Mimics建模到Marc有限元分析的系统工程和实例
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摘要
研究背景：
1.生物力学的研究以前多数是观察临床病例、进行人体标本或者动物标本实验,随着计算机技术的发展,有限元分析方法逐渐广泛应用于生物力学特别是骨科生物力学的研究中。在目前多学科交叉的背景下,工学和医学相结合共同研究医学领域的问题成为常态。有限元分析方法最早应用于工程方面的分析,它在医学领域的应用是工学和医学紧密结合的实例。有限元法研究医学课题有巨大的优势,可以通过分析人体三维模型来了解人体内部结构任一处的应力应变,可以通过对人体三维模型模仿临床手术方便地改变模型的局部结构后再分析,便于手术前后的比对,并且在当前人体尸体标本越来越难以获取的情况下,有限元的模型无限次分析方式更见效果。
有限元分析在生物力学的应用涉及到数学、力学、医学、英语和计算机等多方面知识,如果是个人通过计算机编程使用有限元方法来分析生物力学课题,数学和计算机编程的知识和技巧是绝大多数的研究者难以逾越的障碍,所幸,当前有限元分析的商业软件已比较成熟而且逐步得到推广,应用这些成熟的商业性质的有限元分析软件分析生物力学课题,为医学专业的研究者打开了有限元分析生物力学课题的大门。
在我国具有较大应用人群数量的商业有限元分析软件有Ansys、Abaqus、Adina和MSC.Marc等,MSC.Marc有限元软件是由美国MSC. Software Corporation(简称MSC.Software)公司发行的非线性结构分析的有限元软件,该软件的接触分析和非线性分析能力尤其强大,并且计算的收敛速度快。本研究的依托单位花巨资购买了该软件,但是MSC.Marc作为大型的非线性有限元分析软件,界面复杂,参数众多,需要数学、力学、医学、英语和计算机等多种知识有一定基础的研究人员才能够较好的运用进行医学生物力学的有限元分析,因为该软件使用难度大,市面参考书少,对软件的使用者素质要求高,所以到目前为止还没有充分利用造成浪费。另外,本研究的依托单位还购买了Mimics医学图像处理软件用于三维模型重建。这两个软件中,Mimics软件除了其强大的三维建模功能外,还具有一定的简单的模型修洁功能,但却远远不够；MSC.Marc软件自带了MSC.Mentat有限元前后处理器可进行实体网格划分,但是对复杂模型的实体网格划分其功能限制性太大,并且划分的成功率也难以保证。这两个软件只能算做了有限元分析一头一尾的工作,其间还缺少修洁调整三维模型和网格自动划分的强大衔接工具。在目前情况下,不管是从学术研究的角度出发,还是从资源充分利用的角度考虑,建立一条从Mimics到MSC.Marc的系统而完整的有限元分析路线必要而且迫切。这条路线需要做到以下工作：建立三角片面网格的三维模型,修洁三维模型,创建CAD模型,对CAD模型划分实体网格,设置单元的几何属性和材料特性以及边界条件和载荷条件并提交进行有限元分析,处理有限元分析的结果。
2.随着脊柱固定器械以及融合术式的不断改进,脊柱融合的成功率已经达到较高的水平,脊柱融合固定术成为目前治疗众多脊柱疾病的行之有效的方法。从长期随访资料来看,此项技术安全、有效,已称为治疗脊柱退变性疾病、脊柱不稳、脊柱畸形等脊柱疾病的金标准。但是,术后长期随访发现了邻近节段的退化问题。
因为脊柱融合内固定术后有可能导致邻近节段退变的加剧,一些学者和医生已经开始考虑脊柱非融合手术代替脊柱融合手术进行治疗。人工椎间盘置换术是脊柱非融合手术中的一种。随着世界科技的进步,多种材料多种几何结构的人工椎间盘纷纷出现,极大地提高了人工椎间盘的适用性,但是在其应用过程中也发现了很多新问题。一些专家认为,在某些病症脊柱非融合手术短期确实可以达到一定的疗效,但随之而来又有许多新问题需要更深入的研究,目前,尚无长期随访证据表明非融合技术优于已广泛采用的融合技术,因此,还需要长期的、前瞻性随机研究来判断非融合技术的利与弊。
究竟要不要融合?颈椎前路入路手术行椎间盘切除后融合固定与颈椎前路入路椎间盘切除后置换进人工椎间盘两种手术方法分别是脊柱融合与非融合的典型术式,具有很好的对比性。本研究拟在同一标本上建立颈椎融合固定术与人工椎间盘术两种术后三维有限元模型,对这两类模型进行前屈、后伸、侧弯、旋转,比较两者的手术节段的上下邻近节段的生物力学特性,尝试揭示两种手术的优缺点,从而为临床颈椎适应症的手术的选择提供理论基础。
目的：
1.充分利用本研究的依托单位的现有资源,建立一个完整的从Mimics建模到MSC.Marc有限元分析的系统工程,该系统工程的路径为：建立三角片面网格的三维模型,修洁三维模型,创建CAD模型,对CAD模型划分实体网格,设置单元的几何属性和材料特性以及边界条件和载荷条件并提交进行有限元分析,处理有限元分析的结果。
2.使用"Mimics建模到MSC.Marc有限元分析的系统工程”所阐述的方法和路径,建立颈椎融合固定术与人工椎间盘置换术两种治疗颈椎病的手术的三维模型,对其手术节段的邻近节段的生物力学特性进行有限元分析,尝试揭示两种术式的优缺点,为临床颈椎适应症的手术的选择提供理论基础。
材料和方法：
1.采用Mimics医学图像处理软件以颈椎CT图像为依据重建C3、C4、C5、C6(即第三颈椎、第四颈椎、第五颈椎、第六颈椎)四个颈椎初步的三角片面网格的三维模型,再利用其"Remesh"重新划分修饰网格功能初步修洁这些颈椎三维模型。
2.利用Geomagic Studio逆向工程软件,进一步修洁C3、C4、C5、C6四个颈椎的三维模型。
3.利用Geomagic Studio逆向工程软件,依据前面步骤建立和修洁的C3、C4、C5、C6四个颈椎的三维模型,建立C3与C4之间、C4与C5之间、C5与C6之间的椎间盘、髓核和纤维环。
4.应用Geomagic Studio逆向工程软件先将封闭的三角形面网格模型构建成CAD模型,成为一个几何实体,然后再利用MSC. Patran有限元前后处理软件对这个几何实体进行四面体体网格划分。
5.在MSC. Marc有限元分析软件中对所有的已划分四面体体网格的颈椎三维模型设置单元几何特性、材料参数。
6. Geomagic Studio逆向工程软件、MSC.Patran有限元前后处理软件和MSC.Marc有限元分析软件相配合,建立融合固定术后的颈椎三维体网格模型和人工椎间盘置换术后的颈椎三维体网格模型。
7.应用MSC.Marc有限元分析软件,分别对正常的颈椎三维体网格模型、融合固定术后的颈椎三维体网格模型和人工椎间盘置换术后的颈椎三维体网格模型设置相同的边界条件和载荷条件,分析三者在前屈、后伸、侧弯和旋转15度过程中手术节段的上下邻近节段的生物力学特性。
8.在MSC. Marc有限元分析软件中对有限元分析结果进行后处理。合理应用"History Plot"数据表图并配合剪贴板、文本文件编辑软件、"Microsoft Excel"电子表格获得平均值。
结果：
1.建立了C3、C4、C5、C6四个颈椎和它们间的椎间盘、纤维环、髓核以及人工椎间盘的三角片面网格模型、CAD模型和四面体实体网格模型。这些模型各个部位结构清晰光润,与其相邻结构吻合良好,网格连续而且连接牢固,大小形状符合实际情况,网格经过多次优化处理质量优异,完全可以很好地应用于有限元分析。
2.确定了四种商业软件Mimics、Geomagic Studio、MSC. Patran和MSC.Marc配合使用从而实现了从建模到有限元分析的完整过程。
