胸椎椎弓根根外固定螺钉拔出力的实验研究

目的:比较两种胸椎椎弓根根外固定方法与经椎弓根固定方法的螺钉拔出强度,评价胸椎椎弓根根外固定的生物力学效果。方法:新鲜胸椎标本4具,共32个肋骨-椎骨序列,根据螺钉固定方法不同分为3组,A组采用经椎弓根固定,B组采用经横突-椎体固定,C组采用经改良肋横突法固定。根据所用螺钉规格不同将其分为4种不同测试条件:D1,螺钉直径5.5mm,长度40mm;D2,螺钉直径5.5mm,长度45mm;D3,螺钉直径6.5mm,长度45mm;D4,螺钉直径6.5mm,长度50mm。测试3种固定方法下的螺钉拔出力,并做统计学分析对比。结果:D1条件下A组拔出力为787.0±119.3N,B组为706.2±109.4N,C组为616.1±82.3N,3组间比较有显著性差异(P<0.01);D2条件下A组拔出力为862.3±128.7N,B组为811.4±113.6N,C组为655.1±92.2N,A、B组间比较无显著性差异(P>0.05),A、B组与C组比较有显著性差异(P<0.01);D3条件下,A组拔出力为855.3±117.1N,B组为938.0±131.5N,C组为861.3±117.8N,A、C组间比较无显著性差异(P>0.05),A、C组与B组比较有显著性差异(P<0.01);D4条件下A组拔出力为864.3±120.9N,B组为959.6±135.2N,C组为941.2±115.4N,A组与B、C组比较均有显著性差异(P<0.01),B、C组间比较无显著性差异(P>0.05)。结论:使用直径6.5mm、长度45～50mm的螺钉固定时,胸椎椎弓根根外固定螺钉拔出力优于椎弓根固定,有较好的生物力学效果。     

单侧椎弓根外入路与椎弓根入路PVP治疗胸腰段骨质疏松性椎体压缩骨折

目的比较单侧椎弓根外入路与椎弓根入路经皮椎体成形术(PVP)治疗胸腰段骨质疏松性椎体压缩骨折的临床疗效。方法回顾性分析自2018-10—2019-02诊治的60例胸腰段骨质疏松性椎体压缩骨折,30例采用椎弓根外入路PVP手术治疗(观察组),30例采用经椎弓根入路PVP手术治疗(对照组),比较2组手术时间、术中透视次数、正位穿刺到达中线情况以及术后2d疼痛VAS评分。结果60例均顺利完成手术并获得完整随访,随访时间平均6.5(3~12)个月。观察组手术时间较对照组短,术中透视次数较对照组少,差异有统计学意义(P<0.05)。2组正位穿刺到达中线情况比较差异无统计学意义(P>0.05)。观察组出现2例骨水泥分布不均,1例上位椎间盘骨水泥少量渗漏;对照组出现1例椎体后缘骨水泥少量渗漏,均无特殊不适。2组术后2d疼痛VAS评分比较差异无统计学意义(P>0.05)。结论胸腰段PVP单侧经椎弓根外入路是安全的、有效的,与经椎弓根入路相比,可减少手术时间与透视次数,并且术中穿刺较易到达中线,是值得推广的一种穿刺途径。     

