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

analysis of the tissue mechanics. Both the bridge and sheath variants of the model
performed closest to the experimental data when the bridge/sheath stiffness was two
orders of magnitude greater than the lamellar stiffness. This large relative difference in
stiffness of two adjacent tissue constituents is in agreement with the experimental
observations seen in this study and those of Pezowicz et al. 4 . It is this increased
stiffness of the interlamellar bridges that results in the taut bridges and puckered
boundaries.
Despite similarly high levels of error recorded for both variants of the model, overall it
was concluded that the performance of the sheath model in this test more accurately
characterised deformation of the tissue. This conclusion was based on the correlation of
the interlamellar boundaries in the FE model with those of the experimental model. It
was seen that the puckering of these boundaries in the bridge model was frequently over
exaggerated (Figure 3). This supports the hypothesis presented in several studies in the
literature that the minor interlamellar bridges are part of a wider network of tissue
constituents that penetrate between and around fibre bundles 2,4 .
Throughout the study, isotropic material properties were assigned to the bridge and
sheath materials. As is evident from histological studies 2-5 although the composition of
these tissue components is still unknown, they are clearly fibrous in nature. Thus,
directionally dependent material properties would be more appropriate, to simulate the
varying strengths with and against the fibre direction.
A novel technique for creating specimen specific models of AF tissue samples has been
presented The techniques developed have been successfully used to investigate the
relative material properties of the tissue constituents and, along with supporting
evidence from experimental studies and the literature could provide the basis for
detailed characterisation of tissue constituent behaviour and properties. The techniques
for extracting the displacement of the tissue observed in the experimental study and
applying it to the FE model allowed inhomogenous displacements to be accurately
recreated with ease. This makes this method robust and versatile for application in
further studies.
6. REFERENCES
1. Yu, J., J.C. Fairbank, et al., 2005, Spine, 30 (16): 1815-20.
2. Yu, J., U. Tirlapur, et al., 2007, J. Anatomy 210(4): 460-471
3. Pezowicz, C.A., P.A. Robertson, et al., 2005, J. Anatomy 207(4): 299-312.
4. Pezowicz, C.A., P.A. Robertson, et al., 2006, J. Anatomy 208(3): 317-330
5. Schollum, M.L., P.A. Robertson, et al., 2009, J. Anatomy 214(6): 805-816
6. Broom, N.D., 1984, J. Anatomy 139: 275-294.
7. Luxmoore, B.J. et al., 2011, BORS Annual Meeting