椎弓根钉内固定联合椎体成形术治疗骨质疏松性胸腰椎爆裂骨折的三维有限元研究

目的采用有限元方法比较骨质疏松性胸腰椎爆裂骨折在椎弓根钉内固定联合椎体成形术与椎弓根钉结合伤椎置钉内固定术后的生物力学稳定性。方法建立骨质疏松性L_1椎体爆裂骨折有限元模型,模拟短节段椎弓根钉联合椎体成形术(A组)以及椎弓根钉结合伤椎置钉内固定术(B组),比较2组前屈、后伸、侧屈、旋转载荷下L_1椎体最大位移及内固定物最大应力值。结果在前屈、后伸、侧屈、旋转载荷下,L_1椎体最大位移见于前屈载荷,2组前屈、后伸、侧屈、旋转载荷下L_1椎体最大位移比较差异无统计学意义(P0.05)。在前屈、后伸及侧屈载荷时,内固定物应力最大值为下位螺钉尾部与钛棒联接处,A组前屈、后身、侧屈内固定应力较B组小,差异有统计学意义(P0.05);在旋转载荷时,A组内固定物应力最大部位仍为下位螺钉尾部与钛棒联接处,B组内固定物应力最大部位为伤椎螺钉尾部与钛棒联接处,A组旋转内固定物应力较B组小,差异有统计学意义(P0.05)。结论椎弓根钉内固定联合椎体成形术治疗骨质疏松性胸腰椎爆裂骨折生物力学稳定性强,可获得比椎弓根钉结合伤椎置钉内固定术更小的内固定物应力,能有效防止内固定物失效。     

脊柱Denis B型骨折行单节段与双节段融合后生物力学强度比较

目的 比较脊柱Denis B型骨折行单节段与双节段融合后的生物力学强度.方法 选取因脊柱Denis B型骨折而行后路复位椎弓根螺钉固定+前路双节段融合和行前路单节段融合患者各1例,两例均为L1椎体爆裂性骨折的女性患者,年龄为45岁和41岁,Frankel分级分别为B级和C级.术后1年患者均达到影像学椎间融合标准.收集2例患者术后1年随访时的CT数据,包括行单节段融合患者取及未取椎弓根螺钉的CT数据,行双节段融合患者未取出螺钉的CT数据;将此三组数据导入Mimics软件建立T11～L2三维模型.建模后,将模型再次导入到有限元分析软件ANSYS,设定边界条件并施以260 N的轴向压力及10 Nm扭矩,模拟椎体前屈、后伸、左侧弯、右侧弯、左旋、右旋运动,观察三个模型在上述六个运动方向上的脊柱运动平均位移以及椎间融合后T11-12椎间盘的应力分布云图,并比较椎间盘的平均Von Mises应力.结果 双节段融合与单节段融合未取内固定组脊柱活动平均位移比较,差异无统计学意义.单节段融合取内固定组在上述六个运动方向上均明显高于双节段融合和单节段融合未取内固定组.在上述六个运动方向T11-12椎间盘平均Von Mises应力,双节段融合大于单节段融合取和未取内固定组,单节段融合未取内固定组大于取内固定组.结论 单节段融合手术在椎间融合满意的前提下,取出后路椎弓根螺钉可提高脊柱活动度,减少椎间盘应力,延缓椎间盘退变.     

DRFS系统的体外生物力学测试

目的 测试DRFS系统固定后脊柱标本的刚度及其椎弓根钉的拔出力,评估DRFS系统临床应用的可靠性.方法 选择猪脊柱标本12具,测试其前屈、后伸、侧屈及旋转时的刚度;制成失稳标本后,重复各项运动刚度测试;用DRFS固定失稳标本后,再重复各项运动刚度测试.选择双节段腰椎标本12对,分别拧入DRFS系统椎弓根钉(固定钉、提拉钉)后,进行拔出测试.结果 在猪脊柱标本前屈、后伸、侧屈及旋转活动的刚度测试中,与完整脊柱的刚度相比较,失稳脊柱各项运动的刚度均明显减小(P<0.05);DRFS系统内固定后,脊柱各项运动的刚度均明显高于失稳脊柱(P<0.05),固定钉的拔出力明显大于提拉钉(P<0.01).结论 DRFS系统内固定术后脊柱标本的刚度明显高于失稳标本.其椎弓根钉可提供足够的提拉力.     

