不同内固定手术方式治疗寰枢椎复合骨折稳定性的有限元分析

目的:比较寰枢椎椎弓根螺钉固定及枕颈融合术两种内固定方式治疗寰枢椎复合骨折的生物力学稳定性,为临床治疗寰枢椎复合骨折提供理论依据。方法:选择1例27岁健康男性志愿者,采用64排螺旋CT机扫描枕颈部(C0~C3),利用Simpleware 3.0、Geomagic 8.0、Hypermesh 10.0等软件建立C0~C3节段三维有限元(FEM/intact)模型,并与Panjabi等的结果进行对比验证。在经验证的模型基础上断裂C1前弓和后弓及切断齿状突基底部,模拟Jefferson骨折+Ⅱ型齿状突骨折的复合骨折有限元模型(FEM/fracture)。根据内固定系统的大小规格及临床手术方法在FEM/fracture上分别建立寰枢椎椎弓根螺钉固定术模型(FEM/PSF)及枕颈融合术模型(FEM/OCF)。对不同内固定模型加载前屈、后伸、侧屈、旋转工况,分析各模型在不同工况下Von Mises应力云图及各椎节活动度。结果:(1)建立的FEM/intact外观逼真,几何相似性好。各椎节的活动度与Panjabi发表的结果基本吻合。在相同条件下,FEM/fracture各个工况下的活动度均较FEM/intact明显增大,尤其是C1-C2旋转增加了43.7%,屈伸增加了72.1%。(2)两种加载内固定系统的上颈椎有限元模型与临床实际相符。FEM/PSF的C0-C1屈伸和旋转活动度较FEM/intact分别增加59.2%、68.3%;C1-C2屈伸、侧屈、旋转功能受限,分别降低92.2%、31.3%、99.6%;C2-C3屈伸、侧屈工况下活动度分别降低13.6%、0.6%,旋转工况下活动度增加0.7%。FEM/OCF中C0-C3各椎节活动度较FEM/intact均降低,其中C0-C1屈伸、侧屈、旋转工况下活动度分别降低93.8%、90.4%、90.2%;C1-C2分别降低89%、55.7%、97.4%;C2-C3分别降低92.8%、95.2%、90.5%。(3)FEM/PSF在左右旋转工况下应力值最大,为321.19MPa,主要集中在连接棒和螺钉根部。FEM/OCF在左右侧屈工况下应力值最大,为228.84MPa,主要集中在连接棒及螺钉根部。结论:寰枢椎椎弓根螺钉固定及枕颈融合两种手术方式治疗寰枢椎复合骨折均能起到早期稳定的目的,寰枢椎椎弓根螺钉固定后稳定C1-C2的同时能代偿性增加C0-C1的活动度。     

