Biomechanical analysis of the lumbar spine with anterior interbody fusion on the different locations of the bone grafts

The anterior lumbar interbody fusion is the common procedure in the management of the degenerated disc in the lumbar spine, but the biomechanical behavior of the fused segment would be changed because of the implantation of bone graft at the different locations. To investigate the biomechanical alteration, the study applied the finite element model to undergo the stress analysis.A three-dimensional finite element model of the lumbar spine was established, and modified to the three fusion models consisted of the bone graft at the anterior site, the middle site and the posterior site, respectively. The 12 N m flexion and the 10 N m torsion with pre-load 150 N were imposed on the L1 vertebral body.The results of the finite element model indicated that placing bone graft at anterior site could effectively resist flexion moment, and decreased the tensile force of the posterior ligaments about 15% above. Placing bone graft at posterior site could resist torsional moment, and also led to none of contact force of the facet joint in the fused segment. However, wherever the bone grafts were placed, stress slightly increased on the disc adjacent to interbody fusion about 5% below.     

腰椎椎间融合联合邻近节段半刚性固定的有限元分析

文题释义： 半刚性椎弓根螺钉固定系统：一种经椎弓根的半刚性金属固定系统,介于软固定和坚强固定之间,可以联合融合术,也可单独使用。其椎弓根螺钉之间连接依赖于金属棒,这种金属棒具有一定弹性或者是可以微动的,一定程度上可以起到动态固定的作用,主要包括ISObar系统、Flex系统、DSS系统等。 腰椎邻近节段退变：是指腰椎融合后融合区邻近节段退行性改变,包括椎间隙狭窄、椎间盘信号降低、关节突退变、骨赘形成等异常改变,如果患者同时出现不稳定、椎管狭窄、增生性小关节炎、脊柱侧凸、椎体压缩骨折等,并伴有相应的临床症状称之为邻近节段退行性疾病。 背景：临床中腰椎退行性疾病的发生多伴有多节段病变,为减缓腰椎融合后邻近节段退变,腰椎杂交手术成为一种较好的选择。以往临床观察中WavefleX系统单节段应用取得一定的效果,其在腰椎杂交手术中的应用缺乏生物力学研究结果支持。 目的：应用有限元方法分析腰椎融合联合上一位椎体置入WavefleX系统对邻近节段的生物力学影响。 方法：利用64排西门子螺旋CT机对静止仰卧志愿者行腰椎薄层扫描,扫描范围为T₁₁-S₁,志愿者对实验过程完全知情同意,且得到医院伦理委员会批准。将L_3-5水平CT扫描数据依次导入到Mimics医学图像处理软件及Geomagic Studio逆向工程软件中进行处理,于CAD软件SCDM中构建L_3-5的腰椎实体模型。在已通过验证的L_3-5腰椎模型基础上,分别构建后路椎体间融合模型与Hybrid模型,对3种模型进行赋值和负荷加载,在前屈、后伸、左右侧屈、左右旋转工况下进行有限元分析研究。 结果与结论：①在前屈、后伸、侧屈、旋转状态下,相较后路椎体间融合模型,Hybrid模型L_3-4椎间盘应力值均有明显减小,后伸状态降幅最大,最大值减少约46%;②各状态下,相较后路椎体间融合模型,Hybrid模型L_3-4节段活动度均有明显减小,平均减小约26%,并小于完整模型;③各负荷下,应力云图显示WavefleX系统的连接棒上均有明显的应力集中,双侧的弹性系统的U形开槽凹面处应力明显增大;④位移云图显示,Hybrid模型中WavefleX系统的置入使得其前屈中心后移至弹性结构处;⑤上述结果说明,后路椎体间融合+WavefleX半刚性固定可有效降低上一位邻近节段的椎间盘应力并限其制过度活动,一定程度上维持了腰椎的正常运动特点。 ORCID: 0000-0001-5752-6546(王啸) 中国组织工程研究杂志出版内容重点：人工关节;骨植入物;脊柱;骨折;内固定;数字化骨科;组织工程     

