Cho Woojin, Le Jason T, Shimer Adam L, Werner Brian C, Glaser John A, Shen Francis H
*Department of Orthopaedic Surgery, Albert Einstein College of Medicine, Bronx, NY †Department of Orthopaedic Surgery, University of Virginia School of Medicine, Charlottesville, VA ‡Department of Orthopaedic Surgery, Medical University of South Carolina, Charleston, SC.
Clin Spine Surg. 2017 Jun;30(5):E535-E539. doi: 10.1097/BSD.0000000000000159.
A cadaveric study.
Translaminar screws were initially developed for C2 fixation. Since then, their usage has expanded to include the subaxial cervical spine, and thoracic and lumbar spine. To the best of our knowledge, special anatomy for inserting translaminar screws in the subaxial cervical spine has not been studied.
To report the special anatomy for inserting translaminar screws in the subaxial cervical spine.
A total of 18 cadaveric spines were harvested from C3 to C7 and 1 mm computed tomography (CT) scans and 3D reconstructions were obtained. Bilateral translaminar screw entry points and trajectories were simulated at each level from C3 to C7 utilizing Kodak Carestream/Pacs Ver 10.2. Constructs were selected to achieve maximal bony purchase with 1 screw, designated the "primary screw." The contralateral screw, designated the "secondary screw," was selected to achieve the optimal allowable diameter possible while avoiding a simulated cortical breach, which was not always necessarily the "best purchase" diameter. Initial screw diameters selected were 3.5 mm; however, in the event that a narrower portion was encountered, then a 3.0 mm diameter screw was utilized instead. The crossing area of both screws were calculated geometrically. Maximal thickness of the lamina was considered in determining the diameter of screws. Whenever possible, 3.5 mm screws were selected in both lamina (3.5/3.5 mm); however, if a 3.5 mm screw was utilized as the primary screw, but the permissible range (P) for the secondary screw was <3.5 mm, then a hybrid construct was utilized (3.5/3.0 mm). In cases where P was <3 mm, then both screws were studied at 3 mm (3.0/3.0 mm). Screw diameters that optimized trajectory and bony purchase, while remaining within the permissible range, were analyzed, tabulated, and recorded. On CT, along the trajectory of the screws, the image was cut and measured in terms of screw length, the narrowest portion of the lamina, vertical angle, and horizontal angle in both primary and secondary screws. On the individually separated cervical spine segments in cadavers (11 of 18), we performed caliper measurements on the same portions that were measured on CT. It could not be exactly the same portions, however, due to the 3-dimensional characteristics of the specimens.
For C3, only 1 specimen allowed 2 screws (3/3 mm), while the remaining specimens permitted a unilateral primary screw (3.5 or 3 mm) only. For C4, 37% of specimens allowed 2 screws (3.5/3 mm or 3/3 mm), but the rest allowed only a unilateral primary screw (3.5 or 3 mm). For C5, 58% allowed 2 screws (3.5/3.5, 3.5/3, or 3/3 mm). For C6, 89% of specimen allowed 2 screws (3.5/3.5, 3.5/3, or 3/3 mm). For C7, all levels allowed 2 screws (3.5/3.5, 3.5/3, 4/4, 4/3, 4.5/3, 4.5/3.5, or 4/3.5 mm). On CT, the average lengths of the 1- and 2-degree screws were 26.14 and 24.01 mm, respectively. The average vertical and horizontal angles were 22.26 and 40.66 degrees for the 1-degree screw, and 3.45 and 45.59 degrees for the 2-degree screw. On cadavers, the average lengths of the 1- and the 2-degree screws were 22.58 and 23.44 mm, respectively. The average vertical and horizontal angles were 23.67 and 54.44 degrees for the 1-degree screw, and 2.28 and 54.89 degrees for the 2-degree screw.