枢椎棘突螺钉单侧应用联合对侧椎弓根螺钉固定的有限元分析

目的分析枢椎棘突螺钉单侧应用联合对侧椎弓根螺钉固定在寰枢和枕颈固定中的生物力学稳定性。方法构建正常枢椎解剖、椎板薄和椎动脉变异椎弓根细小3种不同解剖状态下的完整上部颈椎有限元模型作为完整模型组,然后分别模拟齿状突骨折进行寰枢固定和寰椎骨折进行枕颈固定。在寰枢固定中,比较单侧枢椎棘突螺钉+对侧椎弓根螺钉+双侧寰椎侧块螺钉固定组(棘突螺钉组)和枢椎双侧椎弓根螺钉+双侧寰椎侧块螺钉固定组(椎弓根螺钉组);在枕颈固定中,比较单侧枢椎棘突螺钉+对侧椎弓根螺钉+枕骨螺钉固定组(棘突螺钉组)和枢椎双侧椎弓根螺钉+枕骨螺钉固定组(椎弓根螺钉组)。枢椎棘突螺钉分别测试水平、斜向、垂直置钉3种不同的固定技术。模拟颈椎运动,测量枕颈的屈伸、侧屈、旋转的关节活动范围(ROM)。结果在寰枢和枕颈固定中,棘突螺钉组和椎弓根螺钉组的C1~C2屈伸、侧屈、旋转ROM均较完整模型组均明显下降。在寰枢固定中棘突螺钉组C0~C2屈伸、侧屈、旋转的ROM大于椎弓根螺钉组;在枕颈固定中,棘突螺钉组C1~C2侧屈的ROM大于椎弓根螺钉组,棘突螺钉组的C0~C2旋转的ROM大于椎弓根螺钉组。枢椎棘突螺钉分别测试水平、斜向、垂直固定间有差异,但不明显。结论在寰枢和枕颈固定中,枢椎双侧椎弓根螺钉固定和枢椎单侧棘突螺钉联合对侧椎弓根螺钉组合式固定方法均具有良好的稳定性。在寰枢固定中,相对于枢椎棘突螺钉组合式固定,枢椎双侧椎弓根螺钉固定具有更好的寰枢稳定性。在枕颈固定中,枢椎双侧椎弓根螺钉固定在侧屈和旋转活动上较枢椎棘突螺钉组合式固定稳定性更好。枢椎三种棘突螺钉置钉技术间的稳定性差异并不明显。     

寰椎一体式椎板钩与枢椎椎板钉组合应用于非对称内固定生物力学研究

目的本文报道设计一新型寰枢椎内固定组合,并在尸体标本进行生物力学试验,有一定的临床指导意义。方法将6具新鲜尸体颈椎标本置于2Nm载荷下,运用脊柱三维运动测量系统测量C1-2节段的三维运动范围(Range Of Motion,ROM),并将之进行两两对比。实验依完整组、失稳组、双侧寰椎侧块螺钉联合枢椎椎弓根螺钉内固定(Harms技术)组、寰椎侧块螺钉联合单侧枢椎椎板螺钉+对侧枢椎椎弓根螺钉固定组、一侧寰椎一体式椎板钩+枢椎椎板钉联合对侧寰椎侧块螺钉+枢椎椎弓根螺钉内固定组的顺序进行。结果失稳组ROM较完整组显著增加,内固定后ROM显著减小,三种内固定组中:寰椎侧块螺钉联合单侧枢椎椎板螺钉+对侧枢椎椎弓根螺钉固定组在旋转和侧屈方向上具有最小的ROM,双侧寰椎侧块螺钉联合枢椎椎弓根螺钉内固定组在屈伸运动方向上有最小的R0M。一侧寰椎一体式椎板钩+枢椎椎板钉联合对侧寰椎侧块螺钉+枢椎椎弓根螺钉内固定组ROM在旋转、侧屈以及屈伸方向上均较另外两组大,但差异均无统计学意义。结论寰椎一体式椎板钩与枢椎椎板钉组合非对称内固定可提供良好的生物力学稳定性。     

两种寰枢椎后路内固定系统的三维有限元分析

[目的]运用有限元方法评价寰枢椎经关节螺钉联合椎板钩内固定和寰枢椎椎弓根螺钉内固定生物力学稳定性和安全性。[方法]运用有限元软件建立寰枢椎经关节螺钉联合椎板钩和寰枢椎椎弓根螺钉两种内固定系统的有限元模型,并加载到寰枢椎不稳的有限元模型上,进行计算和分析,得出各个有限元模型的活动度(ROM),并提取内固定有限元模型的应力云图。[结果]寰枢椎经关节螺钉联合椎板钩内固定的活动度要略小于寰枢椎椎弓根螺钉内固定。在屈和伸的工况下,寰枢椎经关节螺钉联合椎板钩内固定产生应力值较大,主要集中在螺钉根部和经关节部位;在后伸工况下,寰枢椎椎弓根螺钉内固定产生应力较大,主要集中在螺钉的根部和连接棒。[结论]寰枢椎经关节螺钉联合椎板钩内固定的稳定性略好于寰枢椎椎弓根螺钉内固定。寰枢椎经关节螺钉联合椎板钩内固定在螺钉经关节部位和螺钉根部易产生断钉,而寰枢椎椎弓根螺钉内固定在螺钉根部和连接棒处易产生断钉。     

