The importance of the endplate for interbody cages in the lumbar spine

Intervertebral cages in the lumbar spine represent an advancement in spinal fusion to relieve low back pain. Different implant designs require different endplate preparations, but the question of to what extent preservation of the bony endplate might be necessary remains unanswered. In this study the effects of endplate properties and their distribution on stresses in a lumbar functional spinal unit were investigated using finite-element analyses. Three-dimensional finite-element models of L2-L3 with and without a cage were used. An anterior approach for a monobloc, box-shaped cage was modelled. The results showed that inserting a cage increased the maximum von Mises stress and changed the load distribution in the adjacent structures. A harder endplate led to increased concentration of the stress peaks and high stresses were propagated further into the vertebral body, into areas that would usually not experience such stresses. This may cause structural changes and provide an explanation for the damage occurring to the underlying bone, as well as for the subsequent subsidence of the cage. Stress distributions were similar for the two endplate preparation techniques of complete endplate preservation and partial endplate removal from the centre. It can be concluded that cages should be designed such that they rely on the strong peripheral part of the endplate for support and offer a large volume for the graft. Furthermore, the adjacent vertebrae should be assessed to ensure that they show sufficient density in the peripheral regions to tolerate the altered load transfer following cage insertion until an adequate adaptation to the new loading situation is produced by the remodelling process.     

The biomechanical influence of anterior vertebral body osteophytes on the lumbar spine: A finite element study

BACKGROUND CONTEXT

Anterior vertebral body osteophytes are common with degeneration but their biomechanical influence on the whole lumbar spine remains unclear.

三种椎间融合器对腰椎节段即时稳定性影响的三维运动研究

目的 比较3种不同类型的后路腰椎椎间融合器的生物力学稳定性。方法 采用8具人尸体新鲜腰椎3、4节段标本，模拟后路双侧植入3种椎间融合器。实验分4组7个状态：①对照组(完整标本，Intact)，②螺纹状融合器组(Interfix)，③空心箱形融合器组(syncage)，④实心箱形融合器组(Prospace)，后3组再分别固定椎弓螺钉钢板。随机安排每个标本的融合器植入顺序。在脊柱三维运动试验机上测试不同状态的三维六个方向上的运动范围。结果各融合器的前屈运动范围与完整状态相比具有统计学差异(P＜0．01)；不同融合器之间则无明显差异(P=0．17)。在后伸运动上，各融合器组较完整状态组以及各融合器之间均无明显差异(P=0．25)。侧屈方向，各组融合器的植入均明显提高了稳定性(P＜0．01)，不同融合器之间未表现有明显差异(P=0．15)。不同融合器组在旋转运动时的ROM均较完整状态明显增加(P＜0．01)，同时Intemx组与其它2组融合器之间也有统计学差别(P＜0．01)，Prospace和synCagej之间则无明显差异(P=0．58)。后路崮定椎弓螺钉钢板后，腰椎各向ROM值均较单纯的融合器固定组显著降低(P＜0．01)。结论 3种融合器之间在除外旋转运动的所有方向的稳定性无统计学差异：单独运用3种椎间融合器均无法在所有方向上达到与完整节段一致的生物力学稳定性，结合使用后路椎弓螺钉钢板后腰椎节段的稳定性可明显提高。     

Effect of disc degeneration on the mechanical behavior of the human lumbar spine: a probabilistic finite element study

BACKGROUND CONTEXT

Intervertebral disc degeneration has been subject to numerous in vivo and in vitro investigations and numerical studies during recent decades, reporting partially contradictory findings. However, most of the previous studies were limited in the number of specimens investigated and, therefore, could not consider the vast variety of the specimen geometries, which are likely to strongly influence the mechanical behavior of the spine.

