经寰枢关节间隙螺钉和寰椎椎板钩内固定的力学稳定性

目的评价双侧经寰枢关节间隙螺钉和寰椎椎板钩内固定的力学稳定性。方法将6具新鲜尸体颈椎标本（包括枕骨基底部和C1-C4颈椎节段）置于1．5Nm载荷下，测量C1，2节段的三维运动范围（range of motion，ROM）。标本依Gallie内固定、双侧经寰枢关节间隙螺钉和Gallie内固定、双侧经寰枢关节间隙螺钉内固定、双侧经寰枢关节间隙螺钉和寰椎椎板钩内固定、双侧寰椎侧块螺钉和枢椎椎弓根螺钉内固定的顺序实施固定，每次固定后测量三维运动范围。结果包含经寰枢关节间隙螺钉的内固定组在旋转和侧屈方向上具有最小的ROM，其中双侧经寰枢关节间隙螺钉和寰椎椎板钩内固定组在屈伸运动方向上也具有最小的ROM。寰椎侧块螺钉和枢椎椎弓根螺钉内固定组在旋转方向上ROM大于单纯经寰枢关节间隙螺钉内固定组，但在侧屈和屈伸方向上接近经寰枢关节间隙螺钉，差异无统计学意义；其在侧屈和旋转方向上ROM均小于Gallie内固定组，差异有统计学意义。结论双侧经寰枢关节间隙螺钉和寰椎椎板钩“三点”内固定具有最强的生物力学稳定性。虽然双侧寰椎侧块螺钉和枢椎椎弓根螺钉内固定在生物力学稳定性上不及“三点”内固定，但明显优于Gallie内固定。     

枢椎棘突螺钉单侧应用联合对侧椎弓根螺钉固定的有限元分析

目的分析枢椎棘突螺钉单侧应用联合对侧椎弓根螺钉固定在寰枢和枕颈固定中的生物力学稳定性。方法构建正常枢椎解剖、椎板薄和椎动脉变异椎弓根细小3种不同解剖状态下的完整上部颈椎有限元模型作为完整模型组,然后分别模拟齿状突骨折进行寰枢固定和寰椎骨折进行枕颈固定。在寰枢固定中,比较单侧枢椎棘突螺钉+对侧椎弓根螺钉+双侧寰椎侧块螺钉固定组(棘突螺钉组)和枢椎双侧椎弓根螺钉+双侧寰椎侧块螺钉固定组(椎弓根螺钉组);在枕颈固定中,比较单侧枢椎棘突螺钉+对侧椎弓根螺钉+枕骨螺钉固定组(棘突螺钉组)和枢椎双侧椎弓根螺钉+枕骨螺钉固定组(椎弓根螺钉组)。枢椎棘突螺钉分别测试水平、斜向、垂直置钉3种不同的固定技术。模拟颈椎运动,测量枕颈的屈伸、侧屈、旋转的关节活动范围(ROM)。结果在寰枢和枕颈固定中,棘突螺钉组和椎弓根螺钉组的C1~C2屈伸、侧屈、旋转ROM均较完整模型组均明显下降。在寰枢固定中棘突螺钉组C0~C2屈伸、侧屈、旋转的ROM大于椎弓根螺钉组;在枕颈固定中,棘突螺钉组C1~C2侧屈的ROM大于椎弓根螺钉组,棘突螺钉组的C0~C2旋转的ROM大于椎弓根螺钉组。枢椎棘突螺钉分别测试水平、斜向、垂直固定间有差异,但不明显。结论在寰枢和枕颈固定中,枢椎双侧椎弓根螺钉固定和枢椎单侧棘突螺钉联合对侧椎弓根螺钉组合式固定方法均具有良好的稳定性。在寰枢固定中,相对于枢椎棘突螺钉组合式固定,枢椎双侧椎弓根螺钉固定具有更好的寰枢稳定性。在枕颈固定中,枢椎双侧椎弓根螺钉固定在侧屈和旋转活动上较枢椎棘突螺钉组合式固定稳定性更好。枢椎三种棘突螺钉置钉技术间的稳定性差异并不明显。     