前路单节段融合内固定治疗伴椎弓根断裂的Denis B型胸腰椎爆裂骨折生物力学研究

目的探讨前路单节段融合内固定治疗伴椎弓根断裂的Denis B型胸腰椎爆裂骨折后的脊椎生物力学稳定性。方法取6具新鲜成人尸体胸腰椎标本(T11~L3)作为正常组(A组),采用椎体切除法依次建立L1Denis B型爆裂骨折模型并行前路单节段融合内固定,分别为椎弓根完整组(B组)、单侧椎弓根切断组(C组)和双侧椎弓根切断组(D组)。通过脊柱三维运动机依次测定各组在8.0 N·m纯力偶矩下屈伸、左右侧弯及左右旋转活动度(range of motion,ROM)。结果 B、C、D组T12、L1脊柱运动单元前屈、后伸、左右侧弯ROM均显著低于A组(P0.05),D组显著高于B、C组(P0.05),B、C组间差异无统计学意义(P0.05);B、C组左右旋转ROM均显著低于A、D组(P0.05),B、C组间及A、D组间比较差异无统计学意义(P0.05)。各组间L1、L2脊柱运动单元前屈、后伸、左右侧弯、左右旋转ROM比较,差异均无统计学意义(P0.05)。结论前路单节段融合内固定治疗Denis B型胸腰椎爆裂骨折伴一侧椎弓根断裂时,在屈伸、侧弯及旋转方向能提供足够初始生物力学稳定性,而伴双侧椎弓根断裂时生物力学稳定性差。     

单节段椎弓根螺钉内固定治疗胸腰椎骨折的进展

随着现代工业及交通运输业的迅猛发展,脊柱损伤特别是胸腰椎损伤的发生率明显上升。短节段椎弓根螺钉内固定术（short-segment pedicle instrumentation,SSPI）作为治疗胸腰椎爆裂骨折的主要手术方法被广泛应用于临床[1、2]。近年来,有学者提出应用单节段椎弓根螺钉内固定术（mono-segment pedicle instrumentation,MSPI）治疗胸腰椎骨折[3~7],通过将椎弓根螺钉置入伤椎及相邻椎体,对骨折椎体直接复位、固定,达到重建脊柱稳定性、减少融合节段及术后并发症的目的。现就单节段椎弓根螺钉固定治疗胸腰椎骨折的理论基础及临床应用综述如下。     

椎弓根螺钉内固定治疗胸腰段脊柱单节段骨折效果观察

目的探讨椎弓根螺钉内固定治疗胸腰段脊柱单节段骨折的临床效果。方法应用椎弓根螺钉内固定术治疗70例胸腰段脊柱单节段骨折患者。回顾性分析患者的临床资料。结果本组均顺利完成手术。术后随访1a,手术后患者椎体前缘高度明显比手术前高,Cobb'角度显著低于手术前,差异有统计学意义(P0.05)。患者术后疼痛程度明显比手术前低,且随着康复时间的延长,疼痛程度逐渐降低,差异有统计学意义(P0.05)。结论椎弓根螺钉内固定术治疗胸腰段脊柱单节段骨折,可以有效矫正脊柱畸形,降低疼痛程度,临床效果显著。     