Influence of geometrical factors on the behavior of lumbar spine segments: A finite element analysis

Summary The main objective of this study was the assessment of the influence of geometrical factors on the behavior of lumbar segments. To this end, a three-dimensional, parameterized, finite element model of the lumbar spine was used, and the results were compared with in-house experimental results and with the few published experimental results available concerning either the geometry of the tested samples or the differences observed at different vertebral levels. Furthermore, in order to appreciate the relative importance of the geometry, the influence of the variation of some other parameters was studied, such as the orientation of the facet joints, the gap between the articular processes, and the Young's modulus of the disk fibers. As a first approach, a series of computations was carried out in order to evaluate the role of geometry in the mechanical behavior differences observed at different levels. It has been found that geometrical factors do exert a noticeable influence on the behavior of the spine, especially those which interfere with the dimensions of the intervertebral disk.     

腰1椎体应力的有限元分析及分区

目的:利用有限元分析法研究在不同等级载荷及不同运动状态下腰1(L1)椎体皮质骨及松质骨的应力分布情况,并建立应力分区。方法:选取1例志愿者行胸腰段CT平扫,获取CT原始数据以DICOM导入Mimics、Geomagic、SoliderWorks、HyperMesh、Abaqus等有限元软件,构建正常胸腰段椎体(T11～L2)模型,在T11椎体上缘均匀施加力学载荷,将在载荷500N、弯矩7.5N·m下产生的所有运动状态称为α组,载荷600N、弯矩7.5N·m下产生的所有运动状态称为β组,载荷700N、弯矩7.5N·m下产生的所有运动状态称为γ组。选取L1椎体,从矢状面观正中分割分为上下两部分,上半部分标记为A区,下半部分标记为B区;从椎体正中央至椎体边缘呈同心圆均匀划分6段,上下各构成三维圆弧柱形6部分,从外缘到中央依次标记为1、2、3、4、5、6区,构成A1、A2、A3、A4、A5、A6、B1、B2、B3、B4、B5、B6区域共12部分;分别在α、β、γ三组中均匀采集上述12区域内皮质骨及松质骨应力数据,对皮质骨及松质骨相邻区域内应力值进行两两配对t检验,将差异具有统计学意义的两相邻区...     

腰椎后外侧融合椎弓根钉对相邻节段椎间盘影响的三维有限元分析

目的利用三维有限元法分析腰椎不同运动状态时椎弓根钉的置入位置对邻近节段椎间盘应力的影响。方法利用三维建模软件建立正常人有效性腰骶椎(L_3~S_1)模型。根据椎弓根钉在椎体的位置,分别建立融合模型A、B、C。并根据不同工况对这3种模型施加相应的预载荷及扭矩,分析比较不同腰椎轴向运动时相邻节段椎间盘应力的变化情况。结果成功建立正常有效的L_3~S_1三维有限元模型及椎弓根钉棒系统融合固定三维有限元模型。在后伸状态下,模型A的L_3/L_4椎间盘应力明显增加,而模型B、C较融合前无明显变化;在侧曲状态中,模型B、C的L_3/L_4椎间盘应力变化不大,而模型A显著增加;在其余状态中,3个模型的L_3/L_4椎间盘应力均升高,其中以模型A增加最为明显。3个模型在所有状态下L_5/S_1椎间盘的应力均较融合前略有升高,其中模型B、C应力的变化小于模型A。结论椎弓根钉尖端位于椎体上1/3区域会显著增加融合节段上位邻近椎间盘应力,进而引起相邻节段退变;腰椎融合术不会明显增加邻近下位椎间盘的应力。     

经Coflex固定下腰椎不同节段后的椎间盘

目的 ：模拟临床术式,经Coflex分别固定下腰椎L4,5、L5S1节段,分析其手术节段及邻近节段椎间盘生物力学的差异性。方法：建立下腰椎及Coflex应用于下腰椎的3组有限元模型（完整下腰椎、Coflex固定腰椎L4,5及L5S1节段）。根据脊柱三柱加载理论,模拟下腰椎直立、前屈和后伸3种生理状态下,比较分析纤维环不同区域的应力大小、椎间隙背侧高度变化及髓核内压水平。结果：在直立和后伸工况下,Coflex分别植入L4,5、L5S1节段,均能减少其手术节段纤维环后区应力,限制椎间隙高度变化,并且降低髓核的应力水平。在后伸工况下,Coflex植入L4,5节段可降低L5S1节段的椎间盘应力水平,但Coflex植入L5S1节段不改变L4,5节段椎间盘应力大小。结论：Coflex固定L4,5、L5S1节段均能减少本手术节段椎间盘负载。另外,Coflex固定L4,5节段,起到降低L5S1节段椎间盘负载的生物力学效果。     

