前路腰椎椎间融合术即刻稳定性的生物力学研究

目的 评价应用聚醚醚酮(poly-ether-ether-ketone,PEEK)椎间融合器行前路腰椎椎间融合的即刻生物力学稳定性.方法 采用6具成人尸体腰椎标本,均来源于男性,X线榆查排除腰椎疾患和明显退行性改变,双能X线骨密度检查证实所有标本骨密度均处于正常范围.截取L4～S2节段腰椎,用自凝型聚甲基丙烯酸甲酯将标本两端固定在夹具内.沿腰椎轴线加载500N的预负荷后,分别在生物力学试验机上检测以下三种状态的前屈、后伸及侧屈各方向活动的即刻稳定性:完整腰椎标本,L5S1椎间盘切除、PEEK椎间融合器植入,辅以后路椎弓根螺钉系统固定.结果 L5S1椎间单纯椎间融合器植入后前屈、后伸、左侧屈方向的活动范围较完整腰椎标本分别减少76.9%、66.6%与81.1%;辅以后路惟弓根螺钉系统固定后,前屈、后伸、左侧屈方向的活动范围较完整腰椎标本分别减少93.9%、90%与86.6%.完整腰椎标本的空白对照组L4,5椎间前屈、后伸与左侧屈活动度分别为4.16°±0.33°、4.02°±0.30°、3.48°±0.34.;L5S1单纯椎间融合器组则分别为5.82°±0.36°、5.38°±0.30°、4.96°±0.29°;L5S1椎间融合器辅助椎弓根螺钉固定组则分别为4.82°±0.26°、5.76°±0.31°、3.98°±0.29°.L5S1椎间单纯椎间融合器植入及附加椎弓根螺钉崮定后,L4,5椎间相对活动度显著增加,各组间差异有统计学意义(P=0.000).结论 单纯应用PEEK椎间融合器的前路腰椎椎间融合术即刻稳定性优于完整腰椎标本.辅以后路椎弓根螺钉系统固定后融合节段稳定性得到显著增强.     

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.     

Biomechanical stability of five stand-alone anterior lumbar interbody fusion constructs

Anterior lumbar interbody fusion (ALIF) cages are expected to reduce segmental mobility. Current ALIF cages have different designs, suggesting differences in initial stability. The objective of this study was to compare the effect of different stand-alone ALIF cage constructs and cage-related features on initial segmental stability. Human multi-segmental specimens were tested intact and with an instrumented L3/4 disc level. Five different ALIF cages (I/F, BAK, TIS, SynCage, and ScrewCage) were tested non-destructively in axial rotation, flexion/extension and lateral bending. A cage ‘pull-out’ concluded testing. Changes in neutral zone (NZ) and range of motion (ROM) were analyzed. Cage-related measurements normalized to vertebral dimensions were used to predict NZ and ROM. No cage construct managed to reduce NZ. The BAK and TIS cages had the largest NZ increase in flexion/extension and lateral bending, respectively. Cages did reduce ROM in all loading directions. The TIS cage was the least effective in reducing the ROM in lateral bending. Cages with sharp teeth had higher ‘pull-out’ forces. Antero-posterior and medio-lateral cage dimensions, cage height and wedge angle were found to influence initial stability. The performance of stand-alone ALIF cage constructs generally increased the NZ in any loading direction, suggesting potential directions of initial segmental instability that may lead to permanent deformity. Differences between cages in flexion/extension and lateral bending NZ are attributed to the severity of geometrical cage-endplate surface mismatch. Stand-alone cage constructs reduced ROM effectively, but the residual ROM present indicates the presence of micromotion at the cage-endplate interface. Received: 3 June 1999/Revised: 3 September 1999/Accepted: 8 September 1999     

Biomechanical analysis of lateral interbody fusion strategies for adjacent segment degeneration in the lumbar spine

Background Context

Surgical treatment of symptomatic adjacent segment disease (ASD) typically involves extension of previous instrumentation to include the newly affected level(s). Disruption of the incision site can present challenges and increases the risk of complication. Lateral-based interbody fusion techniques may provide a viable surgical alternative that avoids these risks. This study is the first to analyze the biomechanical effect of adding a lateral-based construct to an existing fusion.

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.     

Changes in the lumbar foramen following anterior interbody fusion with tapered or cylindrical cages.

