快速成型导向模板技术在枢椎椎板交叉螺钉置钉中的应用

 目的 验证在快速成型导向模板辅助下枢椎椎板交叉螺钉置钉的安全性、准确性及偏差因素分析。方法 选取正常颈椎标本18具，行螺旋CT扫描。扫描数据经Mimics软件三维重建后行枢椎椎板交叉螺钉最佳钉道的计算机辅助设计，建立与枢椎椎板及棘突后表面解剖结构互补的基板，组合形成导向模板。在激光快速成型机上进行导向模板实体化，利用导向模板辅助置钉。扫描置钉后的标本，分割重建螺钉钉道路径。将置钉前后的标本配对拟合，测量理想钉道与实际螺钉的进钉点及进钉角度。结果 上、下位椎板螺钉理想钉道长度分别为(29.12±1.39)、(29.62±1.40) mm；内倾角分别为56.20°±2.07°、56.02°±1.72°。下位椎板螺钉实际钉道内倾角和尾倾角分别为56.28°±1.54°、0.13°±0.65°；上位椎板分别为55.48°±1.75°、-0.19°±1.54°。下位椎板螺钉进钉点在X、Y、Z轴上的偏移分别为(0.69±1.79)、(2.54±4.86)、(0.63±1.37) mm；上位椎板分别为(0.64±1.61)、(2.36±4.85)、(0.62±1.38) mm。理想钉道与实际螺钉进钉点、钉道方向的差异无统计学差异。结论 利用数字化快速成型导向模板技术辅助枢椎椎板交叉螺钉置钉提高了置钉的安全性和准确性，理论上可降低椎动脉和脊髓损伤的风险。

A novel computer-assisted drill guide template for C2 crossing laminar screws placement: a cadaveric experimental study

Objective To validate the security and accuracy of C2 crossing laminar screws placement under the assistance of rapid prototyping oriented template. Methods CT scan was performed in the 18 normal cervical specimens. The data were reconstructed by software Mimics 10.01. The ideal trajectory for C2 crossing laminar screws were designed with a baseplate which is a complementary template for posterior lamina and spinous process, then materialize drill guide template in rapid prototyping machine. The screws were segmented in Mimics after CT scanning. The entry point and nail way direction of the ideal and actual trajectory were measured after matching the position of the pre- and post-operative specimen, whose coordinate axis has been fitted. Results The average depth of the superior and inferior C2 laminar screw were 29.12±1.39 and 29.62±1.40 mm, the average introversion of ideal C2 crossing laminar screw was 56.20°±2.07° and 56.02°±1.72°, the mean introversion and elevation angle of the inferior actual C2 laminar screw were 56.28°±1.54° and 0.13°±0.65°, the mean introversion and elevation angle of the superior actual C2 laminar screw were 55.48°±1.75° and -0.19°±1.54°, respectively. The average displacement of the entry point of inferior C2 crossing laminar screw in the X, Y, Z axis were 0.69±1.79, 2.54±4.86, and 0.63±1.37 mm, respectively, which of the superior C2 were 0.64±1.61, 2.36±4.85, and 0.62±1.38 mm, respectively. No statistically significant difference was found between the ideal nail way and actual nail way in the deviation of entry point and nail way direction. Conclusion The safety and accuracy of C2 crossing laminar screws placement has been improved by using computer-assist drill guide template technology, which avoids the risk of vertebral artery and spinal cord injury.