BIOMECHANICAL EFFECTS OF REPETITIVE LOADING ON THE LUMBAR MOTION SEGMENT

流行病学研究表明，重复负荷在背部损伤的发生中起着重要作用 导致早期的椎间盘退变。体外研究证实了损伤的生物学合理性。 超负荷的由于超负荷而发生的然而，体外研究在改善我们的能力方面是有限的 了解所需的大量参数之间存在的复杂关系 描述单次和重复负荷作用的效果，以及椎间盘组织如何在 多年的暴露过程。我们相信，对这些复杂情况的更好理解 关系，即不同等级的圆盘在循环载荷作用下的破坏过程 退变以及小面退变如何改变盘内的加载路径，可以通过以下方式最好地实现 数值技术，如有限元模型(FEM)。到目前为止，我们的研究表明 有限元模型研究各种加载条件下阀瓣响应的可能性。此时，有限元是 一种健康的间盘，而在实际生活中，间盘退化发生得很早，并可能改变 光盘正在加载。已经开发和验证的健康椎间盘的孔弹性有限元将被修改为 反映了椎间盘退变的不同阶段，并将用于检验以下假设：(1)Disc 故障将在较少的重复次数和较低的负载水平下发生，并将在 退变的间盘与健康的间盘相比。(2)盘片存在裂隙、裂隙和裂纹 将导致应力重新分布并引起异常运动，从而进一步增强 阀瓣材料失效。(3)随着光盘上的加载模式和光盘结构的改变，高的区域 应力集中会发生在小关节处，导致小关节软骨破坏。 这些假设将在以下具体目标的帮助下得到解决：(1)确定 在健康和不同程度退变的椎间盘中由于循环载荷引起的破坏进展 使用包括钢筋单元的更精细的多孔弹性有限元来表示环形纤维，并使用 “用户定义”材料模型连续确定循环载荷作用下的破坏进程 进步了。(2)确定外环、内环含裂缝和内、外环含裂缝的效果 终板对退变的椎间盘的破坏进程的影响。孔隙度和孔隙度等孔隙弹性参数 盘部件的透气性也将被修改以反映这些故障。(3)确定载荷 不同退变程度间盘的小关节软骨。

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.