【作者】 肖学军；

【导师】 钟世镇；

【作者基本信息】 南方医科大学 ， 人体解剖与组织胚胎学， 2011， 博士

【摘要】 融合固定手术是目前脊柱疾病最主要的治疗方法。随着脊柱融合技术的不断发展与成熟以及在全世界范围的大规模普及,其并发症也逐渐被人们发现和认识。邻近节段病是近年研究比较多的脊柱融合术并发症之一。对邻近节段病的反思和对传统的以融合术为代表的脊柱牢固内固定的质疑最终促成了“非融合技术”等治疗新概念提出和兴起。脊柱后路动力性固定系统出现后,并没有完全解决问题。有关牢固内固定及邻近节段病发生机制的争论仍在继续。争论的焦点在于传统的以脊柱融合术为代表的牢固固定导致邻近节段生物力学状态的变化,目前仍然缺乏直接和足够的生物力学证据：一方面融合的内固定造成的相邻节段生物力学改变没有让人信服的生物力学数据支持,另一方面非融合的内固定在防止ASD中的作用也尚未得到充分肯定。椎间盘退变是脊柱退变的一个重要方面。而对于牢固固定引起其退变的研究结果仍然存在差异甚至相互矛盾。究其原因,与这些研究中采用的测试手段存在不能回避的技术局限有关。因此,内固定术对相邻节段生物力学究竟产生多大的影响和改变依然没有明确的结论,有必要作进一步探究。软骨终板是椎间盘的重要组成部分,起到缓冲外力和传递应力作用。它在椎间盘完成其生物力学功能方面具有非常重要的作用,同时也是椎间盘获取营养的重要途径。软骨终板退变和椎间盘退变密切相关,它在椎间盘退变中扮演了非常重要的角色。软骨终板的退变早于椎间盘的退变,它是一个自然老化的过程,又可因为炎症、异常应力及细胞过多凋亡而加重,加速其退变的过程。软骨终板退变最先出现钙化,随着病变发展,软骨终板可能出现结构的紊乱和细微的裂纹。如果软骨终板因破裂、钙化等因素而引起营养通路受阻,将会直接导致椎间盘因营养供给不足而出现退变。脊柱三维运动的测量,目前仍是体外研究脊柱生物力学特性的主要手段,也是检验内固定器械效果的一个重要指标。Panjabi等早在1977年就摸索了一套行之有效的测量脊柱三维运动的方法。随着测量技术的发展,后人对其进行了不断的改进,脊柱三维运动的测量精度也不断提高。但目前脊柱离体运动测量方面存在的问题是：研究主要以静态测量为主,没有模拟在体的运动环境和运动条件。另外,此方法仅有形态学资料,而缺乏椎间盘内压力方面的数据,不能全面地反映脊柱的生物力学状态。目前的脊柱生物力学研究,大都采用静态或准静态的匀速加载。而人体在日常活动中无时无刻不处于这样或那样的运动当中,脊柱要承受不同频率和不同大小的交变力的作用,在软骨终板上也会产生一系列应力响应。因此,有必要在体外生物力学实验中对脊柱施加交变的动态载荷,测试脊柱在动态外力下的行为,以加深对脊柱生物力学特性的认识。本研究拟利用Tekscan压力分布测量系统,测量牢固内固定及动力性固定两种不同固定方式下腰椎固定邻近节段的终板软骨-骨界面压力分布,通过对其施加一定频率的垂直压缩交变力,观察脊柱在交变载荷下的行为,以期取得较详尽和全面的有关传统牢固固定与动力性固定对脊柱固定邻近节段生物力学影响的资料。同时拟在以激光三维扫描系统获取脊柱在不同内固定条件下六个方向上ROM变化的同时,加入对其邻近节段软骨终板压力分布的测量,以明确在不同运动状态下,脊柱固定邻近节段的运动学和应力分布的关系,从而对传统牢固内固定引起ASD和动力性固定预防ASD的机制提供生物力学资料支持。整个研究从下面两个部分进行：第一部分：不同脊柱后路内固定对腰椎压缩刚度及椎间盘软骨终板压力分布的影响。首先利用小牛标本作预实验,熟悉实验操作及技巧。正式实验选用新鲜人尸体腰椎标本,常规去除肌肉软组织,保留韧带、关节囊后解冻,采用自创方法由椎体侧面开窗,穿凿骨质,仔细显露完整的软骨终板。放置Tekscan压力传感器,以专用压力接受手柄连接电脑系统。测量正常标本的垂直压缩刚度及埋设压力传感器椎间盘软骨终板的压力。然后按设计切除腰3/4节段部分附件、椎间盘纤维环1/2,制成脊柱失稳模型。分别测量标本的压缩刚度及相应椎间盘软骨终板的压力。第三步,分别以威高短节段椎弓根钉棒固定系统和脊柱后路动力固定upass5.5系统固定标本,再次测量标本的压缩刚度及相应椎间盘软骨终板的压力。第四步,将上述标本置于不同频率的交变载荷下,重复前述测量,观察交变载荷对标本压缩刚度及终板压力分布的影响。第五步,比较固定标本头端加载及以刃状器具加载两种方式对实验结果的影响。结果：随着压缩载荷的增加,腰椎标本的压缩刚度也增加。脊柱腰3/4节段不稳模型及行脊柱后路内固定后腰椎标本的整体压缩刚度无明显变化,说明单节段生物力学性质的改变对腰椎整体的压缩刚度无明显影响。在交变载荷下,标本的刚度随着载荷频率的增加而增加。同时椎间盘软骨终板的压力分布的特点：椎间盘软骨终板的压力均与载荷高度相关,两者成线性关系。腰2/3椎间盘软骨终板的压力高于腰4/5椎间盘压力；在空间分布上,压缩载荷作用下,正常椎间盘软骨终板上压力分布大致均衡。脊柱不稳及脊柱后路内固定后标本其上、下位椎间盘软骨终板压力大于正常标本的相应压力,且压力中心有后移趋势。在施加交变的压缩载荷时,椎间盘软骨终板上的压力不但与载荷的振幅有关,而且随着载荷频率的增加而增加。平板加载与刃具加载两种方式对压缩载荷下软骨终板压力实验的结果无明显影响,但标本的刚度及动刚度结果平板加载要高于刃具加载。第二部分：不同脊柱后路内固定下腰椎三维运动与邻近节段椎间盘软骨终板压力分布的关系。将预处理好并在ElectroForce(?)3510高精度生物材料实验机处进行了正常组试验的标本取下,装置于脊柱三维运动试验机的加载盘和试验台上,将标本尾侧包埋块放置于台钳并固定牢固,标本头侧包埋块上固定好三维运动加载盘,将加载盘上的牵引钢丝与三维运动实验仪上的加载钢丝相连,调整好钢丝的长度,根据实验要求,分别将每端4kg砝码挂在三维运动测试仪上相应钢丝上依次对脊柱标本施加8Nm的前屈、后伸、左侧弯、右侧弯、左旋转及右旋转纯力矩,使脊柱作上述相应运动。用激光摄像机摄取零载荷和最大载荷(8Nm)时脊柱运动状态的图像。利用Geomagic studio8.0系统,读取各个激光标志物的位移,代入专门软件,计算出各个节段的运动范围。结果：不稳组的屈伸活动范围远远大于正常组,为正常组的1.8倍。而牢固固定组及动力性固定组的屈伸运动范围则小于正常组,分别是正常组的23.09%和39.56%。动力性固定组的屈伸范围略大于牢固固定组。正常组、不稳组及动力性固定组的前屈范围大于后伸范围,而牢固固定组的屈伸范围相差不大,均远远小于其它各组。侧方运动中,不稳组的侧方活动范围也远远大于正常组,为正常组的1.53倍。牢固固定组及动力性固定组的左右侧弯运动范围则小于正常组,分别是正常组的24.85%和45.66%。动力性固定组的侧弯范围大于牢固固定组。在旋转运动范围测量中：不稳组的左右旋转活动范围亦远远大于正常组,是正常组的2.61倍。而牢固固定组及动力性固定组的左右旋转运动范围则小于正常组,分别是正常组的41.67%和59.30%。动力性固定组的旋转范围略大于牢固固定组。对不同状态下中性区的观察可以看出：正常组的屈伸运动中性区、侧弯运动中性区及旋转运动中性区的活动范围依次减小。不稳组上述三个方向上运动的中性区与正常组相比大大增加,其中以旋转中性区的增加尤为明显,为正常组的5.63倍。屈伸中性区和侧弯中性区也分别是2.65倍和3.68倍。牢固固定组三个方向的中性区较正常组均有大幅减小,其屈伸中性区、侧弯中性区、旋转中性区分别是正常组的14.88%、48.53%、75.85%。而动力性固定组屈伸中性区、侧弯中性区较正常组数值稍有减小,分别是正常组的46.85%、99.02%,而旋转中性区甚至较正常组略有增加,为正常组的110.47%。动力性固定与牢固固定均可大大减少脊柱在各个方向上的运动范围及其相应的中性区,增加脊柱稳定性。与牢固固定相比,动力性固定的各方向运动范围及相应的中性区均稍大,说明它允许脊柱存在一定的活动范围,从而减少邻近节段退变的发生。但从结果看,动力性固定组的各方向运动范围均接近牢固固定组,而远远小于正常组。脊柱后路固定后邻近节段活动范围均稍有增大,不同内固定方式其增加的范围无明显区别。脊柱标本在作三维运动时,其上位及下位椎间盘软骨终板压力的分布相应会发生一系列变化。