经椎弓根螺钉内固定翻修术的生物力学研究

目的探讨不同直径与长度螺钉翻修及骨水泥强化后椎弓根固定的强度,评价其生物力学效果.方法采用10具新鲜成人尸体T10～L5节段共80个椎体标本.首先置入5.5mm/45mm椎弓根螺钉作为对照组.再将脊椎标本随机平分为Ⅰ、Ⅱ两大组.Ⅰ组中40个椎体各随机选择一侧椎弓根应用6.25mm/45mm螺钉翻修(Ⅰ a组),另一侧椎弓根应用7.0mm/45mm螺钉翻修(Ⅰ b组);Ⅱ组中40个椎体各随机选择一侧椎弓根应用6.25mm/55mm螺钉翻修(Ⅱa组),另一侧椎弓根应用7.0mm/55mm螺钉翻修(Ⅱb组).再随机选择56个椎弓根分别行细小螺钉及粗大螺钉骨水泥强化固定翻修(Ⅲa组、Ⅲb组).在858Mini-MTS生物力学实验机上测试最大拔出力及最大扭力矩,并进行统计分析.结果①6.25mm/45mm螺钉翻修5.5mm/45mm螺钉置入后的椎弓根,其拔出力及扭力矩无明显增加(P＞0.05);应用7.0mm/45mm、6.25mm/55mm及7.0mm/55mm螺钉翻修,把持力及扭力矩均明显增加(P＜0.05).②骨水泥强化固定后,螺钉把持力远大于单纯螺钉翻修组,且与螺钉粗细无关.③在对照组及螺钉翻修组,螺钉把持力与扭力矩间有明显相关性,相关系数r=.86.结论①椎弓根螺钉翻修时,单纯螺钉直径增加1.5mm或直径增加0.75mm、长度增加l0mm以及骨水泥强化均可达到翻修固定的生物力学要求,以骨水泥强化固定更为明显.②增加螺钉直径与长度的翻修中,把持力与扭力矩是一致的;而应用骨水泥强化固定时,螺钉把持力主要取决于骨水泥本身及添加物-骨界面结合强度.     

经椎旁肌间隙入路取出腰椎椎弓根螺钉内固定系统

目的:探讨经椎旁肌间隙入路取出腰椎椎弓根螺钉内固定系统的可行性及临床意义。方法:2003年1月～2011年5月,65例患者在我院行腰椎椎弓根螺钉内固定系统取出,其中行传统后正中入路取出患者30例,行椎旁肌间隙入路取出患者35例。分别统计两组手术时间、手术出血量、术后并发症发生率等,并行组间比较。结果:经椎旁肌间隙入路组平均手术时间45±10min,手术出血量64±25ml,术后出现皮下血肿3例,无脑脊液漏和神经、硬膜损伤,术后并发症发生率为11.4%。传统入路组平均手术时间73±25min,手术出血量220±100ml;术后发生皮下血肿1例,切口愈合不良2例,脑脊液漏1例,术后并发症发生率13.3%。两组手术时间、手术出血量比较具有显著性差异(P<0.05),经椎旁肌间隙入路组优于传统入路组;术后并发症发生率两组无显著性差异(P>0.05)。结论:经椎旁肌间隙入路取出腰椎椎弓根螺钉内固定系统具有时间短、出血少等优点,是一种安全、损伤较小的术式。     

胸椎椎弓根螺钉置入位置的CT评价

目的:探讨胸椎椎弓根螺钉置入的准确性和安全性。方法:对37例胸椎椎弓根螺钉内固定患者术后行CT断层扫描,观察螺钉在椎弓根内的位置,记录螺钉穿透骨壁的位置、数目和距离。结果:37例患者共置入405枚胸椎椎弓根螺钉,124枚螺钉(30.61%)穿透骨壁,其中76枚(18.77%)穿透椎弓根外侧壁,32枚(7.90%)穿透椎弓根内侧壁,16枚(3.95%)穿透椎体前壁。66枚(16.30%)穿透距离<2mm,37枚(9.14%)穿透距离在2mm~4mm之间,21枚(5.9%)穿透距离>4mm。结论:胸椎椎弓根螺钉骨壁穿透率较高,应严格按照胸椎椎弓根螺钉置入方法,仔细操作,避免出现因螺钉置入不当造成神经、血管或内脏损伤等并发症。     

