Evidence-based lumbar spine biomechanics for assessment of treatment-resistant low back pain

Authors: Breen, A., Watts, M., Claerbout, E. and Merifield, J.

Start date: 8 May 2019

Introduction: Increased sophistication in imaging has progressed methods for measuring intervertebral dysfunction from static, at single levels to dynamic, at multiple levels. The former has revealed little association between biomechanics and symptoms, whereas the latter found associations between motion sharing inequality (MSI) and variability (MSV) and nonspecific low back pain [1,2]. To explore possible mechanisms we assessed their relationships with restraint (IV-RoM and laxity).

Objective: To determine the relationships between MSI, MSV and individual level IV-RoM and laxity in the loaded and unloaded lumbar spine during flexion in a healthy control population.

Methods: Fifty-four pain free volunteers (22F, mean age 38, BMI 24.1) received active weight bearing and passive recumbent quantitative fluoroscopy lumbar flexion examinations using standardised protocols. MSI, MSV, as well as individual level laxity and IV-RoM were correlated with each other. (Only significant correlations are reported.) Ethical approval was received from the National Research Ethics Service (REC reference 10/H0106/65). Results: In active weight bearing mode: Laxity was moderately correlated with IV-RoM at L5-S1 only. MSI correlated with IV-RoM positively at L2-3 and L3-4 and negatively at L4-5 and L5-S1. MSV correlated weakly with Laxity at L2-3 and L5-S1. In passive recumbent mode: Laxity correlated positively with IV-RoM at L2-3 and L3-4 and negatively with L4-5 and L5-S1, while MSI correlated negatively and weakly with laxity and IV-ROM at L5-S1 only. MSV correlated positively, but weakly with both laxity and IV-RoM, but only at L2-3. Discussion In weight bearing lumbar flexion, MSI was more strongly associated with restraint in the lower lumbar spine than in recumbent, while MSV had weak associations with segmental restraint. Thus MSI and low back pain may be linked via greater muscular effort in the deep multifidus. In recumbent lumbar flexion, relationships between MSI, MSV and restraint variables were less in evidence. Relationships between laxity and IV-RoM were substantial and opposite at either ends of the lumbar spine, underlining the principle that a lax segment is not necessarily a hypermobile one and vice-versa.

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