【作者】 于博；

【导师】 靳安民；

【作者基本信息】 南方医科大学 ， 骨外科学， 2009， 博士

【摘要】 研究背景和目的腰椎融合术是处理腰椎间盘源性痛、节段性不稳、滑脱等疾患的主要手段,虽然内固定的应用使融合率和临床结果有很大改善,但与此相关的问题仍然不少。目前普遍认为,脊柱部分节段融合术后,可增加邻近融合节段的应力,加速其退变过程。放射学上表现为椎间盘变性或突出、椎间隙狭窄、椎体或小关节骨质增生、节段性失稳或滑脱,严重者可出现椎管狭窄。邻近节段退变的发生率随患者手术后时间的延长而逐渐增加。因此,脊柱动态性内固定（半坚强固定、柔性固定、弹性固定,PDS:posteriordynamic stabilization）的概念被提出并逐渐在国际上得到承认。所谓动态固定系统就是在坚强固定融合的情况下,帮助脊柱运动节段运动和改变负荷传递的内固定系统,其目的是改变运动节段承载负荷的方式,控制节段间的异常活动,这意味着动态固定通过控制异常活动并允许更多的生理性负荷传递缓解疼痛和预防邻近节段退变。一旦恢复正常的运动和负荷传递,只要椎间盘退变的进程不是特别迅速,椎间盘就有可能在动态系统的保护下得到自身修复。目前有多种动态固定系统应用于临床,包括棘突间分离装置（主要有X-STOP、Wallis系统,Minns硅胶系统）、棘突间韧带装置、椎弓根间韧带装置、半坚强及弹性椎弓根间金属固定装置等等。由于具有独特的形状记忆效应和超弹性,镍钛合金目前被广泛的应用于牙齿矫正、血管支架、骨科矫形钉等。其独特的形状记忆效应能够在特定的温度下维持一种形状,当温度下降到特定的临界温度后,其可以变得可以任意塑形,当温度再次加热到趟过临界温度后,其可以自然回复原状;同时,它的另外一个独特的优势是具有良好的超弹性,在一定的形变范围内,可以维持恒定的弹性。镍钛合金具有良好的耐疲劳、抗腐蚀性能,组织相容性很好,对人体毒性小,是一种十分理想的生物功能材料。不仅在材料特性和力学性能上具有优越性,在临床操作上也极为简单方便,同时具有十分大众化的价格优势。镍钛形状记忆合金以其优良的形状记忆效应、超弹性和生物组织相容性在骨科领域得到越来越广泛的应用。近年来,脊柱外科飞速发展,脊柱内固定器械层出不穷,对于极具发展潜力的生物医用材料-镍钛记忆合金备受关注。我科曾对记忆合金节段脊椎内固定器做了深入系统的研究,并成功的应用于腰椎峡部的手术治疗中,记忆合金节段内固定器近似C形,经冰水浸泡后变软而易于操作,复温后,记忆合金形态向其母相回复,产生巨大的回复力,将椎体及椎板牢固地固定在一起,同时将植骨块压向峡部,能对峡部持续稳定地加压,且能随着活动度的增加而增大固定力,不需另行固定,临床应用中具有手术创伤小,方便快捷,后期器械取出也方便等特点,取得了十分满意的临床效果。在进行的相关生物力学实验中表明,峡部裂腰椎接受固定后,其各向稳定性得以明显恢复,接近正常腰椎。基于以上理论和在前期记忆合金研究的基础上,本研究拟将自行研制的镍钛记忆合金棒与钛合金椎弓根钉相结合组成生物弹性内固定系统,本系统具有如下特点:1内固定系统的设计遵循腰椎的解剖与生物力学特点,充分运用记忆合金棒本身和“U”型结构体现的弹性,在材料特性和力学性能上具有优越性,具有一定的弹性变形能力,不仅起到坚强固定,而且有弹性固定作用,能避免单纯刚性固定的一系列缺陷,2内固定系统结合椎弓根钉技术,完成脊柱三维固定,内固定牢靠;3内固定系统在临床操作上极为简单方便,同时具有十分大众化的价格优势,系统在国内外文献未见类似设计报道,具有一定的先进性和创新性。腰椎退行性疾病是脊柱外科的常见、多发病。随着步入老年社会,患病群体在逐年扩大。镍钛合金腰椎椎弓根弹性内固定作为一种新型的弹性内固定系统具有良好的疾病人群,该项装置兼顾腰椎的稳定性和活动性,无需植骨融合。此外,该金属由无毒元素构成,生物相容性好,无需再次手术取出,具有独立知识产权的国产产品在价格上也会具有一定的优势。产品兼顾简易、安全、耐用、便宜的优点使患者更易于接受。上述优点将使该系统具有广泛的临床应用前景。本研究共分为四部分:第一部分腰椎弹性内固定系统的设计目的:传统观念认为,脊柱融合术是下腰痛和腰椎不稳的主要治疗方法,随着生物学技术（包括骨形态发生蛋白和椎弓根螺钉固定技术等）的出现,融合率可以达到90-100%。然而,虽然目前融合率不断的提高,但临床疗效却没有相应改善。同时,目前有证据发现融合会加重临近节段的生物力学负荷,导致一部分行融合术后的病例发生临近节段的病变。这些问题的发生使科研人员寻找稳定腰椎的新方法。其中一种方法就是动态内固定,或者软固定。随着NiTi记忆合金材料在医学领域的广泛应用和不断拓展,其独特的超弹性性能及较好的形状记忆的特点使其在脊柱外科中的应用取得了较好的效果,如脊柱畸形矫正及腰椎峡部裂节段内固定等,本研究拟根据脊柱动态内固定的理论,利用镍钛合金的超弹性设计一种记忆合金棒与钛合金椎弓根钉相结合组成生物弹性内固定系统,该系统能够维持脊柱固定节段较好的弹性性能,能避免单纯刚性固定的临近节段退变等一系列缺陷,提高临床治疗效果。设计理念:该内固定器由两组组件组成,每一组组件包括一连接腰椎相邻两节段的构件和将该构件两头固定于腰椎弓上的自攻螺钉,构件为棒状,其中部弯曲构成一个或两个U形的弯部。内固定器遵循椎体的解剖与其在整个脊柱中的力学特点,采用钉棒结构的设计思想,时将棒状构件的中部弯曲成U形的弯部,从而大大改善了棒状构件效果,使整个内固定器在三维空间内都具有良好的弹性效果。结果和结论:我们利用NiTi记忆合金的形状记忆效应和超弹性特征,根据腰椎退变性疾病病理生理状况和腰椎椎弓根内固定思路,我们能够设计出较为满意的“U”型弹性内固定系统,设计思路符合腰椎弹性内固定理念,预计可有效避免目前传统的内固定系统的缺点。第二部分NiTi合金“U”型弹性内固定系统有限元模型的建立及力学分析目的:在NiTi合金“U”型弹性内固定器二维平面设计的基础上,利用计算机软件进行三维模型建立,并对其进行有限元力学分析,进而评价初始设计的合理性,提高NiTi合金腰椎“U”型弹性内固定器的设精度,简化和节约制作成本。方法腰椎“U”形弹性内固定系统的连接棒中段设计为“U”形,采用的材料为上海钢铁研究所医用镍钛记忆合金,镍含量为50.8 at%—51.8 at%,余为钛,弹性模量（马氏体态）达到71400MPa,并委托中科院金属研究所加工制作:椎弓根螺钉为钛合金材料,整个螺钉设计为向下的锥型,相对螺钉的根径从远端至近端逐渐增粗,螺纹宽度一致,螺纹深度从钉尖向上逐渐变浅。选择一名成年男性志愿者,以腰4,5节段为研究对象,采用螺旋CT对其进行层厚1.0 mm的连续水平扫描,借助Mimics11.11软件,建立L4,5节段三维非线性有限元模型。同时根据椎弓根螺钉、连接棒的几何尺寸及力学参数分别添加螺钉和连接棒模型,建立腰椎“U”形弹性内固定的三维有限元模型,分别施加垂直压缩、前屈、后伸、侧屈及旋转等各种生理载荷,对不同载荷下模型各部分的应力进行观察和分析。