Chen Lihua, Wang Haiyan, Xu Guangming, Liu Hao
Department of Rehabilitation, Shenzhen Bao'an Traditional Chinese Medicine Hospital, Guangzhou University of Chinese Medicine, Shenzhen, China.
Department of Famous Traditional Chinese Medicine Hall, Shenzhen Bao'an Chinese Medicine Hospital, Shenzhen, Guangdong, China.
Front Bioeng Biotechnol. 2024 Aug 29;12:1371548. doi: 10.3389/fbioe.2024.1371548. eCollection 2024.
In recent years, the number of artificial cervical disc replacements has increased, and paravertebral ectopic ossification is a common complication. Although the exact mechanism is not clear, some studies suggest that it is related to the concentration of tissue stress caused by incomplete coverage of the trailing edge of the endplate. Therefore, this study performed a quantitative analysis to compare the biomechanical effects of different sagittal distances at the posterior edge of the endplate of the upper and lower prosthesis on the cervical spine and to explore the mechanical response of incomplete coverage of the posterior edge of the endplate on the paravertebral tissues.
A C2-C7 nonlinear finite element model of the cervical spine was established and validated. Based on the cervical spine model, cervical disc replacement surgery models were constructed with different distances of sagittal distance at the posterior edge of the upper prosthetic endplate (0, 1, 2, 3 mm, respectively) and sagittal distance at the posterior edge of the lower prosthetic endplate (1, 2, 3 mm, respectively). Each model was subjected to the same 1Nm torque and 73.6N driven compressive load. Range of motion (ROM), intervertebral disc pressure (IDP), facet joint force (FJF), and endplate stress were measured at the cervical surgical and other segments.
Compared to the intact cervical spine model, the sagittal distance of the posterior edge of the prosthesis endplate at different distances increased the stress on the intervertebral disc and the capsular joint in the adjacent vertebral body segments to different degrees, especially in extension. In different directions of motion, the posterior margin sagittal distance of the posterior edge of the endplate of the lower prosthesis has a greater mechanical influence on the cervical spine compared to the posterior margin sagittal distance of the posterior edge of the endplate of the upper prosthesis. Compared with the intact model, the biomechanical parameters (ROM, FJF, endplate stress) of the C5-C6 segment increased the most when the sagittal distance of the posterior edge of the endplate of the upper prosthesis was 3 mm. Compared with the intact model, the maximum intervertebral disc stress of C4-C5 and C6-C7 was 0.57 MPa and 0.53 MPa, respectively, when the sagittal distance of the posterior edge of the upper prosthetic endplate was 3 mm.
After the sagittal distance of the posterior edge of the prosthetic endplate was completely covered, the mechanical influence of the entire cervical spine was low. The sagittal distance at the posterior edge of the endplate of different sizes changed the motion pattern and load distribution of the implanted segment to some extent. When the sagittal distance between the prosthesis and the upper endplate was greater than or equal to 3 mm, the mechanical indices of the implanted segment increased significantly, increasing the risk of local tissue injury, especially during extension motion. Compared to the sagittal distance at the posterior edge of the endplate of the lower prosthesis, increasing the sagittal distance at the posterior edge of the endplate of the upper prosthesis has a greater effect on the mechanics of the cervical spine.
近年来，人工颈椎间盘置换的数量有所增加，椎旁异位骨化是一种常见并发症。虽然确切机制尚不清楚，但一些研究表明，这与终板后缘覆盖不完全所导致的组织应力集中有关。因此，本研究进行了定量分析，以比较上下假体终板后缘不同矢状距离对颈椎的生物力学影响，并探讨终板后缘覆盖不完全对椎旁组织的力学响应。
建立并验证了C2-C7颈椎非线性有限元模型。基于该颈椎模型，构建了上假体终板后缘矢状距离不同（分别为0、1、2、3毫米）和下假体终板后缘矢状距离不同（分别为1、2、3毫米）的颈椎间盘置换手术模型。每个模型均施加相同的1牛米扭矩和73.6牛驱动压缩载荷。在颈椎手术节段及其他节段测量活动度（ROM）、椎间盘压力（IDP）、小关节力（FJF）和终板应力。
与完整颈椎模型相比，不同距离的假体终板后缘矢状距离不同程度地增加了相邻椎体节段椎间盘和关节囊的应力，尤其是在伸展时。在不同运动方向上，下假体终板后缘矢状距离对颈椎的力学影响比上假体终板后缘矢状距离更大。与完整模型相比，当上假体终板后缘矢状距离为3毫米时，C5-C6节段的生物力学参数（ROM、FJF、终板应力）增加最为明显。当上假体终板后缘矢状距离为3毫米时，C4-C5和C6-C7的最大椎间盘应力分别为0.57兆帕和0.53兆帕。
假体终板后缘矢状距离完全覆盖后，对整个颈椎的力学影响较小。不同大小的终板后缘矢状距离在一定程度上改变了植入节段的运动模式和载荷分布。当假体与上终板之间的矢状距离大于或等于3毫米时，植入节段的力学指标显著增加，增加了局部组织损伤的风险，尤其是在伸展运动时。与下假体终板后缘矢状距离相比，增加上假体终板后缘矢状距离对颈椎力学的影响更大。
