Funcion Y Disfuncion De Columna

Journal of Electromyography and Kinesiology 13 (2003) 303–304 www.elsevier.com/locate/jelekin

Editorial

Muscle function and dysfunction in the spine

Although there have been much data generated from research conducted in the area of spine biomechanics and muscle function, these results have not yet lead to the emergence of credible unifying theories on the mechanisms of low back pain and its treatment. Neither have the diagnostic techniques that provide more than partial information, materialized. Instead, conflicting results and their lax interpretations guide clinicians and therapists in their choices of treatment. This special journal issue comprises the collection of papers presented at two scientific meetings that attempted to address the above problems. The first meeting was the Seminar on Assessment of Back Muscle Weakness and Fatigue held as part of the XIVth congress of the International Society of Electrophysiology and Kinesiology from June 22-25, 2002 in Vienna, Austria. A while later, a special emphasis symposium, entitled “Muscle Function and Dysfunction in the Spine”, was held in conjunction with the IVth World Congress on Biomechanics, August 4-9, 2002 in Calgary, Canada. The goal of these meetings was to gather often-conflicting opinions of several of the leading scientists in the area of spine mechanics to reach consensus on the following points: 1. To delineate the current state of knowledge on which most researchers can agree. 2. To outline the areas where conflicting results are present. 3. To prioritize the areas in most need of future research.

Because the conference format of 15-20 minutes per presentation did not even begin to address the above issues, we asked the invited panelists to contribute a fulllength paper summarizing their views on muscle function and dysfunction in the spine in relation to low back pain and its treatment in the framework of their area of expertise. Eight papers were contributed [1–8]. Although we encourage the readers to interpret this collection of work themselves, we would like to point out several remarkable themes that stood out when we ∗

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listened to the presenters and later when we were assembling this special issue. Our point of view, we hope, may also motivate the readers to explore this collection of papers in its entirety. A variety of methods for studying spinal mechanics are presented in this collection. From animal models, in vitro and in vivo experiments, to mathematical and theoretical hypotheses formulation, the problem of muscle function and dysfunction has been approached from many different directions. Despite such diversity in the applied methods, many authors identified the motor control system as a key factor in the etiology of low back pain. We believe that this reflects a shift in focus in the literature on back function and dysfunction in general. In the past the morphological and mechanical properties of passive spinal tissues have received much interest. Much of the literature has focused on muscle dysfunction and especially muscle fatigue in patients with low back pain. In this issue, two independent research groups provided compelling data to question the validity of the traditional muscle fatigue assessment procedures based on time and frequency domain analyses of surface EMG signals [2,4]. Also in the current issue, Lariviere et al. [4] and van Diee¨n et al. [1] showed that traditional outcome measures on muscle function do not clearly set patients with low back pain apart from healthy control subjects. Although novel methods may provide more insight, as is indicated by Farina et al. [2], it seems that motor control aspects deserve increasing attention. In the present issue consensus emerges on muscle activation patterns exhibited by patients with low back pain being different from those in healthy subjects. However, the interpretations of such findings are divergent. First, there is no answer yet to the question of causality. In other words, we don’t know whether poor motor control leads to low back pain or low back injury and pain results in altered motor control. Furthermore, the same changes in motor control can be interpreted as functional or dysfunctional depending on the point of view. For example, van Dieen et al. [1] and Hodges and Moseley [3] performed extensive literature reviews. Both groups concluded that muscle activation patterns in low back pain population are not consistent with either painspasm-pain nor pain-adaptation models proposed in the

