脊柱失稳节段经椎弓根螺钉内固定器固定后对邻近节段三维运动的影响

目的研究经椎弓根螺钉内固定器固定脊柱失稳节段后对邻近节段三维运动范围的影响.方法在7例新鲜成人尸体T10～L4脊柱标本上,模拟L1骨折后安放经椎弓根螺钉内固定器,在10.0N@m载荷下进行三维运动测试.分析脊柱固定阶段(T12～L2)、邻近节段(T11～T12、L2～L3)和总节段(T11～L3)的前屈、后伸、轴向旋转和侧弯运动范围.结果经椎弓根螺钉内固定器固定后能使固定节段屈伸、侧弯运动方向上运动范围减少,轴线旋转运动恢复至正常完整节段运动范围.但同时邻近节段屈伸、侧弯运动运动范围增加,轴向旋转运动范围无明显变化.固定后总节段比正常完整总节段屈伸、侧弯运动运动范围增加,轴向旋转运动范围无明显变化.结论经椎弓根螺钉内固定器固定使邻近节段屈伸和侧弯运动范围代偿性增加,但不能代偿丢失的运动范围,对邻近节段的轴向旋转无明显影响.     

脊柱前中柱稳定性对椎弓根螺钉内固定器前屈压缩刚度的影响及其意义

目的 分析脊柱前中柱稳定性对椎弓根螺钉内固定器固定后前屈压缩刚度的影响,并探讨其临床意义。方法 收集7具新鲜猪T_(10)～L_4节段胸腰椎脊柱标本,“Ⅴ”形切除L_1椎体并压缩至闭合,造成前中柱不稳,模拟L_1骨折后安放AF椎弓根内固定器,进行前屈-压缩测试,分别计算完整标本、损伤标本和内固定后标本的前屈-压缩刚度。结果 完整标本、损伤标本和固定后标本的前屈-压缩刚度分别为413.9±118.6N/mm、136.6±31.6N/mm、240.5±51.4N/mm。相互间差异显著 (P<0.001)。结论 脊柱前中柱失稳后,经椎弓根螺钉内固定器械固定不能使其恢复到正常的机械力学性质,特别是前屈-压缩方向上。胸腰椎脊柱骨折经椎弓根螺钉系统固定后恢复前中柱的机械力学性质,减少其载荷分享是防止术后角度丢失,避免内固定器械固定失败的关键。     

动力内固定对羊脊柱后外侧融合稳定性的影响

根据“载荷分享”的原理，我们设计了一种动力椎弓根螺钉内固定器，体外生物力学实验推测能增加载荷分享，减少应力遮挡效应。本实验用活体山羊脊柱内固定后外侧融合模型，进一步比较动力内固定和相对坚强内固定对脊柱后外侧融合稳定性的影响，探讨动力内固定能否增加载荷分享，促进脊柱融合。     

动力内固定融合术对失稳脊柱稳定作用的实验研究

目的：探讨动力椎弓根螺钉内固定的优越性。方法：18只山羊随机分为3组，正常对照组（A组，仅作脊柱后路皮肤切开，L2～L4节段椎旁肌剥离）、动力固定融合组（B组，在A组基础上切除L3后部结构后行动力固定融合）和坚强同定融合组（C组，同B组但改为坚强固定融合）。术后24周处死动物，截取L1-L6节段脊柱标本，在脊柱三维运动试验机上测试固定节段运动范围，然后在MTS 858试验机上进行压缩刚度测试。A组标本测试完后切除L3后部结构作为损伤组（D组）重复稳定性和刚度测试，B组和C组取出内固定器后重复刚度测试。结果：与D组相比．B组和C组屈伸、侧弯和轴向旋转活动范围明显减少（P〈0．01），而且在屈伸、侧弯方向上比A组更稳定。与D组相比，B组和C组刚度均显著性提高（P〈0.01）；B组和C组内固定器取出后与取出前刚度之比的均值分别为85．51％、74．49％，有显著性差异（P〈0．05）。结论：动力内固定和坚强内固定融合均能恢复山羊失稳脊柱的稳定性，但动力内同定能增加载荷分享。     

