Effects of Tissue-­Level Ductility on Trabecular Bone Strength

Osteoporosis is one of the most common skeletal diseases that lead to an accelerated bone loss due to an imbalance in bone turnover. This low bone mass and degraded bone microarchitecture cause a reduction in mechanical properties and an associated increase in fracture risk. If individual trabeculae become more brittle with aging, disease, or drug treatment, how does that influence the strength of the overall trabecular bone? This multi-scale issue, which relates energy absorption or tissue ductility at one scale to load-carrying capacity or strength at a higher scale, is particularly relevant in osteoporosis applications since it is well known that aging and drug treatments can influence tissue-level ductility. However, the link between tissue ductility and apparent-level strength for trabecular bone is poorly understood and thus is it not currently possible to infer how known changes in tissue ductility translate into the higher scale and more clinically relevant changes in trabecular strength. To provide insight into this issue, our goal in this study was to determine how trabecular strength is altered when the tissue is changed from perfectly brittle to perfectly ductile – the two extremes of possible tissue-level ductility. The results show that overall trabecular strength can vary two-fold if the tissue is entirely brittle compared to entirely ductile. The comparison with the experimental data suggests that at low bone volume fraction, real variations in tissue ductility could be important since the real behavior is situated between the ductile and brittle behaviors. If so, this implies that future studies assessing the structural consequence of changes in tissue-level ductility need to consider the bone volume fraction. Our analyses are unique since they are the first to account for the complex 3D geometric detail of real trabecular microarchitecture and this study is the first to mechanistically link tissue-level ductility, a potentially important aspect of tissue material behavior, to the apparent-level strength, which is relevant clinically.