上位软骨终板的压力高于下位软骨终板；脊柱后伸时压力高于脊柱前屈时压力。终板的后半部分的压力较高,这在脊柱前屈时尤为明显。下位椎间盘软骨终板的压力在侧弯时下降较明显,且压力中心偏向弯曲方向。脊柱在作旋转运动时上位椎间盘软骨终板的压力仍主要集中在终板后半部分,但下位椎间盘软骨终板的压力则较平均地分布在四个象限。脊柱不稳与脊柱后路固定对邻近节段软骨终板压力的影响主要表现在脊柱在作前屈运动时,这时上下位椎间盘压力高于正常组,并伴随有压力中心的改变,而脊柱在作其它方向的运动时,单节段生物力学性质的改变对邻近节段软骨终板压力影响不大。在对比两种方式加载对椎间盘软骨终板压力分布结果影响的研究中,两种加载方式下的结果无明显统计学差异。在对压缩刚度的测量中,平板加载所得数据数值要略高于刃具加载方式,而随着载荷频率的增加,平板加载方式的刚度在5Hz时增加明显,刃具加载方式则较平缓。本研究结论：①在压缩载荷下,较上位的椎间盘软骨终板的压力高于相对下位的椎间盘软骨终板的压力。②在200N到800N的范围内,椎间盘软骨终板上的压力与载荷相正相关,两者呈线性关系③脊柱不稳标本及脊柱后路内固定后标本其上、下位椎间盘软骨终板压力大于正常标本的相应压力,且压力中心有后移趋势。④在施加交变的压缩载荷时,椎间盘软骨终板上的压力不但与载荷的振幅有关,而且随着载荷频率的增加而增加。⑤脊柱在做前屈运动时,脊柱不稳标本与脊柱后路固定标本上下位椎间盘压力高于正常组,并伴随有压力中心的改变。⑥动力性固定与牢固固定均可大大减少脊柱在各个方向上的运动范围及其相应的中性区,增加脊柱稳定性。动力性固定的各方向运动范围及相应的中性区均稍大,说明它允许脊柱存在一定的活动范围,从而减少邻近节段退变的发生。⑦平板加载与刃具加载两种方式对压缩载荷下软骨终板压力的实验结果无明显影响。但标本的刚度及动刚度平板加载要大于刃具加载。更多还原

【Abstract】 Spinal fusion is the most common treatment of degenerative disc diseases. Along with the development and spread of this technique worldwide, its complications have become to be known and studied by people. Adjacent segment diseases are among the mostly researched complications of spinal fusion in recent years.Researches on adjacent segment disease and questioning on the traditional firm internal fixation represented by spinal fusion eventually lead to birth of the concept "non-fusion". But the problems haven’t been solved even after the posterior spinal dynamic stabilization system appeard. Debate about spinal fusion and the mechanism of adjacent segment disease continued. Arguments focus on the lacking of direct and enough biological mechanical evidences that spinal fusion leads to the degeneration of adjacent segments:On one hand, biomechanical changes of adjacent segments caused by spinal fusion didn’t have the support of convincing biomechanical data, on the other hand, the role-of non-fusion spinal fixation in prevention of ASD is not quite clear yet.Intervertebral disc degeneration is an important aspect of spinal degeneration. Yet researches on how fusion causes its degeneration still vary or even contradicted with each other. The reason lies on that the test methods used in these studies have inevitable technical restriction. Therefore, how much of an impact spinal fusion has on the biomechanical behavior of adjacent segments still has no clear conclusion, and further researches are neededCartilage end-plate is an important component of an intervertebral disc, it can buffer forces and pass stresses applied on intervertebral disc, which is very important in spinal biomechanical behavior. It is also the main approach interverbral disc gets nutrients. Degeneration of cartilage endplate is closely related with the intervertebral disc degeneration, it played a very important role in intervertebral disc degeneration, cartilage endplate degeneration occurred before intervertebral disc degeneration. Although cartilage endplate degeneration is a natural aging process, it can be accelerated by excessive inflammation, abnormal stress and cell apoptosis. When degeneration takes place, calcification of cartilage endplate appears first. Along with the development of the disease, disordered structure and micro-cracks appear on cartilage endplate. When the nutrition transportation is blocked because of cartilage end-plate calcification and/or rupture, intervertebral disc degeneration occurs due to insufficient supply of nutrients.Measurement of three dimensional movements of the spine, is still the major means of researches