Umale Sagar, Yoganandan Narayan
Department of Neurosurgery, Medical College of Wisconsin, Milwaukee, WI, USA.
Department of Orthopaedic Surgery, Medical College of Wisconsin, Milwaukee, WI, USA.
Asian Spine J. 2018 Oct;12(5):910-918. doi: 10.31616/asj.2018.12.5.910. Epub 2018 Sep 10.
Determination of human cervical spine disc response under cyclic loading.
To explain the potential mechanisms of intervertebral disc injury caused by cyclic loading.
Certain occupational environments in civilian and military populations may affect the cervical spine of individuals by cyclic loading. Research on this mechanism is scarce.
Here, we developed a finite element model of the human C4-C5 disc. It comprised endplates, five layers of fibers, a nucleus, and an annulus ground substance. The endplates, ground substance, and annular fibers were modeled with elastic, hyperviscoelastic, and hyper-elastic materials, respectively. We subjected the disc to compressive loading (150 N) for 10,000 cycles at frequencies of 2 Hz (low) and 4 Hz (high). We measured disc displacements over the entire loading period. We obtained maximum and minimum principal stress and strain and von Mises stress distributions at both frequencies for all components. Further, we used contours to infer potential mechanisms of internal load transfer within the disc components.
The points of the model disc displacement versus the loading cycles were within the experimental corridors for both frequencies. The principal stresses were higher in the ground matrix, maximum stress was higher in the anterior and posterior annular regions, and minimum stress was higher along the superior and inferior peripheries. The maximum principal strains were radially directed, whereas the minimum principal strains were axially/obliquely directed. The stresses in the fibers were greater and concentrated in the posterolateral regions in the innermost layer.
Disc displacement was lower at high frequency, thus exhibiting strain rate stiffening and explaining stress accumulation at superior and interior peripheries. Greater stresses and strains at the boundaries explain disc injuries, such as delamination. The greater development of stresses in the innermost annular fiber layer (migrating toward the posterolateral regions) explains disc prolapse.
测定人体颈椎间盘在循环加载下的反应。
解释循环加载导致椎间盘损伤的潜在机制。
平民和军人中的某些职业环境可能通过循环加载影响个体的颈椎。对此机制的研究很少。
在此，我们建立了人体C4 - C5椎间盘的有限元模型。它包括终板、五层纤维、髓核和纤维环基质。终板、基质和环形纤维分别用弹性、超粘弹性和超弹性材料建模。我们在2 Hz（低）和4 Hz（高）频率下对椎间盘施加150 N的压缩载荷，持续10000个循环。我们测量了整个加载过程中的椎间盘位移。我们获得了所有组件在两个频率下的最大和最小主应力、应变以及冯·米塞斯应力分布。此外，我们使用等高线来推断椎间盘组件内部载荷传递的潜在机制。
模型椎间盘位移与加载循环的点在两个频率的实验范围内。主应力在基质中较高，最大应力在前部和后部环形区域较高，最小应力在上部和下部周边较高。最大主应变沿径向方向，而最小主应变沿轴向/倾斜方向。纤维中的应力更大，集中在最内层的后外侧区域。
高频下椎间盘位移较低，从而表现出应变率硬化，并解释了上部和内部周边的应力积累。边界处更大的应力和应变解释了椎间盘损伤，如分层。最内层环形纤维层（向后外侧区域迁移）中应力的更大发展解释了椎间盘突出。