寰枢椎后路“三点式”经椎弓根固定的生物力学评价

【摘要】 目的：评价寰枢椎后路椎弓根钉棒系统“三点式”固定方法的生物力学稳定性。方法：采用6具新鲜人体颈椎标本制作6种状态,分别为正常组（A组）及失稳后固定组,用磨钻切除寰椎前弓约1.5cm,用摆锯于基底部切断齿状突,切断寰枢间所有韧带,切开寰枢侧块关节囊后半部分制成寰枢椎失稳的模型,再根据不同的固定方式将失稳后固定组分为Brooks钢丝固定组（B组）、左侧C1～C2椎弓根螺钉固定组（C组）、C1双侧椎弓根螺钉+C2左侧椎弓根螺钉棒固定组（“三点式”固定,D组）,C1左侧椎弓根螺钉+C2双侧椎弓根螺钉棒固     

改良Brooks技术和寰枢椎椎弓根螺钉内固定系统生物力学特点

目的 通过有限元分析比较改良Brooks技术和寰枢椎椎弓根螺钉内固定系统的生物力学性能.方法 对健康青年男性进行上颈椎(枕骨底～C3)CT薄层扫描,建立健康上颈椎有限元模型,再构建齿突Ⅱ型骨折伴寰枢椎不稳模型,并在该模型中模拟改良Brooks技术和寰枢椎椎弓根螺钉内固定,分析前屈、后伸、侧曲及旋转工况下上颈椎各节段的活...     

新型寰椎钩棒及椎板钩联合枢椎椎弓根螺钉内固定的生物力学

目的 评价自行研制的寰椎后弓环抱钩棒及椎板钩联合枢椎椎弓根螺钉内固定系统的生物力学稳定性,为临床应用提供实验依据. 方法 6具新鲜尸体枕颈部标本,采用脊柱三维运动试验机依次对其齿状突切断后(A组)、寰椎椎板钩联合枢椎椎弓根螺钉内固定(B组)、自制寰椎钩棒及椎板钩联合枢椎椎弓根螺钉内固定(C组)、寰椎椎弓根螺钉联合枢椎椎弓根螺钉内固定(D组)等4种状态进行三维运动范围测试;分析比较新型寰枢椎后路内固定系统的稳定性. 结果 B组后伸平均ROM明显大于C、D组,差异均有统计学意义(P＜0.05);C、D组后伸平均ROM差异无统计学意义(P＞0.05);而B、C、D组间在其他角度ROM(前屈、侧屈、旋转)差异均无统计学意义(P＞0.05).结论 采用自制寰椎后弓钩棒及椎板钩联合枢椎椎弓根螺钉进行内固定,可为失稳的寰枢关节提供良好的即刻和较长期稳定性.     

寰枢椎后路动态固定系统有效性的实验研究

【摘要】 目的：测试自主设计的寰枢椎后路动态固定系统的有效性。方法：根据寰枢椎的解剖特征及常规寰枢椎后路椎弓根螺钉置钉技术,设计符合寰枢椎运动方式的新型寰枢椎后路动态固定系统,并测试其有效性。将8具成人枕颈标本（C0~C4）依次按完整状态组（A组）、寰枢椎不稳状态组（B组）、寰枢椎后路动态固定状态组（C组）及寰枢椎后路椎弓根螺钉固定状态组（D组）的顺序进行测试。在三维运动试验机（KD-101）上测试4组模型的颈椎运动范围（range of motion,ROM）,所有标本测试时施加1.50N·M力偶矩按前屈/后伸、左/右侧屈、左/右轴向旋转的顺序进行,取其均值,所得结果进行比较。结果：B组与A组在屈伸状态、侧屈状态和轴向旋转状态的ROM分别相差41%、44%、9%,差异有统计学意义（P<0.05）。C组与A组在屈伸、侧屈和轴向旋转状态的ROM分别相差8%、9%、9%,差异无统计学意义（P>0.05）;C组ROM与B组比较分别相差46%、50%、17%,差异有统计学意义（P<0.001）。D组固定后在屈伸、侧屈、轴向旋转状态的ROM与A组分别相差35%、46%、58%,差异有统计学意义（P<0.001）;与B组分别相差62%、70%、61%,差异有统计学意义（P<0.001）;与C组分别相差30%、41%、53%,差异有统计学意义（P<0.001）。结论：寰枢椎后路动态固定系统能够有效地限制寰枢椎的不稳,同时又能保留寰枢椎一定的屈伸、侧屈和旋转活动功能。     

