颅底凹陷有限元模型的建立及合并寰枢椎脱位发生机制的研究

Basilar invagination (BI) is one of the commonly seen pathological malformation in craniocervical region. The clinical symptoms and signs of BI are usually associated with atlanto-axial dislocation(AAD), which could lead to dizastrous result if the pathological course could not be interupted with appropriate treatment. The mechanism of AAD in BI patients is not clear, and totally different from that of trauma and inflammatory arthropathies, which could lead to central atlanto-axial joint dislocation with the ligments laceration and subsequent joint capsule laxation aroud the odontoid process. Clinical evidence has suggested that congenital anormalies of the lateral atlanto-axial facet joints and their abnormal dimentional position might have close relationship with AAD; but there has been no relative research to prove it until now. Because of the impossiblity to get BI-AAD cadaver specimen and absence of animal model for high-standard biomechanical research, the aforementioned postulation of the machanism of AAD could not be studied by conventional technique. .With the advancement of computer simulation and neuroimage technique , three dimentional computered simulation biomechanics has offered us a new method to resolve this problem. The kinematics ,kinetics and internal strains and stress of the atlanto-axial joint are all possible subjects for study. In our research, a finite element model of the pathological BI-AAD is going to be developed on the basis of high resolution computered-tomographic image of the craniocervical region. The intra-joint cavity pressure change and joint capsule shear force change of atlanto-axial joint in patient with BI-AAD, escepially the stress change of the central atlanto-axial joint caused by lateral facet joints dimentional abnormality could be cauculated in this model, which could be used to analyze the devoloping mechnism of BI-AAD and to afford further assistance for theraputic theory of clinical treatment.

颅底凹陷（BI）为常见的颅颈交界区畸形之一，多由于寰枢椎脱位（AAD）后出现症状，如不经治疗临床后果严重。与外伤、炎性病变等直接引起寰枢中央关节脱位等不同，这类病人发生AAD的机制目前还不清楚。临床研究发现，寰枢侧方关节的位置关系可能与寰枢中央关节脱位的发生有关。但到目前为止还没有相关的研究予以证实。由于不可能获得BI-AAD的尸体标本或动物模型供生物力学研究，三维计算机模拟生物力学的发展为我们的进一步研究提供了一种新的方法。本研究基于颅颈交界区CT图像构建BI-AAD的三维非线性有限元模型，运用有限元计算方法模拟BI病人寰枢椎关节内的压力变化以及关节囊韧带的应力变化，计算由于寰枢侧方关节的先天性形态改变引起的寰枢中央关节受力变化，分析BI病人AAD的发生机制，为临床治疗提供理论依据。

颅底凹陷（BI）为常见的颅颈交界区畸形之一，多由于寰枢椎脱位（AAD）后出现症状，,与外伤、炎症病变等直接引起寰枢中央关节脱位等不同，这类病人发生AAD的机制目前还不清楚。临床研究发现，寰枢侧方关节的位置关系可能与寰枢中央关节脱位的发生有关。本研究基于颅颈交界区CT图像构建BI-AAD的三维非线性有限元模型，运用有限元计算方法模拟BI病人寰枢椎关节内的压力变化及关节囊压力变化，计算由于寰枢侧方关节先天性形态改变引起的寰枢中央关节受力变化，分析BI病人AAD的发生机制。.尸体标本实验发现，正常组和外伤性寰枢椎脱位组进行对比，在前屈、左右侧弯及左旋载荷下，外伤性寰枢椎脱位组寰枢椎左右侧方关节的最大压力比正常组的减小。后伸和右旋载荷下，外伤性寰枢椎脱位组寰枢椎右侧方关节的最大压力也比正常组的减小。但后伸载荷下，外伤性寰枢椎脱位组寰枢椎左侧方关节的最大压力不变，右旋载荷下，外伤性寰枢椎脱位组寰枢椎左侧方关节的最大压力稍有增加。由此可以推断，寰枢关节上、下关节面间有向前滑动的趋势导致寰枢椎侧方关节的承重减小。此时，向腹侧前方移动会被支持寰枢椎的韧带包括横韧带、翼状韧带及寰枢外侧关节囊韧带所限制。尽管这些韧带的力量相当强大，但随着时间的推移，它们会逐渐地疲乏损坏、变性、部分甚至完全破坏，最终就会导致AAD的发生。.对正常及BI-AAD(寰枕融合合并C2-C3融合)三维非线性有限元模型计算分析，结果发现，在前屈后伸、左右侧弯、左右旋转6种生理载荷下，BI-AAD有限元模型与正常有限元模型相对比，寰枢侧方关节应力应变明显增加。横韧带应力应变，在前屈后伸与左右旋转4种载荷下明显减小，而在左右侧弯2种载荷下有所增加。关节囊韧带应力应变除后伸外，其他5种载荷下明显增加。寰枢关节运动范围在6种生理载荷下都明显增大。建立正常与BI-AAD有限元模型，计算比较寰枢侧方关节与横韧带、关节囊韧带应力应变和寰齿间距，从而分析BI-AAD的力学机理，为临床诊断与治疗提供理论依据。