Ludwig S C, Kramer D L, Balderston R A, Vaccaro A R, Foley K F, Albert T J
Department of Orthopaedic Surgery, Milton S. Hershey Medical Center, Pennsylvania State College of Medicine, Hershey, PA, USA.
Spine (Phila Pa 1976). 2000 Jul 1;25(13):1655-67. doi: 10.1097/00007632-200007010-00009.
This investigation was conducted in two parts. In the first part, a morphometric analysis of critical cervical pedicle dimensions were measured to create guidelines for cervical pedicle screw fixation based on posterior cervical topography. In the second part of the study, a human cadaver model was used to assess the accuracy and safety of transpedicular screw placement in the subaxial spine using three different surgical techniques: 1) using surface landmarks established in the first part of the study, 2) using supplemental visual and tactile cues provided by performing laminoforaminotomies, and 3) using a computer-assisted surgical guidance system.
To assess the accuracy of transpedicular screw placement in the cervical spine using three surgical techniques.
A three-column fixation device implanted to secure an unstable cervical spine can be a valuable tool with a biomechanical advantage in the spine surgeon's armamentarium. Despite this advantage, concerns over surgical neurovascular complications have surfaced. Cadaver-based morphometric measurements used to guide the surgeon in the placement of a pedicle screw show significant variability, raising legitimate concerns as to whether transpedicular fixation can be applied safely.
Precise measurements of 14 human cadaveric cervical spines were made by two independent examiners of pedicle dimensions, angulation, and offset relative to the lateral mass boundaries. On the basis of this analysis, guidelines for pedicle screw placement relative to posterior cervical topography were derived. In the second part of the study, 12 human cadaveric cervical spines were instrumented with 3.5-mm screws placed in the pedicles C3-C7 according to one of three techniques. Cortical integrity and neurovascular injury were then assessed by obtaining postoperative computed tomography scans (1-mm cuts) of each specimen. Cortical breaches were classified into critical or noncritical breaches.
Linear measurements of pedicle dimensions had a wide range of values with only fair interobservercorrelation. Angular measurements showed similarangulation in the transverse plane (40 degrees ) at each level. With respect to the sagittal plane, both C3 and C4 pedicles were oriented superiorly relative to the axis of the lateral mass, whereas the C6 and C7 pedicles were oriented inferiorly. The dorsal entry point of the pedicle on the lateral mass defined by transverse and sagittal offset had similar mean values with wide ranges, although there often was excellent correlation between observers. There were no significant interlevel, right/left, or male/female differences noted with respect to offset. Using one of three techniques, 120 pedicles were instrumented. In group 1 (morphometric data): 12.5% of the screws were placed entirely within the pedicle; 21.9% had a noncritical breach; and 65. 5% had a critical breach. In group 2 (laminoforaminotomy), 45% of the screws were within the pedicle; 15.4% had a noncritical breach; and 39.6% had a critical breach. In group 3 (computer-assisted surgical guidance system), 76% of the screws were entirely within the pedicle; 13.4% had a noncritical breach; and 10.6% had a critical breach. Regardless of the technique used, the vertebral artery was the structure most likely to be injured.
On the basis of the morphometric data, guidelines for cervical spine pedicle screw placement at each subaxial level were derived. Although a statistical analysis of cadaveric morphometric data obtained from the cervical spine could provide guidelines for transpedicular screw placement based on topographic landmarks, sufficient variation exists to preclude safe instrumentation without additional anatomic data. Insufficient correlation between different surgeons' assessments of surface landmarks attests to the inadequacy of screw insertion techniques in the cervical spine based on such specific topographic guide
本研究分为两个部分。第一部分，对颈椎关键椎弓根尺寸进行形态测量分析，以根据颈椎后路形态创建颈椎椎弓根螺钉固定的指导方针。在研究的第二部分，使用人体尸体模型，采用三种不同的手术技术评估下颈椎经椎弓根螺钉置入的准确性和安全性：1）使用在研究第一部分中确定的表面标志；2）使用通过椎板间孔切开术提供的补充视觉和触觉线索；3）使用计算机辅助手术导航系统。
使用三种手术技术评估颈椎经椎弓根螺钉置入的准确性。
植入用于固定不稳定颈椎的三柱固定装置，在脊柱外科医生的器械库中是一种具有生物力学优势的宝贵工具。尽管有此优势，但手术神经血管并发症的问题也已出现。用于指导外科医生放置椎弓根螺钉的基于尸体的形态测量显示出显著的变异性，这引发了对经椎弓根固定能否安全应用的合理担忧。
由两名独立检查人员对14具人体尸体颈椎的椎弓根尺寸、角度和相对于侧块边界的偏移进行精确测量。基于此分析，得出相对于颈椎后路形态的椎弓根螺钉置入指导方针。在研究的第二部分，根据三种技术之一，在12具人体尸体颈椎上，于C3 - C7椎弓根置入3.5毫米螺钉。然后通过获取每个标本的术后计算机断层扫描（1毫米层厚）评估皮质完整性和神经血管损伤情况。皮质破裂分为严重或非严重破裂。
椎弓根尺寸的线性测量值范围广泛，观察者间的相关性一般。角度测量显示每个节段在横断面的角度相似（40度）。在矢状面，C3和C4椎弓根相对于侧块轴线向上，而C6和C7椎弓根向下。由横向和矢状偏移确定的侧块上椎弓根的背侧入点的平均值相似但范围较宽，尽管观察者之间通常有很好的相关性。在偏移方面未发现节段间、左右或男女之间存在显著差异。使用三种技术之一，共置入120枚椎弓根螺钉。在第1组（形态测量数据组）：12.5%的螺钉完全置入椎弓根内；21.9%有非严重破裂；65.5%有严重破裂。在第2组（椎板间孔切开术组），45%的螺钉在椎弓根内；15.4%有非严重破裂；39.6%有严重破裂。在第3组（计算机辅助手术导航系统组），76%的螺钉完全置入椎弓根内；13.4%有非严重破裂；10.6%有严重破裂。无论使用何种技术，椎动脉都是最易受损的结构。
基于形态测量数据，得出每个下颈椎节段颈椎椎弓根螺钉置入的指导方针。尽管对从颈椎获得的尸体形态测量数据进行统计分析可为基于地形标志的经椎弓根螺钉置入提供指导方针，但存在足够的变异性，若无额外的解剖数据则无法确保安全置入。不同外科医生对表面标志评估之间的相关性不足，证明基于此类特定地形指导的颈椎螺钉置入技术不够完善。
