Scofix器械(脊柱侧凸固定器)的设计与临床应用

目的介绍Scofix器械的结构、原理并观察其临床应用效果。方法Scofix器械由不同型号的开口椎弓根螺钉、开口椎弓根钩、连接棒、阻塞器和横向连接器等组成。在脊柱侧凸稳定区内的各脊椎节段上选择数枚开口椎弓根螺钉行连续或间断固定,通过连接棒进行连接固定,采用撑开、加压或旋转矫正的方法对畸形脊柱进行矫正。共治疗33例脊柱侧凸患者,平均年龄14.4岁。特发性侧凸19例,先天性侧凸14例;术前平均Cobb角分别为70°和68°。根据畸形程度和脊柱柔韧性,采用一次性矫正或分期矫正。结果特发性脊柱侧凸患者,手术后平均Cobb角为29.4°,矫正率为59.1%;先天性脊柱侧凸患者,手术后平均Cobb角为33.3°,矫正率为52.3%。无严重并发症发生。结论根据CD矫正器的原理及国人青少年脊柱结构特点设计的Scofix器械,对脊柱具有撑开、加压及旋转矫正功能,为适用于不同年龄脊柱侧凸患者的内固定器械,其矫正力大,且不占据椎管空间。由于胸椎椎弓根螺钉固定难度较大、风险较高,故应具备一定的技术条件方可使用,必要时可代之以椎弓根钩。     

青少年胸椎椎弓根影像学特征及其临床意义

目的 :探讨青少年胸椎椎弓根影像学特征及其临床意义。方法 :随机选择正常青少年 42人 ,平均年龄12 .4岁 ,摄胸椎X线片 ,对 2 7人行全胸椎椎弓根CT扫描 ,分别测量各节段椎弓根横径、螺钉进钉点和深度 ,以及椎弓根轴线与矢状面夹角等 ,并根据X线测量方法 ,对 10 3例脊柱侧凸患者进行节段椎弓根螺钉器械矫正。结果 :正常C4椎弓根横径最小 (3 .9± 0 .66)mm ,胸椎椎弓根钉进钉点均位于横突根部上缘与中点之间 ,T11、12 椎弓根矢状角为负角 ,其余为正角。 10 3例患者共置入 10 82枚胸椎椎弓根螺钉 ,穿透椎弓根内外侧及椎前皮质的螺钉分别占 18.6%、 14 .5 %和 2 .1% ,仅 1例患者出现了与椎弓根穿透内侧皮质有关的神经系统症状 ,无其他相关并发症。结论 :认真阅读X线片 ,了解与掌握不同节段椎弓根形态特征及周围解剖关系 ,有助于进行正确的胸椎椎弓根螺钉置入。     

后路椎弓根螺钉系统矫正青少年特发性脊柱侧凸术后主动脉位置变化分析

【摘要】 目的：评价接受后路椎弓根螺钉系统矫正手术的青少年特发性脊柱侧凸患者术前、术后1周和术后2年主动脉相对于脊柱的空间位置变化。方法：研究对象为接受后路椎弓根螺钉系统矫正手术的22例右胸主弯的青少年特发性脊柱侧凸患者。通过三维重建CT测量患者术前、术后1周、术后2年主动脉位置和顶椎旋转畸形情况,测量参数包括主动脉-椎体距离、主动脉-椎体角、主动脉-椎管距离、左侧椎弓根螺钉长度和顶椎旋转角。通过X线片测量胸主弯的Cobb角和胸椎后凸角。结果：术前主胸弯Cobb角为57.5°±9.8°,术后1周矫正至13.6°±6.5°,术后2年时为16.2°±6.8°;主胸弯Cobb角矫正率术后1周时为77.5%,术后2年时为73.3%。术前顶椎轴面旋转角为29.4°±9.3°,术后1周矫正至14.6°±6.9°,术后2年时为17.4°±6.8°;顶椎旋转畸形的矫正率术后1周时为49.5%,术后2年时为39.7%。主动脉-椎体距离在T6～T11节段术前显著大于术后1周（P<0.05）;在T7～T9节段术后2年显著大于术后1周（P<0.05）。主动脉-椎体角在T5～T11节段术前显著大于术后1周（P<0.05）;在T7～T10节段术后2年显著大于术后1周（P<0.05）。主动脉-椎管距离在T7～T11节段术前显著小于术后1周（P<0.05）;在T6～T10节段术后2年显著小于术后1周（P<0.05）。结论：右胸主弯的青少年特发性脊柱侧凸患者中,术后主动脉相对于脊柱的位置较术前向前内侧移位,术后2年较术后向后外侧移位。在使用椎弓根螺钉系统治疗特发性脊柱侧凸的手术中应该避免椎弓根螺钉穿出椎体前皮质或者椎弓根外侧皮质而导致主动脉损伤。     

