新型钛合金颈椎前路钢板的生物力学评价
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摘要
前言
目前,颈椎前路钢板已经广泛应用于颈椎创伤、畸形、退行性变以及颈椎肿瘤的治疗,其能增强术后颈椎的即刻稳定性,降低假关节发生率,并且能够减少颈椎后凸畸形的产生。但在临床上颈椎前路减压融合应用钢板固定,术后在植骨吸收或下沉时钢板会对植骨区域产生应力屏蔽,影响融合效果。针对这一现象,我们在研究了各种颈椎前路钢板系统的基础上,应用新型超弹性低模量医用钛合金研制了颈椎前路多功能钢板系统(Multifunctional cervical plate,MCP),并且对此钢板系统对颈椎的三维稳定作用进行了评价。随着颈椎前路钢板在临床应用的日渐增多,由于疲劳或是周期性的运动所导致的钢板螺钉的松动、脱出甚至断裂等情况也时有报道,因此,本文对钢板系统也进行了疲劳测试和三维有限元分析,以期为临床应用提供参考。
方法
收集24具6个月左右宰杀的猪颈椎标本随机分为四组,每组6具标本。在连续的四种状态下,即完整状态、植骨状态、钢板固定状态以及疲劳测试后状态,对颈椎C_(3-7)施加2.0Nm的纯力矩,测量标本前屈、后伸、左右侧屈、左右旋转的活动范围(rang of motion;ROM)和中性区(neutral zone;NZ)。
依据ASTM标准(F1717-96)对限制性MCP和C-mark钢板(C-mark plate,CMP)进行疲劳试验,将MCP、CMP上、下两端分别固定于两块高19mm的超高分子量聚乙烯模块(Ultra high molecular weight polyethylene,UHMWPE)上,制成类似椎体切除的模型。将钢板固定于制作的椎体切除术UHMWPE模型上,通过穿入UHMWPE模块的一对直径9.6mm金属棒将这套试验装置连接在与试验机夹头配套的夹具上,然后把整套试验装置连接到INSTRON-8871材料试验机上。随之进行压缩试验和疲劳试验,加载负荷均采用压弯加载,在压缩和拉伸时两固定块以金属棒为轴转动,保证载荷垂直作用于固定块上。
采用Unigraphics建立MCP的几何模型,并导入MSC三维有限元软件中进行力学分析。三维有限元网格采用四面体单元,模拟MCP在螺钉受力作用下的变形和受力情况。MCP模型采用弹塑性模型,材料选用生物医用钛合金,螺钉也采用弹塑性模型,并与MCP之间为变形体接触连接,压板采用刚性体。MCP模型采用四面体单元,并在几何形状复杂的部位和模型的内部进行了网格细化,该模型划分了16,409个节点,72,198个四面体单元,螺钉模型采用简单的圆柱体,并同样进行网格剖分,将压板与螺钉接触模拟MCP的受力情况。
结果
所有节段在6个方向的ROM上,MCP固定状态、MCP疲劳状态、CMP固定状态、CMP疲劳状态之间相比较,差异没有统计学意义(P＞0.05),但与完整状态、植骨状态相比较,差异均有显著统计学意义(P＜0.01)。在前屈、左右侧屈方向的ROM上,植骨状态与完整状态相比较,差异有显著统计学意义(P＜0.01)。在屈伸NZ上,MCP固定状态、MCP疲劳状态、CMP固定状态、CMP疲劳状态之间相比较,差异没有统计学意义(P＞0.05),但与完整状态、植骨状态相比较,差异均有显著统计学意义(P＜0.01)。在侧屈NZ上,除完整状态与其它状态之间有统计学意义外(P＜0.01),其它状态之间没有差异(P＞0.05)。在旋转NZ上,所有状态之间均没有统计学意义(P＞0.05)。MCP抗压载荷为180N,在应用63N的压缩载荷下,疲劳试验进行到10~6次时钢板仍然没有发生断裂。三维有限元分析显示钢板钉孔周围为应力、应变集中处。
讨论
为了实现钢板在稳定颈椎作用不变的情况下,有效降低植骨区域的应力屏蔽,本研究应用超弹性低模量医用钛合金研制了MCP。MCP具有以下特点:(1)钢板螺钉均应用68GPa的新型钛合金制成,与目前临床普遍应用的医用钛合金(Ti-6Al-4V,110GPa)相比具有超弹性低模量的优点,更为接近皮质骨的弹性模量,有效降低应力屏蔽效应;(2)MCP包括CMCP、SCMCP、HMCP三种系统,能够根据患者具体情况选择应用合适的钢板系统。在颈椎前路植骨融合的过程中,通常会发生植骨的吸收和/或下沉。当植骨发生吸收和/或下沉时,SCMCP和HMCP的椎体可调角度螺钉可在一定范围内适应植骨的吸收或下沉,根据Wolf定律,有利于植骨区的融合;(3)均匀布置的横条形植钉区设计:①有利于固定螺钉的横向任意植入;②在进行椎体次全切除时,固定螺钉可用于固定植骨块;③在进行椎间盘切除时,固定螺钉可用于固定椎体;④联合进行椎体次全切除和椎间盘切除时,固定螺钉可以同时固定植骨块和椎体;(4)带有锁定装置,安全方便,可有效防止退钉现象。
三维稳定性试验结果显示,颈椎前路椎体次全切除植骨后颈椎的活动范围明显降低,在MCP固定后颈椎的活动范围进一步降低。在施加2.0Nm的纯力矩时,MCP固定后能够达到与CMP同样的三维稳定效果;在进行疲劳测试后MCP仍然能够维持颈椎的三维稳定性,并且能够达到与CMP同样的稳定效果。在未施加载荷时,所有固定节段在屈伸、侧屈、旋转方向上,MCP固定以及疲劳测试后同CMP相比较没有差异。
疲劳试验结果显示,MCP的抗压载荷为180N,在63N的压缩载荷下,钢板疲劳试验能够达到10~6次,相当于正常人颈椎生理运动4～6个月,能够满足体内颈椎植骨融合的需要。椎体固定螺钉孔周围以及条形植钉区是钢板的应力集中部位。扫描电镜观察结果显示MCP断裂的疲劳萌生区在钢板的上表面,钢板发生断裂时裂纹由钢板的上表面逐渐往下表面延伸,直至断裂。
三维有限元分析结果显示,MCP的植钉区、椎体固定螺钉孔的外下缘以及视窗孔的外侧缘为MCP发生应力、应变的集中区域,这些集中区域即为实际疲劳试验过程中最有可能发生断裂的区域,本试验中MCP的应力、应变集中区域有限元模拟结果与实际进行疲劳试验的钢板的断裂区域相一致。
结论
本试验研究显示MCP够给颈椎提供足够的三维稳定性,在进行扭转疲劳试验后仍然能给颈椎提供足够的三维稳定性;在63N的压缩载荷下,钢板疲劳试验能够达到10~6次,能够满足术后植骨融合的需要;三维有限元分析显示钢板的应力、应变集中区域有限元模拟结果与实际进行疲劳试验的钢板的断裂区域是一致的。
Preface
