Wang Michael Y
Department of Neurological Surgery, Keck School of Medicine, University of Southern California, Los Angeles, California 90033, USA.
Neurosurgery. 2006 Jul;59(1 Suppl 1):ONS84-8; discussion ONS84-8. doi: 10.1227/01.NEU.0000219900.24467.32.
C2 screw fixation through the pars or pedicle involves a small but finite risk of vertebral artery injury. Recently, C2 crossing laminar screws were described as a method for rigid fixation of the axis. This technique, confined to the dorsal aspect of C2, presents minimal chance of injury to the neighboring neural or vascular structures.
Morphometric analysis was performed on 38 cadaveric spines obtained from the Keck School of Medicine at the University of Southern California. Critical measurements were determined for screw entry points, trajectories, and lengths for application of the technique, as described by Wright, using 3.5 and 4.0 mm screws.
The average maximal screw length was 32 mm with a range of 27 to 37 mm. The minimal total laminar cross sectional area averaged 75 mm2, and the cancellous bone cross sectional area averaged 39 mm2. The minimal laminar cross sectional diameter was determined to be too small to accommodate a 3.5-mm diameter screw, assuming a 1 mm tolerance on each side, in 16 sides of 14 specimens, and to be too small to accommodate a 4.0 mm diameter screw, assuming a 1 millimeter tolerance, in 32 sides of 18 specimens.
C2 laminar screw placement is straightforward and carries little risk of injury to the neural and vascular structures as long as the implants remain intraosseous. However, the highly variable thickness of the C2 lamina necessitates preoperative computed tomographic scanning to ensure that the patient's anatomy can accommodate screws entirely within the bone.
经椎弓根或椎弓根进行C2螺钉固定存在虽小但有一定风险的椎动脉损伤。最近，C2交叉椎板螺钉被描述为一种用于枢椎坚强固定的方法。该技术局限于C2的背侧，对相邻神经或血管结构造成损伤的可能性极小。
对从南加州大学凯克医学院获取的38具尸体脊柱进行形态学分析。按照赖特所描述的技术，使用3.5毫米和4.0毫米的螺钉，确定了螺钉置入点、轨迹和长度的关键测量值。
螺钉的平均最大长度为32毫米，范围为27至37毫米。椎板的最小总横截面积平均为75平方毫米，松质骨横截面积平均为39平方毫米。在14个标本的16侧，假定每侧有1毫米的公差，确定椎板最小横径太小，无法容纳直径3.5毫米的螺钉；在18个标本的32侧，假定有1毫米的公差，确定其太小，无法容纳直径4.0毫米的螺钉。
只要植入物保持在骨内，C2椎板螺钉置入操作简单，对神经和血管结构造成损伤的风险很小。然而，C2椎板厚度高度可变，因此术前需要进行计算机断层扫描，以确保患者的解剖结构能够完全容纳骨内的螺钉。
