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。     

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 comparison of cervical discectomy/fusion model using allograft spacers between anterior and posterior fixation methods (lateral mass and pedicle screw)

BackgroundThe purpose of this study is to investigate effects of different fixation methods on the physical stress on allospacers, endplate-vertebral body, and implants using finite element model analyses.MethodsStress distribution and subsidence risk according to the fixation methods under the condition of hybrid motion control were analyzed. The detailed finite element model of a previously validated, three-dimensional, intact cervical spinal segment model, with C5–C6 segmental fusion using allospacer, was used to evaluate the biomechanical characteristics of different fixation combinations, such as anterior plate/screws, lateral mass screw, and posterior pedicle screw.FindingsThe load sharing on allospacers increased in extension in order of posterior pedicle screws (21.4%), lateral mass screws (31.5%), and anterior plate/screws (56.6%). lateral mass screw demonstrated the highest load sharing (68.1%) on the allospacer in flexion. The Peak von Mises stress of the allospacer was the lowest in flexion and axial rotation but the highest in extension with anterior plate/screws. Allospacer subsidence risk was the lowest in extension, lateral bending, and axial rotation with posterior pedicle screws but the lowest in flexion with anterior plate/screws. The bone-screw loosening risk was the lowest in all modes with posterior pedicle screws but the highest with anterior plate/screws.InterpretationPosterior pedicle screws demonstrated the best mechanical stability of allospacer failure-subsidence and the lowest risk of screw loosening. Different motion restrictions depending on the fixation method should be considered for implant and allospacer safety.     

Biomechanical stability of five pedicle screw fixation systems in a human lumbar spine instability model

In this study, the three-dimensional biomechanical stabilizing capabilities of five pedicle screw fixation systems and facet screw fixation were determined. These systems were the Ace device without and with transverse wiring, AO device, CD device, Steffee plate, Wiltse device with single and double rods, and facet screw fixation. All systems were applied to the L₅---S₁ level in a human in vitro spine rendered unstable by transection of the posterior ligaments and transverse holes drilled through the intervertebral disc. There were no statistically significant differences in the biomechanical stability provided by any of the pedicle screw devices, where stability was defined as the average stiffness from the load-displacement curve. All devices restored motion to less than 50% of intact levels under flexion moments. In extension, all devices, except the facet screw method, restored motion to below intact levels. In lateral bending, all devices restricted motion to less than 50% of intact motion. Under axial torque, the CD device provided the least motion while the AO device did not restore motion to the intact level.     

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.     

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.     

Loads on an internal spinal fixation device during physical therapy.

BACKGROUND AND PURPOSE: Modified internal spinal fixation devices allow the measurement of the forces and moments acting on the implants. The aim of this study was to measure the loads on internal fixation devices for selected body positions and movements during physical therapy. SUBJECTS AND METHODS: Loads on an internal spinal fixation device were measured in 10 patients with degenerative instability or compression fractures using a telemeterized implant. RESULTS: Relatively low implant loads were found in the recumbent body positions. Most exercises performed in a lying position caused implant loads less than that measured for standing and are therefore not likely to increase the risk of screw breakage. Fixation device loads were lower for sitting relaxed than for standing. The highest implant loads (128% of the value for standing) were measured during walking. Standing up, sitting down, and lateral bending and axial rotation of the upper body while standing led to fixation device loads between 111% and 120% related to the value for standing. Even higher fixation device loads were measured for ventral flexion and extension of the upper body while standing. Kneeling on hands and knees, and flexing and extending the back in this position, caused implant loads that were lower than for standing. DISCUSSION AND CONCLUSION: Standing up, sitting down, and lateral bending and axial rotation of the upper body while standing may slightly increase the risk of pedicle screw breakage, whereas ventral flexion and extension of the upper body while standing may increase this risk considerably if the region bridged by the implant is distracted (the distance between upper and lower screws was increased) during surgery. However, walking is the exercise that plays the major role concerning pedicle screw breakage because it causes the highest bending moments of all exercises studied and it loads the fixation devices most frequently.     

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。     

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.     