退变性椎间盘应力分布变化的有限元分析

【摘要】 目的：分析退变性腰椎间盘在不同生理载荷下应力分布的变化情况。方法：建立正常人体L3~S1三维有限元模型及L4/5椎间盘退变模型,导入Ansys软件进行分析,在L3椎体上表面施加500N压力模拟轴向压缩,施加10Nm的力矩模拟腰椎前屈、后伸、侧屈和旋转等各种生理载荷,测量不同载荷下正常与退变椎间盘不同部位的应力,分析退变椎间盘应力分布变化的情况。结果：正常椎间盘垂直载荷时椎间盘应力集中于椎弓根附近,应力最大的分区中压力为29.649N;各种屈曲位时,屈曲侧应力较高,分区中压力最高为59.514N,向对侧逐渐减少,拉力最高为32.686N。相同载荷下,退变椎间盘应力分布发生了变化,髓核压力由45.170~55.308N降至5.471~8.046N;纤维环压力增加,内层纤维环由80.379~95.923N增加至98.898~120.557N,中层纤维环由107.160~140.983N增加至118.549~156.827N,外层纤维环由160.872~204.867N增加至169.302N~216.298N。结论：椎间盘退变后其髓核和纤维环的应力分布会发生变化,在总应力变化不大的前提下,髓核所受应力明显减小,而纤维环所受应力则相应增加,尤以内层和中层纤维环为主。这可能是椎间盘突出和椎间盘源性腰痛的原因之一。     

Comparison of the effects of bilateral posterior dynamic and rigid fixation devices on the loads in the lumbar spine: a finite element analysis

A bilateral dynamic stabilization device is assumed to alter favorable the movement and load transmission of a spinal segment without the intention of fusion of that segment. Little is known about the effect of a posterior dynamic fixation device on the mechanical behavior of the lumbar spine. Muscle forces were disregarded in the few biomechanical studies published. The aim of this study was to determine how the spinal loads are affected by a bilateral posterior dynamic implant compared to a rigid fixator which does not claim to maintain mobility. A paired monosegmental posterior dynamic implant was inserted at level L3/L4 in a validated finite element model of the lumbar spine. Both a healthy and a slightly degenerated disc were assumed at implant level. Distraction of the bridged segment was also simulated. For comparison, a monosegmental rigid fixation device as well as the effect of implant stiffness on intersegmental rotation were studied. The model was loaded with the upper body weight and muscle forces to simulate the four loading cases standing, 30° flexion, 20° extension, and 10° axial rotation. Intersegmental rotations, intradiscal pressure and facet joint forces were calculated at implant level and at the adjacent level above the implant. Implant forces were also determined. Compared to an intact spine, a dynamic implant reduces intersegmental rotation at implant level, decreases intradiscal pressure in a healthy disc for extension and standing, and decreases facet joint forces at implant level. With a rigid implant, these effects are more pronounced. With a slightly degenerated disc intersegmental rotation at implant level is mildly increased for extension and axial rotation and intradiscal pressure is strongly reduced for extension. After distraction, intradiscal pressure values are markedly reduced only for the rigid implant. At the adjacent level L2/L3, a posterior implant has only a minor effect on intradiscal pressure. However, it increases facet joint forces at this level for axial rotation and extension. Posterior implants are mostly loaded in compression. Forces in the implant are generally higher in a rigid fixator than in a dynamic implant. Distraction strongly increases both axial and shear forces in the implant. A stiffness of the implant greater than 1,000 N/mm has only a minor effect on intersegmental rotation. The mechanical effects of a dynamic implant are similar to those of a rigid fixation device, except after distraction, when intradiscal pressure is considerably lower for rigid than for dynamic implants. Thus, the results of this study demonstrate that a dynamic implant does not necessarily reduce axial spinal loads compared to an un-instrumented spine.     