To date,anterior cervical plate has been widely performed in spinal fractures, spinal tumors,and degenerative cervical diseases.Anterior cervical plate is advocated for the reconstruction of anterior and middle column defects,to establish appropriate anterior spinal load-sharing.The usefulness of the anterior cervical plate is manifold:to maintain the bone graft in place,to promote fusion by providing stability between the bone graft and donor vertebrae,and to keep proper cervical alignment.In this study,we have designed a multifunctional cervical plate(MCP) made by a new titanium-alloy and evaluated the flexibility of the MCP on the cervical spine after simulated static and cyclic physiologic loads.However,with the increasing of anterior cervical plating in spinal surgery,the failure directly related to the instrumentation,such as instrumentation loosening,screw backout,decreased load sharing,and poor compensation for graft subsidence,may happen by the reasons of fatigue and cyclic motion in vivo.Therefore,we have also done fatigue testing and three-dimensional finite element analysis to detecting the designed MCP whether or not to meet the needs of the fusion.
Methods
24 porcine specimens(C3-C7)(median age 6 months) were collected and randomly divided into four groups with six specimens of each group.Each specimen was loaded in vitro with pure moments of±2.0 Nm in flexion/extension,lateral bending, and axial rotation.Range of motion(ROM) and neutral zone(NZ) were measured in the intact state,with anterior cervical corpectomy in C4-C6 without plating,after addition of either a MCP or C-mark plate(CMP) and after 2000 cycles of axial torsion.
The constrained MCP and CMP systems were assembled and tested in accordance with the corpectomy model defined in ASTM F1717-96 for compression testing.The testing standard consisted of the use of an ultra high molecular weight polyethylene (UHMWPE) model simulating a total corpectomy defect and the application of a compressive bending load.The use of UHMWPE blocks removes variability related to the bone density and quality of the vertebral bodies thus providing a reproducible test bed to evaluate the properties of the fixation systems.During construction of the implant assemblies,the manufacturers' recommendations were followed exactly.A pair of stainless steel yokes with pins supported the UHMWPE blocks and permitted free rotation of the blocks in the sagittal plane during deformation of the assembly.All mechanical testing was performed on a servo-hydraulic materials testing machine under software control(INSTRON,8871,England).The static compression testing and fatigue testing were made subsequently.