经皮与Wiltse入路椎弓根螺钉内固定治疗胸腰椎骨折比较

[目的]比较经皮与Wiltse入路椎弓根螺钉内固定治疗单节段无神经损伤的胸腰椎骨折的临床效果。[方法]回顾性分析本院2015年4月～2017年10月收治的38例单节段无神经损伤的胸腰椎骨折患者。根据椎弓根螺钉置入方式分为经皮组(20例),Wiltse入路组(18例)。比较两组临床资料。[结果]所有患者均顺利完成手术,术中均无血管、神经及脊髓损伤。经皮组患者手术切口长度、术中出血量及住院时间均显著低于Wiltse入路组,差异有统计学意义(P<0.05),但手术时间及术中X线透视次数高于Wiltse入路组,差异有统计学意义(P<0.05)。经皮组切口均一期愈合,Wiltse入路组术后发生1例切口血肿,经换药等处理后延迟愈合。38例患者随访12～15个月。术后1周时两组患者的VAS评分和ODI评分均较术前显著改善,差异均有统计学意义(P<0.05),且经皮组VAS评分及ODI评分显著低于Wiltse入路组,差异均有统计学意义(P<0.05);术后3个月及12个月时,两组患者的VAS评分和ODI评分进一步改善,差异有统计学意义(P<0.05),但两组间比较差异无统计学意义(P>0.05)。影像评估方面,经皮组与Wiltse入路组患者术后伤椎椎体前缘高度及后凸畸形角度较术前均显著改善(P<0.05),但相应时间点,两组间比较差异无统计学意义(P>0.05)。[结论]经皮与Wiltse入路椎弓根钉内固定治疗单节段无神经损伤的胸腰椎骨折均可以获得满意的伤椎椎体前缘高度及后凸畸形角度恢复。虽然经皮椎弓根钉内固定增加了手术时间及术中透视次数,但可以显著减少手术创伤,减轻术后早期疼痛,缩短住院时间。     

胸椎椎弓根螺钉固定矫治青少年脊柱侧凸

目的 :探讨青少年胸椎椎弓根螺钉的固定方法及注意事项。方法 :测量 2 0例正常青少年胸椎椎弓根影像学参数 ,并在此基础上采用自行设计的胸椎椎弓根螺钉固定器械 (Scofix器械 ) ,对 32例青少年脊柱侧凸进行了矫正治疗。结果 :正常青少年T4椎弓根横径最小 ( 3 9± 0 6 6mm) ,胸椎椎弓根中点均位于横突根部上缘与中点之间 ,椎弓根与矢状面夹角在T11、T12为负角 ,T10以上为正角 ,T1最大 ( 35 8°± 0 84°)。 2 7例患者术后平均随访 11个月 ,特发性和先天性侧凸的矫正率分别为 5 7 8%和 46 4% ,无严重并发症。结论 :根据测量结果 ,如选择好进钉点、方向及深度 ,Scofix器械对青少年脊柱侧凸的矫正可获得更好的稳定性和固定强度     

椎弓根螺钉固定的生物力学研究进展

椎弓根螺钉固定性的生物力学研究对提高其固定技术、增强固定的稳定性、减少并发症和改进固定器械起着重要的促进作用。椎弓根的结构特点是椎弓根螺钉固定的解剖基础。螺钉的大小、形状、疲劳特性和椎体的骨密度是影响强度的主要因素,螺道的准备、螺钉的植入点和植入方向以及辅助的椎板钩、骨水泥的应用、合理的植骨是影响固定强度不可忽视的技术因素。椎弓根螺钉固定的体外试验不能很好的反映器械与人体相互作用的生物力学特性,体内研究有待进一步开展。     

胸椎后路半椎弓根钉置入的生物力学测试

[目的]评价胸椎半椎弓根钉置入固定方法的生物力学可靠性,为临床应用提供必要的安全参数。[方法]从尸体标本上应用半椎弓根置钉固定,对固定好的中上胸椎进行力学试验。采用应变电测试验技术。测试固定好的标本的抗压强度、扭矩与转角关系曲线、剪切强度和弯曲强度。[结果]当载荷从100 N逐渐加载到600 N的过程中,载荷与应变曲线呈正相关,表明模型的整体结构处于稳定状态。在中心加载时各试件加载至400 N时位移量在0.6～1.3 mm,说明位移变化不大。弯扭矩与试件两端之间相对扭转角呈线性关系,当扭转角达到10°时最大扭矩为12.40 N·m、弯矩为5.60 N·m。[结论]生物力学研究表明,在抗压强度、抗扭转时的剪切强度和弯曲强度上,半椎弓根钉置入技术在较粗规格的螺钉固定下,足够达到内固定及矫形的要求。     

