Mechanical Properties of Human Lumbar Intervertebral Discs and Design of an Artificial Structure to Substitute for the Mechanical Function

人体脊柱由多个椎骨和椎间盘组成，具有复杂的结构和三维几何形状。由于躯干的运动是由于椎间盘的弹性变形，椎间盘在椎骨之间也具有减震能力，因此椎间盘受到相当多的力和力矩。特别是，腰椎比其他部分承受更大的载荷和更复杂的运动。因此，腰椎间盘是维持腰椎稳定性和活动性的最重要组成部分。人类腰椎的许多疾病往往是由椎间盘的力学因素引起的，如椎间盘退变和椎间盘损伤。因此，在生物力学研究中，必须对腰椎产生有用的信息。本研究旨在探讨人体腰椎间盘的力学特性，并设计一种人工结构来替代其力学功能。首先，在生理载荷范围内，通过循环轴向压缩-拉伸试验和循环轴向扭转试验证实L4/5椎间盘的静态载荷响应。其次，提出了一种估算圆盘局部弹性模量的方法。此外，在屈曲和伸展状态下，评价了体内椎间盘矢状面上发生的应变状态。最后，提出了一种新的人工椎间盘，以重建人体腰椎间盘的稳定性和活动性的机械功能。

The human spine is composed of many vertebrae and intervertebral discs, and has the complex structure and three dimensional geometry. Because the motion of trunk is due to the elastic deformation of intervertebral discs which have also shockabsorbing ability between vertebrae, intervertebral discs are subjected to a considerable variety of forces and moments. In particular, the lumbar spine is subjected to a larger load and more complex movement than the other sections. The lumbar disc, therefore, is the most important component to maintain stability and mobility of the lumbar spine. Many diseases of human lumbar spine are often caused by the mechanical factors of disc, as disc degeneration and disc injuries. Therefore, useful information in biomechanical researches must be produced on the lumbar spine. The purpose of this study is to investigate the mechanical properties of the human lumbar intervertebral discs and to design an artificial structure to substitute for the mechanical function. First, the static loading response of L4/5 disc was confirmed by the cyclic axial compression-tension test and the cyclic axial torsion test within the range of physiological loads. Next, a method of the estimation of elastic modulus at a local region in a disc was presented. In addition, the state of strain occurring on the sagittal plane of a disc in vivo was evaluated under flexion and extension. Finally, a new artificial intervertebral disc was proposed to reconstruct the stability and mobility of the mechanical function of a human lumbar disc.