寰椎一体式椎板钩与枢椎椎板钉组合应用于非对称内固定生物力学研究

目的本文报道设计一新型寰枢椎内固定组合,并在尸体标本进行生物力学试验,有一定的临床指导意义。方法将6具新鲜尸体颈椎标本置于2Nm载荷下,运用脊柱三维运动测量系统测量C1-2节段的三维运动范围(Range Of Motion,ROM),并将之进行两两对比。实验依完整组、失稳组、双侧寰椎侧块螺钉联合枢椎椎弓根螺钉内固定(Harms技术)组、寰椎侧块螺钉联合单侧枢椎椎板螺钉+对侧枢椎椎弓根螺钉固定组、一侧寰椎一体式椎板钩+枢椎椎板钉联合对侧寰椎侧块螺钉+枢椎椎弓根螺钉内固定组的顺序进行。结果失稳组ROM较完整组显著增加,内固定后ROM显著减小,三种内固定组中:寰椎侧块螺钉联合单侧枢椎椎板螺钉+对侧枢椎椎弓根螺钉固定组在旋转和侧屈方向上具有最小的ROM,双侧寰椎侧块螺钉联合枢椎椎弓根螺钉内固定组在屈伸运动方向上有最小的R0M。一侧寰椎一体式椎板钩+枢椎椎板钉联合对侧寰椎侧块螺钉+枢椎椎弓根螺钉内固定组ROM在旋转、侧屈以及屈伸方向上均较另外两组大,但差异均无统计学意义。结论寰椎一体式椎板钩与枢椎椎板钉组合非对称内固定可提供良好的生物力学稳定性。     

两种不同C2椎弓根螺钉加“Ω”形横连治疗Ⅱ型Hangman骨折的生物力学研究

目的:探讨普通C2椎弓根螺钉和双螺纹中空万向螺钉(新型)加"Ω"形横连固定Ⅱ型Hangman骨折的生物力学特点。方法:选择1名健康成年男性志愿者对其颈椎C0-3椎节进行CT扫描,获得CT图像原始数据。利用Mimics 10.01等软件建立正常颈椎C0-3椎节三维有限元模型(包含椎间盘、韧带等组织),并进行有效性验证。在已验证的有限元模型的基础上,分别建立以下模型:Hangman骨折模型(Levine-EdwardsⅡ型);Hangman骨折+普通C2椎弓根螺钉+"Ω"横连模型;Hangman骨折+新型C2椎弓根螺钉+"Ω"横连模型;比较各模型在不同工况(屈伸、侧屈、旋转)下的三维活动范围(ROM)及置入螺钉所受应力情况,运用秩和检验方法进行统计学分析。结果:生理载荷下Hangman骨折模型在屈伸、侧屈、扭转方向上的ROM较正常颈椎模型明显增大,集中表现在C2-3椎节,各工况下分别增加3.89°、5.65°、2.10°;内固定模型不同椎节ROM较骨折模型显著减小,其中两内固定模型之间的ROM差别无统计学意义(P0.05)。不同工况下,内固定模型中螺钉均在后伸时所受应力最大,分别为403.3MPa、370.4MPa,应力主要集中在螺钉通过骨折线的部分,而新型C2椎弓根螺钉在各工况下最大应力均小于普通C2椎弓根螺钉(P0.05)。结论:两种不同C2椎弓根螺钉(普通和新型)加"Ω"横连固定装置在最大限度保留颈椎生理性活动的同时,均能有效恢复Ⅱ型Hangman骨折颈椎稳定性;"Ω"横连下新型C2椎弓根螺钉较普通C2椎弓根螺钉具有更好的抗疲劳性能。     

