骨水泥通过前移椎体运动轴心影响椎弓根螺钉抗疲劳能力的作用和生物力学机制

Polymethylmethacrylate-augmented pedicle screw (PMMA screw) can significantly improve the biomechanical stability of internal fixation in lumbar spondylolisthesis with osteoporosis, and the method has achieved a good clinical effect. So far, PMMA dosage and application strategy are still in a disordered state, more importantly, its strengthening mechanism needs to be further clarified. Our previous studies found that the amount of PMMA and the anti-fatigue ability of screw showed a dose-effect relationship similar to inverted U-shape. With the increase of PMMA dosage, the typical failure mode of internal fixation gradually changed from cancellous bone failure to pedicle failure.The motion axis of the vertebral body moves towards the tip of the screw. It is inferred that PMMA can change the fatigue failure mode of pedicle screw by moving forward the axis of vertebral motion, thus affecting the anti-fatigue ability of pedicle screw. This project takes the axis of vertebral motion under fatigue load as the research point, and adopts standardized three-dimensional finite element model and cadaveric model to analyse the influence of different PMMA dosage and application mode on the motion mode of vertebral body and the anti-fatigue ability of PMMA screw. The results are expected to elucidate the biomechanical mechanism of PMMA in enhancing the stability of pedicle screw from a new perspective, and provide important theoretical basis for the optimal design and rational clinical application of PMMA screw.

骨水泥强化椎弓根螺钉（PMMA螺钉）可显著提高腰椎滑脱伴骨质疏松内固定的生物力学稳定性，并已获得良好的临床疗效。迄今，PMMA用量与螺钉使用策略仍处于无序状态，其强化机制有待进一步阐明。我们的前期研究发现，PMMA用量与螺钉抗疲劳能力可能呈“先升后降”的量效关系；且随着PMMA用量增加，内固定的典型失效模式由椎体内松质骨失效逐渐改变为椎弓根失效，椎体运动轴心向螺钉尖端转移。据此推测，PMMA通过前移椎体运动轴心改变其疲劳失效模式从而影响椎弓根螺钉抗疲劳能力。本项目以疲劳载荷下椎体运动轴心为切入点，采用标准化三维有限元模型和尸体模型，分析不同PMMA用量、不同螺钉使用方式对滑脱椎体运动模式以及PMMA螺钉抗疲劳能力的影响。研究结果有望从新的视角阐明PMMA增强椎弓根螺钉稳定性的生物力学机制，为PMMA螺钉的优化设计及合理临床应用提供重要的理论依据。

迄今，骨水泥螺钉（CICPS）使用策略仍处于无序状态，骨水泥（PMMA）强化椎弓根螺钉的生物力学机制有待进一步阐明。本项目通过扫描腰椎CT，构建并验证了骨质疏松腰椎滑脱的有限元模型，成功搭建CICPS精细化研究平台。分析完成了0ml-5mlPMMA用量时，螺钉及松质骨最大应力分布情况及瞬时旋转中心的变化规律。进一步构建了单节段腰椎滑脱内固定有限元模型，以不同CICPS强化方式及不同PMMA用量为变量，观察在各种工况下（屈伸、左右侧倾、左右旋转、压缩、前剪切）的椎间活动度和最大应力分布。结果证实了CICPS“反雨刮效应”的失效机制，即PMMA的使用使螺钉尖端应力集中分散，椎体瞬时旋转中心从椎弓根部逐渐前移至骨水泥-螺钉复合体。同时，发现了CICPS可能存在的最佳使用方式及最佳PMMA用量（1.5 ml）。临床数据分析证实，CICPS可有效的用于腰椎滑脱中，临床效果良好；并且证实单侧两颗强化和双侧四颗强化临床效果类似，即采用单侧两颗强化已足够，不必过多应用。本项目首次以PMMA改变椎体运动轴心为切入点，探讨PMMA增强椎弓根螺钉抗疲劳能力的规律和生物力学机制，为椎弓根螺钉内固定系统的稳定性研究开创了新的研究视角；通过明确PMMA强化椎弓根螺钉的内在机制，确定最佳PMMA用量，制定最佳临床应用策略，为PMMA螺钉的合理临床应用提供重要的理论依据，达到既能满足康复早期稳定性需求，又能减少PMMA螺钉使用数量的目的，从而避免过度使用所带来的相关问题。