数字矩阵建模在寰椎椎弓根螺钉通道研究中的应用

目的 观察寰椎椎弓根通道在不同水平面角(TSA)、矢状面角(SSA)的变化规律,以及使用不同规格螺钉的变化规律,探讨数字矩阵建模在术前设计寰椎椎弓根螺钉进钉方案中的作用. 方法 将9位健康成人受试者(男5例,女4例;年龄26 ～ 70岁,平均45岁)的寰椎CT连续断层扫描数据导入Mimics 10.0l软件,三维重建后用.dwg文件导入3dnax2009.确定三维参照坐标和进钉点,用3dmax中参考建模命令建立17×17×2,间距2.5°,TSA 0 ～ 40°、SSA 0～40°,共578个元素模拟椎弓根螺钉矩阵模型,观察当模拟螺钉进钉角度、直径、长度变化时椎弓根螺钉通道的变化规律. 结果 TSA、SSA均明显影响左、右侧螺钉进钉长度,差异有统计学意义(P＜0.05).TSA=0°、SSA=10°时螺钉长度最佳[左侧平均为(1.91 ±0.26) mm,右侧平均为(1.51±0.29)mml.直径为3.5 mm、长为22 mm的螺钉在寰枢椎进钉数目较直径为3.5 mm、长度为26 mm的螺钉多,直径为3.5mm、长度为22mm螺钉在寰枢椎进钉数目较直径为4.0 mm、长度为22 mm的螺钉多,差异均有统计学意义(P＜0.05). 结论 利用数字矩阵建模能够简化复杂逆向建模可以全方位观察不同TSA、SSA、螺钉规格变化时椎弓根通道的变化规律.术前设计时不仅需要综合考虑椎弓根螺钉本身的TSA、直径及长度,而且要考虑SSA,以确定个性化的进钉方案.     

胸椎椎弓根进钉通道随外偏角变化的数字解剖学研究

目的应用数字技术探讨胸椎椎弓根进钉通道不同外偏角方向的变化规律。方法健康成人胸椎CT连续扫描数据集,应用Mimics 10.01三维重建胸椎数字解剖模型,将模型导入UG Imageware12.0,确定椎骨正中矢状切面和经椎弓根中部水平面为0o正交平面,0o水平面为头尾偏角参考平面,正中矢状切面为水平面角参考平面,确定左右椎弓根各个方向进钉通道的正投影,获得椎弓根进钉通道的正投影内边界和内边界内切圆,以及内切圆在正投影方向经椎板、椎弓根与椎体的进钉通道长度和各内切圆半径,对获取的相关数据进行统计学分析和可视化显示。结果 (1)T2～T12内切圆半径:在节段之间T7最小,内切圆半径2.3～4.5mm;在角度之间,内切圆半径2.3～3.5mm,其中0o～20o内切圆半径分别为:左3.4～3.5mm,右3.3～3.5mm,相差0.1～0.2mm。进钉通道长度:在节段之间,通道长度26.9～47.8mm,T2最小,T9最大;在角度之间,通道长度23.1～53.2mm,其中0o～20o通道长度分别为:左23.1～39.7mm,右24.8～41.6mm。(2)胸椎椎弓根通道长度随着角度的增大而增大,内切圆半径的大小随着角度的增大先逐渐增大而后又逐渐减小。胸椎不同节段、不同水平面角的内切圆半径和通道长度各不相同,部分节段的内切圆半径和通道长度在左右侧别之间存在差异。结论 (1)椎弓根进钉通道是任意方向椎弓根内部三维空间正投影内边界在椎体与椎板之间的通道。它是一个动态的变化空间,一定范围内任意一个三维空间方向对应着一个椎弓根进钉通道,该椎弓根进钉通道对应着一个最大螺钉通道,该最大螺钉通道对应着最佳轴线和进钉点。(2)T2～T12左右侧0o～20o水平面角之间是内切圆半径相对较大而通道长度相对较短的区域,25o～40o则相反。     

