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

Table 1: Material properties (Malandrino et al, 2011)
Material E (MPa)
Poisson’s
ratio
Initial
Void Ratio
Permeability
(mm 4 /Ns)
Annulus fibrosus 0.756 0.35 3.08 0.0002*
Nucleus pulposus 0.388 0.17 4.88 0.0009*
Cartilage endplate 20 0.4 4 0.0025*
Bony endplate
*From Eq. 1
10,000 0.17 0.05 26,800
a) b)
c) d)
Posterior IVD | Anterior IVD
Fig. 1: Paths studied (red lines) represented on model 3 mesh: a) Path 1, b) Path 2, c)
Path 3, d) Path 4.
Green: AF; Blue: NP; Cream: Bony endplates; Purple: Cartilage endplate
4. RESULTS
Under extension, models 2, 3, and 4 led to similar SED predictions, whereas in axial
rotation, neither model 2 nor model 3 converged to the results given by model 4 (Fig.
2). For all models, FV oscillations occurred along the mid-sagittal plane (Fig. 3a).
a) b)
Fig. 2: SED predictions along Path 2, a) under extension and b) under axial rotation.
Although SED calculations indicated that model 3 had not an optimal mesh size under
axial rotation, this model was chosen to explore the FV instabilities because of the low
computation time (1h) compared to model 4 (16h). Accordingly, oscillations were
investigated only under sagittal extension.
Among the strategies applied to avoid the oscillations, neither local refinement