三维有限元法分析前纵韧带对腰椎生物力学影响

该文基于人体 DICOM 图像建立了更符合人体解剖结构的 L4/5 节段腰椎三维有限元模型,模拟腰椎前屈、后伸、 侧弯及扭转 4 种运动状态下的生物力学响应。前纵韧带（ALL）受损后腰椎的关节活动度（ROM）增大,后伸时增大最显著。ALL 受损后应力减小且分布发生改变,后伸时应力最大位置由韧带上部转移至韧带下部,侧弯时应力作用范围明显缩小。ALL 受损后应变分布发生不同程度的改变,产生明显的纵向形变。除扭转外,其他运动状态下 ALL 应变增大,后伸和侧弯应变增加量最大。ALL 主要限制后伸运动,ALL 受损后腰椎稳定性下降。ALL 受损后进行后伸和侧弯运动时可能会加重已有的损伤,因此 ALL 受损患者应尽量减少过度后伸和侧弯运动。该文的仿真实验可对韧带损伤疾病的诊断治疗提供支持和参考。     

新型腰椎后路动态稳定系统的三维有限元分析

目的对新型腰椎后路动态稳定系统进行三维有限元分析,研究其在稳定节段及邻近节段的生物力学影响,为下腰痛的脊柱内植物的设计和应用提供参考。方法基于正常腰椎有限元模型,构建腰椎不稳损伤模型,即腰椎切除腰4和腰5之间的双侧小关节、腰4椎板下1/2、后纵韧带,形成脊柱失稳模型,分别在失稳模型上进行坚强内固定系统和后路动态稳定系统,比较两种术式对手术节段和临近阶段的活动度、各个节段的弯曲刚度、椎间盘应力水平、前纵韧带应力水平及小关节韧带拉力的变化情况。结果对内固定桥接节段(腰4/腰5)应用新型腰椎后路动态稳定系统和坚强内固定系统后,在屈伸、侧屈、轴向旋转方向上的活动度均明显减小,但坚强固定后活动度减小更明显,应用动态稳定系统活动度更接近于正常腰椎节段;腰4/腰5椎间盘最大应力均减小,但坚强固定后活动度减小更明显,应用动态稳定系统活动度更接近于正常腰椎节段;对邻近节段(腰3/腰4、腰5/S1)应用新型腰椎后路动态稳定系统和坚强内固定系统后,在屈伸、侧屈、轴向旋转方向上的活动度均有所增大,但坚强固定后活动度增加更明显,应用动态稳定系统邻近节段活动度更接近于正常腰椎节段;邻近节段椎间盘最大应力均增大,但坚强固定后增大更明显,应用动态稳定系统更接近于正常腰椎节段;应用腰椎内固定后,邻近节段的小关节应力峰值增大,并且应用腰椎坚强内固定模型的小关节应力增大更多;应用腰椎动态固定的模型邻近关节应力峰值更加接近完整腰椎模型。结论新型腰椎后路动态稳定系统对比坚强内固定系统能够使失稳节段的活动更加接近于正常,减小邻近节段的活动度增加,减小邻近节段椎间盘及小关节压力,说明新型腰椎动态稳定系统达到设计要求。     

