The contralateral lamina: a reliable guide in subaxial,cervical pedicle screw placement

We have assessed the clinical observation that the angle of the contralateral lamina matches the angle required from the sagital plane for the placement of pedicle screws in the subaxial cervical spine. Fifty-four randomly chosen axial CT scans taken between December 2003 and December 2004 were examined. Subjects were excluded if the scan showed signs of fracture, tumour or gross abnormality. The digitised images were analysed on the Philips PACS system using SECTRA software. One hundred and sixty-eight individual vertebrae were assessed between C3 and C7. The following were measured; the angle of the pedicle relative to the sagital plane, the smallest internal and external diameter of the pedicles and the angle of the lamina. Angular measures had a CV% of 3.9%. The re-measurement error for distance was 0.5 mm. Three hundred and thirty-six pedicles were assessed in 25 females and 29 males. Average age was 48.2 years (range 17–85). Our morphologic data from live subjects was comparable to previous cadaveric data. Mean pedicle external diameter was 4.9 mm at C3 and 6.6 mm at C7. Females were marginally smaller than males. Left and right did not significantly differ. In no case was the pedicle narrower than 3.2 mm. Mean pedicle angle was 130° at C3 and 140° at C7. The contralateral laminar angle correlated well at C3, 4, 5 (R ² = 0.9, C3 P = 0.002, C4 P = 0.06, C5 P = 0.0004) and was within 1° of pedicle angle. At C6, 7 it was within 11°. In all cases a line parallel to the lamina provided a safe corridor of 3 mm for a pedicle implant. The contralateral lamina provides a reliable intraoperative guide to the angle from the sagital plane for subaxial cervical pedicle instrumentation in adults.     

颈椎椎弓根个体化固定技术治疗261例颈椎疾患临床观察

目的:探讨颈椎椎弓根内固定技术在颈椎疾患的个体化方案设计及临床疗效。方法:对261例颈椎疾患,置入1102枚椎弓根螺钉,其中上颈椎疾患83例,下颈椎疾患178例。应用图像存储传输系统(picture archiving and communication system,PACS),采用X线片及64排CT片,对2 000例正常人颈椎椎弓根的冠状位、矢状位、横断位进行精确测量,得出中国人椎弓根的长度、宽度、高度、向内侧倾斜、向头、尾侧倾斜角度的数据值。术前对每位患者拟固定颈椎的椎弓根精确测量,术中应用自制的颈椎椎弓根定位导向器,准确定位入钉点及角度。结果:一次成功1 086枚,16枚经调整后成功,一次成功率98.55%。术后235例患者获12～73个月随访,平均随访时间18.74个月。采用JOA评分标准[1],优131例,良82例,可17例,差5例,优良率88.1%。所有患者X线片示寰椎完全复位,枢椎齿状突骨折处对位良好,均获得骨性融合,未发现钉板断裂。CT片示螺钉与椎动脉及脊髓位置关系良好。下颈椎患者中,15例患者16枚椎弓根螺钉术后拍片位置不理想,行二次手术调整,无脊髓及椎动脉损伤。119例骨折脱位的患者中117例完全复位,融合率为98.3%。结论:应用椎弓根技术治疗颈椎疾患可以获得即刻三维稳定,融合率高,是一种可行值得推广的方法。     

The anatomic variability of human cervical pedicles: considerations for transpedicular screw fixation in the middle and lower cervical spine

Transpedicular screw fixation has recently been shown to be successful in stabilizing the middle and lower cervical spine. Controversy exists, however, over its efficacy, due to the smaller size of cervical pedicles and the proximity of significant neurovascular structures to both lateral and medial cortical walls. To aid the spinal surgeon in the insertion of pedicle screws, a number of studies have been performed to quantify the gross dimensions and angulations of the cervical pedicle. Notwithstanding these quantitative studies, there has been a conspicuous absence of research reporting the qualitative characteristics of the cervical pedicle. The purpose of our study was to provide comparative graphical data that would systematically document the anatomic variability in cervical pedicle morphology. Such information should better elucidate the complexity of the pedicle as a three-dimensional structure and provide the spinal surgeon with a more complete understanding of cervical pedicle architecture. Twenty-six human cervical vertebrae (C3–C7) from six fresh-frozen spines were secured to a thin sectioning apparatus to produce three 0.7-mm- thick pedicle slices along its axis. Radiographs taken of these pedicle slices were scanned, digitized, and traced to facilitate visual comparison. The pedicle slices were found to exhibit substantial variability in composition and shape, not only between individual spines and vertebral levels, but also within the pedicle axis. However, the lateral cortex was consistently found to be thinner than the medial cortex in all samples. These physical findings must be noted by surgeons attempting transpedicular screw fixation in the cervical spine. Received: 3 May 1999/Revised: 13 August 1999/Accepted: 21 August 1999     

Transpedicular screw fixation

Spinal fixation employing transpedicular screws has recently been the focus of increased attention at various institutions throughout the world, but concerns about the safety and efficacy of transpedicular screws linger. This study was undertaken to address some of these concerns. The study included evaluation of the internal and external morphology of the vertebral pedicles, which revealed that adequate bone stock is generally available at T2, T7, T12, and L1-L5 spinal levels to accept screws in the 4-7-mm diameter range. The pedicle was observed to be composed of abundant cancellous bone internally with relatively thick cortical walls. The method of pilot hole preparation for pedicle screws was also examined. Screws inserted in pilot holes prepared with a 3.4-mm blunt probe (ganglion knife) resulted in higher pullout forces in eight of 10 trials as compared with those with pilot holes prepared using a 3.2-mm drill. Furthermore, the probes afford greater control of hole depth and alignment. Fatigue studies on three screw designs revealed a graduation of strength between a 7.0-mm pedicle screw, a 5.5-mm pedicle screw, and a modified 6.5-mm cancellous lag screw. The modified cancellous lag screw has an inherent stress riser that affected fatigue life. It was noted that extreme care must be exercised to prevent bending of the pedicle screws during implantation. If bending occurs one can expect a 50% reduction in the number of cycles to failure.     

Complexity of the thoracic spine pedicle anatomy

Transpedicular screw fixation provides rigid stabilization of the thoracolumbar spine. For accurate insertion of screws into the pedicles and to avoid pedicle cortex perforations, more precise knowledge of the anatomy of the pedicles is necessary. This study was designed to visualize graphically the surface anatomy and internal architecture of the pedicles of the thoracic spine. Fifteen vertebrae distributed equally among the upper, middle, and lower thoracic regions were used. For the purpose of mapping surface anatomy, each pedicle was cleaned, spraypainted white, and marked with more than 100 fine points. Using an optoelectronic digitizer, three-dimensional coordinates of the marked points and three additonal points, representing a coordiate system, were digitized. A solid modeling computer program was used to create three-dimensional surface images of the pedicle. To obtain cross-sectional information, each pedicle was sectioned with a thin diamond-blade saw to obtain four slices, 1 mm in thcikness and 0.5 mm apart. The pedicle slices were X-rayed and projected onto a digitizer. The internal and external contours were digitized and converted into graphs by a computer. The pedicles exhibited significant variability in their shape and orientation, not only from region to region within the thoracic spine, but also within the same region and even within the same pedicle. These variations are extremely significant in light of current techniques utilized in transpedicular screw fixation in the thoracic spine. Information documenting the three-dimensional complexity of pedicle anatomy should be valuable for surgeons and investigators interested in spinal instrumentation.