The geometry of the MCP was accomplished in the software Unigraphics.Then the created geometry was imported into MSC software,to accomplish the finite element method analysis.The plastic model and the biomedical titanium alloy were used in the MCP system.The deformable body contacted at the plate-screw interface, and the rigid board was adopted on the depressor.This analysis begins with the discretization of the model.The mesh was made with four nodes tetrahedral elements, obtaining a mesh of 16,409 nodes and 72,198 elements.The nodes of the screws were made coincide with the plate where they are placed.The stress and the strain of the MCP were analysis through the load which the depressors exert to the vertebrae screws.
Results
All the segments in all loading directions of ROM,no differences were found among MCP fixed state,MCP fatigue state,CMP fixed state and CMP fatigue state.But when the above states compared with the intact and grafted state,significant differences were found(P＜0.01).In flexion and lateral bending of ROM,significant difference was found between the intact and the grafted state(P＜0.01).In the NZ of flexion/extension, no differences were found among MCP fixed state,MCP fatigue,state,CMP fixed state and CMP fatigue state.But when the above states compared with the intact and grafted state,significant differences were found(P＜0.01).In the lateral NZ,significant difference was found between the intact state and other states(P＜0.01),but no significant differences were found among other states.In the rotational NZ,no significant differences were found among all the states.The ultimate bending failure load of the MCP was 180 N.In the application of 63 N under bending loads,the MCP was still not broken when the fatigue test was carried out 10~6 times.The stress and the strain concentration were found in the hole of the MCP in the three-dimensional finite element analysis.
Discussion
In this study,the MCP system was designed and evaluated in a porcine cadaveric anterior cervical corpectomy model.The MCP has some attractive characteristics. Firstly,the material used in our design is a new kind of titanium-alloy (Ti-24Nb-4Zr-7.9Sn),which is non-toxic with lacking noxious metals such as aluminum.The new alloy has a lower modulus of elasticity and is more flexible compared with currently used Ti-6AL-4V alloy.Secondly,the MCP system has the option of constrained,semiconstrained and hybrid constructs.The suitable plate was selected for the specific conditions of the patients.Graft subsidence is common during healing after anterior cervical fusion surgery.The variable-angle screws of the semiconstrained MCP and the hybrid MCP can accommodate with the absorption and/or sinking of bone in a certain range.Semiconstrained plates,in theory,allow continued contact between the graft and the end plate after graft subsidence has occurred,thus improving the chance of obtaining a fusion by maintaining a compressive load on the graft.Thirdly,a set of trabecules holes were designed in the MCP uniformly.The multifunction of the MCP was manifested in several aspects:1) the fixed screw can be set any position of the horizontal hole.2) when the anterior cervical corpectomy fusion was performed,the fixed screw can be used to fix the implanted graft.3) when the anterior cervical discectomy fusion was performed,the fixed screws can be used to fix the vertebrae body.4) when the anterior cervical discectomy and corpectomy was performed simultaneously,the fixed screws can be used to fix the implanted graft and vertebrae body.Fourthly,screw backout is effectively prevented by the locked screws.
With grafting alone,the grafted state with anterior cervical corpectomy in C4-C6 without plating did substantially decrease ROM compared with the intact state in the flexion and lateral bending.When the MCP was implanted,the ROM was further decrease compared with the grafted state.The MCP can provide the same stability compared with the CMP,and it also provided enough stability after the fatigue test. Furthermore,the MCP can provide the same stability after the torsional fatigue test compared with the CMP.When there was no load on the plate,there were no differences on MCP and CMP in all the segments in all directions.Also,there was no difference on MCP before and after the fatigue test.
The ultimate bending failure load of the MCP was 180 N.In the application of 63 N under bending loads,the MCP was still not broken when the fatigue test was carried out 10~6 times.It was revealed that it could be satisfied the requirement of fusion when graft was implanted.The stress concentration of the MCP in the fatigue test was found in the outside edge of the hole of vertebral screws and the cross section of the fixed screws.It revealed that the original fracture zone was found in the upper surface of the MCP through the electron microscope scanning.
The stress and the strain of the MCP were located around the area which fixed screws were implanted,the outside of the vertebrae screws hole and window through the three-dimensional finite element analysis.The concentrated stress and strain region is actually the most possible broken area.The stress and strain concentration area of the MCP in the three-dimensional finite element analysis coincided with the actual area in which the MCP was broken in the fatigue test.
