Since Panjabi’s seminal 1992 papers, how have studies that combine lumbar kinematic and muscle activity measurements improved understanding of sub-system interactions? A systematic review

Background:
Spinal stability was interpreted by Panjabi (1992) to be dependent on co-ordinated interactions between three sub-systems, the passive, the active, and the neural control systems. If there is dysfunction within a specific system, compensation may be provided by adaptations in another [1]. To improve understanding of these interactions, it is necessary to take an approach that incorporates the concurrent measurement of several systems [2], requiring instrumentation that can do so dynamically. Physical activities involving sagittal bending are commonplace activities of daily living [3], and so an improved knowledge of sub-system interaction during lumbar flexion would be of clinical interest. To the author’s knowledge, there is currently no review of studies that have investigated dynamic flexion movements using a combination of EMG and lumbar kinematic measurements. As such it is not clear how understanding of Panjabi’s spinal stability concepts has advanced with regards to this functional movement of the spine.

Methods:
Pubmed and Cochrane databases were searched in March 2017. The search was performed using combinations of the following keywords: Electromyography (EMG), Flexion Relaxation (FR), Kinematics, Range of Motion, Low Back Pain (LBP), Lumbar Spine, Flexion, Bending, Stability and Stabilisation. Articles had to incorporate the concurrent in vivo investigation of lumbar kinematic and EMG variables during dynamic lumbar flexion to be included. The review adhered to the PRISMA guidelines [4], and used a quality assessment tool developed by Abboud et al. [5]. Abboud et al. 2017 also created an assessment to interpret the quality of studies incorporating EMG, based on SENIAM guidelines [6]. This novel assessment was also incorporated.

Results:
Out of a total of 736 articles identified through the literature search only 21 satisfied the inclusion/exclusion criteria. The screening process is outlined in the PRISMA flowchart. The combined overall and EMG quality index scores ranged from 47-100% with a mean total score of 77%. All studies could be placed in one of 4 categories, FR, comparison between LBP and controls groups, EMG activation and spinal modelling. The studies generally supported the notion that increased muscle activity is a mechanism that increases spinal stability, and that it is possible to distinguish between LBP and healthy control groups using kinematic and EMG variables.

Conclusions:
Whilst no reviewed study specifically explored sub-system interaction, many related their findings to such mechanisms. A common weakness in study design was the use of regional measurements, which can only ever provide a broad interpretation of sub-system interaction. In addition sample sizes were typically small, and there was no consistency in methodology. Until one can measure in vivo inter-vertebral dynamic kinematics and relate it to one of the other sub-systems in detail, it will not be possible to make significant progress in this area. This lack of progression was reflected in this review, and highlights the requirement for new approaches to research that incorporate these elements.

References:
[1] Panjabi, M.M., The stabilising system of the spine - Part 1: Function, dysfunction, adaptation and enhancement. Journal of Spinal Disorders, 1992. 5(4): p. 383-389.
[2] Dankaerts, W., O'Sullivan, P.B., Burnett, A.F., Straker, L.M., Davey, P., Gupta, R., Discriminating Healthy Controls and Two Clinical Subgroups of Nonspecific Chronic Low Back Pain Patients Using Trunk Muscle Activation and Lumbosacral Kinematics of Postures and Movements. Spine, 2009. 34(15): p. 1610-1618.
[3] Colloca, C.J. and R.N. Hinrichs, The biomechanical and clinical significance of the lumbar erector spinae flexion-relaxation phenomenon: A review of literature. Journal of Manipulative and Physiological Therapeutics, 2005. 28(8): p. 623-631.
[4] Moher, D., Liberati, A., Tetzlaff, J., Altman, D.G., for the PRISMA Group, Preferred reporting items for systematic reviews and meta-analyses: the PRISMA statement. British Medical Journal, 2009. 339: p. 332-336.
[5] Abboud, J., et al., Effects of Muscle Fatigue, Creep, and Musculoskeletal Pain on Neuromuscular Responses to Unexpected Perturbation of the Trunk: A Systematic Review. Frontiers in Human Neuroscience, 2017. 10.
[6] Hermens, H.J., et al., European Recommendations for Surface Electromyography. Results of the SENIAM project. 1999.