椎弓根螺钉固定在脊柱侧凸治疗中的应用

目的　探讨椎弓根螺钉固定在脊柱侧凸治疗中的应用效果。方法　采用连续或间断椎弓根螺钉固定技术治疗 93例脊柱侧凸患者 ,平均年龄 14 .3岁 ,特发性 5 1例 ,先天性 4 2例 ,术前Cobb角分别为 71.2°和 6 8.3° ,根据畸形程度和脊柱柔韧性 ,采用一次性矫形或分期矫形。结果　特发性侧凸术后Cobb角和矫正率分别为 2 8.7°和 6 1.5 % ,先天性侧凸为 32 .6°和 5 3.8% ,无严重并发症发生。结论　椎弓根螺钉固定对脊柱产生撑开、加压及旋转矫正作用 ,其矫正力大 ;且不占据椎管空间。尽管胸椎椎弓根螺钉固定难度较大 ,风险较高 ,但因其能对脊柱产生撑开、加压及旋转矫正作用 ,矫正力大 ,且不占据椎管空间 ,因此在具备一定技术条件时 ,该方法应被推广应用     

青少年脊柱侧凸矫正术中胸椎椎弓根螺钉植入技术

[目的]探讨在青少年脊柱侧凸矫正术中胸椎椎弓根螺钉植入的力学基础及解剖学基础,并总结胸椎椎弓根螺钉植入的临床经验。[方法]应用胸腰椎椎弓根螺钉系统治疗青少年脊柱侧凸,通过比较手术前后冠状面矢状面Cobb′s角、顶椎移位、顶椎旋转的变化进行疗效评价。[结果]本组57例,随诊12~41个月,术前冠状面Cobb′s角平均67·8°,术后平均21·2°;矢状面畸形胸后突术前Cobb′s角平均51°,术后31·7°,平背畸形术前Cobb′s角平均10°,术后26·7°;顶椎旋转术前平均3·4°,术后1·7°;顶椎移位术前平均47mm,术后14·5mm。[结论]胸椎椎弓根螺钉贯穿脊柱三柱,能有效地控制整个椎体,具有三维固定和矫正功能,是一项矫正力强且安全可靠的技术,有利于对僵硬侧凸的矫正和控制。     

非影像监视下行脊柱侧凸胸椎椎弓根螺钉置入的临床应用

目的:探讨脊柱侧凸胸椎椎弓根螺钉非影像监视下徒手置入的方法及可行性。方法:57例脊柱侧凸患者行后路椎弓根螺钉系统矫形手术,徒手法置入胸椎椎弓根螺钉。术后常规拍摄脊柱全长X线片,随机选取10例患者行CT扫描观察,了解螺钉置入的准确性。结果:共置入胸椎椎弓根螺钉362枚。术后X线片观察到10枚螺钉偏外,4枚螺钉偏下,其中2枚螺钉引起轻微肋间神经痛,3周后完全缓解。CT观察47枚螺钉有2枚螺钉导致椎弓根内壁膨胀内移,没有相应神经症状。主弯Cobb角术前平均60.4°(32°～121°),术后平均18.3°(1°～70°),平均矫正率71.9%(38.1%～98.0%)。结论:徒手法置入脊柱侧凸胸椎椎弓根螺钉是可行的。     