新型寰枢椎后路动态固定系统的生物力学评价

目的测试并评价新型寰枢椎后路动态固定系统的生物力学性能。方法新鲜成人枕颈标本（C0-4）8例,分成4组：完整状态组、寰枢椎不稳状态组、寰枢椎后路动态固定状态组和寰枢椎后路椎弓根螺钉固定状态组。通过加载1.50 N·m的力矩,对4组标本C1/C2、C2/C3节段的前屈/后伸,左/右侧弯和左/右旋转等6种运动方式下的运动范围（range of movement,ROM）及稳定性指数（stability index,SI）进行测试。结果采用新型寰枢椎后路动态固定系统后,C1/C2、C2/C3节段的ROM与正常完整标本相比较,差异无统计学意义（P〉0.05）;而采用常规椎弓根螺钉固定与动态固定法相比,C1/C2、C2/C3节段的ROM差异有统计学意义（P〈0.001）。采用寰枢椎后路动态固定系统固定与采用后路椎弓根螺钉固定,C1/C2SI均上升,与完整状态组相比差异均有统计学意义,分别为（P〈0.05）和（P〈0.001）。C2/C3测试结果显示,采用动态固定时SI分别上升为109%、107%和112%;而采用椎弓根螺钉固定,三维运动范围SI反而分别下降为77%、71%和87%,比动态固定SI分别低29%、34%和22%,差异具有统计学意义（P〈0.001）。结论新型寰枢椎后路动态固定系统既可维持寰枢椎的部分旋转功能,又可达到坚固固定的稳定性,同时能够有效地减少对邻近节段的影响,具有良好的研究前景。     

新型寰枢椎内固定系统的生物力学评价

目的 评价一种新型寰枢椎内固定系统的生物力学性能.方法 选取12头猪颈椎标本制作寰枢椎不稳模型,采用该新型内固定系统进行固定,测量三维运动范围,并与寰枢椎椎弓根钉棒系统进行比较.结果 新型寰枢椎内固定系统的特点是设计新颖、操作简单、使用安全;生物力学实验结果表明其在旋转、屈伸及侧弯状态的活动度与寰枢椎椎弓根钉棒差异无统...     

双节段后路腰椎椎体间融合术单侧椎弓根钉固定的生物力学稳定性

目的 分析对模拟双节段腰椎后路椎体间融合术(PLIF)采用单侧椎弓根钉固定(单侧固定)的生物力学稳定性.方法 将6具新鲜成人尸体腰椎标本(L2～S2)分别制备成L4～S1的PLIF模型,应用MTS 858实验机模拟产生屈伸、侧弯、轴向旋转,并按初始状态、单侧不稳、单侧不稳-单侧固定、双侧不稳-单侧固定、双侧不稳-双侧固定、双侧不稳的顺序进行测试,动态摄取记录各个节段角位移运动范围(ROM)与中性区值(NZ).结果 单侧不稳-单侧固定屈伸、侧弯、轴向旋转方向ROM值依次为2.53±1.12、4.03±2.19、2.78±1.00,NZ值依次为1.14±0.70、1.96±1.13、1.28±0.71,均显著小于初始状态(P<0.05),相比双侧不稳-双侧固定,各方向ROM与NZ值分别增加60.13%与17.52%、315.46%与243.86%、8.17%与6.20%,但差异无统计学意义(P>0.05).双侧不稳-单侧固定侧弯与旋转状态ROM与NZ值较双侧不稳-双侧固定显著增加(P<0.05).结论 单侧固定对人腰椎标本模拟双节段单侧PLIF可提供与双侧固定相似的生物力学稳定性,而对于模拟双节段双侧PLIF则单侧固定在大多数三维运动方向上不能提供足够的力学稳定性.