新型脊柱内固定器的设计和生物力学测试

目的作者设计一种新型脊柱内固定器,经生物力学测试对该器械进行评价。方法取7具新鲜成人尸体T10－L4脊柱标本上,模拟L1骨折后安装该器械进行脊柱三维运动范围和前屈－压缩刚度测试。结果该器械能在屈伸、侧弯运动方向上显著加强损伤节段的稳定性(P<0.001～0.01)。使轴向旋转运动恢复正常运动范围(P<0.05)。结论新型脊柱内固定器(池氏钉)设计合理,对损伤脊柱节段固定具有较强稳定性,不失为一种较为理想的内固定器械。     

寰枢椎后路椎弓根螺钉固定的生物力学评价

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

不同骨密度对胸腰椎椎弓根内固定早期稳定性的生物力学研究

目的研究不同骨密度对椎弓根螺钉内固定早期稳定性的影响,为临床工作提供生物力学参考。方法取新鲜成年绵羊胸腰椎脊柱标本(T13-L2)36具,采用随机数字表法分为4组,分别为A(HCL脱钙0 h)、B(HCL脱钙2 h)、C(HCL脱钙4h)、D(HCL脱钙6h)组,每组9个。采用EXPERT-XL双能X线骨密度仪(Lunar公司)对四组脊柱椎体进行测量,依据骨密度的不同分为骨量正常组骨量减少组骨质疏松组严重骨质疏松组。4组均采用在T14-L2上置入椎弓根钉棒系统。以(300±105)N的载荷对4组模型进行250 000次循环4个方向(前屈、后伸、左侧弯、右侧弯)加载,比较4组模型的脊柱活动范围、螺钉的最大拔出力、轴向压缩刚度。结果疲劳试验后,A、B、C、D组脊柱的运动范围值(ROM)、轴向压缩刚度依次增大、螺钉的最大拔出依次减小,各组间差异有统计学意义(P0.05)。结论 1.脊柱骨密度越低,椎弓根固定后脊柱早期的稳定性越差。2.对于骨密度在骨质疏松范围内的患者不能行单纯椎弓根螺钉固定,而且在骨性愈合期间应减少脊柱的活动量。     

滑动椎弓根钉系统稳定性体外生物力学测试

[目的]对滑动椎弓根钉系统(SPSS)与通用椎弓根钉系统(USS)在脊柱侧凸固定强度、刚度和稳定性等方面进行生物力学比较,以测试滑动椎弓根螺钉内固定系统稳定性的生物力学性能.[方法]采用12具猪新鲜脊柱标本,随机分成两组分别测量不同工况下T12椎体的位移,并计算其强度和刚度进行比较.[结果]滑动组和通用组无论在轴向压缩、前屈、后伸、侧屈情况下,主应变、位移变化及固定强度、刚度均无显著性差异(P>0.05).[结论]滑动椎弓根钉系统治疗脊柱侧凸同样能够达到通用椎弓根钉系统相同的矫形效果及生物力学稳定性,同时它不影响青少年生长发育.     

下颈椎后路内固定器对失稳颈椎固定作用的生物力学评价

目的 评价下颈椎后路内固定器重建失稳颈椎稳定性的生物力学性能。方法 5具新鲜颈椎尸体标本制造脱位模型后依次用棘突钢丝、侧块螺钉、自制螺钉、椎弓根螺钉固定，用脊柱三维运动测量系统测算其运动范围。结果 棘突钢丝在屈伸和侧弯时的运动范围可恢复完整颈椎水平，但旋转时的运动范围比完整颈椎大。侧块螺钉和自制螺钉的运动范围均较完整颈椎小，且侧弯和旋转的运动范围明显小于棘突钢丝。椎弓根螺钉侧弯和旋转的运动范围最小。内固定相邻节段的运动范围虽有变化，但差异无显著性(P＞0．05)。结论 棘突钢丝可重建失稳颈椎的屈伸稳定性，但侧弯和旋转稳定性欠佳，侧块螺钉和自制螺钉优于棘突钢丝，椎弓根螺钉的稳定性最强。     