3.正常的颈椎三维体网格模型、融合固定术后的颈椎三维体网格模型和人工椎间盘置换术后的颈椎三维体网格模型在前屈、后伸、侧弯和旋转15度过程中,手术节段的上下邻近节段内髓核最大应力随着角度的增大而增大。前屈后伸时,人工椎间盘模型手术节段C4—C5的上位邻近节段C3—C4之间和下位邻近节段C5—C6之间的髓核内最大应力较融合模型小；侧弯时,人工椎间盘模型手术节段C4—C5的上位邻近节段C3—C4之间的髓核内最大应力较融合固定模型明显减小,但是在下位邻近节段C5—C6之间的髓核内最大应力较融合固定模型要大；旋转时,人工椎间盘模型手术节段C4—C5的上位邻近节段C3—C4之间的髓核内最大应力较融合固定模型稍小,同样在下位邻近节段C5—C6之间的髓核内最大应力又较融合固定模型要大。
结论：
1.本研究通过不断尝试,配合使用四种商业软件Mimics、Geomagic Studio、MSC.Patran和MSC.Marc,以颈椎C3—C6(即第三颈椎到第六颈椎)三个节段为例实现了一个完整的Mimics建模到MSC.Marc有限元分析的系统工程。该系统工程的路径为：使用Mimics医学图像处理软件依据颈椎CT断层图像对C3、C4、C5、C6四个颈椎重建三角片面网格三维模型并在一定程度上对其修洁；使用Geomagic Studio逆向工程软件依据C3、C4、C5、C6四个颈椎三角片面网格三维模型建立其间的椎间盘,并进一步对所有模型进行修洁,随后构建它们的CAD模型；使用MSC.Patran有限元前后处理软件在保证相邻模型的单元的连续性和连接牢固性基础上对所有三角片面网格三维模型划分四面体实体网格；使用MSC.Marc有限元分析软件针对模型的不同状态分别分析其生物力学特性。
2.综合前屈、后伸、侧弯和旋转的有限元分析数据,仅侧弯和旋转时,在手术节段的下位邻近节段处髓核的最大应力人工椎间盘置换术较融合固定术应力高。应力在邻近节段的集中可能导致融合固定术后邻近节段的退变,人工椎间盘置换术也可能同样无法避免,并且在手术节段的下位邻近节段相对于上位邻近节段更有可能发生退变。
主要创新点：
1.配合使用四种商业软件Mimics、Geomagic Studio、MSC. Patran和MSC. Marc,实现了一个完整的Mimics建模到MSC.Marc有限元分析的系统工程。
2.提出了在Mimics医学图像处理软件中一种新颖的先进的建模方法,先着色整体建模区域,再使用编辑工具中的一个象素大小的圆形选择工具分开相邻椎体的界限,令得各个重建后的三维模型边界清晰并且距离微小,便于后续的实体网格划分和有限元分析。
3.确定了Mimics软件Remesh网格重划分时"Smoothing"参数的值为0.1,这个值既可令模型光顺,同时也控制了误差。
4.创建了一种准确、快捷建立椎间盘的方法。在Geomagic Studio软件中,依据相邻椎体的底和顶,配合“填充孔”工具,建立的椎间盘边界圆滑清楚,与上下椎骨紧密相贴,共用节点,有利于实体网格划分时相邻体的网格连续性和牢固性,便于后续的有限元分析。
5.提出了使用刚性面带动椎骨精准运动来进行有限元分析的方法。
6.提供了人工椎间盘置换术其手术节段的下位邻近节段相对于上位邻近节段也更有可能发生退变的有限元分析证据。
Background:
1. Biomechanical study methods were usually to observe clinical cases, test human cadaver or animal experiment ago. Along with the development of computer FEA (Finite Element Analysis) gradually widely apply in biomechanical study, especially orthopedics biomechanical study. FEA is firstly applied in engineering research, but in recent years FEA begin to be applied in medical research. The methos have enormous advantages. It can analyse stress and strain of human inner structure, simulate surgery operation, and analyse times without number. The marerials of human cadaver experiments are difficultly acquired and only used up once, however, FEA is especially predominant.
Application of FEA in biomechanical study relates to mathematics, mechanics, medicine, English and computeracy. If FEM (Finite Element Method) is based on researchers personally programme, the most researchers would come up against impassable obstacles about mathematics and computer programme. It is a lucky that business software of FEA had popularized and they have opend doorstep which researchers investigate biomechanics by right of FEA.
Business software of FEA of which a large number of people make use have Ansys, Abaqus, Adina and MSC.Marc et al. MSC.Marc software is issued by MSC. Software Corporation of America. The software is very powerful in contact and nonlinear analysis,and can rapidly converge. The support organization of the research used large amount of money to purchase MSC.Marc software several years ago. MSC.Marc software is a large-scale non-linear FEA software which also relates to mathematics, mechanics, medicine, English and computeracy, so its manipulators are hard well up in it. Otherwise, there are few reference books in market, so the software has not