结果借助Mimics11.11软件,我们成功的建立了腰椎“U”型弹性内固定系统的三维有限元模型,对模型施加生理载荷后,弹性内固定系统各部分于垂直压缩时所受应力小于其它状态(主效应:F_Part=397.771,P_Part=0.000;F_Movement=158.471,P_Movemet=0.000;交互效应:F_{Pan×Movement}=52.147,P_{Part×Movement}=0.000。);不同载荷下应力主要分布在“U”形弹性棒上,螺钉各部受力较为均匀。结论腰椎“U”形弹性内固定器设计独特,能减少术后应力遮挡及椎弓根螺钉应力集中,有望成为腰椎内固定较好的一种装置。第三部分腰椎弹性内固定系统与刚性内固定的应力比较研究目的:通过有限元的方法比较自行研制的腰椎“U”型弹性内固定器与传统的刚性内固定器之间的应力分布差异。方法选择一名成年患者腰椎标本,以L4/5节段为研究对象,采用64排螺旋CT对其进行层厚1.0 mm的连续水平扫描,将所得图像进行轮廓提取和阈值分割后,借助三维重建软件Mimics 11.1、Simpleware和有限元软件Abaqus 6.51软件,建立L4,5节段三维非线性有限元模型。同时根据椎弓根螺钉、连接棒的几何尺寸,力学参数,分别建立两种不同内固定器的有限元模型。然后分别施加压缩、前屈、后伸、侧屈及旋转等各种生理载荷,观察各模型不同载荷下螺钉、连接棒的应力分布。结果两种内固定器的应力差异有统计学意义(主效应:F_分组=179.238,P_分组=0.000;F_Part=1064.772,P_Fart=0.000。交互效应:F_分组×Part=68.934,P_分组×part=0.000。),刚性固定的椎弓根螺钉与棒连接处是应力集中的部位,该部位的应力远大于弹性固定器,而弹性内固定应力“U”型连接棒最大,两模型固定节段螺钉及棒的最大有效应力均出现于前屈时。结论在加载相同的纵向载荷条件下,刚性内固定器应力主要集中在螺钉与棒交界处,容易易发生螺钉断裂,“U”型弹性内固定器的应力均匀分布在“U”型连接棒上,可以减少断钉的现象发生。第四部分腰椎弹性内固定棒的有限元研究目的:我们自行研制了“U”型镍钛记忆合金棒与钛合金椎弓根钉相结合组成生物弹性内固定系统,拟通过有限元的方法进一步评价“U”型镍钛记忆合金棒的力学特点。方法:电脑硬件配置:P4 3.0 GHz双核超线程CPU,4GDDR800内存,6800GT双128 M PCIE图形加速卡。建模方法:对“U”型记忆合金棒进行螺旋CT扫描,层距1mm,由螺旋CT机USB接口直接提取图像,保存为BMP灰度图。利用Matlab6.0提取图片中轮廓线数据矩阵,转换为dat文档后输入ANSYS8.0建模。赋予单元材料特性（“U”型记忆合金棒弹性模量E=71400 MPa,泊松比μ=0.33）。然后利用ANSYS8.0软件自适应划分网格,根据分析问题的具体需要,预估计应力/应变变化大的区域或需仔细了解的区域,网格划分较其他区域细致,预估计应力/应变变化小的区域或不作要求的区域,网格划分较其他区域粗糙。实验中“U”型记忆合金棒的三维有限元模型共划分了8 456个单元,65 246个结点。模型分别施加压缩、前屈及拉伸等各种生理载荷,观察各模型不同载荷下弹性内固定器的应力分布,并与传统的钛合金内固定棒进行比较。结果:成功建立了“U”型弹性内固定棒的有限元模型,可以预测内固定棒在变形过程中其本身结构中各节点、单元的受力、位移情况。在垂直压缩、前屈和后伸状态下内固定棒应力分布合理,在3种状态下应力集中的部位主要在“U”型弹性内固定棒的中部。结论:在加载相同的纵向载荷条件下,U型弹性内固定器的应力分布在U型连接棒的“U”型区上,应力应变曲线表现出较好的弹性作用,该内固定棒可能成为治疗下腰痛的新型节段内固定棒。更多还原

【Abstract】 BackgroundFor the treating of the degenerative disc disease,open surgical intervention and fusion are main techniques to stabilize the spinal column.Advancements in technology have added to the surgeon’s fusion rate and the clinical result,however, there are also some problem related to the fusion.It is widely accepted that,after the fusion,the discs in adjacent segments may also become affected a few years after surgical fusion of a degenerated disc.It is casually hypothesized that the load reduction of a slightly degenerated disc may postpone fusion surgery and adjacent disc disease.Several flexible posterior spinal fixation systems are clinically used.These so-called dynamic stabilization devices are designed to reduce the disc load.In contrast to solid fusion,the non-fusion systems are intended to maintain intersegmental motions or reduce them to magnitudes found in the intact spine.There have been a number of dynamic stabilization devices trialed in lumbar spinal disease, many with differing biomechanical principles.Some examples include the interspinous implants;the Graf Ligament,the Dynesis Spinal System(Zimmer Spine, Warsaw,IN),and the FASS system(AO International,Davos,Switzerland),all of which are pedicle screw based.Because