新型寰椎内径锥形螺钉的设计与拔出力的测试

目的比较两种设计的寰椎椎弓根钉的最大拔出力,为临床选择寰椎推弓根钉类型提供生物力学依据。方法设计制作两种寰椎椎弓根钉,根据螺纹部分分为皮质骨螺钉(A型螺钉)、内径锥形螺钉(B型螺钉),利用24节新鲜猪寰椎标本,置入两种类型的椎弓根钉,进行拔出试验,测定每种螺钉的最大拔出力,进行统计学分析比较。结果同一长度,不同设计的螺钉抗拔出力接近,均无显著性差异;同一直径两种设计的螺钉,28 mm比26 mm的抗拔出力略大,但均无显著性差异。结论新型寰椎内径锥形螺钉(3.0 mm)抗拔力高,螺钉根部强度好,抗弯曲、断裂性能好,可提供足够的即刻稳定性,是寰椎椎弓根固定的理想螺钉类型。     

以枢椎椎弓峡部内上壁为解剖标志行枢椎椎弓根置钉的CT测量及临床应用

目的:探讨以枢椎椎弓根峡部内上壁为解剖标志的枢椎椎弓根螺钉置钉的可行性及安全性。方法:57例成人枢椎行三维CT重建,在三维重建图像上测量枢椎左右侧椎弓根的中部宽度L1和高度L2;以枢椎椎弓峡部内上壁为标志横断面确立左右侧的最外侧模拟进钉点B和最内侧模拟进钉点A到峡部距离;测量最佳进钉点S(经过枢椎椎弓根中部宽度连线的中垂线与峡部后侧皮质交点)到峡部内壁距离,分别测量A、B、S点横断面进钉角度最大置钉角度区间;冠状面上测量S点距离峡部内上壁距离;测量S点进钉最佳内倾角及上倾角。选择2007年10月～2011年7月收治的33例患者采用枢椎椎弓根峡部内上壁为标志实施枢椎椎弓根螺钉内固定术,其中新鲜齿状突骨折13例,陈旧性齿状突骨折10例,横韧带损伤伴寰枢椎脱位7例,寰椎骨折3例。观察手术中与枢椎椎弓根螺钉置钉相关的并发症,术后三维CT重建观察螺钉的位置。结果:CT横断面测量进钉点A、B、S到峡部的距离为1.75mm、9.01±0.62mm、5.77±0.53mm,S点置钉角度区间与A、B点置钉角度区间比较有显著性差异(P<0.05)。冠状面上S点距离峡部内上壁距离为4.30±0.49mm;S点进钉内倾角为30°、上倾角为26°时为最佳进钉角度。临床共置入枢椎椎弓根螺钉66枚,术中显露良好,未出现椎动脉、静脉丛损伤出血及脊髓、神经根损伤等并发症。术后三维CT复查显示所有枢椎椎弓根螺钉均未误入椎管或椎动脉孔,术中测量枢椎椎弓根螺钉进钉点横断面上与枢椎椎弓峡部内壁水平间距为5.44±0.72mm,冠状面上距离峡部内上壁为4.50±0.52mm,与术前S点测量值相比较均无显著性差异。结论:枢椎椎弓根与峡部存在恒定位置关系,以枢椎椎弓峡部内上壁为解剖参照行枢椎椎弓根置钉是安全可行的。     

前路枢椎椎弓根螺钉固定通道的CT测量及临床应用

目的:探讨CT扫描测量指导前路枢椎椎弓根螺钉置人的临床应用价值.方法:对20具干燥枢椎标本行椎弓根螺钉置入,然后应用CT测量进针的角度、钉道长度以确定最佳进钉点,并根据测量数据和术前影像学检查对10例难复性寰枢椎脱位患者行前路寰枢椎复位椎弓根螺钉固定植骨融合术,观察寰枢椎复位及螺钉位置情况.结果:枢椎椎弓根的平均长度为25mm,进针点距离枢椎正中线6.6mm,安全进钉的角度向外倾斜21°±2°,下倾10°±2°.10例患者寰枢椎均完全复位,枢椎椎弓根螺钉均位于椎弓根钉道内.结论:前路寰枢椎椎弓根螺钉固定有较高的安全性,术前行CT扫描对于前路寰枢椎内固定手术有重要的指导意义.     