寰椎椎板钩联合枢椎椎弓根螺钉内固定的力学稳定性评价

目的 评价寰椎椎板钩联合枢椎椎弓根螺钉内固定的生物力学稳定性.方法 取6具新鲜尸体颈椎标本置于1.5 N·m载荷下,测量C_(1-2)节段的三维运动范围(ROM).标本按随机顺序,依次行完整状态(完整状态组)、不稳状态(齿状突周围韧带切除,为不稳状态组)、经寰枢关节间隙螺钉联合Gallic内固定(固定A组)、寰椎椎板钩联合枢椎椎弓根螺钉内固定(固定B组)、寰枢椎椎弓根螺钉内固定(固定C组)5种状态下的三维ROM值测量.比较各组标本的屈伸、侧屈、旋转ROM值.结果 完整状态组、不稳状态组、固定A、B、C组的平均屈伸ROM值分别为17.78°、30.69°、2.25°、2.93°、2.73°,组间比较差异有统计学意义(F=216.69,P=0.000);平均侧屈ROM值分别为9.56°、17.18°、1.91°、2.30°、2.05°,组间比较差异有统计学意义(F=122.75,P=0.000);平均旋转ROM值分别为44.19°、57.30°、1.22°、2.88°、2.07°,组间比较差异有统计学意义(F=154.54,P=0.000).固定A、B、C组较完整状态组和不稳状态组各个方向的ROM值均明显减少,差异均有统计学意义(P<0.05),但固定A、B、C组之间符个方向的ROM值比较差异均无统计学意义(P>0.05).结论 寰椎椎板钩联合枢椎椎弓根螺钉内固定可提供与经寰枢关节间隙螺钉联合Gallic内固定和寰枢椎椎弓根螺钉内固定相当的力学稳定性.在以上两种方法无法实施时,可作为一种安全的替代.     

C2/3经关节螺钉固定的临床应用解剖研究

目的研究C2/3侧块关节螺钉固定的解剖可行性,为颈椎后路钉板固定在枢椎提供新的螺钉锚点.方法利用20例配套颈椎干骨标本,测量枢椎和第三颈椎侧块的宽度和高度.设定C2/3侧块关节螺钉的进钉点和进钉方向,即进钉点在头尾方向上位于枢椎侧块的中下1/3交界处,在内外方向上位于枢椎侧块的中央,螺钉穿枢椎侧块经由C2/3侧块关节进入C3侧块;进钉方向与人体矢状面平行,并与C2/3侧块关节面呈90°角,测量螺钉分别在枢椎和第三颈椎侧块内的长度.结果枢椎侧块的平均宽度和高度分别是14.83mm和9.63mm;第三颈椎侧块的平均宽度和高度分别是13.86mm和11.27mm.螺钉在枢椎和第三颈椎侧块内的平均长度分别是6.24mm和9.70mm,螺钉总长平均15.94mm.结论经C2/3侧块关节进行螺钉固定在解剖学上是可行的,可以作为枢椎后路螺钉固定的补充方法.     

寰椎侧块后路螺钉固定的可行性研究

目的 :通过应用解剖学及生物力学测试了解寰椎侧块后路螺钉固定的可行性。方法 :对 3 0例中国成年人的寰椎干骨标本具有临床意义的数据进行解剖学测量 ;对 6例新鲜颈椎尸体标本的后入路C2 神经根与寰椎侧块的关系进行观察 ;同时 ,通过测试寰椎侧块螺钉的拔出力 ,并与枕骨螺钉及枢椎椎弓根螺钉的拔出力进行比较。选 6例新鲜上颈椎标本 ,将标本造成侧块骨折模型后予以后路侧块螺钉固定 ,标本分为 :A组 -正常对照组 ,B组 -侧块及同侧前弓骨折组 ,C组 -侧块后路螺钉固定后组。测量 3组的三维运动范围 (Rangeofmotion ,ROM ) ,并比较其相互间的差异。结果 :寰椎中线至侧块中点、椎动脉内侧壁、椎弓根内缘的距离分别为 :(17.6± 1.2 )mm、(2 3 .0± 1.7)mm及 (14 .2± 1.1)mm ;侧块中部的宽度为 (11.6± 1.4)mm ,侧块中心点的厚度为 (12 .7± 1.0 )mm ;后弓与侧块移行处中点至下关节面间距为 (4 .1± 0 .7)mm ;椎动脉沟处后弓厚度为 (4 .7± 1.0 )mm。解剖学观察见C2 神经根出脊髓后沿C1/ 2 关节间隙的下方向外下行走 ,且C2 神经根有较大的移动度。寰椎侧块螺钉的拔出力平均为 (1718.2± 42 2 .7)N ,明显小于枕骨螺钉的拔出力 ,但与枢椎椎弓根螺钉的拔出力无明显差异。侧块骨折后C0～ 1及C1～ 2 间的ROM在各个     

