BIOMECHANICAL EFFECTS OF REPETITIVE LOADING ON THE LUMBAR MOTION SEGMENT

流行病学研究表明，重复负荷是重要的发展，背部受伤 导致早期椎间盘退化。体外研究已经证实了损伤的生物相容性 由于过度装载而引起的。然而，体外研究在改善我们的免疫功能方面的能力有限。 了解所需的大量参数之间存在的复杂关系， 描述单次和重复载荷应用的影响以及椎间盘组织如何在 经过多年的曝光。我们认为，对这些复杂的 关系，即在循环载荷下，不同等级的 退变以及小关节退变如何改变椎间盘内的载荷路径，最好通过以下方式实现： 数值技术，如有限元模型（FEM）。我们迄今为止的研究表明， 有限元模型的潜力，研究光盘的各种负载条件下的反应。此时，FEM 一个健康的椎间盘，而在实际生活中椎间盘退变发生早期，并可能改变反应的 光盘加载已经开发和验证的健康椎间盘的多孔弹性FEM将被修改， 反映了椎间盘退变的不同阶段，并将用于测试以下假设：（1）椎间盘 故障将在较少的重复和较低的载荷水平后发生，并将在 与健康的椎间盘相比。(2)圆盘中存在裂缝、裂口和裂纹 将引起应力的重新分布并引起异常运动，从而进一步增强 圆盘材料失效。(3)随着盘上的载荷模式和盘结构的改变，高应力区域的应力增加。 在小平面关节中将出现应力集中，导致小平面关节软骨的破坏。 这些假设将在以下具体目标的帮助下得到解决：（1）确定 健康椎间盘和不同退变程度椎间盘中循环载荷导致的失效进展 使用更精细的多孔弹性FEM，其包括表示环形纤维的钢筋单元，并使用 “用户自定义”材料模型，以确定随着循环载荷的持续失效进展 进步。(2)确定包括外环和内环中的裂缝以及 终板对退变椎间盘破坏进展的影响。孔隙弹性参数，如孔隙度和 阀瓣部件的渗透性也将被修改以反映这些失效。(3)确定载荷 对不同程度退变椎间盘的关节突软骨的影响。

Epidemiological studies suggest that repetitive loading is of importance in the development of back injuries leading to early disc degeneration. In vitro studies have confirmed the biological plausibility of injuries occurring from excess loading. However, in vitro studies are limited in their ability to improve our understanding of the complex relationships that exist between the large numbers of parameters needed to describe the effects of single and repetitive load applications and how disc tissues break down over the course of many years of exposure. We believe that an improved understanding of these complex relationships, namely how failure progresses under cyclic loading in discs with different grades of degeneration and how facet degeneration changes the load path within the disc, can best be achieved by numerical techniques such as the Finite-Element Model (FEM). Our studies to date have shown the potential of FE models to study disc responses to a variety of loading conditions. At this time the FEM is one of a healthy disc, while in actual life disc degeneration occurs early and may alter the response of the disc to loading. The already developed and validated poro-elastic FEM of a healthy disc will be modified to reflect various stages of disc degeneration and will be used to test the following hypotheses: (1) Disc failure will occur after fewer repetitions and at lower load levels and will propagate more rapidly in degenerative discs compared to healthy discs. (2) The existence of fissures, clefts and cracks in the disc will cause redistribution of the stresses and cause abnormal motions resulting in further enhancing the failure of disc material. (3) As the loading pattern on the discs and the disc structure changes, areas of high stress concentrations will occur in the facet joints leading to failure of the facet joint cartilage. These hypotheses will be addressed with the help of the following specific aims: (1) Determine the failure progression due to cyclic loads in a healthy disc and in discs of different grades of degeneration using a more refined poro-elastic FEM which includes re-bar elements to represent annular fibers and uses "user-defined" material models to determine failure progression continuously as the cyclic loading progresses. (2) Determine the effect of including fissures in the outer and inner annulus and cracks in the endplates on the progression of failure in degenerated discs. Poro-elastic parameters such as porosity and permeability of the disc components will also be modified to reflect these failures. (3) Determine the loads on facet cartilage in discs of different grades of degeneration.