枢椎椎弓峡部引导下寰椎椎弓根置钉的CT测量及其应用

目的:探讨在枢椎椎弓峡部引导下实施寰椎椎弓根螺钉置钉的可行性及安全性。方法:对48例成人寰枢椎行三维CT重建,取枢椎椎弓峡部内上缘与寰椎的横断面图像。测量椎管正中线至寰椎椎弓根内壁、外壁及枢椎椎弓峡部内壁、外壁的距离,分别为L1、D1、L2、D2;0°内倾角置钉时,以枢椎椎弓峡部内上壁为解剖标志,确立最内侧进钉点A和最外侧进钉点B,减去螺钉半径1.75mm,A、B点至枢椎椎弓峡部内上壁的距离分别为(L1-L2+1.75mm)、(D1-L2-1.75mm),寰椎后弓上置钉时螺钉允许的最大内倾角与最大外倾角大致相等时的点为最佳进钉点(M点),记录M点至枢椎椎弓峡部内上壁水平间距。自2004年3月～2009年3月对29例患者采用以枢椎椎弓峡部为标志实施后路寰枢椎椎弓根螺钉内固定手术,其中陈旧性齿状突骨折24例,横韧带损伤并寰椎前脱位5例。观察手术过程中与寰椎椎弓根螺钉置钉相关的并发症,术后三维CT重建观察螺钉的位置。结果:0°内倾角置钉时,CT测量最内侧进钉点A、最外侧进钉点B、最佳进钉点M至枢椎椎弓根峡部内上壁的水平间距分别为4.22±0.54mm、8.66±0.73mm、5.79±0.63mm。临床共置入寰椎椎弓根螺钉58枚,术中枢椎椎弓峡部内上壁均得到良好显露,未出现椎动脉、静脉丛损伤出血及脊髓、C2神经根损伤等并发症。术后三维CT复查显示所有寰椎椎弓根螺钉均未误入椎管或椎动脉孔,测量寰椎椎弓根螺钉进钉点与枢椎椎弓峡部内上壁水平间距为5.45±0.82mm,与术前M点测量值相比较无显著性差异。结论:在纠正寰椎旋转移位后,以枢椎椎弓峡部内上壁作为解剖参照,寰椎椎弓根存在一定的置钉安全区间,利用该解剖标志行寰椎椎弓根置钉是安全可行的。     

寰椎侧块螺钉与寰椎椎弓根螺钉的解剖与生物力学对比研究

目的对寰椎侧块螺钉和寰椎椎弓根螺钉进行解剖和生物力学研究,为临床选择寰椎螺钉的固定方式提供依据。方法利用12例新鲜标本的寰椎进行单皮质和双皮质的椎弓根螺钉或侧块螺钉固定,测试比较其螺钉拔出强度和钉道长度。结果寰椎椎弓根螺钉的最大进钉长度为29·79mm±1·68mm,其中10·15mm在寰椎后弓内,19·65mm在寰椎侧块内。寰椎侧块螺钉的最大进钉长度为24·88mm±0·41mm,其进钉点与寰椎后弓后缘的平均距离为9·93mm±1·35mm。双皮质寰椎椎弓根螺钉的拔出力量最大,平均1757·0N±318·7N;单皮质寰椎椎弓根螺钉(1192·5N±172·6N)与双皮质寰椎侧块螺钉(1243·8N±350·0N)无明显差异,单皮质寰椎侧块螺钉最小(794·5N±314·8N)。结论在同时适用寰椎椎弓根螺钉和寰椎侧块螺钉固定的患者,宜首先选择寰椎椎弓根螺钉固定,次选寰椎侧块螺钉固定。     

