Biomechanical comparison of the angle of inserted screws and the length of anterior cervical plate systems with allograft spacers

BackgroundComparative studies of the biomechanical effects of plates of varying lengths and different screw insertion angles on allograft spacers are lacking.MethodsFinite element model analysis of a previously validated, three-dimensional, intact cervical spinal segment model of C3–6 was conducted in the present study. On the C5–6 segment, anterior discectomy and fusion were performed using allograft spacers and different combinations of anterior plates and screws. The biomechanical characteristics of combinations of short, medium, and maximal length plates with screw insertion angles of 0°, 8°, 16°, and 32° were analyzed.FindingsIn flexion and extension, the risk of allograft spacer subsidence decreased as screw angles increased. Short plates with a screw insertion angle of 32° posed the lowest subsidence risk, similar to medium length plates with a screw insertion angle of 16°, in all motion conditions. The risk of bone yielding increased as plate length increased, but decreased as the screw insertion angle increased.InterpretationShort plates with a large screw insertion angle (32°) showed the highest mechanical stability and load sharing of allograft spacers and the lowest risk of screw loosening. Accordingly, we recommend the use of a short plate and large screw insertion angle for anterior cervical discectomy and fusion.     

不稳定Hangman骨折颈椎前后路融合金属植入物内固定方式的对比

背景:对于Hangman骨折,采用颈前路融合钢板置入内固定和后路C2椎弓根、C3侧块钉棒置入内固定,目前存在争议。目的:比较颈前路融合钢板置入内固定和后路C2椎弓根、C3侧块钉棒置入内固定治疗Hangman骨折的临床效果。方法:将26例Hangman骨折患者按随机数字表法分为2组,分别行颈前路减压植骨钛合金钢板置入内固定与后路C2椎弓根、C3侧块钉棒置入内固定治疗。结果与结论:与后路C2椎弓根、C3侧块钉棒置入内固定治疗比较,颈前路减压植骨钛合金钢板置入内固定治疗手术时间更短,术中出血与术后引流量更少(P<0.05)。两组术中、术后并发症差异无显著性意义。提示与颈椎后路手术内固定相比,颈椎前路融合植入物内固定手术治疗Hangman骨折手术时间短,术中出血量少,术后颈椎功能恢复良好。     

不稳定Hangman骨折颈椎前后路融合金属植入物内固定方式的对比

背景：对于Hangman骨折,采用颈前路融合钢板置入内固定和后路C2椎弓根、C3侧块钉棒置入内固定,目前存在争议。目的：比较颈前路融合钢板置入内固定和后路C2椎弓根、C3侧块钉棒置入内固定治疗Hangman骨折的临床效果。方法：将26例Hangman骨折患者按随机数字表法分为2组,分别行颈前路减压植骨钛合金钢板置入内固定与后路C2椎弓根、C3侧块钉棒置入内固定治疗。结果与结论：与后路C2椎弓根、C3侧块钉棒置入内固定治疗比较,颈前路减压植骨钛合金钢板置入内固定治疗手术时间更短,术中出血与术后引流量更少（P〈0.05）。两组术中、术后并发症差异无显著性意义。提示与颈椎后路手术内固定相比,颈椎前路融合植入物内固定手术治疗Hangman骨折手术时间短,术中出血量少,术后颈椎功能恢复良好。     

