The Effects of Changing Artificial Disc Shape on PE Loading Distribution

• Main Authors: Yu-Wen Chen, 陳裕文
• Other Authors: Cheng-Kung Cheng
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/22718353180676486526

碩士 === 國立陽明大學 === 醫學工程研究所 === 96 === Spinal interbody fusion and disc replacement are the main surgical treatments for low back pain resulted from intervertebral disc degeneration. Spinal interbody fusion is an effective way to achieve the purpose of nerve root decompression, but it also increases risk of accelerating adjacent disc degeneration. Previous coMParative studies about cages and artificial discs in biomechanical performances were mostly done with finite element analyses, but still it has never been analyzed with changing artificial disc curve. Three-dimensional finite element model of human L4-L5 was reconstructed with CT images in this study, and convex, concave and ellipse artificial disc models were also established referring to commercially available products with CAD software. Simulations included:(1) three types of PE were implanted inferiorly (2) concave and convex PE components implanted on superior or inferior sides of lumbar spine in flexion/extension, lateral bending and axial rotation in lumbar spine. Shear stresses and von Mises stresses on PE were evaluated for their loading distributions. The results showed high shear stresses of all types occurred in flexion, and convex PE was 23.81 MPa at best. In all conditions, stresses distributed more evenly and lower than those on the convex sides. The elliptic geometry enabled to confine the rotation of the motion unit. The elliptic geometry enabled to confine the rotation angle. However, the von Mises stress in rotation was 61.36 MPa on ellipse which was larger than other motions excepted flexion. Convex PE placed on superior side resulted in larger shear stress and von Mises stress than on inferior side, excepted for shear stress in rotation, but no significant difference was found. Concave PE placed on superior side resulted in large stress than on inferior side. The shear force on convex design could induce transverse crack because the shear stress exceeded yielding shear stress. The concave design not only decreased loading concentration but had relatively low stress. Such a design may be applicable in the future. Further study will aim at the design about two principal axes of the ellipse shape and its motion patterns.