BACKGROUND CONTEXT: Anterior lumbar interbody fusion (ALIF) using both cylindrical and tapered threaded interbody cages has been shown to restore disc height, reduce segmental motion, and relieve low back pain. The effectiveness of these stand-alone cage designs in restoration and maintenance of intervertebral foraminal dimensions has received little attention. PURPOSE: To investigate the effects of anterior implantation of cylindrical and tapered interbody cages on morphologic changes of the lumbar neuroforamen and maintenance of foraminal dimensions under dynamic loading. STUDY DESIGN/SETTING: A biomechanical study using bovine calf spine model to compare the deformation of foraminal space after ALIF with either tapered cages or cylindrical cages. METHODS: Sixteen fresh calf spines were randomly assigned to undergo ALIF at the L3-L4 level using either two threaded cylindrical or two tapered cages. Lumbar spines were subjected to unconstrained loading in flexion, extension, and lateral bending. Rotation of the L3-L4 segment and dynamic deformation in foraminal height were obtained through a motion analysis system, and compared between the two cage groups. Foraminal dimensions were assessed before and after tapered or cylindrical cage implantation with digitized measurement of bilateral foraminal molds. RESULTS: Regardless of cage design, anterior implantation of cages increased neuroforaminal area by 17% (p=.0005) and increased the foraminal height by 9% (p=.0004) in the neutral unloaded position. In dynamic loading conditions, foraminal height was significantly stabilized in all loading directions by the cylindrical cages (p=.01) and on both sides during lateral bending by the tapered cages (p<.03). Foraminal stabilization provided by either cage was most prominent in the direction of lateral bending (26-37% of the intact values), while cylindrical cages also provided substantial stabilization in flexion (26% of the intact value). Significant linear relationships were found between foraminal height and residual fusion segment motion under dynamic loading conditions. CONCLUSION: Results from this bovine model biomechanical study indicate that stand-alone anterior interbody fusion cages with either tapered or cylindrical design are effective in restoring neuroforaminal height and stabilize the spine to withstand foraminal deformation during daily loading. The degree of stabilization was influenced substantially by the loading direction, to a lesser degree by the cage type, and was strongly dependent on the segment mobility. Although bovine lumbar spine is widely accepted for comparative studies, direct clinical interpretation should be made with caution owing to the anatomical differences from human.     

腰椎横突间入路椎体间融合术的生物力学评价

目的 观察腰椎横突间入路椎体间融合术(ILIF)及附加椎弓根钉固定后的生物力学稳定性.方法 采用小牛脊柱运动节段标本12具,依序进行不同处理后分为以下7组:(1)正常对照组(IS);(2)左侧小关节切除+椎间融合器植入组(TLIF);(3)TLIF附加同侧椎弓根钉固定组;(4)TLIF附加双侧椎弓根钉固定组;(5)左侧横突间入路椎间融合器植入组(ILIF);(6)ILIF附加同侧椎弓根钉固定组;(7)ILIF附加双侧椎弓根钉固定组.分别测试各组在轴向压缩、前屈、后伸、左右侧屈时的载荷-应变、载荷-位移变化以及轴向刚度和双向扭转稳定性等生物力学指标,并进行统计学比较.结果 所有生物力学指标中ILIF组稳定性均大于TLIF组(P<0.05),在定量扭矩扭角方面差距最大达72%.ILIF+BPSF的稳定性最高,在前屈载荷应变方面较IS组差异最大达53%,而ILIF+HPSF组与ILIF+BPSF组比较差异无统计学意义(P>0.05). 结论 ILIF手术生物力学稳定性优于TLIF手术;ILIF附加同侧椎弓根钉固定与附加双侧椎弓根钉固定生物力学稳定性相当,使用ILIF术式附加侧同椎弓根螺钉固定,可提供较好的即刻稳定性.     