Biomechanical evaluation of a dynamic pedicle screw fixation device

BACKGROUND: Recent innovations in dynamic devices have promised a reduction in stress shielding, protection of adjacent segment degeneration, and decreased implant failure. However, there have been few studies comparing the biomechanical properties of a rigid device in comparison to a dynamic posterior fixation device. The purpose of this study was to compare the immediate stability of a new dynamic pedicle screw fixation device with an equivalent rigid device. METHODS: Six thoracolumbar cadaver spines (T10-L4) were fixed in a biomechanical testing frame. Pure moments of 10Nm were loaded in six directions: flexion, extension, right and left lateral bending, and right and left axial rotation. For each spine, four different stages were tested: intact, destabilization of the middle segment, fixation with the dynamic device, and fixation with the rigid device. Ranges of motion were measured using stereophotogrammetry. The specimens with each device were then subjected to flexion-compression loading for five cycles on a MTS 858 Universal Testing Machine. The average stiffness of the last three cycles was recorded. FINDINGS: Both dynamic and rigid devices were found to provide stability for the injured segment in flexion-extension and lateral bending. In axial rotation, the devices could restore the stability to levels similar to those in an intact spine. Results also indicated a slight increase in range of motion in flexion-extension and significant reduction in stiffness of flexion-compression with the dynamic device (P < 0.01), in comparison to the rigid device. INTERPRETATION: The dynamic device offers a system that may alter favorably the movement and load transmission of a spinal motion segment without sacrificing construct stability.     

Biomechanical analysis of differing pedicle screw insertion angles

BACKGROUND: Pedicle screw fixation to stabilize lumbar spinal fusion has become the gold standard for posterior stabilization. A significant percentage of surgical candidates are classified as obese or morbidly obese. For these patients, the depth of the incisions and soft tissue makes it extremely difficult to insert pedicle screws along the pedicle axis. As such, the pedicle screws can only be inserted in a much more sagittal axis. However, biomechanical stability of the angled screw insertion has been controversial. We hypothesized that the straight or parallel screw was a more stable construct compared to the angled or axially inserted screw when subjected to caudal cyclic loading. METHODS: We obtained 12 fresh frozen lumbar vertebrae from L3 to L5 from five cadavers. Schantz screws (6.0 mm) were inserted into each pedicle, one angled and along the axis of the pedicle and the other parallel to the spinous process. Fluoroscopic imaging was used to guide insertion. Each screw was then subjected to caudal cyclic loads of 50 N for 2000 cycles at 2 Hz. Analysis of initial damage, initial rate of damage, and total damage during cyclic loading was undertaken. FINDINGS: Average total fatigue damage for straight screws measured 0.398+/-0.38 mm, and 0.689+/-0.96 mm for angled screws. Statistical analysis for total fatigue damage ratio of angled to straight screws revealed that a significant stability was achieved in straight-screw construct (P<0.03). INTERPRETATION: This study showed that straight screw insertion results in a more stable pedicle-screw construct. The angled screw insertion technique resulted in more scattered values of damage indicating that the outcome from the angled screw fixation is less predictable. This validates the use of this technique to implant pedicle screws across the axis of the pedicle (parallel to the mid sagittal line) rather than along the axis, and has broad implications in instrumented posterior lumbar spinal surgery.     

Biomechanical testing of a polycarbonate-urethane-based dynamic instrumentation system under physiological conditions

BackgroundPosterior dynamic stabilization systems are developed to maintain the healthy biomechanics of the spine while providing stabilization. Numerous dynamic systems incorporate polycarbonate urethane with temperature- and moisture-dependent material properties. In the underlying study, a novel test rig is used to evaluate the biomechanical performance of a system containing polycarbonate urethane.MethodsThe test rig is composed of two hydraulic actuators. An environmental chamber, filled with water vapor at body temperature, is included in the set up. The translational and rotational degrees of freedom of vertebrae and pedicle screws are measured using a magnetic tracking system. The Transition® device is tested in five lumbar spines (L2–L5) of human cadavers. Pure moment tests are performed for flexion-extension, lateral bending, and axial rotation. Three test conditions are compared: 1. native specimens, 2. dynamic instrumentation at L4–L5, 3. dynamic instrumentation with decompression at L4–L5.FindingsThe ranges of motion, the centers of rotation, and the pedicle screw loosening are calculated and evaluated. During daily motions such as walking, the loads on the lumbar spine differ from the standardized test protocols. To allow a reproducible data evaluation for smaller deformations, all moment-rotation curves are parameterized using sigmoid functions.InterpretationIn flexion-extension, the Transition® device provides the highest stiffening of the segment and the largest shift of the center of rotation. No shift in the center of rotation, and the smallest supporting effect on the segment is observed for axial rotation. In lateral bending, a mediate reduction of the range of motion is observed.     

