title: On the relative relevance of subject-specific geometries and degeneration-specific mechanical properties for the study of cell death in human intervertebral disk models.
abstract: Capturing patient- or condition-specific intervertebral disk (IVD) properties in finite element models is outmost important in order to explore how biomechanical and biophysical processes may interact in spine diseases. However, disk degenerative changes are often modeled through equations similar to those employed for healthy organs, which might not be valid. As for the simulated effects of degenerative changes, they likely depend on specific disk geometries. Accordingly, we explored the ability of continuum tissue models to simulate disk degenerative changes. We further used the results in order to assess the interplay between these simulated changes and particular IVD morphologies, in relation to disk cell nutrition, a potentially important factor in disk tissue regulation. A protocol to derive patient-specific computational models from clinical images was applied to different spine specimens. In vitro, IVD creep tests were used to optimize poro-hyperelastic input material parameters in these models, in function of the IVD degeneration grade. The use of condition-specific tissue model parameters in the specimen-specific geometrical models was validated against independent kinematic measurements in vitro. Then, models were coupled to a transport-cell viability model in order to assess the respective effects of tissue degeneration and disk geometry on cell viability. While classic disk poro-mechanical models failed in representing known degenerative changes, additional simulation of tissue damage allowed model validation and gave degeneration-dependent material properties related to osmotic pressure and water loss, and to increased fibrosis. Surprisingly, nutrition-induced cell death was independent of the grade-dependent material properties, but was favored by increased diffusion distances in large IVDs. Our results suggest that in situ geometrical screening of IVD morphology might help to anticipate particular mechanisms of disk degeneration.
authors.affiliation: Biomechanics and Mechanobiology, Institute for Bioengineering of Catalonia , Barcelona , Spain.
authors.forename: Andrea
authors.initials: A
authors.lastname: Malandrino
authors.affiliation: Center for Computational Imaging and Simulation Technologies in Biomedicine (CISTIB), Department of Mechanical Engineering, The University of Sheffield , Sheffield , UK.
authors.forename: José M
authors.initials: JM
authors.lastname: Pozo
authors.affiliation: Center for Computational Imaging and Simulation Technologies in Biomedicine (CISTIB), Department of Mechanical Engineering, The University of Sheffield , Sheffield , UK.
authors.forename: Isaac
authors.initials: I
authors.lastname: Castro-Mateos
authors.affiliation: Center for Computational Imaging and Simulation Technologies in Biomedicine (CISTIB), Department of Mechanical Engineering, The University of Sheffield , Sheffield , UK.
authors.forename: Alejandro F
authors.initials: AF
authors.lastname: Frangi
authors.affiliation: Orthopaedic Biomechanics, Department of Biomedical Engineering, Eindhoven University of Technology , Eindhoven , Netherlands.
authors.forename: Marc M
authors.initials: MM
authors.lastname: van Rijsbergen
authors.affiliation: Orthopaedic Biomechanics, Department of Biomedical Engineering, Eindhoven University of Technology , Eindhoven , Netherlands.
authors.forename: Keita
authors.initials: K
authors.lastname: Ito
authors.affiliation: Center of Musculoskeletal Research Ulm, Institute of Orthopaedic Research and Biomechanics, University of Ulm , Ulm , Germany.
authors.forename: Hans-Joachim
authors.initials: HJ
authors.lastname: Wilke
authors.affiliation: UTC CNRS UMR 7338, Biomécanique et Biongénierie (BMBI), Université de Technologie de Compiègne , Compiègne , France.
authors.forename: Tien Tuan
authors.initials: TT
authors.lastname: Dao
authors.affiliation: UTC CNRS UMR 7338, Biomécanique et Biongénierie (BMBI), Université de Technologie de Compiègne , Compiègne , France.
authors.forename: Marie-Christine
authors.initials: MC
authors.lastname: Ho Ba Tho
authors.affiliation: Biomechanics and Mechanobiology, Institute for Bioengineering of Catalonia , Barcelona , Spain.
authors.forename: Jérôme
authors.initials: J
authors.lastname: Noailly
keywords: Lumbar spine; damage model; disk cell nutrition; finite element modeling; intervertebral disk degeneration; poroelasticity; subject-specific modeling