Chagnon Amélie, Aubin Carl-Eric, Villemure Isabelle
Department of Mechanical Engineering, Ecole Polytechnique de Montreal, Montréal, QC, Canada.
J Biomech Eng. 2010 Nov;132(11):111006. doi: 10.1115/1.4002550.
Spine degeneration is a pathology that will affect 80% of the population. Since the intervertebral disks play an important role in transmitting loads through the spine, the aim of this study was to evaluate the biomechanical impact of disk properties on the load carried by healthy (Thompson grade I) and degenerated (Thompson grades III and IV) disks. A three-dimensional parametric poroelastic finite element model of the L4/L5 motion segment was developed. Grade I, grade II, and grade IV disks were modeled by altering the biomechanical properties of both the annulus and nucleus. Models were validated using published creep experiments, in which a constant compressive axial stress of 0.35 MPa was applied for 4 h. Pore pressure (PP) and effective stress (S(E)) were analyzed as a function of time following loading application (1 min, 5 min, 45 min, 125 min, and 245 min) and discal region along the midsagittal profile for each disk grade. A design of experiments was further implemented to analyze the influence of six disk parameters (disk height (H), fiber proportion (%F), drained Young's modulus (E(a),E(n)), and initial permeability (k(a),k(n)) of both the annulus and nucleus) on load-sharing for disk grades I and IV. Simulations of grade I, grade III, and grade IV disks agreed well with the available published experimental data. Disk height (H) had a significant influence (p<0.05) on the PP and S(E) during the entire loading history for both healthy and degenerated disk models. Young's modulus of the annulus (E(a)) significantly affected not only S(E) in the annular region for both disk grades in the initial creep response but also S(E) in the nucleus zone for degenerated disks with further creep response. The nucleus and annulus permeabilities had a significant influence on the PP distribution for both disk grades, but this effect occurred at earlier stages of loading for degenerated than for healthy disk models. This is the first study that investigates the biomechanical influence of both geometrical and material disk properties on the load transfer of healthy and degenerated disks. Disk height is a significant parameter for both healthy and degenerated disks during the entire loading. Changes in the annulus stiffness, as well as in the annulus and nucleus permeability, control load-sharing in different ways for healthy and degenerated disks.
脊柱退变是一种会影响80%人群的病理状况。由于椎间盘在通过脊柱传递负荷方面起着重要作用，本研究的目的是评估椎间盘特性对健康（汤普森I级）和退变（汤普森III级和IV级）椎间盘所承载负荷的生物力学影响。建立了L4/L5运动节段的三维参数化多孔弹性有限元模型。通过改变纤维环和髓核的生物力学特性对I级、II级和IV级椎间盘进行建模。利用已发表的蠕变实验对模型进行验证，其中施加0.35 MPa的恒定轴向压缩应力持续4小时。分析了加载后（1分钟、5分钟、45分钟、125分钟和245分钟）孔隙压力（PP）和有效应力（S(E)）随时间的变化以及每个椎间盘等级沿矢状面轮廓的椎间盘区域情况。进一步实施实验设计以分析六个椎间盘参数（椎间盘高度（H）、纤维比例（%F）、纤维环和髓核的排水杨氏模量（E(a)，E(n)）以及初始渗透率（k(a)，k(n)））对I级和IV级椎间盘负荷分担的影响。I级、III级和IV级椎间盘的模拟结果与现有的已发表实验数据吻合良好。对于健康和退变椎间盘模型，在整个加载过程中，椎间盘高度（H）对PP和S(E)有显著影响（p<0.05）。纤维环的杨氏模量（E(a)）不仅在初始蠕变响应中对两个椎间盘等级的纤维环区域的S(E)有显著影响，而且在进一步蠕变响应中对退变椎间盘的髓核区域的S(E)也有显著影响。髓核和纤维环的渗透率对两个椎间盘等级的PP分布都有显著影响，但这种影响在退变椎间盘加载的早期阶段比健康椎间盘模型出现得更早。这是第一项研究几何和材料椎间盘特性对健康和退变椎间盘负荷传递的生物力学影响的研究。在整个加载过程中，椎间盘高度对于健康和退变椎间盘都是一个重要参数。纤维环刚度以及纤维环和髓核渗透率的变化，以不同方式控制健康和退变椎间盘的负荷分担。