Abstract：

Objective To analyze the biomechanical efficacy of unilateral pedicle screw fixation on human cadaveric lumbar spine model simulated by two-level posterior lumbar interbody fusion (PLIF). Methods Six fresh-frozen adult human cadaveric lumbar spine motion segments (L2-S2) were simulated to unilateral/bilateral L4-S1 PLIF constructs augmented by unilateral/bilateral pedicle screw fixation sequentially and respectively. All configurations were tested by MTS 858 in the following sequential construct order: the intact, UI (unilateral instability), UIUF1C (unilateral instability via unilateral pedicle screw fixation plus one cage) , BIUF1C (bilateral instability via unilateral pedicle screw fixation plus one cage) , BIBF1C (bilateral instability via bilateral pedicle screw fixation plus one cage) and BI (bilateral instability without pedicle screw and cage). Each specimen was nondestructively tested in flexion/extension, lateral performed between different simulated constructs with One Way of ANOVA and Post hoc LSD tests. Results BIBF1C had the lowest ROM and NZ of L4-S1 fusion segments in all loading models, which were significantly lower than those of any uninstmmented construct (the intact, UI and BI) (P < 0. 05). In flexion/extension, lateral bending, and axial rotation, the ROM of UIUF1C was respectively 2.53 ± 1. 12, 4.03 ± 2. 19, 2. 78 ±1.00 and the NZ of UIUF1C was respectively 1.14 ±0.70, 1.96 ±1. 13, 1.28 ±0.71, which were significantly lower than those of the intact (P <0. 05). Compared to BIBF1C, the ROM and NZ were respectively increased 60.13% and 17.52% in flexion/extension, 315.46% and 243.86% in lateral bending, 8. 17% and 6. 20% in axial rotation, however, there were no significant differences between these two constructs (P > 0. 05). In lateral-bending and axial rotation, the ROM and NZ of BIUF1C were significantly higher than those of BIBF1C (P < 0. 05). In flexion/extension, the ROM and NZ of BIUF1C were higher than those of BIBF1C but there were no significant differences (P >0. 05). Compared to the intact, BIUF1C had lower ROM and NZ except for higher NZ in axial rotation, and there were significant differences only in flexion/extension (P < 0. 05). Conclusions All tested two-level unilateral fixation on simulated human cadaveric model with unilateral PLIF can achieve similar initial biomechanical stability in comparison with two-level bilateral pedicle screw fixation. However in most test modes, two-level unilateral pedicle screw fixation on simulated human cadaveric model with bilateral PLIF can not achieve enough biomechanical efficacy in comparison with two-level bilateral pedicle screw fixation.     

Biomechanical comparison of unilateral and bilateral pedicle screws fixation for transforaminal lumbar interbody fusion after decompressive surgery -- a finite element analysis

