快速成型导向模板辅助下寰枢椎椎弓根螺钉置钉的偏差因素分析

A novel computer-assisted drill template for atlantoaxial pedicle screw placement： a cadaveric experimental study

目的验证在快速成型导向模板辅助下寰枢椎椎弓根螺钉置钉的准确性及偏差因素。方法选取正常颈椎标本16具，采用64排螺旋CT层厚1mm扫描后获得Dicom格式数据。获取数据经Mimics软件三维重建后进行寰枢椎椎弓根螺钉最佳安全钉道的计算机辅助设计，并建立与寰枢椎后表面解剖结构三维互补的基板，组合形成导向模板。在激光快速成型机上进行导板实体化，利用导向模板辅助置钉。在计算机软件中将置钉前后的标本配对拟合，重新定义三维空间坐标轴后，测量理想钉道和实际螺钉的进针点、角度和钉道方向。结果寰椎椎弓根螺钉左侧和右侧进针点在x、y、z轴上的偏移分别为（0．14±0．59）、（0．31±1．32）、（0．27±0．68）、（0．23±0．55）、（0．43±1．21）、（0．30±0．72）mm。枢椎椎弓根螺钉左侧和右侧进针点在m、n、p轴上的偏移平均值分别为（0．25±0．85）、（0．52±1．52）、（-0．27±0．67）、（0．44±0．87）、（0．38±1．48）、（-0．14±0．62）mm。寰枢椎椎弓根螺钉最佳安全钉道和实际钉道的进针点、钉道方向的偏差无统计学差异（P〉0．05）。结论寰枢椎椎弓根螺钉快速成型导向模板辅助置钉偏差原因主要为软硬件存在的固有因素和人为产生的因素所致。该导向模板技术具有操作简易和个体化设计等优点，能提高置钉精准性及减少螺钉偏差。

Objective To validate the accuracy of atlanto-axial pedicle screw placement with a rapid prototyping drill guide template and analyze the factors of screw deviations. Methods Computed tomography （CT） scan was performed in 16 cervical specimens. And three-dimension cervical vertebrae was reconstructed by Mimics software. The ideal trajactory for atlanto-axial pedicle screws was designed with a complementary basal template for posterior surface of atlanto-axial corresponding anatomical structure. Then drill guide template was materialized in a rapid prototyping machine. These templates were used during operation. The entry point and ideal and actual trajaetories were measured after matching the positions of preoperative and postoperative specimens at designated coordinate axis. Results The average displacement of entry point of left and right C1 pediele screw in x, y, z axis was （0.14 ±0.59）,（0.31 ±1.32）, （0. 27 ±0. 68）, （0. 23 ±0. 55）, （0. 43 ±1.21） and （0. 30 ±0. 72） mm. And the average displacement of entry point of left and right C2 pedicle screw in m, n, p axis was （0.25±0.85）, （0.52 ± 1.52）, （ -0. 27 ±0. 67）, （0. 44 ±0. 87）, （0. 38 ±1.48）, （ - 0. 14 ±0. 62） mm. No statistically significant difference existed （ P 〉 0.05 ） in deviation of entry point and between ideal and actual trajectories. Conclusion Both human handling and inherent hardware and software factors are main reasons for a deviation of C1-C2 pedicle screw placement assisted by a rapid prototyping drill guide template. Ease of operation and individualized design are the advantages of drill guide template so as to greatly improve the precision of screw placement and reduce screw deviation.