胸腰椎骨折伤椎短椎弓根钉固定的生物力学研究

[目的]通过生物力学测试对胸腰椎爆裂性骨折伤椎单侧短椎弓根钉固定的稳定性及刚度进行评价.[方法]取18具新鲜小牛胸腰段(T11 ～L3)标本,制作成胸腰椎爆裂性骨折模型,测试跨节段4枚椎弓根钉固定(4钉组)、伤椎单侧短椎弓根钉固定(5钉组)、伤椎双侧椎弓根钉固定(6钉组)标本模型的轴向压缩刚度及三维6个方向的运动范围(ROM).[结果]4钉组、5钉组、6钉组三种固定方式,均能提高骨折模型的稳定性及刚度;5钉组、6钉组模型刚度均明显高于4钉组,差异有统计学意义(P＜0.05),5钉组、6钉组模型在屈伸、侧弯、旋转6个方向的运动范围(ROM)均明显低于4钉组,差异有统计学意义(P＜0.05);而5钉组与6钉组模型之间的刚度比较差异无统计学意义(P＞0.05),5钉组与6钉组模型在屈伸、侧弯、旋转6个方向的运动范围(ROM)的比较差异无统计学意义(P＞0.05).[结论]对于胸腰椎爆裂性骨折,伤椎置钉固定能明显提高脊柱的刚度及稳定性,经伤椎单侧短椎弓根钉固定与伤椎双侧椎弓根钉固定对脊柱刚度及稳定性的影响无明显差异.     

Stability analysis of an enhanced load sharing posterior fixation device and its equivalent conventional device in a calf spine model

STUDY DESIGN: An in vitro test of calf spine lumbar segments to compare biomechanical stabilization of a rigid versus a dynamic posterior fixation device. OBJECTIVES: To compare flexibility of a dynamic pedicle screw fixation device with an equivalent rigid device. SUMMARY OF BACKGROUND DATA: Dynamic pedicle screw device studies are not as prevalent in the literature as studies of rigid devices. These devices contain the potential to enhance load sharing and optimize fusion potential while maintaining stability similar to that of rigid systems. METHODS: Load-displacement tests were performed on intact and stabilized calf spines for the dynamic and rigid devices. Stability across a destabilized L3-L4 segment was restored by insertion of either a 6 mm x 40 mm dynamic or rigid pedicle screw fixation device across the L2-L4 segment. The screws then were removed, 7 mm x 45 mm pedicle screws of the opposite type were inserted, and the construct then was re-tested. Axial pull-out tests were performed to assess the likely effects of pedicle screw replacement on the load-displacement data. RESULTS: Results indicated a 65% reduction in motion in flexion-extension and a 90% reduction in lateral bending across the destabilized level for both devices, compared with intact spine values. Reduction in axial rotation motion was much smaller than in other modes. Axial pull-out tests showed no weakening of the bone-screw interface. CONCLUSIONS: Both devices provided significant stability of similar magnitudes in flexion, extension, and lateral bending. In axial rotation, the devices only could restore stability to levels similar to those in an intact spine. The dynamic device offers a design that may enhance load sharing without sacrificing construct stability.     

Pedicle screw adjustments affect stability of thoracolumbar burst fracture.

STUDY DESIGN: An in vitro biomechanical study of the stabilizing effect of pedicle screw instrumentation on experimental thoracolumbar burst fractures. OBJECTIVES: To evaluate the effects of different adjustments applied by the pedicle screw fixation device on the stability of the spine-device construct. SUMMARY OF BACKGROUND DATA: Pedicle screw devices are widely used to accomplish spinal reduction and provide stability to an injured spine. In previous biomechanical studies the stability of the spine-device constructs has been examined for many devices. However, no study has quantitatively assessed the associations between the device adjustments and the stability of the construct. METHODS: Five-vertebrae human cadaveric specimens with burst fracture at L1 vertebra were studied. Pedicle screw fixation device was attached to the T12 and L2 vertebrae. Five device adjustments (pure compression, pure distraction, pure extension, a combination distraction-extension, and neutral posture) were studied. Multidirectional flexibility test was performed when intact, after burst fracture, and after each device adjustment to document spinal stability. RESULTS: The construct stability had a complex association to the device adjustment. For example, the maximum flexion and extension stabilities were achieved by pure compression and distraction-extension combination adjustments, respectively. Pure distraction and pure extension adjustments decreased the construct stability. CONCLUSIONS: The device adjustments affected the spinal construct stability differently in different directions. Although pure compression provided the most stability in most directions, the combined distraction-extension adjustment may be more suitable considering the neural decompression also.     