计算机3D建模模拟个体化枢椎椎弓根钉最佳进钉方式的应用

[目的]利用3D建模技术观察枢椎椎弓根通道,置钉安全区,测量最佳置钉方案。制订标准、简化的枢椎椎弓根螺钉进钉术前设计方案。[方法]从本院PACS系统14例健康成人(男7例,女7例;年龄30⁶8岁,平均45岁)的枢椎CT连续断层扫描数据导入Mimics 10.01软件,三维重建后利用.dwg文件导入3dmax2009。确定三维参照坐标和进钉点,用3 dmax中参考建模命令建立17×17×2间距2.5°TSA(水平面角)068岁,平均45岁)的枢椎CT连续断层扫描数据导入Mimics 10.01软件,三维重建后利用.dwg文件导入3dmax2009。确定三维参照坐标和进钉点,用3 dmax中参考建模命令建立17×17×2间距2.5°TSA(水平面角)0⁴0°,SSA(矢状面角)040°,SSA(矢状面角)0⁴0°共578元素模拟椎弓根螺钉阵列模型,通过透视图观察直径为3.5 mm,长度为24 mm模拟螺钉在椎弓根通道中情况,从而确定安全区,最后测量最佳置钉方案螺钉角度。[结果]14例受试者矩阵研究元素总数目为17×17×2×14共8 092个元素单位。其中395个元素符合进钉要求。螺钉最远距离进行比较,差异无统计学意义(P>0.05)。[结论]利用数字3D建模技术能建立标准、简化、精确的术前设计方案。     

经后路寰椎椎弓根螺钉固定的置钉研究

目的探讨经后路寰椎椎弓根螺钉固定的可行性. 方法利用20具颈椎尸体标本,模拟经后路寰椎椎弓根螺钉固定.在寰椎后弓后缘表面,经枢椎下关节突中心点纵垂线与寰椎后弓上缘下方3 mm水平线的交点作为进钉点,按内斜10度、上斜5度钻孔,经寰椎椎弓根置入直径3.5 mm的皮质骨螺钉.测量进钉点与寰椎椎弓根中线平面的距离、螺钉最大进钉深度、螺钉内斜角度和螺钉上斜角度等解剖指标,观察螺钉是否突破椎弓根和侧块骨皮质,以及椎动脉、硬膜、脊髓是否损伤等. 结果共放置40枚寰椎椎弓根螺钉,测得进钉点与寰椎椎弓根中线的平均距离为(2.20±0.42) mm,螺钉最大进钉深度平均(30.51±1.59) mm,螺钉内斜角度平均(9.70±0.67)度,上斜角(4.60±0.59)度.其中1枚螺钉因上斜角度过大穿破椎弓根上缘,8枚因后弓高度过小而突破椎弓根下缘,5枚进钉过深突破寰椎侧块前缘皮质,但均未对脊髓和椎动脉造成损伤. 结论经后路行寰椎椎弓根螺钉固定是安全可行的,但应注意进钉角度和深度.     

改良寰椎椎弓根螺钉固定置钉方法的轴位CT测量研究

目的:通过改变进钉点和进钉角度获得新的寰椎椎弓根螺钉钉道,运用轴位CT扫描测量评价改良置钉方法的安全性和准确性。方法:选择30具成人颈椎尸体标本,按标本提供的顺序随机将同一标本两侧分成A、B两组,A组经枢椎侧块中点作纵垂线,与寰椎后弓上缘交点的正下方3.0mm处作为螺钉的进钉点,向内倾斜10°、向上倾斜5°置钉。B组进钉点偏外2mm,内倾角为15°,上倾5°。置钉后通过轴位CT扫描,分别测量A组和B组可利用间隙(SAS)即钉道宽度;钉道长度(LST);外侧安全间隙(OSC),即横突孔内侧缘到螺钉外缘的最短距离;内侧安全间隙(ISC),即椎管外侧缘到螺钉内缘的最短距离;选出内外侧间隙中较小者(SSC),计算出内外侧安全间隙距离差的绝对值(|LSC-MSC|)。应用SPSS13.0软件比较两组间的差异。结果:SAS值A组为6.8±11.7mm,B组为7.8±13.0mm,两组间差异有显著性(P<0.01);A组的钉道长度比B组的钉道长度短(P<0.01);A组的SSC值为2.1±0.1mm,B组为3.0±0.1mm,两组间比较差异有显著性(P<0.01);A组的|LSC-MSC|平均值为1.5±0.1mm,B组为0.6±0.1mm,两组间比较差异有显著性(P<0.01)。结论:寰椎椎弓根钉进钉点选于枢椎侧块中点外侧2mm,与寰椎后弓上缘交点的正下方3.0mm处,向内倾15°,头倾5°置钉,充分使用了可利用间隙,识别标志与椎弓根的位置关系相对恒定,对临床准确置钉、提高固定效果具有较好的指导意义。     

