O型臂联合CT三维导航系统辅助颈椎椎弓根螺钉置入的准确性研究

目的:探讨O型臂联合CT三维导航系统辅助颈椎椎弓根螺钉置钉的准确性,并与侧块螺钉置钉进行比较.方法:回顾性分析2017年3月～2021年2月在我院分别使用O型臂联合CT三维导航系统辅助置入椎弓根螺钉与徒手置入侧块螺钉行颈椎后路内固定术的54例患者,其中男44例,女10例,年龄42～79岁(58.3±9.3岁).根据置钉...     

Robot-assisted and fluoroscopy-guided pedicle screw placement: a systematic review

Purpose

At present, most spinal surgeons undertake pedicle screw implantation using either anatomical landmarks or C-arm fluoroscopy. Reported rates of screw malposition using these techniques vary considerably, though the evidence generally favors the use of image-guidance systems. A miniature spine-mounted robot has recently been developed to further improve the accuracy of pedicle screw placement. In this systematic review, we critically appraise the perceived benefits of robot-assisted pedicle screw placement compared to conventional fluoroscopy-guided technique.

Methods

The Cochrane Central Register of Controlled Trials, PubMed, and EMBASE databases were searched between January 2006 and January 2013 to identify relevant publications that (1) featured placement of pedicle screws, (2) compared robot-assisted and fluoroscopy-guided surgery, (3) assessed outcome in terms of pedicle screw position, and (4) present sufficient data in each arm to enable meaningful comparison (>10 pedicle screws in each study group).

Results

A total of 246 articles were retrieved, of which 5 articles met inclusion criteria, collectively reporting placement of 1,308 pedicle screws (729 robot-assisted, 579 fluoroscopy-guided). The findings of these studies are mixed, with limited higher level of evidence data favoring fluoroscopy-guided procedures, and remaining comparative studies supporting robot-assisted pedicle screw placement.

Conclusions

There is insufficient evidence to unequivocally recommend one surgical technique over the other. Given the high cost of robotic systems, and the high risk of spinal surgery, further high quality studies are required to address unresolved clinical equipoise in this field.     

Techniques and accuracy of thoracolumbar pedicle screw placement

Pedicle screw instrumentation has been used to stabilize the thoracolumbar spine for several decades. Although pedicle screws were originally placed via a free-hand technique, there has been a movement in favor of pedicle screw placement with the aid of imaging. Such assistive techniques include fluoroscopy guidance and stereotactic navigation. Imaging has the benefit of increased visualization of a pedicle’s trajectory, but can result in increased morbidity associated with radiation exposure, increased time expenditure, and possible workflow interruption. Many institutions have reported high accuracies with each of these three core techniques. However, due to differing definitions of accuracy and varying radiographic analyses, it is extremely difficult to compare studies side-by-side to determine which techniques are superior. From the literature, it can be concluded that pedicles of vertebrae within the mid-thoracic spine and vertebrae that have altered morphology due to scoliosis or other deformities are the most difficult to cannulate. Thus, spine surgeons would benefit the most from using assistive technologies in these circumstances. All other pedicles in the thoracolumbar spine should theoretically be cannulated with ease via a free-hand technique, given appropriate training and experience. Despite these global recommendations, appropriate techniques must be chosen at the surgeon’s discretion. Such determinations should be based on the surgeon’s experience and the specific pathology that will be treated.     

Placement of pedicle screws in thoracic idiopathic scoliosis: a magnetic resonance imaging analysis of screw placement relative to structures at risk

In posterior pedicle screw instrumentation of thoracic idiopathic scoliosis, screw malposition might cause significant morbidity in tems of possible pleural, spinal cord, and aorta injury. Preoperative axial magnetic resonace images (MRI) in 12 consecutive patients with right thoracic adolescent scoliosis, all with King type 3 curves, were analyzed in order to evaluate the relationship between the inserted pedicle screw position to pleura, spinal cord, aorta. Axial vertebral images for each thoracic level were scanned and the simulation of pedicle screw insertion was performed using a digital measurement programme. The angular contact value for each parameter regarding the pleura and spinal cord was measured on both sides of the curve. The aorta-vertebral distance was also measured. Aorta-vertebral distance was found to be decreasing gradually from the cephalad to the caudad with the shortest distance being measured at T12 with a mean of 1.2 mm. Concave-sided screws on T5–T9 and convex-sided screws on T2–T3 had the greatest risk to spinal cord injury. Pleural injury is most likely on T4–T9 segments by the convex side screws. T4–T8 screws on the concave side and T11–T12 screws on the convex side may pose risk to the aorta. This MRI-based study demonstrated that in pedicle instrumentation of thoracic levels, every segment deserves special consideration, where computer scanning might be mandatory in immature spine and in patients with severe deformity.     