不同载荷下腰1椎体内应力分布规律的有限元分析

目的:观察腰1(L1)椎体在不同载荷作用下椎体内应力分布情况,探讨其应力分布规律及临床意义.方法:选取1例27岁健康男性志愿者,以层厚1 mm进行T12～L2脊柱节段CT扫描,将原始数据存盘.运用3D软件、Auto CAD系统及ANSYS 6.0有限元软件建立正常人体胸腰段(T12～L2)运动节段的三维有限元模型.在T12椎体上表面施加不同等级的压力(400N、600N、800N、1000N、1200N),模拟脊柱的轴向压缩载荷;在T12椎体上表面施加不同等级压力(400N、600N、800N、1000N、1200N)的同时再施30N·m的弯矩,模拟脊柱的屈曲压缩载荷.将连接L1椎体上下终板凹面最低点的连线7等份,在此基础上将T1椎体中的松质骨划分为7个具有统计节点的层面,每个统计层面划分成9个统计区(椎体前部A1、A2和A3区,椎体中部M1、M2和M3区,椎体后部P1、P2和P3区).测量L1椎体松质骨中间3个层面9个统计区的平均应力值,将9个统计区划分成6个组,分别为Ⅰ组A1、A2、A3,Ⅱ组M1、M2、M3,Ⅲ组P1、P2、P3,Ⅳ组A1、M1、P1Ⅴ组A2、M2、P2,Ⅵ组A3、M3、P3.比较同一等级载荷下9个统计区的应力分布情况,并对6个组内的松质骨应力值进行两两配对t检验,分析L1椎体内不同载荷作用下应力分布情况.结果:轴向加载时同一等级载荷下,Ⅲ组内P2松质骨平均应力值与P1、P3比较,Ⅳ组内P1与A1、M1比较,Ⅴ组内P2与A2、M2比较,Ⅵ组内P3与A3、M3比较,差异均有统计学意义(P＜0.05);而Ⅰ组、Ⅱ组内的数据经两两比较均无统计学差异(P＞0.05);椎体后部P区(P1,P2,P3)的应力值与M区、A区比较最大,其中P2区应力最大.屈曲加载时同一等级载荷下,Ⅰ组内A2与A1、A3比较,Ⅱ组内M2与M1、M3比较,Ⅲ组内P2与P1、P3比较,Ⅳ组内A1与M1、P1比较,Ⅴ组内A2与M2、P2比较,Ⅵ组内A3与M3、P3比较,差异均有统计学意义(P＜0.05);Ⅰ组内A1与A3比较,Ⅱ组内M1与M3比较,Ⅲ组内P1与P3比较,Ⅳ组内M1与P1比较,均无统计学差异(P＞0.05);椎体前部A区(A1,A2,A3)的应力值与M区、P区比较最大,A2区应力最大.结论:L1椎体在不同载荷作用下,松质骨内存在着应力分布的集中趋势;轴向加载时应力集中的部位靠近椎体后缘中央,屈曲加载时应力集中的部位靠近椎体前缘中央.     

