【作者】 李筱贺；

【导师】 徐达传；

【作者基本信息】 南方医科大学 ， 临床解剖学， 2010， 博士

【摘要】 研究背景中下胸椎爆裂骨折随着建筑业、交通业等现代工业的高速发展,临床上日益多见,病情往往较为严重、致残率高,需要尽快采取减压融合固定。如只行后路固定,而不作椎体重建,则将使载荷后移,90%的应力集中在椎体与器械之间,内植物张力强度会明显增加,将产生内植物断裂、恢复的伤椎高度丧失、假关节形成和后突畸形等缺陷。经侧前路减压、椎体间植骨、内固定术是近十余年来脊柱外科的主要进展之一,该术式能直观地定位伤椎,减压彻底,减少融合节段,保留其活动度,对已损伤的神经无刺激,同时通过椎体间支撑植骨,恢复伤椎高度和脊柱矢状面的平衡,为神经恢复提供了最大的椎管和椎间孔空间,也使脊柱恢复近似正常的载荷分布。中下胸椎侧前方固定其技术关键是选择置钉点,但由于节段特征和个体特点的不同而导致相关解剖技术参数变异显著,使得脊柱胸腰段侧前方内固定的难度和危险性急剧增大,任何一项解剖参数的失误都将会造成临近诸多血管、神经、内脏器官的损伤。因此寻找一种有形的、恒定的置钉点参照物极为重要。因此本课题拟将人体解剖学、现代影像学、计算机三维重建数字化技术应用于脊柱中下胸椎侧前方固定新置钉点的研究,针对椎体钉如何定位、定向、定深问题开展研究,以减少手术并发症的发生；通过对内固定器械计算机有限元模拟仿真,为其固定器械的改进提供数字物理模型参考并填补国内相关空白；同时探索一种椎体三维数字化,准确的定位、定量研究方法。目的(1)建立脊柱中、下胸椎三维数字模型数据库。(2)三维数字化测量中、下段胸椎椎体相关9组解剖学参数,为椎体压缩性骨折术前分级与术后疗效评估提供参考。(3)三维数字化测量中、下段胸椎肋头相关10组解剖学参数,为制定置钉点坐标提供依据。(4)制定中、下段胸椎椎体侧前方置钉坐标,数字化模拟置钉并测量钉道长与前后安全角,验证以肋头前缘为置钉点参照物的可行性,并提供置钉参数供临床参考。(5)对T11、T12前路短节段单钉单棒刚性固定系统有限元分析,并对其器械改进提出建议。(6)对T11、T12前路镍钛合金弹性内固定系统有限元分析并与刚性系统对照,验证弹性内固定系统应用于下胸椎前方固定的可行性,并为器械的设计改进提出建议。方法(1)CT原始数据与椎体三维模型数据库的建立：健康成人体检CT连续扫描数据30例(T1-L1,年龄25-43岁,平均34岁),扫描条件：电压120Kv,电流150mA,层厚1.25mm,512×512矩阵。在CT工作站中,通过调整图像灰度、增加对比度等对图像观察细节进行调整,得到清晰骨窗断层图像后,将其保存Dicom格式的文件。将Dicom格式文件导入图像三维重建软件Mimics10.0中,利用软件自带的域值设定Bone (CT),三维重建模型,建立备用数据库。(2)椎体相关参数的测量：通过Mimics (10.0)3种不同断面(水平面、冠状面、矢状面)进行图像配准,确定测量点,激活Tools工具栏,选择Distance measuretool在图像上测量以下参数,椎体正中冠状面左缘、右缘高；椎体正中矢状面前缘、中部、后缘高；椎体上、下终板矢状径及横径。(3) Mimics (10.0)3种不同断面(水平面、冠状面、矢状面)进行图像配准,确定测量点,激活Tools工具栏,选择Distance measure tool在二维图像测量左、右肋头前缘与椎孔前缘、椎体前缘间距离；在三维重建图像上,点击(?)(Rotate once)配准所测椎体的位置,以保证在三维视窗上测量面与椎体矢状面重合,点击Med CAD选择Draw line工具分别在椎体上缘、肋头下缘及椎体下缘平行于水平面划线,激活Tool工具栏,选择Measure 3D distance测量肋头下缘切线与椎体上下终板间距离；计算左、右侧肋头遮挡比。(4)在重建好的6套中、下段胸椎三维图像上,以肋头下缘为X轴,以肋头前缘切线为Y轴建立坐标系,在同一个坐标系内将在Pro-E4.0建好的直径为3.0mm,长为40.0mm的椎体钉导入模型,配准螺钉的位置。模拟平行于冠状面和水平面置钉,并选择Measure 3D distance测量钉道长；调整螺钉在水平面置钉方向测量前、后安全角。(5)选择1名非脊柱疾患患者影像学数据,将CT扫描的数据导入Mimics13.0利用软件自带的域值设定(Threshold)选择T11、T12拟重建部分,参数化建立6种7条韧带数字模型。通过软件的测量功能确定切除T11椎体下缘5mm,T12上缘5mm,以.stl格式输出。利用Mimics13.0 MedCAD建模功能直接建立直径为10mm,高为13mm的圆柱形移植骨块,同时导入单钉单棒刚性固定系统。用Ansys products 11.0建立其有限元模型,固定模型T12椎体下缘表面,在垂直加载500N载荷的同时,于T11椎体上表面施加15Nm力矩,分前屈、后伸、侧屈、旋转等4种情况加载,分析螺钉中部、根部、连接棒上、中、下段应力分布。(6)利用Wegoortho公司提供U-Front胸腰椎前路固定系统的螺钉,直径为3.0mm；长为40.0mm；“U”形棒采用“U”型记忆合金棒,其材料为医用NiTi记忆合金,Ni的含量为50.8%-51.8%,弹性模量(马氏体态)达71400Mpa,长度为50.0mm,宽度及厚度均为6.0mm,“U”型弹性区厚度为4.0mm。利用Pro-E4.0机械建模模块,建立椎体侧前方弹性固定系统,以.iges格式文件输出导入已建好的T11、T12运动节段前路椎间植骨有限元模型中,固定模型T12椎体下表面,在垂直加载500N载荷的同时,于T11椎体上表面施加15Nm力矩,分前屈、后伸、侧屈、旋转等4种情况加载,分析螺钉中部、根部、“U”型棒上、中、下段应力分布,并与刚性固定系统对照研究。结果(1)中、下段胸椎椎体正中冠状面左、右缘,正中矢状面前、中、后缘高：前两者均随椎序的增加逐渐的增大,左、右两侧除T6外均无显著性差异；后三者均随椎序的增加而逐渐增大,前缘高与中部高除T4、T5、T7无显著性差异外,其余均有显著性差异；后缘与中部高均有显著性差异；前、后缘高除T4,T10，T12外,其余均有显著性差异；椎体上、下终板矢状径及横径均随椎序的增加而增大。(2)中、下段胸椎肋头前缘与椎孔前缘间距离：随着椎序的增加,距离逐渐减小,左、右侧别间除T4、T6外,均有显著性差异,左侧大于右侧,T11以下为负值；肋头前缘与椎体前缘间距离：随着椎序的增加,肋头前缘与椎体前缘间距离逐渐增大,左右侧别间除T4,T10-12外,均有显著性差异,右侧大于左侧；肋头遮挡比均随着椎序的增加(头侧到尾侧)逐渐减小,到T11开始为负值；肋头下缘与上终板上缘的距离：随着椎序的增加,距离逐渐增大,左右侧别间无显著性差异；肋头下缘与下终板下缘的距离：随着椎序的增加,逐渐减小,除T7、T9外,左、右侧别间无显著性差异。