寰椎椎弓根螺钉联合经寰枢关节螺钉内固定稳定性的生物力学研究

【摘要】 目的：评估寰椎椎弓根螺钉联合经寰枢关节螺钉固定技术的力学稳定性。方法：选取成人颈椎新鲜标本6具,解剖剔除肌肉制备上颈椎完整模型（完整组）,用生物力学测试及计算机视觉分析软件测量在1.5Nm力矩下前屈后伸、左右侧弯和左右旋转时C1-C2的活动度（ROM）;破坏寰椎前弓和侧块制备不稳模型（失稳组）,再次测量相同力矩下各运动方向C1-C2的ROM活动度。随后暴露寰枢椎置钉点,根据先后顺序置入寰椎椎弓根螺钉+枢椎椎弓根螺钉固定（C1P+C2P组）、单纯经寰枢关节螺钉固定（TA组）、寰椎椎弓根螺钉+经寰枢关节螺钉固定（C1P+TA组）,依次分别测量相同力矩下各运动方向C1-C2的ROM,比较各组C1-C2 ROM的差异。结果：失稳组相较于完整组在六个方向上有更大的ROM,两组所有方向上的ROM均有显著性差异（P<0.05）;C1P+C2P组、C1P+TA组、TA组与失稳组比较,所有方向上的ROM均有显著性减少（P<0.05）,三组间比较,前屈、后伸、左旋转和右旋转方向上的ROM存在统计学差异（P<0.05）,C1P+TA组相似文献   

下腰椎不同固定方式的生物力学对比研究

目的 观察下腰椎不同固定方式对腰椎稳定性的影响.方法 新鲜成人尸体下腰椎标本6具,测定L4/5节段屈伸、左右侧屈、左右旋转6个方向ROM和刚度值的变化,按5组顺序依次测试:A组(正常下腰椎标本组);B组(单侧椎板关节突螺钉固定+椎间单枚Cage);C组(单侧椎弓根螺钉固定+椎间单枚Cage);D组(单侧椎弓根螺钉联合对侧椎板关节突螺钉固定+椎间单枚Cage);E组(双侧椎弓根螺钉固定+椎间单枚Cage).结果 与A组比较,B组各运动状态ROM有减少,而刚度明显增加,差异有统计学意义(P＜0.05);与B组比较,C组各运动方向ROM与刚度,差异无统计学意义(P＞0.05);与C组比较,D组各运动状态ROM有减少,而刚度增加,差异有统计学意义(P＜0.05);与E组比较,D组各运动方向ROM与刚度,差异无统计学意义(P＞0.05);与E组比较,C组各运动状态ROM有增加,而刚度减少,差异有统计学意义(P＜0.05).结论 单侧椎板关节突螺钉固定并椎间融合器植骨方法提供了一定的稳定性,而单侧椎弓根螺钉联合对侧椎板关节突螺钉固定并椎间融合器植骨具有与双侧椎弓根螺钉固定相同的稳定性,临床上可根据病例的具体情况,如身高体质量指数、病变类型及病变节段稳定程度选择性地应用上述两种固定融合方法.     

枢椎经椎板螺钉固定的研究进展

椎(C2)螺钉无论是对于寰枢融合还是在下颈椎固定中均提供着重要的稳定性.目前临床常用的C2固定技术包括2椎弓根螺钉、侧块螺钉、经1/2关节螺钉和经2/3关节螺钉,以上技术均有着损伤椎动脉的风险.2004年Wright[1]首次提出2经椎板螺钉固定技术,并进行了10例临床应用,取得了良好的临床疗效.尽管2经椎板螺钉固定有其优点,但至今仍没有得到广泛的应用.     

枕颈部后路不同内固定的生物力学比较

目的评价不同内固定重建枕颈部稳定性的生物力学性能。方法12具新鲜人体枕颈部标本,在标本完整、枕寰枢不稳、枕颈部植骨块钛缆固定(A组)、枕颈部经关节螺钉内固定(B组)、SUM-MIT枕颈部内固定系统固定(C组)五种状态下,依次用脊柱三维运动测量系统测试其OcC1、C1,2节段的运动参数。同时对固定后的OcC1经关节螺钉(OcC1TA组)、C1,2经关节螺钉(C1,2TA组)、枢椎椎弓螺钉(C2IS组)和枕骨螺钉(Oc Screw组)在生理载荷下三维六自由度运动时,运用电测法测定四种螺钉的拔出应力,并行统计学分析。结果在OcC1节段,B组在屈伸运动中的运动范围和中性区显著大于C组。在侧屈和旋转运动中,A组的运动范围和中性区均明显大于B、C组。在C1,2节段,B组各方向运动的运动范围和中性区均明显小于A组。B组在旋转运动中的运动范围和中性区均显著小于C组。电测法结果显示,侧屈状态下所有螺钉局部应变均接近0;前屈和旋转时螺钉承受不同程度的拉应力,后伸时螺钉承受压应力。Oc Screw组在屈伸和旋转运动状态下,所承受的任何载荷应力均大于其他三种置钉方法。结论枕颈部后路经关节螺钉内固定和SUMMIT枕颈内固定在控制旋转和侧屈的稳定性上有优点。枕骨螺钉承受的拉应力最大,生理环境下枕骨螺钉可能更易发生松动和断裂。     

