Parametric Study Of Cervical Disc Degeneration And Biomechanical Study Of Cervical Disc Replacement Surgery

The cervical spine is an important part of the connection between the head and the body,supporting the head and providing it with greater mobility,and protecting important tissues such as blood vessels and the nerve spinal cord.In modern society,the cervical spine is the most vulnerable and degenerative part of the human spine,and its incidence has been increasing year after year,with a trend toward younger age,and it has gradually become a serious social problem.Therefore,it is important to investigate the biomechanics of cervical disc degeneration and post-surgery.In this paper,a parametric study of how cervical disc degeneration affects the transient center of rotation of its segments;a study of the repair effect of artificial disc replacement(CDR)after cervical disc degeneration;and a study of the biomechanical effects of resection of the uncovertebral joint in CDR and ACDF on cervical segments were conducted by means of finite element analysis,respectively.The instantaneous center of rotation(ICR)of the cervical spine is an important kinematic indicator of dynamic changes in vertebral motion quality.Investigating the effect of cervical degeneration on the position of the instantaneous center of rotation of the cervical spine is essential for understanding the mechanisms of cervical spine disease and improving the quality of cervical vertebral interbody motion.To assess the effect of different degrees of cervical spine single parameter degeneration on the ICR position during cervical flexion and extension motion.After establishing a three-dimensional nonlinear finite element model of the normal cervical spine,the geometry or material properties of its single segment(C5/6)were modified to simulate the four types of cervical degenerative factors(anterior osteophyte enlargement,disc height loss,endplates curvature flattening,and disc material properties degeneration).The same loading constraints were applied to all models respectively,and the ICR of each model was compared.The results showed that the parametric variable "disc height loss" had the most significant effect on the ICR position in the degenerated segment;the more the disc height loss,the more the mean ICR moved anteriorly in the degenerated segment.This finding further reminds physicians and scholars to focus on changes in the quality of cervical motion when conducting future studies of cervical spine surgery and cervical degeneration.Compared to conventional fusion surgery,CDR is able to preserve more motion of the cervical degenerative segment.In order to understand the different treatment effects produced by different artificial discs after placement in cervical degenerative segments from a biomechanical point of view,a C3-C7 finite element model including single-segment degeneration(C5/6)was developed in this study based on CT images of a subject with single-segment degenerative disease of the cervical spine.Three artificial cervical disc prosthesis models,Mobi-C,Bryan,Prodisc-C,and a new artificial prosthesis designed by the study were developed and placed into the finite element model to simulate different CDR procedures.The results showed that all prostheses were effective in restoring the motion of the degenerated segments;further reducing the risk of degeneration of adjacent segments;and reducing pain in facet joint of the neck.The placement of the new artificial prosthesis designed in this study was also effective in improving the quality of motion between degenerated cervical vertebrae and reducing the stress at the interface of prosthesis placement.ACDF can effectively relieve patient pain and was once the gold standard surgical approach for the treatment of cervical degenerative disease,but there is no conclusive evidence as to whether intraoperative resection of the uncovertebral joint is beneficial for maintaining the biomechanical properties of the operating segment.Therefore,in this study,further cervical spine surgery models with resection or preservation of the uncovertebral joint during ACDF and CDR were established,and the same load and boundary conditions were uniformly applied to each model.The effects of resection of the uncovertebral joint on the biomechanical properties of the cervical spine during ACDF and CDR were investigated.The results showed that resection of the uncovertebral joint in ACDF resulted in an increase in the Range of Motion(ROM)and a consequent increase in the stress on the surrounding bone,while resection of the uncovertebral joint in CDR resulted in an increase in the ROM of the surgical segment.This study suggests that the uncovertebral joint should not be routinely resected during ACDF;preserving the uncovertebral joint may create better conditions for cervical fusion;and the simultaneous resection of the uncovertebral joint during CDR is advocated to restore motion in the cervical replacement segment,which is consistent with the original design goal of CDR.