一期改良后路经单侧椎弓根入路病灶清除植骨内固定术治疗胸椎结核

目的探讨改良一期后路经单侧椎弓根入路病灶清除、椎间植骨融合内固定治疗胸椎结核的可行性及疗效。方法 2005年1月-2009年12月,收治胸椎结核22例,采用一期后路经单侧椎弓根入路椎体间病灶清除,对侧经肋椎关节排脓,椎间及单侧后外侧椎板间植骨融合椎弓根螺钉内固定术治疗。其中男12例,女10例;年龄22～52岁,平均39.4岁。病程3个月～10年,平均1.2年。患者累及节段为T5～12,其中2个椎体受累17例,3个5例。术前脊柱后凸Cobb角为(31.2±14.5)°。脊髓损伤按Frankel分级:A级2例,B级1例,C级8例,D级5例,E级1例,无神经症状5例。结果患者术后切口均Ⅰ期愈合。22例均获随访,随访时间12～65个月,平均22.2个月。术后2周患者腰背部疼痛均得到不同程度缓解。术后3个月植骨区均发生融合。术前有神经症状患者术后均明显好转,末次随访时Frankel分级为:B级1例,C级2例,D级4例,E级7例;无神经症状8例。后凸Cobb角为(16.2±3.6)°,与术前比较差异有统计学意义(t=5.952,P=0.001)。术后1年随访时无内固定物松动、断裂、脱出及气胸等并发症。结论对于胸椎结核,一期经单侧椎弓根入路病灶清除椎间植骨融合,必要时行对侧经肋椎关节排脓、椎弓根螺钉固定是一种安全、有效、可行的方法。     

Pullout resistance of thoracic extrapedicular screws used as a salvage procedure.

BACKGROUND CONTEXT: Extrapedicular screws are placed more laterally than intrapedicular screws and pass through the transverse process or rib head before entering the vertebral body. These screws are sometimes placed to salvage failed pedicle screws, but the change in pullout resistance of extrapedicular screws after salvage has not been quantified. PURPOSE: To quantify the pullout resistance of thoracic extrapedicular screws compared with intrapedicular screws and the pullout resistance of newly inserted screws compared with extrapedicular screws used as salvage for failed intrapedicular screws. STUDY DESIGN: In vitro paired comparison of screw pullout resistance in isolated thoracic vertebrae. METHODS: Tapered monoaxial pedicle screws were inserted in the left or right pedicle of 11 human cadaveric thoracic vertebrae. An extrapedicular screw was inserted on the contralateral side. Both screws were pulled out axially at 0.5 mm/s using a servohydraulic test frame while applied load was recorded. Then a fresh extrapedicular screw was inserted as a salvage screw on the intrapedicular screw side and pulled out. RESULTS: In uncompromised vertebrae, the pullout strength of extrapedicular screws was 80+/-32% of that of intrapedicular screws (p=.073, repeated-measures one-way analysis of variance/Tukey). Salvage screws restored pullout strength to 65+/-30% of that of intrapedicular screws (p=.003). CONCLUSIONS: Extrapedicular screws provided comparable but slightly lower pullout resistance to intrapedicular screws in uncompromised vertebrae. They are therefore a feasible salvage technique when a compromised pedicle precludes reinsertion of an intrapedicular screw, but the salvage screw is significantly weaker than the original screw.     

AF椎弓根螺钉内固定治疗胸腰椎骨折

2006年2月～2007年11月,我科经后路AF椎弓根螺钉内固定治疗胸腰椎骨折8例,疗效满意。1材料与方法1.1病例资料本组8例,均为男性,年龄25～43岁。高处跌伤5例,重物砸伤3例。损伤节段：T111例,T123例,L13例,L3～41例。骨折分类：爆裂骨折6例,骨折脱位1例,Chance骨折1例。脊髓神经功能分级：A级1例,B级1例,C级3例,D级3例。受伤至手术时间8h～8d。     