Wallis腰椎非融合系统的有限元分析**☆

背景：目前Wallis非融合系统临床应用短期效果明显。 目的：构建Wallis腰椎非融合系统有限元模型,分析Wallis腰椎非融合在腰椎不同生理运动情况下的应力分布。 方法：选取8例腰椎间盘轻度退变的志愿者采用连续螺旋CT扫描,导入Materialise Mimics 10.01软件,三维重建L4~5椎体及椎间盘三维模型,与文献结果进行对比,验证模型有效性。在AutoCAD 2009软件中建立Wallis系统模型,导入Materialise 3-Matic 4.3 软件,将重建的Wallis模型按标准手术模式与腰椎模型拟合,导入Abaqus 6.9软件,生成有限元模型,并进行分析腰椎前屈、后伸、侧屈及旋转运动时Wallis腰椎非融合系统的应力变化。 结果与结论：实验所建立的腰椎三维有限元模型共有233 438个单元,48 174个节点;所建立的Wallis系统的三维有限元模型,共有11 857个单元,3 398个节点,将二者拟合,模型共有245 295个单元,51 572个节点,重建的三维模型可以精确地模拟Wallis非融合系统固定情况。通过应力云图显示前屈、后伸、侧屈及旋转运动下Wallis系统的应力分布情况,此模型说明Wallis系统参与了腰椎不同方向的活动,与腰椎很好地匹配,顺应了腰椎的运动,位于上下棘突之间的部分应力较大,且与下位椎体棘突相接触部分的应力最高。说明应用CT扫描技术及Mimics软件能直接与Abaqus软件进行对接,并能根据CT值直接赋值使Wallis腰椎非融合系统有限元模型的建立更加快捷和精确,Wallis棘突间撑开器植入后可分担椎间盘应力和小关节压力,Wallis系统本身和棘突应力升高,有棘突骨折及植入物疲劳性断裂的可能性。     

下腰椎融合术后路单、双侧椎弓根固定的有限元比较研究

目的　建立正常人L4~5节段椎间盘切除后单/双侧椎弓根螺钉固定椎间融合的有限元模型,对两者在不同运动载荷下的稳定性和应力分布进行比较研究。 方法　通过正常人L4~5节段CT扫描获取断层图像,然后利用mimics软件重建人体L4~5三维模型,再通过Ansys软件前处理功能建立有限元模型,并在此基础上分别建立椎间盘切除后单侧（A）、双侧（B）椎弓根螺钉固定+椎间Cage融合模型,对两组模型分别施加5 N?m的前屈、后伸、左/右屈曲和左/右旋转载荷,比较分析椎体及植入物在不同工况下的位移及应力峰值。 结果　各种工况下,A组在固定侧侧屈时椎体间位移及椎弓根螺钉应力峰值最大,在后伸时椎体应力峰值最大。B组在后伸时椎体间位移峰值最大,在旋转时螺钉及椎体应力峰值最大。在后伸和固定侧侧屈工况下A组椎体间位移峰值、螺钉及椎体应力峰值较B组相差最大。 结论　与双侧固定相比,单侧固定融合术后在固定侧侧屈及后伸工况下发生不稳及螺钉松动、断钉的潜在风险最大。单侧固定融合术后的病人在椎间骨融合前应特别减少后伸及固定侧侧屈动作,以降低风险。     

聚醚醚酮/羟基磷灰石/碳纤维复合材料的生物力学分析

目的利用有限元分析法比较聚醚醚酮/羟基磷灰石/碳纤维复合材料（75PEEK/10HA/15CF）与钛合金的生物力学。方法建立C4～C6有限元模型,于C5～C6间植入75PEEK/10HA/15CF或钛合金人工椎间盘和椎间融合器,计算在前屈、后伸、侧弯和旋转时临近椎体、椎间盘的wonMises应力变化和C5～C6节段的活动度及植入物上的应力分布。结果在正常情况下,钛合金人工椎间盘置换模型在前屈时C5椎体、C4~5椎间盘平均won Mises应力改变率分别为75PEEK/10HA/15CF人工椎间盘模型的1.50倍和1.67倍;在侧弯时C6椎体的平均won Mises应力改变率为75PEEK/10HA/15CF人工椎间盘置换模型的1.33倍。融合器模型,在前屈时C5椎体、C4~5椎间盘应力改变率前者为后者的1.48倍和1.87倍;在侧弯时C6椎体应力改变率,前者为后者的1.67倍。钛合金植入物的最大应力为75PEEK/10HA/15CF的4.5倍,并出现应力集中。结论与钛合金相比,75PEEK/10HA/15CF能更好地将负荷传递,增加融合率,能有效地减少临近椎体的应力,减少植入物沉降的发生。     