adequately used in the support organization of the research and it is wasteful. The support organization of the research has also purchased Mimics software which is provided with powerful three-dimensional reconstruction and simple trimming model. But the function of simple trimming model of Mimics software is insufficient. MSC.Marc software is provided with MSC.Mentat which is a fore-and-aft processing unit of FEA and can plot out entity gridding. But the function of ploting out entity gridding of MSC.Mentat is too weak in the face of complex entity and successful rate is not enough. Mimics software can complete first step of FEA, and MSC.Marc can complete last step of FEA, but they miss middle process such as trimming model and ploting out entity gridding. Not only take into account science research, but also take into account to make the best of resource, it is necessary and impending to set up a systemic and intact path of FEA from 3D reconstruction in Mimics to FEA in Marc. Along with the path, there are many works to complete, such as three-dimensional reconstruction of triangle surface grids partitioning, trimming 3D model, establishing CAD model, geometry meshing on CAD model, setting geometric properties and material properties of elements, setting boundary conditions and load, submitting to FEA, dealing with the results of FEA.
2. With the development of fixation instrument and fusion procedures of spine, successful rate of the spine fusion with bone graft and internal fixation has been very high, and the spine fusions with bone graft and internal fixation become the most effective way that cure spinal degeneration, instability and malformation. However, the degeneration of the adjacent segments comes forth after long term follow up.
Some scholars and doctors begin to non-fusion spinal operations in place of fusion operation. The artificial disc replacement is one of non-fusion spinal operations. Mamy experts think that non-fusion spinal operations are sure-enough in effect in treat some symptoms, however, there are more problems to solve, and there are not evidences to make sure non-fusion better than fusion at the present time, so more long term researchs could judge advantages and disadvantages of non-fusion.
Fusion or non-fusion? Anterior cervical discectomy and fusion with bone graft belongs to spinal fusion. Artificial cervical disc replacement belongs to spinal non-fusion. The two operations are two good comparison objects. If we can find advantages and disadvantages depend on FEA of two operation models, then provide theory for selecting operations of clinic cervical vertebrae indication.
Objectives:
1. On the basis of making the best of existing resources, to set up a systemic and intact path of FEA from 3D reconstruction in Mimics to FEA in Marc. Along with the path, there are many works to complete, such as three-dimensional reconstruction of triangle surface grids partitioning, trimming 3D model, establishing CAD model, geometry meshing on CAD model, setting geometric and material properties of elements, setting boundary and load conditions, submitting to FEA, dealing with the results of FEA.