腰椎间融合后路非对称与对称固定螺钉应力的有限元比较

背景：经椎间孔腰椎间融合非对称固定的生物力学稳定性研究,发现固定效果与双侧椎弓根螺钉接近,可满足临床应用所需生物力学要求。经关节突椎弓根螺钉参与经椎间孔腰椎间融合非对称固定的螺钉力学安全性又会怎样呢？目的：建立L4＋s功能节段左侧经椎间孔腰椎间融合后,分别予以同侧椎弓根螺钉＋对侧经关节突椎弓根螺钉、同侧椎弓根螺钉＋对侧经椎板关节突螺钉及双侧椎弓根螺钉固定的三维有限元模型,施加相同的载荷,分析不同运动状态下螺钉应力分布特点,比较3种螺钉应力状况。方法：对一成人正常L4—5椎节段标本、椎间融合器、椎弓根螺钉和皮质骨螺钉进行64排螺旋CT扫描,通过Mimicsll．1建立左侧经椎间孔腰椎间融合后3种内固定组合（同侧椎弓根螺钉＋对侧经椎板关节突螺钉、同侧椎弓根螺钉＋对侧经关节突椎弓根螺钉及双侧椎弓根螺钉固定）的几何模型,利用Simpleware3．1软件分别建立三维有限元模型,模拟500N惦Nm载荷下前屈、后伸、左＼右侧弯、左＼右侧旋等6种运动状态,用Abaqus6．8软件进行螺钉应力变化和分布特点分析。结果与结论：由于经椎间孔腰椎间融合入路切除了左侧关节突,造成内植物应力分布不对称,对弹性模量大的内固定器械一椎弓根螺钉应力影响最大,尤其是在左旋运动时。在不对称组合内固定中,由于关节突关节螺钉的使用,使对侧椎弓根螺钉应力相应增加,以左旋运动时尤为明显,但关节突关节螺钉断裂的危险性增高不明显。提示为降低螺钉断裂的风险,经椎间孔腰椎间融合后路3种组合内固定均应严格限制旋转运动,尤其是关节突切除侧的旋转运动。     

Biomechanical evaluation of anterior lumbar interbody fusion with various fixation options: Finite element analysis of static and vibration conditions

BackgroundAnterior lumbar interbody fusion combined with supplementary fixation has been widely used to treat lumbar diseases. However, few studies have investigated the influence of fixation options on facet joint force and cage subsidence. The aim of this study was to explore the biomechanical performance of anterior lumbar interbody fusion with various fixation options under both static and vertical vibration loading conditions.MethodsA previously validated finite element model of the intact L1–5 lumbar spine was employed to compare five conditions: (1) Intact; (2) Fusion alone; (3) Fusion combined with anterior lumbar plate; (4) Fusion combined with Coflex-F fixation; (5) Fusion combined with bilateral pedicle screw fixation. The models were analyzed under static and vertical vibration loading conditions respectively.FindingsBilateral pedicle screws provided highest stability at surgical level. Applying supplementary fixation diminished the dynamic responses of lumbar spine. Compared with anterior lumbar plate and Coflex-F device, bilateral pedicle screws decreased the stress responses of the endplates and cage under both static and vibration conditions, while increased the facet joint force at adjacent levels. As for comparison between Coflex-F device and anterior lumbar plate, results showed a similarity in biomechanical performance under static loading, and a slightly higher dynamic response of the latter under vertical vibration.InterpretationThe biomechanical performance of lumbar spine was significantly influenced by the variation of fixations under both static and vibration conditions. Bilateral pedicle screws showed advantages in stabilizing surgical segment and relieving cage subsidence, but may increase the facet joint force at adjacent levels.     

The traumatic spondylolisthesis of the axis. A biomechanical in vitro evaluation of an instability model and clinical relevant constructs for stabilization