Conclusion
Three-dimensional stability of the cervical spine was provided by the MCP in the flexibility test.After the torsional fatigue test,the MCP can still provide enough stability.In the application of 63 N under bending loads,the MCP was still not broken when the fatigue test was carried out 10~6 times.It was revealed that it could be satisfied the requirement of fusion when graft was implanted.The stress and the strain concentration area of the MCP in the three-dimensional finite element analysis coincided with the actual area in which the MCP was broken in the fatigue test.
目前,颈椎前路钢板已经广泛应用于颈椎创伤、畸形、退行性变以及颈椎肿瘤的治疗,其能增强术后颈椎的即刻稳定性,降低假关节发生率,并且能够减少颈椎后凸畸形的产生。但在临床上颈椎前路减压融合应用钢板固定,术后在植骨吸收或下沉时钢板会对植骨区域产生应力屏蔽,影响融合效果。针对这一现象,我们在研究了各种颈椎前路钢板系统的基础上,应用新型超弹性低模量医用钛合金研制了颈椎前路多功能钢板系统(Multifunctional cervical plate,MCP),并且对此钢板系统对颈椎的三维稳定作用进行了评价。随着颈椎前路钢板在临床应用的日渐增多,由于疲劳或是周期性的运动所导致的钢板螺钉的松动、脱出甚至断裂等情况也时有报道,因此,本文对钢板系统也进行了疲劳测试和三维有限元分析,以期为临床应用提供参考。
方法
收集24具6个月左右宰杀的猪颈椎标本随机分为四组,每组6具标本。在连续的四种状态下,即完整状态、植骨状态、钢板固定状态以及疲劳测试后状态,对颈椎C_(3-7)施加2.0Nm的纯力矩,测量标本前屈、后伸、左右侧屈、左右旋转的活动范围(rang of motion;ROM)和中性区(neutral zone;NZ)。
依据ASTM标准(F1717-96)对限制性MCP和C-mark钢板(C-mark plate,CMP)进行疲劳试验,将MCP、CMP上、下两端分别固定于两块高19mm的超高分子量聚乙烯模块(Ultra high molecular weight polyethylene,UHMWPE)上,制成类似椎体切除的模型。将钢板固定于制作的椎体切除术UHMWPE模型上,通过穿入UHMWPE模块的一对直径9.6mm金属棒将这套试验装置连接在与试验机夹头配套的夹具上,然后把整套试验装置连接到INSTRON-8871材料试验机上。随之进行压缩试验和疲劳试验,加载负荷均采用压弯加载,在压缩和拉伸时两固定块以金属棒为轴转动,保证载荷垂直作用于固定块上。
采用Unigraphics建立MCP的几何模型,并导入MSC三维有限元软件中进行力学分析。三维有限元网格采用四面体单元,模拟MCP在螺钉受力作用下的变形和受力情况。MCP模型采用弹塑性模型,材料选用生物医用钛合金,螺钉也采用弹塑性模型,并与MCP之间为变形体接触连接,压板采用刚性体。MCP模型采用四面体单元,并在几何形状复杂的部位和模型的内部进行了网格细化,该模型划分了16,409个节点,72,198个四面体单元,螺钉模型采用简单的圆柱体,并同样进行网格剖分,将压板与螺钉接触模拟MCP的受力情况。
结果
所有节段在6个方向的ROM上,MCP固定状态、MCP疲劳状态、CMP固定状态、CMP疲劳状态之间相比较,差异没有统计学意义(P＞0.05),但与完整状态、植骨状态相比较,差异均有显著统计学意义(P＜0.01)。在前屈、左右侧屈方向的ROM上,植骨状态与完整状态相比较,差异有显著统计学意义(P＜0.01)。在屈伸NZ上,MCP固定状态、MCP疲劳状态、CMP固定状态、CMP疲劳状态之间相比较,差异没有统计学意义(P＞0.05),但与完整状态、植骨状态相比较,差异均有显著统计学意义(P＜0.01)。在侧屈NZ上,除完整状态与其它状态之间有统计学意义外(P＜0.01),其它状态之间没有差异(P＞0.05)。在旋转NZ上,所有状态之间均没有统计学意义(P＞0.05)。MCP抗压载荷为180N,在应用63N的压缩载荷下,疲劳试验进行到10~6次时钢板仍然没有发生断裂。三维有限元分析显示钢板钉孔周围为应力、应变集中处。
讨论
为了实现钢板在稳定颈椎作用不变的情况下,有效降低植骨区域的应力屏蔽,本研究应用超弹性低模量医用钛合金研制了MCP。MCP具有以下特点:(1)钢板螺钉均应用68GPa的新型钛合金制成,与目前临床普遍应用的医用钛合金(Ti-6Al-4V,110GPa)相比具有超弹性低模量的优点,更为接近皮质骨的弹性模量,有效降低应力屏蔽效应;(2)MCP包括CMCP、SCMCP、HMCP三种系统,能够根据患者具体情况选择应用合适的钢板系统。在颈椎前路植骨融合的过程中,通常会发生植骨的吸收和/或下沉。当植骨发生吸收和/或下沉时,SCMCP和HMCP的椎体可调角度螺钉可在一定范围内适应植骨的吸收或下沉,根据Wolf定律,有利于植骨区的融合;(3)均匀布置的横条形植钉区设计:①有利于固定螺钉的横向任意植入;②在进行椎体次全切除时,固定螺钉可用于固定植骨块;③在进行椎间盘切除时,固定螺钉可用于固定椎体;④联合进行椎体次全切除和椎间盘切除时,固定螺钉可以同时固定植骨块和椎体;(4)带有锁定装置,安全方便,可有效防止退钉现象。