中华长城椎弓根螺钉系统治疗青少年特发性脊柱侧凸

目的 :探讨中华长城椎弓根螺钉系统治疗青少年特发性脊柱侧凸的方法及临床效果。方法 :对 2 5例青少年特发性脊柱侧凸患者应用中华长城椎弓根螺钉系统行后路矫形手术。结果 :2 5例患者中侧凸平均矫正Cobb角 36 .7° ,矫正率 77%,经 18个月～ 3年随访 ,融合良好。结论 :中华长城椎弓根螺钉系统具有三维空间矫形力 ,矫形明显、持久 ,临床效果显著。     

后路半椎体切除椎弓根器械固定治疗小儿先天性脊柱侧凸

目的评价单纯后路半椎体切除椎弓根器械固定治疗小儿先天性脊柱侧凸的疗效。方法12例半椎体所致的先天性脊柱侧凸病例均行单纯后路半椎体切除椎弓根器械内固定术。结果12例均获得随访,时间6~42个月(平均18个月)。脊柱侧凸Cobb角由42.5°±6.7°纠正到16.2°±3.2°,纠正率64.7%。5例明显后凸的Cobb角由33.5°±5.2°纠正到13.3°±5.6°,纠正率53.2%。最后随访时侧凸和后凸分别为15.6°±5.8°和14.2°±3.3°,与术后相比无纠正丢失。无神经损伤、感染等并发症。结论单纯后路半椎体切除椎弓根器械内固定是早期治疗小儿先天性脊柱侧凸的有效术式,能够通过较短节段的融合获得满意的矫正,并且对小儿是一种相对简单、安全、微创的手术方法。     

后路凸侧椎板楔形截骨经肋椎关节松解胸椎间隙治疗青少年重度脊柱侧后凸

【摘要】 目的：评价经后路凸侧椎板楔形截骨经肋椎关节松解胸椎间隙矫形治疗青少年重度脊柱侧后凸畸形的安全性和早期临床效果。方法：2014年5月~2016年12月对我院15例青少年重度脊柱侧后凸患者行经后路凸侧椎板楔形截骨经肋椎关节松解胸椎间隙手术治疗,术前仅1例严重脊柱侧后凸患者行头盆环牵引。男6例,女9例,年龄13～18岁（16.1±1.6岁）。其中先天性脊柱侧后凸3例,特发性11例,神经纤维瘤病性1例。术前侧凸Cobb角82°～144°（102.5°±17.6°）,侧凸的柔韧性为6.4％～28.5％[（21.56±5.70）%];后凸50°～95°（68.1°±15.3°）,冠状位躯干偏移距离（C7中垂线与骶骨中垂线距离）2.0～6.8cm（3.40±1.37cm）。术前四肢肌力及感觉均正常。观察治疗效果。结果：椎板楔形截骨5.20±0.56个（4~6个）,松解椎间隙5.20±0.56个（4~6个）,手术时间6.1～7.9h（7.00±0.51h）,术中出血量1050～2500ml（1450.0±521.3ml）。术后侧凸Cobb角18°～40°（28.0°±6.6°）,矫正率72.5%;后凸22°～42°（27.8°±6.1°）,矫正率58.4%;冠状位躯干偏移距离0～2cm（0.85±0.74cm）,矫正率72.8%。随访25～41个月（33.1±5.4个月）。末次随访时侧凸Cobb角19°～43°（30.0°±6.9°）,矫正率70.6%;后凸22°～42°（28.6°±6.5°）,矫正率57.2%;冠状位躯干偏移距离0.2～2.3cm（1.10±0.72cm）,矫正率71.3%。无胸膜破裂,无假关节形成,无内固定断裂及松动,矫正度无显著丢失。1例患者术前骨盆牵引发生钉道感染,经局部换药及抗生素应用,2周后感染控制;1例术后第3天发生十二指肠系膜上动脉综合征,采取禁食水、持续胃肠减压、维持水电解质平衡、左侧卧位,术后2周痊愈;1例T4左侧椎弓根螺钉侵入椎管压迫神经,术后5h发生左下肢不完全性瘫痪,术后8h去除T4左侧椎弓根螺钉,术后5个月左下肢功能完全恢复。结论：采用后路凸侧椎板楔形截骨经肋椎关节松解胸椎间隙治疗青少年重度脊柱侧后凸畸形,不需要剥离椎体侧方胸膜,手术解剖层次表浅和创伤小,不仅有助于增加脊柱柔韧性,而且可提供足够的压缩和闭合空间来矫正脊柱侧后凸,能获得良好的脊柱三维矫正。     

