ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

3.1 Generation of the vertebral surfaces
The surfaces of the vertebral bodies are generated from a computer tomograph (CT)
data set of cast models of human vertebrae which represent the Central European size of
vertebral bodies. A specially developed segmentation algorithm provides the smooth
surfaces of the vertebrae. Contact between the bony parts is realized in ten facet joints in
the region of the assigned spinous processus.
3.2 Modeling of the intervertebral discs
Fig.1 MBS model of the lumbar spine
In the model the intervertebral discs are realized as elastic elements between the
corresponding vertebral bodies. Resultant transmitted forces and torques cause
movements of the vertebrae which are described by 6 degrees of freedom.
The mechanical behaviour of force, deformation and deformation velocity is described
by the relation
F c r CSA d r
(1)
which considers the deformation r and the deformation velocity r as well as the
cross section area (CSA) of the disc and the parameters for stiffness c and damping d.
The values of the parameters are found by cadaver experiments and additional
sensitivity analysis. The mechanical behavior of torsion is implemented by
characteristic curves for each direction (flexion/extension, lateral bending and axial
rotation). They are calculated following the results of experimental measurements of
isolated postmortem disc material [1]. In Fig.2 the characteristic curves of the disc
Sacrum-L5 in 3 degrees of freedom is described.