Finite element analysis of the spondylolysis in lumbar spine

Spondylolysis is a fracture of the bone lamina in the pars interarticularis and has a high risk of developing spondylolisthesis, as well as traction on the spinal cord and nerve root, leading to spinal disorders or low back pain when the lumbar spine is subjected to high external forces. Previous studies mostly investigated the mechanical changes of the endplate in spondylolysis. However, little attention has been focused on the entire structural changes that occur in spondylolysis. Therefore, the purpose of this study was to evaluate the biomechanical changes in posterior ligaments, disc, endplate, and pars interarticularis between the intact lumbar spine and spondylolysis. A total of three finite element models, namely the intact L2-L4 lumbar spine, lumbar spine with unilateral pars defect and with bilateral pars defect were established using a software ANSYS 6.0. A loading of 10 N.m in flexion, extension, left torsion, right torsion, left lateral bending, and right lateral bending respectively were imposed on the superior surface of the L2 body. The bottom of the L4 vertebral body was completely constrained. The finite element models estimated that the lumbar spine with a unilateral pars defect was able to maintain spinal stability as the intact lumbar spine, but the contralateral pars experienced greater stress. For the lumbar spine with a bilateral pars defect, the rotation angle, the vertebral body displacement, the disc stress, and the endplate stress, was increased more when compared to the intact lumbar spine under extension or torsion.     

青少年特发性脊柱侧凸腰主弯患者腰椎-骨盆的生物力学分析

文题释义： 青少年特发性脊柱侧凸：为脊柱三维平面上的畸形,会导致青少年脊柱结构发生明显的改变,结构的改变会导致椎骨及椎间盘应力发生相应的改变,且腰椎、骨盆在人体中的力学作用极为重要,青少年时期为人体脊柱生长发育的高峰期,脊柱结构及应力的改变在该时期的进展尤为明显。 背景：青少年特发性脊柱侧凸导致脊柱结构和应力发生改变,腰椎在脊柱中承受的载荷最大,骨盆也起着传导重力的作用,故青少年特发性脊柱侧凸腰主弯患者腰椎骨盆的生物力学分析尤为重要。 目的：建立青少年特发性脊柱侧凸腰主弯腰椎-骨盆三维数字化模型并进行有限元分析。 方法：根据1例13岁女性特发性脊柱侧凸腰主弯患者的腰椎-骨盆CT薄层数据,应用Mimics 15.0软件重建三维数字化模型,以Pro/E 5.0软件建立初步几何模型并导入Hypermesh 13.0进行网格划分,最终通过Abaqus 6.14软件对该模型进行有限元分析。分析有限元模型在6种载荷条件下的位移、应力变化及该模型各椎体及椎间盘的应力变化。患者家属对试验方案知情同意,且得到医院伦理委员会批准。 结果与结论：①建立了青少年特发性脊柱侧凸腰主弯患者的腰椎-骨盆的三维有限元模型;②模型在6种载荷条件下,L₁椎体上部在左、右侧屈时位移变化最大,骶骨下端在前屈时位移最大;③椎间盘右缘在右侧屈运动条件下所受应力最大;前屈位时,腰椎间盘所受应力为前缘最大,左缘所受应力最小;后伸位时后缘所受应力最大,而右缘所受应力最小;侧屈位及旋转位时,右缘所受应力最大,前缘所受应力最小;④L₅在6种运动中应力均最大,其中应力集中于上下关节突及椎弓根,尤其以右侧最为集中;⑤提示青少年特发性脊柱侧凸不同载荷会引起椎体或椎间盘不同位置受力及位移有相应变化,研究结果对脊柱侧凸的治疗和预防具有重要意义。 ORCID: 0000-0001-5810-6674(张聪) 中国组织工程研究杂志出版内容重点：组织构建;骨细胞;软骨细胞;细胞培养;成纤维细胞;血管内皮细胞;骨质疏松;组织工程     

