可膨胀融合器联合后路内固定治疗颅底凹陷寰枢椎脱位的生物力学研究

Biomechanical Study for Treating Basilar Invagination with Atlantoaxial Dislocation by Expandable Cage Combined with Posterior Internal Fixation

摘要: 目的：研究颅底凹陷寰枢椎脱位(Basilar invagination with atlantoaxial dislocation, BI-AAD)采用寰枢椎可膨胀融合器和静态融合器各自联合后路内固定系统治疗的生物力学特性，为寰枢椎可膨胀融合器的设计研发提供理论依据。方法：基于BI-AAD患者术后枕颈CT图像数据结合临床手术方案，建立寰枢椎关节间可膨胀融合器(高度7~10 mm，角度5˚~8˚)联合枕骨板和C2椎弓根螺钉后路内固定(ECage + C2PS + OP)和静态融合器联合后路内固定系统(Cage + C2PS + OP)的上颈椎三维有限元模型，分析寰枢椎关节活动度、植入融合器、椎弓根螺钉系统和上下终板的应力分布等情况。结果：ECage + C2PS + OP与Cage + C2PS + OP相比在屈伸、侧弯和旋转工况下寰枢关节活动度降低了11%、33.33%、0.04%；C2终板应力峰值在四种工况下分别降低−0.01%、58.16%、47.53%、67.39%。可膨胀融合器的应力分布于壳体中间“H”部位，在不同工况下可膨胀融合器最大应力值均有所下降，最大值为后伸工况的21.38 MPa，比静态融合器降低了48.6%。而枕骨板和C2椎弓根螺钉应力整体趋势大于静态融合器组。结论：可膨胀融合器能够适用于寰枢椎特定的高度和角度的撑开调整，从而实现对颈椎生理曲度的调节。设计的可膨胀寰枢关节间融合器较静态融合器沉降率风险更低，但是撑开装置具有断裂风险需要进一步优化设计。

Abstract: Objective: To explore the biomechanical characteristics of atlantoaxial dislocation (BI-AAD) after treatment with atlantoaxial expandable cageand static cage, respectively, in combination with pos-terior internal fixation systems, to provide a theoretical basis for the design and development of expandable cage of the atlantoaxial spine. Methods: Based on the postoperative occipital and cervi-cal CT images of BI-AAD patients combined with the clinical surgical protocol, a posterior atlantoax-ial expandable fusion (7~10 mm height, 5˚~8˚ angle) combined with occipital plate and C2 pedicle screw (ECage + C2PS + OP) and a static fusion combined with a posterior internal fixation system (Cage + C2PS + OP) were developed. The three-dimensional finite element models of the upper cer-vical spine were used to analyze the mobility of the atlantoaxial joint, the stress distribution of the implanted fusion, the pedicle screw system and the upper and lower endplates. Results: The atlan-toaxial joint range of motion (ROM) was reduced by 11%, 33.33% and 0.04% in flexion-extension, lateral bending and rotation for ECage + C2PS + OP compared to Cage + C2PS + OP; the peak stresses in the C2 endplate were reduced by −0.01%, 58.16%, 47.53% and 67.39% in the four conditions, respectively. The stresses of the expandable cage were distributed in the middle “H” part of the shell, and the maximum stress value of the expandable cage decreased under different conditions, with the maximum value of 21.38 MPa in the posterior extension condition, which was 48.6% lower than that of the static cage. The overall trend of occipital plate and C2 pedicle screw stresses was greater than that of the static cage group. Conclusion: The expandable cage can be used to adjust the atlantoaxial spine at specific heights and angles, thus allowing adjustment of the cervical physi-ological curvature. The designed expandable inter-articular cage has a lower risk of settling rate than the static fusion, but the fracture risk of the spacer device requires further design optimiza-tion.