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

Figure 4. Degeneration sensitivity for principal minimum and maximum strains
5. DISCUSSION
The results show that degeneration induced material property changes play a more
important role in the cortical shell strain increase than the degeneration induced disc
geometry changes.
Some limitations of the present study were present. Firstly, the degeneration induced
spinal geometry changes involves also bony geometry changes, like micro-structure
deterioration of trabeculae, thinning of the cortical shell, osteophytes, facet joint
orientation or endplate contour flatten [7], which were neglected in this study. Secondly,
the model was only loaded statically under uniaxial compression. Physiologically the
spine is loaded dynamically under compression, bending moments and torsion. In
future, the strain changes will be investigated under more physiological conditions.
Thirdly, due to the limitation of CT resolution and the lack of MRI data, the thickness of
the cortical shells, the gap between the facet cartilages, and the geometry of the discs,
especially the nucleuses, were estimated. In addition, the locations of the strain gauges
for the strain comparisons and the orientation of the spine in respect to the load
direction were estimated from photos of the in vitro experiment setup. Last but not least,
the material properties were restricted to linear elastic behavior.
6. CONCLUSION
The results of this study indicate that spinal degeneration increases the cortical shell
strain, thus the fracture risk, especially in the fully degenerated situation. It was also
found that the degeneration induced material property changes increase the cortical shell
strain more than the degeneration induced disc geometry changes. This implies that for
spinal degeneration treatment and the prevention of vertebral fractures, augmentation of
the material would be a more effective method.
7. ACKNOWLEDGEMENTS
This study was supported by the Bundesministerium für Bildung und Forschung
(BMBF), Germany; Federal Institute for Occupational Safety and Health (BAuA),
Germany and the State of Hamburg (FHH,BSG).