多孔钛腰椎融合器在不同入路椎间融合术中的生物力学性能

目的探究采用多孔融合器在不同入路腰椎融合术的生物力学性能。方法建立完整腰椎三维有限模型,通过实验方法获得多孔材料的力学参数。针对多孔融合器在前路腰椎椎间融合术(anterior lumbar interbody fusion, ALIF)、后路腰椎椎间融合术(posterior lumbar interbody fusion, PLIF)、经椎间孔腰椎椎间融合术(transforaminal lumbar interbody fusion, TLIF)和直接外侧椎体间融合术(direct lateral interbody fusion, DLIF)中的生物力学性能进行对比研究。结果在施行椎间融合术后,DLIF、ALIF模型预测的活动度(range of motion, ROM)和融合器应力明显低于PLIF、TLIF模型,DLIF、ALIF和TLIF模型预测的终板应力明显低于PILF模型。结论采用多孔融合器的DLIF模型显示出较优的生物力学性能,而且在临床过程中操作简单适于微创术式。DLIF手术具有更优的综合性能。     

不同腰椎生理曲度下牵引的三维有限元分析

文题释义：腰椎牵引：是指令患者平卧于治疗床上,使用束带将患者前臂固定,达到医者固定患者双臂的目的;波浪式滚动气柱以腰背部为作用点进行顶推,控制多层气柱叠加高度使受试者腰部逐渐过伸牵引脊柱关节,实现对软组织的牵伸,并结合自身重力过伸牵引脊柱关节,能够增大椎间隙及调整椎小关节,最终达到理筋整复的作用。 三维有限元分析：是指在获取腰椎的CT图像数据,并导入到Mimics等软件当中建立的有限元模型基础上,将L₃的发生的位移变化带入MSC.Nastam软件中,高度仿真模拟人体在不同生理曲度下,计算分析出全腰椎各节段椎体、椎间关节、椎间盘、前纵韧带的应力值及分布情况的变化。 背景：近年来利用有限元分析方法研究腰椎生物力学成为热点,研究认为腰椎生理性前凸可减少腰椎间盘压力负荷,而对腰椎起保护效应。 目的：研究腰椎在正常生理曲度、屈曲位及最大过伸位下进行腰椎牵引时对L₁-L₅腰椎各节段的生物力学效应,并评估腰椎牵引的最佳生理曲度。 方法：选取1名健康男性志愿者,26岁,身高174 cm,体质量60 kg,既往体健,排除腰椎骨骼异常疾病。以受试者L₃为作用点徒手操作南少林倒盖金被法,利用DR机分别获得受试者腰椎起始位和最大过伸位的腰椎侧位片,构建全腰椎有限元模型。计算腰椎不同生理曲度下全腰椎各节段椎体、椎间关节、椎间盘、前纵韧带的应力值及分布情况的变化。研究方案的实施符合福建中医药大学附属康复医院相关伦理要求,受试者对试验过程完全知情同意。 结果与结论：①模拟腰椎前屈、后伸,左右侧弯,左右旋转6种工况活动度：L₁-L₂的前屈与后伸活动度之和为9.31°,左右侧弯9.84°,左右旋转4.43°;L₂-L₃：前屈与后伸10.22°,左右侧弯12.35°,左右旋转4.57°;L₃-L₄的前屈与后伸的活动度之和为11.20°,左右侧弯11.63°,左右旋转5.32°;L₄-L₅前屈与后伸活动度之和13.16°,左右侧弯11.58°,左右旋转5.05°;②在正常生理曲度牵引腰椎时,腰椎各个结构的应力值远大于过伸位牵引的应力值;前纵韧带应力值正常曲度是2.47 MPa,过伸位是21.20 MPa;L₃的椎体应力值达到最大,是过伸位牵引应力值的4倍;L₂-L₃的椎间关节及椎间盘的应力值在腰椎各个节段是最大的;③结果说明,腰椎在过伸位较正常生理曲度牵引下椎体、椎间关节、椎间盘的压力减轻更大,而且前纵韧带的压力值始终在安全范围内。腰椎在过伸位牵引时可能获得更好的临床疗效,同时具备一定的安全性。 ORCID: 0000-0002-4468-1464(李民) 中国组织工程研究杂志出版内容重点：组织构建;骨细胞;软骨细胞;细胞培养;成纤维细胞;血管内皮细胞;骨质疏松;组织工程     