of the shape memory and superelastic property,At present,the shape memory nickel-titanium alloy is clinically used in wires for orthodontic tooth alignment,vascular applications,osteosynthesis staples.The nickel-titanium alloy has a unique shape-memory phenomenon,which can memorize a particular shape at a particular temperature,when it was cooled below a transformation temperature,the alloy becomes malleable,and the shape can be changed.However when it is reheated to above the transformation temperature,the original shape is restored.Another unique characteristic of nichel-titamium alloy is its superelasticity,in which, regardless of whether the material is under loading or unlading,and within a range of deformation,the recovery force produced is constant.NiTi shape alloy also has excellent biocompatibility,corrosion resistance and fatigue endurence.It not only has the biomechanical superiority over the other material,the clinical usage is also very easy.Because of its special properties,the nearly equiatomic nickel-titanium alloy is widely used in the orthopaedics field.Recently,with the spinal surgery developing very fast,more and more spinal instruments came into use,and so much attention,was payed to the NiTi alloy.In recent years,our department have reported an original technique using a "C" shape nickel-titanium alloy intrasegmental fixation instrument for spondylolysis repair and have used the device in the spondylolysis patients successfully.Because the alloy can become malleable and the shape can be changed in the cold condition of 0±4℃,it can be fixed on the spondylolisis vertebrae, when the temperature was up to 37℃of the human body temperature,the shape-memory effect of the instrument was activated and the par defects can be fixed by the constantly stress of the shape-memory effect.The biomechanical study showed that after the "C" shape nickel-titanium alloy intrasegmental fixation instrument was fixed to the spondylolysis specimen,the biomechanical property is similar to the intact spine.Based on the above theory and the NiTi alloy study before,this study planed to invent an original technique using a "U" shape nickel-titanium alloy stick and titanium pedicle screw to form a dynamic fixation instrument for degenerative disc disease.We hepothesis that the "U" shape lumbar dynamic fixation instrument may have the following characteristics:1 the shape of the instrument abides by the mechanical characteristics of the lambar spine.Superimposing the shape-memory material,the instrument can produce stable and persistent elastic strength for the lumbar fixation segment.2 It is three-dimension fixation,which makes the fixation firm,avoiding the chance of gliding and shedding of the fixation instrument.3 The operative procedure is simple.It is a simple,safe,time-saving and labor-saving procedure.This study was divided into 4 part:PARTⅠ:Design of