Accuracy and safety of pedicle screw placement in neuromuscular scoliosis with free-hand technique

It is a retrospective analytic study of 1,009 transpedicular screws (689 thoracic and 320 lumbosacral), inserted with free-hand technique in neuromuscular scoliosis using postoperative CT scan. The aim of paper was to determine the accuracy and safety of transpedicular screw placement with free-hand technique in neuromuscular scoliosis and to compare the accuracy at different levels in such population. All studies regarding accuracy and safety of pedicle screw in scoliosis represent idiopathic scoliosis using various techniques such as free-hand, navigation, image intensifier, etc., for screw insertion. Anatomies of vertebrae and pedicle are distorted in scoliosis, hence accurate and safe placement of pedicle screw is prerequisite for surgery. Between 2004 and 2006, 37 consecutive patients, average age 20 years (9–44 years), of neuromuscular scoliosis were operated with posterior pedicle screw fixation using free-hand technique. Accuracy of pedicle screws was studied on postoperative CT scan. Placement up to 2 mm medial side and 4 mm lateral side was considered within-safe zone. Of the 1,009 screws, 273 screws were displaced medially, laterally or on the anterior side showing that 73% screws (68% in thoracic and 82.5% in lumbar spine) were accurately placed within pedicle. Considering the safe zone, 93.3% (942/1009, 92.4% in thoracic and 95.3% in lumbar spine) of the screws were within the safe zone. Comparing accuracy according to severity of curve, accuracy was 75% in group 1 (curve <90°) and 69% in group 2 (curve >90°) with a safety of 94.8 and 91.2%, respectively (P = 0.35). Comparing the accuracy at different thoracic levels, it showed 67, 64 and 72% accuracy in upper, middle and lower thoracic levels with safety of 96.6, 89.2 and 93.1%, respectively, exhibiting no statistical significant difference (P = 0.17). Pedicle screw placement in neuromuscular scoliosis with free-hand technique is accurate and safe as other conditions.     

低龄儿童脊柱侧凸矫正术中椎弓根螺钉置入的精确性和安全性评估

目的:评估10岁及以下脊柱侧凸患儿侧凸矫正术中椎弓根螺钉置入的精确性及安全性,并分析其相关影响因素。方法:回顾性分析2008年2月~2008年7月我院收治的行后路椎弓根螺钉固定的10岁及以下脊柱侧凸41例患儿的临床资料,所有患者术前、术后均行CT检查,男26例,女15例,年龄2~10岁,平均5.4岁。先天性脊柱侧凸36例,特发性脊柱侧凸2例,神经肌肉源性脊柱侧凸2例,先天性软骨发育不全伴脊柱侧凸1例。术中根据解剖标志徒手置入椎弓根螺钉。在PACS系统上通过Pacs Client软件测量螺钉尖距椎弓根内壁、外壁、上壁、下壁以及椎体前缘的距离。若左侧椎弓根螺钉穿破椎弓根外壁或椎体前缘,测量钉尖与主动脉的距离。根据椎弓根螺钉所在位置(节段、凹凸侧、脊椎发育是否异常)分析其破壁率差别。不良置钉定义为椎弓根螺钉穿破椎弓根内、外壁或椎体前缘的距离超过2mm,和椎弓根螺钉进入椎间孔或穿破终板进入椎间盘。结果:本组病例共置入242枚椎弓根螺钉,胸椎128枚,腰椎114枚,平均每例患者置入5.8枚螺钉。螺钉完全在椎弓根内208枚,占86.0%。破壁34枚(占14.0%),其中不良置钉18枚(占7.4%),18枚中有5枚穿破外壁,8枚穿破内壁,5枚穿破椎体前缘。形态异常椎和凹侧的椎弓根螺钉的破壁率较高(分别为24.1%和17.9%)。术中一枚螺钉拔出,未出现其他螺钉置入相关并发症。穿破椎体前缘螺钉距离主动脉距离平均2.3mm。结论:10岁及以下儿童椎弓根螺钉的徒手置入有较高的精确性和安全性,但在发育不良椎体及凹侧置钉时应谨慎。     

