Guo Li-Xin, Li Rui, Zhang Ming
School of Mechanical Engineering and Automation, Northeastern University, Shenyang, 110819, China.
Interdisciplinary Division of Biomedical Engineering, The Hong Kong Polytechnic University, Hong Kong, China.
Acta Bioeng Biomech. 2016;18(2):19-29.
This study is to reveal the deformation of intervertebral disc (IVD), the stress distribution of solid phase and liquid phase, the variation of fluid flux and flow velocity in lumbar spine and the influence of different permeability parameters on them under intermittent compressive loading.
A poroelastic FEM of L4-L5 is assigned with different permeability parameters to analyze the deformation, stress distribution and fluid convection under intermittent compressive loads.
The results show that the pore pressure of IVD decreases with time, but the effective stress increases under intermittent compressive loads. The axial and radial strain will increase and fluid loss will recover at a more rapid rate if the permeability of endplate increases during unloading period. The velocity vectors show that most of the liquid in the disc flows into vertebrae through endplates and only a small quantity of liquid flows through the annulus fibrosus at the loading step, however, at the unloading step, almost all the liquid flowing into IVD is through the endplates.
The changing rate of pore pressure and effective stresses of nucleus pulposus and annulus fibrosus with higher permeability is smaller than that with smaller permeability. The degenerated endplate (with low permeability) yields high flow velocity decreasing gradient, which might impede liquid inflowing/outflowing smoothly through the endplates. The fluid flowing velocity in loading phase is faster than that in unloading phase, so a short resting time can relieve fatigue, but could not recover to the original liquid condition in IVDs.
本研究旨在揭示腰椎间盘在间歇性压缩载荷作用下的变形、固相和液相的应力分布、流体通量和流速的变化以及不同渗透参数对它们的影响。
对L4-L5的多孔弹性有限元模型赋予不同的渗透参数，以分析间歇性压缩载荷下的变形、应力分布和流体对流。
结果表明，在间歇性压缩载荷作用下，椎间盘的孔隙压力随时间降低，但有效应力增加。如果在卸载期间终板的渗透率增加，轴向和径向应变将增加，流体损失将以更快的速率恢复。速度矢量表明，在加载步骤中，椎间盘内的大部分液体通过终板流入椎体，只有少量液体通过纤维环流动，然而，在卸载步骤中，几乎所有流入椎间盘的液体都是通过终板。
渗透率较高时，髓核和纤维环的孔隙压力和有效应力变化率小于渗透率较低时。退变的终板（渗透率低）导致流速下降梯度较大，这可能会阻碍液体顺利通过终板流入/流出。加载阶段的流体流速比卸载阶段快，因此短时间的休息可以缓解疲劳，但不能使椎间盘恢复到原来的液体状态。
