目的 验证在快速成型导向模板(rapid prototyping drill template,RPDT)辅助下经后路寰枢椎经关节突关节螺钉置钉的安全性、准确性及偏差因素分析. 方法 选取正常颈椎标本12具,采用64排螺旋CT(层厚1 mm)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经关节突关节螺钉最佳安全钉道的计算机辅助设计,并建立与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RPDT辅助置钉.扫描置钉后的标本,分割重建出螺钉钉道路径.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 置入寰枢椎经关节突关节螺钉24枚,均未穿破骨皮质.寰枢椎经关节突关节螺钉左右侧最佳安全钉道深度分别为(37.34±2.31) mm、(37.11 ±2.21) mm.寰枢椎经关节突关节螺钉左右侧最佳安全钉道内倾角均为0°.寰枢椎经关节突关节螺钉左右侧实际钉道内倾角分别为(0.15±0.58)°、(0.11±0.46)°.寰枢椎经关节突关节螺钉左右侧最佳安全钉道尾仰角分别为(49.35±1.62)°、(48.83 ± 1.83)°.寰枢椎经关节突关节螺钉左右侧实际钉道平均尾仰角分别为(49.29±1.68)°、(49.10±1.45)°.寰枢椎经关节突关节螺钉左侧进针点在x、y、z轴上的偏移值分别为(0.21 ±0.65) mm、(0.69 ±1.48) mm、(0.39±0.11) mm.寰枢椎经关节突关节螺钉右侧进针点在x、y、z轴上的偏移值分别为(0.19 ±0.66) mm、(0.53±1.45) mm、(0.38±0.13) mm.寰枢椎经关节突关节螺钉最佳安全钉道和实际钉道的进针点、钉道方向的偏差差异无统计学意义(P＞0.05). 结论 寰枢椎经关节突关节螺钉RPDT辅助置钉偏差原因主要为硬件和软件存在的固有因素和操作过程中人为产生的因素.RPDT技术具有操作简易和个体化设计等优点,能极大地提高置钉精准性及减少螺钉偏差,有较广泛的适用人群.%Objective To validate the safety and accuracy of a rapid prototyping drill template (RPDT) for posterior atlantoaxial transarticular screw placement and analyze factors for screw deviation.Methods Twelve normal cadaveric cervical spines were examined using 64 slice CT with 1-mm thick scan and data in Dicom format were recorded.After data was processed using software Mimics 10.01 for three-dimensional (3-D) model reconstruction,computer-assisted design of optimum trajactory for atlantoaxial transarticular screw placement was worked out and made into a drill template,where the surface was created as the inverse of axial posterior surface.The drill template was materialized in a rapid prototyping machine and used to place the screws.After surgery,the position of posterior atlantoaxial transarticular screw was evaluated by X-ray and CT scan.Screw entry point,angle and orientation of the optimal and actual trajactory were determined after fitting the position of the pre-operative and post-operative specimen in computer software and the redefining the 3-D coordinate axis.Results Twenty-four screws were implanted with no cortex perforation.Depth of the optimum save screw trajectory for atlantoaxial transarticular fixation was (37.34 ± 2.31) mm on the left side and (37.11 ± 2.21) mm on the right side.Introversion angles of the optimum save screw trajectory was 0° in both sides,but the actual angle was (0.15 ±0.58)°on the left side and (0.11 ±0.46)°on the right side.Elevation angle of the optimum save screw trajectory was (49.35 ± 1.62) °on the left side and (48.83 ± 1.83) ° on the right side,but the actual angle was (49.29 ± 1.68) °and (49.10 ± 1.45) °respectively.Average displacement of screw entry point in the x,y and z axis was respective (0.21 ±0.65) mm,(0.69 ± 1.48) mm and (0.39 ±0.11) mm on the right side,while (0.19 ± 0.66) mm,(0.53 ± 1.45) mm and (0.38 ± 0.13) mm on the left side.There were no statistically significant differences in deviation levels of entry point and orientation between the optimum and actual screw trajectory (P ＞ 0.05).Conclusions Causes for deviation in RPDT-assisted placement of atlantoaxial transarticular screw are mainly intrinsic factors of the hardware and software and human factors in the operation.RPDT is easy in operation and has individualized design,which greatly improves the accuracy of screw placement and reduces screw deviation.RPDT can be widely used in clinical practice.
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