Abstract

Background and aim: One of the important 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. One of the most common sites for osteoporosis-related fractures is the spine. Current assessment of osteoporosis status is based on bone densitometry tools like QCT (Quantitative Computed Tomography) or DEXA (Dual Energy X-ray absorptionmetry). With these methods it is only possible to estimate density regardless of the morphology of trabecular constructing parts (rods and plates). 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 model parametrical for trabecular bone as a rod like structure based on cellular solids method.

Materials & Methods: In order to model trabecular bone as foam, like what exists 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, the model has been reconstructed for 6 bone samples were taken from two different vertebrae donors one has 78 years old and the other one has 91 years old then stiffness and strength predictions have been done.

Results: The results have shown that the mechanical properties of experimental results fall between lower and upper limits of model output and it is due to unknown connectivity level for all samples. The model is capable of presenting a band for mechanical properties. Plus the lattices that simulated bone samples taken from cadavers can predict stiffness and strength better than density-based relationships for mechanical properties.

Conclusion: 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.

Keywords: Cellular solids, Risk of fracture, Vertebrae, Trabecular bone, Finite element model