脊柱骨折经伤椎椎弓根置钉附加横连短节段固定的稳定性测试

目的:探讨脊柱骨折经伤椎椎弓根置钉附加横连短节段钉棒固定的稳定性.方法:5具新鲜冰冻小牛腰椎标本(L1～L5)制备成L3椎体爆裂骨折模型,依次进行单纯经伤椎和上下相邻椎体椎弓根置钉短节段6钉固定(单纯经伤椎6钉固定组)和附加横连经伤椎和上下相邻椎体椎弓根置钉短节段6钉固定(附加横连经伤椎6钉固定组),测试L2～L4损伤前(对照组)、损伤后(骨折组)及单纯经伤椎6钉固定组和附加横连经伤椎6钉固定组的三维6个方向的运动范围(ROM),比较各组间的差异.结果:L3椎体爆裂骨折后L2～L4各方向的ROM明显增加,与损伤前比较均有显著性差异(P<0.05);单纯经伤椎6钉固定组与附加横连接经伤椎6钉固定组各方向的ROM均明显减小,与骨折组相比均有显著性差异(P<0.05),在前屈、后伸、侧弯运动方向的ROM小于对照组,差异有显著性(P<0.05),旋转方向上大于对照组(P<0.05).两种固定方式在前屈、后伸、侧弯方向上的ROM无显著性差异(P>0.05),附加横连经伤椎6钉固定组较单纯经伤椎6钉固定组在旋转方向上的ROM小,差异有显著性(P<0.05).结论:经伤椎椎弓根置钉短节段钉棒固定可提高骨折模型各个运动方向上的生物力学稳定性,附加横连经伤椎6钉固定技术较单纯经伤椎6钉固定技术在轴向旋转运动方向上可提供更强的力学稳定性.     

退变性腰椎侧弯单节段与双节段固定融合术后邻近节段的生物力学分析

目的利用有限元分析方法探讨单节段和双节段内固定+椎间融合术治疗退变性腰椎侧弯后对邻近节段影响的生物力学变化。方法基于一例退变性腰椎侧弯患者T12-S1上段连续的CT扫描图像,建立完整、有效的三维有限元模型。对其分别采用单节段和双节段椎管减压+椎间植骨融合+椎弓根螺钉内固定术治疗,在各种工况下对术后模型进行力学加载,比较两种治疗方法对脊柱活动度及固定邻近节段椎间盘、关节突关节的影响。结果单节段固定融合术后腰段脊柱前屈活动度增大,双节段固定融合术后腰段脊柱活动度减小,单节段固定融合术较双节段固定融合术更能增加邻近节段的活动范围;两种方法固定术后邻近节段椎间盘应力均有所集中,以邻近上节段明显,且单节段固定融合术的影响更大;两种方法固定术后对固定相邻下节段关节突关节软骨的应力影响较大,对相邻上节段影响相对较小,均以旋转运动明显,但单-双节段固定融合术对关节突关节软骨的影响无统计学差异。结论单-双节段内固定+椎间融合术后均可改变脊柱活动度并增加邻近节段活动度,且对固定邻近节段椎间盘及关节突关节的应力有所影响,有可能造成术后侧弯的加重。     

经后路伤椎单节段椎弓根螺钉固定治疗胸腰段骨折的体会

[目的]探讨后路单节段椎弓根螺钉内固定治疗胸腰椎骨折的临床疗效。[方法]自2009年2月²011年3月行后路单节段椎弓根螺钉内固定治疗胸腰椎骨折21例,男12例,女9例,年龄232011年3月行后路单节段椎弓根螺钉内固定治疗胸腰椎骨折21例,男12例,女9例,年龄23⁶4岁,平均34岁,观察骨折椎的椎弓根螺钉位置及手术前后伤椎复位高度和后凸Cobb角。[结果]术后CT示伤椎椎弓根螺钉均在正常骨性结构内,术后无脊髓损伤、感染等并发症发生。伤椎椎体前缘高度百分比从术前平均(54.75±0.06)%恢复至术后平均(92.35±0.12)%,(P<0.05);骨折椎后凸Cobb角从术前平均(25.13±2.67)°恢复至(4.83±1.43)°(P<0.05)。患者VAS评分改善明显(P<0.05)。所有骨折全部获得骨性愈合,骨折椎体高度无明显丢失,无钉棒弯曲、松动或断裂。[结论]后路单节段椎弓根螺钉内固定对于胸腰段骨折治疗有效。只要手术适应证选择正确,后路单节段椎弓根螺钉内固定可用于治疗胸腰段骨折。     