Development and validation of a quantitative method to assess pedicle screw loosening in posterior spine instrumentation on plain radiographs

Purpose

Currently, the diagnosis of pedicle screw (PS) loosening is based on a subjectively assessed halo sign, that is, a radiolucent line around the implant wider than 1 mm in plain radiographs. We aimed at development and validation of a quantitative method to diagnose PS loosening on radiographs.

Methods

Between 11/2004 and 1/2010 36 consecutive patients treated with thoraco-lumbar spine fusion with PS instrumentation without PS loosening were compared with 37 other patients who developed a clinically manifesting PS loosening. Three different angles were measured and compared regarding their capability to discriminate the loosened PS over the postoperative course. The inter-observer invariance was tested and a receiver operating characteristics curve analysis was performed.

Results

The angle measured between the PS axis and the cranial endplate was significantly different between the early and all later postoperative images. The Spearman correlation coefficient for the measurements of two observers at each postoperative time point ranged between 0.89 at 2 weeks to 0.94 at 2 months and 1 year postoperative. The angle change of 1.9° between immediate postoperative and 6-month postoperative was 75 % sensitive and 89 % specific for the identification of loosened screws (AUC = 0.82).

Discussion

The angle between the PS axis and the cranial endplate showed good ability to change in PS loosening. A change of this angle of at least 2° had a relatively high sensitivity and specificity to diagnose screw loosening.     

经椎弓根内固定的形态与生物力学研究

目的：提高临床医师对椎弓根内固定技术的理论认识。方法：应用直径４．５ｍｍ,５．５ｍｍ,６．２５ｍｍ和７．０ｍｍ４种不同直径的椎弓根螺钉１６具Ｔ６～Ｓ１节段的新鲜尸体脊柱标本上观察：（１）穿钉失败率;（２）椎弓根膨胀变形率;（３）椎弓根螺钉把持力;（４）椎弓根椎体损伤分类。结果：穿钉失败率与操作技术和椎弓根横径相关,在下胸椎失败率高主要与椎弓根横径密切相关,没有发生穿钉失败的椎弓根膨胀率２８．６％～     

椎弓根螺钉植入导向器的研制及体外应用研究

目的　分析自制椎弓根螺钉导向器提高椎弓根螺钉植入的准确性。　方法　根据椎弓根的解剖特点 ,研制椎弓根螺钉植入导向器。用多层螺旋 CT测量 2具胸椎标本 (T1 ～ T1 0 )椎弓根的三维定量解剖数据。依据其中轴的水平位角 (transverse section angle,TSA)和矢状位角 (sagittal section angle,SSA)值 ,调节导向器水平和矢状刻度盘角度。植入螺钉后拔出 ,用显影剂填充钉道。 CT测量显影钉道的 TSA和 SSA值。　结果　析因设计资料方差分析显示 ,椎弓根显影钉道的 TSA、SSA与其中轴的 TSA、SSA间差异无统计学意义 (P>0 .0 5 )。　结论　椎弓根螺钉导向器操作简便 ,其导向使钉道达到理想角度 ,能减少椎弓根穿破的发生。     

手外伤带蒂皮瓣修复不同时间断蒂的临床研究

目的探讨手外伤带蒂皮瓣修复不同时间断蒂的临床效果。方法将300例手外伤行带蒂皮瓣修复的患者随机分为观察组和对照组各150例,观察组术后14天断蒂,对照组21天断蒂。于术后第1、7、14天及断蒂后观察记录皮瓣颜色、温度、皮瓣毛细血管反应和针刺出血率,断蒂前观察断流试验,以及皮瓣存活率、住院时间和住院费用,术后随访1年。结果两组患者皮瓣颜色、温度、皮瓣毛细血管反应、针刺出血率和断流试验比较,差异均无统计学意义(P>0.05);两组患者断蒂后皮瓣全部成活,无感染病例发生;观察组患者住院时间和医疗费用明显少于对照组,P<0.05。术后随访1年,两组患者手外形及功能恢复良好。结论手外伤带蒂皮瓣修复术后14天断蒂是可行的,并可减少住院时间,节省住院费用,值得临床推广应用。     