2. According to "Systems Engineering from 3D Reconstruction in Mimics to FEA in Marc", to construct 3D model of cervical discectomy and fusion with bone graft and artificial cervical disc replacement which are all operations to cure cervical diseases, to find advantages and disadvantages depend on FEA of two operation models, then provide theory for selecting operations of clinic cervical vertebrae indication.
Materials and Method:
1. Adopt Mimics software to reconstruct three-dimensional triangle surface grids partitioning model of C3, C4, C5 and C6, and make use of "Remesh" to trimming 3D model.
2. Adopt Geomagic Studio software to better trimming 3D model of C3, C4, C5 and C6.
3. Adopt Geomagic Studio software to constructe 3D model of intervertebral discs, nucleus pulposus and anulus fibrosus between C3 and C4, between C4 and C5, between C5 and C6.
4. Firstly adopt Geomagic Studio software to constructe CAD model from 3D model of close triangle surface grids, and then adopt MSC.Patran software which is a fore-and-aft processing software of FEA to mesh tetrahedron on CAD model.
5. Set geometric and material properties of all elements, and set boundary and load conditions of entire cervical vertebrae segments model in MSC.Marc software.
6. Combine Geomagic Studio, MSC.Patran and MSC.Marc software to constructe 3D tetrahedron model of cervical discectomy and fusion with bone graft and artificial cervical disc replacement.
7. Adopt MSC.Marc software to respectively set boundary and load conditions on 3D model of normal, discectomy and fusion with bone graft and artificial cervical disc replacement, and analysis biomechanical characteristics of adjacent segments of three models in the course of anterior flexion 15 degree, extension 15 degree, lateral bending 15 degree and axial rotation 15 degree.
8. Adopt MSC.Marc software to post processing the results of FEA.
Results:
1. The research has constructed many 3D models, including triangle surface grids partitioning models, CAD models and tetrahedron models of C3, C4, C5, C6, and intervertebral discs, nucleus pulposus and anulus fibrosus between C3 and C4, between C4 and C5, between C5 and C6. All 3D models structure is clear and smooth, and meshes are continuous between adjacent models, and enough good to FEA.
2. The research comes true from 3D reconstruction to FEA on the basis of combining Mimics, Geomagic Studio, MSC.Patran and MSC.Marc software.
3. The maximal stresses of adjacent segment nucleus pulposus of three-dimensional models of normal, discectomy and fusion with bone graft and artificial cervical disc replacement ascend with the rise of degree during anterior flexion 15 degree, extension 15 degree, lateral bending 15 degree and axial rotation 15 degree. The maximal stress of superior and inferior adjacent segment nucleus pulposus of 3D model of artificial cervical disc replacement is less than discectomy and fusion with bone graft's during anterior flexion and extension 15 degree. The maximal stress of superior adjacent segment nucleus pulposus of 3D model of artificial cervical disc replacement is enormous less than discectomy and fusion with bone graft's during lateral bending and axial rotation 15 degree. However, the maximal stress of inferior adjacent segment nucleus pulposus of 3D model of artificial cervical disc replacement is bigger than discectomy and fusion with bone graft's during lateral bending and axial rotation 15 degree.
Conclusions:
1. The research implements a systems engineering from 3D reconstruction in Mimics to FEA in MSC.Marc on the basis of combining Mimics, Geomagic Studio, MSC.Patran and MSC.Marc software. The path completes three-dimensional reconstruction of triangle surface grids partitioning by Mimics software, trimming 3D model by Geomagic Studio software, establishing CAD model by Geomagic Studio software, geometry meshing on CAD model by MSC.Patran software, setting geometric properties and material properties of elements, setting boundary conditions and load, submitting to FEA, dealing with the results of FEA by MSC.Marc software.
2. Summing-up the results of FEA, the maximal stress of inferior adjacent segment nucleus pulposus of 3D model of artificial cervical disc replacement is bigger than discectomy and fusion with bone graft's during lateral bending and axial rotation 15 degree. Stress concentration of adjacent segment maybe result in adjacent segment degeneration after discectomy and fusion with bone graft, and artificial cervical disc replacement is maybe avoidless similarly, and degeneration probability of inferior adjacent segment is bigger than superior adjacent segment.