椎弓根钉单节段固定术治疗胸腰椎不稳定骨折

目的探讨后路椎弓根钉单节段固定术治疗胸腰椎不稳定骨折的临床效果。方法应用经椎弓根螺钉内固定系统单节段固定术治疗胸腰椎不稳定骨折6例,进行后路减压、植骨融合,比较神经功能及骨折愈合情况。结果全部病例获得随访,神经功能按Frankel分级,有1～3级的恢复,全部骨折均顺利愈合,椎体高度无再丢失。结论椎弓根钉单节段内固定术治疗胸腰椎不稳定骨折,可有效重建脊柱稳定性,脊柱融合率高,临床效果满意。     

Non-fusion instrumentation of the lumbar spine with a hinged pedicle screw rod system: an in vitro experiment

In advanced stages of degenerative disease of the lumbar spine instrumented spondylodesis is still the golden standard treatment. However, in recent years dynamic stabilisation devices are being implanted to treat the segmental instability due to iatrogenic decompression or segmental degeneration. The purpose of the present study was to investigate the stabilising effect of a classical pedicle screw/rod combination, with a moveable hinge joint connection between the screw and rod allowing one degree of freedom (cosmicMIA). Six human lumbar spines (L2–5) were loaded in a spine tester with pure moments of ±7.5 Nm in lateral bending, flexion/extension and axial rotation. The range of motion (ROM) and the neutral zone were determined for the following states: (1) intact, (2) monosegmental dynamic instrumentation (L4-5), (3) bisegmental dynamic instrumentation (L3–5), (4) bisegmental decompression (L3–5), (5) bisegmental dynamic instrumentation (L3–5) and (6) bisegmental rigid instrumentation (L3–5). Compared to the intact, with monosegmental instrumentation (2) the ROM of the treated segment was reduced to 47, 40 and 77% in lateral bending, flexion/extension and axial rotation, respectively. Bisegmental dynamic instrumentation (3) further reduced the ROM in L4-5 compared to monosegmental instrumentation to 25% (lateral bending), 28% (flexion/extension) and 57% (axial rotation). Bisegmental surgical decompression (4) caused an increase in ROM in both segments (L3–4 and L4–5) to approximately 125% and approximately 135% and 187–234% in lateral bending, flexion/extension and axial rotation, respectively. Compared to the intact state, bisegmental dynamic instrumentation after surgical decompression reduced the ROM of the two-bridged segments to 29–35% in lateral bending and 33–38% in flexion/extension. In axial rotation, the ROM was in the range of the intact specimen (87–117%). A rigid instrumentation (6) further reduced the ROM of the two-bridged segments to 20–30, 23–27 and 50–68% in lateral bending, flexion/extension and axial rotation, respectively. The results of the present study showed that compared to the intact specimen the investigated hinged dynamic stabilisation device reduced the ROM after bisegmental decompression in lateral bending and flexion/extension. Following bisegmental decompression and the thereby caused large rotational instability the device is capable of restoring the motion in axial rotation back to values in the range of the intact motion segments.     

Is a single anterolateral screw-plate fixation sufficient for the treatment of spinal fractures in the thoracolumbar junction? A Biomechanical in vitro Investigation

Controversy exists about the indications, advantages and disadvantages of various surgical techniques used for anterior interbody fusion of spinal fractures in the thoracolumbar junction. The purpose of this study was to evaluate the stabilizing effect of an anterolateral and thoracoscopically implantable screw-plate system. Six human bisegmental spinal units (T12–L2) were used for the biomechanical in vitro testing procedure. Each specimen was tested in three different scenarios: (1) intact spinal segments vs (2) monosegmental (T12/L1) anterolateral fixation (macsTL, Aesculap, Germany) with an interbody bone strut graft from the iliac crest after both partial corpectomy (L1) and discectomy (T12/L1) vs (3) bisegmental anterolateral instrumentation after extended partial corpectomy (L1), and bisegmental discectomy (T12/L1 and L1/L2). Specimens were loaded with an alternating, nondestructive maximum bending moment of ±7.5 Nm in six directions: flexion/extension, right and left lateral bending, and right and left axial rotation. Motion analysis was performed by a contact-less three-dimensional optical measuring system. Segmental stiffness of the three different scenarios was evaluated by the relative alteration of the intervertebral angles in the three main anatomical planes. With each stabilization technique, the specimens were more rigid, compared with the intact spine, for flexion/extension (sagittal plane) as well as in left and right lateral bending (frontal plane). In these planes the bisegmental instrumentation compared to the monosegmental case had an even larger stiffening effect on the specimens. In contrast to these findings, axial rotation showed a modest increase of motion after bisegmental instrumentation. To conclude, the immobilization of monosegmental fractures in the thoracolumbar junction can be secured by means of bone grafting and the implant used in this study for all three anatomical planes. After bisegmental anterolateral stabilization a sufficient reduction of the movements was registered for flexion/extension and lateral bending. However, the observed slight increase of the range of motion in the transversal plane may lead to loosening of the implant before union. Therefore, the use of an additional dorsal fixation device should be considered.     