(3)模拟中、下段胸椎左、右侧置钉点坐标与钉道长度(以直径为3.0mm椎体钉为例)：在坐标系中,随着椎序的增加,其置钉点坐标由坐标系的第一象限移向第二象限,呈向上斜长“∽”型；X轴坐标从T4到T12逐渐减小,T8以下均为负；Y轴坐标随椎序的增加而逐渐增加；数字化钉道长随着椎序的增加逐渐变长,左侧钉道T4-T7为(25-30)mm,T8-T10为(30-35)mm,T11到T12为(35-40)mm；右侧钉道T4-T8为(25-30)mm,T9-T10为(30-35)mm,T11到T12为(35-40)mm；左右侧别间除T7外均无显著性差异；左右两侧前安全角随着椎序的增加变化不大,从T4逐渐增加到T8,其中T8、T9和T10为峰值段,Tll、T12又逐渐降低,两侧前安全角无显著性差异；两侧后安全角随着椎序的增加逐渐减小,由正值变为负值,侧别间无显著性差异。(4)利用三维重建软件Mimics和有限元软件Ansys成功建立T11、T12运动节段前路椎间植骨侧前方刚性固定有限元模型,共有21,256个单元,22,494个节点,建成后的三维有限元模型与实体组织有较好的几何相似性；该模型在四种运动状态下,对于螺钉,其根部是应力最为集中的部位,且总是下位大于上位；对于连接棒其下段是应力最集中的部位。下位螺钉根部四种运动间应力比较总是旋转>后伸>侧弯或前屈；连接棒下段四种运动间应力比较,总是旋转>前屈或后伸>侧弯。(5)利用Mimics和Ansys成功建立T11、T12节段前路椎间植骨侧前方弹性内固定有限元模型,共有32,421个单元,34,658个节点,建成后的三维有限元模型与实体组织有较好的几何相似性；弹性内固定系统在四种运动状态下,对于螺钉,其根部是应力最为集中的部位,且总是下位大于上位；对于“U”形棒其中部是应力最集中的部位；下位螺钉根部四种运动间应力比较,总是旋转>前屈或后伸>侧弯；“U”形棒中段四种运动间应力比较,前屈与后伸、前屈与侧弯、前屈与旋转间均无显著性差异；弹性系统和刚性系统在同一运动状态下同一部位间比较,除下位螺钉中部和下位螺钉根部间没有显著性差异外,其余节段均有显著性差异。结论(1)在中、下段胸椎椎体上缘置钉,其中T4-T5选择25mm长的螺钉,T6-T9选择30mm长的螺钉,T10-T12则选择35mm长的螺钉较为适宜。而椎体下缘置钉T4-T8选择30mm长的螺钉,T9-T10选择35mm长的螺钉,而T11-T12则选择40mm长的螺钉较为适宜；由于椎体的横径始终大于矢状径(3-4)mm,建议在取材和修剪移植松质骨块时应将骨块修成横行的长方体(长大于宽约3mm-4mm)这样以最大程度恢复损伤椎体的前后和左右的生理载荷。从椎体高度相关测量数据可知,两椎体(中间跨越一个椎体)之间的距离范围为：在T4-T7,为(52-56)mm,T8-T12，为(44-48)mm,在临床应参考以上数据选择合适的纵行棒进行固定。(2)肋头作为中、下段胸椎较为恒定、有形的解剖学标志,具有易识别(术中直接可通过手指触摸到肋头即可确认其位置)、位置相对确定[本文测量数据表明,其位置变化符合一定规律,可以根据肋头的位置来判断椎孔的位置(脊髓的位置)和上下终板的位置],位置优良(在其附近置钉符合生物力学实验验证的置钉原则)等的优点,使其作为中下段胸椎侧前方固定置钉点参照物成为可能。T4-T7节段胸椎肋头遮挡了椎体后三分之一,所以为了使螺钉与椎体间把持力最大,有效钉道最长,需要临床医生将该节段肋头切除,在肋头的后方置钉；而T8-T10肋头的前缘几乎与椎孔的前缘重合,T11以下甚至位于椎孔前缘的后方(为负值),所以在T8以下节段胸椎要在肋头前一定距离处进行置钉,从而避免椎体钉置入椎管损伤脊髓神经。(3)置钉点坐标由坐标系第一象限逐渐向第二象限上方移动,即随着椎序的增加,应由在肋头的后方置钉逐渐转移在肋头的前上缘置钉；T4-T7坐标均位于第一象限,即在此节段需将肋头切除,在肋头前缘后方一定距离置钉；T8-T12均位于坐标系的第二象限,即在此节段需在肋头的前上缘一定距离置钉。本文通过软件分别模拟了椎体钉最大前方安全角和后方安全角,临床置钉时,椎体钉向腹侧偏离不能超过56°；向背侧偏离T4到T5不能超过22°,T6不能超过15°,T7、T8不能超过10°,T9、T1o不能超过5°,T11、T12置钉不能向背侧偏斜。(4)根据本文以肋头前缘为参照物的置钉原则,成功进行T11，T12节段前路椎间植骨侧前方固定有限元模型网格划分,建成后的模型与实体组织具有良好的几何相似性。单钉单棒刚性固定系统在用于侧前方固定时,其下位螺钉根部与连接棒下段承受应力始终较大,而螺钉的中部与连接棒的中、上部则较小。在4种运动状态下,侧弯运动对于固定器械各个部分加载的应力较小,而旋转运动则较大。T11,T12节段前路椎间植骨侧前方单钉单棒刚性内固定的病人在做旋转运动时最容易引起下位椎体钉根部与连接棒下段断裂。我们建议中、下段胸椎前路椎间植骨侧前方固定术后应当严格采用可靠支具,即使以后拆除支具,也应当禁止或减少旋转运动；将椎体钉(连接棒)设计成根部(下段)较前端(上段)粗的锥体形,以提高这两个部位的机械承载能力；同时也要加高下位椎体钉压紧螺母的高度与螺纹的深度,以提高下位椎体钉与连接棒下段的固定强度,降低高应力区两个部件间松动与滑脱的可能性。(5)单钉单棒弹性固定系统用于侧前方固定有限元分析表明,其下位螺钉根部与“U”形棒中段承受应力始终较大,而螺钉中部与“U”形棒的上部则较小。螺钉根部在4种运动状态下,旋转运动应力最大,而侧弯运动最小,“U”型棒中部在四种运动状态下应力均较大,但所有部位的应力都小于镍钛合金正常体温下屈服强度。故T11、T12运动节段前路椎间植骨单钉单棒弹性固定患者在正常运动状态下不会由于固定器械某部位应力过高而导致断钉断棒。弹性固定系统不仅能使固定刚度下降,减少应力遮挡效应,更能减少螺钉根部与连接棒间的应力,降低下位螺钉与连接棒间断裂的可能性。更多还原