Comparison of the effects of bilateral posterior dynamic and rigid fixation devices on the loads in the lumbar spine: a finite element analysis

A bilateral dynamic stabilization device is assumed to alter favorable the movement and load transmission of a spinal segment without the intention of fusion of that segment. Little is known about the effect of a posterior dynamic fixation device on the mechanical behavior of the lumbar spine. Muscle forces were disregarded in the few biomechanical studies published. The aim of this study was to determine how the spinal loads are affected by a bilateral posterior dynamic implant compared to a rigid fixator which does not claim to maintain mobility. A paired monosegmental posterior dynamic implant was inserted at level L3/L4 in a validated finite element model of the lumbar spine. Both a healthy and a slightly degenerated disc were assumed at implant level. Distraction of the bridged segment was also simulated. For comparison, a monosegmental rigid fixation device as well as the effect of implant stiffness on intersegmental rotation were studied. The model was loaded with the upper body weight and muscle forces to simulate the four loading cases standing, 30° flexion, 20° extension, and 10° axial rotation. Intersegmental rotations, intradiscal pressure and facet joint forces were calculated at implant level and at the adjacent level above the implant. Implant forces were also determined. Compared to an intact spine, a dynamic implant reduces intersegmental rotation at implant level, decreases intradiscal pressure in a healthy disc for extension and standing, and decreases facet joint forces at implant level. With a rigid implant, these effects are more pronounced. With a slightly degenerated disc intersegmental rotation at implant level is mildly increased for extension and axial rotation and intradiscal pressure is strongly reduced for extension. After distraction, intradiscal pressure values are markedly reduced only for the rigid implant. At the adjacent level L2/L3, a posterior implant has only a minor effect on intradiscal pressure. However, it increases facet joint forces at this level for axial rotation and extension. Posterior implants are mostly loaded in compression. Forces in the implant are generally higher in a rigid fixator than in a dynamic implant. Distraction strongly increases both axial and shear forces in the implant. A stiffness of the implant greater than 1,000 N/mm has only a minor effect on intersegmental rotation. The mechanical effects of a dynamic implant are similar to those of a rigid fixation device, except after distraction, when intradiscal pressure is considerably lower for rigid than for dynamic implants. Thus, the results of this study demonstrate that a dynamic implant does not necessarily reduce axial spinal loads compared to an un-instrumented spine.     

Biomechanical studies of a dynamized anterior thoracolumbar implant

STUDY DESIGN: An in vitro investigation into the biomechanical properties of a dynamized anterolateral compression implant that allows controlled subsidence. OBJECTIVES: To determine the extent to which both modes of the anterolateral compression implant (controlled collapsing and rigid) are able to reestablish the stability of the lumbar spine after L4 corpectomy. SUMMARY OF BACKGROUND DATA: Over time, anterior and posterior spinal implants have been associated with progressive angulation, and occasionally implant failure and breakage. To circumvent this occurrence and provide better graft loading, dynamized or collapsing devices for clinical use have been developed. METHODS: Eight fresh calf spines (L1-L6) were placed in a biomechanical testing frame. Pure moments of 6 Nm were loaded onto the intact spine in six directions: flexion, extension, right and left lateral bending, and right and left axial rotation. A total L4 corpectomy then was performed, and the defect grafted with a wooden dowel. Loading was repeated after the specimens were stabilized using the two modes of the anterolateral compression implant in succession. RESULTS: The results showed that both modes of the implant (the rigid mode in particular) restore the stiffness of the unstable spine to normal levels of flexion, extension, and right and left lateral bending, even to levels exceeding normal. These devices, however, fall short of achieving normal stability in right and left axial rotation. CONCLUSION: In the cadaveric calf spine after L4 corpectomy, restoration of stability with a dynamized anterior spinal implant is possible in flexion, extension, and right and left lateral bending, but not in axial rotation.     

5种后路脊柱内固定器械的生物力学评价

采用７具新鲜尸体胸腰段脊柱标本（Ｔ８～Ｌ５），损伤Ｔ１２～Ｌ１的后部结构造成脊柱失稳。在失稳的脊柱标本上轮流安装５种常用后路内固定器械，分别进行脊柱稳定性测试，得出５种内固定器械对损伤节段的固定效果。结果表明，５种内固定器械对失稳脊柱节段的屈／伸及右／左侧弯运动均有良好的固定作用，但对轴向旋转运动均不能控制到完整脊柱的稳定水平。相对而言，Ｄｉｃｋ钉的作用较优。     

In vitro evaluation of stiffness and load sharing in a two-level corpectomy: comparison of static and dynamic cervical plates

