Yang Haisheng, Jekir Michael G, Davis Maxwell W, Keaveny Tony M
Orthopaedic Biomechanics Laboratory, Department of Mechanical Engineering, University of California, Berkeley, CA, USA.
Orthopaedic Biomechanics Laboratory, Department of Mechanical Engineering, University of California, Berkeley, CA, USA.
J Biomech. 2016 May 3;49(7):1134-1140. doi: 10.1016/j.jbiomech.2016.02.045. Epub 2016 Feb 27.
The mechanism of vertebral wedge fractures remains unclear and may relate to typical variations in the mechanical behavior of the intervertebral disc. To gain insight, we tested 16 individual whole discs (between levels T8 and L5) from nine cadavers (mean±SD: 66±16 years), loaded in compression at different rates (0.05-20.0% strain/s), to measure a homogenized "effective" linear elastic modulus of the entire disc. The measured effective modulus, and average disc height, were then input and varied parametrically in micro-CT-based finite element models (60-μm element size, up to 80 million elements each) of six T9 human vertebrae that were virtually loaded to 3° of moderate forward-flexion via a homogenized disc. Across all specimens and loading rates, the measured effective modulus of the disc ranged from 5.8 to 42.7MPa and was significantly higher for higher rates of loading (p<0.002); average disc height ranged from 2.9 to 9.3mm. The parametric finite element analysis indicated that, as disc modulus increased and disc height decreased across these ranges, the vertebral bone stresses increased but their spatial distribution was largely unchanged: most of the highest stresses occurred in the central trabecular bone and endplates, and not anteriorly. Taken together with the literature, our findings suggest that the effective modulus of the human intervertebral disc should rarely exceed 100MPa and that typical variations in disc effective modulus (and less so, height) minimally influence the spatial distribution but can appreciably influence the magnitude of stress within the vertebral body.
椎体楔形骨折的机制尚不清楚，可能与椎间盘力学行为的典型变化有关。为了深入了解，我们测试了来自9具尸体（平均±标准差：66±16岁）的16个单个完整椎间盘（T8至L5节段），以不同速率（0.05 - 20.0%应变/秒）进行压缩加载，以测量整个椎间盘的均匀化“有效”线性弹性模量。然后，将测得的有效模量和平均椎间盘高度输入基于微CT的六个T9人体椎体有限元模型（单元尺寸60μm，每个模型多达8000万个单元）中，并通过均匀化椎间盘将其虚拟加载至3°的中度前屈。在所有标本和加载速率下，测得的椎间盘有效模量范围为5.8至42.7MPa，加载速率越高，有效模量越高（p<0.002）；平均椎间盘高度范围为2.9至9.3mm。参数化有限元分析表明，在这些范围内，随着椎间盘模量增加和椎间盘高度降低，椎骨应力增加，但其空间分布基本不变：大部分最高应力出现在中央小梁骨和终板，而非前部。结合文献来看，我们的研究结果表明，人类椎间盘的有效模量应很少超过100MPa，椎间盘有效模量（以及较小程度上的高度）的典型变化对空间分布影响最小，但可显著影响椎体内应力的大小。