全椎弓根螺钉技术在脊柱畸形矫治术中应用的疗效分析

目的对脊柱侧凸矫治术中应用全椎弓根螺钉技术的疗效进行回顾性分析,并评价其安全性。方法自2002年7月~2004年12月对40例特发性脊柱侧凸患者应用全椎弓根螺钉技术进行矫治,其中男12例,女28例。根据Lenke分型,Ⅰ型16例,Ⅱ型2例,Ⅲ型5例,Ⅴ型7例,Ⅵ型10例。与同期54例应用胸椎弓根、椎板钩联合腰椎弓根螺钉的脊柱侧凸患者进行比较,通过比较2组主侧凸冠状面矫正率、代偿侧凸自动矫正率、躯干平衡指标及矫正度丢失来评价其疗效。并对其中侧凸类型、节段完全一致的10例LenkeⅠ型患者的远端融合节段进行比较。结果随访6~20个月,平均12个月。术前主侧凸冠状面平均Cobb角62.4°,代偿侧凸33.7°,术后矫正率与自发矫正率分别为71.2%与65.4%,优于对照组的59.6%与60.2%,术后矢状面矫正与对照组相比无明显差异;随访中矫正度丢失平均1.9,°亦优于对照组的3.3°。远端融合节段比对照组平均节约1.2个。未发生神经系统并发症。结论掌握脊柱侧凸椎弓根解剖变化(尤其在胸椎),辅助影像学检查及神经功能监测,应用全椎弓根螺钉技术能取得较好的矫形效果及较少的并发症,远期疗效有待进一步随访观察。     

Biomechanical comparison of pedicle screws versus spinous process screws in C2 vertebra: A cadaveric study

Background:

Biomechanical studies have shown C2 pedicle screw to be the most robust in insertional torque and pullout strength. However, C2 pedicle screw placement is still technically challenging. Smaller C2 pedicles or medial localization of the vertebral artery may preclude safe C2 pedicle screw placement in some patients. The purpose of this study was to compare the pullout strength of spinous process screws with pedicle screws in the C2.

Materials and Methods:

Eight fresh human cadaveric cervical spine specimens (C2) were harvested and subsequently frozen to −20°C. After being thawed to room temperature, each specimen was debrided of remaining soft tissue and labeled. A customs jig as used to clamp each specimen for screw insertion firmly. Screws were inserted into the vertebral body pairs on each side using one of two methods. The pedicle screws were inserted in usual manner as in previous biomechanical studies. The starting point for spinous process screw insertion was located at the junction of the lamina and the spinous process and the direction of the screw was about 0° caudally in the sagittal plane and about 0° medially in the axial plane. Each vertebrae was held in a customs jig, which was attached to material testing machine (Material Testing System Inc., Changchun, China). A coupling device that fit around the head of the screw was used to pull out each screw at a loading rate of 2 mm/min. The uniaxial load to failure was recorded in Newton''st dependent test (for paired samples) was used to test for significance.

Results:

The mean load to failure was 387 N for the special protection scheme and 465 N for the protection scheme without significant difference (t = −0.862, P = 0.403). In all but three instances (38%), the spinous process pullout values exceeded the values for the pedicle screws. The working distances for the spinous process screws was little shorter than pedicle screws in each C2 specimen.

Conclusion:

Spinous process screws provide comparable pullout strength to pedicle screws of the C2. Spinous process screws may provide an alternative to pedicle screws fixation, especially with unusual anatomy or stripped screws.     

徒手胸椎椎弓根螺钉置入技术治疗青少年特发性脊柱侧凸的安全性评价

目的 评价徒手胸椎椎弓根螺钉置入技术治疗青少年特发性脊柱侧凸的安全性。方法从2002年7月～2004年6月对38例青少年特发性脊柱侧凸患者，徒手应用胸椎椎弓根螺钉进行后路矫形内固定，所有患者术中进行神经电生理监测及X线透视确认，术后进行X线成像、CAT扫描评估螺钉位置，并对其中35例进行随访，从而评价本技术的安全性。结果共置入胸椎椎弓根螺钉326个，每一水平置入的螺钉数如下：T1,n=2；T2，n=10;T3，n=19；T4，n=27；L，n=28；T6，n=24；T7，n=23；TB，n=25；T9，n=29；T10,n=34；T11,n=48；T12，n=57。通过胸椎CT扫描评价326枚置入畸形胸椎的螺钉位置。共有19枚螺钉（5．8％）有中等程度的皮质穿破，即螺钉的中线在椎弓根壁皮质之外，其中6枚螺钉（1．8％）穿破椎弓根内侧壁。对35例患者进行术后跟踪随访，平均随访时间2年，未发现任何与置入的胸椎椎弓根螺钉（全部326枚螺钉）相关的神经、血管或内脏并发症。结论遵循严格步骤，逐步置入胸椎椎弓根螺钉的徒手技术在治疗青少年特发性脊柱侧凸中具有可靠的安全性。     