ABSTRACT: BACKGROUND: Little is known about the biomechanical effectiveness of transforaminal lumbar interbody fusion (TLIF) cages in different positioning and various posterior implants used after decompressive surgery. The use of the various implants will induce the kinematic and mechanical changes in range of motion (ROM) and stresses at the surgical and adjacent segments. Unilateral pedicle screw with or without supplementary facet screw fixation in the minimally invasive TLIF procedure has not been ascertained to provide adequate stability without the need to expose on the contralateral side. This study used finite element (FE) models to investigate biomechanical differences in ROM and stress on the neighboring structures after TLIF cages insertion in conjunction with posterior fixation. METHODS: A validated finite-element (FE) model of L1-S1 was established to implant three types of cages (TLIF with a single moon-shaped cage in the anterior or middle portion of vertebral bodies, and TLIF with a left diagonally placed ogival-shaped cage) from the left L4-5 level after unilateral decompressive surgery. Further, the effects of unilateral versus bilateral pedicle screw fixation (UPSF vs. BPSF) in each TLIF cage model was compared to analyze parameters, including stresses and ROM on the neighboring annulus, cage-vertebral interface and pedicle screws. RESULTS: All the TLIF cages positioned with BPSF showed similar ROM (<5 %) at surgical and adjacent levels, except TLIF with an anterior cage in flexion (61 % lower) and TLIF with a left diagonal cage in left lateral bending (33 % lower) at surgical level. On the other hand, the TLIF cage models with left UPSF showed varying changes of ROM and annulus stress in extension, right lateral bending and right axial rotation at surgical level. In particular, the TLIF model with a diagonal cage, UPSF, and contralateral facet screw fixation stabilize segmental motion of the surgical level mostly in extension and contralaterally axial rotation. Prominent stress shielded to the contralateral annulus, cage-vertebral interface, and pedicle screw at surgical level. A supplementary facet screw fixation shared stresses around the neighboring tissues and revealed similar ROM and stress patterns to those models with BPSF. CONCLUSIONS: TLIF surgery is not favored for asymmetrical positioning of a diagonal cage and UPSF used in contralateral axial rotation or lateral bending. Supplementation of a contralateral facet screw is recommended for the TLIF construct.     

Evaluation of biomechanical properties of anterior atlantoaxial transarticular locking plate system using three-dimensional finite element analysis

Purpose

To evaluate a new anterior atlantoaxial transarticular locking plate system using finite element analysis.

Methods

Thin-section spiral computed tomography was performed from occiput to C₂ region. A finite element model of an unstable atlantoaxial joint, treated with an anterior atlantoaxial transarticular locking plate system, was compared with the simple anterior atlantoaxial transarticular screw system. Flexion, extension, lateral bending, and axial rotation were imposed on the model. Displacement of the atlantoaxial transarticular screw and stress at the screw–bone interface were observed for the two internal fixation systems.

Results

Screw displacement was less using the anterior atlantoaxial transarticular locking plate system compared to simple anterior atlantoaxial transarticular screw fixation under various conditions, and stability increased especially during flexion and extension.

Conclusions

The anterior atlantoaxial transarticular locking plate system not only provided stronger fixation, but also decreased screw-bearing stress and screw–bone interface stress compared to simple anterior atlantoaxial transarticular screw fixation.     

A Biomechanical Comparison of Three Different Posterior Fixation Constructs Used for C6–C7 Cervical Spine Immobilization: A Finite Element Study

The intralaminar screw construct has been recently introduced in C6–C7 fixation. The aim of the study is to compare the stability afforded by three different C7 posterior fixation techniques using a three-dimensional finite element model of a C6–C7 cervical spine motion segment. Finite element models representing three different cervical anchor types (C7 intralaminar screw, C7 lateral mass screw, and C7 pedicle screw) were developed. Range of motion (ROM) and maximum von Mises stresses in the vertebra for the three screw techniques were compared under pure moments in flexion, extension, lateral bending, and axial rotation. ROM for pedicle screw construct was less than the lateral mass screw construct and intralaminar screw construct in the three principal directions. The maximum von Misses stress was observed in the C7 vertebra around the pedicle in all the three screw constructs. Maximum von Mises stress in pedicle screw construct was less than the lateral mass screw construct and intralaminar screw construct in all loading modes. This study demonstrated that the pedicle screw fixation is the strongest instrumentation method for C6–C7 fixation. Pedicle screw fixation resulted in least stresses around the C7 pedicle-vertebral body complex. However, if pedicle fixation is not favorable, the laminar screw can be a better option compared to the lateral mass screw because the stress around the pedicle-vertebral body complex and ROM predicted for laminar screw construct was smaller than those of lateral mass screw construct.     

