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

A POROELASTIC APPROACH FOR AN OPEN SOURCE FINITE
ELEMENT MODEL OF THE INTERVERTEBRAL DISC
ABSTRACT
A. Castro 1 , W. Wilson 2 , J. M. Huyghe 3 , K. Ito 4 , J. L. Alves 5
Degenerative Disc Disease (DDD) is one of the largest health problems faced
worldwide, based on lost working time and associated costs. This works deals with
the development of a biomimetic Finite Element (FE) model of the Intervertebral
Disc (IVD). Several recent studies have emphasized the importance of an accurate
biomechanical modeling of the IVD. Thus, a hyper-visco-poro-elastic formulation
is briefly addressed throughout this paper. The FE implementation and numerical
simulations are being carried out on a home-developed open source FE solver. The
validation of the newly implemented biphasic formulation was performed through
Terzaghi’s test for confined compression, and some preliminary simulations of a
poro-viscoelastic IVD FE model were carried out, being their results briefly
discussed. The next step is to include the poroelastic swelling behavior.
INTRODUCTION
The Human spine is composed by twenty four motion segments (MS). Each one of
these load-sharing units is composed by two vertebral bodies (VB), connected by
an IVD (Fig. 1) and two facet joints. The IVDs are fibro-cartilaginous cushions
serving as a shock absorbing system of the spine, which protect the vertebrae,
brain, and other structures, providing both flexibility and load support. They are
composed by three major components: the nucleus pulposus (NP), the annulus
fibrosus (AF) and the cartilaginous endplate (CEP) [1]. Each IVD deals with
complex loads, leaving it vulnerable for both acute and chronic injuries. For many
years, a considerable amount of studies developed significant efforts to understand
and find possible solutions for such phenomena. In fact, spine problems are a
major cause of disability on western societies, with an emphasis on DDD [1].
One of the major issues about studying the IVD behavior is the fact that they are
hardly accessible to in vivo studies. In fact, even most of the surgical techniques to
heal degenerated IVDs are invasive [2]. Numerical simulation, for instance by the
FE method, is a good choice to evaluate the pathways for degeneration of the IVD,
and even to propose new treatments. Experimental and numerical studies have
proven that the IVD presents hyper-visco-poro-elastic biomechanical behavior,
1 PhD Candidate, Mechanical Engineering Department, University of Minho, 4800-058 Guimarães,
Portugal (apgcastro@dem.uminho.pt)
2 Researcher, Biomedical Engineering Department, Eindhoven University of Technology, 5600 MB
Eindhoven, The Netherlands
3 Associate Professor, Biomedical Engineering Department, Eindhoven University of Technology, 5600
MB Eindhoven, The Netherlands
4 Full Professor, Biomedical Engineering Department, Eindhoven University of Technology, 5600 MB
Eindhoven, The Netherlands
5 Assistant Professor, Mechanical Engineering Department, University of Minho, 4800-058 Guimarães,
Portugal