OBJECTIVE: Stepwise destabilization of the traumatic spondylolisthesis C2 with an increasing anterior defect of C2-C3 was investigated. The three-dimensional stabilizing capabilities of posterior transpedicle screw osteosynthesis and two anterior plate systems C2-C3, the H-plate and the titanium locking plate were tested. DESIGN: A biomechanical in vitro study was performed using a standardized experimental protocol in a spine tester. BACKGROUND: The extent of the instability of the traumatic spondylolisthesis of C2 within its different types remains unclear. Posterior and anterior approaches for stabilization exist for patients with isthmusfractures at C2, the stabilizing effect has not been demonstrated yet. METHODS: The motion levels from C2-C3 in six human specimen were tested in flexion, extension, right and left lateral bending and left and right axial rotation. The specimens were tested intact, after destabilization and after stabilization. RESULTS: In extension and axial rotation, each step of destabilization decreased the moment significantly, to achieve the range of motion of the intact specimen. In flexion a statistical significant destabilization after separation of the posterior longitudinal ligament was present. The flexibility tests showed an increasing range of motion of the posterior transpedicle screws, with increasing anterior instability markedly in flexion and extension. After H-plate and locking plate fixation, a significant decrease of the range of motion resulted in flexion. The stiffness in flexion and extension increased consecutively, while in lateral bending and axial rotation the transpedicle screw fixation showed the highest stiffness. CONCLUSIONS/RELEVANCE: The traumatic spondylolisthesis of C2 is a significantly unstable injury in case of additional segmental damage of C2-C3. Anterior stabilization in these injuries is mandatory.     

Do facet screws provide the required stability in lumbar fixation? A biomechanical comparison of the Boucher technique and pedicular fixation in primary and circumferential fusions

Background

Transfacet pedicle screws are scarcely used in primary posterior fixation, and have limited use unilaterally or with existing anterior instrumentation. Nevertheless, the incomplete literature suggests equivalent or better performance of ipsilateral, bilateral, facet screws compared to bilateral pedicle screws.

Methods

Two groups of seven human cadaver spines (L3-S1) were tested under pure moments of 6 Nm. Each specimen was tested in a primary and circumferential fixation (Spacer, Spacer + Plate) environment. Both transfacet and bilateral pedicle screws were used as posterior fixation, in separate groups. Motion was obtained at L4-L5 for single-level constructs in flexion-extension, lateral bending and axial rotation modes.

Findings

In primary fixation, both transfacet and bilateral pedicle screws reduced motion below intact levels. Statistically, the level of circumferential fixation (anterior, posterior, or both) proved to be more influential than the type of posterior fixation. Incorporating a spacer and plate with pedicle screws provided a greater relative gain in stability than with facet screws. The interpretation is explained through a model describing the location of fixation with respect to the center-of-rotation of the vertebral bodies. In lateral bending and axial rotation, bilateral pedicle screw constructs were stiffer than transfacet pedicle screw constructs as a trend.

Interpretation

Transfacet pedicle screws provided similar fixation to bilateral pedicle screws in primary and circumferential fixations during flexion-extension. In the other modes, transfacet screw rigidity is, on average, less than bilateral pedicle screws when used alone, but with the addition of other anterior instrumentation the differences are minimized. Therefore, facet screws are warranted based on the surgical effect desired, and in the presence of additional anterior fixation.     

Biomechanical testing of different posterior fusion devices on lumbar spinal range of motion

BackgroundRecent minimal-invasive posterior fusion devices are supposed to provide stability and obtain fusion in combination with interbody cages in the instrumented segment. The aim of the present study is to evaluate the primary stability of two minimal-invasive posterior prototypes compared to an established spinous process plate and standard pedicle screw instrumentation.MethodsSeven fresh frozen human cadaver lumbar spines (L2–L5) were tested in a spinal testing device with a moment of 7.5 Nm. Spinal stability was determined as mean range of motion (RoM) in the segment L3/L4 during extension-flexion, lateral bending and axial rotation. The RoM was measured during five conditions: 1. intact; 2. working prototype composed of an interspinous device and process plates; 3. an established spinous process fixation device 4. working prototype of facet fixation and 5. pedicle screw fixation.FindingsAll devices caused a significant reduction of RoM during extension-flexion. The RoM during lateral bending was significantly reduced to 37% (of intact) by pedicle screws and 68% by facet fixation prototype. During axial rotation the RoM was significantly reduced to 52% by pedicle screws and to 86% by facet fixation prototype. The other devices had no significant influence on RoM during lateral bending and axial rotation.InterpretationThe facet fixation prototype provided less primary stability compared to pedicle screws, but had significant advantages over spinous process fixation techniques. The results encourage further testing of this implant as a minimal-invasive approach for posterior fixation.     

