Effects of bone structural unit (BSU) geometry and material properties on crack growth through idealized trabecular microstructures

Abstract

Bones containing large proportions of trabecular bone tissue such as the hip, wrist, and spinal column are highly susceptible to fracture. These fractures occur more frequently in the older populations, putting a large burden on the healthcare system and the society as a whole. Bone fracture prediction methods rely heavily on bone quantity measurements when predicting fracture risks. However, research has shown that only using bone quantity as the main predictor fails to identify a large number of patients with a high risk of bone fracture. Recent studies have shown that with age, the microstructure of the trabeculae changes as the patchwork of bone structural units (BSU), also known as trabecular packets, reduce in size due to the remodeling process. Unfortunately, little is known about the mechanical consequences of these changes on the trabeculae’s ability to resist cracking. Smaller BSU with age may reduce fracture risk due to crack blunting or redirection. Conversely, smaller BSU results in a larger proportion of brittle cement line which could provide more preferential paths for crack growth. The present work used extended finite element method (XFEM) crack modeling techniques, which have recently been applied to simulate crack growth in cortical bone, to model crack propagation through idealized trabeculae in 2D. The material properties for the BSU and cement line, as well as the size of the BSU themselves, were varied through parametric studies. Smaller BSU were found to accelerate crack growth within bone. Other geometric parameters like aspect ratio and angle of crack deflection were also identified as major contributors to the bones ability to resist cracks. Future work should investigate more representative BSU geometries to further clarify the role these structures have on fracture risk.