【Abstract】 BackgroundWith the rapid development of building industry and communication,bursting fracture of thoracicolumbar vertebrae took place usually,the state of an illness were serious and the mutilation rate was higher than others.These patients had to take the surgery of decompression fusion-stabilization as soon as possible.If patients only being taken posterior fixation,and no rebuilding of vertebrae body,it lead to retrude stress. Ninety percent of stress concentrated on vertebrae body and fixation instrument, the tensile strengh of fixation would increase obviously. It leads to fragmentation of fixation, lossing refectious of vertebrae body height, pseudoarticulation formation, abnormity of posterior process,et al.Anterior decompression,bone graft,internal fixation were mainly progress of spinal surgery,it would find injury vertebrate directly, decompress thoroughly, decrease segment of fusion, retain its range of motion, decrease excitation nerve. It would provid enough room for nerve recovery, and also make spine recovery to normal stress distribution. It was the most important to anterior thoracicolumbar fixation how to choose screw position.But with the difference of segment and individuality,the difference of surgery anatomy was also variance.It would lead to increase difficulty of anterior fixation surgery,any fault of anatomy parameter would also lead to damage to blood vessel,nerve, internal organ. So it is important to find a permanent anatomical position of screw reference.So we used human anatomy, modern imageology,3-D reconstruction of computer technique to research thoracicolumbar anterior fixation new screw position,how to orientate,and decrease complicatiom.With finite element analysis simulation technique,we supplied digital physical model to improve fixation,and also established a way on how to study with 3-D digital,precise position and quantitative.Objective (1) To reconstructed middle and lower thoracic vertebra data bank(2) To provide a basis of compression fracture of vertabral body, Nine anatomical parameters of thoracic vertebra were measured. (3) To provide a basis of definiting screw coordinate, Ten anatomical parameters of thoracic vertebra rib head were measured.(4) To definite screw coordinate of anterior approach internal fixation point of middle and lower thoracic vertebra,and simulate putting screw digitally and measure screw canals (anterior safety angles and posterior safety angles),and verificate the feasibility of according to rib head as reference of screw point. (5) To construct a 3-D finite element(FE) model of anterior screw fixation on lower thoracic vertebra and evaluated the stress of screw, stick stress and to supply the suggestion of fixation improvement. (6) To construct a 3-D finite element(FE) model of anterior screw NI-TI elasticity fixation on lower thoracic vertebra and evaluated the stress of screw,stick stress and to compare with rigidity system.To supply the suggestion of fixation improvement and verificate the feasibility of NI-TI elasticity fixation application. Methods (1) To collect CT primary data and establish database of 3-D reconstruction models:CT scanning images of health adult physical examination were collected.Scanning condition is that voltage is 120kv,electric current is 150mA, level thickness is 1.25mm and 512×512 matrix.The data included 30 cases healthy adults (T1-L1,25-43 years old, average 34 years old).(2) The parameter of vertebra body:With Mimics registry three plane(transverse plane,coronal plane,sagittal plane),active "Tool" toolbar,choose "Distance measure tool"to measure follow parameter on 2-D imaging:Left height of vertebral body,LHV;Right height of vertebral body,RHV;Anterior height of vertebral body,AHV;Middle height of vertebral body,MHV;Posterior height of vertebral body,PHV;Superior sagittal diameter of vertebral body,SSDV; Superior transverse diameter of vertebral body,STDV) ,inferior sagittal diameter of vertebral body,ISDV; Inferior transverse diameter of vertebral body,ITDV.(3)To measure the following parameter on 2-D imaging:The distance between left (or right) anterior border of rib head and vertebral foramen,L(R)RF;The distance between left (or right) anterior border of rib head and vertebral body,L(R)RB. To adjust three plane on 3-D imaging, and take "Med CAD",choose "Draw line"to draw line paralleling with superior border of vertebral body ,inferior border of rib head and inferior border of vertebra body.To use "Measure 3D distance" to measure follow parameter:The distance between inferior border of left (or right)rib head and superior border of upper-end-plate,IL(R)RSU;The distance between inferior border of left (or right) rib head and inferior border of lower-end-plate,IL(R)RIL,and to calculate percent vertebra obscured by left (or right) rib head-PVOL(R)R.(4)To set up coordinate system on six middle and lower thoracic vertebra imagings, as inferior border of rib head for X axial,anterior border of rib head for Y axial.We import vertebra screw (diameter:3.0mm;length:40.0mm; reconstruced by Pro-E) to coordinate system,adjusted screw.We simulated screw to parallel with coronal and horizon plane,measured screw canal;adjusted direction on horizon plane,measured anterior and posterior safety angle.(5)A young man’s thoracic spine was scanned by CT with 1mm interval. Then, the jpg-format data of CT was input into computer. Used Mimics 13.0 "Threshold" to choose T11-T12 reconstuction segment,We constructed 6 species and 7 ligaments digital models. With measurement function of software we cut off 5mm from inferior border of T11 and superior border of T12,exported by "Stl" files.With "Mimics13.0 MedCAD" we reconstruced bone graft(diameter:10mm,height:13mm, cylindrical),put it between L11and L12,at same time imported fixation into the same system. With Ansys products 11.0,We construced finite element model,fixed inferior border of T12 vertebra body,loaded 500N and 15Nm moment of force on T11 superior vertebra body, classify by "flexion condition", "extension condition" "in lateral bending condition" "in rotation condition",Analysised stress on middle/tail of screw and upper/middle/lower segment of stick.(6)Using "U-Front" anterior thoracicolumbar fixation screw (diameter:3.0mm,length:40mm), "U" stick was been choosen remembrance alligation.The material was NiTi alligation(50.8%-51.8% of Ni; elastic modulus was 71400Mpa;Length:50mm;Width and thinkness was 6mm; Width and thinkness of "U" segment were 4mm).We exported "iges" files into anterior fixation FEA model of T11,T12 motion segment. We construced finite element model,fixed inferior border of T12 vertebra body,loaded 500N and 15Nm movment of force on T11 superior vertebrae body, classify by "flexion condition", "extension condition", "lateral bending condition", "rotation condition",analysised stress on middle/tail of screw and upper/middle/lower segment of "U" stick,and contrasted with rigidy system.Results (1) Left(right) height of vertebral body[L(R)HV],anterior (middle,posterior) height of vertbral body[A(M,P)HV], superior(inferior) sagittal diameter of vertebral body[S(I)SDV],Superior (inferior)transverse diameter of vertebral body[S(I)TDV] To caudal of thoracic vertebra, L(R)HV gradually increased, There were no difference between two sides,except for T6; To caudal of thoracic vertebra,A(M,P)HV also gradually increased, There were difference between AHV and MHV,except T4,T5,T7, There were difference between MHV and PHV, There were difference between AHV and PHV except T4, T10, T12. S(I)SDV and S(I)TDV gradually increased from T4 toT12.(2) The distance between left (or right) anterior border of rib head and vertebral foramen,L(R)RF:There were difference between two sides,LRF was bigger than RRF,except for T4,T6.To caudal of thoracic vertebra, L(R)RF gradually decreased.Below T11,the data of measurement were negtive value; The distance between left (or right) anterior border of rib head and vertebral body[L(R)RB]:There were difference between two sides (right greater than left)except for T4,T10-12.To caudal of thoracic veterbra, L(R)RB gradually increased; Percent vertebra obscured by left (or right) rib head---PVOL(R)R:To caudal of thoracic veterbra, PVOL(R)R gradually decreased. Below T11,the data of measurement were negtive value. The distance between inferior border of left (or right)rib head and superior border of upper-end-plate[IL(R)RSU]:There were no difference between two sides. To caudal of thoracic vertebrae, IL(R)RSU gradually increased. The distance between inferior border of left (or right) rib head and inferior border of lower-end-plate[IL(R)RIL]: There were no difference between two sides except T7,T9. To caudal of thoracic vertebrae, IL(R)RIL gradually decreased.(3) The simulation of coordinate on anterior fixation of middle and lower thoracic vertebra and measurement of the length of srew canal (LSC)(screw diameter:3.0mm):To caudal of thoracic vertebra,the screw of coordinate moved from the first quadrant to the second, liked long "∽" shape. From T4to T12,the "X" axile value decreased;From T8,the X value were negtive.From T4 to T12,the value of Y gradually increased;Digital screw canal gradully increased to caudal of thoracic vertebra.Left screw canal were 25mm-30mm on T4-T7,T8-T10 were 30mm-35mm,T11-T12were 35 mm-40mm,there were difference between two sides.Left and right anterior safety angle increased from T4 to T12,but the variance range was small.The value gradually increased from T4-T8,T8-T10 segment was peak value segment.From T11 to T12,the value gradually decreased,There are no difference between two sides; Left and right posterior safety angle decreased from T4 to T12.Below T11,the value were negtive, there were no difference between two sides.(4)We reconstructed anterior bone graft fixation of T11.T12 movement segment finite element models.There were 21,256 elements and 22,494 nodes, there were same geometric similarity as human body; On four movement states, anterior GSS-V fixation of T11..T12 bone graft movment segment,the tails of screw were localized stress, lower tails of screws stress were bigger than upper.While the lower of stick localized stress. There were difference among four motion of lower tails of screws, Stress of rotation was the biggest while lateral bending was smallest; There were difference among four motion of lower segment of stick, Stress of rotation was the biggest while lateral bending was smallest.(5)We reconstructed anterior bone graft elasticcity fixation of T11. T12 movement segment finite element models.There were 32,421 elements and 34,658 nodes, there were same geometric similarity as human body; On four movement states, anterior "U" fixation of T11.T12 bone graft movment segment,the tails of screw were localized stress, lower tails of screws stress were bigger than upper.While the middle of stick localized stress. There were difference among four motion of lower tails of screws, stress of rotation was the biggest, latter bending was smallest. There were no difference among four motion of middle segment of stick. Conclusion:(1) When fixed screw on vertebra body of middle and lower thoracic,you would choose 25mm length of screw for T4-T5,30mm for T6-T9,35mm for T10-T12.While fixed screw on lower vertebra body, you would choose 30mm length of screw for T4-T8,35mm for T9-Tio,40mm for T11-T12.Because transverse diameter of vertebra bodies were always bigger than sagittal diameter for(3-4)mm,we suggested that bone graft should prun into laterigrade cuboid, it could recovery A-P and bilateral physiological functions load. We could also conclude that height of vertebra body increased from T4 to T12.The distance between two vertebra (interval one vertebra) range were (52-56) mm for T4-T7, (44-48)mm for T8-T12, the surgeons could collate these data to choose suitable stick length.