Biomechanical in vitro comparison of different mono- and bisegmental anterior procedures with regard to the strategy for fracture stabilisation using minimally invasive techniques

Endoscopic minimally invasive techniques have become an established method of fracture stabilisation in the spine. In view of this fact, anterior stabilisation strategies must be reconsidered, as monosegmental A 3.1 compression fractures are increasingly being stabilised endoscopically from the anterior aspect using minimally invasive techniques. This study investigated the biomechanical necessity of anterior two-point or four-point stabilisation in the instrumentation of mono- and bisegmental fractures. In three biomechanical in vitro studies, burst fracture stabilisation was simulated, and anterior short fixation devices were tested under load with pure moments up to 3.75 Nm to evaluate the biomechanical stabilising characteristics of different kinds of instrumentations in flexion/extension, lateral bending, and axial rotation. Only anterior four-point stabilisation resulted in sufficient primary stability both in mono- and bisegmental instrumentation and therefore represents the standard procedure in open as well as in minimally invasive spinal surgery.An erratum to this article can be found at     

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.     

In vitro biomechanical studies of an anterior thoracolumbar implant

After L1 corpectomy in T11-L3 human cadaveric spine, anterior thoracolumbar instrumentation with strut grafting restores spinal stability. T12-L2 angular rotation was measured in response to moments of 0.0, 1.5, 3.0, 4.5, and 6.0 Nm in flexion, extension, lateral bending, and axial rotation, respectively. The spines were tested: 1) intact; 2) after partial L1 corpectomy, grafting, and instrumentation (Profile plate, DePuy-AcroMed, Raynham, MA), with the wooden dowel graft screwed to the plate; 3) without graft screw fixation; and 4) after flexion-extension cyclic fatiguing for 5000 cycles at a load of +/-3.0 Nm. Before and after fatiguing, the instrumented spine was significantly (p 相似文献   

Less invasive posterior fixation method following transforaminal lumbar interbody fusion: a biomechanical analysis.

BACKGROUND CONTEXT: Current surgical trends increasingly emphasize the minimization of surgical exposure and tissue morbidity. Previous research questioned the ability of unilateral pedicle screw instrumentation to adequately stabilize posterior fusion constructs. No study to date has addressed the effects of reduced posterior instrumentation mass on interbody construct techniques. Unilateral surgical exposure for transforaminal lumbar interbody fusion (TLIF) allows ipsilateral pedicle screw placement. Theoretically, percutanous contralateral facet screw placement could provide supplemental construct support without additional surgical exposure. PURPOSE: Identify the biomechanical effects of reduced spinal fusion instrumentation mass on interbody construct stability. STUDY DESIGN: An in vitro biomechanical study using human lumbar spines comparing stability of TLIF constructs augmented by: (1) bilateral pedicle screw fixation, (2) unilateral pedicle screw fixation, or (3) a novel unilateral pedicle screw fixation supplemented with contralateral facet screw construct. METHODS: Seven fresh frozen human cadaveric specimens were tested in random construct order in flexion/extension, lateral bending, and axial rotation using +/-5.0 Nm torques and 50 N axial compressive loads. Analysis of torque rotation curves determined construct stability. Using paired statistical methods, comparison of construct stiffness and total range of motion within each specimen were performed using the Wilcoxon signed ranks test with a Holm-Sidák multiple comparison procedure (alpha=0.05). RESULTS: In flexion/extension, lateral bending, and axial rotation, there were no measurable differences in either stiffness or range of motion between the standard bilateral pedicle screw and the novel construct after TLIF. After TLIF, the unilateral pedicle screw construct provided only half of the improvement in stiffness compared with bilateral or novel constructs and allows for significant off-axis rotational motions, which could be detrimental to stability and the promotion for fusion. CONCLUSIONS: All tested TLIF constructs with posterior instrumentation decreased segmental range of motion and increased segmental stiffness. While placing unilateral posterior instrumentation decreases overall implant bulk and dissection, it allows for significantly increased segmental range of motion, less stiffness, and produces off-axis movement. The technique of contralateral facet screw placement provides the surgical advantages of unilateral pedicle screw placement with stability comparable to TLIF with bilateral pedicle screws.     