腰椎“U”形弹性内固定器的研制及力学评价

目的介绍腰椎“U”形弹性内固定器的研制．并利用有限元方法对其生物力学特性进行评价。方法采用镍钛合金设计一种腰椎弹性内固定器。选择1名成年男性志愿者,以L4、5节段为研究对象,采用螺旋CT对其进行层厚1．0mm的连续水平扫描,借助Mimics 11．11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。结果弹性内固定系统各部分于垂直压缩时所受应力远小于其他状态（P〈0.001）;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．有望成为较好地进行腰椎弹性内固定的一种装置。     

Biomechanical evaluation of diagonal fixation in pedicle screw instrumentation.

STUDY DESIGN: Flexibility tests and finite element analyses were performed for the biomechanical evaluation of diagonal transfixation in pedicle screw instrumentation. OBJECTIVE: To assess the biomechanical advantages of diagonal transfixation compared with conventional horizontal transfixation. SUMMARY AND BACKGROUND DATA: A few pedicle screw instrumentation systems allow the use of cross-links in the diagonal direction. Such a diagonal transfixation is anticipated to improve the surgical construct stability, but its biomechanical qualities have not been completely evaluated. METHODS: Flexibility tests were performed on 10 calf lumbar spines (L2-L5). Specimens were subjected to pure moments up to 8.2 Nm in flexion, extension, lateral bending, and extension while the resulting movements of L3 and L4 were measured by a three-dimensional motion analysis system. The tested cases included (1) intact, (2) pedicle screw fixation without transfixation after total removal of the L3-L4 disc, (3) pedicle screw fixation with diagonal transfixation, and (4) pedicle screw fixation with horizontal transfixation. Three-dimensional finite element models of the tested surgical constructs were also developed by use of three-dimensional beam elements to investigate the effect of diagonal transfixation and horizontal transfixation on the construct stability and the corresponding stress changes in the screws. RESULTS: When compared with no transfixation, horizontal transfixation significantly improved the lateral bending and axial rotation stability by 15.7% and 13.9%, respectively, but there was no improvement of stability in flexion and extension. By contrast, diagonal transfixation significantly improved the flexion and extension stability by 12% and 10.7%, respectively, but not the lateral bending and axial rotation stability in comparison with no transfixation. Comparison between horizontal transfixation and diagonal transfixation showed that the stabilizing effect of diagonal transfixation was greater in flexion and extension (13% and 11%, P < 0.01) than that of horizontal transfixation but smaller in lateral bending (11%, P < 0.05) and axial rotation (6.6%, P > 0.1). Finite element model predictions of the motion changes were similar to the changes observed in flexibility tests. In horizontal transfixation, the load changes, compared with no transfixion, were a 0.02% increase in flexion-extension, a 27.5% increase in lateral bending, and a 58% decrease in axial rotation, and the magnitudes of the moments applied on both the right and left pedicle screws were identical. However, when diagonal transfixation was achieved by connecting the left superior screw and the right inferior screw, the loads in the left screw were increased by 11.5% in flexion-extension, 43.6% in lateral bending, and 7.9% in axial rotation, whereas the loads in the right screw were decreased by 10.9% in flexion-extension, increased by 0.06% in lateral bending, and decreased by 18.1% in axial rotation. CONCLUSIONS: The results of this study showed that diagonal transfixation provides more rigid fixation in flexion and extension but less in lateral bending and axial rotation in comparison with horizontal transfixation. Furthermore, greater stresses in the pedicle screws were predicted in the diagonal transfixation model. These limitations of diagonal transfixation should be considered carefully for clinical application.     