旋转手法对腰椎骨盆和股骨上端结构有限元模型的分析

目的:研究腰椎旋转手法时腰椎骨盆和股骨上端各结构位移和应力的特点。方法:使用腰椎CT片,以Mimics10.01软件建立腰椎骨盆和股骨上端几何模型,经Geomagic9对模型进行修改后导入Hypermesh10划分4面体网格并添加椎间盘与韧带。根据手法作用原理,将腰椎旋转手法进行分解,把各项力学参数导入三维有限元模型。利用Abaqus求解模块对4工况下模型的位移和应力进行计算分析,得到腰椎旋转手法作用时腰椎骨盆和股骨上端各结构位移和应力的变化。结果:①相同工况下腰椎位移的大小顺序是:L1>L2>L3>L4>L5,前柱>中柱>后柱。②不同工况下腰椎的位移大小顺序是:工况3>工况1>工况4>工况2。③相同工况下椎间盘从L1,2-L5S1各椎间盘位移大小顺序是:L1,2>L2,3>L3,4>L4,5>L5S1,同一椎间盘内各象限位移大小顺序为:第2象限>第3象限>第1象限>第4象限。④不同工况下各椎间盘的位移大小顺序是:L1,2>L2,3>L3,4>L4,5>L5S1,同一椎间盘不同工况下位移大小顺序是:工况3>工况4>工况1>工况2。⑤骨盆和髋关节在手法作用过程中存在明显的位移和应力集中。结论:①旋转手法的作用原理与腰椎骨盆和股骨上端各相应解剖部位因旋转而引起的相对位移有关;②在手法的操作过程中,不能随意加大侧弯和前屈的角度;③在腰椎旋转手法的施术过程中,必须综合考虑腰椎骨盆和股骨上端各部位的具体情况以确定适应证和禁忌证。     

应用有限元技术对OLIF术后生物力学的分析与研究

背景:经腹膜外侧前方入路腰椎椎间融合术(oblique lumbar interbody fusion,OLIF)已被越来越多地应用到腰椎退行性疾病的治疗中.与传统后路椎间融合术相比,OLIF能否达到相同的稳定性仍值得商榷.目的:利用有限元技术探究不同OLIF手术术后融合器、固定装置和腰椎主要结构的应力变化及稳定性.方...     

Three-dimensional finite element analysis of the pediatric lumbar spine. Part I: pathomechanism of apophyseal bony ring fracture

The purpose of this study was to (1) develop a three-dimensional, nonlinear pediatric lumbar spine finite element model (FEM), and (2) identify the mechanical reasons for the posterior apophyseal bony ring fracture in the pediatric patients. The pediatric spine FE model was created from an experimentally validated three-dimensional adult lumbar spine FEM. The size of the FEM was reduced to 96% taking into account of the ratio of the sitting height of an average 14-years-old children to that of an adult. The pediatric spine was created with anatomically specific features like the growth plate and the apophyseal bony ring. For the stress analyses, a 10-N m moment was applied in all the six directions of motion for the lumbar spine. A preload of 351 N was applied which corresponds to the mean body weight of the 14-years-old group. The stresses at the apophyseal bony ring, growth plate and endplate were calculated. The results indicate that the structures surrounding the growth plate including apophyseal bony ring and osseous endplate were highly stressed, as compared to other structures. Furthermore, posterior structures in extension were in compression whereas in flexion they were in tension, with magnitude of stresses higher in extension than in flexion. Over time, the higher compression stresses along with tension stresses in flexion may contribute to the apophyseal ring fracture (fatigue phenomena).Part II of this article can be found at .     