原位及复位融合腰椎滑脱的三维有限元分析

背景：由于脊柱结构复杂,对复位或原位融合后融合的腰椎节段应力分布变化特点的精确生物力学分析一直是个难点。 目的：通过建立L₄/₅节段退变性滑脱原位椎间融合椎弓根钉内固定和复位椎间融合椎弓根钉内固定的三维有限元模型来比较腰椎滑脱原位融合和复位融合两种手术方式在各种载荷下的生物力学变化及其对腰椎稳定的影响。 方法：根据健康成年男性的下腰椎CT数据,利用mimics,Catia和Patran,Marc等软件建立起L₄/₅节段的三维有限元模型,利用此模型模拟退变性腰椎滑脱,在此基础上建立L₄/₅节段原位椎间融合椎弓根钉内固定和复位椎间融合内固定模型,分析两模型在各种载荷下的应力分布特点,并比较异同。 结果与结论：L₄/₅节段退变性滑脱原位椎间融合椎弓根钉内固定和复位椎间融合椎弓根钉内固定三维有限元模型在前屈后伸侧屈旋转负荷下,该节段各部结构,包括椎体,椎弓根钉内固定器和椎间融合器上的应力变化没有显著差异。两模型都显示椎间融合器和椎弓根螺钉内固定器上分布的应力最大。结果表明退变性腰椎滑脱,行原位椎间融合内固定和复位椎间融合内固定后,复位与否对该节段生物力学没有显著影响。     

新型关节突钉板系统联合单侧椎弓根螺钉固定的生物力学研究

目的 研究经椎间孔入路椎体间融合术(transforaminal lumbar interbody fusion,TLIF)结合新型关节突钉板系统(articular process fixation system,APFS)的腰椎稳定性.方法 在已验证的有限元模型L3～S1完整节段(模型A)上,模拟TLIF手术,建立...     

基于Simpleware全颈椎三维有限元模型的构建与分析

目的 利用Simpleware软件构建全颈椎三维有限元模型,并对模型进行验证和分析,为探讨颈椎损伤机制提供可靠模型。方法 基于CT断层扫描图像,利用医学图像处理软件Simpleware、逆向工程软件Geomagic建立C1~7全颈椎三维实体模型,导入Hypermesh进行颈椎网格划分、添加韧带并引入小关节突接触关系等,建立C1~7全颈椎有限元模型,在ANSYS中模拟前屈、后伸、侧弯和轴向旋转工况下颈椎的生物力学性能。结果 建立的模型准确可靠,在前屈、后伸、侧弯和轴向旋转时,活动范围与文献中离体实验和有限元分析结果相近。椎间盘应力集中在椎体受压侧,C4/5最易产生应力集中。结论 建立的C1~7全颈椎有限元模型能够有效模拟颈椎的生物力学特性,为后续颈椎挥鞭样损伤的生物力学研究奠定良好的基础。     

Biomechanical effect of anterior cervical spine fusion on adjacent segments.

The biomechanical effects of superior (C4-C5) and inferior (C5-C6) level fusions with different graft materials on the adjacent unaltered components were quantified using an anatomically accurate and experimentally validated C4-C5-C6 finite element model. Smith-Robinson and Bailey-Badgley fusion procedures were analyzed with five different types of inter-body fusion materials with varying stiffnesses. Intact and surgically altered finite element models were subjected to physiologic compression, flexion, extension and lateral bending. The external axial and angular stiffness, and the internal unaltered intervertebral disc (C5-C6 for the superior and C4-C5 for inferior fusion) and C5 vertebral body stresses were determined. The superior level fusion resulted in the highest increase in external response in lateral bending for all implant materials in both surgical procedures. In contrast, the inferior level fusion produced a higher increase in the C4-C5 disc and C5 vertebral body stresses in compression than the superior level fusion in both surgical procedures. The increased internal stress responses reflecting the changes in the load-sharing following inferior level fusion may explain clinical observations such as enhanced degeneration subsequent to surgery. Because of the inclusion of three levels in the present multi-segment finite element model, it was possible to determine these responses in the unaltered adjacent components of the cervical spine.     

