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Are Coupled Rotations in the Lumbar Spine Largely Due to the Osseoligamentous Anatomy?

Little, J. Paige, Pearcy, Mark J., & Adam, Clayton J. (2007) Are Coupled Rotations in the Lumbar Spine Largely Due to the Osseoligamentous Anatomy? In Williamson, Owen (Ed.) Annual Scientific Meeting of the Spine Society of Australia, 20-22 April, 2007, Hobart, Australia.

Abstract

Introduction Previous clinical studies have suggested that abnormal motions in the lumbar spine may be a possible cause for lumbar spinal disorders. In vivo and in vitro studies have found that primary rotations in the lumbar spine are accompanied by coupled out-of-plane rotations. However, it is not clear how much of this accompanying rotation is separately attributable to the actions of the muscles and ligaments in the normal spine. The aim of this study was to use a finite element model of the visible man lumbar spine, which included the major spinal ligaments, to determine three-dimensional rotations in the loaded spine.

Methods CT data for the bony anatomy of the visible man lumbar spine was converted to a finite element mesh. Attachment origins and ligament stiffnesses for the major spinal ligaments were based on data reported in the literature. No muscles were included.

Loading conditions simulated torso compression (500N) as well as rotation representing physiological ranges of motion1. Six separate analyses were carried out for primary rotations in the six degrees of rotational freedom. The rotation was applied as a pure rotation boundary condition applied to the centre of rotation, while holding the L5 vertebra in all degrees of freedom.

Nucleus pulposus pressure in the intervertebral discs was compared with in vivo data2 to establish the models ability to predict physiological pressures. Primary and accompanying rotations at each vertebral level (L1-2, L2-3, L3-4 and L4-5) were determined such that pure rotations between each vertebra were compared without any associated translations.

Results Nucleus pressures in the four lumbar intervertebral discs were comparable to in vivo data2 under torso compression (95-106% of in vivo values). Primary rotations at all vertebral levels were either the same as the average in vivo primary rotation or within the first standard deviation. In general, the computed results for flexion, extension and axial rotation were similar to the in vivo results, with coupled rotations within the first standard deviation of the reported in vivo data and in the same direction. However, analysis of left and right lateral bending consistently demonstrated higher coupled axial rotations than were observed in vivo. For left bending, computed axial rotations were as high as 5o while in vivo rotations only reached 3o. For right bending, computed axial rotations were as high as 5o while the maximum in vivo rotations were 2o. However, these computed coupled rotations under lateral bending were consistently in the same direction as observed in vivo.

Discussion The observed similarity in computed and in vivo nucleus pressures and primary rotations at each spinal level validated the models' ability to predict the in vivo response of the osseoligamentous lumbar spine.

Coupled rotations due to primary motions in the sagittal and transverse planes appear to be caused by the osseoligamentous anatomy. However, for lateral bending, data for the computed coupled rotations suggest that the osseoligamentous anatomy alone does not account for the observed coupled rotation in vivo, and the muscles therefore play a key role in the coupled response of the spine under this motion.

References 1. Pearcy, M. J., Acta Orthop Scand Supl, vol:56, 1985 2. Nachemson, A. L., Spine, vol 6: 93-97, 1981

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ID Code: 7496
Item Type: Conference Paper
Additional Information: Abstract only. For more information contact the author at j2.little@qut.edu.au
Additional URLs:
Subjects: Australian and New Zealand Standard Research Classification > ENGINEERING (090000) > BIOMEDICAL ENGINEERING (090300) > Biomechanical Engineering (090302)
Divisions: Past > QUT Faculties & Divisions > Faculty of Built Environment and Engineering
Current > Institutes > Institute of Health and Biomedical Innovation
Deposited On: 10 May 2007
Last Modified: 03 Mar 2011 15:42

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