1.生物力学的研究以前多数是观察临床病例、进行人体标本或者动物标本实验,随着计算机技术的发展,有限元分析方法逐渐广泛应用于生物力学特别是骨科生物力学的研究中。在目前多学科交叉的背景下,工学和医学相结合共同研究医学领域的问题成为常态。有限元分析方法最早应用于工程方面的分析,它在医学领域的应用是工学和医学紧密结合的实例。有限元法研究医学课题有巨大的优势,可以通过分析人体三维模型来了解人体内部结构任一处的应力应变,可以通过对人体三维模型模仿临床手术方便地改变模型的局部结构后再分析,便于手术前后的比对,并且在当前人体尸体标本越来越难以获取的情况下,有限元的模型无限次分析方式更见效果。
有限元分析在生物力学的应用涉及到数学、力学、医学、英语和计算机等多方面知识,如果是个人通过计算机编程使用有限元方法来分析生物力学课题,数学和计算机编程的知识和技巧是绝大多数的研究者难以逾越的障碍,所幸,当前有限元分析的商业软件已比较成熟而且逐步得到推广,应用这些成熟的商业性质的有限元分析软件分析生物力学课题,为医学专业的研究者打开了有限元分析生物力学课题的大门。
在我国具有较大应用人群数量的商业有限元分析软件有Ansys、Abaqus、Adina和MSC.Marc等,MSC.Marc有限元软件是由美国MSC. Software Corporation(简称MSC.Software)公司发行的非线性结构分析的有限元软件,该软件的接触分析和非线性分析能力尤其强大,并且计算的收敛速度快。本研究的依托单位花巨资购买了该软件,但是MSC.Marc作为大型的非线性有限元分析软件,界面复杂,参数众多,需要数学、力学、医学、英语和计算机等多种知识有一定基础的研究人员才能够较好的运用进行医学生物力学的有限元分析,因为该软件使用难度大,市面参考书少,对软件的使用者素质要求高,所以到目前为止还没有充分利用造成浪费。另外,本研究的依托单位还购买了Mimics医学图像处理软件用于三维模型重建。这两个软件中,Mimics软件除了其强大的三维建模功能外,还具有一定的简单的模型修洁功能,但却远远不够；MSC.Marc软件自带了MSC.Mentat有限元前后处理器可进行实体网格划分,但是对复杂模型的实体网格划分其功能限制性太大,并且划分的成功率也难以保证。这两个软件只能算做了有限元分析一头一尾的工作,其间还缺少修洁调整三维模型和网格自动划分的强大衔接工具。在目前情况下,不管是从学术研究的角度出发,还是从资源充分利用的角度考虑,建立一条从Mimics到MSC.Marc的系统而完整的有限元分析路线必要而且迫切。这条路线需要做到以下工作：建立三角片面网格的三维模型,修洁三维模型,创建CAD模型,对CAD模型划分实体网格,设置单元的几何属性和材料特性以及边界条件和载荷条件并提交进行有限元分析,处理有限元分析的结果。
2.随着脊柱固定器械以及融合术式的不断改进,脊柱融合的成功率已经达到较高的水平,脊柱融合固定术成为目前治疗众多脊柱疾病的行之有效的方法。从长期随访资料来看,此项技术安全、有效,已称为治疗脊柱退变性疾病、脊柱不稳、脊柱畸形等脊柱疾病的金标准。但是,术后长期随访发现了邻近节段的退化问题。
因为脊柱融合内固定术后有可能导致邻近节段退变的加剧,一些学者和医生已经开始考虑脊柱非融合手术代替脊柱融合手术进行治疗。人工椎间盘置换术是脊柱非融合手术中的一种。随着世界科技的进步,多种材料多种几何结构的人工椎间盘纷纷出现,极大地提高了人工椎间盘的适用性,但是在其应用过程中也发现了很多新问题。一些专家认为,在某些病症脊柱非融合手术短期确实可以达到一定的疗效,但随之而来又有许多新问题需要更深入的研究,目前,尚无长期随访证据表明非融合技术优于已广泛采用的融合技术,因此,还需要长期的、前瞻性随机研究来判断非融合技术的利与弊。
究竟要不要融合?颈椎前路入路手术行椎间盘切除后融合固定与颈椎前路入路椎间盘切除后置换进人工椎间盘两种手术方法分别是脊柱融合与非融合的典型术式,具有很好的对比性。本研究拟在同一标本上建立颈椎融合固定术与人工椎间盘术两种术后三维有限元模型,对这两类模型进行前屈、后伸、侧弯、旋转,比较两者的手术节段的上下邻近节段的生物力学特性,尝试揭示两种手术的优缺点,从而为临床颈椎适应症的手术的选择提供理论基础。
目的：
1.充分利用本研究的依托单位的现有资源,建立一个完整的从Mimics建模到MSC.Marc有限元分析的系统工程,该系统工程的路径为：建立三角片面网格的三维模型,修洁三维模型,创建CAD模型,对CAD模型划分实体网格,设置单元的几何属性和材料特性以及边界条件和载荷条件并提交进行有限元分析,处理有限元分析的结果。
2.使用"Mimics建模到MSC.Marc有限元分析的系统工程”所阐述的方法和路径,建立颈椎融合固定术与人工椎间盘置换术两种治疗颈椎病的手术的三维模型,对其手术节段的邻近节段的生物力学特性进行有限元分析,尝试揭示两种术式的优缺点,为临床颈椎适应症的手术的选择提供理论基础。
材料和方法：
1.采用Mimics医学图像处理软件以颈椎CT图像为依据重建C3、C4、C5、C6(即第三颈椎、第四颈椎、第五颈椎、第六颈椎)四个颈椎初步的三角片面网格的三维模型,再利用其"Remesh"重新划分修饰网格功能初步修洁这些颈椎三维模型。
2.利用Geomagic Studio逆向工程软件,进一步修洁C3、C4、C5、C6四个颈椎的三维模型。
3.利用Geomagic Studio逆向工程软件,依据前面步骤建立和修洁的C3、C4、C5、C6四个颈椎的三维模型,建立C3与C4之间、C4与C5之间、C5与C6之间的椎间盘、髓核和纤维环。
4.应用Geomagic Studio逆向工程软件先将封闭的三角形面网格模型构建成CAD模型,成为一个几何实体,然后再利用MSC. Patran有限元前后处理软件对这个几何实体进行四面体体网格划分。
5.在MSC. Marc有限元分析软件中对所有的已划分四面体体网格的颈椎三维模型设置单元几何特性、材料参数。
6. Geomagic Studio逆向工程软件、MSC.Patran有限元前后处理软件和MSC.Marc有限元分析软件相配合,建立融合固定术后的颈椎三维体网格模型和人工椎间盘置换术后的颈椎三维体网格模型。