三维稳定性试验结果显示,颈椎前路椎体次全切除植骨后颈椎的活动范围明显降低,在MCP固定后颈椎的活动范围进一步降低。在施加2.0Nm的纯力矩时,MCP固定后能够达到与CMP同样的三维稳定效果;在进行疲劳测试后MCP仍然能够维持颈椎的三维稳定性,并且能够达到与CMP同样的稳定效果。在未施加载荷时,所有固定节段在屈伸、侧屈、旋转方向上,MCP固定以及疲劳测试后同CMP相比较没有差异。
疲劳试验结果显示,MCP的抗压载荷为180N,在63N的压缩载荷下,钢板疲劳试验能够达到10~6次,相当于正常人颈椎生理运动4～6个月,能够满足体内颈椎植骨融合的需要。椎体固定螺钉孔周围以及条形植钉区是钢板的应力集中部位。扫描电镜观察结果显示MCP断裂的疲劳萌生区在钢板的上表面,钢板发生断裂时裂纹由钢板的上表面逐渐往下表面延伸,直至断裂。
三维有限元分析结果显示,MCP的植钉区、椎体固定螺钉孔的外下缘以及视窗孔的外侧缘为MCP发生应力、应变的集中区域,这些集中区域即为实际疲劳试验过程中最有可能发生断裂的区域,本试验中MCP的应力、应变集中区域有限元模拟结果与实际进行疲劳试验的钢板的断裂区域相一致。
结论
本试验研究显示MCP够给颈椎提供足够的三维稳定性,在进行扭转疲劳试验后仍然能给颈椎提供足够的三维稳定性;在63N的压缩载荷下,钢板疲劳试验能够达到10~6次,能够满足术后植骨融合的需要;三维有限元分析显示钢板的应力、应变集中区域有限元模拟结果与实际进行疲劳试验的钢板的断裂区域是一致的。
Preface
To date,anterior cervical plate has been widely performed in spinal fractures, spinal tumors,and degenerative cervical diseases.Anterior cervical plate is advocated for the reconstruction of anterior and middle column defects,to establish appropriate anterior spinal load-sharing.The usefulness of the anterior cervical plate is manifold:to maintain the bone graft in place,to promote fusion by providing stability between the bone graft and donor vertebrae,and to keep proper cervical alignment.In this study,we have designed a multifunctional cervical plate(MCP) made by a new titanium-alloy and evaluated the flexibility of the MCP on the cervical spine after simulated static and cyclic physiologic loads.However,with the increasing of anterior cervical plating in spinal surgery,the failure directly related to the instrumentation,such as instrumentation loosening,screw backout,decreased load sharing,and poor compensation for graft subsidence,may happen by the reasons of fatigue and cyclic motion in vivo.Therefore,we have also done fatigue testing and three-dimensional finite element analysis to detecting the designed MCP whether or not to meet the needs of the fusion.
Methods
24 porcine specimens(C3-C7)(median age 6 months) were collected and randomly divided into four groups with six specimens of each group.Each specimen was loaded in vitro with pure moments of±2.0 Nm in flexion/extension,lateral bending, and axial rotation.Range of motion(ROM) and neutral zone(NZ) were measured in the intact state,with anterior cervical corpectomy in C4-C6 without plating,after addition of either a MCP or C-mark plate(CMP) and after 2000 cycles of axial torsion.