Does pedicle screw fixation of the subaxial cervical spine provide adequate stabilization in a multilevel vertebral body fracture model? An in vitro biomechanical study

BackgroundCervical vertebral body fractures generally are treated through an anterior-posterior approach. Cervical pedicle screws offer an alternative to circumferential fixation. This biomechanical study quantifies whether cervical pedicle screws alone can restore the stability of a three-column vertebral body fracture, making standard 360° reconstruction unnecessary.MethodsRange of motion (2.0 Nm) in flexion-extension, lateral bending, and axial rotation was tested on 10 cadaveric specimens (five/group) at C2–T1 with a spine kinematics simulator. Specimens were tested for flexibility of intact when a fatigue protocol with instrumentation was used to evaluate construct longevity. For a C4–6 fracture, spines were instrumented with 360° reconstruction (corpectomy spacer + plate + lateral mass screws) (Group 1) or cervical pedicle screw reconstruction (C3 and C7 only) (Group 2).FindingsResults are expressed as percentage of intact (100%). In Group 1, 360° reconstruction resulted in decreased motion during flexion-extension, lateral bending, and axial rotation, to 21.5%, 14.1%, and 48.6%, respectively, following 18,000 cycles of flexion-extension testing. In Group 2, cervical pedicle screw reconstruction led to reduced motion after cyclic flexion-extension testing, to 38.4%, 12.3%, and 51.1% during flexion-extension, lateral bending, and axial rotation, respectively.InterpretationThe 360° stabilization procedure provided the greatest initial stability. Cervical pedicle screw reconstruction resulted in less change in motion following cyclic loading with less variation from specimen to specimen, possibly caused by loosening of the shorter lateral mass screws. Cervical pedicle screw stabilization may be a viable alternative to 360° reconstruction for restoring multilevel vertebral body fracture.     

伤椎椎弓根置钉治疗胸腰椎压缩性骨折的三维有限元分析

背景：有文献报道伤椎置钉技术较传统4钉跨阶段固定具有更强的牢固性,可有效避免内固定的松动断裂,但其生物力学机制研究尚显不足。目的：构建脊柱胸腰椎单纯压缩性骨折的三维有限元模型,探讨伤椎附加椎弓根螺钉置入治疗胸腰椎压缩性骨折的生物力学效应。方法：将一T12椎体压缩性骨折患者脊柱胸腰段超薄CT扫描数据输入Mimics软件中,构建T12椎体压缩性骨折的有限元模型,在此模型基础上模拟伤椎置6钉和跨节段4钉内固定,对两个模型分别施加垂直压缩、前屈、后伸、左屈及右旋载荷。结果与结论：两组固定模式各种载荷下的应力均集中在螺钉根部,在垂直载荷下,螺钉的应力最小,右旋和左屈载荷下的应力最大;在垂直压缩、前屈、后伸、左侧弯及右旋运动下,上位螺钉较下位螺钉应力大（P〈0.05）。伤椎置6钉固定组螺钉应力较跨节段4钉固定组小（P〈0.05）。两组T11椎体最大位移无差别。表明伤椎附加椎弓根螺钉置入可以优化内固定的载荷,减少断钉率。     

