不同内倾角置入寰椎后路侧块螺钉的安全性比较

Safety of posterior C1 lateral mass screw under different introversion angles

目的：将寰椎后路侧块螺钉上倾角固定在15°的情况下,比较不同内倾角度置钉相对应的寰椎侧块有效宽度和进钉深度,以确定寰椎后路侧块螺钉在横断面上的最佳内倾角度。方法：募集颈椎结构正常的健康成年国人64名,男32名,女32名;年龄32.7±7.8岁（18～60岁）,进行颈椎CT平扫,通过Mimics软件对志愿者的颈椎CT数据进行测量,在寰椎后路侧块螺钉上倾角为15°的情况下,分别测量内倾角度为0°、5°、10°、15°、20°、25°、30°和理想内倾角（β角）时的寰椎侧块有效宽度和寰椎后路侧块螺钉的进钉深度;测量正中矢状面与寰椎后弓最后缘的交点与进钉点之间的距离和进钉点处的后弓下缘侧块高度;并进行统计学数据分析。结果：寰椎后路侧块螺钉的β角男性为20.01°±2.97°,女性为21.89°±3.14°。寰椎后路侧块螺钉内倾角度为0°、5°、10°、15°、20°、25°、30°和β角时的寰椎侧块有效宽度男性分别为8.95±1.18、9.51±1.14、10.00±1.17、10.42±1.20、10.39±1.29、9.41±1.25、8.04±1.21、11.02±0.96mm,女性分别为7.64±1.01、8.31±1.11、8.88±1.10、9.32±1.11、9.51±1.09、8.90±1.02、7.62±1.07、9.97±0.98mm;进钉深度男性分别为19.03±1.34、19.60±1.39、20.28±1.47、21.20±1.48、22.11±1.54、23.06±1.63、24.19±1.97、22.37±1.52mm,女性分别为17.47±1.68、17.90±1.64、18.50±1.79、19.31±1.93、20.47±2.03、21.67±2.18、22.89±2.38、21.26±1.99mm。相较于其他内倾角,β角对应的寰椎侧块有效宽度最大且差异有统计学意义（P〈0.01）。寰椎后路侧块螺钉内倾角为β时,寰椎后路侧块螺钉进钉点距离正中矢状面与寰椎后弓最后缘的交点距离男性为28.35±1.75mm,女性为26.70±1.60mm;进钉点处的后弓下缘侧块高度男性为4.38±0.85mm,女性为4.13±0.80mm。结论：寰椎后路侧块螺钉上倾15°时,以所对应的寰椎侧块有效宽度最大的内倾角β角进钉,理论上损伤椎动脉、脊髓等结构的几率最低。

Objectives： To compare different introversion angle related to the width and depth of screw in C1 lateral mass when placing the cephalic inclination of posterior C1 lateral mass screw at 15 °, and to find optimal introversion angle for posterior C1 lateral mass screw placement. Methods： Computed tomography（CT）scan was performed on normal cervical spine of 64 healthy Chinese adults（32 males, 32 females; age range,18-60 years; mean age, 32.7 years）, the 3-D morphology of each atlas was reconstructed by using the Mim-ics software. When fixing the cephalic inclination of posterior C1 lateral mass screw at 15 °, the effective width and screw length of C1 lateral mass under different introversion angles ranged from 0° to 30° with a uniform interval of 5° and ideal medial angle（β）, the effective width and screw length was measured, the height for screw entry point on the posterior surface of the lateral mass and the distance between screw entry point and the intersection of the mid-sagittal plane and the posterior arch of the atlas were also measured respectively. All data were analyzed by SPSS 18.0. Results： The ideal medial angle was 20.01°±2.97°（male）and 21.89°±3.14°（female）, and the relative result of effective width was 11.02±0.96mm（male） and 9.97±0.98mm（female）. When the introversion angle was 0°, 5°, 10°, 15°, 20°, 25°, 30° and β, the lateral mass effective width of male was 8.95±1.18 mm, 9.51±1.14 mm, 10.00±1.17 mm, 10.42±1.20 mm, 10.39±1.29 mm, 9.41±1.25 mm,8.04±1.21 mm, 11.02±0.96 mm respectively, while the datum of female was 7.64 ±1.01 mm, 8.31±1.11 mm, 8.88±1.10 mm, 9.32 ±1.11 mm, 9.51 ±1.09 mm, 8.90 ±1.02 mm, 7.62 ±1.07 mm, 9.97 ±0.98 mm respectively; the screw length of male was 19.03 ±1.34 mm, 19.60 ±1.39 mm, 20.28 ±1.47 mm, 21.20 ±1.48 mm, 22.11 ±1.54 mm, 23.06 ±1.63 mm, 24.19±1.97 mm, 22.37±1.52 mm respectively, while that of female was 17.47±1.68 mm, 17.90±1.64 mm,18.50 ±1.79 mm, 19.31 ±1.93 mm, 20.47 ±2.03 mm, 21.67 ±2.18 mm, 22.89 ±2.38 mm, 21.26 ±1.99 mm respectively.When the introversion angle was β, the lateral mass effective width was significantly bigger than that of other angles（P〈0.01）. When the medial angle was β, the distance between screw entry point and the intersection of the mid-sagittal plane and the posterior arch of the atlas was 28.35±1.75mm（male） and 26.70±1.60mm（female）.The height for screw entry in the lateral mass of posterior surface was 4.38±0.85 mm in male, and was 4.13±0.80 mm in female. Conclusions： When the cephalic inclination of posterior C1 lateral mass screw is fixed at15°, the effective width of lateral mass is the widest, which can be used as the ideal introversion angle to minimize the risk of injury to the vertebral artery and spinal cord during instrumentation.