Computational formulation of material laws for intervertebral discs

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Nagy, G.T., 2002. Computational formulation of material laws for intervertebral discs. PhD, Nottingham Trent University.

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Abstract

The lack of a good understanding of the detailed mechanical behaviour of all the parts of the spine is a major obstacle to improving the safety and health of people in a wide variety of situations, ranging from simple lifting operations to passenger vehicle crashes. Early computational modelling of soft tissues as nonlinear springs had some success, particularly with ligaments in situations where they only deform axially. Similar treatment of the discs, however, was recognised as having many shortcomings. Although the overall static load/deflection properties of the disc could be reproduced accurately, a detailed representation of the pressure, shear and torsion in the individual components did not fit the available in vitro data. It is therefore necessary to attempt a complete characterisation of the material properties of the annulus fibrosus, even though this is an almost insumiountable task due to lack of engineering data.

In the presented study a novel approach to implementing a fully non-linear, anisotropic material into the LS-Dyna3D dynamic finite element solver was developed, implemented, and tested. An experimental study was carried out on a large-scale model of the L2-L3 motion segment estabhshing the role of the main components of the disc and their influence on the overall disc behaviour. An analytical study was also completed on the disc bulge. Finally a detailed FEM of the full ligamentous LI-SI lumbar spine was built and tested showing the future direction. Throughout the simulations, the features of the disc which are governed by the individual properties were of special interest. A material property sensitivity study was undertaken on all models establishing important information on the intervertebral disc mechanics. Using the novel approach modelling the annulus fibrosus a greater accuracy was proven. Validation of the model by comparison of its response with literature data shows excellent matching in terms of vertical displacement for complex loading situations. The validation results of the disc confmi'i that the presented way of implementing non-linear materials into FEM solvers is a promising approach to full computational simulation of nonlinear anisotropic materials such as the annulus of the intervertebral disc.

Item Type:

Thesis

Creators:

Nagy, G.T.

Date:

2002

ISBN:

9781369325959

Identifiers: