【作者】 张亘瑷；

【导师】 陈建庭； 金大地；

【作者基本信息】 南方医科大学 ， 脊柱外科学， 2008， 博士

【摘要】 1.研究背景自从1959年,Boucher采用长螺钉经椎板、椎弓根达椎体固定腰骶关节取得成功以来,经过不断发展完善,椎弓根螺钉内固定系统因其贯穿三柱、固定坚强而成为当今临床使用最为广泛的脊柱后路内固定器械。应用于治疗脊柱退行性病变,脊柱骨折,脊柱畸形及骨转移瘤等病症,这也是生物力学理论在脊柱内固定实践方面的体现。椎弓根螺钉固定的可靠性取决于骨-螺钉界面把持力的维持,在临床上,螺钉的把持力不够或术后承载过大时,均会造成椎弓根螺钉的松动或拔出,尤其是在骨质疏松的患者中更为常见。此外,在术中植入椎弓根螺钉的过程中,常出现首次植钉失败,需要再次拧入螺钉,这也导致螺钉植入后把持力下降,螺钉松动、脱出。随着椎弓根内固定术的广泛应用,导致手术失败的螺钉松动、脱出、假关节形成等屡有报道,针对这些失败病例的翻修手术也越来越多。如何提高椎弓根螺钉的稳定性已成为当今脊柱外科研究的焦点之一。通常的翻修手术有增加椎弓根螺钉直径、长度,在钉道内充填其他材料等。但实践证明,增加椎弓根螺钉直径可增加椎弓根处骨折,损伤神经根的危险,且对多数病人并不适合;增加螺钉长度则可增加椎体前缘骨质穿破,损伤椎体前方重要血管和脏器的危险;而在钉道内充填固定材料也存在着一些弊端。因此,如何在椎体的解剖限制范围内有效提高骨-螺钉界面的把持力,确保固定的可靠性及稳定性,成为经椎弓根内固定器械的研究热点。目前聚甲基丙烯酸甲酯（Polymethyl Methacrylate,PMMA）强化是使用最多的椎弓根螺钉翻修术式。研究证实,PMMA能显著增加椎弓根螺钉的拔出力,随着PMMA强化方式的不同,椎弓根螺钉的固定强度可增加49%-183%。然而PMMA强化有潜在的危险性,一旦泄露,急性反应可出现骨水泥的热效应损伤神经、血管、脊髓等,而远期更有椎管内异物存留导致压迫等危险。骨水泥注射过程中粘合剂过稠则难以均匀分布,过稀则有椎体外渗漏危及邻近营养血管和神经根之虞。有鉴于此,本课题希望设计一种可定向灌注椎弓根螺钉,使得骨水泥灌注方向可控,减少骨水泥渗漏的发生率,更减少骨水泥渗漏入椎管和椎间孔引起脊髓压迫和神经根变性的发生率,并为椎弓根螺钉翻修术提供新的选择。2.目的2.1使用计算机辅助设计技术建立一种新型的、具有定向灌注能力的椎弓根螺钉模型。2.2比较实心椎弓根螺钉与空心的定向灌注椎弓根螺钉的材料力学性质,完善模型设计并制造出螺钉。2.3比较实心椎弓根螺钉和空心的定向灌注椎弓根螺钉的生物力学特性,为椎弓根螺钉翻修提供新选择。2.4计算机流体力学模拟定向灌注,实验验证。3.方法3.1定向灌注椎弓根螺钉的设计和建模使用计算机辅助设计软件Pro/ENGINEER建模,设计空心、带有导向侧孔和定位标志的椎弓根螺钉及配套的定向灌注钉芯,具体步骤为:螺钉草绘、赋值、建立半截面、旋转成胚、螺旋扫描螺纹,切割中轴孔、导向侧孔、定位标志以及定位槽,建模完成后进行虚拟装配和仿真运动,观察定向是否成功以及组建是否存在相互干扰,根据结果进一步修正与完善建模。3.2定向灌注椎弓根螺钉的结构分析、制作以及材料力学研究3.2.1计算机辅助结构分析建模完毕后,模型导入机构/运动/结构/热力分析模块Pro/MECHANISM中,将模型简化为悬臂梁,定义材料、约束、负荷,划分有限元,进行结构分析,找出应力过分集中或运动干涉等不合理部分,调整建模,直至满意,同时比较中空和实心椎弓根螺钉的应力、应变分布。3.2.2螺钉制作使用医用钛合金TC4制作螺钉,由佛山施泰宝外科植入物有限公司制造,中空和侧孔部分由广东工业大学机电系DMU 60T数控高速加工中心加工。3.2.3材料力学实验3.2.3.1三点折弯实验10个定向灌注椎弓根螺钉（空心）和10个外形相同的实心螺钉使用858 MiniBionix MTS材料试验机进行三点折弯试验,快速垂直加载至4000N,载荷信号由计算机采集系统记录,TeststarⅡ测试分析软件计算。3.2.3.2剪切实验10个定向灌注椎弓根螺钉（空心）和10个外形相同的实心螺钉使用858 MiniBionix MTS材料试验机上进行,30N/s,快速垂直加载至4000N,载荷信号由计算机采集系统记录,TeststarⅡ测试分析软件计算。数据采用SPSS13.0统计软件包,两独立样本t检验。3.3定向灌注椎弓根螺钉的生物力学研究3.3.1标本选择6具新鲜成人尸体胸腰段椎体标本（男5具,女1具,年龄28～57岁）去除软组织、自椎间盘处离断,制成T₁₂～L₅共36个椎体,随机选取30个椎体进行试验。3.3.2分组及螺钉置入随机表法将30个椎体平均分成对照组（模拟普通椎弓根植入）、修复固定组（模拟椎弓根翻修术）、强化固定组（模拟椎弓根强化）共3组,按“人字嵴”进钉法两端分别植入空心和实心螺钉。3.3.3标本包埋固定和最大轴向拔出力试验使用自凝义齿基脱粉包埋已植入椎弓根螺钉的椎体,在材料试验机上进行最大轴向拔出力实验,记录最大拔出力和发生最大拔出力时的线性位移。进行广义线性模型之随机单位组设计资料方差分析。3.4定向灌注的模拟和实验研究Gambit建模,划分并优化网格,导入Fluent中求解。使用材料试验机制作压缩骨折模型后经定向灌注椎弓根螺钉注入PMMA并拍X线片4.结果4.1定向灌注椎弓根螺钉的设计和建模建模并调整、完善后在Pro/ENGINEER虚拟装配,对组合模型使用Pro/MECHANISM模块检验运动,在规定的自由度内零件和活动中没有出现平面相互干扰现象,特别是钉芯侧孔和螺钉的目标侧孔完全吻合,保证了单一通道的通畅性,仿真结果显示建模达到设计目的。4.2定向灌注椎弓根螺钉的结构分析、制作以及材料力学研究4.2.1计算机辅助结构分析最初设计的模型导入Pro/ENGINEER的结构分析模块Pro/Mechanism分析后发现椎弓根螺钉模型根部应力高度集中,存在结构上的薄弱点,检验模型,进行模型修正与优化后应力集中改善;比较中空和实心螺钉的应力分布、应变、应变能量、位移曲线基本一致,4.2.2材料力学实验4.2.2.1三点折弯实验快速垂直加载至4000N,空、实心螺钉均未出现折断,两种钉应变相同,均为0.17,实验过程中恒定未变,应力-应变曲线接近,0-4000N加压过程中均未出现下降波。4.2.2.2剪切实验以30N/s加速度加压,在位移6mm左右、应力达到约4000N时空、实心螺钉均断裂,二者应力-应变曲线几乎重合。空心螺钉和实心螺钉承受的平均最大应力分别为（3983.17±10.28）N和（3992.48±9.68）N,两独立样本t检验结果,两样本均数统计学上没有显著差异（t=2.085,P=0.052）。4.3定向灌注椎弓根螺钉的生物力学研究4.3.1最大轴向拔出力实验空心侧孔椎弓根螺钉对照组拔出力为（798.24±139.86）N,修复组为（1476.21±223.09）N,强化组为（1741.33±317.79）N;实心螺钉对照组拔出力为（904.37±212.03）N,修复组为（1828.42±239.68）N,强化组为（1783.37±250.49）N。对照组拔出力显著低于其他两组（P值均等于0.000）,强化固定组和修复固定组间差异无显著性意义（P=0.330）4.3.2线性位移比较空心侧孔椎弓根螺钉对照组拔出力为（1.68±0.24）mm,修复组为（3.16±0.70）mm,强化组为（3.13±0.62）mm;实心螺钉对照组拔出力为（1.85±0.37）mm,修复组为（3.43±0.98）mm,强化组为（3.36±0.98）mm。对照组发生最大拔出力时的线性位移LVDT显著小于其他两组（P值均等于0.000）,强化固定组和修复固定组间差异无显著性意义（P=0.971）。4.3.3在强化组和修复组,植入空心椎弓根螺钉侧的椎弓根表面无骨水泥渗漏,而实心钉植入侧,骨水泥渗漏较为多见。4.4定向灌注的计算机模拟和实验研究计算机流体力学模拟实现了定向灌注并获得静态压力、速度分布;实验中定向灌注成功并获得X线照片验证。5.结论5.1应用Pro/ENGINEER进行参数化建模,再应用其匹配的Pro/MECHANISM和Pro/MECHANICA模块对模型进行动态仿真和结构分析,从设计思路、模型构建、动态仿真、计算机流体流体力学上都直观而且精确地保证了设计思想中定向灌注主要特性的实现,同时,也得到了实验验证。5.2使用CAE软件可以对所建模型进行方便、直观的结构分析,并随时修正和完善模型,经理论推导、计算机模拟、材料力学实验以及统计学推断均证明,本研究中设计的空心螺钉与实心螺钉的强度无显著差异。5.3使用定向灌注椎弓根螺钉灌注PMMA能显著增强螺钉的稳定性,并能减少PMMA向椎弓根外或椎管内溢出,可以作为翻修手术较为安全的新选择。更多还原

【Abstract】 1.BackgroundSince the introduction of the transpedicular screw system by Boucher,because of the strong fixation through three columns,the applications of this system in the treatment of degenerative disorders,unstable fractures,deformities and tumors of the spine have become very popular in the last two decades.It is also the characterization of biomechanical theory in the practice of spinal internal fixation.The advantages of pedicle screw fixation are dependent on their ability to retain bony purchase until the fusion mass is stable.The bone-screw interface is a major determinant in the stability of spinal instruction systems.Loosening and failure of the screws are among the most common complications reported,especially for osteoporosis.Besides that,during the operations,because surgeons can not successfully insert screws into proper position at the first time,the turning back of the screws will be necessary.It also reduces the holding strength.Revision is often necessary.More and more loosening,prolapse and pseudoarthrosis are being reported along with the popularized employment of transpedicular fixations.It has been one of the focal points within spinal surgery how to improve the stability of pediele screws.Increasing the diameter and/or length of the pedicle screws appears to provide the best solution.However,increasing screw diameter may not always be possible because of anatomical constraints.There is an increased risk of pedicle fracture with possible neural injury if larger screws are used.The use of longer screws increases the risk of anterior body penetration with possible vascular or visceral injury.Besides that, to enhance fixation of salvage screws in case of severe bone loss,some surgeons have chosen to fill the void with a variety of materials,including corticocancellous bone grafts,polymethyl methacrylate(PMMA),and so on.But there are always somewhat defects in the revisions with filling materials.So it has been a highlight on how to increase the bone-screw interface strength.Filling and strengthening with PMMA is the most popular revision methods at present.It has been confirmed that pull-out force can be enhanced by 49%-183%according to different strengthening mode. However,PMMA is not frequently used in spine surgery because of the potential danger to adjacent nutrient vessel and nerve roots if leakage into the spinal were to occur.Immediate risks resulting from leakage into the spinal canal are the result of the exothermic reaction present in the curing process of PMMA,whereas long-term risks are secondary to a non-degradable foreign body in the spinal canal.In view of this,our goal in current study was to design a new type of pedicle screws with the capability of directional injection and evaluate the mechanical properties of it.With the characteristic of oriented injection,the incidence of bone cement leakage can be reduced,which lead to spinal compression and nerve root’s denaturation.We hope this kind of screw can afford new options for revisions and augmentations.2.Objectives2.1 To design a model of the pedicle screw with capability of directional injection.2.2 To compare if there are some differences of the property and mechanics of materials between solid screws and hollow ones,then amend the model and get it into realization.2.3 To evaluate if there are some differences of biomechanics property and determine whether new options can be offered to revisions and augmentations of transpedicular operations or not..2.4 To simulate the directional injection with Fluent and then vertificate in experiments.3.Materials and methods3.1 Designing and modeling of the pedicle screws with capability of directional injection.A new type of hollow pedicle screw with lateral holes was designed with Pro/ENGINEER,a CAD(computer aided design) software.Then a model was established(Concrete steps included sketch,valuation,assignment,finishing semi-section,revolving to create billet,cutting screw threads,extruding and drilling holes,directional marks and etc).Then virtual assembling and moving were performed to find out if the function of directional injection can run and whether there was any mutual interference.3.2 Structural and materials analysis of directional-injection pedicle screws.3.2.1 Computer aided structural analysisFinished model was imported into the module of Pro/MECHANISM and simplified as a projecting beam.Then the model was defined with materials, constrains and loads before divided into meshes and performed with structural analysis.Where stress concentrated or motion contradicted was find out to amend.At the same time,stress and strain distribution of solid and hollow screws has been examined.3.2.2 Manufacturing of the screwsThe screws were made of Titanium Alloys TC4 by STB Surgical implants,LTD. In Foshan.The axial and lateral holes were drilled by DMU 60T high-speed DECKEL MAHO in Guangdong University of Technology. 3.2.3 Material mechanics tests3.2.3.1 Three points bending test10 hollow and 10 solid screws were investigated by material testing machine with three point bending test under the quick loading to 4000N.3.2.3.2 Shear test10 hollow and 10 solid screws were investigated by material testing machine with shear test under the quick loading to 4000N(30N/s).The information was captured and analyzed.Then two sample t-test was performed.3.3 Biomechanical analysis3.3.1 SpecimensSix fresh thoracolumbar spine specimens(5 males,1 femals) were divided into 36 vertebraes and 30were employed.3.3.2 Grouping and implantingAccording to random num table,30 vertebraes were divided into three groups: Control Group(Group C),Augmentation Group(Group A) and Restoration Groups (Group R).Entry point of screws was at the“人”shape crest.3.3.3 Vertebrae embedding and F-max testVertebraes implanted with screws were embedded into rackets with dental base acrylic resin powder before F-max test.Then the peak pull-out forces and Linear Displacements(LD) were recorded.And analysis of variance(ANOVA) test of a randomized block were employed.3.4 CFD simulation and experimental verification for directional injectionA model of directional injection was established with Gambit,and then solved in Fluent.Compression fracture model was employed with MTS.PMMA was injected into the fractured vertebrae via directional screws and then get X-ray photo captured.4.Results4.1 Designing and modeling of the pedicle screws with capability of directional injection. After virtual assembling and moving were performed,there was no mutual interference found out in the defined degree of freedom.The function of directional injection ran precisely.4.2 Structural and materials analysis of directional-injection pedicle screws.4.2.1 Computer aided structural analysisStress concentrated of the model was find out and amended at the end.The curves of stress,strain,strain energy and displacement of solid and hollow screws has been compared but little differences were find out.4.2.2 Material mechanics tests4.2.2.1 Three points bending testNo broken screw was found.The strains of two kinds of screws were just identical(0.17),and no decent curve was recorded in the course of quick loading to 4000N.4.2.2.2 Shear testAll screws broke when the quick loading added up to 4000N(30N/s). Coincidence stress-strain curves of solid and hollow screws were reported by the data. The max shear forces of the hollow and solid screws were(3983.17±10.28)N and (3992.48±9.68)N.There was no significant difference was found between them (t=2.085,P=0.052).4.3 Biomechanical analysis4.3.1 F-max testFor hollow screws,peak pullout forces were(798.24±139.86) N in Group C, (1476.21±223.09) N in Group R,(1741.33±317.79)N in Group A;For solid screws, peak pullout forces were(904.37±212.03)N in Group C,(1828.42±239.68)N in Group R and(1783.37±250.49)N in Group A.The peak pull-out force of Group C was significantly lower than the other two groups(P=0.000),but there was no significant differences between Group R and Group A(P=0.330).For hollow screws,LD were(1.68±0.24)mm in Group C,(3.16±0.70) mm in Group R,(3.13±0.62)mm in Group A;For solid screws,the LD were (1.85±0.37)mm in Group C,(3.43±0.98)mm in Group R and(3.36±0.98)mm in Group A.The LD of Group C was significantly lower than the other two groups (P=0.000),but there was no significant differences between Group R and Group A (P=0.971).4.3.2 About bone cement leakageNo PMMA was found in the vertebral canal or on the surface of pedicle of vertebral arch when PMMA was infused through the hollow screws,while PMMA was easily found in the vertebral canal or on the surface of the pedicle when using solid screws.4.4 CFD simulation and experimental study of directional injectionDirectional injection was simulated by CFD,static pressure and velocity distribution obtained,realized in experiment,vertifieated by X-ray photography.5.Conclusions1.Parametric modeling and real time dynamic simulations with Pro/ENGINEER afforded a precise and Intuitive way to realize the design thinking,directional injection.2.With computer aided engineering(CAE),convenient structural analysis and model revision had been performed.It has been confirmed by theoretical derivation, computer simulation,material mechanics testing,and statistical inference that the strength of hollow screw has no significant difference with the solid ones’.3.PMMA can significantly increase the stabilization of vertebral arch when it is infused in with directional injection screws,which offer a new and safe option for revision.更多还原