The constrained MCP and CMP systems were assembled and tested in accordance with the corpectomy model defined in ASTM F1717-96 for compression testing.The testing standard consisted of the use of an ultra high molecular weight polyethylene (UHMWPE) model simulating a total corpectomy defect and the application of a compressive bending load.The use of UHMWPE blocks removes variability related to the bone density and quality of the vertebral bodies thus providing a reproducible test bed to evaluate the properties of the fixation systems.During construction of the implant assemblies,the manufacturers' recommendations were followed exactly.A pair of stainless steel yokes with pins supported the UHMWPE blocks and permitted free rotation of the blocks in the sagittal plane during deformation of the assembly.All mechanical testing was performed on a servo-hydraulic materials testing machine under software control(INSTRON,8871,England).The static compression testing and fatigue testing were made subsequently.
The geometry of the MCP was accomplished in the software Unigraphics.Then the created geometry was imported into MSC software,to accomplish the finite element method analysis.The plastic model and the biomedical titanium alloy were used in the MCP system.The deformable body contacted at the plate-screw interface, and the rigid board was adopted on the depressor.This analysis begins with the discretization of the model.The mesh was made with four nodes tetrahedral elements, obtaining a mesh of 16,409 nodes and 72,198 elements.The nodes of the screws were made coincide with the plate where they are placed.The stress and the strain of the MCP were analysis through the load which the depressors exert to the vertebrae screws.
Results
All the segments in all loading directions of ROM,no differences were found among MCP fixed state,MCP fatigue state,CMP fixed state and CMP fatigue state.But when the above states compared with the intact and grafted state,significant differences were found(P＜0.01).In flexion and lateral bending of ROM,significant difference was found between the intact and the grafted state(P＜0.01).In the NZ of flexion/extension, no differences were found among MCP fixed state,MCP fatigue,state,CMP fixed state and CMP fatigue state.But when the above states compared with the intact and grafted state,significant differences were found(P＜0.01).In the lateral NZ,significant difference was found between the intact state and other states(P＜0.01),but no significant differences were found among other states.In the rotational NZ,no significant differences were found among all the states.The ultimate bending failure load of the MCP was 180 N.In the application of 63 N under bending loads,the MCP was still not broken when the fatigue test was carried out 10~6 times.The stress and the strain concentration were found in the hole of the MCP in the three-dimensional finite element analysis.
Discussion
In this study,the MCP system was designed and evaluated in a porcine cadaveric anterior cervical corpectomy model.The MCP has some attractive characteristics. Firstly,the material used in our design is a new kind of titanium-alloy (Ti-24Nb-4Zr-7.9Sn),which is non-toxic with lacking noxious metals such as aluminum.The new alloy has a lower modulus of elasticity and is more flexible compared with currently used Ti-6AL-4V alloy.Secondly,the MCP system has the option of constrained,semiconstrained and hybrid constructs.The suitable plate was selected for the specific conditions of the patients.Graft subsidence is common during healing after anterior cervical fusion surgery.The variable-angle screws of the semiconstrained MCP and the hybrid MCP can accommodate with the absorption and/or sinking of bone in a certain range.Semiconstrained plates,in theory,allow continued contact between the graft and the end plate after graft subsidence has occurred,thus improving the chance of obtaining a fusion by maintaining a compressive load on the graft.Thirdly,a set of trabecules holes were designed in the MCP uniformly.The multifunction of the MCP was manifested in several aspects:1) the fixed screw can be set any position of the horizontal hole.2) when the anterior cervical corpectomy fusion was performed,the fixed screw can be used to fix the implanted graft.3) when the anterior cervical discectomy fusion was performed,the fixed screws can be used to fix the vertebrae body.4) when the anterior cervical discectomy and corpectomy was performed simultaneously,the fixed screws can be used to fix the implanted graft and vertebrae body.Fourthly,screw backout is effectively prevented by the locked screws.
With grafting alone,the grafted state with anterior cervical corpectomy in C4-C6 without plating did substantially decrease ROM compared with the intact state in the flexion and lateral bending.When the MCP was implanted,the ROM was further decrease compared with the grafted state.The MCP can provide the same stability compared with the CMP,and it also provided enough stability after the fatigue test. Furthermore,the MCP can provide the same stability after the torsional fatigue test compared with the CMP.When there was no load on the plate,there were no differences on MCP and CMP in all the segments in all directions.Also,there was no difference on MCP before and after the fatigue test.
The ultimate bending failure load of the MCP was 180 N.In the application of 63 N under bending loads,the MCP was still not broken when the fatigue test was carried out 10~6 times.It was revealed that it could be satisfied the requirement of fusion when graft was implanted.The stress concentration of the MCP in the fatigue test was found in the outside edge of the hole of vertebral screws and the cross section of the fixed screws.It revealed that the original fracture zone was found in the upper surface of the MCP through the electron microscope scanning.