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.     

矢向轴动态椎弓根钉棒系统固定腰椎失稳有限元分析

[目的]利用有限元方法对矢向轴动态椎弓根钉棒内固定系统固定腰椎失稳模型的生物力学特性进行评价,为此动态内固定系统临床应用提供生物力学基础和理论依据.[方法]采用预先获取的健康成年中国男性志愿者的腰椎CT数据建立腰椎正常模型及L4,5失稳模型.根据矢向轴动态椎弓根钉棒系统和坚强椎弓根钉棒系统的材料参数计算和构建有限元模型,并将其导入已通过验证的腰椎失稳模型,分别构建L4,5单节段动态固定模型和坚强固定模型.约束L5椎体下终板,在轴向500N载荷和10N·m力矩下分别模拟人体腰椎正常生理轴向载荷、前屈、后伸、侧弯和旋转五种工况,分别记录4种模型轴向载荷工况下L4,5轴向位移及后四种工况下L4,5固定节段及L3,4邻近节段活动度、椎间盘应力、邻近节段小关节的应力和器械应力,并进行分析比较.[结果]矢向轴动态椎弓根钉棒系统固定失稳腰椎可让固定节段椎间关节留有大于坚强固定组、小于完整脊柱组运动范围的适当活动度,对邻近节段腰椎活动度的影响也小于坚强固定组,同时固定节段椎间盘应力较坚强固定组大,器械应力却小于坚强椎弓根钉棒系统,邻近节段腰椎间盘及椎间小关节应力也小于坚强固定组.[结论]应用矢向轴动态椎弓根钉棒系统固定失稳腰椎,既保留了腰椎固定节段适当活动性,又能提供即刻的稳定性;同时该系统与脊柱合力承担载荷,能有效避免因术后应力遮挡及器械应力集中引起的内固定失效等并发症;它也能降低邻近节段椎间盘及椎间关节的应力,对邻近节段腰椎活动度影响也较坚强固定小,理论上有利于减少和预防邻近节段退变.     

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.     

