Parameter study for the finite element modelling of long bones with computed-tomography-imaging-based stiffness distribution.

The research focuses on exploring parameters for the finite element modelling of long bones using CT-imaging-based stiffness distribution. The study examined four horse radius bones under torsion and three-point bending, creating detailed models from CT images to simulate these tests. The findings suggested that orthotropic material definition better enhances the finite element analysis of long bones.

Modelling and Testing of Horse Radius Bones

• The researchers conducted experiments on four radii from different horses. These bones were subjected to two kinds of tests – three-point bending and pure torsion. These tests were designed to measure the bones’ response under stress and twisting forces respectively.
• Detailed models of these bones were then created using computed-tomography (CT) images. The models replicated the internal structure of the bone and allowed for the simulation of the aforementioned physical tests.

Stiffness Distribution and Material Definition

• The study sought to assign the local isotropic material stiffness. To do this, individual exponential functions were applied. The use of these functions allows researchers to more accurately depict the variation in stiffness throughout the bone.
• The factor and exponent in the functions were determined by fitting them to the measured torsional stiffness and bending stiffness of the bones. The results had exponents between 1.5 and 2, which agreed well with Young’s modulus – a measure of stiffness – obtained from samples cut from the bones.
• An additional study was conducted based on a model with a local orthotropic material definition. Unlike isotropic materials, orthotropic materials have different properties in different directions. This step was taken to understand the sensitivities of the finite element analysis results due to variations in the orthotropic elastic constants.

Conclusion and Implications

• The research concludes that using an orthotropic material definition for the finite element analysis of long bones led to enhanced simulation results for the bending tests. This was achieved by significantly reducing Young’s modulus in directions perpendicular to the bone axis.
• This suggests that using an orthotropic model is preferable for finite element analysis of long bones, also implying the importance of considering directional changes in bone material properties for better predictive modelling.