胸腰椎椎弓根螺钉误置的原因分析及对策

目的 探讨胸腰椎椎弓根螺钉误置的原因及对策。方法 1996-2002年对293例脊柱疾病患者施行椎弓根螺钉内固定术发生的螺钉误置情况进行回顾性总结，分析。结果 293例共置入椎弓根螺钉1256枚，螺钉植入节段错误7例，占2.38%；上胸椎（T2-7）置钉113枚，有11枚螺钉穿破椎弓根皮质，占9.74%；下胸椎（T8-12）置钉261枚，有9枚螺钉穿破椎弓根皮质，占3.45%；腰骶椎置钉882枚，有16枚穿破椎弓根皮质，占1.81%，共计36枚螺钉，占2.87%；螺钉角异常65枚，占5.81%。结论 椎弓根螺钉误置与操作技术，解剖学变异及脊柱病损因素密切相关；良好的手术技巧，术前影像资料的认真观测及术中必要的影像监控是准确置钉的关键。     

骨科机器人辅助下脊柱椎弓根螺钉置入准确性与安全性的临床研究

目的:探讨骨科机器人与C形臂X线透视辅助下脊柱椎弓根螺钉置入的准确性与安全性.方法:对2019年1月至2020年8月采用外科治疗的36例脊柱疾患病例进行回顾性分析.36例患者中18例采用骨科机器人辅助下的椎弓根螺钉置入(观察组),男12例,女6例;年龄16～61 (38.44±3.60)岁;青少年脊柱侧弯1例,脊柱结核...     

Early complications of spinal pedicle screw

The complications of 648 consecutively inserted Universal AO pedicle screws (140 in the thoracic spine and 508 in the lumbar spine) performed by one surgical team to treat 91 patients with spinal problems, were reviewed. The spinal pathology consisted of: scoliosis (34 patients), degenerative lower lumbar spinal disease (25 patients), neoplastic spinal disease (11 patients), thoracic kyphosis (8 patients), spinal fractures (7 patients), lumbo-sacral spondylolisthesis (3 patients), and osteomyelitis (3 patients). Intraoperative complications were: screw misplacement (n = 3), nerve root impingement (n = 1), cerebrospinal fluid leak (n = 2) and pedicle fracture (n = 2). Postoperative complications were; deep wound infection (n = 4), screw loosening (n = 2) and rod-screw disconnection (n = 1). The conclusion was that pedicle screw fixation has an acceptable complication rate and neurological injury during this procedure is unlikely.     

Accuracy of pedicle screw placement: a systematic review of prospective in vivo studies comparing free hand,fluoroscopy guidance and navigation techniques

Introduction  

With the advances and improvement of computer-assisted surgery devices, computer-guided pedicle screws insertion has been applied to the lumbar, thoracic and cervical spine. The purpose of the present study was to perform a systematic review of all available prospective evidence regarding pedicle screw insertion techniques in the thoracic and lumbar human spine.     

青少年特发性脊柱侧凸应用Ball tip技术置入椎弓根钉的准确性

目的针对需要手术治疗的青少年特发性脊柱侧凸,通过与传统徒手置钉技术比较来评价一种新的椎弓根置钉技术—Ball tip技术置入椎弓根钉的准确性。方法自2009年5月~2011年5月,对28例青少年特发性脊柱侧凸,术中应用椎弓根球形探针(ball tip probe)置入椎弓根。结果采用Ball tip技术共置入193枚椎弓根钉,传统徒手技术置入161枚螺钉。术后CT扫描显示Ball tip组椎弓根钉钉道准确率为89.1%,共有21枚(10.9%)置钉不良螺钉,其中5枚(2.6%)穿透椎弓根内侧骨皮质,16枚(8.3%)穿透外侧骨皮质。徒手置钉组准确率为75.2%,共有40枚(24.8%)置钉不良螺钉,其中11枚(6.8%)穿透椎弓根内侧骨皮质,29枚(18.0%)穿透外侧骨皮质。两组置钉准确率的差异具有统计学意义(P<0.01),两组螺钉穿透椎弓根内侧、外侧骨皮质的差异具有统计学意义(P<0.05)。结论与传统徒手置钉技术相比,椎弓根Ball tip技术,可准确地置入椎弓根钉,减少因螺钉误置所导致的术后并发症。     

