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

spinal behavior except the maximal strain on the lateral spot. This could be due to the
strain concentration in this area, as it is quite close to the anterior-posterior connection.
4.2 Influence of spinal degeneration on cortical shell strain
Since the degenerated FE models
cannot be validated, it is assumed that
these models do correctly predict the
behavior of degenerated spines as it
was shown for the healthy situation.
The same loading condition was
applied in all three FE models. The
predicted maximum and minimum
+7.231e-5
-3.208e-4
-7.138e-4
-1.107e-3
-1.500e-3
-9.427e-2
Figure 2. Min. principal strain [] distribution
in L4 with ventral and lateral spots
principal strains from the three models were compared (Figure 3). For the fully
degenerated model the maximum principal strain increased on both spots. The strain
changes for the mildly degenerated model were minor with 21% for the ventral spot and
quite small (-6%) for the lateral spot. The minimum principal strains increased on both
measurement spots with the progress of spinal degeneration. On the ventral spot, the
strain increased by 10% and 68% for mildly and fully degenerated models, respectively.
The lateral right spot showed the strain increases of 16% and 77% respectively.
Figure 3. Principal strain changes for the different FE models
In order to find out more about the spinal degeneration mechanism, a sensitivity study
was performed to investigate the influence of degeneration induced material property
change and disc geometry change on cortical shell strain separately. To do this, two
more types of models were created: one with only the degeneration induced material
property changes and the other with only the degeneration induced geometry changes.
Then the same loading scenario was simulated. The predicted principal strains from the
different models were compared (Figure 4). For the fully degenerated models,
maximum and minimum strains on both spots showed deviations of less than 5%, if
only degeneration induced geometry changes were considered. The strains were
decreased by 19% and 24% for the ventral and lateral spots of the minimum strain and
12% and 37% for the ventral and lateral spots of the maximum strain. For mildly and
fully degenerated model, both minimum and maximum principal strains increased on
both measurement sites due to degeneration induced material property changes. The
minimum strain increased by 29% and 39% for the mild, and 33% and 77% for the full
degeneration of the ventral and lateral spot, respectively. The maximum strains
increased by 31% and 19% for the mild, and 57% and 38% for the full degeneration
models of the ventral and lateral spot, respectively.