7.应用MSC.Marc有限元分析软件,分别对正常的颈椎三维体网格模型、融合固定术后的颈椎三维体网格模型和人工椎间盘置换术后的颈椎三维体网格模型设置相同的边界条件和载荷条件,分析三者在前屈、后伸、侧弯和旋转15度过程中手术节段的上下邻近节段的生物力学特性。
8.在MSC. Marc有限元分析软件中对有限元分析结果进行后处理。合理应用"History Plot"数据表图并配合剪贴板、文本文件编辑软件、"Microsoft Excel"电子表格获得平均值。
结果：
1.建立了C3、C4、C5、C6四个颈椎和它们间的椎间盘、纤维环、髓核以及人工椎间盘的三角片面网格模型、CAD模型和四面体实体网格模型。这些模型各个部位结构清晰光润,与其相邻结构吻合良好,网格连续而且连接牢固,大小形状符合实际情况,网格经过多次优化处理质量优异,完全可以很好地应用于有限元分析。
2.确定了四种商业软件Mimics、Geomagic Studio、MSC. Patran和MSC.Marc配合使用从而实现了从建模到有限元分析的完整过程。
3.正常的颈椎三维体网格模型、融合固定术后的颈椎三维体网格模型和人工椎间盘置换术后的颈椎三维体网格模型在前屈、后伸、侧弯和旋转15度过程中,手术节段的上下邻近节段内髓核最大应力随着角度的增大而增大。前屈后伸时,人工椎间盘模型手术节段C4—C5的上位邻近节段C3—C4之间和下位邻近节段C5—C6之间的髓核内最大应力较融合模型小；侧弯时,人工椎间盘模型手术节段C4—C5的上位邻近节段C3—C4之间的髓核内最大应力较融合固定模型明显减小,但是在下位邻近节段C5—C6之间的髓核内最大应力较融合固定模型要大；旋转时,人工椎间盘模型手术节段C4—C5的上位邻近节段C3—C4之间的髓核内最大应力较融合固定模型稍小,同样在下位邻近节段C5—C6之间的髓核内最大应力又较融合固定模型要大。
结论：
1.本研究通过不断尝试,配合使用四种商业软件Mimics、Geomagic Studio、MSC.Patran和MSC.Marc,以颈椎C3—C6(即第三颈椎到第六颈椎)三个节段为例实现了一个完整的Mimics建模到MSC.Marc有限元分析的系统工程。该系统工程的路径为：使用Mimics医学图像处理软件依据颈椎CT断层图像对C3、C4、C5、C6四个颈椎重建三角片面网格三维模型并在一定程度上对其修洁；使用Geomagic Studio逆向工程软件依据C3、C4、C5、C6四个颈椎三角片面网格三维模型建立其间的椎间盘,并进一步对所有模型进行修洁,随后构建它们的CAD模型；使用MSC.Patran有限元前后处理软件在保证相邻模型的单元的连续性和连接牢固性基础上对所有三角片面网格三维模型划分四面体实体网格；使用MSC.Marc有限元分析软件针对模型的不同状态分别分析其生物力学特性。
2.综合前屈、后伸、侧弯和旋转的有限元分析数据,仅侧弯和旋转时,在手术节段的下位邻近节段处髓核的最大应力人工椎间盘置换术较融合固定术应力高。应力在邻近节段的集中可能导致融合固定术后邻近节段的退变,人工椎间盘置换术也可能同样无法避免,并且在手术节段的下位邻近节段相对于上位邻近节段更有可能发生退变。
主要创新点：
1.配合使用四种商业软件Mimics、Geomagic Studio、MSC. Patran和MSC. Marc,实现了一个完整的Mimics建模到MSC.Marc有限元分析的系统工程。
2.提出了在Mimics医学图像处理软件中一种新颖的先进的建模方法,先着色整体建模区域,再使用编辑工具中的一个象素大小的圆形选择工具分开相邻椎体的界限,令得各个重建后的三维模型边界清晰并且距离微小,便于后续的实体网格划分和有限元分析。
3.确定了Mimics软件Remesh网格重划分时"Smoothing"参数的值为0.1,这个值既可令模型光顺,同时也控制了误差。
4.创建了一种准确、快捷建立椎间盘的方法。在Geomagic Studio软件中,依据相邻椎体的底和顶,配合“填充孔”工具,建立的椎间盘边界圆滑清楚,与上下椎骨紧密相贴,共用节点,有利于实体网格划分时相邻体的网格连续性和牢固性,便于后续的有限元分析。
5.提出了使用刚性面带动椎骨精准运动来进行有限元分析的方法。
6.提供了人工椎间盘置换术其手术节段的下位邻近节段相对于上位邻近节段也更有可能发生退变的有限元分析证据。
Background:
1. Biomechanical study methods were usually to observe clinical cases, test human cadaver or animal experiment ago. Along with the development of computer FEA (Finite Element Analysis) gradually widely apply in biomechanical study, especially orthopedics biomechanical study. FEA is firstly applied in engineering research, but in recent years FEA begin to be applied in medical research. The methos have enormous advantages. It can analyse stress and strain of human inner structure, simulate surgery operation, and analyse times without number. The marerials of human cadaver experiments are difficultly acquired and only used up once, however, FEA is especially predominant.
