nociception can exceed tissue tolerances, cause damage, and thus facilitate the development of neuropathic pain. Concurrent feedback phenomena can affect neuromuscular control and function. (B) This scheme illustrates how social, biobehavioral, psychological, and patient-specific features and phenomena can influence central pain processing, pain experience, and ultimately disability. The circle highlights features and phenomena that can contribute dynamic bidirectional (“top-down,” “bottom-up”) influences. Abbreviations: ACE = agreeableness, conscientiousness, extraversion; PTSD = post-traumatic stress disorder.

Figure 2.

Course-grained theoretical schemes. (A) A scheme used to support intervention-focused discussions emphasizing psychological and social perspectives. The idealized central scheme depicts the canonical sequence of features and phenomena characterizing cLBP experiences and their functional consequences. On both sides are categories of factors that can influence the central process and vice versa. (B) This scheme supports ongoing TMWG discussions of phenotypes, interventions, explanatory theories, machine learning, etc. Factors in A are reorganized into five broad domain clusters. The scheme specifies plausible, bidirectional interactions between factors within clusters and between those factors and central features. A peripheral stimulus source is included between anatomy and nociception. ACE = agreeableness, conscientiousness, extraversion; ACC = anterior cingulate cortex; ANS = autonomic nervous system; BMI = body mass index; HRV = heart rate variability; HPA = hypothalamic-pituitary-adrenal axis; NAc = nucleus accumbens; PTSD = post-traumatic stress disorder; PFC = prefrontal cortex; PRO = patient-reported outcome; SES = socioeconomic status.

Figure 3.

Illustrations highlighting selected aspects contributing to the complexity of an individual’s cLBP condition when current pain is one of three types. Temporal changes are not illustrated. (A) Nociceptive pain: The three concentric groupings depict dynamically networked (entangled) features within brain, spine, and lower back. All other features are grouped into one of four categories, represented by colored triangles—two internal (left: green and red) and two external (right: blue and brown). (B) Nociplastic pain emerges from altered nociception despite no clear evidence of actual or threatened tissue damage. (C) Neuropathic pain can be caused by an abnormality or disease of the somatosensory nervous system. The top speech balloon depicts the same clinical assessment question being posed. Each subjective response is based on the individual’s current or recalled pain experience, illustrated by the different-colored thought balloons. All three responses can be identical even though an individual’s experience is unique and dependent on pain type. An individual’s current cLBP condition might (or might not) involve a combination of pain types.