下颈椎全脊椎切除术后两种内固定重建方法的有限元分析

研究下颈椎C5椎体全脊椎切除术(TS)之后,前后路不同联合内固定重建方法对颈椎稳定性的影响。基于CT图像建立下颈椎C3-C7节段完整无损模型,在无损模型基础上,建立C5全脊椎切除术后两种内固定重建模型：一为钛网重建+前路钢板+后路单节段椎弓根螺钉模型(TM+AP+SPS);二为钛网重建+前路钢板+后路双节段椎弓根螺钉模型(TM+AP+DPS)。对模型分别施加0.5、1.0、1.5、2.0 N·m的扭矩,分析两种模型在前屈、后伸、左右侧弯和左右扭转等工况下的关节活动度（ROM）以及钛网、钢板、椎弓根螺钉的应力分布情况。结果表明,重建节段ROM随着扭矩的增大而增加,呈现出非线性的趋势,TM+AP+SPS模型的增加幅度较大。1.0 N·m工况下,两种模型重建节段ROM均减少83%以上;TM+AP+SPS模型在后伸、侧弯和扭转时,邻近节段的ROM均增加11%以上,C6-C7节段的ROM在扭转时增加41.79%,TM+AP+DPS模型的邻近节段ROM则显著降低。TM+AP+SPS模型和TM+AP+DPS模型中钛网应力分别集中于受压侧和后方。TM+AP+SPS模型的邻近节段有较大的代偿活动,TM+AP+DPS模型各节段ROM均大幅度减小,TM+AP+DPS模型的稳定性更好。     

Biomechanical comparison between lumbar disc arthroplasty and fusion

The artificial disc is a mobile implant for degenerative disc replacement that attempts to lessen the degeneration of the adjacent elements. However, inconsistent biomechanical results for the neighboring elements have been reported in a number of studies. The present study used finite element (FE) analysis to explore the biomechanical differences at the surgical and both adjacent levels following artificial disc replacement and interbody fusion procedures. First, a three-dimensional FE model of a five-level lumbar spine was established by the commercially available medical imaging software Amira 3.1.1, and FE software ANSYS 9.0. After validating the five-level intact (INT) model with previous in vitro studies, the L3/L4 level of the INT model was modified to either insert an artificial disc (ProDisc II; ADR) or incorporate bilateral posterior lumbar interbody fusion (PLIF) cages with a pedicle screw fixation system. All models were constrained at the bottom of the L5 vertebra and subjected to 150N preload and 10Nm moments under four physiological motions. The ADR model demonstrated higher range of motion (ROM), annulus stress, and facet contact pressure at the surgical level compared to the non-modified INT model. At both adjacent levels, ROM and annulus stress were similar to that of the INT model and varied less than 7%. In addition, the greatest displacement of posterior annulus occurred at the superior-lateral region. Conversely, the PLIF model showed less ROM, less annulus stress, and no facet contact pressure at the surgical level compared to the INT model. The adjacent levels had obviously high ROM, annulus stress, and facet contact pressure, especially at the adjacent L2/3 level. In conclusion, the artificial disc replacement revealed no adjacent-level instability. However, instability was found at the surgical level, which might accelerate degeneration at the highly stressed annulus and facet joint. In contrast to disc replacement results, the posterior interbody fusion procedure revealed possibly accelerative degeneration of the annulus and facet joint at both adjacent levels.     

