The mechanical response of the ovine lumbar anulus fibrosus to uniaxial, biaxial and shear loads

Little, Judith Paige, Pearcy, Mark J., Tevelen, Gregory, Evans, John H., Pettet, Graeme J., & Adam, Clayton J. (2010) The mechanical response of the ovine lumbar anulus fibrosus to uniaxial, biaxial and shear loads. Journal of the Mechanical Behavior of Biomedical Materials, 3(2), pp. 146-157.

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Analytical and computational models of the intervertebral disc (IVD) are commonly employed to enhance understanding of the biomechanics of the human spine and spinal motion segments. The accuracy of these models in predicting physiological behaviour of the spine is intrinsically reliant on the accuracy of the material constitutive representations employed to represent the spinal tissues. There is a paucity of detailed mechanical data describing the material response of the reinforced­ground matrix in the anulus fibrosus of the IVD. In the present study, the ‘reinforced­ground matrix’ was defined as the matrix with the collagen fibres embedded but not actively bearing axial load, thus incorporating the contribution of the fibre-fibre and fibre-matrix interactions. To determine mechanical parameters for the anulus ground matrix, mechanical tests were carried out on specimens of ovine anulus, under unconfined uniaxial compression, simple shear and biaxial compression.

Test specimens of ovine anulus fibrosus were obtained with an adjacent layer of vertebral bone/cartilage on the superior and inferior specimen surface. Specimen geometry was such that there were no continuous collagen fibres coupling the two endplates. Samples were subdivided according to disc region - anterior, lateral and posterior - to determine the regional inhomogeneity in the anulus mechanical response. Specimens were loaded at a strain rate sufficient to avoid fluid outflow from the tissue and typical stress-strain responses under the initial load application and under repeated loading were determined for each of the three loading types.

The response of the anulus tissue to the initial and repeated load cycles was significantly different for all load types, except biaxial compression in the anterior anulus. Since the maximum applied strain exceeded the damage strain for the tissue, experimental results for repeated loading reflected the mechanical ability of the tissue to carry load, subsequent to the initiation of damage.

To our knowledge, this is the first study to provide experimental data describing the response of the ‘reinforced­ground matrix’ to biaxial compression. Additionally, it is novel in defining a study objective to determine the regionally inhomogeneous response of the ‘reinforced­ground matrix’ under an extensive range of loading conditions suitable for mechanical characterisation of the tissue. The results presented facilitate the development of more detailed and comprehensive constitutive descriptions for the large strain nonlinear elastic or hyperelastic response of the anulus ground matrix.

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21 citations in Scopus
17 citations in Web of Science®
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ID Code: 32269
Item Type: Journal Article
Refereed: Yes
Additional URLs:
Keywords: lumbar spine, intervertebral disc, anulus fibrosus, stiffness, mechanical testing, uniaxial compression, biaxial compression, simple shear
DOI: 10.1016/j.jmbbm.2009.09.002
ISSN: 1751-6161
Subjects: Australian and New Zealand Standard Research Classification > ENGINEERING (090000) > BIOMEDICAL ENGINEERING (090300) > Biomechanical Engineering (090302)
Divisions: Current > Schools > School of Teacher Education & Leadership
Past > QUT Faculties & Divisions > Faculty of Built Environment and Engineering
Current > Institutes > Institute of Health and Biomedical Innovation
Past > Schools > School of Engineering Systems
Copyright Owner: Copyright 2010 Elsevier
Deposited On: 17 May 2010 04:46
Last Modified: 25 Mar 2013 08:11

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