Natarajan Raghu N, Williams Jamie R, Andersson Gunnar B J
Department of Orthopedic Surgery, Rush University Medical Center, 1653 West Congress Parkway, Chicago, IL 60612, USA.
J Bone Joint Surg Am. 2006 Apr;88 Suppl 2:36-40. doi: 10.2106/JBJS.F.00002.
Mechanical response of the spine to various dynamic loading conditions can be analyzed by way of in vitro and in vivo studies. Ethical concerns, interpretation of conclusions reached in animal studies, and lack of detailed stress distributions in the disc components are the major disadvantages of relying solely on in vivo studies. Intraspecimen variability, difficulty in including muscle activity, and inability to mimic fluid exchange into the disc during unloading are some of the disadvantages of in vitro models. The poroelastic finite element models can provide a method of understanding the relationship between biomechanical performance of the disc due to cyclic loading and disc degeneration. A poroelastic finite element model, including regional variation of strain-dependent permeability and osmotic pressure, was used to study the effect of disc degeneration on biomechanical properties as well as propagation of failure in the disc components when cyclic loading was applied to the lumbar disc. The results predicted that healthy discs were much more flexible than degenerated discs, and the disc stiffness decreased with increasing the number of load cycles independent of degenerative condition. Failure was found to progress as the drained elastic properties of the disc components decreased due to the presence of failure. Poroelastic finite element modeling, including strain-dependent permeability and osmotic pressure, is the most advanced analytical tool currently available that can be used to understand how cyclic loading affects the biomechanical characteristics of a degenerated lumbar disc. However, a complete understanding of behavior of the intervertebral disc will ultimately be achieved only with use of a combination of computational models together with in vitro and in vivo experimental methods. Finite element models of discs with varying degrees of disc degeneration will help clinicians understand the initiation and progression of disc failure and degeneration and will assist in the development of approaches to stimulate the regeneration of disc tissues.
脊柱对各种动态载荷条件的力学响应可以通过体外和体内研究来分析。伦理问题、动物研究所得结论的解读以及椎间盘各组成部分缺乏详细的应力分布是仅依赖体内研究的主要缺点。体外模型的缺点包括样本内变异性、难以纳入肌肉活动以及在卸载过程中无法模拟液体进入椎间盘的情况。多孔弹性有限元模型可以提供一种方法，来理解由于循环加载导致的椎间盘生物力学性能与椎间盘退变之间的关系。一个包含应变依赖性渗透率和渗透压区域变化的多孔弹性有限元模型，被用于研究椎间盘退变对生物力学性能的影响，以及当对腰椎间盘施加循环载荷时椎间盘各组成部分的破坏扩展情况。结果预测，健康的椎间盘比退变的椎间盘更具柔韧性，并且椎间盘刚度随着加载循环次数的增加而降低，与退变状况无关。由于破坏的存在，发现随着椎间盘各组成部分的排水弹性性能下降，破坏会不断进展。包含应变依赖性渗透率和渗透压的多孔弹性有限元建模，是目前可用的最先进的分析工具，可用于理解循环加载如何影响退变腰椎间盘的生物力学特性。然而，只有将计算模型与体外和体内实验方法结合使用，才能最终全面了解椎间盘的行为。不同程度椎间盘退变的有限元模型将有助于临床医生理解椎间盘破坏和退变的起始及进展，并将有助于开发刺激椎间盘组织再生的方法。