Finite element analysis of the lumbar spine with a new cage using a topology optimization method

In recent years, degenerative spinal instability has been effectively treated with a cage. However, little attention is focused on the design concept of the cage. The purpose of this study was to develop a new cage and evaluate its biomechanical function using a finite element method (FEM). This study employed topology optimization to design a new cage and analyze stress distribution of the lumbar spine from L1 to L3 with a new cage by using the commercial software ANSYS 6.0. A total of three finite element models, namely the intact lumbar spine, the spine with double RF cages, and with double new cages, were established. The loading conditions were that 10Nm flexion, extension, lateral bending, and torsion, respectively, were imposed on the superior surface of the L1 vertebral body. The bottom of the L3 vertebral body was constrained completely. The FEM estimated that the new cage not only could be reduced to 36% of the volume of the present RF cage but was also similar in biomechanical performance such as range of motion, stress of adjacent disc, and lower subsidence to the RF cage. The advantage of the new cage was that the increased space allowed more bone graft to be placed and the cage saved material. The disadvantage was that stress of the new cage was greater than that of the RF cage.     

半坚强与坚强内固定邻近节段腰椎间盘角位移及应力的比较

BACKGROUND: Theoretically, lumbar semi-rigid fixation can slow down the degeneration of adjacent segments, but there is still a lack of biomechanical support. OBJECTIVE: To explore the biomechanical effect of semi-rigid fixation system, taking Isobar TTL for instance, on adjacent segment disc by means of finite element analysis. METHODS: The finite element models of USS and Isobar TTL were constructed by putting respective parameters into a validated L2-S5 lumbar model. The angular displacement and von Mises stress of adjacent segments were recorded when the models were subjected to 400 N preload and 7.5 N•m moment of forces under different conditions: flexion, extension, lateral bending and axial rotation. RESULTS AND CONCLUSION: The angular displacement and inter-vertebral disc stress of adjacent segments in the USS and Isobar TTL models were higher than those of an intact state in every condition. But the values in Isobar TTL model were lower than the USS model in varying degrees. Compared with the USS model, the decrease rates of angular displacement in Isobar TTL model for flexion, extension, left bending, right bending, left axial rotation and right axial rotation were 19.2%, 15.1%, 11.1%, 12.2%, 18.4% and 22.1%, respectively. The decrease rates of von Mises stress were 33.0%, 20.2%, 23.9%, 18.6%, 28.8% and 28.0%, respectively. The results suggested that the Isobar TTL, when compared with the USS, partially reduced the angular displacement and inter-vertebral disc stress of adjacent segments.       

骨质疏松骨折椎体及相邻椎体骨水泥注入前后的有限元分析

背景：目前有限元构建模型主要是基于医学图像的建模方法,骨水泥注入主要是人为假设的,而文章中治疗前后的数据直接来源于CT扫描,可靠性更高。 目的：构建骨水泥注入前后骨质疏松性腰椎骨折椎体的三维有限元模型,分析治疗前后病椎及邻椎的应力变化。 方法：选取1例75岁骨质疏松性L₂椎体压缩性骨折患者,经双侧椎弓根注入少量骨水泥获得良好疗效,随访2年病椎及邻椎无新发骨折,局部无疼痛。根据其治疗前后的腰椎CT数据,构建三维有限元模型,模拟腰椎屈伸、左右侧屈、旋转等运动,统计分析治疗前后同一运动状态下的应力变化。 结果与结论：建立了腰椎压缩骨折骨水泥注入前后的三维有限元模型,共生成222 727个单元。骨水泥注入增加了L₂椎体(病椎)屈、伸、侧屈各运动时的应力(P < 0.05),对其旋转时的应力无明显影响(P > 0.05);对L₁,L₃椎体(邻椎)在屈、伸、侧屈及旋转时的应力亦无影响(P > 0.05)。提示少量骨水泥注入治疗老年骨质疏松性腰椎骨折可增加病椎强度及应力,但不改变相邻椎体应力。