This is a report of the anatomy of the lamina in the subaxial cervical spine with the special reference to translaminar screws. It was analyzed with CT and cadaveric spines along with simulated screw trajectories. For the 1-degree translaminar screw, the entry point is the distance of the diameter of desired screw superior to the inferior margin of lamina-spinous process junction. The trajectory should be targeted toward the most superomedial corner of lateral mass. For the 2-degree translaminar screw, the entry point is the distance of the diameter of desired screw below the superior margin of lamina-spinous process junction, and the target is the most superolateral corner of lateral mass, which is typically horizontal. Further studies are needed to assess the feasibility of translaminar screw insertion in the actual subaxial cervical spine.
尸体研究。
经椎板螺钉最初用于C2固定。从那时起，其应用范围已扩展至下颈椎、胸椎和腰椎。据我们所知，尚未对下颈椎经椎板螺钉置入的特殊解剖结构进行研究。
报告下颈椎经椎板螺钉置入的特殊解剖结构。
共采集18具尸体的C3至C7椎体，进行1毫米层厚的计算机断层扫描（CT）及三维重建。利用柯达Carestream/Pacs Ver 10.2软件模拟C3至C7各节段双侧经椎板螺钉的进钉点和轨迹。选择构建物以实现单枚螺钉的最大骨质把持，该螺钉称为“主螺钉”。对侧螺钉称为“副螺钉”，选择其直径以在避免模拟皮质骨穿破的情况下达到最佳允许直径，而该直径不一定总是“最佳把持”直径。最初选择的螺钉直径为3.5毫米；然而，若遇到较窄部位，则使用3.0毫米直径的螺钉。通过几何方法计算两枚螺钉的交叉区域。在确定螺钉直径时考虑椎板的最大厚度。只要可能，在两侧椎板均选择3.5毫米螺钉（3.5/3.5毫米）；然而，如果将3.5毫米螺钉用作主螺钉，但副螺钉的允许范围（P）<3.5毫米，则采用混合构建物（3.5/3.0毫米）。若P<3毫米，则两枚螺钉均采用3毫米（3.0/3.0毫米）进行研究。分析、列表并记录在允许范围内优化轨迹和骨质把持的螺钉直径。在CT上，沿螺钉轨迹切割图像，测量主副螺钉的螺钉长度、椎板最窄部位、垂直角度和水平角度。在尸体上单独分离的颈椎节段（18个中的11个）上，我们对CT测量的相同部位进行卡尺测量。然而，由于标本的三维特性，测量部位不可能完全相同。
对于C3，仅1个标本允许置入2枚螺钉（3/3毫米），而其余标本仅允许单侧主螺钉（3.5或3毫米）。对于C4，37%的标本允许置入2枚螺钉（3.5/3毫米或3/3毫米），但其余标本仅允许单侧主螺钉（3.5或3毫米）。对于C5，58%的标本允许置入2枚螺钉（3.5/3.5、3.5/3或3/3毫米）。对于C6，89%的标本允许置入2枚螺钉（3.5/3.5、3.5/3或3/3毫米）。对于C7，所有节段均允许置入2枚螺钉（3.5/3.5、3.5/3、4/4、4/3、4.5/3、4.5/3.5或4/3.5毫米）。在CT上，1度和2度螺钉的平均长度分别为26.14毫米和24.01毫米。1度螺钉的平均垂直角度和水平角度分别为22.26度和40.66度，2度螺钉分别为3.45度和45.59度。在尸体上，1度和2度螺钉的平均长度分别为22.58毫米和23.44毫米。1度螺钉的平均垂直角度和水平角度分别为23.67度和54.44度，2度螺钉分别为2.28度和54.89度。
本文报告了下颈椎椎板的解剖结构，特别提及经椎板螺钉。通过CT、尸体脊柱及模拟螺钉轨迹进行分析。对于1度经椎板螺钉，进钉点位于椎板棘突交界处下缘上方所需螺钉直径的距离处。轨迹应朝向侧块的最上内侧角。对于2度经椎板螺钉，进钉点位于椎板棘突交界处上缘下方所需螺钉直径的距离处，目标是侧块的最上外侧角，通常为水平方向。需要进一步研究以评估在下颈椎实际应用中经椎板螺钉置入的可行性。
