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Massé-Alarie H1, Hammer G2, Salomoni S2, Hodges P2
1Université Laval, Rehabilitation, Quebec City, Canada, 2University of Queensland, School of Health and Rehabilitation Sciences, St. Lucia, Australia
Background: People with chronic low back pain (CLBP) move differently. Differences in the brain motor areas might be a mechanism underlying spine movement alteration. In contrast, there is limited evidence regarding potential differences in the function of spinal networks that might contribute to alteration in spine motor control. Recent research used noxious stimuli over different trunk sites to elicit nociceptive withdrawal reflex (NWR). Stimuli evoked NWR organized in receptive fields specific to each muscle that were consistent with their mechanical function and were elicited at a latency suggesting a spinal origin. NWR of the trunk might inform about the excitability and organization of spinal motor networks controlling trunk muscles.
Purpose: This study aimed to determine whether the organization and the excitability of the trunk NWR differ between individuals with and without CLBP. The specific aims were: (i) whether excitability of the NWR differs between groups; and (ii) whether the organization (i.e. pattern of muscle activation) of the NWR of the trunk differed between groups. Based on data from other conditions, we hypothesized that CLBP would involve; (i) a lower threshold for the trunk NWR consistent with sensitization, (ii) lower specificity in the organization of trunk NWR with respect to the site stimulated.
Methods: Noxious electrical stimuli were delivered at 1.2 times of the NWR threshold at four sites (S1, L3 and T12, and Right Rib) to elicit NWR in 12 individuals with LBP and 13 healthy controls. Activation of lumbar multifidus (LM), thoracic erector spinae, rectus abdominus, obliquus internus and obliquus externusabdominis muscles were recorded. Due to large NWR threshold variability in individuals with CLBP, two subgroups were delineated: participants with High- and Low-threshold, and compared with the healthy controls. Independent-test assessed differences in NWR excitability. Generalized estimating equation tested differences in NWR organization.
Results: Although the CLBP group presented with a large difference in NWR threshold compared to controls (CLBP: 24.3 ± 9.1 mA; CTL: 8.3 ± 2.8 mA), it narrowly missed significance due to large inter-subject variability. In High-threshold subgroup, the amplitude of abdominals NWR were larger, especially after stimulation of the Rib. Also, LM NWR was less frequently evoked in both CLBP subgroups than controls, despite the use of a higher stimulus intensity and a similar pain intensity elicited by the noxious stimulation.
Conclusion(s): From one perspective, CLBP presented hyposensitivity to 'local' lower lumbar spine stimulation which might represent an adaptive mechanism to protect spine structures. From another perspective, in a subgroup of CLBP participants, abdominal muscles were overactive following 'remote' Rib stimulation suggesting hypersensitivity. These results in addition with the differences in trunk muscle 'receptive fields' suggest that spinal motor networks controlling trunk muscles may contribute to differences in function/organization in spine sensorimotor control in individuals with CLBP.
Implications: These results indicate that interpretation of sensitization in people with clinical pain cannot be generalized and may vary between sensory domains and between individuals. This advocates for individualization of interventions to patient's characteristics rather than a one-size-fit-all treatment.
Keywords: Central nervous system, low back pain, sensorimotor control
Funding acknowledgements: This study was funded by NHMRC. HMA was supported by CIHR and PH by a Senior Principal Research (NHMRC).
Purpose: This study aimed to determine whether the organization and the excitability of the trunk NWR differ between individuals with and without CLBP. The specific aims were: (i) whether excitability of the NWR differs between groups; and (ii) whether the organization (i.e. pattern of muscle activation) of the NWR of the trunk differed between groups. Based on data from other conditions, we hypothesized that CLBP would involve; (i) a lower threshold for the trunk NWR consistent with sensitization, (ii) lower specificity in the organization of trunk NWR with respect to the site stimulated.
Methods: Noxious electrical stimuli were delivered at 1.2 times of the NWR threshold at four sites (S1, L3 and T12, and Right Rib) to elicit NWR in 12 individuals with LBP and 13 healthy controls. Activation of lumbar multifidus (LM), thoracic erector spinae, rectus abdominus, obliquus internus and obliquus externusabdominis muscles were recorded. Due to large NWR threshold variability in individuals with CLBP, two subgroups were delineated: participants with High- and Low-threshold, and compared with the healthy controls. Independent-test assessed differences in NWR excitability. Generalized estimating equation tested differences in NWR organization.
Results: Although the CLBP group presented with a large difference in NWR threshold compared to controls (CLBP: 24.3 ± 9.1 mA; CTL: 8.3 ± 2.8 mA), it narrowly missed significance due to large inter-subject variability. In High-threshold subgroup, the amplitude of abdominals NWR were larger, especially after stimulation of the Rib. Also, LM NWR was less frequently evoked in both CLBP subgroups than controls, despite the use of a higher stimulus intensity and a similar pain intensity elicited by the noxious stimulation.
Conclusion(s): From one perspective, CLBP presented hyposensitivity to 'local' lower lumbar spine stimulation which might represent an adaptive mechanism to protect spine structures. From another perspective, in a subgroup of CLBP participants, abdominal muscles were overactive following 'remote' Rib stimulation suggesting hypersensitivity. These results in addition with the differences in trunk muscle 'receptive fields' suggest that spinal motor networks controlling trunk muscles may contribute to differences in function/organization in spine sensorimotor control in individuals with CLBP.
Implications: These results indicate that interpretation of sensitization in people with clinical pain cannot be generalized and may vary between sensory domains and between individuals. This advocates for individualization of interventions to patient's characteristics rather than a one-size-fit-all treatment.
Keywords: Central nervous system, low back pain, sensorimotor control
Funding acknowledgements: This study was funded by NHMRC. HMA was supported by CIHR and PH by a Senior Principal Research (NHMRC).
Topic: Musculoskeletal: spine; Pain & pain management; Neurology
Ethics approval required: Yes
Institution: The University of Queensland
Ethics committee: Medical Research Ethics Committee
Ethics number: 20040000654
All authors, affiliations and abstracts have been published as submitted.
