Study Of Cortical Bone Research Articles

Design, Manufacturing and Testing of a Bone Shaft Fatigue Machine

To determine the mechanical properties of materials subjected to repetitive loading, fatigue testing is a well–established method in engineering studies. It is believed that the cause of stress fractures in cortical bone are due to the repetitive loading. There is currently no cost–effective device that accounts for the variety of factors influencing the fatigue behaviour of bone in vivo. The Bone Shaft Fatigue Machine is proposed as a possible solution and designed as a rotating bending fatigue tester with a constant stress amplitude. Sheep metatarsal bone shaft specimens designed and machined for fatigue tests. The results were determined to be in accordance with the expected fatigue stresses and cycles reported in current literature. The Bone Shaft Fatigue Machine was also found to be cost-effective and applicable to the testing of materials in research areas other than the study of cortical bone.

Fatigue-induced microdamage in cancellous bone occurs distant from resorption cavities and trabecular surfaces

Impaired bone toughness is increasingly recognized as a contributor to fragility fractures. At the tissue level, toughness is related to the ability of bone tissue to resist the development of microscopic cracks or other tissue damage. While most of our understanding of microdamage is derived from studies of cortical bone, the majority of fragility fractures occur in regions of the skeleton dominated by cancellous bone. The development of tissue microdamage in cancellous bone may differ from that in cortical bone due to differences in microstructure and tissue ultrastructure. To gain insight into how microdamage accumulates in cancellous bone we determined the changes in number, size and location of microdamage sites following different amounts of cyclic compressive loading. Human vertebral cancellous bone specimens (n=32, 10 male donors, 6 female donors, age 76±8.8, mean±SD) were subjected to sub-failure cyclic compressive loading and microdamage was evaluated in three-dimensions. Only a few large microdamage sites (the largest 10%) accounted for 70% of all microdamage caused by cyclic loading. The number of large microdamage sites was a better predictor of reductions in Young’s modulus caused by cyclic loading than overall damage volume fraction (DV/BV). The majority of microdamage volume (69.12±7.04%) was located more than 30μm (the average erosion depth) from trabecular surfaces, suggesting that microdamage occurs primarily within interstitial regions of cancellous bone. Additionally, microdamage was less likely to be near resorption cavities than other bone surfaces (p<0.05), challenging the idea that stress risers caused by resorption cavities influence fatigue failure of cancellous bone. Together, these findings suggest that reductions in apparent level mechanical performance during fatigue loading are the result of only a few large microdamage sites and that microdamage accumulation in fatigue is likely dominated by heterogeneity in tissue material properties rather than stress concentrations caused by micro-scale geometry.

Limitations of clinical CT in assessing cortical thickness and density

The peak CT number and full width at half maximum (FWHM) were obtained from the image profiles of aluminium of thickness ranging from 0.1-9.5 mm. The scans were performed at different fields of view (FOVs) and with different reconstruction algorithms (`bone' and `standard'). Above 3 mm, and FWHM provide measures of the density and thickness which are largely independent of FOV (i.e. pixel size) and algorithm. Below 3 mm, falls progressively whilst FWHM remains relatively constant. At these small thicknesses the effect of FOV on is more pronounced when the bone algorithm is used, whilst FWHM remains relatively constant and independent of both FOV and algorithm. The results are discussed in terms of thickness relative to pixel size and spatial resolution as characterized by the point spread function. A linear relationship was found between the product and thickness that is independent of both FOV and algorithm. This product may be useful in studies of cortical bone and changes due to osteoporosis.