The stress and the strain of the MCP were located around the area which fixed screws were implanted,the outside of the vertebrae screws hole and window through the three-dimensional finite element analysis.The concentrated stress and strain region is actually the most possible broken area.The stress and strain concentration area of the MCP in the three-dimensional finite element analysis coincided with the actual area in which the MCP was broken in the fatigue test.
Conclusion
Three-dimensional stability of the cervical spine was provided by the MCP in the flexibility test.After the torsional fatigue test,the MCP can still provide enough stability.In the application of 63 N under bending loads,the MCP was still not broken when the fatigue test was carried out 10~6 times.It was revealed that it could be satisfied the requirement of fusion when graft was implanted.The stress and the strain concentration area of the MCP in the three-dimensional finite element analysis coincided with the actual area in which the MCP was broken in the fatigue test.
引文
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4 Paramore CG,Dickman CA,Sonntag VK.Radiographic and clinical follow-up review of Caspar plates in 49 patients.J Neurosurg,1996;84:957-961.
5 Ning X,Wen Y,Xiao-Jian Y,et al.Anterior cervical locking plate-related complications;prevention and treatment recommendations.Int Orthop,2008,32:649-655.
6 Yue WM,Brodner W,Highland TR.Long-term results after anterior cervical discectomy and fusion with allograft and plating:a 5- to 11-year radiologic and clinical follow-up study.Spine,2005,30:2138-2151.
7 Hao YL,Li S J,Sun SY,et al.Super-elastic Titanium Alloy with Unstable Plastic Deformation.Appl Phys Lett,2005;87:091906-8.
8 Hao YL,Li S J,Sun SY,et al.Elastic deformation behavior of Ti-24Nb-4Zr-7.9Sn for biomedical applications.Acta Biomater,2007;3:277-286.
9 崔显峰,朱悦,李春树,等.腰椎新型钛合金动态内固定系统的稳定性研究.中华骨科杂志,2008;7:592-595.
10 Zhu Q,Ouyang J,Lu W,et al.Traumatic instabilities of the cervical spine caused by high-speed axial compression in a human model.An in vitro biomechanical study.Spine 1999;24:440-444.
11 Wilke HJ,Wenger K,Claes L.Testing criteria for spinal implants:recommendations for the standardization of in vitro stability testing of spinal implants.J Eur Spine 1998,7:148-154.
12 Stanford RE,Loefler AH,Stanford PM,et al.Multiaxial pedicle screw designs:static and dynamic mechanical testing.Spine,2004;29:367-375.
13 Black J.Orthopaedic biomaterials in research and practice.Churchill-Livingstone,1988:72-73.
14 Bohler J,Ganderhak T.Anterior plate stabilization for fracture-dislocations of lower cervical spine.J Trauma,1980,20:203-205.
15 Apfelbaum RI,Dailey AT,Soleau S,et al.Clinical experience with a new load-sharing anterior cervical plate.International Congress Series,2002,1247:563-579.
16 Reidy D,Finkelstein J,Nagpurkar A,et al.Cervical spine loading characteristics in a cadaveric C5 corpectomy model using a static and dynamic plate.J Spinal Disord,2004,17:117-122.
17 Closkey RF,Parsons JR,Lee CK,et al.Mechanics of interbody spinal fusion.Analysis of critical bone graft area.Spine,1993;18:1011-1015.
18 Tye GW,Graham RS,Broaddus WC,et al.Graft subsidence after instrument-assisted anterior cervical fusion.J Neurosurg,2002;97:186-192.
19 Brodke DS,Gollogly S,Mohr RA,et al.Dynamic cervical plates:biomechanical evaluation of load sharing and stiffness.Spine,2001;26:1324-1329.
20 Truumees E,Demetropoulos CK,Yang KH,et al.Effects of a cervical compression plate on graft forces in an anterior cervical discectomy model.Spine,2003;28:1097-1102.
21 Schulte K,Clark CR,Goel VK.Kinematics of the cervical spine following discectomy and stabilization.Spine,1989;14:1116-1121.
22 Cunningham BW,Setter JC,Shono Y,et al.Static and cyclical biomechanical analysis of pedicle screw spinal constructs.Spine,1993;18:1677-1688.
23 Pienkowski D,Stephens GC,Doers TM,et al.Multicycle mechanical performance of titanium and stainless steel transpedicular spine implants.Spine,1998;23:782-788.
24 Ashman RB,Birch JG,Bone LB,et al.Mechanical testing of spinal instrumentation.Clin Orthop,1988;227:113-125.
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48 Wang JC,McDonough PW,Kanim LE,et al.Increased fusion rates with cervical plating for three-level anterior cervical discectomy and fusion.Spine,2001,26:643-647.