腰椎单侧椎板间开窗双侧减压术后腰椎生物力学改变的有限元分析

【摘要】 目的：采用有限元分析方法评估单侧椎板间开窗双侧减压手术（unilateral laminotomy for bilateral decompression,ULBD）后L4~L5节段的生物力学状态,为ULBD治疗腰椎退变性疾病提供理论依据。方法：提取1名健康志愿者腰椎CT薄层扫描数据,应用高保真三维有限元方法建立L4~L5正常模型、ULBD术后模型和椎板间开窗单侧减压（lumbar fenestration,LF）术后模型,对所有模型完全固定L5椎体下终板,在L4上终板施加500N轴向载荷及在前屈、后伸、左侧屈、右侧屈、左旋转、右旋转六个方向分别施加10N·m的弯矩载荷。对比分析不同载荷下三种模型的L4/5椎间盘压缩高度、椎间活动角度、椎间盘内应力分布和关节突间压力等生物力学特性。结果：正常模型在六个方向的活动度均在既往尸体实验研究测量结果的区间内,所建模型有效。正常模型、ULBD术后模型和LF术后模型在500N轴向载荷下椎间盘压缩高度分别为0.74mm、0.85mm、0.85mm。叠加10N·m的弯矩载荷在前屈、后伸、左侧屈、右侧屈、左旋转、右旋转六个方向上,正常模型椎间活动度分别为6.1°、4.2°、5.1°、4.6°、2.9°、2.6°,ULBD术后模型分别为6.5°、4.8°、6.0°、5.2°、3.2°、2.9°,LF术后模型分别为6.4°、4.6°、5.6°、5.1°、3.0°、2.8°;三种模型椎间盘内应力分布无明显差异,最大von Mises应力都分布在椎间盘受压侧外纤维环处;前屈、后伸、左侧屈、右侧屈、左旋转、右旋转时正常模型椎间盘最大von Mises应力分别为0.52、0.66、0.81、0.87、0.46、0.40MPa,ULBD术后模型分别0.64、0.76、1.06、1.13、0.60、0.64MPa,LF术后模型分别0.65、0.80、1.00、1.06、0.66、0.65MPa。左、右旋转状态下关节突间有显著的压力,正常模型左、右旋转状态时的压力分别为60N、69N,ULBD术后模型为30N、87N,LF术后模型为79N、120N。结论：ULBD术后腰椎间盘压缩高度、椎间活动度、椎间盘内应力和关节突间压力均有明显改变,与LF手术相比,ULBD对腰椎生物力学稳定性影响较小。     

新型颈前路翼形钛网三维有限元分析

目的运用三维有限元法分析新型翼形钛网（aliform titanium mesh cage,ATMC）的生物力学性能;评价该内固定的外形设计及生物力学合理性并提出优化指导方案。方法在C4～C6三维有限元模型的基础上,利用Ansys9.0软件前处理器的建模功能建立颈前路椎体次全切减压翼形钛网植骨固定手术模型。对模型施加73.6N轴向压缩载荷及1.8Nm力矩,分析记录前屈、后伸、侧弯及旋转工况下新型翼形钛网内部应力分布及大小情况。结果在后伸、侧弯、旋转工况下,翼板基底部及钉孔周围均出现应力集中现象。应力集中以旋转工况最明显。各工况下笼内植骨块应力总体均匀,大小适宜。结论新型翼形钛网总体外形设计合理,模拟力学安全性能可靠;同时在翼板、翼板基底部存在应力集中现象,需待优化。     

人工腰椎间盘植入后椎体应力分布的比较研究

目的 通过三维有限元的方法研究正常腰椎间盘、髓核摘除术后腰椎间盘、人工腰椎间盘3组椎体的应力分布,探讨人工腰椎间盘植入对椎体应力分布的影响。方法 利用有限元软件MSC．MARK,建立正常腰椎间盘、髓核摘除、人工腰椎间盘及L4-5运动节段的三维模型,然后模拟腰椎节段的运动,进行椎体应力分布的比较研究。结果 人工腰椎间盘植入后在各种运动状态下椎体松质骨的应力水平显著低于正常腰椎间盘及髓核摘除术后腰椎间盘,且应力呈均布状态,但髓核摘除后椎体松质骨的应力水平较正常腰椎间盘组有所提高,并且在不同运动状态下应力的分布状态有所不同,前屈时,应力集中于椎体松质骨的前部,后伸时集中于椎体松质骨的后部,右侧弯时集中于椎体松质骨的右侧,压缩、旋转时,应力较为均布。结论 从人工腰椎间盘植入对椎体的生物力学影响来看,用人工腰椎间盘置换术重建椎间盘的功能是合理的。     

The influence of cancellous bone density on load sharing in human lumbar spine: a comparison between an intact and a surgically altered motion segment

