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

the study of Polikeit et al. [10]. The properties of the ligament elements were taken from to
literature ([2, 11, 12]) and modified by adding toe region.
The FE model representing the average vertebra geometry, disc height and lordotic angle was
used to validate the simulation procedures. For this purpose, the model was loaded with a
2500 N compressive follower load to compare its response to the in-vitro test results reported
be Eberlein et al [13]. In addition, the predicted range of motion from simulation results was
also compared to the in-vitro results reported in Bowden et al. [14] by loading the models
with a 7.5 Nm pure bending moment in flexion and extension, respectively.
For investigating the influence of disc anatomy on the mechanical response of the IVD, and
for identifying the window of uniaxial mechanical properties for a candidate implant material,
nine FE-model geometries were created (see fig. 1). This was done by varying the disc size in
the disc plane within the range for lumbar vertebra geometries reported by Panjabi et al. [5].
The disc height and lordotic angle were also varied within the range of values reported by
Abuzayed et al. [6]. All models were investigated under four different load cases, generated
by loading the vertebrae with a 7.5 Nm moment about different axis (flexion, extension,
lateral bending and torsion respectively) in addition to a follower load of 1000 N
(compression). The load was applied in 10 incremental steps until maximum loading was
achieved. Principal stresses and principal strains were sampled for all annulus elements over
the full range of model geometries and loading cases to assemble representative ranges
defining appropriate candidate implant material properties.
Fig.2. Principal stresses vs. principal strains for all annulus elements for all load steps and all
load cases for the nine different vertebra geometries simulated.