A preliminary study of reliability of impedance measurement to detect iatrogenic initial pedicle perforation (in the porcine model)

Accidental perforation of the vertebral pedicle wall is a well-known complication associated with standard approach of pedicle screw insertion. Depending on detection criteria, more than 20% of screws are reported misplaced. Serious clinical consequences, from dysesthesia to paraplegia, although not common, may result from these misplaced screws. Many techniques have been described to address this issue such as somatosensory evoked potentials, electromyography, surgical navigation, etc. Each of these techniques presents advantages and drawbacks, none is simple and ergonomic. A new drilling tool was evaluated which allows for instant detection of pedicle perforation by emission of variable beeps. This new device is based on two original principles: the device is integrated in the drilling or screwing tool, the technology allows real-time detection of perforation through two independent parameters, impedance variation and evoked muscular contractions. A preliminary animal study was conducted to assess the safety and efficacy of this system based upon electrical conductivity. A total of 168 manual pedicle drillings followed by insertion of implants were performed in 11 young porcine lumbar and thoracic spines. The presence or absence of perforation detection, which defines the reliability of the device, was correlated with necropsic examination of the spines. Using this protocol the device demonstrated 100% positive predictive value, 96% negative predictive value, 100% specificity, and 97% sensitivity. Of 168 drillings there were three (1.79%) false-negatives, leading to a minor effraction, cranially in the intervertebral disks, nine (5.36%) screw threads breaching the vertebral cortex when inserting screws, although preparation of the holes did not indicate any perforation, 34 (36%) breaches detected by the instrument and not detected by the surgeon. These results confirm that the impedance variation detection capability of this device offers a simple and effective means to detect perforation in vertebral pedicle, prior to insertion of pedicle screws. Due to the porcine nerve root anatomy, it was not possible to evaluate the added benefit of cross-linking impedance and EMG detection. A future clinical study may further explore the subject of current study. An erratum to this article is available at .     

胸椎经"椎弓根-肋骨间"螺钉与椎弓根螺钉固定的抗拔出力比较

目的比较胸椎经"椎弓根-肋骨间"螺钉与椎弓根螺钉固定的抗拔出力.方法5例新鲜尸体脊柱(T6～T10)标本,自椎间盘、小关节及上位椎体下肋椎关节处分解为单椎体(附带双侧肋骨)25个.根据配对随机分组的原则,随机选取椎体一侧作椎弓根螺钉固定组,另一侧则为配对的"椎弓根-肋骨间"螺钉固定组,共组成25个配对组.同组中"椎弓根-肋骨间"螺钉长度较椎弓根螺钉长10mm,直径与椎弓根螺钉相同.将25组的50个螺钉分别进行拔出测试(5mm/min的速度垂直方向拔出).结果"椎弓根-肋骨间"螺钉的抗拔出力为423.1±198.7N;椎弓根螺钉的抗拔出力为783.3±199.5N.前者的抗拔出力显著小于后者(P＜0.01).结论"椎弓根-肋骨间"螺钉的力学性能不及椎弓根螺钉,建议仅将前者作为后者的一种补充,特别是在无法完成椎弓根螺钉置入的部分胸椎节段.     

Simple technique for removing broken pedicular screw with plain and serviceable screwdriver

Removing the broken pedicular screw after spinal hardware failure is usually problematic. A specially designed simple screwdriver and easy removal technique of broken pedicular screw with this screwdriver are described in this article.     