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。     

磷酸钙骨水泥强化椎弓根螺钉固定的生物力学特性

背景:聚甲基丙烯酸甲酯能改善椎弓根螺钉和周围骨质间界面的情况、显著提高螺钉固定强度,但它在术中和术后伴有聚合热损伤效应、毒性和不可吸收等缺点。磷酸钙骨水泥具有生物相容性和生物安全性好、可降解、不产生聚合热等优点,是一种较理想的聚甲基丙烯酸甲酯替代材料。目的:从生物力学方面评价磷酸钙骨水泥对椎弓根螺钉固定的强化作用。设计:随机对照,重复观察测量。单位:南京医科大学第二附属医院骨科。材料:实验于2002-08/2003-02在华中科技大学同济医学院完成。①由同济医科大学解剖教研室提供两具新鲜男性尸体椎骨,一具52岁,一具50岁。各取10个椎骨(T8～12,L1～5)分别构成52岁组和50岁组。摄X线片排除先天性畸形、骨折和肿瘤等病变。两组椎骨均为Ⅰ级骨质疏松,符合实验要求。②磷酸钙骨水泥固相主要成分是磷酸四钙和磷酸三钙超细粉末,液相主要成分是枸橼酸盐溶液,使用时按1g固相:1mL液相的比例进行配制,初步凝固时间15min,最终凝固时间12h,最大压缩强度介于45～57MPa。③椎弓根螺钉自制,螺钉直径5mm,螺纹段长34mm,螺距2mm,螺纹深0.8mm。方法:①磷酸钙骨水泥最终凝固时强化椎弓根螺钉固定的生物力学测试:取50岁组椎骨作为测试对象。对照侧:钉道直接置入椎弓根螺钉;强化侧:填入磷酸钙骨水泥再置入椎弓根螺钉。置钉后的椎骨在37℃恒温箱里放置12h,然后测定椎弓根螺钉的最大轴向拔出力。②磷酸钙骨水泥初步凝固时强化椎弓根螺钉固定的生物力学测试:取52岁组椎骨作为测试对象。用同样方法在椎弓根对照侧直接置入椎弓根螺钉,强化侧填入骨水泥后再置入椎弓根螺钉,37℃恒温箱里放置15min,测定椎弓根螺钉初步凝固时的最大轴向拔出力。③磷酸钙骨水泥强化松动椎弓根螺钉固定的生物力学测试:取测试后的50岁组椎骨,用磷酸钙骨水泥重新固定12h后拔松的椎弓根螺钉,测定其两侧的最大轴向拔出力。主要观察指标:①磷酸钙骨水泥最终凝固时强化椎弓根螺钉固定的生物力学测试结果。②磷酸钙骨水泥初步凝固时强化椎弓根螺钉固定的生物力学测试结果。③磷酸钙骨水泥强化松动椎弓根螺钉固定的生物力学测试结果。结果:①50岁组对照侧和强化侧的椎弓根螺钉最大轴向拔出力中位数分别为620N和1136N,强化侧较对照侧增加83%(P<0.01)。强化骨-螺钉界面的抗剪切应力中位数从1.16N/mm2增加到2.13N/mm2。②52岁组对照侧和强化侧的椎弓根螺钉最大轴向拔出力中位数分别为554.5N和859.5N,强化侧较对照侧增加55%(P<0.01)。强化骨-螺钉界面的抗剪切应力中位数从1.039N/mm2增加到1.61N/mm2。③50岁组椎骨对照侧和强化侧重新固定12h后最大轴向拔出力中位数分别为517N和876N,和同侧松动后轴向拔出力中位数比较,分别增加了63.6%和54.2%(P均<0.01)。结论:磷酸钙骨水泥初步凝固和最终凝固时能强化椎弓根螺钉的固定,并且椎弓根螺钉松动后使用磷酸骨水泥能使螺钉重新获得固定。椎体强化侧的椎弓根螺钉均从骨-螺界面剥离开来,不伴周边骨质和椎弓根的严重损害,有利于螺钉松动、拔出后的二次置入。     

寰枢椎后路植入物短节段固定方案：强度增加对颈椎旋转屈伸运动影响较少

背景：寰枢椎是生命中枢所在区域,由于解剖结构独特,手术治疗上颈椎疾患难度大、风险高.寰枢椎后路手术是重建上颈椎稳定性的常用方案,最佳固定方式为短节段坚强固定,不仅固定坚强且对颈椎的旋转和屈伸运动损失较少.目的：对寰枢椎后路内固定方案做一综述.方法：由第一作者检索至2014年5月为止的PubMed数据（http：//www.ncbi.nlm.nih.gov/PubMed）及万方医学网（http：//med.wanfangdata.com.cn/）,以“upper cervical,intemal fixation,atlas,axis,postenor approach”为英文检索词,“上颈椎,内固定,寰椎,枢椎,后路”为中文检索词,采用上述检索词不同的组合进行检索,总计英文文献267篇,中文文献189篇.计算机初检得到的文献,再经过阅读标题和摘要进行初筛,排除中英文文献重复报道、研究内容类似及文献内容与上颈椎内固定不相关的内容,最终48篇文献符合纳入标准.结果与结论：由于寰枢椎解剖学的特殊性,寰枢椎内固定也明显与下颈椎不同,内固定技术发展多种多样,针对不同的病损情况,医生可以自由选择不同的内固定方式.椎板类内固定包括Gallie技术、Brooks技术、Sonntag技术、椎板夹、扣座节段间固定技术和枢椎椎板交叉螺钉技术,是需要椎板完整的,对于需要切除椎板减压的情况是不能应用的.除了枢椎交叉椎板螺钉外,其余几种方法都需要椎管内侵入操作,对脊髓有一定的搔扰,抗旋转能力相对较差,优点是操作相对简单.不依赖于椎板完整性的内固定技术是近年发展起来的,包括经关节突螺钉、寰椎侧块螺钉、寰椎椎弓根螺钉、枢椎峡部螺钉、枢椎椎弓根螺钉等,其特点是应用螺钉,生物力学强度显著增强,融合率增加,不影响椎板减压,缺点就是对螺钉置入操作技术要求较高,如果螺钉置入偏差,会损伤脊髓或椎动脉引起严重并发症.寰枢椎区域接近人体生命中枢,熟练此区域?     

