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Cracking intervertebral disc herniation

TUE : Materials Technology (Mate) group
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  • Chemistry
  • Medicine
  • Physics


12 /mhj Cracking Intervertebral Disc Herniation Famke Kraaijeveld, Jacques M. Huyghe and Frank P.T. Baaijens Eindhoven University of Technology, Department of Biomedical Engineering Introduction During intervertebral disc (IVD) degeneration global (os- motic) pre-stress decreases, while chance of an injury in- creases. This is a paradox. Is it then genetically driven? No, mechanics must play a role. Materials like tissues endure instability during swelling or shrinking [2]. This can lead to localization [6] and therefore fracturing. We believe this is the cause of intervertebral disc (IVD) herniation during degeneration and not just genetics or chance. a b Figure 1: a) Schematic of IVD position. b) Different stages of IVD herniation: A: Grade I (15-40) years; B: Grade II (35-70) years; C: Grade III (Male 31) Annulus bulging into nucleus; D: Grade VI (Male 31) Internal collapse of annulus Objective We hypothesize that existing cracks open and propagate un- der decreasing osmotic pressure, i.e. global decrease of pre- stress. [3,4] This will be tested by FE simulations on a small piece of annulus (see figure 2). a b Figure 2: a) Schematic cross-section of IVD; calculation domain is a part of the annulus. b) Opening and growth of crack under decreas- ing osmotic pressure Materials and Method Materials Lanir’s theory [3] is used to represent the bulk behavior. Shear faulting (mode-II ) causes high pressure gradients which are approximated by jumps [µf ] (see also fig. 4). Opening of the crack (mode-I ) causes fluid flow into the crack (µfΓ). This balance of mass can be derived from figure 3. Figure 3: Schematic overview of forces (t) and fluid flow (f and qΓ at crack In figure 4 the total distribution of chemical potential is given for arbitrary (mixed-mode) loading, so with both [µf ] and µfΓ. Figure 4: Chemical potential distribution: jumps approximate high gradients, luid flow into the crack goes with. Method Partition of Unity (PU-FEM) is used.[1] This method is me

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