全椎弓根螺钉系统矫正特发性脊柱侧凸

[目的]探讨胸椎椎弓根螺钉的植入方法,总结钉棒系统矫正脊柱侧凸的效果.[方法]咬除进钉点骨皮质,以据术前测量的深度和旋转的程度,分别先后用1.5 mm、2.5 mm克氏针沿椎弓根方向钻孔,如阻力加大、克氏针弯曲,说明遇到骨皮质,调整进针方向.达到测定的深度停止进针,球形探子探查无误后改用锤子将导锥顺着制造的钉道小心缓慢击入,深度一致后,再次用球形探子探查,植入螺钉.[结果]胸椎椎弓根螺钉一次性植入成功率胸段97%(600/619),腰段99%(733/740).术后未出现脊髓损伤和神经功能障碍,无切口感染.术后冠状面平均矫正率73%.矢状面后凸Cobb's角(T1～T12)6°～30°,平均23°.旋转畸形矫正Ⅰ～Ⅱ度.103例平均随访4.9年,躯干平衡良好,无平背畸形,植骨融合良好,末次随访冠状面角度丢失率平均为3.7%,迟发性感染1例,螺钉断裂2例,均行内固定取出.[结论]克氏针制备螺钉钉道,是胸椎椎弓根螺钉植入的较好方法.钉棒结构具有良好的三维矫正控制力.全椎弓根螺钉系统矫正特发性脊柱侧凸效果良好.     

椎弓根螺钉治疗胸腰椎爆裂型骨折

胸腰椎爆裂骨折往往伴有脊髓伸经损伤,目前公认的治疗方法是早期复位内固定,恢复脊柱的正常排列及椎管容积,使受损脊髓神经获得减压。2001年3月～2003年3月,笔者对37例胸腰椎爆裂型骨折患者采用椎弓根螺钉复位内固定,取得较好疗效。     

椎弓根钉技术治疗不稳定性上胸椎损伤

[目的]总结用后路椎弓根钉技术治疗不稳定性上胸椎损伤的临床经验、技术要点及临床效果。[方法]将应用椎弓根钉后路固定治疗的49例不稳定性上胸椎损伤病人的临床资料和随访资料进行分组总结，找出预防脊髓损伤、神经根损伤等并发症发生的有效方法。[结果]椎弓根钉技术可有效恢复脊椎的解剖结构，纠正上位脊椎的移位、成角畸形（P〈0.05），促进脊髓损伤的恢复（P〈0．05），脊髓损伤的概率低（P〈0．05）。[结论]椎弓根钉技术治疗上胸椎不稳定性损伤是一种坚强、安全、有效的方法。     

Posterior fusion only for thoracic adolescent idiopathic scoliosis of more than 80°: pedicle screws versus hybrid instrumentation