Biomechanical comparison of two different concepts for stand alone anterior lumbar interbody fusion

Segmental instability in degenerative disc disease is often treated with anterior lumbar interbody fusion (ALIF). Current techniques require an additional posterior approach to achieve sufficient stability. The test device is an implant which consists of a PEEK-body and an integrated anterior titanium plate hosting four diverging locking screws. The test device avoids posterior fixation by enhancing stability via the locking screws. The test device was compared to an already established stand alone interbody implant in a human cadaveric three-dimensional stiffness test. In the biomechanical test, the L4/5 motion segment of 16 human cadaveric lumbar spines were isolated and divided into two test groups. Tests were performed in flexion, extension, right and left lateral bending, right and left axial rotation. Each specimen was tested in native state first, then a discectomy was performed and either of the test implants was applied. Finite element analysis (FE) was also performed to investigate load and stress distribution within the implant in several loading conditions. The FE models simulated two load cases. These were flexion and extension with a moment of 5 Nm. The biomechanical testing revealed a greater stiffness in lateral bending for the SynFix-LR™ compared to the established implant. Both implants showed a significantly higher stiffness in all loading directions compared to the native segment. In flexion loading, the PEEK component takes on most of the load, whereas the majority of the extension load is put on the screws and the screw–plate junction. Clinical investigation of the test device seems reasonable based on the good results reported here.     

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.     

Biomechanical evaluation of lumbar lateral interbody fusion for the treatment of adjacent segment disease

BACKGROUND CONTEXT

Adjacent segment disease (ASD) is a well-known complication after lumbar fusion. Lumbar lateral interbody fusion (LLIF) may provide an alternative method of treatment for ASD while avoiding the morbidity associated with revision surgery through a traditional posterior approach. This is the first biomechanical study to evaluate the stability of lateral-based constructs for treating ASD in existing multilevel fusion model.

Anterior lumbar interbody fusion in comparison with transforaminal lumbar interbody fusion: implications for the restoration of foraminal height, local disc angle, lumbar lordosis, and sagittal balance

OBJECT: A primary consideration of all spinal fusion procedures is restoration of normal anatomy, including disc height, lumbar lordosis, foraminal decompression, and sagittal balance. To the authors' knowledge, there has been no direct comparison of anterior lumbar interbody fusion (ALIF) with transforaminal lumbar interbody fusion (TLIF) concerning their capacity to alter those parameters. The authors conducted a retrospective radiographic analysis directly comparing ALIF with TLIF in their capacity to alter foraminal height, local disc angle, and lumbar lordosis. METHODS: The medical records and radiographs of 32 patients undergoing ALIF and 25 patients undergoing TLIF from between 2000 and 2004 were retrospectively reviewed. Clinical data and radiographic measurements, including preoperative and postoperative foraminal height, local disc angle, and lumbar lordosis, were obtained. Statistical analyses included mean values, 95% confidence intervals, and intraobserver/interobserver reliability for the measurements that were performed. RESULTS: Our results indicate that ALIF is superior to TLIF in its capacity to restore foraminal height, local disc angle, and lumbar lordosis. The ALIF procedure increased foraminal height by 18.5%, whereas TLIF decreased it by 0.4%. In addition, ALIF increased the local disc angle by 8.3 degrees and lumbar lordosis by 6.2 degrees, whereas TLIF decreased the local disc angle by 0.1 degree and lumbar lordosis by 2.1 degrees. CONCLUSIONS: The ALIF procedure is superior to TLIF in its capacity to restore foraminal height, local disc angle, and lumbar lordosis. The improved radiographic outcomes may be an indication of improved sagittal balance correction, which may lead to better long-term outcomes as shown by other studies. Our data, however, demonstrated no difference in clinical outcome between the two groups at the 2-year follow-up.     

Biomechanical Comparison of Different Surgical Approaches for the Treatment of Adjacent Segment Diseases after Primary Transforaminal Lumbar Interbody Fusion: A Finite Element Analysis

Background and objective

Adjacent segment disease (ASD) is a well-known complication after interbody fusion. Revision surgery is necessary for symptomatic ASD to further decompress and fix the affected segment. However, no optimal construct is accepted as a standard in treating ASD. The purpose of this study was to compare the biomechanical effects of different surgical approaches for the treatment of ASD after primary transforaminal lumbar interbody fusion (TLIF).

Methods

A finite element model of the L1-S1 was conducted based on computed tomography scan images. The primary surgery model was developed with a single-level TLIF at L4-L5 segment. The revision surgical models were developed with anterior lumbar interbody fusion (ALIF), lateral lumbar interbody fusion (LLIF), or TLIF at L3-L4 segment. The range of motion (ROM), intradiscal pressure (IDP), and the stress in cages were compared to investigate the biomechanical influences of different surgical approaches.