后路寰椎侧块螺钉联合枢椎椎板钩内固定的生物力学稳定性

目的研究后路寰椎侧块螺钉联合枢椎椎板钩内固定的生物力学稳定性。方法取6例新鲜尸体颈椎标本,每具标本分别依次进行完整(正常组)、寰枢椎不稳(失稳组)、寰枢侧块螺钉联合枢椎椎弓根螺钉钉棒固定(Harms组)、寰椎侧块螺钉联合枢椎椎板钩固定(钉钩组)状态的生物力学测试,每组6个标本,将各标本装载在脊柱三维运动机上,分别施予1.5 N·m力矩,记录标本在前屈后伸、左右侧曲、左右旋转3个方向上的活动度(ROM),比较各组ROM。结果相对于正常组标本,失稳组标本在上述3个方向上的ROM显著增大;相较于正常和失稳组标本,Harms组和钉钩组的标本在上述3个方向上ROM显著减小;钉钩组与Harms组间在上述3个方向的ROM差异无统计学意义(P0.05)。结论后路寰椎侧块螺钉联合枢椎椎板钩内固定在生物力学稳定性上与Harms固定相似,可以起到良好的固定效果。     

枢椎棘突作为第三锚定点枕颈固定的生物力学有限元分析

目的:通过有限元方法分析枢椎棘突作为第三锚定点枕颈固定的生物力学稳定性。方法:选择一位健康成年人的C0-C3 CT资料,利用Mimics、Hypermesh和Abaqus等软件建立上颈椎有限元模型(完整模型)。模拟寰椎Jefferson骨折后进行枕颈固定,分别为双侧枢椎椎弓根螺钉+枢椎棘突螺钉+枕骨螺钉钉棒固定(第三锚定点枕颈固定组)和双侧枢椎椎弓根螺钉+枕骨螺钉钉棒固定(双侧枢椎椎弓根螺钉枕颈固定组)。在骨折模型前和固定后,分别施加50N垂直载荷,模拟头部重力作用,施加1.5N·m纯扭矩,从而模拟颈椎前后屈伸、左右旋转、左右侧屈6种状态。在动态加载中,计算固定前和后C0/1、C1/2、C2/3关节间在前屈、后伸、左右侧屈和旋转6个方向上的活动度(ROM)。结果:本研究建立的上颈椎(C0-C3)三维非线性有限元模型外形与正常上颈椎解剖结构相符,韧带连接一致,能较好地体现上颈椎的解剖特点。在边界范围和载荷条件相同的情况下,本研究完整模型的ROM在体外标本实验研究参考文献的实验数据范围内,具有很好的关联性。双侧枢椎椎弓根螺钉固定组和第三锚定点固定组在屈伸、侧屈和旋转运动C0-C2 ROM结果均较完整模型组显著降低,其中差异最大的在C1/2旋转活动上。可见,两种固定方法都可以对骨折模型起到较好的稳定作用。除C0/1的侧屈活动外,第三锚定点固定组在其余各个方向上C0-C2固定后ROM均较双侧椎弓根螺钉固定组降低,其中差异最大的在C0/1屈伸活动上。结论:枕颈固定融合中枢椎棘突作为第三锚定点也许可以进一步加强枕颈屈伸的稳定性,减少内固定失败的发生。     

寰枢椎后路椎弓根螺钉固定的生物力学评价

目的：评价寰枢椎后路椎弓根螺钉固定的生物力学稳定性。方法：6具新鲜颈椎标本，按随机顺序，对每一标本先后行C1-C2椎弓根螺钉、Magerl螺钉、Brooks钢丝以及螺钉联合钢丝固定，在脊柱三维运动实验机上测量其三维运动范围。结果：Magerl螺钉或C1-C2椎弓根螺钉联合Brooks钢丝组成的固定系统的三维运动范围最小。C1-C2椎弓根螺钉固定的前后屈伸运动范围与Brooks钢丝固定无差异，但大于Magerl螺钉；其左右侧屈运动范围小于Brooks钢丝固定，大于Magerl螺钉；其轴向旋转角度明显小于Brooks钢丝固定，但与Magerl螺钉无统计学差异。结论：C1-C2椎弓根螺钉的三维稳定性与Magerl螺钉相当，联合Brooks钢丝固定可进一步提高其稳定性。