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Parametric Finite Element Modeling of the Vertebral Trabecular Bone Behavior Based on Cellular Solids Theory

Amjadi Kashani, Mohammad Reza | 2013

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 44294 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Jalali, Mir Abbas; Parnianpour, Mohammad
  7. Abstract:
  8. Spine column is the most important musculoskeletal structures. One of the serious health problems in societies, especially among aged population is osteoporosis. Loss of bone density in bone structures is called osteoporosis which increases the risk of fracture due to a decrease of bone stiffness and bone strength. Spine is the most common sites for osteoporosis-related fractures. Current assessment of osteoporosis status is based on bone densitometry tools like QCT (Quantitative Computed Tomography) or DEXA (Dual Energy X-ray absorptiometry). With these methods it is only possible to estimate density without any consideration the morphology of trabecular making parts like rods and plates. Studies show that the mechanical properties of trabecular bone depend on both density and morphology. Trabecular bone is a spongy or foam-like structure that can be found in vertebrae core or femoral neck. The microstructure of cancellous bone in the vertebrae can be varied based on age, sex, race, etc. The cellular solids theory is a common procedure to model porous materials and we have attempted to present a parametrical model for trabecular bone as a rod like structure based on cellular solids method. In order to modeling trabecular bone as a foam like structure specially in vertebrae core, a finite element code has been written by APDL capability in ANSYS. This parametric code can produce different lattices that can represent various structural and material properties. Then each cubic sample was loaded under compression displacement to failure point to obtain the stress-strain curve. The stress-strain curve is used to calculate mechanical properties of simulated bone model. In order to compare with experimental results we reconstruct our model for 6 bone samples was taken from two different vertebrae one has 78 years old and the other one has 91 years old. The results have shown that the mechanical properties of experimental results fall between lower and upper limits of model answer. This band varied from the worst state of connectivity to good state of connectivity. Plus the lattices that simulated bone samples taken from cadavers can predict stiffness and strength better than density-based relationships for mechanical properties. Stiffness surface responses based on anisotropic model, show good r-square (0.99) and RMSE=4 Mpa with Normalized-RMSE=0.37%. However these parameters for lattice yield stress are r-square (0.97), RMSE=0.22 Mpa, Normalized-RMSE=2%. According to the findings of the current study, the strength and stiffness or other mechanical properties of trabecular tissues in vertebrae are highly affected by many parameters like material specification of bone tissue and morphology characteristics like connectivity. It can be concluded that risk of fracture in vertebrae is a function of various factors beyond the bone mineral density that is evaluated by measurements such as DEXA and QCT. This has been shown that our cellular solid model may improve the assessments of mechanical properties of trabecular bone structures
  9. Keywords:
  10. Finite Element Model ; Spine ; Lumbar Vertebral ; Cellular Solid Theory ; Fracture Risk ; Trabeculal Bone

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