Results

The results indicated that all the three surgical approaches can stabilize the spinal segment by reducing the ROM at revision level. The ROM and IDP at adjacent segments of revision model of TLIF was greater than those of other revision models. While revision surgery with ALIF and LLIF had similar effects on the ROM and IDP of adjacent segments. Compared among all the surgical models, cage stress in revision model of TLIF was the maximum in extension and axial rotation.

Conclusion

The IDP at adjacent segments and stress in cages of revision model of TLIF was greater than those of ALIF and LLIF. This may be that direct extension of the surgical segment in the same direction results in stress concentration.     

Posterior lumbar interbody fusion

Posterior lumbar interbody fusion (PLIF) and transforaminal lumbar interbody fusion (TLIF) create intervertebral fusion by means of a posterior approach. Both techniques are useful in managing degenerative disk disease, severe instability, spondylolisthesis, deformity, and pseudarthrosis. Successful results have been reported with allograft, various cages (for interbody support), autograft, and recombinant human bone morphogenetic protein-2. Interbody fusion techniques may facilitate reduction and enhance fusion. The rationale for PLIF and TLIF is biomechanically sound. However, clinical outcomes of different anterior and posterior spinal fusion techniques tend to be similar. PLIF has a high complication rate (dural tear, 5.4% to 10%; neurologic injury, 9% to 16%). These findings, coupled with the versatility of TLIF throughout the entire lumbar spine, may make TLIF the ideal choice for an all-posterior interbody fusion.     

前路和经椎间孔入路腰椎椎体间融合术治疗腰椎术后综合征的比较

目的:比较前路腰椎椎体间融合术(anterior lumbar interbody fusion,ALIF)和经椎间孔入路腰椎椎体间融合术(transfomminal lumbar interbody fusion,TLIF)治疗腰椎术后综合征的效果.方法:2005年3月～2007年3月收治31例腰椎术后综合征患者.其中14例行ALIF,17例行TLIF,观察两组患者手术前后Oswestry功能障碍指数(ODI)、模拟疼痛评分(VAS)、椎体间高度、椎体间角度,比较两组患者疗效、融合情况和并发症.结果:AUF组手术时间平均为110min,术中出血量平均为210ml,TLIF组分别为160min、620ml,两组比较有显著性差异(P<0.05).AUF组出现2例腹膜撕裂,予缝合后愈合:3例发生腹膜后血肿、麻痹性肠梗阻,经保守治疗完全恢复正常.TLIF组出现2例硬膜撕裂,予缝合后愈合;2例神经根牵托伤,经脱水、非甾体类消炎止痛药物治疗完全恢复正常.随访12～24个月,平均18个月,每组术后1年时ODI和VAS均较术前明显减少(P<0.01),椎间高度、角度均明显增加(P<0.05);两组间术前及术后1年ODI、VAS、椎间高度、椎间角度无明显差异(p>0.05);ALIF组疗效优良率为85.7%,TLIF组为82.4%.两组之间无显著性差异(P>0.05);两组椎间融合率均为100%.结论:AUF和TLIF治疗腰椎术后综合征均可达到满意的椎间融合率和临床效果,ALIF手术时间相对较短、出血量相对较少.     

Segmental stability and compressive strength of posterior lumbar interbody fusion implants

STUDY DESIGN: Human cadaveric study on initial segmental stability and compressive strength of posterior lumbar interbody fusion implants. OBJECTIVES: To compare the initial segmental stability and compressive strength of a posterior lumbar interbody fusion construct using a new cortical bone spacer machined from allograft to that of titanium threaded and nonthreaded posterior lumbar interbody fusion cages, tested as stand-alone and with supplemental pedicle screw fixation. SUMMARY OF BACKGROUND DATA: Cages were introduced to overcome the limitations of conventional allografts. Radiodense cage materials impede radiographic assessment of the fusion, however, and may cause stress shielding of the graft. METHODS: Multisegmental specimens were tested intact, with posterior lumbar interbody fusion implants inserted into the L4/L5 interbody space and with supplemental pedicle screw fixation. Three posterior lumbar interbody fusion implant constructs (Ray Threaded Fusion Cage, Contact Fusion Cage, and PLIF Allograft Spacer) were tested nondestructively in axial rotation, flexion-extension, and lateral bending. The implant-specimen constructs then were isolated and compressed to failure. Changes in the neutral zone, range of motion, yield strength, and ultimate compressive strength were analyzed. RESULTS: None of the stand-alone implant constructs reduced the neutral zone. Supplemental pedicle screw fixation decreased the neutral zone in flexion-extension and lateral bending. Stand-alone implant constructs decreased the range of motion in flexion and lateral bending. Differences in the range of motion between stand-alone cage constructs were found in flexion and extension (marginally significant). Supplemental posterior fixation further decreased the range of motion in all loading directions with no differences between implant constructs. The Contact Fusion Cage and PLIF Allograft Spacer constructs had a higher ultimate compressive strength than the Ray Threaded Fusion Cage. CONCLUSIONS: The biomechanical data did not suggest any implant construct to behave superiorly either as a stand-alone or with supplemental posterior fixation. The PLIF Allograph Spacer is biomechanically equivalent to titanium cages but is devoid of the deficiencies associated with other cage technologies. Therefore, the PLIF Allograft Spacer is a valid alternative to conventional cages.     