New means in spinal pedicle hook fixation

Summary Pedicle hooks which are used as an anchorage for posterior spinal instrumentation may be subjected to considerable three-dimensional forces. In order to achieve stronger attachment to the implantation site, hooks using screws for additional fixation have been developed. The failure loads and mechanisms of three such devices have been experimentally determined on human thoracic vertebrae: the Universal Spine System (USS) pedicle hook with one screw, a prototype pedicle hook with two screws and the Cotrel-Dubousset (CD) pedicle hook with screw. The USS hooks use 3.2-mm self-tapping fixation screws which pass into the pedicle, whereas the CD hook is stabilised with a 3-mm set screw pressing against the superior part of the facet joint. A clinically established 5-mm pedicle screw was tested for comparison. A matched pair experimental design was implemented to evauluate these implants in constrained (series I) and rotationally unconstrained (series II) posterior pull-out tests. In the constrained tests the pedicle screw was the strongest implant, with an average pull-out force of 1650 N (SD 623 N). The prototype hook was comparable, with an average failure load of 1530 N (SD 414 N). The average pull-out force of the USS hook with one screw was 910 N (SD 243 N), not significantly different to the CD hook's average failure load of 740 N (SD 189 N). The result of the unconstrained tests were similar, with the prototype hook being the strongest device (average 1617 N, SD 652 N). However, in this series the difference in failure load between the USS hook with one screw and the CD hook was significant. Average failure loads of 792 N (SD 184 N) for the USS hook and 464 N (SD 279 N) for the CD hook were measured. A pedicular fracture in the plane of the fixation screw was the most common failure mode for USS hooks. The hooks usually did not move from their site of implantation, suggesting that they may be well-suited for the socalled segmental spinal correction technique as used in scoliosis surgery. In contrast, the CD hook disengaged by translating caudally from its site of implantation in all cases, suggesting a mechanical instability. The differences in observed hook failure modes may be a function of the type and number of additional fixation screws used. These results suggest that additional screw fixation allows stable attachment of pedicle hooks to their implantation site. Hooks using additional fixation screws passing obliquely into the pedicle apparently provide the most rigid attachment. The second fixation screw of the prototype hook almost doubles the fixation strength. Thus, the prototype hook might be considered as an alternative to the pepdicle screw, especially in the upper thoracic region.     

Potential contribution of pedicle screw design to loosening rate in patients with degenerative diseases of the lumbar spine: An observational study

BACKGROUNDThe majority of published data report the results of biomechanical tests of various design pedicle screw performance. The clinical relevance and relative contribution of screw design to instrumentation stability have been insufficiently studied.AIMTo estimate the contribution of screw design to rate of pedicle screw loosening in patients with degenerative diseases of the lumbar spine.METHODSThis study is a prospective evaluation of 175 patients with degenerative diseases and instability of the lumbar spine segments. Participants underwent spinal instrumentation employing pedicle screws with posterior only or transforaminal interbody fusion. Follow-up was for 18 mo. Patients with signs of pedicle screw loosening on computed tomography were registered; logistic regression analysis was used to identify the factors that influenced the rate of loosening.RESULTSParameters included in the analysis were screw geometry, type of thread, external and internal screw diameter and helical pitch, bone density in Hounsfield units, number of levels fused, instrumentation without anterior support, laminectomy, and unilateral and bilateral total facet joint resection. The rate of screw loosening decreased with the increment in outer diameter, decrease in core diameter and helical pitch. The rate of screw loosening correlated positively with the number of fused levels and decreasing bone density. Bilateral facet joint removal significantly favored pedicle screw loosening. The influence of other factors was insignificant.CONCLUSIONScrew parameters had a significant impact on the loosening rate along with bone quality characteristics, the number of levels fused and the extensiveness of decompression. The significance of the influence of screw parameters was comparable to those of patient- and surgery-related factors. Pedicle screw loosening was influenced by helical pitch, inner and outer diameter, but screw geometry and thread type were insignificant factors.     

无X线定位经椎弓根螺钉脊柱内固定的探讨

在无X线监视下行经椎弓根螺钉脊柱内固定术48例,置钉214枚。术后X线片检查置钉位置优良149枚(69.6％),差65枚(30.4％),错0枚。作者认为熟悉椎弓根的定性定量解剖是正确置钉的基础,“盲目”置钉法对无X线监护条件的医院开展本术式有一定的实用价值。