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Editorial / Journal of Electromyography and Kinesiology 13 (2003) 303–304

past. However, while van Dieen et al. [1] emphasized possible functional adaptations by pointing out positive effects of altered muscle recruitment patterns, Hodges and Moseley [3] emphasized dysfunction by outlining deleterious effects of such changes. Importantly both show that simple hard-wired control mechanisms triggered by pain cannot account for the data and higherlevel control is implicated. This indicates that task constraints may have important effects on the motor control changes and consequently these changes may be highly context specific. An emphasis on the effects of various muscle activation patterns on spinal stability resonated in several papers. McGill et al. [5] focused on correct muscle recruitment pattern and timing to assure spine stability during all physical tasks. Panjabi [6] stressed the importance of interactions of spinal structures, trunk muscles, and the nervous system. Collectively, the papers by Solomonow et al. [7] and by Panjabi [6] emphasized the sensory role played by spinal structures. However, the work of Stokes et al. [8] suggests that the stability of the spine may be more robust than we have previously thought, because the osteoligamentous spine stiffens significantly under the combined compressive action of the trunk muscles, regardless of their relative activation patterns. The papers in this issue highlight that the mechanical functioning of the spine is the outcome of a highly complex system. Therefore, in theorizing about spine function, we need to develop a view that encompasses effects of all relevant structures, such as muscles, intervertebral discs, ligaments, the nervous system, and their interactions, which become apparent in motor control. Even when considering only mechanical low back pain, the theory needs to account additionally for non-mechanical e.g. cognitive influences such as fear of pain. Such a theory will probably predict that findings in back pain patients such as altered muscle recruitment are highly context specific, and thus allow substantial between- and within-subject variance. This variability poses a tremendous challenge in translating the research findings into the clinical context, but this task appears to be a prerequisite for further progress in this field. We hope that this special issue of the Journal of Electromyography and Kinesiology will amplify the impact of the objectives set out by the two symposia. We would

like to thank all of the panelists and contributors to this issue for the privilege of guest-editing their work. A special mention is due to the sponsors of the speakers at the Vienna meeting: Institut Robert-Sauve´ de recherche en sante´ et se´ curite´ du travail (IRSST) du Que´ bec and the Centre de recherche interdisciplinaire en re´ adaptation (CRIR) de Montre´ al. Jacek Cholewickia, Jaap H. van Diee¨ nb, A. Bertrand Arsenaultc, a Yale University School of Medicine, Department of Orthopaedics and Rehabilitation, Biomechanics Research Laboratory, PO Box 208071, 333 Cedar Street, New Haven, CT 06520-8071, USA E-mail address: [email protected] b Institute for Fundamental and Clinical Human Movement Sciences, Faculty of Human Movement Sciences, Vrije Universiteit, Amsterdam, The Netherlands c School of Rehabilitation, Faculty of Medicine, University of Montreal and CRIR/Montreal Rehabilitation Institute, Montreal, QC, Canada doi:10.1016/S1050-6411(03)00038-5

References [1] J.H. van Diee¨ n, L.P.J. Selen, J. Cholewicki, Trunk muscle activation in low-back pain patients, an analysis of the literature, Electromyogr Kinesiol 13 (2003) xxx. [2] D. Farina, M. Gazzoni, R. Merletti, Assessment of low back muscle fatigue by surface EMG signal analysis: methodological aspects, J Electromyogr Kinesiol 13 (2003) xxx. [3] P.W. Hodges, G.L. Moseley, Pain and motor control of the lumbopelvic region: effect and possible mechanisms, J Electromyogr Kinesiol 13 (2003) xxx. [4] C. Larivie`re, A.B. Arsenault, D. Gagnon, P. Loisel, Surface electromyography assessment of back muscle intrinsic properties, J Electromyogr Kinesiol 13 (2003) xxx. [5] S.M. McGill, S. Grenier, N. Kavcic, J. Cholewicki, Coordination of muscle activity to assure stability of the lumbar spine, J Electromyogr Kinesiol 13 (2003) xxx. [6] M.M. Panjabi, Clinical spinal instability and low back pain, J Electromyogr Kinesiol 13 (2003) xxx. [7] M. Solomonow, R.V. Baratta, B.-H. Zhou, E. Burger, A. Zieske, A. Gedalia, Muscular dysfunction elicited by creep of lumbar viscoelastic tissues, J Electromyogr Kinesiol 13 (2003) xxx. [8] I.A.F. Stokes, M. Gardner-Morse, Spinal stiffness increases with load: another stabilizing consequence of muscle action, J Electromyogr Kinesiol 13 (2003) xxx.