Assessment of the elastic properties of human vertebral trabecular bone using computational mechanical tests and x-ray microtomography—a subvolume analysis

Abstract

Trabecular bone structures can be modeled as a linear elastic solid, with a heterogeneous and anisotropic structure. The HR-pQCT technique is ideal for the characterization of trabecular bone to measure aspects of bone quality in diseases such as osteoporosis. In this investigation, twelve human vertebrae were used for the investigation of the mechanical properties of trabecular bone by finite element analysis (FEA). A virtual cube sample with 18.5 mm sides was extracted from each vertebrae and four smaller central cubes were obtained from it, with a 20% reduction of volume for each cube. The direct mechanics approach by FEA was performed (FAIM v6.0, Numerics88 Solutions Ltd) and mean values on three mean directions of loading resulting in: E1 = 294 MPa, E2 = 258 MPa, E3 = 153 MPa, G23 = 86 MPa, G31 = 103 MPa, G12 = 100 MPa. The Statistical Analysis was applied showing that E1 values are statically different from E3, and E2 are statically different from E3, with E2 equal to E1. This indicates that there are two different mean directions of loading on these trabecular bone samples of human vertebrae. The assessment of microstructural properties showed a tendency to increased connectivity of trabeculae, which occurs as the reduction of the analyzed subvolumes (100% to 20% or 18.5 mm to 3.7 mm) followed by an addition of bone volume fraction values. Those results highlight the idea that mechanical properties are better described in local regions, in other words, a local assessment with smaller sample size maintain the volume fraction and connectivity improving the prediction of bone strength. The mechanical properties are better associated with microstructural information in the subvolume, reducing the time of scan and radiation dose, which can generate bone quality parameters, for the diagnosis of bone diseases and prediction of fracture risk of bone structures with higher accuracy.