Department of Orthopedics, West China Hospital, Sichuan University, No. 37 Guo Xue Xiang, Chengdu, Sichuan Province 610041, China.
Department of Radiology, West China Hospital, Sichuan University, No. 37 Guo Xue Xiang, Chengdu, Sichuan Province 610041, China.
Spine J. 2017 Dec;17(12):1926-1931. doi: 10.1016/j.spinee.2017.07.009. Epub 2017 Jul 13.
BACKGROUND CONTEXT: Facet tropism is defined as the angular difference between the left and the right facet orientation. Facet tropism was suggested to be associated with the disc degeneration and facet degeneration in the lumbar spine. However, little is known about the relationship between facet tropism and pathologic changes in the cervical spine and the mechanism behind. PURPOSE: This study was conducted to investigate the biomechanical impact of facet tropism on the intervertebral disc and facet joints. STUDY DESIGN: A finite element analysis study. METHODS: The computed tomography (CT) scans of a 28-year-old male volunteer was used to construct the finite element model. First, a symmetrical cervical model from C2 to C7 was constructed. The facet orientations at each level were simulated using the data from our previously published study. Second, the facet orientations at the C5-C6 level were altered to simulate facet tropism with respect to the sagittal plane. The angular difference of the moderate facet tropism model was set to be 7 degrees, whereas the severe facet tropism model was set to be 14 degrees. The inferior of the C7 vertebra was fixed. A 75 N follower loading was applied to simulate the weight of the head. A 1.0 N⋅m moments was applied on the odontoid process of the C2 to simulate flexion, extension, lateral bending, and axial rotation. RESULTS: The intradiscal pressure (IDP) at the C5-C6 level of the severe facet tropism model increased by 49.02%, 57.14%, 39.06%, and 30.67%, under flexion, extension, lateral bending, and axial rotation moments, in comparison with the symmetrical model. The contact force of the severe facet tropism model increased by 35.64%, 31.74%, 79.26%, and 59.47% from the symmetrical model under flexion, extension, lateral bending, and axial rotation, respectively. CONCLUSIONS: Facet tropism with respect to the sagittal plane at the C5-C6 level increased the IDP and facet contact force under flexion, extension, lateral bending, and axial rotation. The results suggested that facet tropism might be the anatomic risk factor of the development of cervical disc degeneration or facet degeneration. Future clinical studies are in need to verify the biomechanical impact of facet tropism on the development of degenerative changes in the cervical spine.
背景：小关节倾斜定义为左、右小关节面的夹角差异。小关节倾斜被认为与腰椎间盘退变和小关节退变有关。然而，小关节倾斜与颈椎病变的关系及其背后的机制知之甚少。 目的：本研究旨在探讨小关节倾斜对椎间盘和小关节的生物力学影响。 研究设计：有限元分析研究。 方法：使用 28 岁男性志愿者的计算机断层扫描（CT）扫描构建有限元模型。首先，构建了从 C2 到 C7 的对称颈椎模型。使用我们之前发表的研究数据模拟每个节段的小关节方位。其次，模拟 C5-C6 水平的小关节方位以模拟矢状面的小关节倾斜。中度小关节倾斜模型的角度差设定为 7 度，严重小关节倾斜模型的角度差设定为 14 度。C7 椎体的下侧固定。施加 75N 的跟随载荷以模拟头部的重量。在 C2 的齿状突上施加 1.0N·m 的力矩以模拟屈伸、侧屈和轴向旋转。 结果：与对称模型相比，严重小关节倾斜模型在屈伸、侧屈和轴向旋转时，C5-C6 水平的椎间盘内压（IDP）分别增加了 49.02%、57.14%、39.06%和 30.67%。在屈伸、侧屈和轴向旋转时，严重小关节倾斜模型的接触力分别比对称模型增加了 35.64%、31.74%、79.26%和 59.47%。 结论：C5-C6 水平矢状面的小关节倾斜增加了屈伸、侧屈和轴向旋转时的 IDP 和小关节接触力。结果表明，小关节倾斜可能是颈椎间盘退变或小关节退变发展的解剖危险因素。需要进一步的临床研究来验证小关节倾斜对颈椎退行性改变发展的生物力学影响。
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