on spinal Biomechanics characteristics in vitro, which is also an important indicator for effects of internal fixations. Panjabi, as early as 1977, pioneered a proven method for measuring three dimensional movement of the spine. With the development of measurement technology, a continuous improvement was made by posterities, precision of this technique continues to increase. But now most of in vitro measurement of the spine is statically, no in vivo environmental condition of the motion are considered. Furthermore, the results are only morphological data, lacking data of pressure inside the intervertebral disc, thus cannot fully reflect the Biomechanics of the spine.Most of current studies on Biomechanics of the spinal columns use static or quasi static loading strategies. But in daily activities human bodies are always on the move in one way or another. Therefore spine is subject to alternating forces of different frequency and amplitude. The cartilage end-plates also response these load. So, it is necessary to impose on the spinal column with alternating dynamic load, testing the behavior of the spine under alternating forces, so that a deeper understanding of the Biomechanics of the spine can be achieved.This research intend measure the distribution of pressure in cartilage-bone interface of segments near lumbar vertebral segment fixed with firm or dynamic posterior spinal fixation using Tekscan pressure distribution measurement system. Imposing a certain vertical alternating compression on the specimen, observe the behavior of spinal column under alternating load, with a view to obtain more detailed and full-scale biomechanical information about effects of traditional spinal fusion and dynamic fixation on adjacent segments. On the same time measure the pressure distribution on the adjacent segments when testing ROM of the specimen, with a view to explicitly understand the relation between pressure distribution and kinematics of adjacent segments under different ROM. Therefore provide information support for comprehension of mechanism how spinal fusion inducing ASD and how dynamic fixation preventing ASD. The study is divided into two parts:1 Effects of different posterior internal fixation on vertical compression stiffness of lumbar vertebra and pressure distribution of intervertebral disc cartilage end-plate.First, pre-experiments are done with calf specimens, and skills in experiment are exercised. Fresh human body specimens of lumbar vertebra are chosen for the experiment, muscle and soft tissue are removed as routine. After Thawed the specimens are excavated on either side of the chosen centrums, following a protocol designed by ourselves. Complete cartilage endplates are exposed. Placing Tekscan pressure sensors, attach them to computer system via a special pressure-reception handlebar. Compression stiffness and pressure distribution of normal specimens are measured. And then models of unstable spine made by resecting part of the posterior annex, posterior 1/2 of annulus fibrosus of L3/4 segment, the same measurements done. And third, short-segment pedicle screw Rod fixation system and posterior spinal dynamic upass5.5 system are applied on the specimens in turn and the same measurements continue. The fourth step, the specimens are placed under alternating loads of different frequency, the measurements before repeated, informations under alternating load obtained. Fifth step, effects of two loading