49 Yue WM,Brodner W,Highland TR.Long-term results after anterior cervical discectomy and fusion with allograft and plating:a 5-to 11-year radiologic and clinical follow-up study.Spine,2005,30:2138-21.
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2 Wang JC,McDonough PW,Endow KK,et al.Increased fusion rates with cervical plating for two-level anterior cervical discectomy and fusion.Spine,2000,25:41-45.
3 Wang JC,McDonough PW,Kanim LE,et al.Increased fusion rates with cervical plating for three-level anterior cervical discectomy and fusion.Spine,2001,26:643-647.
4 Paramore CG,Dickman CA,Sonntag VK.Radiographic and clinical follow-up review of Caspar plates in 49 patients.J Neurosurg,1996;84:957-961.
5 Ning X,Wen Y,Xiao-Jian Y,et al.Anterior cervical locking plate-related complications;prevention and treatment recommendations.Int Orthop,2008,32:649-655.
6 Yue WM,Brodner W,Highland TR.Long-term results after anterior cervical discectomy and fusion with allograft and plating:a 5- to 11-year radiologic and clinical follow-up study.Spine,2005,30:2138-2151.
7 Hao YL,Li S J,Sun SY,et al.Super-elastic Titanium Alloy with Unstable Plastic Deformation.Appl Phys Lett,2005;87:091906-8.
8 Hao YL,Li S J,Sun SY,et al.Elastic deformation behavior of Ti-24Nb-4Zr-7.9Sn for biomedical applications.Acta Biomater,2007;3:277-286.
9 崔显峰,朱悦,李春树,等.腰椎新型钛合金动态内固定系统的稳定性研究.中华骨科杂志,2008;7:592-595.
10 Zhu Q,Ouyang J,Lu W,et al.Traumatic instabilities of the cervical spine caused by high-speed axial compression in a human model.An in vitro biomechanical study.Spine 1999;24:440-444.
11 Wilke HJ,Wenger K,Claes L.Testing criteria for spinal implants:recommendations for the standardization of in vitro stability testing of spinal implants.J Eur Spine 1998,7:148-154.
12 Stanford RE,Loefler AH,Stanford PM,et al.Multiaxial pedicle screw designs:static and dynamic mechanical testing.Spine,2004;29:367-375.
13 Black J.Orthopaedic biomaterials in research and practice.Churchill-Livingstone,1988:72-73.
14 Bohler J,Ganderhak T.Anterior plate stabilization for fracture-dislocations of lower cervical spine.J Trauma,1980,20:203-205.
15 Apfelbaum RI,Dailey AT,Soleau S,et al.Clinical experience with a new load-sharing anterior cervical plate.International Congress Series,2002,1247:563-579.
16 Reidy D,Finkelstein J,Nagpurkar A,et al.Cervical spine loading characteristics in a cadaveric C5 corpectomy model using a static and dynamic plate.J Spinal Disord,2004,17:117-122.
17 Closkey RF,Parsons JR,Lee CK,et al.Mechanics of interbody spinal fusion.Analysis of critical bone graft area.Spine,1993;18:1011-1015.
18 Tye GW,Graham RS,Broaddus WC,et al.Graft subsidence after instrument-assisted anterior cervical fusion.J Neurosurg,2002;97:186-192.
19 Brodke DS,Gollogly S,Mohr RA,et al.Dynamic cervical plates:biomechanical evaluation of load sharing and stiffness.Spine,2001;26:1324-1329.
20 Truumees E,Demetropoulos CK,Yang KH,et al.Effects of a cervical compression plate on graft forces in an anterior cervical discectomy model.Spine,2003;28:1097-1102.
21 Schulte K,Clark CR,Goel VK.Kinematics of the cervical spine following discectomy and stabilization.Spine,1989;14:1116-1121.
22 Cunningham BW,Setter JC,Shono Y,et al.Static and cyclical biomechanical analysis of pedicle screw spinal constructs.Spine,1993;18:1677-1688.
23 Pienkowski D,Stephens GC,Doers TM,et al.Multicycle mechanical performance of titanium and stainless steel transpedicular spine implants.Spine,1998;23:782-788.
24 Ashman RB,Birch JG,Bone LB,et al.Mechanical testing of spinal instrumentation.Clin Orthop,1988;227:113-125.
1 Aebi M,Zuber K,Marchesi D.Treatment of cervical spine injuries with anterior plating.Indications,techniques,and results.Spine,1991,16:38-45.
2 Adams MS,Crawford NR,Chamberlain RH,et al.Biomechanical comparison of anterior cervical plating and combined anterior/lateral mass plating.Spine,2001,1:166-170.
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