Lu Y M, Hutton W C, Gharpuray V M
Department of Bioengineering, Clemson University, South Carolina, USA.
Spine (Phila Pa 1976). 1996 Nov 15;21(22):2570-9. doi: 10.1097/00007632-199611150-00006.
A finite element model of a lumbar motion segment was constructed.
The model was directed toward understanding the effect of compression, bending and twisting, and diurnal fluid changes in the disc on the propensity to disc prolapse. Tensile stresses in the anulus fibers were computed and used to determine the successive steps required to create a fissure in the disc.
Disc prolapse is more likely under combined loading involving compression and bending and twisting. Changes in fluid content in the disc also affect the mechanical behavior of the disc.
The three-dimensional model accounted for the viscoelastic material properties of the anulus fibers and ligaments. Diurnal fluid exchange was simulated by changing the fluid content in the nucleus of the disc. Combined with bending and twisting, a compressive load was applied at different loading rates.
The maximum tensile stress in the anulus fibers always occurred in the fibers at the inner posterior anulus at the junction of the disc and the endplate. Of the three models tested, the "weakest" (or the first to fail) was the saturated disc subjected to compression and bending and twisting. As the loading rate increased, anulus fiber failure was initiated at a lower value of compressive load. An increasing compressive load applied to a flexed, twisted, and saturated disc resulted in progressive failure, or fissure propagation, starting at the posterior inner anulus at the junction of the disc and the endplate.
The results from this study suggest that there are several key factors involved in the initiation and propagation of anulus failure: axial compressive load, bending and twisting, and disc saturation. If one of these is lacking, anulus failure is harder to achieve.
构建了腰椎运动节段的有限元模型。
该模型旨在了解压缩、弯曲、扭转以及椎间盘内昼夜液体变化对椎间盘突出倾向的影响。计算纤维环中的拉应力，并用于确定在椎间盘中形成裂缝所需的连续步骤。
在涉及压缩、弯曲和扭转的联合载荷作用下，椎间盘更易突出。椎间盘内液体含量的变化也会影响椎间盘的力学行为。
三维模型考虑了纤维环和韧带的粘弹性材料特性。通过改变椎间盘髓核中的液体含量来模拟昼夜液体交换。结合弯曲和扭转，以不同的加载速率施加压缩载荷。
纤维环中的最大拉应力总是出现在椎间盘与终板交界处后内侧的纤维中。在测试的三个模型中，“最弱的”（或最先失效的）是受到压缩、弯曲和扭转的饱和椎间盘。随着加载速率的增加，在较低的压缩载荷值时纤维环就开始失效。对弯曲、扭转且饱和的椎间盘施加不断增加的压缩载荷会导致从椎间盘与终板交界处后内侧开始的渐进性失效或裂缝扩展。
本研究结果表明，纤维环失效的起始和扩展涉及几个关键因素：轴向压缩载荷、弯曲和扭转以及椎间盘饱和。如果缺少其中一个因素，纤维环失效就更难发生。