strategy are compared to see if there is any difference between them.Results:With the increase in vertical compression, compression stiffness of lumbar specimens also increases. For unstable model of spine and specimens with posterior fixation the overall compression stiffness of whole specimens has no significant change, illuminating mechanical properties of lumbar column are not affected by structural changes in one segment. For alternating loads, stiffness increases with the increase in loading frequency. About pressure distribution on intervertebral disc cartilage endplate:pressure and load are highly correlated, with a linear relationship between the two. Pressure on cartilage endplate of L2/3 is higher than that of L4/5; on the spatial distribution, under vertical compression loading, pressure on the normal intervertebral disc cartilage endplate is evenly distributed Specimens of instability and posterior spinal internal fixation have a higher pressure with the centers move to rear. When an alternating load applied, pressure on the intervertebral disc cartilage endplate is not only related with the amplitude of the load, but also varys with the frequency of load. Plate loading strategy and blade loading strategy have no difference in results of pressure distribution on cartilage endplate, but as to stiffness and dynamic stiffness, plate loading strategy has a relatively higher outcome.2 Three dimensional movements of spine and the pressure distribution on adjacent segment cartilage endplates under different posterior spinal fixations.Specimens pre-processed are fit on spinal three dimensional movement test machine, caudal sides buried in denture acrylic and fixed on special clamp firmly, cephalic sides of specimens fixed into the loading disc. Loads are applied via steel wire,4kgs on each side. According to experimental design, movements of extension and flexion, left turn and right turn, left rotation and right rotation are performed. Images are taken by laser camera. Use Geomagic studio8.0 system for data reading and processing. Ranges of motions of each segment (ROMs) are obtained.Results:ROMs of flexion and extension in specimens of instability are 1.8 times larger than those of normal group. But firm fixation group and dynamic fixation group have smaller ROMs than normal group, which are 23.09% and 39.56%, respectively. ROMs of dynamic group are slightly larger than those of firm fixation group. Normal group and dynamic fixation group, group of instability have bigger ROMs in flexion than extension, but in firm fixation group, ROMs of flexion and extension are almost the same and much smaller than in other groups. In lateral movements, instability group’s ROMs are much larger than those of normal group, 1.53 times those of the normal group. Firm fixation group and dynamic fixation group bend much less on either side than normal group,24.85% and 45.66%, respectively. Bigger ROMs are found in dynamic fixation group’s lateral bending compared with firm fixation group. In measurements of rotation ranges:instability group are much greater than normal group, are 2.61 times greater than the normal group, while Firm fixation group and dynamic fixation group are less than normal. Observation of the neutral zone under different conditions shows that:in normal group, the neutral zones of extension and flexion, bending, rotation become smaller in turn. All these neutral zones greatly increased in instability group