应力下金属棒形变的弹塑性有限元法预测及其在青少年特发性脊柱侧凸矢状面重建中的应用

Adolescent idiopathic scoliosis is a three-dimensional deformity of the spine with numerous etiologies and large socio-economic burden. Inadequate attention was given to predict the the management of sagittal plane deformity. The current instrumentation and surgical techniques for sagittal plane corrections shares common disadvantages and unsatisfying clinical outcomes. Using an elasto-plastic finite element model, this study aims to simulate the deformation of metal rods under certain stress to predict the pre-contoured angles of metal rods during operations and postoperative sagittal plane restoring. Elasto-plastic finite element model is established on basis of the 3D geometric model of a contoured rod with pre-set postoperative angles, and the displacement vector of the finite element model is modified to evaluate the changes in pull-out strength of screws following the alterations in displacement vector: when the pull-out strength approaches the maximum strength of screws, the angel of the metal rod should be regarded as the pre-contoured angel, while the maximum pull-out strength of screws could be measured via cadaveric biomechanical methods. Our research group has obtained achievements in saggital plane deformities management, cadaveric biomechanical studies and finite element studies in AIS, thereby laid a solid foundation for the novel elasto-plastic finite element study. The successful launch of our study will provide theoretical basis for individualized and quantitative strategy for sagittal plane restoring in AIS patients, hence achieving a better clinical protocol for sagittal plane deformity correction.

青少年特发性脊柱侧凸（AIS）是不明原因引起的脊柱三维畸形，危害较大。AIS矢状面畸形的治疗长期被忽视，现有的用于重建矢状面的器械及技术存在较多的缺陷，治疗效果差。本项目拟应用弹塑性有限元模型，通过模拟应力下金属棒的形变来预测术中金属棒的预弯弧度及术后矢状面重建的效果：预设术后金属棒弧度，根据其三维几何模型构建弹塑性有限元模型，然后对有限元模型进行位移矢量的变化，检测位移矢量变化带来的螺钉拔出力变化，当拔出力接近螺钉所能耐受的最大拔出力时，此时金属棒的弧度就是术中金属棒所需要预弯的弧度。而螺钉的最大拔出力可以通过尸体生物力学测定。课题组前期已在矢状面畸形诊治、尸体生物力学及AIS有限元研究等方面做了大量工作，为弹塑性有限元模型的研究奠定了坚实的基础。本项目的成功开展将为个体化、定量化AIS矢状面重建方案的制定铺平道路，将显著改善矢状面畸形的治疗效果，临床应用前景广泛。

青少年特发性脊柱侧弯（adolescent idiopathic scoliosis, AIS）是脊柱三维平面畸形。随着椎弓根螺钉的应用，AIS能够在冠状面和横轴面很好矫正畸形。但是椎弓根螺钉带来强大的三维矫形力量的同时，也导致脊柱矢状面胸椎后凸以及腰椎前凸生理弧度的丢失。本课题围绕应力下金属棒形变的弹塑性有限元法预测及其在AIS矢状面重建中的应用展开研究。首先，基于长海医院脊柱外科AIS 数据库，初步探讨明确中国人群中AIS胸椎椎弓根形态类型的分布基本特点：上胸椎T1-T3，所有椎弓根均不具有宽大的松质骨通道，绝大部分为皮质骨通道，甚至在CT上表现为通道的缺如。 对于T5-T8节段，绝大部分为小松质骨通道。下胸段T9-T12，绝大部分为粗大松质骨通道。定量探讨了，随着固定节段增加，下端固定椎螺钉拔出增加的规律。明确了当固定节段大于4个节段时，最下端固定椎拔出力会明显增加。建立了国人AIS应力下金属棒形变的弹塑性有限元模型，探讨不同材料预弯棒弧度对AIS矢状面重建的影响。明确了Ponte截骨能够显著降低螺钉拔出应力；钴铬棒比钛合金棒更好的恢复脊柱矢状面序列。进一步临床回顾性研究表明，钴铬棒能够更好恢复胸椎后凸和腰椎前凸。前瞻比较不同预弯弧度钴镉棒对矢状面力线恢复影响，表明当棒预弯弧度小于25度时，患者容易发生术后平背；建议棒的预弯弧度应该在35度左右。因此，本课题从临床观察、生物力学、有限元研究和临床前瞻性研究的角度，为AIS的手术矫形策略提供了参考。