胸腰椎爆裂骨折三种后路内固定方法的稳定性生物力学研究

[目的]比较长节段固定术、短节段固定术和短节段结合椎体成形固定术治疗胸腰椎爆裂骨折的稳定性。[方法]收集6具新鲜尸体的脊柱(T9～L5)标本,对每一具标本依次按完整状态、骨折状态、长节段固定、短节段固定和短节段结合椎体成形的顺序进行测试,计算其在屈曲、背伸、左右侧弯和左右旋转6个方向的运动范围,比较各组间差异。[结果]骨折后脊柱在6个方向上的运动范围均增加(P<0.05);各内固定组的运动范围均小于完整组(P<0.05);长节段固定和短节段结合椎体成形固定的运动范围小于单纯短节段固定组(P<0.05);短节段结合椎体成形固定在屈曲和左右侧屈方向上的运动范围与长节段固定无差别(P>0.05),而在背伸和左右旋转方向上的运动范围短节段结合椎体成形固定则大于长节段固定(P<0.05)。[结论]通过延长固定节段与联合椎体成形均能够增加短节段固定的稳定性,在屈曲和左右侧屈方向上短节段联合椎体成形已经能够达到长节段固定所能够达到的稳定性。     

Biomechanical comparison of two-level cervical locking posterior screw/rod and hook/rod techniques.

BACKGROUND CONTEXT: Locking posterior instrumentation in the cervical spine can be attached using 1) pedicle screws, 2) lateral mass screws, or 3) laminar hooks. This order of options is in order of decreasing technical difficulty and decreasing depth of fixation, and is thought to be in order of decreasing stability. PURPOSE: We sought to determine whether substantially different biomechanical stability can be achieved in a two-level construct using pedicle screws, lateral mass screws, or laminar hooks. Secondarily, we sought to quantify the differential and additional stability provided by an anterior plate. STUDY DESIGN: In vitro biomechanical flexibility experiment comparing three different posterior constructs for stabilizing the cervical spine after three-column injury. METHODS: Twenty-one human cadaveric cervical spines were divided into three groups. Group 1 received lateral mass screws at C5 and C6 and pedicle screws at C7; Group 2 received lateral mass screws at C5 and C6 and laminar hooks at C7; Group 3 received pedicle screws at C5, C6, and C7. Specimens were nondestructively tested intact, after a three-column two-level injury, after posterior C5-C7 rod fixation, after two-level discectomy and anterior plating, and after removing posterior fixation. Angular motion was recorded during flexion, extension, lateral bending, and axial rotation. Posterior hardware was subsequently failed by dorsal loading. RESULTS: Laminar hooks performed well in resisting flexion and extension but were less effective in resisting lateral bending and axial rotation, allowing greater range of motion (ROM) than screw constructs and allowing a significantly greater percentage of the two-level ROM to occur across the hook level than the screw level (p<.03). Adding an anterior plate significantly improved stability in all three groups. With combined hardware, Group 3 resisted axial rotation significantly worse than the other groups. Posterior instrumentation resisted lateral bending significantly better than anterior plating in all groups (p<.04) and resisted flexion and axial rotation significantly better than anterior plating in most cases. Standard deviation of the ROM was greater with anterior than with posterior fixation. There was no significant difference among groups in resistance to failure (p=.74). CONCLUSIONS: Individual pedicle screws are known to outperform lateral mass screws in terms of pullout resistance, but they offered no apparent advantage in terms of construct stability or failure of whole constructs. Larger standard deviations in anterior fixation imply more variability in the quality of fixation. In most loading modes, laminar hooks provided similar stability to lateral mass screws or pedicle screws; caudal laminar hooks are therefore an acceptable alternative posteriorly. Posterior two-level fixation is less variable and slightly more stable than anterior fixation. Combined instrumentation is significantly more stable than either anterior or posterior alone.     

