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

eduction in height of the L1L2 disc was greater than or equal to 20%, which was
checked by a quick scout-view scan. Disc height measurements were taken at five
points across the mid coronal slice.
3.3 Specimen Specific Modelling Methods
Both the µCT and MRI scan data were processed using the same techniques. All image
data was resampled to the same cubic resolution of 0.2mm. Image registration
techniques were used to align the three sets of image data by aligning landmark features
and markers on the image data. Proprietary software (ScanIP, version 4, Simpleware
Limited, Exeter, U.K.) was used to construct 3D masks from the image data to
accurately represent the geometry of the vertebral bodies (VB), AF and NP. The VBs
were virtually cropped in half in the axial direction to account for symmetrical loading
of the FSU. The model was meshed into a combination of solid, linear, tetrahedral
elements (~400,000) and exported to an analysis software package (ABAQUS CAE 6.9-
1, Simulia Corp, Providence, RI, USA). The meshed model prior to loading is shown in
Figure 1.
Figure 1 - Screen-shot images of the specimen specific model created from the µCT and MRI image data
for specimen 2. Vertebral bodies are shown in grey and the AF in blue. The lower right image shows the
disc isolated from the vertebral bodies with the descretised AF and NP (darker shade).
Material properties for the main tissues were developed in a previous study 5 , in which
linear, isotropic material models were calibrated to in vitro studies from the literature.
These are summarised in Table 2.
AF E=12.85MPa, ν=0.4
NP E=1.5MPa, ν=0.5 (hybrid elements)
VB E=200MPa, ν=0.2
Table 2 - Material properties assigned to the model components, where E is elastic modulus and v is
poisson’s ratio.
The model was loaded in compression by applying a displacement to a rigid plate
attached to the upper surface of the superior vertebral body. The magnitude of the
displacement was assigned to result in the same change in disc height (the average taken