Application of FEA in biomechanical study relates to mathematics, mechanics, medicine, English and computeracy. If FEM (Finite Element Method) is based on researchers personally programme, the most researchers would come up against impassable obstacles about mathematics and computer programme. It is a lucky that business software of FEA had popularized and they have opend doorstep which researchers investigate biomechanics by right of FEA.
Business software of FEA of which a large number of people make use have Ansys, Abaqus, Adina and MSC.Marc et al. MSC.Marc software is issued by MSC. Software Corporation of America. The software is very powerful in contact and nonlinear analysis,and can rapidly converge. The support organization of the research used large amount of money to purchase MSC.Marc software several years ago. MSC.Marc software is a large-scale non-linear FEA software which also relates to mathematics, mechanics, medicine, English and computeracy, so its manipulators are hard well up in it. Otherwise, there are few reference books in market, so the software has not adequately used in the support organization of the research and it is wasteful. The support organization of the research has also purchased Mimics software which is provided with powerful three-dimensional reconstruction and simple trimming model. But the function of simple trimming model of Mimics software is insufficient. MSC.Marc software is provided with MSC.Mentat which is a fore-and-aft processing unit of FEA and can plot out entity gridding. But the function of ploting out entity gridding of MSC.Mentat is too weak in the face of complex entity and successful rate is not enough. Mimics software can complete first step of FEA, and MSC.Marc can complete last step of FEA, but they miss middle process such as trimming model and ploting out entity gridding. Not only take into account science research, but also take into account to make the best of resource, it is necessary and impending to set up a systemic and intact path of FEA from 3D reconstruction in Mimics to FEA in Marc. Along with the path, there are many works to complete, such as three-dimensional reconstruction of triangle surface grids partitioning, trimming 3D model, establishing CAD model, geometry meshing on CAD model, setting geometric properties and material properties of elements, setting boundary conditions and load, submitting to FEA, dealing with the results of FEA.
2. With the development of fixation instrument and fusion procedures of spine, successful rate of the spine fusion with bone graft and internal fixation has been very high, and the spine fusions with bone graft and internal fixation become the most effective way that cure spinal degeneration, instability and malformation. However, the degeneration of the adjacent segments comes forth after long term follow up.
Some scholars and doctors begin to non-fusion spinal operations in place of fusion operation. The artificial disc replacement is one of non-fusion spinal operations. Mamy experts think that non-fusion spinal operations are sure-enough in effect in treat some symptoms, however, there are more problems to solve, and there are not evidences to make sure non-fusion better than fusion at the present time, so more long term researchs could judge advantages and disadvantages of non-fusion.
Fusion or non-fusion? Anterior cervical discectomy and fusion with bone graft belongs to spinal fusion. Artificial cervical disc replacement belongs to spinal non-fusion. The two operations are two good comparison objects. If we can find advantages and disadvantages depend on FEA of two operation models, then provide theory for selecting operations of clinic cervical vertebrae indication.
Objectives:
1. On the basis of making the best of existing resources, to set up a systemic and intact path of FEA from 3D reconstruction in Mimics to FEA in Marc. Along with the path, there are many works to complete, such as three-dimensional reconstruction of triangle surface grids partitioning, trimming 3D model, establishing CAD model, geometry meshing on CAD model, setting geometric and material properties of elements, setting boundary and load conditions, submitting to FEA, dealing with the results of FEA.
2. According to "Systems Engineering from 3D Reconstruction in Mimics to FEA in Marc", to construct 3D model of cervical discectomy and fusion with bone graft and artificial cervical disc replacement which are all operations to cure cervical diseases, to find advantages and disadvantages depend on FEA of two operation models, then provide theory for selecting operations of clinic cervical vertebrae indication.
Materials and Method:
1. Adopt Mimics software to reconstruct three-dimensional triangle surface grids partitioning model of C3, C4, C5 and C6, and make use of "Remesh" to trimming 3D model.
2. Adopt Geomagic Studio software to better trimming 3D model of C3, C4, C5 and C6.
3. Adopt Geomagic Studio software to constructe 3D model of intervertebral discs, nucleus pulposus and anulus fibrosus between C3 and C4, between C4 and C5, between C5 and C6.
4. Firstly adopt Geomagic Studio software to constructe CAD model from 3D model of close triangle surface grids, and then adopt MSC.Patran software which is a fore-and-aft processing software of FEA to mesh tetrahedron on CAD model.
