Yoganandan Narayan, Umale Sagar, Stemper Brain, Snyder Bryan
Department of Neurosurgery, Medical College of Wisconsin, Milwaukee, WI, United States; Department of Orthopaedic Surgery Medical College of Wisconsin, Milwaukee, WI, United States.
Department of Orthopaedic Surgery Medical College of Wisconsin, Milwaukee, WI, United States.
J Mech Behav Biomed Mater. 2017 May;69:30-38. doi: 10.1016/j.jmbbm.2016.11.026. Epub 2016 Dec 15.
Numerous studies have been conducted since more than fifty years to understand the behavior of the human lumbar spine under fatigue loading. Applications have been largely driven by low back pain and human body vibration problems. The human neck also sustains fatigue loading in certain type of civilian occupational and military operational activities, and research is very limited in this area. Being a visco-elastic structure, it is important to determine the stress-relaxation properties of the human cervical spine intervertebral discs to enable accurate simulations of these structures in stress-analysis models. While finite element models have the ability to incorporate viscoelastic material definitions, data specific to the cervical spine are limited. The present study was conducted to determine these properties and understand the responses of the human lower cervical spine discs under large number of cyclic loads in the axial compression mode. Eight disc segments consisting of the adjacent vertebral bodies along with the longitudinal ligaments were subjected to compression, followed by 10,000 cycles of loading at 2 or 4Hz frequency by limiting the axial load to approximately 150 N, and subsequent to resting period, subjected to compression to extract the stress-relaxation properties using the quasi-linear viscoelastic (QLV) material model. The coefficients of the model and disc displacements as a function of cycles and loading frequency are presented. The disc responses demonstrated a plateauing effect after the first 2000 to 4000 cycles, which were highly nonlinear. The paper compares these responses with the "work hardening" phenomenon proposed in clinical literature for the lumbar spine to explain the fatigue behavior of the discs. The quantitative results in terms of QLV coefficients can serve as inputs to complex finite element models of the cervical spine to delineate the local and internal load-sharing responses of the disc segment.
五十多年来，人们进行了大量研究，以了解人体腰椎在疲劳载荷下的行为。这些研究的应用主要是由腰痛和人体振动问题推动的。在某些类型的民用职业和军事作战活动中，人体颈部也会承受疲劳载荷，而这一领域的研究非常有限。作为一种粘弹性结构，确定人体颈椎椎间盘的应力松弛特性对于在应力分析模型中准确模拟这些结构非常重要。虽然有限元模型能够纳入粘弹性材料定义，但针对颈椎的特定数据有限。本研究旨在确定这些特性，并了解人体下颈椎椎间盘在轴向压缩模式下大量循环载荷作用下的反应。对八个由相邻椎体以及纵向韧带组成的椎间盘节段进行压缩，然后以2或4Hz的频率施加10000次循环载荷，将轴向载荷限制在约150N，在休息期后，再次进行压缩，以使用准线性粘弹性（QLV）材料模型提取应力松弛特性。给出了模型系数以及椎间盘位移随循环次数和加载频率的函数关系。椎间盘的反应在前2000至4000次循环后呈现出平稳效应，这是非线性的。本文将这些反应与临床文献中提出的腰椎“加工硬化”现象进行比较，以解释椎间盘的疲劳行为。以QLV系数表示的定量结果可作为颈椎复杂有限元模型的输入，以描绘椎间盘节段的局部和内部载荷分担反应。