多节段椎弓根螺钉内固定系统矫正胸椎侧凸畸形的有效性和安全性评价

目的:评价多节段椎弓根螺钉内固定系统矫正胸椎侧凸畸形的有效性和安全性。方法:回顾我院1994年3月～2002年3月应用椎弓根钉-棒系统矫治的118例胸椎侧凸畸形患者的临床资料,分析评价其手术并发症、侧凸矫正率及长期随访结果。结果:胸椎椎弓根总计置入螺钉916枚,术中及术后螺钉松动16枚;螺钉位置不良12枚;椎弓根骨折7例;脑脊液漏3例;1例术后螺钉松动压迫脊髓。术后平均随访5年,脊柱侧凸畸形平均矫正率为75%,平均矫正度丢失率1.2%,1例出现交界性后凸再次手术治疗。结论:多节段椎弓根螺钉内固定系统是矫正脊柱侧凸畸形一种较安全、有效的三维内固定方式。     

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.     

寰椎椎弓根进钉通道的数字解剖学研究

目的:探讨寰椎椎弓根进钉通道在矢状面角(SSA)为0°时不同水平面角(TSA)方向投影的变化规律。方法:将20例健康成年志愿者(男12例,女8例;年龄24~68岁,平均45岁)的寰椎CT连续断层扫描数据导入Mimics 10.01软件,三维重建寰椎数字解剖模型,将重建的结果以.stl格式保存,再将寰椎数字模型导入UG Imageware 12.0,建立寰椎椎弓根进钉通道数字化分析方法,确定三维参考平面,分析在SSA为0°时左右椎弓根TSA分别从0°～30°,均匀间隔5°,观察280个寰椎椎弓根进钉通道的长度和内切圆半径的变化规律。结果:280个寰椎椎弓根进钉通道的长度为20.54～33.21mm,其中11个通道长度小于最短椎弓根螺钉长度(22mm);TSA为0°进钉时左右通道长度均最大,左右侧比较无显著性差异(P0.05),5°～30°进钉时同一进钉角度左右侧比较有显著性差异(P0.05);同侧不同进钉角度比较无显著性差异(P0.05)。280个寰椎椎弓根螺钉通道的内切圆半径为1.38～2.51mm,其中有42个内切圆半径小于最小椎弓根螺钉半径(1.75mm);同一进钉角度右侧内切圆半径与左侧比较及同侧不同进钉角度比较均无显著性差异(P0.05)。结论:不同个体甚至同一个体的左右两侧椎弓根形态之间有较大差异。部分寰椎椎弓根进钉通道长度和内切圆半径小于椎弓根螺钉最小长度和最小半径,椎弓根进钉通道内切圆半径小于最小椎弓根螺钉半径时置钉会穿破椎弓根的皮质骨,不适合采用经寰椎椎弓根螺钉内固定技术。术前用数字化技术测量寰椎椎弓根进钉通道可以实现个体化置钉。     

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.     

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.     

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.