Background contextAnterior cervical plating has been accepted in corpectomy and fusion of the cervical spine. Constrained plates were criticized for stress shielding that may lead to subsidence and pseudarthrosis. A dynamic plate allows load sharing as the graft subsides. Ideally, the dynamic plate design should maintain adequate stiffness of the construct while providing a reasonable load sharing with the strut graft.PurposeThe purpose of the study was to compare dynamic and static plate kinematics with graft subsidence.Study design/settingThe study designed was an in vitro biomechanical study in a porcine cervical spine model.MethodsTwelve spines were initially tested in intact condition with 20-N axial load in 15 degrees of flexion and extension range of motion (ROM). Then, a two-level corpectomy was created in all specimens with spines randomized to receive either a static or dynamic plate. The spines were retested under identical conditions with optimal length and undersized graft. Range of motion and graft loading were analyzed with a one-way analysis of variance (p<.05).ResultsBoth plates significantly limited ROM compared with the intact spine in both graft length conditions. In extension graft, load was significantly higher (p=.001) in the static plate with optimal length, and in flexion, there was a significant loss of graft load (p=.0004). In flexion, the dynamic plate with undersized graft demonstrated significantly more load sustained (p=.0004).ConclusionsBoth plates reasonably limited the ROM of the corpectomy. The static plate had significantly higher graft loads in extension and significant loss of graft load in flexion, whereas the dynamic plate maintained a reasonable graft load in ROM even when graft contact was imperfect.     

不同类型前路钢板固定应用于颈椎屈曲牵张型损伤的生物力学研究

目的探讨采用前路钢板固定颈椎屈曲牵张型损伤治疗的可靠性,并比较静力化固定和动力化固定等不同设计类型钢板在恢复损伤节段稳定性方面的差异。方法采用12具小牛颈椎标本,在C_(4,5)节段制作屈曲牵张损伤模型,切除椎间盘、植骨后随机分为3组,分别采用Orion、Codman、Window钢板、螺钉固定,测试手术固定各组在颈椎前屈、后伸、侧屈及旋转运动时的稳定性并与正常标本比较。结果颈椎屈曲损伤后,无论采用哪种钢板固定,其术后运动范围(ROM值)均比正常颈椎要大。Orion固定最接近正常标本,但在旋转运动时有明显差异。Codman固定仅在侧曲时的稳定性接近正常和Orion固定组。Window固定最弱,在各运动状态下的刚度均明显低于正常组。结论在颈椎屈曲牵张型损伤时,前路静力化固定相对稳定,动力化固定可能牺牲一定的固定强度,尤其是选择平移类设计的钢板固定更要谨慎。     

短节段脊柱固定器的生物力学实验研究

自行设计的一种可调式脊柱前路固定器，以粗大螺纹钉置入椎体和坚强螺棒作支柱，结构简单稳固，易于操作。生物力学测试表明，新固定器抗压平均屈服强度为１．６７ＫＮ，轴向抗扭平均屈服强度为８．７Ｎｍ。并与其他４种短节段脊柱固定器在新鲜冷冻人体腰椎制成的前中柱损伤模型上进行比较研究。实验表明：（１）对于脊柱前中柱损伤，前路固定器更有利于重建其稳定性。（２）综合比较，新固定器在各个方向稳定性均较好，不失为一种较好的可供选用的脊柱前路固定器。     

Biomechanical evaluation of spinal fixation devices. Part III. Stability provided by six spinal fixation devices and interbody bone graft

The three-dimentional stability provided by six spinal fixation devices with or without interbody bone graft has been studied in an in vitro biomechanical model using five-vertebral (T11-L3) fresh cadaveric thoracolumbar specimens. An injury was created at T12-L1 by complete transection of the posterior elements and posterior half of the intervertebral disc, leaving the anterior half of the intervertebral disc and anterior longitudinal ligament intact. The three-dimensional rotations and translations, measures of biomechanical instabilities, were determined under physiologic loads for the intact spine and the spinal constructs, ie, injured spine plus instrumentation. The tested devices were: Harrington reverse ratchet rods (HR); Luque rectangle rod (LR); Kaneda device without transverse fixator (KD); Kaneda device with transverse fixators (KT); transpedicular external fixator (EF). In addition, stability tests were performed for KT, EF, and Harrington compression rods with interbody bone graft following a corpectomy (KTB, EFB, and HCB). The constructs were more stable than the intact spine under the four loads in the following order: flexion: EFB, HCB, EF, HR, LR, KTB, and KT; extension: EFB, LR, EF, KTB, HR, and KT; lateral bending: KTB, KT, EFB, KD, EF, HCB, and HR; and axial rotation: EFB.