寰枢椎后路悬臂樑支撑线缆牵拉复位固定的生物力学稳定性评价

背景:目前治疗齿状突骨折致寰枢椎脱位的内固定方式多种多样,但均强调固定前复位,尚无一种既有满意的生物力学稳定性,又有较好的术中复位能力的内固定方式。目的:分析后路悬臂樑支撑线缆牵拉复位固定技术这一新的内固定方式的生物力学性能。方法:取12具新鲜尸体寰枢椎骨韧带标本,制成齿状突Anderson2型骨折试验模型,对每一标本先后行Brooks钛缆固定、Magerl螺钉固定、双侧寰枢椎侧块螺钉+枢椎椎弓根螺钉固定和悬臂樑支撑线缆牵拉复位固定,在1.5Nm载荷下模拟人体的寰枢椎三维运动,并用三维扫描仪对寰枢椎的三维运动范围进行测量。结果与结论:在1.5Nm载荷作用下,经后路悬臂樑支撑线缆牵拉复位内固定的寰枢椎前屈、左右侧弯范围均小于其他各组(P<0.05);后伸范围大于Magerl螺钉固定组(P<0.05),小于Brooks钢丝固定和钉棒固定组(P<0.05);左右旋转范围与Magerl螺钉固定组无差异(P>0.05),但小于Brooks钢丝固定组和钉棒固定组(P<0.05)。结果可见后路悬臂樑支撑线缆牵拉复位固定的三维稳定性优于双侧寰枢椎侧块螺钉+枢椎椎弓根螺钉固定和Brooks钛缆固定;仅在后伸方面稳定性不及Magerl螺钉。     

下颈椎前路内固定联合后路经关节金属螺钉置入固定的生物力学稳定性

背景：对退变性颈椎管狭窄单纯采用前路椎体次全切除或椎间盘切除或单纯后路单开门椎管扩大成行均不能彻底完成脊髓减压和脊柱三柱稳定。目的：探讨下颈椎前路固定联合后路经关节螺钉固定的生物力学稳定性。方法：正常成人尸体颈椎标本,每具分别制作以下两种模型：①经后路C3～C7单开门和下颈椎前路C5椎体次全切除钛网支撑植骨、ORION内固定模型（对照组）。②经后路C3～C7单开门和经关节螺钉内固定及下颈椎前路C5椎体次全切除钛网内植骨、ORION内固定模型（实验组）。结果与结论：实验组在前屈、后伸、左、右侧屈及左、右旋转移位角度均小于对照组（P〈0.001）。提示：①在生物力学实验中,下颈椎前路固定联合后路经关突节螺钉固定的生物力学性能优良,对抗前屈、后伸、左、右旋转的作用力更强,颈椎可获得更可靠的稳定性。②下颈椎前路固定联合后路经关节螺钉固定在对抗颈椎前屈运动时力学稳定性更为强大。     

Biomechanical evaluation of different surgical procedures in single-level transforaminal lumbar interbody fusion in vitro

BackgroundsA variety of improved surgical methods were adopted in the transforaminal lumbar interbody fusion. A mechanical stability provides an ideal environment for the formation of a fusion mass and is the basis of their good outcomes. The object of this study is to evaluate the initial similarities and differences of four commonly-used posterior surgical procedures biomechanically.MethodsBiomechanical testing was performed at L3–4 motion segment in 6 fresh-frozen human cadaveric lumbar spines (L2–L5), including the following sequentially tested configurations: 1) intact motion segment; 2) bilateral pedicle screw fixation; 3) unilateral pedicle screw fixation; 4) unilateral pedicle screw plus contralateral translaminar facet joint screw fixation according to the Magerl technique; and 5) bilateral pedicle screw fixation with bilateral facetectomies. The range of motion, neutral zone and stiffness of each method and intact segment were collected and compared.FindingsAll of four methods reduce the range of motion significantly in flexion and extension and lateral bending but not in axial torsion compared with the native segment. There is no significant difference among four procedures about the range of motion in all loading modes. All of methods increase the stiffness of segmental motion compared with intact segment in all loading modes, but only bilateral pedicle screw fixation showed significant increases in stiffness in flexion and extension(p = 0.02) and lateral bending(p = 0.023). The stiffness offered by instrumented constructs in different methods showed no significant difference in all loading modes.InterpretationThe stiffness offered by four different posterior fixations in single segmental transforaminal lumbar interbody fusion is not significantly different.     