the "U" shape lumbar fixation device from NiTi alloyObjective:Traditionally,spinal fusion has been the mainstay of surgical approaches to the management of low back pain or lumbar instability.Advances in biomedical technology,including pedicle screw fixationl and bone morphogenic proteins,have enabled surgeons to achieve fusion rates between 90%and 100%. However,despite the improvement in radiographic fusion rates,there are some authors who think that there has not been a corresponding improvement in clinical outcomes.Furthermore,there is some evidence that fusion may increase the biomechanical stresses imposed on the adjacent segments leading to transitional disease,which may occur at an earlier rate in instrumented fusion cases.These issues have led some investigators to explore novel approaches to "stabilize" the lumbar spine.One such concept is that of "dynamic stabilization," or "soft stabilization." Dynamic stabilization has been defined as:"a system that would alter favorably the movement and load transmission of a spinal motion segment,without the intenvention of fusion of the segrnent."In other words,such a system would restrict motion in the direction or plane that produces pain,or painful motion,but would otherwise allow a full range of motion.Recently,the use of NiTi shape memory alloy in medical field is more and more extensive.In order to find a new way to treat the degenerative disc diseases,we attempted to utilize the characteristics of hyper-elasticity and shape memory effect of NiTi alloy and attempted to design a new dynamic fixation system.The design concept:The dynamic fixation system include the pedicle screws,which can fix to the pedicle of the lumbar vertebral and the sticks,which can connect the pedicle screws.the middle part of the stick is bend to a "U" shape.The dynamic fixation system abide by the anatomy and biomechanical character of the lumbar spine.the design adopt screw and stick binding concept,bending the middle part of the stick to a "U" shape can make the stick a good flexible effect.Conclusion:By using the super-elastic and shape memory feature of the NiTi alloy,and based on the pedicle screw fixation concept,we can design a "U" shape dynamic fixation system.We assume this system can avoid the disadvantages of the traditional fixation system.PartⅡ:Finite element analysis OF the "U" shape lumbar dynamic fixation systemObjective To evaluate the biomechanical properties of the "U" shape dynamic fixation system for lumbar with finite element method.Method The L4,5 motion segment data were obtained from CT scans(at 1 mm width increments) of the lumbar spine of an adult man.After these images were processed,a three-dimensional finite element model of the L4,5 was established by Mimics11.11.Meanwhile,the three-dimensional finite element model of the vertebral pedicle screw and "U" rod were established by Mimics11.11.According