Residual motion of different posterior instrumentation and interbody fusion constructs

Purpose

To elucidate residual motion of cortical screw (CS) and pedicle screw (PS) constructs with unilateral posterior lumbar interbody fusion (ul-PLIF), bilateral PLIF (bl-PLIF), facet-sparing transforaminal lumbar interbody fusion (fs-TLIF), and facet-resecting TLIF (fr-TLIF).

Methods

A total of 35 human cadaver lumbar segments were instrumented with PS (n = 18) and CS (n = 17). Range of motion (ROM) and relative ROM changes were recorded in flexion/extension (FE), lateral bending (LB), axial rotation (AR), lateral shear (LS), anterior shear (AS), and axial compression (AC) in five instrumentational states: without interbody fusion (wo-IF), ul-PLIF, bl-PLIF, fs-TLIF, and fr-TLIF.

Results

Whereas FE, LB, AR, and AC noticeably differed between the instrumentational states, AS and LS were less prominently affected. Compared to wo-IF, ul-PLIF caused a significant increase in ROM with PS (FE + 42%, LB + 24%, AR + 34%, and AC + 77%), however, such changes were non-significant with CS. ROM was similar between wo-IF and all other interbody fusion techniques. Insertion of a second PLIF (bl-PLIF) significantly decreased ROM with CS (FE -17%, LB -26%, AR -20%, AC -51%) and PS (FE − 23%, LB − 14%, AR − 20%, AC − 45%,). Facet removal in TLIF significantly increased ROM with CS (FE + 6%, LB + 9%, AR + 17%, AC of + 23%) and PS (FE + 7%, AR + 12%, AC + 13%).

Conclusion

bl-PLIF and TLIF show similarly low residual motion in both PS and CS constructs, but ul-PLIF results in increased motion. The fs-TLIF technique is able to further decrease motion compared to fr-TLIF in both the CS and PS constructs.

     

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.     

A biomechanical comparison between anterior and transverse interbody fusion cages.

STUDY DESIGN: Human cadaveric lumbar spines underwent placement of threaded fusion cages (TFCs) in either an anterior or transverse orientation. Spines underwent load testing and angular rotation measurement in the intact state, after diskectomy, after cage placement, and after fatiguing. Angular rotations were compared between cage orientations and interventions. OBJECTIVE: To determine which cage orientation resulted in greater immediate stability. SUMMARY OF BACKGROUND DATA: There has been extensive biomechanical study of interbody fusion cages. The lateral orientation has been increasingly used for intervertebral fusion, but a direct biomechanical comparison between cages implanted either anteriorly or transversely in human cadaveric spines has not been performed. METHODS: Fourteen spines were randomized into the anterior group (anterior diskectomy and dual anterior cage placement) and the lateral group (lateral diskectomy and single transverse cage placement). Pure bending moments of 1.5, 3.0, 4.5, and 6.0 Nm were applied in flexion, extension, lateral bending, and axial rotation. Load testing was performed while intact, after diskectomy, after cage placement, and after fatiguing. Angular rotation was compared between anterior and lateral groups and, within each group, among the different interventions. RESULTS: Segmental ranges of motion were similar between spines undergoing either anterior or lateral cage implantation. CONCLUSIONS: These results demonstrate few differences between angular rotation after either anterior or lateral TFC implantation. These findings add to data that find few differences between orientation of implanted TFCs. Combined with a decreased risk of adjacent structure injury through a lateral approach, these data support a lateral approach for lumbar interbody fusion.     

