W. van den Bos, D.L. van Duersen, and I. Kingma (The Netherlands)
Intervertebral disc, finite element model, parameter study, biomechanics, anulus fibrosis, low backpain.
In order to understand and describe the non-linear mechanical reactions of the intervertebral disc an axisymmetric finite element model has been built. The model predicts a disc behaviour which is consistent with several experiments. This together with smoothly changing and mesh independent values of pressure, stress and strain give confidence in the overall results. The most important conclusions of this research are: • A linear stress-strain model for the collagen fibers underestimates the maximum fiber stresses • The non-linear stress-strain relation of collagen fibers is responsible for mechanical coupling between disc height increase and torsion • Degenerated discs can be simulated with very low fluid bulk moduli. This extreme low values of fluid compressibility amplify the disc height increase due to torsion The height increase due to torsion is important in everyday life disc mechanics because it may be related to the ‘mechanical pumping’ by the millions of small rotations experienced in life, that is likely to be vital for nutrition of the disc. This can also contribute to the clinical relevance of significant spinal motion over the day, to maintain mechanical tissue strength and restrict degenerative changes.
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