Department of Mechanical and Biomedical Engineering, National University of Ireland, Galway, Ireland.
Biomech Model Mechanobiol. 2013 Aug;12(4):685-703. doi: 10.1007/s10237-012-0434-3. Epub 2012 Sep 16.
Interbody fusion device subsidence has been reported clinically. An enhanced understanding of the mechanical behaviour of the surrounding bone would allow for accurate predictions of vertebral subsidence. The multiaxial inelastic behaviour of trabecular bone is investigated at a microscale and macroscale level. The post-yield behaviour of trabecular bone under hydrostatic and confined compression is investigated using microcomputed tomography-derived microstructural models, elucidating a mechanism of pressure-dependent yielding at the macroscopic level. Specifically, microstructural trabecular simulations predict a distinctive yield point in the apparent stress-strain curve under uniaxial, confined and hydrostatic compression. Such distinctive apparent stress-strain behaviour results from localised stress concentrations and material yielding in the trabecular microstructure. This phenomenon is shown to be independent of the plasticity formulation employed at a trabecular level. The distinctive response can be accurately captured by a continuum model using a crushable foam plasticity formulation in which pressure-dependent yielding occurs. Vertebral device subsidence experiments are also performed, providing measurements of the trabecular plastic zone. It is demonstrated that a pressure-dependent plasticity formulation must be used for continuum level macroscale models of trabecular bone in order to replicate the experimental observations, further supporting the microscale investigations. Using a crushable foam plasticity formulation in the simulation of vertebral subsidence, it is shown that the predicted subsidence force and plastic zone size correspond closely with the experimental measurements. In contrast, the use of von Mises, Drucker-Prager and Hill plasticity formulations for continuum trabecular bone models lead to over prediction of the subsidence force and plastic zone.
体内融合装置沉降在临床上已有报道。对周围骨骼机械性能的深入了解将能够准确预测椎体沉降。在微观和宏观尺度上研究了小梁骨的多轴弹塑性行为。使用微计算机断层扫描衍生的微观结构模型研究了静水和受压条件下小梁骨的屈服后行为，阐明了宏观水平上压力相关屈服的机制。具体而言，微观结构小梁模拟预测了在单轴、受限和静水压缩下，表观应力-应变曲线上的明显屈服点。这种明显的表观应力-应变行为是由于小梁微观结构中的局部应力集中和材料屈服所致。事实证明，这种现象与小梁水平上采用的塑性公式无关。通过使用压敏泡沫塑性公式的连续体模型，可以准确地捕捉到这种独特的响应，其中会发生压敏屈服。还进行了椎体装置沉降实验，提供了小梁塑性区的测量结果。结果表明，为了复制实验观察结果，必须在小梁骨的连续体宏观模型中使用压敏塑性公式，进一步支持了微观研究。在椎体沉降的模拟中使用压敏泡沫塑性公式，表明预测的沉降力和塑性区尺寸与实验测量结果非常吻合。相比之下，使用 von Mises、Drucker-Prager 和 Hill 塑性公式的连续体小梁骨模型会导致沉降力和塑性区的过度预测。