Guidelines for cortical screw versus pedicle screw selection from a fatigued decompressive lumbar laminectomy model show similar stability and less bone mineral density dependency

BackgroundTraditional pedicle screws are the gold standard for lumbar spine fixation; however, cortical screws along the midline cortical bone trajectory may be advantageous when lumbar decompression is required. While biomechanic investigation of both techniques exists, cortical screw performance in a multi-level lumbar laminectomy and fusion model is unknown. Furthermore, longer-term viability of cortical screws following cyclic fatigue has not been investigated.MethodsFourteen human specimens (L1–S1) were divided into cortical and pedicle screw treatment groups. Motion was captured for the following conditions: intact, bilateral posterior fixation (L3–L5), fixation with laminectomy at L3–L5, fixation with laminectomy and transforaminal lumbar interbody fusion at L3–L5 both prior to, and following, simulated in vivo fatigue. Following fatigue, screw pullout force was collected and “effective shear stress” [pullout force/screw surface area] (N/mm²) was calculated; comparisons and correlations were performed.FindingsIn flexion-extension and lateral bending, all operative constructs significantly reduced motion compared to intact (P < 0.05), regardless of pedicle or cortical screws; only posterior fixation with and without laminectomy significantly reduced motion in axial rotation (P < 0.05). Pedicle screws significantly increased average pullout strength (944.2 N vs. 690.2 N, P < 0.05), but not the “effective shear stress” (1.01 N/mm² vs. 1.1 N/mm², P > 0.05).InterpretationIn a posterior laminectomy and fusion model, cortical screws provided equivalent stability to pedicle screw fixation, yet had significantly lower screw pullout force. No differences in “effective shear stress” warrant further investigation of the effect of screw length/diameter in the aforementioned screw trajectories.     

两种固定器固定脊柱骨折脱位的生物力学分析

背景:胸腰椎脊柱骨折脱位的治疗方法主要是通过手术以内、外固定器械进行复位固定.脊柱骨折脱位固定治疗是国内外学者们研究的重要课题.目的:从生物力学角度对临床应用治疗脊柱骨折脱位的椎弓根钉和钢板固定器进行定量分析,为临床提供力学参数.方法:在日本岛津电子万能试验机上对模拟L_1椎体骨折脱位以钢板固定和以椎弓根钉固定标本进行前屈、后伸、压缩、扭转实验,实验速度为5 mm/min,在扭转试验机上进行扭转实验,实验速度为0.05(°)/s.以统计分析和配对t检验方法处理实验数据.结果与结论:实验结果表明各组压缩实验结果差异无显著性意义(P>0.05).椎弓根钉固定组左、右扭转角度小于钢板固定组(P<0.05).椎弓根钉固定组前屈、后伸位移小于钢板固定组(P<0.05).提示骨折脱位后钢板内固定效果不如椎弓根固定,而锥弓根钉内固定有利于促进骨折愈合和复位,所以椎弓根钉固定是一种较好的内固定方法.     