to the above mentioned,the L4,5 model was combined with the model of the vertebral pedicle screw and "U" rod,and established the three-dimensional finite element model of the L4,5 "U" shape dynamic fixation.Loads used in this study were axial compressive,flexion,extension,lateral bending,and rotation forces.The distribution of von mises stress of the fixation segment were analyzed and compared.Result In the same shearing load of 500 N,the stress of the"U" shape dynamic fixation system was lower at axial compressive than flexion,extension,lateral bending,and rotation forces(P＜0.001).The stress of the "U" shape dynamic fixation system for lumbar mainly concentrated on the "U" shape elastic rod,and the stress distribution of the vertebral pedicle screw was comparatively uniform. Conclusion The "U" shape dynamic fixation system has a unique design, which can reduce the stress block and stress concentration of the vertebral pedicle screw,may be a better fixation instrument for the lumbar degenerative disease.PartⅢ:Biomechanical comparison between the "U" shape lumbar dynamic fixation system and traditional fixation systemObjective:To compare the biomechanics features between a new "U" shape lumbar dynamic fixation system and traditional rigid fixation system.Method:Finite element analysis of the two fixation system were created on the basis of a three-dimensional model reconstructed from the images of CT scanning of an adult cadaveric lumbar at 1 mm interval.The stress and displacement of every nodule and element in the course of deformation of the internal fixation were tested.Result:In the same shearing load of 500 N,The force of the dynamic fixation system was concentrated on the "U" shape elastic zone,The force of the rigid fixation system was concentrated on the posterior 1/3 of the lower screw.Conclusion:We demonstrates the new "U" shape lumbar dynamic fixation system has a totally different biomechanical property compare to the traditional rigid fixation system.This dynamic fixation system may be a choice to replace the rigid fixation system for the lumbar degenerative disease.PartⅣ:Finite element analysis of a "U" shape lumbar dynamic fixation stickObjective:To evaluate the biomechanics features of a new "U" shape lumbar dynamic fixation stick.Method:Finite element analysis of the "U" shape stick were created on the basis of a three-dimensional model reconstructed from the images of CT scanning.The stress and displacement of every nodule and element in the course of deformation of the stick were tested. Result:In axial compression,extension and flexion load of 300 N,The force of the dynamic stick was concentrated on the "U" shape elastic zone.Conclusion:This article demonstrates the "U" shape stick has a good biomechanical property.This dynamic fixation system may be a choice to replace the rigid fixation system for the lumbar degenerative disease.更多还原