(2) As a constancy,stabile shap anatomical landmarker, rib head were easy recognized(you could easy touch rib head,and confirm its situation),the situation were constancy[the variance were regularity, you could judgement the situation of vertebral foramen (the situation of spinal cord) and superior (inferior) end-plate according to rib head.The situation of rib head were as screw point (consistent with biomechanical principle).Rib head can be as anterior fixation of middle and lower thoracic.Rib head obscured posterior 1/3 of vertebra body on T4-T7, in order to increase screw holding strength, reseced rib head was very important;While rib heads were coincidence with vertebra foramen on Ts-T1o and posterior of vertebra foramen on T11-T12,we should fix screw posterior of rib head below T8 in order to avoid injury spinal cord. To caudal of thoracic vertebra.the screw of coordinate moved from the first quadrant to the second,the screw point removed from posterior to anterior of rib head.The coordinate of T4-T7 situated at the first quadrant,so we should resect on rib head; The coordinate of T8-T12 situated at the second quadrant,so we should fix screw on anterior of rib head. With CAD module,we simulated anterior and posterior safety angle. Angles of ventralward were not exceed 56°, angles of dorsoward were not exceed 22°on T4-T5,while 15°for T6,10°for T7-T8,5°for T9-T10, were not towards dorsoward on T11-T12.(3)According to rib head as screw point,we reconstrued FE model of anterior bone graft fixation of T11, T12 movement segment, there were same geometric similarity as human body. The finit element analysis indicated:The lower tails screw and inferior of stick were loaded bigger stress,while the middle of screw and middle/superior of stick were loaded little.Under four movment situation,all segment of fixation sysytem were loaded little on lateral bending,while opposited it on rotation. Patients of anterior bone graft fixation of T11T12 segment, lower tails of screw and inferior stick would tend to break on rotation.So we suggested the patient of anterior fixation should adept orthosis,and prohibit cyclovergence movement. We also suggest we should design screw and stick to cone shape,it would increae ablility of loading stress,meanwhile increased height of impacted screw nut,and depth of screw thread to increase lower screw and stick fixation intension,decrease loosening and sliping possibility.(4)The finit element analysis indicated:The lower tails screw and middle of "U"stick were loaded bigger stress,while the middle of screw and superior of "U"stick were loaded little.Under four movment situation,all segment of fixation sysytem were loaded larger on rotation,while opposited it on extention. Elasticity fixation didn’t break on normal movement. Elasticity fixation would decrease stress and breakage of screw and stick.更多还原