Low back pain and control of segmental lumbar movement

Authors: Breen, A.

Conference: 9th World Conference on Low Back and Pelvic Pain

Dates: 31 October-3 November 2016


Introduction Chronic, nonspecific low back pain (CNSLBP) is a biopsychosocial problem, but psychosocial factors explain only small parts of the variance in outcome and their use in guiding treatment has only small effects9, 17. However, even if the main factors in pain generation and prognosis do turn out to be biological ones, there are three of them; chemical, mechanical and neuroplastic – all of which can be present at the same time. Therefore, it seems questionable whether a mechanical phenomenon such as lumbar movements could alone provide a marker of sufficient robustness to identify phenotypes and pain generators in CNSLBP populations8. Better, perhaps, to develop subgrouping models without them.

Even though all or none of these three physical factors may participate in a given patient’s pain generation, it remains that almost all CNSLBP is affected by movement or position, so it is likely that mechanical factors will have a role. Therefore, it is worth trying to find out if the measureable ones are more prevalent in people with CNSLBP than in those without –and if they are, whether they are causes of pain episodes and moderators or mediators their outcomes. This paper presents a view of chronic, nonspecific back pain that includes lumbar segmental mechanics and suggests ways of using such mechanical assessments to identify factors that may be important in back pain generation and perpetuation – and therefore in physical treatment.

The measurement of intervertebral motion Lumbar motion at a segmental level can be measured by digitally registering the positions of individual vertebral segments on fluoroscopic sequences and measuring the movement between them, comparing patients and controls. This technique has been the subject of a number of validation studies 2-5, 7, 13-15, 18, 20. So far, the measurement properties of a range of kinematic variables have been evaluated, including intervertebral range of motion (IV-RoM), anterior-posterior translation, disc height, finite centre of rotation, intervertebral laxity (as initial rotational attainment rate), phase shift and proportional motion pattern variability. So far, there is little evidence that IV-RoM, translation, disk height change or laxity are any different in people with CNSLBP, even though there is some that translation and laxity are important when back pain is linked to injury 10-12, 16.

There is also some evidence that proportional motion, representing the sharing of bending across segments, is more variable in people with CNSLBP. It was demonstrated by Abbott et al using flexion-extension radiographs, that patients with back pain had proportional IV-RoM and translation ranges outside of reference intervals derived from healthy controls 1. Later on, significant differences between patients and matched controls with CNSLBP were found using continuous fluoroscopic sequences combining left, right, flexion and extension motion to get a single summary measure of the variability of motion sharing 14. Recently, further independent groups of CNSLBP patients and matched controls have been investigated in studies which replicated and expanded these findings. Implications The fact that motion sharing variability has been found to be significantly greater in independent samples of people with CNSLBP than in controls, suggests that it is sufficiently dominant to be worthy of further exploration as a biomechanical marker - and perhaps also as a moderator of CNSLBP outcomes. Good intra-subject reliability over 6 weeks makes it an appropriate measure for identifying population subgroups. However, poor agreement suggests that it may be unsuitable for use as a mediator or outcome measure. Because data can be recorded during passive recumbent lumbar motion, as well as during standardised weight bearing active motion, results can be extrapolated to make inferences about both intervertebral restraint (passive mode) and performance (upright mode) in terms of the control of motion of the lumbar spine as a whole.

Uneven motion sharing at segmental levels is a consequence of heterogeneity in passive system restraint. This may be the result of structural factors, such as disc degeneration or ligament tightening {Lao, 2015 #7068}. If these are related to abnormal motion patterns, then treatment options for altering the patterns could be tested as interventions. Likewise, relationships between aberrant motion in the upright position and the presence of back pain means that the pain may be generated by the effects of untoward muscular effort and/or consistency of loading, where metabolic deficit in the former, or rapid displacements in the latter, could be responsible. Either way, they are almost certainly related to the degree of control that is achieved at segmental levels.

This model could be expanded to accommodate other health factors, both biological and personal. One example is contemporaneous muscle electrical activity, which has shown relationships to individual level IV-RoM and laxity in healthy controls 6. Evidence that intervertebral mechanics in CNSLBP matters enough to show through in patient groups that were not stratified beyond basic triage to exclude other biopsychosocial factors justifies further explanatory studies. Clinical and laboratory research could include more diverse sets of variables that involve muscle metabolic deficit, inflammatory markers{Li, 2016 #7479}, mathematical modelling to infer loads with input from combined QF and 3-D MRI, relationships between segmental motion and EMG patterns in back pain, lumbar configuration (e.g. lordotic curve) and response to perturbation and changes in balance. Relationships between segmental motion patterns and patient reported data, such as directional preference, pain impact, kinesiophobia, distress and somatisation may also be important to outcomes. The extent to which these mechanical factors may together or in combination, be predictors of susceptibility to new back pain episodes or of the outcomes of current episodes in different treatment and occupational scenarios could also be explored using multivariate modelling.

Conclusions Mechanical dysfunction has been rightly called into doubt as a single explanatory variable for CNSLBP and the view that a biological approach alone is inadequate is indisputable19. However, through the mist of complexity, this does not leave us free to discount mechanical abnormalities, especially if they are objectively measurable, frequently present and able to discriminate patients from controls.

Source: Manual