PubMed · 5197149
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W C Kouters. 1969-12-01. [The damaged intervertebral disk].. https://pubmed.ncbi.nlm.nih.gov/5197149/
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An axisymmetric finite element model of a body-disc-body unit has been developed and used to study the relative effects of two distinct direction-dependent material representations of the disc annulus on the predicted state of stresses in the disc. The annulus fibrosus is modelled either as nonhomogeneous fibre reinforced composite or alternatively as homogeneous orthotropic with transverse isotropy. In order to have identical states of displacements and hence strains, the unknown properties of the latter model are chosen to be equivalent with those of the former. The fibre slopes of 20 degrees, 30 degrees, and 40 degrees are considered in this study. The stresses in the annulus matrix in the circumferential planes parallel to the fibre layers are predicted to be significantly different depending on the annulus model used. In the nonhomogeneous model, the fibre membranes while under tensile forces, in turn, apply compression to the annulus matrix and, hence, decrease the annulus normal stresses in the above planes. Had the membranes carried compressive forces, a reverse trend would have resulted. The foregoing relative differences are dependent on the fibre orientation, and the magnitude of the tensile forces carried by the fibre layers. The latter also depends, amongst others, on the orientation of the fibres, decreasing as the fibre slope increases from 20 degrees to 30 degrees and 40 degrees. On the basis of the annulus micro-structure and the relative mechanical functions of its components, namely the annulus bulk and the collagenous fibre layers, it appears that nonhomogeneous fibre reinforced composite model of the disc annulus is more realistic resulting in a more accurate computation of stresses in the annulus fibrosus.
This report concerns the manner in which the intervertebral disc and the posterior elements share loads placed on a lumbar motion segment. A two-dimensional biomechanical model was used to examine this. The model incorporated two rigid bodies to represent the vertebrae and six elastic springs to represent the tissues of the intervertebral disc and the posterior elements. Compression loads were resisted almost totally by the model intervertebral disc, but both the intervertebral disc and the posterior elements contributed substantially to resisting anteroposterior shear and flexion-extension loads. Motion segment morphology was a major determinant of load-sharing in model response to anteroposterior shear.
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