The treatment of thoracic adolescent idiopathic scoliosis (AIS) of more than 80° traditionally consisted of a combined procedure, an anterior release performed through an open thoracotomy followed by a posterior fusion. Recently, some studies have reassessed the role of posterior fusion only as treatment for severe thoracic AIS; the correction rate of the thoracic curves was comparable to most series of combined anterior and posterior surgery, with shorter surgery time and without the negative effect on pulmonary function of anterior transthoracic exposure. Compared with other studies published so far on the use of posterior fusion alone for severe thoracic AIS, the present study examines a larger group of patients (52 cases) reviewed at a longer follow-up (average 6.7 years, range 4.5–8.5 years). The aim of the study was to evaluate the clinical and radiographic outcome of surgical treatment for severe thoracic (>80°) AIS treated with posterior spinal fusion alone, and compare comprehensively the results of posterior fusion with a hybrid construct (proximal hooks and distal pedicle screws) versus a pedicle screw instrumentation. All patients (n = 52) with main thoracic AIS curves greater than 80° (Lenke type 1, 2, 3, and 4), surgically treated between 1996 and 2000 at one institution, by posterior spinal fusion either with hybrid instrumentation (PSF–H group; n = 27 patients), or with pedicle screw-only construct (PSF–S group; n = 25 patients) were reviewed. There were no differences between the two groups in terms of age, Risser’s sign, Cobb preoperative main thoracic (MT) curve magnitude (PSF–H: 92° vs. PSF–S: 88°), or flexibility on bending films (PSF–H: 27% vs. PSF–S: 25%). Statistical analysis was performed using the t test (paired and unpaired), Wilcoxon test for non-parametric paired analysis, and the Mann–Whitney test for non-parametric unpaired analysis. At the last follow-up, the PSF–S group, when compared to the PSF–H group had a final MT correction rate of 52.4 versus 44.52% (P = 0.001), with a loss of −1.9° versus −11.3° (P = 0.0005), a TL/L correction of 50 versus 43% (ns), a greater correction of the lowest instrumented vertebra translation (−1.00 vs. −0.54 cm; P = 0.04), and tilt (−19° vs. −10°; P = 0.005) on the coronal plane. There were no statistically significant differences in sagittal and global coronal alignment between the two groups (C7-S1 offset: PSF–H = 0.5 cm vs. PSF–S = 0 cm). In the hybrid series (27 patients) surgery-related complications necessitated three revision surgeries, whereas in the screw group (25 patients) one revision surgery was performed. No neurological complications or deep wound infection occurred in this series. In conclusion, posterior spinal fusion for severe thoracic AIS with pedicle screws only, when compared to hybrid construct, allowed a greater coronal correction of both main thoracic and secondary lumbar curves, less loss of the postoperative correction achieved, and fewer revision surgeries. Posterior-only fusion with pedicle screws enabled a good and stable correction of severe scoliosis. However, severe curves may be amenable to hybrid instrumentation that produced analogous results to the screws-only constructs concerning patient satisfaction; at the latest follow-up, SRS-30 and SF-36 scores did not show any statistical differences between the two groups. Presented at 8th Annual Meeting of the Spine Society of Europe, October 2006, Istanbul, Turkey.     

Pullout strength of misplaced pedicle screws in the thoracic and lumbar vertebrae - A cadaveric study

Background:

The objective of this cadaveric study was to analyze the effects of iatrogenic pedicle perforations from screw misplacement on the mean pullout strength of lower thoracic and lumbar pedicle screws. We also investigated the effect of bone mineral density (BMD), diameter of pedicle screws, and the region of spine on the pullout strength of pedicle screws.

Materials and Methods:

Sixty fresh human cadaveric vertebrae (D10–L2) were harvested. Dual-energy X-ray absorptiometry (DEXA) scan of vertebrae was done for BMD. Titanium pedicle screws of different diameters (5.2 and 6.2 mm) were inserted in the thoracic and lumbar segments after dividing the specimens into three groups: a) standard pedicle screw (no cortical perforation); b) screw with medial cortical perforation; and c) screw with lateral cortical perforation. Finally, pullout load of pedicle screws was recorded using INSTRON Universal Testing Machine.

Results:

Compared with standard placement, medially misplaced screws had 9.4% greater mean pullout strength and laterally misplaced screws had 47.3% lesser mean pullout strength. The pullout strength of the 6.2 mm pedicle screws was 33% greater than that of the 5.2 mm pedicle screws. The pullout load of pedicle screws in lumbar vertebra was 13.9% greater than that in the thoracic vertebra (P = 0.105), but it was not statistically significant. There was no significant difference between pullout loads of vertebra with different BMD (P = 0.901).

Conclusion:

The mean pullout strength was less with lateral misplaced pedicle screws while medial misplaced pedicle screw had more pullout strength. The pullout load of 6.2 mm screws was greater than that of 5.2 mm pedicle screws. No significant correlation was found between bone mineral densities and the pullout strength of vertebra. Similarly, the pullout load of screw placed in thoracic and lumbar vertebrae was not significantly different.