青少年脊柱侧凸患者胸椎椎弓根螺钉置入的准确性和安全性评价

目的：探讨青少年脊柱侧凸患者胸椎椎弓根螺钉置入的准确性和安全性，以减少相关手术并发症。方法：32例青少年脊柱侧凸患者术前均对畸形脊柱进行标准俯卧位CT加密扫描，测量进钉点至椎体前缘的深度、进针角度、椎弓根直径和椎体的旋转角度，根据测得数据确定椎弓根螺钉置入的深度和方向，置入螺钉后再行脊柱全长X线片及CT扫描评价置钉的准确性和安全性。结果：32例共置入226枚胸椎椎弓根螺钉，术后CT加密和X线片观察到205枚螺钉（90．7％）完全在椎弓根皮质骨内。10例21枚螺钉（9.3％）发生错置，7枚螺钉（3．1％）偏外，5枚螺钉（2．2％）偏前外侧（其中2枚螺钉靠近节段血管），4枚螺钉（1．8％）偏下，4枚螺钉（1．8％）直径过大导致椎弓根内壁膨胀内移，1枚螺钉（0．4％）误入椎管导致完全性脊髓损伤。T1～T4错置12枚（18．2％），T5～T12错置9枚（6．1％）；凸侧椎根螺钉置入的准确率为93．8％，凹侧为83．1％。结论：脊柱畸形患者术前应常规采用标准俯卧位CT加密扫描，根据扫描图像测得的相关数据可为术中准确置入椎弓根螺钉提供重要参考依据。在青少年脊柱侧凸患者胸椎椎弓根螺钉置入有一定的误置率，螺钉发生错置多见于上胸椎和凹侧．术中应高度重视。     

计算机导航辅助椎弓根螺钉固定

目的将计算机导航技术应用于临床椎弓根螺钉固定并做仞步分析。方法2004年2～12月在计算机导航系统辅助下，对30例患(年龄18～60岁，平均45．3岁)共行134枚椎弓根螺钉固定。结果手术顺利，未发生血管和神经损伤并发症，螺钉大小选择合适，固定位置及方向准确．术中透视次数及手术室人员所受X线辐射量明显减少。结论计算机导航辅助椎弓根螺钉固定是一项安全的手术，且手术精度高。     

O型臂3D导航与徒手置钉在上颈椎椎弓根螺钉置入中的精确性比较

目的 :比较O型臂3D导航下C1、C2椎弓根螺钉置钉与徒手置钉精确性的差异,探讨O型臂导航在上颈椎椎弓根螺钉置钉中的应用价值。方法:纳入我院C1、C2椎弓根螺钉内固定患者62例,分为导航置钉组(A组)与徒手置钉组(B组)。A组:2014年1月~2015年3月,O型臂导航下行C1、C2后路椎弓根螺钉内固定术22例,男15例,女7例,年龄17~58岁(40.8±12.7岁);B组:2005年3月~2013年12月经徒手置入C1及C2椎弓根螺钉患者40例,男26例,女14例,年龄12~70岁(42.0±15.6岁)。所有患者术后均行颈椎CT平扫,按照Neo等的方法,根据椎弓根螺钉穿破椎弓根皮质的程度将置钉精确性分为四级(0级,螺钉完全处于椎弓根中,没有穿破骨皮质;1级,螺钉穿破皮质2mm,或小于螺钉直径的50%;2级,螺钉穿破皮质≥2mm且﹤4mm,或大于螺钉直径的50%但没完全穿出;3级,完全穿出皮质,螺钉处于椎管或椎动脉孔内),分别评估两组的置钉精确性并比较两组间的差异。结果:A组共置入C1、C2椎弓根螺钉67枚(C1 28枚,C2 39枚),其中0级60枚(89.6%),1级7枚(10.4%),无2级或3级不良置钉;B组共置入C1、C2椎弓根螺钉134枚(C1 64枚,C2 70枚),其中0级116枚(86.6%),1级13枚(9.7%),2级4枚(3.0%),3级1枚(0.7%)。两组间置钉精确性分级(P=0.49)及0级置钉率(P=0.55)均无统计学差异;A组未发现不良置钉,B组不良置钉发生率为3.7%,但组间无统计学差异(P=0.17)。两组均无置钉相关的血管、神经并发症发生。结论:术中O型臂导航与徒手置钉在上颈椎椎弓根螺钉置钉精确性上并无统计学差异,虽然导航能提供清晰的术中3D图像,但该技术未能完全避免置钉时螺钉轻度穿破骨皮质的发生,仍需提高术者与导航系统间的交互作用,完善操作技术,进一步提高置钉精确性。     