5. Set geometric and material properties of all elements, and set boundary and load conditions of entire cervical vertebrae segments model in MSC.Marc software.
6. Combine Geomagic Studio, MSC.Patran and MSC.Marc software to constructe 3D tetrahedron model of cervical discectomy and fusion with bone graft and artificial cervical disc replacement.
7. Adopt MSC.Marc software to respectively set boundary and load conditions on 3D model of normal, discectomy and fusion with bone graft and artificial cervical disc replacement, and analysis biomechanical characteristics of adjacent segments of three models in the course of anterior flexion 15 degree, extension 15 degree, lateral bending 15 degree and axial rotation 15 degree.
8. Adopt MSC.Marc software to post processing the results of FEA.
Results:
1. The research has constructed many 3D models, including triangle surface grids partitioning models, CAD models and tetrahedron models of C3, C4, C5, C6, and intervertebral discs, nucleus pulposus and anulus fibrosus between C3 and C4, between C4 and C5, between C5 and C6. All 3D models structure is clear and smooth, and meshes are continuous between adjacent models, and enough good to FEA.
2. The research comes true from 3D reconstruction to FEA on the basis of combining Mimics, Geomagic Studio, MSC.Patran and MSC.Marc software.
3. The maximal stresses of adjacent segment nucleus pulposus of three-dimensional models of normal, discectomy and fusion with bone graft and artificial cervical disc replacement ascend with the rise of degree during anterior flexion 15 degree, extension 15 degree, lateral bending 15 degree and axial rotation 15 degree. The maximal stress of superior and inferior adjacent segment nucleus pulposus of 3D model of artificial cervical disc replacement is less than discectomy and fusion with bone graft's during anterior flexion and extension 15 degree. The maximal stress of superior adjacent segment nucleus pulposus of 3D model of artificial cervical disc replacement is enormous less than discectomy and fusion with bone graft's during lateral bending and axial rotation 15 degree. However, the maximal stress of inferior adjacent segment nucleus pulposus of 3D model of artificial cervical disc replacement is bigger than discectomy and fusion with bone graft's during lateral bending and axial rotation 15 degree.
Conclusions:
1. The research implements a systems engineering from 3D reconstruction in Mimics to FEA in MSC.Marc on the basis of combining Mimics, Geomagic Studio, MSC.Patran and MSC.Marc software. The path completes three-dimensional reconstruction of triangle surface grids partitioning by Mimics software, trimming 3D model by Geomagic Studio software, establishing CAD model by Geomagic Studio software, geometry meshing on CAD model by MSC.Patran software, setting geometric properties and material properties of elements, setting boundary conditions and load, submitting to FEA, dealing with the results of FEA by MSC.Marc software.
2. Summing-up the results of FEA, the maximal stress of inferior adjacent segment nucleus pulposus of 3D model of artificial cervical disc replacement is bigger than discectomy and fusion with bone graft's during lateral bending and axial rotation 15 degree. Stress concentration of adjacent segment maybe result in adjacent segment degeneration after discectomy and fusion with bone graft, and artificial cervical disc replacement is maybe avoidless similarly, and degeneration probability of inferior adjacent segment is bigger than superior adjacent segment.
引文
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[1]Huang RC, FP Giardi, MR Lim, et al. Advantages and disadvantages of nonfusion technology in spine surgery[J]. Orthopedic Clinics of North America, 2005,36(3):263-9.
[2]Delamarter RB, Bae HW, Pradhan BB. Clinical Results of ProDisc-Ⅱ Lumbar Total Disc Replacement:report from the United States Clinical Trial[J]. Orthopedic Clinics of North America,2005,36(3):301-13.
[3]Aota Y, Kumano K, Hirabayashi S. Postfusion instability at the adjacent segments after rigid pedicle screw fixation for degenerative lumbar disorders [J]. J Spinal Disord,1995,8(6):464-9.
[4]Lee CK. Accelerated degeneration of the segment adjacent to a lumbar fusion [J].Spine,1988,13(3):375-7.
[5]Krag MH. Biomechanics of thoracolumbar spinal fixation:a review [J]. Spine, 1991,16(Suppl3):S84-99.
[6]Rahm MD, Hall BB. Adjacent-segment degeneration after lumbar fusion with instrumentation:a restrospective study [J]. J Spinal Disord,1996,9(5): 392-400.
[7]Eck JC, Humphreys SC, Hodges SD. Adjacent-segment degeneration after lumbar fusion:a review of clinical, biomechanical, and radiologic studies [J]. Am J orthop,1999,28(6):336-40.
[8]陈君生,包健,朱大成,等.脊柱融合术后邻近节段的加速退变(附107例报告)[J].中国矫形外科杂志,2002,10(14)：1437-8.
[9]丁宇,阮狄克,赵卫东,等.脊柱融合内固定致邻近节段退变的生物力学机制[J].中国临床解剖学杂志,2003,21(3)：371-4.
[10]邱贵兴,徐宏光,翁习生.脊柱固定融合术后邻近节段病[J].中国医学科学院学报,2005,27(2)：249-53.
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