The aim of the current study is twofold: first, to compare load sharing in compression between an intact and a surgically repaired lumbar spine motion segment L3/4 using a biomechanically validated finite element approach; second, to analyse the influence of bone mineral density on load sharing. Six cadaveric human lumbar spine segments (three segments L2/3 and three segments L4/5) were taken from fresh human cadavers. The intact segments were tested under axial compression of 600 N, first without preload and then following instrumented stabilisation. These results were compared to a finite element model simulating the effect of identical force on the intact segments and the segments with constructs. The predictions of both the intact and the surgically altered finite element model were always within one standard deviation of the mean stiffness as analysed by the biomechanical study. Thus, the finite element model was used to analyse load sharing under compression in an intact and a surgically repaired human lumbar spine segment model, using a variety of E moduli for cancellous bone of the vertebral bodies. In both the intact and the surgically altered model, 89% of the applied load passed through the vertebral bodies and the disc if an E modulus of 25 MPa was used for cancellous bone density. Using 10 MPa--representing soft, osteoporotic bone--this percentage decreased, but it increased using 100 MPa in both the intact and the altered segment. Thus, it is concluded that reconstruction of both the disc and the posterior elements with the implants used in the study recreates the ability of the spine to act as a load-sharing construction in compression. The similarity in load sharing between normal and instrumented spines appears to depend on assumed bone density, and it may also depend on applied load and loading history.     

Influence of different fusion techniques in lumbar spine over the adjacent segments: A 3D finite element study

The most conventional technique to treat the intervertebral disc degeneration consists on fusing the affected segment with a posterior screw fixation and sometimes with the insertion of a cage in the intersomatic space. However, this kind of surgeries had controversial results in the adjacent discs. The aim of this work was to prove the stabilization of the spine and the decompression of the disc and to analyze the influence over the adjacent segments. With this purpose, four different models were built and simulated under different loading conditions. The stabilization of the spine was ensured by the screw fixation which reduced dramatically the relative motion in the affected segment. On the other hand, the pore pressure showed a high fall in the operated models proving the decompression of the neural structures. In the adjacent segments, the ROM increased up to 50% in the upper disc and 70% in the lower one. The pore pressure and principal stresses also increased after both surgeries. The observed results suggested that the fusion procedure could trigger a cascade degeneration effect over the adjacent discs, while it is also seen that cage insertion helps to maintain disc height in a better way than screw fixation only. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:993–1000, 2015.     

L4/5关节突关节融合后椎间盘应力变化的三维有限元分析

目的 :建立正常人L3~L5三维非线性有限元模型,运用有限元分析方法模拟分析L4/5双侧关节突关节未融合与融合后L4/5椎间盘的应力分布情况和L4/5节段活动度。方法:选取1例健康成年男性志愿者,年龄27岁,身高175cm,体重70kg,既往无腰痛病史。采用64排螺旋CT对T12~S1行薄层平扫,得到Dicom格式数据,经Mimics软件选取L3~L5椎体二维图像数据,再经Geomagic软件简化、光滑处理,3-matic软件划分面网格和体网格,Mimics软件赋值,最终导入Ansys软件中重建腰椎关节突关节未融合和融合(融合L4/5双侧关节突关节)的三维有限元模型。利用Ansys软件约束L5椎体下表面各向活动度,给予L3椎体上表面垂直向下的面载荷500N,并给予7.5N·m的力矩模拟正常人体垂直压缩、前屈、后伸、左侧屈、右侧屈、左旋转、右旋转7种运动状态,对L4/5双侧关节突未融合与融合后L4/5椎间盘的应力分布情况和L4/5节段活动度进行分析。结果:成功建立了正常人L3~L5关节突关节未融合和融合的三维有限元模型,未融合模型L3/4、L4/5节段活动度与既往文献中腰椎活动度趋势一致。与未融合模型比较,关节突关节融合模型在各运动状态下L4/5椎间盘后方应力明显减小,差异有统计学意义(P0.05);前方应力未见明显改变。关节突关节融合模型L4/5节段活动度明显减小。结论:腰椎关节突关节融合可以降低融合节段椎间盘后方应力,减少融合节段的活动度,有利于维持节段的稳定性。