脊柱机器人置钉错误的多因素分析

目的 探讨Renaissance机器人系统辅助椎弓根螺钉置入错误的危险因素。方法 回顾性分析2017年6月至2019年12月在西安交通大学医学院附属红会医院脊柱病医院使用Renaissance机器人系统辅助椎弓根螺钉置入的162例（1 023枚螺钉）的临床资料。根据术后CT平扫结果对螺钉进行Gertzbein Robbins评级,被评估为A级和B级的螺钉纳入满意组,被评估为C级、D级、E级、术中调整螺钉及非技术原因导致的无法注册的螺钉纳入不满意组。计算置钉成功率和准确率。将年龄、性别、身体质量指数（body mass index, BMI）、骨密度以及疾病类型、椎体旋转程度和螺钉置入类型（经皮植入或开放植入）进行单因素分析筛选危险因素,再采用多因素Logistic回归分析确定机器人置钉错误的独立危险因素。结果 有37枚螺钉注册失败,术后共评估986枚螺钉;满意组897枚,不满意组126枚,置钉成功率为87.67%（897/1 023）,置钉准确率为90.97%（897/986）。经二元Logistic回归分析,机器人辅助置钉错误的独立危险因素为肥胖、骨质疏松、椎体重度旋转和先天性脊柱侧凸。结论 肥胖、骨质疏松、椎体重度旋转和先天性脊柱侧凸是导致机器人辅助置钉错误的危险因素;建议避免病例存在单个或多个危险因素,以确保手术的安全性。     

Robotic-assisted pedicle screw placement: lessons learned from the first 102 patients

Introduction

Surgeons’ interest in image and/or robotic guidance for spinal implant placement is increasing. This technology is continually improving and may be particularly useful in patients with challenging anatomy. Only through careful clinical evaluation can its successful applications, limitations, and areas for improvement be defined. This study evaluates the outcomes of robotic-assisted screw placement in a consecutive series of 102 patients.

Methods

Data were recorded from technical notes and operative records created immediately following each surgery case, in which the robotic system was used to guide pedicle screw placement. All cases were performed at the same hospital by a single surgeon. The majority of patients had spinal deformity and/or previous spine surgery. Each planned screw placement was classified as: (1) successful/accurately placed screw using robotic guidance; (2) screw malpositioned using robot; (3) use of robot aborted and screw placed manually; (4) planned screw not placed as screw deemed non essential for construct stability. Data from each case were reviewed by two independent researchers to indentify the diagnosis, number of attempted robotic guided screw placements and the outcome of the attempted placement as well as complications or reasons for non-placement.

Results

Robotic-guided screw placement was successfully used in 95 out of 102 patients. In those 95 patients, 949 screws (87.5 % of 1,085 planned screws) were successfully implanted. Eleven screws (1.0 %) placed using the robotic system were misplaced (all presumably due to “skiving” of the drill bit or trocar off the side of the facet). Robotic guidance was aborted and 110 screws (10.1 %) were manually placed, generally due to poor registration and/or technical trajectory issues. Fifteen screws (1.4 %) were not placed after intraoperative determination that the screw was not essential for construct stability. The robot was not used as planned in seven patients, one due to severe deformity, one due to very high body mass index, one due to extremely poor bone quality, one due to registration difficulty caused by previously placed loosened hardware, one due to difficulty with platform mounting and two due to device technical issues.