腰椎微创极外侧经椎间孔椎体间融合术的生物力学评价

目的 通过生物力学测试比较腰椎微创极外侧经椎间孔椎体间融合术(E-TLIF)与传统术式的生物力学稳定性.方法 采用正常猪脊柱运动节段标本24副,随机进行不同处理后分为正常对照组(CG组)、单纯椎弓根螺钉内固定组(SG组)、经椎间孔腰椎体间融合术(TLIF)组、E-TLIF组;分别测试不同载荷时各组在轴向压缩、前屈、后伸、左侧屈时的应变、位移变化及左侧扭转稳定性等生物力学指标,并进行统计学比较.结果 E-TLIF组的载荷-应变和位移、最大载荷下轴向稳定性、扭转稳定性等生物力学指标与TLIF组比较差异无统计学意义(P＞0.05).在左侧屈活动中,E-TLIF组[线性位移(3.40 ±0.09)mm,角位移2.57°±0.12°]稳定性优于TLIF组[线性位移(3.98 ±0.22)mm,角位移3.03°±0.18°](t=2.61,P＜0.05),E-TLIF组和TLIF组在轴向(前屈、后伸)、侧屈、旋转方向上的力学稳定性均高于SG组(t=4.17 ～4.53,P＜0.01).结论 E-TLIF手术是一种安全、有效的腰椎椎体间融合术式.     

Biomechanical evaluation of an expandable meshed bag augmented with pedicle or facet screws for percutaneous lumbar interbody fusion

Objective

To evaluate the biomechanics of lumbar motion segments instrumented with stand-alone OptiMesh system augmented with posterior fixation using facet or pedicle screws and the efficacy of discectomy and disc distraction.

Background context

OptiMesh bone graft containment system has been used for vertebral compression fractures and percutaneous lumbar interbody fusion. The filled mesh bag serves as the interbody device providing structural support to the motion segment being fused. No biomechanical data of this new device are available in the literature.

Methods

Twenty-four fresh human cadaveric lumbar motion segments were divided into two groups. In the control group, multidirectional flexibility testing was conducted after an intact condition and standard transforaminal lumbar interbody fusion (TLIF) procedure. In the OptiMesh group, testing was performed following intact, stand-alone OptiMesh procedure, OptiMesh with facet screws (placed using the transfacet approach), and OptiMesh with pedicle screws and rods. Range of motion (ROM) was calculated for each surgical treatment. The lordosis and disc height change of intact and instrumented specimens were measured in the lateral radiographs to evaluate the disc space distraction. In the OptiMesh group, cyclic loading in flexion extension (FE) was applied to measure cage subsidence or collapse (10,000 cycles at 6 Nm). After biomechanical testing, all the specimens were dissected to inspect the discectomy and end plate preparation. The area of discectomy was measured.

Results

The mean ROM of the intact specimens was 2.7°, 7.4°, and 7.2° in axial torsion (AT), lateral bending (LB), and FE, respectively. There was no difference between the control group and OptiMesh group. The mean ROM of the stand-alone OptiMesh system decreased to 2.4°, 5.1°, and 4.3° in AT, LB, and FE. The ROM decreased to 0.9° in AT, 2.2° in LB, and 0.9° in FE with OptiMesh system and facet screws. On average, OptiMesh system with pedicle screws and rods reduced the ROM to 1.3° in AT, 1.6° in LB, and 1.1° in FE. Compared with the intact condition and stand-alone OptiMesh system, both posterior fixation options had significant statistical difference (p<.001). In AT, ROM of facet screws was lower than that of pedicle screws (p<.05). There was no statistical difference between the facet and pedicle screws in LB and FE (p>.05). The mean volume of bone graft packed into each bag was 8.3±1.5 cc. The average increase of lordosis was 0.6°±1.0° after meshed bag was deployed. The average distraction achieved by the OptiMesh system was 1.0±0.6 mm. The average prepared area of discectomy was 42% of the total disc. The disc height change after cyclic loading was 0.2 mm. No subsidence or collapse was noticed.

Conclusions

The OptiMesh system offers large volume of bone graft in the disc space with small access portals. The OptiMesh system had similar construct stability to that of standard TLIF procedure when posterior fixation was applied. However, the amount of distraction was limited without additional distraction tools. With the anterior support provided by the expandable meshed bag, facet screws had comparable construct stability to that of pedicle screws. Slightly higher stability was observed in facet screws in AT.