The biomechanical impact of the facet tropism on the intervertebral disc and facet joints in the cervical spine

Publication date: Available online 13 July 2017
Source:The Spine Journal
Author(s): Xin Rong, Beiyu Wang, Chen Ding, Yuxiao Deng, Hua Chen, Yang Meng, Weijie Yan, Hao Liu
Background ContextThe facet tropism is defined as the angular difference between the left and right facet orientation. The 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 the facet tropism and pathological changes in the cervical spine and the mechanism behind.PurposeThis study was conducted to investigate the biomechanical impact of the facet tropism on the intervertebral disc and facet joints.Study DesignA finite element analysis study.MethodsThe CT scans of a 28 year-old male volunteer was used to construct the finite element model. Firstly, a symmetrical cervical model from C2 to C7 was constructed. The facet orientations at each level was simulated using the data from our previously published study. Secondly, the facet orientations at the C5-C6 level was altered to simulate the 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.ResultsThe 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 to 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.ConclusionsThe 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 the facet tropism might be the anatomical risk factor for 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.



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