单侧腰椎弓根螺钉及经椎板关节突螺钉固定与双侧固定的比较

背景：经椎板关节突关节螺钉固定、椎问植骨融合治疗脊柱疾患是一种独特的固定方法,可用于退变性腰椎的融合。目的：比较采用微创经腰椎间孔椎体融合联合单侧椎弓根螺钉及经椎板关节突螺钉固定与常规开放后路腰椎体间融合术联合双侧椎弓根螺钉固定治疗下腰痛疾病的临床效果。方法：纳入2010年6月至2012年6月于武警广东总队医院就诊的腰椎间盘突出伴腰椎轻度不稳患者49例,均采用后路减压椎间融合器植骨内固定治疗。其中24例采用微创经椎间孔椎体融合术联合单侧椎弓根螺钉及经椎板关节突螺钉固定,25例采用常规开放后路腰椎体间融合术联合双侧椎弓根螺钉固定,比较两种固定方法的临床疗效。结果与结论：两种固定方法术后椎体融合率、日本矫形外科协会评分及疼痛目测类比评分改善率差异均无显著性意义（P〉0．05）。可见对无严重不稳的单节段退变性腰椎疾病患者,两种治疗方法的效果相当,均能有效提高椎间融合率,使小关节稳定,解除临床症状,门诊随访满意。但采用微创经椎间孔椎体融合术联合单侧椎弓根螺钉及经椎板关节突螺钉固定的患者手术切口长度、手术时间、术中出血量、术后切口引流液量明显减少（P〈0．05）,说明该方法具有创伤小、操作简单的优势。     

脊柱外固定器治疗相邻双节段腰椎骨折的生物力学测试

背景：胸腰椎骨折固定后相邻节段退变发生的一个重要因素是相邻运动节段出现过度活动,导致该节段应力集中,并且相邻节段的头侧较尾侧更容易发生退变,固定节段数量越多,相邻节段的应力越集中,退变概率越大。目的：通过对相邻双节段腰椎爆裂性骨折经皮椎弓根螺钉外固定进行生物力学测试,评价脊柱外固定器的即刻生物力学稳定性以及上位相邻椎体的运动范围退变情况。方法：选取6具新鲜成年猪脊柱标本（T14-S1,猪胸椎共有14个椎体）。每具标本均按以下顺序进行生物力学测试：正常组、骨折组（L3,L4椎体制作成爆裂性骨折模型）、外固定组（L2,L5椎体行脊柱外固定器固定）、内固定组（取出脊柱外固定器后行L2,L5椎体传统开放后路内固定）。测试标本的固定节段（L2-L5）和上位相邻节段（L1）应用跨相邻2伤椎4钉外固定与内固定后的前屈、后伸、侧屈、轴向旋转角位移运动变化。结果与结论：骨折组各方位角位移运动范围均大于正常组,差异有显著性意义（P〈0．05）;两种固定状态下固定节段（L2-L5）各方位角位移运动范围均显著小于正常状态和骨折状态,差异有显著性意义（P＜0．01）,且两种固定状态下各方位的即刻稳定指数比较,差异均无显著性意义（P〉0．05）;与正常组比较,两种固定状态上位椎体（L1）的各方位角位移运动范围均增加;外固定组与正常组上位椎体（L1）三维运动范围比较：前屈、后伸时差异无显著性意义（P〉0．05）,侧屈、旋转时差异均有显著性意义（P〈0．01）;内固定组与正常组比较：前屈、后伸、侧屈、旋转时差异均有显著性意义（P＜0．01）。结果可见应用脊柱外固定器治疗相邻双节段腰椎爆裂性骨折,其即刻生物力学稳定性与传统开放后路内固定系统相当;两种固定方式均能引起上位正常相邻椎体侧屈、旋转的角位移增加,但脊柱外固定器较传统内固定在前屈、后伸时不会引起上位相邻椎体的运动范围显著增加。