compared with those in the normal group. Firm fixation group’s neutral zones substantially decreased compared with normal group, with their flexion extension neutral zone, bending neutral zone, rotation neutral zone 14.88%,48.53%,75.85% that of normal group, respectively. Dynamic fixation has slightly reduced neutral zone compared to normal group.Dynamic fixation and firm fixation can greatly reduced the ranges of motion of the spine in all directions and the neutral zone, increasing the stability of spine. Compared with firm fixation, dynamic fixation has a larger ROM in all directions, thus it allows the spine has a range of activities, so as to reduce the possibility of adjacent segment degeneration. But from the results, we can see dynamic fixation group’s ROMs are very close to firm fixation group, and far less than normal.After spinal posterior fixation, the ROMs of adjacent segments are slightly increased, no significant difference found between two internal fixation groups.When three dimensional movements of the specimens are tested, the pressure distribution on upper and lower intervertebral discs cartilage endplates are measured. In flexion of the spine, pressure on upper and lower cartilage endplates of spinal instability specimens and posterior fixation specimen is higher than that of the normal group, accompanied by change of pressure center. In extension, bending and rotation position, no effects are found of posterior internal fixation on endplate pressure.Results of pressure distribution on cartilage endplate obtained by two different Loading strategies are almost the same. As to pressure distribution on cartilage endplate of L2/3, results obtained by blade loading strategy are slightly higher, but no significant differences are found. when come to compression stiffness measurements, results obtained by plate loading strategy are slightly higher, with the increasing of loading frequency, the stiffness of plate loading group increases quickly while the result is more gentle when applied with blade.Conclusions:①Under the vertical compressive loading, pressure on upper cartilage endplate is higher than that on the lower one.②When load is less than 800N, pressure on intervertebral disc cartilage endplate is closly linear related to load.③In an unstable or posteriorly fixed specimen, higher pressure on upper and lower intervertebral disc cartilage endplate can be found, with pressure center tending to move backward.④When alternating compression load applied, pressure on intervertebral disc cartilage endplate is not only correlated with amplitude, but also varies with the changes of frequency.⑤When flexion of the specimens are tested, the pressure on upper and lower intervertebral disc cartilage endplate in instability group and posterior fixation group is higher than that on normal group, with transfer of pressure center.⑥Dynamic fixation and firm fixation can greatly reduce the ranges of motions of the spine in all directions and the neutral zones, increasing the stability of spine. dynamic fixation has larger ROMs in all directions, thus it allows the spine has a range of activities, so as to reduce the possibilities of adjacent segment degeneration.⑦Results of pressure distribution on cartilage endplate obtained by two different Loading strategies have no significant difference, but plate loading strategy has a higher stiffness or dynamic stiffness outcome compared with blade loading strategy.更多还原