Conclusion

Of the 960 screws that were implanted using the robot, 949 (98.9 %) were successfully and accurately implanted and 11 (1.1 %) were malpositioned, despite the fact that the majority of patients had significant spinal deformities and/or previous spine surgeries. “Tool skiving” was thought to be the inciting issue with the misplaced screws. Intraoperative anteroposterior and oblique fluoroscopic imaging for registration is critical and was the limiting issue in four of the seven aborted cases.     

CT-navigation versus fluoroscopy-guided placement of pedicle screws at the thoracolumbar spine: single center experience of 4,500 screws

Purpose

Single center evaluation of the placement accuracy of thoracolumbar pedicle screws implanted either with fluoroscopy or under CT-navigation using 3D-reconstruction and intraoperative computed tomography control of the screw position. There is in fact a huge variation in the reported placement accuracy of pedicle screws, especially concerning the screw placement under conventional fluoroscopy most notably due to the lack of the definition of screw misplacement, combined with a potpourri of postinstrumentation evaluation methods.

Methods

The operation data of 1,006 patients operated on in our clinic between 1995 and 2005 is analyzed retrospectively. There were 2,422 screws placed with the help of CT-navigation compared to 2,002 screws placed under fluoroscopy. The postoperative computed tomography images were reviewed by a radiologist and an independent spine surgeon.

Results

In the lumbar spine, the placement accuracy was 96.4 % for CT-navigated screws and 93.9 % for pedicle screws placed under fluoroscopy, respectively. This difference in accuracy was statistically significant (Fishers Exact Test, p = 0.001). The difference in accuracy became more impressing in the thoracic spine, with a placement accuracy of 95.5 % in the CT-navigation group, compared to 79.0 % accuracy in the fluoroscopy group (p < 0.001).

Conclusion

This study underlines the relevance of CT-navigation-guided pedicle screw placement, especially when instrumentation of the middle and upper thoracic spine is carried out.     

枢椎椎动脉孔分型对枢椎椎弓根置钉的临床意义

目的:探讨基于椎动脉走行的枢椎椎动脉孔分型在枢椎椎弓根置钉中的应用价值;方法:30例共60个枢椎椎弓根,术前接受薄层CT扫描,根据扫描图像上椎动脉入口与椎管外壁的最小距离和椎动脉球部的高度将枢椎椎动脉孔分为Ⅰ(松散低拐)、Ⅱ(紧密高拐)、Ⅲ(紧密低拐)、Ⅳ(松散高拐)型,并测量椎弓根长度、内倾角等指标,为手术提供参考。结果:枢椎椎动脉孔Ⅰ型44个、Ⅱ型8个、Ⅲ型6个、Ⅳ型2个。Ⅰ、Ⅲ、Ⅳ型共52个椎弓根实施螺钉固定,术后CT钉道扫描显示48个椎弓根螺钉位于椎弓根管内,位置良好;4个椎弓根螺钉偏外,指向或进入椎动脉孔,无螺钉偏内侧者。置钉成功率92.3%,椎动脉损伤风险率7.7%。结论:术前对患者枢椎椎弓根进行螺旋CT薄层扫描后测量相关数据,根据椎动脉孔的相关参数进行分型,有助于提高枢椎椎弓根螺钉的置钉成功率。     

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。     

Accuracy of pedicle screw insertion: A prospective CT study in 30 low back patients

A prospective study of the accuracy of titanium pedicle screw placement in 30 low back operations was performed. The postoperative plain radiographs and CT reformation images were evaluated by two independent radiologists. Thirty-two out of 152 screws (21%) perforated the pedicle cortex. One-tenth of the perforations was detected with conventional radiography. In ten patients (33%) all the screws were located within the pedicle. The clinical significance of this study lies in the finding that pedicle perforations are more frequent than is generally believed and that, in spite of the many malplacements, no screw that perforated by less than 4.0 mm caused neurological problems. Only one nerve root lesion was detected.