In vitro biomechanical comparison of an anterior and anterolateral lumbar plate with posterior fixation following single-level anterior lumbar interbody fusion

OBJECT: Anterior lumbar interbody fusion (ALIF) is often supplemented with instrumentation to increase stability in the spine. If anterior plate fixation provided the same stability as posterior pedicle screw fixation (PSF), then a second approach and its associated morbidity could be avoided. METHODS: Seven human cadaveric L4-5 spinal segments were tested under three conditions: ALIF with an anterior plate, ALIF with an anterolateral plate, and ALIF supplemented by PSF. Range of motion (ROM) was calculated for flexion/extension, lateral bending, and axial torsion and compared among the three configurations. RESULTS: There were no significant differences in ROM during flexion/extension, lateral bending, or axial torsion among any of the three instrumentation configurations. CONCLUSIONS: The addition of an anterior plate or posterior PS/rod instrumentation following ALIF provides substantially equivalent biomechanical stability. Additionally, the position of the plate system, either anterior or anterolateral, does not significantly affect the stability gained.     

Two column lesions in the thoracolumbar junction: anterior,posterior or combined approach? A comparative biomechanical in vitro investigation

There are various surgical techniques for the treatment of spinal fractures in the thoracolumbar region. Several implants have been developed for anterior or posterior instrumentation. Optimal treatment of unstable thoracolumbar osseous and ligamentous injuries remains controversial. To compare the stabilizing effects of an antero-lateral, thoracoscopically implantable plate system (macsTL, Aesculap, Germany) with the stability provided by a fixateur interne (SOCON, Aesculap, Germany), this in vitro investigation examined six human bisegmental (T12–L2) spinal units. Specimens were tested intact, and with simulation of osseous lesions in the anterior and ligamentous lesions in the posterior column (combined A/B-fracture). While loaded in the main anatomical planes such as flexion/extension, left and right lateral bending and left and right axial rotation with a bending moment of 7.5 Nm in a special testing jigs, motion analysis was performed. Quantitative interpretation of the stabilizing effect was achieved using a contactless three-dimensional motion analysis system. Each specimen was tested in four different scenarios: the first step measured movements of intact spinal segments. For the second step, specimens underwent simulation of combined A/B-fracture provided with bisegmental (T12/L2) antero-lateral fixation and bone strut graft from the iliac crest. For the third step, segments were additionally stabilized by the fixateur interne. The last measurement (fourth step) was performed after removing the anterior instrumentation. Range of motion (ROM) values were compared and statistically evaluated. Compared to the intact specimens the anterior instrumentation of the combined lesion, simulated A/B-fracture, leads to a stabilizing effect in flexion/extension and lateral bending. In contrast to these findings the torsional instability increased for the upper segment and bisegmentally. A maximum rigidity, beyond intact values, was registered for each anatomical plane with the combined instrumentation: antero-lateral and fixateur interne. After removing the anterior screw plate system maximum movements, in all segments for flexion/extension and lateral bending, bisegmentally and for the upper segment in axial rotation, were less than ROM values measured with the anterior system only. With respect to these findings a combined ventro-dorsal stabilization procedure should be considered for ligamentous disruptions of the posterior column in combination with A-fractures in the thoracolumbar junction.