胫骨平台后外侧骨折3种内固定方式的有限元分析

背景：如今胫骨平台骨折的研究已由起初的内外侧＂双轨道结构＂逐步转型为＂360°全方位立体结构＂,国内外学者们更关注平台后侧结构的稳定性、复位情况以及对复位后功能恢复的影响。后侧平台的内固定材料的选择仍无明确定论,存在较大争议。目的：探讨胫骨平台后外侧骨折3种内固定方式的生物力学特性。方法：通过计算机三维有限元技术,模拟胫骨平台后外侧1/2和后外侧1/4骨折。分别使用前侧2枚6.5 mm拉力螺钉、外侧4.5 mm L型钢板以及后侧3.5 mm T型钢板置入内固定骨折块。在胫骨平台中心处加载500 N纵向应力,比较3种内固定方式的生物力学状态。结果与结论：在1/2骨块模型中,前侧拉力螺钉与后侧钢板在各个方向上的位移较小,外侧钢板的位移较其他两种固定方式大。而在1/4骨块模型中,前侧拉力螺钉在各方向的位移优势更明显,后侧钢板的位移居次,外侧钢板的位移最大。1/2骨块上,前侧拉力螺钉的最大应力为36.523 MPa,外侧钢板为153.372 MPa,后侧钢板为115.922 MPa;而在骨块上的最大应力前侧拉力螺钉模型为4.309 MPa,外侧钢板为4.37 MPa,后侧钢板为3.124 MPa。1/4骨块上前侧拉力螺钉的最大应力为36.803 MPa,外侧钢板为153.336 MPa,后侧钢板为104.234 MPa;而在骨块上的最大应力前侧拉力螺钉模型为1.195 MPa,外侧钢板为0.827 MPa,后侧钢板为1.196 MPa。提示前侧拉力螺钉能够承担更大的应力,并在受到应力后位移变化较小,可提供较稳定的支持。而后侧钢板在骨块较大（1/2骨块）时,能够提供较强的稳定性,与拉力螺钉相仿;而在骨块较小（1/4骨块）时,稳定性不如前侧拉力螺钉。外侧钢板在固定胫骨平台后外侧骨折时,稳定性较差,不如前侧拉力螺钉和后侧钢板。     

Posterior cervical spine crisscross fixation: Biomechanical evaluation

BackgroundBiomechanical/anatomic limitations may limit the successful implantation, maintenance, and risk acceptance of posterior cervical plate/rod fixation for one stage decompression-fusion. A method of posterior fixation (crisscross) that resolves biomechanical deficiencies of previous facet wiring techniques and not reliant upon screw implantation has been devised. The biomechanical performance of the new method of facet fixation was compared to the traditional lateral mass plate/screw fixation method.MethodsThirteen human cadaver spine segments (C2-T1) were tested under flexion-compression loading and four were evaluated additionally under pure-moment load. Preparations were evaluated in a sequence of surgical alterations with intact, laminectomy, lateral mass plate/screw fixation, and crisscross facet fixation using forces, displacements and kinematics.FindingsCombined loading demonstrated significantly lower bending stiffness (p < 0.05) between laminectomy compared to crisscross and lateral mass plate/screw preparations. Crisscross fixation showed a comparative tendency for increased stiffness. The increased overall motion induced by laminectomy was resolved by both fixation techniques, with crisscross fixation demonstrating a comparatively more uniform change in segmental motions.InterpretationThe crisscross technique of facet fixation offers immediate mechanical stability with resolution of increased flexural rotations induced by multi-level laminectomy. Many of the anatomic limitations and potentially deleterious variables that may be associated with multi-level screw fixation are not associated with facet wire passage, and the subsequent fixation using a pattern of wire connection crossing each facet joint exhibits a comparatively more uniform load distribution. Crisscross wire fixation is a valuable addition to the surgical armamentarium for extensive posterior cervical single-stage decompression-fixation.     

骶骨S2椎弓根外进钉固定的生物力学分析

背景：模拟骶骨骨折S2椎弓根钉外进钉固定拔出力与在拔出椎弓钉时的应变电测分析鲜有报道。目的：测量S2椎弓根外进钉固定拔出力与骶骨应变分布,为临床提供生物力学参数。方法：取正常国人新鲜尸体骶骨标本,以椎弓根钉外进钉方法固定于S2椎弓根,以小型力传感器与椎弓根钉固定装置连接测量椎弓根钉的拔出力,同时以动静态电阻应变仪,对预先粘贴在4个椎弓根螺栓固定边缘部位和骶骨不同部位的应变片进行应变电测量。1号进钉点位置为左侧第1骶后孔下缘最低点,2号进钉点位置为右侧第1骶后孔下缘最低点,3号进钉点为左侧第1骶后孔连线与骶外侧嵴的交点,4号进钉点为右侧第1骶后孔连线与骶外侧嵴的交点。测量椎弓根螺钉最大拔出力和骶骨各测点应变值。结果与结论：外进钉1号螺钉拔出力为（399.0±7.2）N,2号螺钉拔出力为（281.0±5.2）N,3号螺钉拔出力为（196.0±4.3）N,4号螺钉拔出力为（220.1±4.6）N。应变电测量最小应变发生在2号螺钉8号测点,应变为（13.5±1.1）με;最大应变发生在1号螺钉1号测点,应变为（96.8±6.5）με。提示S2椎弓根钉外进钉固定方法符合生物力学原理。     