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。     

前路经寰枢关节螺钉内固定术治疗寰枢关节不稳定的解剖学及临床研究

目的 为前路经寰枢关节螺钉内固定术提供临床解剖学依据.方法 在100对中国成人干燥寰、枢椎配对标本上,对与临床前路经寰枢关节螺钉内固定术相关的数据进行解剖学测量.并对11例创伤性寰枢椎不稳定患者施行了前路经寰枢关节螺钉内固定术,在齿状突与寰椎前结节后方置入颗粒状松质骨.结果 前路经寰枢关节螺钉内固定术冠状面上螺钉植入最小外偏角(5.5±2.0)度,最大外偏角(23.6±2.1)度,矢状面上螺钉植入最小后倾角(14.9±2.6)度,最大后倾角(25.6 ±2.5)度,内侧钉道距离(16.58±1.49)mm,外侧钉道距离(26.44±1.75)mln.11例患者中,1例颈脊髓完全损伤患者,术后1个月死于肺部感染.其余10例病例获得随访,时间7个月～3年,平均17个月,无椎动脉及脊髓损伤,所有病例获得骨性融合.结论 前路经寰枢关节螺钉内固定术,操作简便,损伤脊髓或椎动脉的风险较小,为寰枢椎不稳定患者提供了一种新的内固定治疗方法.     

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.     

Atlantoaxial fusion using anterior transarticular screw fixation of C1–C2: technical innovation and biomechanical study

This study is an attempt to describe a new technique for anterior transarticular screw fixation of the atlantoaxial joints, and to compare the stability of this construct to posterior transarticular screw fixation with and without laminar cerclage wiring. Nine human cadaveric specimens were included in this study. The C1–C2 motion segment was instrumented using either anterior transarticular screws (group 1), posterior transarticular screws alone (group 2), or posterior screws with interlaminar cerclage wires (group 3). Using an unconstrained mechanical testing machine, the specimens were tested in rotation, lateral bending, and flexion-extension using nondestructive loads of ±2 N m. The specimens were also tested in translation using nondestructive loads of ±100 N. All values for the three groups with regards to anterior-posterior displacement, rotation, and lateral bending were similar as determined using a Kruskal–Wallis rank sum test with a significance level of p<0.05. The only significant difference was registered in flexion-extension where the cerclage wire added some strength to the construct. Anterior transarticular screw fixation of the atlantoaxial spine has several advantages over posterior fixation techniques, and is as stable as posterior transarticular fixation in all clinically significant planes of motion. The addition of posterior interlaminar cerclage wiring further improves resistance to flexion-extension forces. Anterior transarticular screw fixation of the atlantoaxial joint is a useful technique for achieving C1–C2 stabilization.     

Biomechanical evaluation of five different occipito-atlanto-axial fixation techniques

