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A finite element investigation of upper cervical instrumentation.

机译：上颈椎器械的有限元研究。

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STUDY DESIGN: The finite element technique was used to predict changes in biomechanics that accompany the application of a novel instrumentation system designed for use in the upper cervical spine. OBJECTIVE: To determine alterations in joint loading, kinematics, and instrumentation stresses in the craniovertebral junction after application of a novel instrumentation system. Specifically, this design was used to assess the changes in these parameters brought about by two different cervical anchor types: C2 pedicle versus C2-C1 transarticular screws, and unilateral versus bilateral instrumentation. SUMMARY OF BACKGROUND DATA: Arthrodesis procedures can be difficult to obtain in the highly mobile craniovertebral junction. Solid fusion is most likely achieved when motion is eliminated. Biomechanical studies have shown that C1-C2 transarticular screws provide good stability in craniovertebral constructs; however, implantation of these screws is accompanied by risk of vertebral artery injury. A novel instrumentation system that can be used with transarticular screws or with C2 pedicle screws has been developed. This design also allows for unilateral or bilateral implantation. However, the authors are unaware of any reports to date on the changes in joint loading or instrumentation stresses that are associated with the choice of C2 anchor or unilateral/bilateral use. METHODS: A ligamentous, nonlinear, sliding contact, three-dimensional finite element model of the C0-C1-C2 complex and a novel instrumentation system was developed. Validation of the model has been previously reported. Finite element models representing combinations of cervical anchor type (C1-C2 transarticular screws vs. C2 pedicle screws) and unilateral versus bilateral instrumentation were evaluated. All models were subjected to compression with pure moments in either flexion, extension, or lateral bending. Kinematic reductions with respect to the intact (uninjured and without instrumentation) case caused by instrumentation use were reported. Changes in loading profiles through the right and left C0-C1 and C1-C2 facets, transverse ligament-dens, and dens-anterior ring of C1 articulations were calculated by the finite element model. Maximum von Mises stresses within the instrumentation were predicted for each model variant and loading scenario. RESULTS: Bilateral instrumentation provided greater motion reductions than the unilateral instrumentation. When used bilaterally, C2 pedicle screws approximate the kinematic reductions and instrumentation stresses (except in lateral bending) that are seen with C1-C2 transarticular screws. The finite element model predicted that the maximum stress was always in the region in which the plate transformed into the rod. CONCLUSIONS: To the best of the authors' knowledge, this is the first report of predicting changes in loading in the upper cervical spine caused by instrumentation. The most significant conclusion that can be drawn from the finite element model predictions is that C2 pedicle screw fixation provides the same relative stability and instrumentation stresses as C1-C2 transarticular screw use. C2 pedicle screws can be a good alternative to C2-C1 transarticular screws when bilateral instrumentation is applied.
机译：研究设计：有限元技术被用来预测生物力学的变化，伴随着新型仪器系统的应用，该仪器被设计用于上颈椎。目的：确定应用新型仪器系统后颅骨交界处关节负荷，运动学和仪器应力的变化。具体而言，该设计用于评估由两种不同的颈锚类型引起的这些参数的变化：C2椎弓根对比C2-C1经关节螺钉，以及单侧器械与双侧器械。背景数据摘要：在高度活动的颅椎交界处，很难获得关节固定术。消除运动后，很可能实现实体融合。生物力学研究表明，C1-C2跨关节螺钉在颅骨椎体结构中具有良好的稳定性。但是，植入这些螺钉会伴有椎动脉损伤的风险。已经开发出可以与经关节螺钉或与C2椎弓根螺钉一起使用的新型器械系统。该设计还允许单侧或双侧植入。但是，作者至今尚未发现任何与选择C2锚钉或单边/双边使用相关的关节负荷或器械应力变化的报告。方法：建立了C0-C1-C2复合物的韧带，非线性，滑动接触，三维有限元模型和新型的仪器系统。该模型的验证先前已有报道。评估了代表颈椎锚类型（C1-C2经关节螺钉与C2椎弓根螺钉）以及单侧器械与双侧器械组合的有限元模型。所有模型均在弯曲，伸展或侧向弯曲时承受纯力矩。据报告，由于使用仪器引起的完整（未受伤且无仪器）病例的运动学减少。通过有限元模型计算出C1关节的左右C0-C1和C1-C2小面，横向韧带-窝和窝-前环的载荷分布变化。针对每种模型变体和负载情况，预测了仪器内部的最大冯·米塞斯应力。结果：与单侧仪器相比，双侧仪器提供了更大的运动减少。当双向使用时，C2椎弓根螺钉近似于运动减少和器械应力（横向弯曲除外），这在C1-C2跨关节螺钉中可见。有限元模型预测最大应力始终在板转变为杆的区域内。结论：据作者所知，这是第一篇有关预测由仪器引起的上颈椎负荷变化的报告。可以从有限元模型预测中得出的最重要结论是，C2椎弓根螺钉固定提供与C1-C2经关节螺钉使用相同的相对稳定性和器械应力。当使用双边器械时，C2椎弓根螺钉可以很好地替代C2-C1经关节螺钉。

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