三种固定方式修复胫骨平台后外侧骨折的生物力学比较

背景：胫骨平台后外侧骨折修复方案包括后侧钢板螺钉、外侧钢板螺钉和前后拉力螺钉内固定;选择何种内固定方法主要是靠医师的临床经验,研究结果也大多是临床报道,缺乏力学实验的依据。目的：从生物力学角度比较外侧钢板螺钉组、后侧钢板螺钉组、前后拉力螺钉组3种固定方式修复胫骨平台后外侧骨折的生物力学变化。方法：采用6具成年男性防腐尸体胫骨标本共12个进行干骺端骨密度测定。电动摆锯建立胫骨平台后外侧1/2骨折模型,模型随机分3组进行前后拉力螺钉固定、外侧钢板螺钉固定、后侧钢板螺钉固定。利用有限元法和生物力学方法在250,500,1000 N的轴向载荷下测试骨折块的轴向位移值及最大位移值分布区。结果与结论：3组标本干骺端平均骨密度差异无显著性意义（P〉0.05）。在轴向载荷为250 N时,有限元实验中骨折块的位移值,前后拉力螺钉组最小,为0.013521 mm;后侧钢板螺钉组居中,为0.016991 mm;外侧钢板螺钉组最大,为0.138200 mm,在500,1000 N时情况类似。实验生物力学结果显示,前后拉力螺钉组的位移值明显小于外侧钢板螺钉组和后侧拉力螺钉组（P〈0.05）;后侧钢板螺钉组与外侧钢板螺钉组比较差异无显著性意义（P〉0.05）,两种测试方法最大位移值分布区域都在近侧胫腓关节交界区。提示在生物力学稳定性方面,前后拉力螺钉组最具优势,外侧钢板螺钉组较差。临床可以考虑将前后拉力螺钉固定作为修复胫骨平台后外侧骨折的首选方案。     

腰椎滑脱不同融合术式的三维有限元研究

目的通过建立腰椎后路椎间(PLIF)和后外侧(PLF)两种融合术的三维有限元模型,比较并判断融合后融合节段的稳定性以椎弓根螺钉和融合器上的应力及椎体位移有无显著性差异。方法利用健康志愿者L1～L5CT扫描的DICOM数据,通过计算机软件重建腰椎模型,进行有限单元网格划分,在腰4/腰5间置入椎弓根钉内固定系统,然后分别在椎间置入融合器生成腰椎后路椎间融合术式三维有限元模型,在横突间植入自体骨生成腰椎后外侧融合术式三维有限元模型。通过对模型进行轴向加压、前屈,后伸、侧弯及轴向扭转五种加载方法进行实验。结果建立L4/L5腰椎滑脱模型及后路腰椎椎间融合及腰椎后外侧融合的有限元模型,①观察对模型分别施加轴向压缩、侧弯、前屈、后伸、旋转载荷,PLF应力多集中在椎弓根钉与钛棒连接处、PLIF内固定系统应力为Cage所分散,未见明显应力集中;②对比在五种载荷下两种不同内固定位移PLIF组均小于PLF,P0.05。结论①建立了L4/L5滑脱不同后路融合术式的三维有限元模型。②在前屈、后伸、压缩、侧弯及扭转载荷下,相比PLF,PLIF位移更小,证实椎体间融合的稳定性优于和椎弓根螺钉内固定加后外侧植骨融合;③PLF应力多集中在椎弓根钉与钛棒连接处、PLIF内固定系统应力为Cage所分散,未见明显应力集中。