STUDY DESIGN: The stabilizing effects of five different occipitocervical fixations were compared. OBJECTIVES: To evaluate the construct stability provided by five different occipito-atlanto-axial fixation techniques. SUMMARY OF BACKGROUND DATA: Few studies have addressed occipitocervical reconstruction stability and no studies to data have investigated anterior-posterior translational stiffness. METHODS: A total of 21 human cadaveric spines were used. After testing intact spines (CO-C2), a type II dens fracture was created and five different reconstructions were performed: 1) occipital and sublaminar wiring/rectangular rod, 2) occipital screws and C2 lamina claw hooks/rod, 3) occipital screws, foramen magnum screws, and C1-C2 transarticular screws/rod, 4) occipital screws and C1-C2 transarticular screws/Y-plate, and 5) occipital screws and C2 pedicle screws/rod. Biomechanical testing parameters included axial rotation, flexion/extension, lateral bending, and anterior-posterior translation. RESULTS: Pedicle screw fixation demonstrated the highest stiffness among the five reconstructions (P < 0.05). The two types of transarticular screw methods provided greater stability than hook or wiring reconstructions (P < 0.05). The C2 claw hook technique resulted in greater stability than sublaminar wiring fixation in anterior-posterior translation (P < 0.05). However, the wiring procedure did not significantly increase the stiffness levels beyond the intact condition under anterior-posterior translation and lateral bending (P > 0.05). DISCUSSION: C2 transpedicular and C1-C2 transarticular screws significantly increased the stabilizing effect compared to sublaminar wiring and lamina hooks. The improved stability afforded by C2 pedicular and C1-C2 transarticular screws offer many potential advantages including a high rate of bony union, early ambulation, and easy nursing care. CONCLUSION: Occipitocervical reconstruction techniques using C1-C2 transarticular screws or C2 pedicle screws offer biomechanical advantages compared to sublaminar wiring or lamina hooks. Pedicle screw fixation exhibited the highest construct stiffness among the five reconstructions.     

Augmentation of occipitocervical contoured rod fixation with C1-C2 transarticular screws.

BACKGROUND CONTEXT: The technique of occipitocervical fusion using a threaded contoured rod attached with sublaminar wires to the occiput and upper cervical vertebrae is widely used throughout the world and has been clinically proven to provide effective fixation of the destabilized spine. However, this system has some disadvantages in maintaining stability, especially at C1-C2 because of the large amount of axial rotation at this level. In some clinical situations such as fracture of the C1 lamina, C1 laminectomy, and excessively lordotic curvature, it is not always possible to wire C1 directly into the construct. In such cases, combination of other stabilization methods that include C1 indirectly can be used to achieve a reliable posterior internal fixation. PURPOSE: Primarily, to evaluate whether a contoured rod construct in which C1 is indirectly included using C1-C2 transarticular screws is biomechanically equivalent to a standard, fully wired contoured rod construct. Secondarily, to evaluate the biomechanical benefit of adding C1-C2 transarticular screws to a fully wired contoured rod construct. STUDY DESIGN: Repeated-measures nondestructive in vitro biomechanical testing of destabilized cadaveric human occipitocervical spine specimens. METHODS: Six human cadaveric specimens from the occiput to C3 were studied. Angular and linear displacement data were recorded while nonconstraining nondestructive loads were applied. Three methods of fixation were tested: contoured rod incorporating C1 with and without transarticular screws and contoured rod with transarticular screws without incorporating C1. RESULTS: All three constructs reduced motion to well within normal range. In contoured rod constructs with C1 wired, addition of transarticular screws slightly but significantly improved stability. In constructs with transarticular screws, incorporation of C1 into the contoured rod wiring did not improve stability significantly. CONCLUSIONS: Adding C1-C2 transarticular screws to a wired contoured rod construct where C1 is included only slightly improves stability. As the absolute reduction in motion from adding transarticular screws is small (<1 degree), it is doubtful whether any enhanced fusion from this additional procedure outweighs the surgical risks. However, transarticular screws provide an effective alternate method to fixate C1 when the posterior arch of C1 is absent or has been fractured.     

Posterior C2 fixation using bilateral, crossing C2 laminar screws: case series and technical note

Rigid screw fixation of the axis, for either atlantoaxial fixation or for incorporation of C2 into subaxial cervical constructs, provides significant stability and excellent long-term fusion results but remains technically demanding due to the danger of injury to the vertebral artery. Anatomic variability of the foramen transversarium in the body of the axis can preclude safe transarticular C1-C2 screw placement in up to 20% of patients. Although more recent methods of C2 screw fixation with pedicle screws allow safer fixation in a higher number of patients, there remains a significant risk to the vertebral artery with C2 pedicle screw placement. The author describes a novel technique of C2 rigid screw fixation using bilateral, crossing C2 laminar screws, not previously reported in the literature, which does not place the vertebral artery at risk during C2 fixation. This technique has been successfully used by the author in cases of craniocervical and atlantoaxial fixation as well as for incorporation of C2 into subaxial fixations. The technique is illustrated, and the author's initial experience in treating 10 patients with crossing, bilateral C2 aminar screws for indications of trauma, neoplasm, pseudarthrosis, and degenerative disease is reviewed. The possible advantages of C2 fixation with C2 laminar screws are discussed.