寰椎后弓侧块螺钉进钉角度的影像学研究及临床应用

The research of directions of screw trajectory in atlas via posterior arch and lateral mass and its clinical significance

目的探讨寰椎后弓侧块螺钉置钉安全角度及临床应用价值。方法对30名寰枢椎形态正常者行颈椎侧位X线摄片和寰枢椎轴位CT扫描,在影像学图像上对寰椎后弓最小高度、矢状面最大进钉倾斜角、最大进钉内倾角等参数进行测量。应用影像学观测的进钉角度对21例上颈椎不稳定患者行后路寰椎后弓侧块螺钉固定,术中观察后弓侧块螺钉置入后对周围重要组织结构的影响,术后观察有无神经症状加重。其中13例行手术前后CT检查,并测量螺钉置入前后的相关参数,评估置钉的安全性。结果(1)寰椎后弓侧块矢状面进钉倾斜角最大头倾10°、最大尾倾6°,最大倾斜角随寰椎后弓最小高度的增加有增大的趋势;(2)当进钉点由内侧改为外侧时,置钉内倾角需作0°～30°的相应调整;(3)手术实际进钉角度与术前预测有一定的差异,但均在预测范围内;(4)临床病例均置钉成功,影像学显示在常用的进钉区域内置钉无螺钉伤及椎动脉、脊髓等周围组织的现象。结论寰椎后弓侧块置钉在矢状面和轴平面上均有一定的安全角度范围,依据此范围置钉可增加寰椎后弓侧块螺钉固定的安全性和可操作性。

Objective To investigate the sate directions ot screw trajectory in atlas wa posterior arch and lateral mass and its clinical significance. Methods Lateral radiographs and CT axial scans of atlases were performed in 30 cases with normal morphology of atlases and axes. The minimal height of posterior arch, the maximum inclination of screw projection relative to sagittal plane, and the maximum medial angle of screw projection relative to axial plane were evaluated radiologically. According to the safe directions obtained radiologically 21 cases of atlantoaxial instability were treated with screw fixation atlas via posterior arch and lateral mass. During operation the influence of screws on surrounding structures was investigated and postoperative neural symptoms were documented also. Preoperative and postoperative radiographs and CT scans of 13 patients were available and some related parameters were measured to evaluate the safety of the screw placements. Results 1） The maximum angle of screw projection to sagittal plane is about 10° cephalad to 6° caudal, with the tendency of increasing maximum angle as the minimal height of posterior arch increases. 2） When the entry point on the posterior arch was switched laterally, the medial angle of screw projection should be adjusted from 0° to 30°, correspondingly. 3） The actual directions of screw trajectory might differ from preoperative ones, but all were in the estimation range. 4） All screws were placed successfully, and the postoperative radiographs and CT scans shows no neural or vascular complications relative to atlantal screws placed in traditional way. Conclusion There is a safe range to insert atlas screw via posterior arch and lateral mass both in sagittal and axial plane.