Design for posterior atlantoaxial internal fixation system with fusion cage based on imaging data

doi:10.12307/2022.431

Abstract

Abstract: BACKGROUND: The report for posterior atlantoaxial fusion cage is few and there are still many shortages. There is a lack of fusion cages with convenient operation, large bone graft area and stable bone grafting.
OBJECTIVE: To design a posterior atlantoaxial internal fixation system with fusion cage according to the anatomical characteristics and study its feasibility.
METHODS: The imaging data of 100 cases (50 males and 50 females) of normal posterior arch of atlas and axis lamina were collected. The sagittal plane was used to measure the height and the thickness of the posterior arch of atlas, the slope of the axis lamina, the height of the posterior inferior margin of atlas to the upper margin of the axis, and the height of the atlantoaxial intervertebral space. The distance between the lateral margin of the pedicle of the atlas on both sides and the distance from the posterior tubercle to this line were measured to calculate the radius of the lateral margin of the posterior arch. The point which was 4 mm to the posterior tubercle was taken as the nailing point to measure the inserting length of the screw and the angle between the screw and the middle line of the posterior arch. The anatomic parameters were analyzed to design the posterior atlantoaxial internal fixation system with fusion cage.
RESULTS AND CONCLUSION: (1) The height from the lower edge of the posterior arch of atlas to the upper edge of the axis spinous process was (19.07±2.73) mm. The height of the atlantoaxial intervertebral space was (6.83±2.01) mm. The slope of the axis lamina was (58.34±7.60)°. The radius of the lateral edge of the posterior arch of atlas was (26.77±2.14) mm. The height of the posterior tubercle of atlas was (10.45±1.61) mm. The thickness of the posterior tubercle of atlas was (8.12±1.57) mm. The inserting length of the posterior arch screw of atlas was (11.21±1.61) mm, and the angle was (53.34±6.30)°. The data difference between the two sides had no statistical significance. (2) According to the measurement of the imaging data, the design of the atlantoaxial internal fixation system is successful and is applied for the national patent. The atlantoaxial internal fixation system with fusion cage provides a new fixation method for posterior atlantoaxial internal fixation.

Key words: atlantoaxial, imaging, anatomy, CT measurement, posterior, internal fixation, cage, posterior arch screw of atlas

CLC Number:

Pan Baoshun, Fang Zhen, Gao Mingjie, Fang Guiming, Chen Jinshui. Design for posterior atlantoaxial internal fixation system with fusion cage based on imaging data[J]. Chinese Journal of Tissue Engineering Research, 2022, 26(9): 1372-1376.

Figures/Tables 4

(1)寰椎后弓钢板：在前期设计的新型寰椎后弓钢板的基础上改进为寰椎后弓后侧钢板[14]，钢板为圆弧形，总长度为30 mm，左右对称，以后结节为中心对称性变窄，板厚2 mm，半径28 mm，钢板具有2个3.5 mm锁定螺钉孔，以及4个钩状结构，构成寰椎环抱钩。寰椎后侧钢板为凹陷弧形结构设计，符合寰椎后弓解剖学，中间2孔为锁定螺钉孔，可与锁定螺钉锁定，钉孔方向与寰椎后弓平行，可以节约手术时间，具有操作简单、置钉安全等优势，后弓钩可以与后弓环抱增加内固定稳定性。 (2)寰枢椎椎间融合器：经测量，后弓至枢椎棘突高度为12.84-26.34 mm，平均19.07 mm，指导设计融合器外侧高度为19 mm；寰枢椎椎间隙高度为3.80-12.65 mm，平均6.83 mm，依据参数设计融合器内侧高度为6.8 mm；枢椎椎板斜率为14.65°-77.90°，平均58.34°，设计融合器下缘由内侧至外侧倾斜度为58°。寰椎后弓厚度均> 3.5 mm，因此设计融合器厚度为3.5 mm，避免损伤脊髓。融合器上缘外侧为寰椎后弓钢板，融合器内侧缘与外侧缘平行。采用寰椎后弓下缘至枢椎棘突和椎板作为植骨融合区域，具有植骨区域大、融合率高等优势。 (3)枢椎后侧钢板：钢板同时提供椎板螺钉和椎弓根钉2种选择的钉孔，为枢椎螺钉的置入提供不同方式。3部分为一体构成带融合器的寰枢椎后路内固定器。 2.3.2 螺钉设计参数后弓螺钉直径为3.5 mm，长度为12-14 mm，锁定螺钉；枢椎椎板螺钉长度为22-30 mm，枢椎椎弓根螺钉长度为20-26 mm，直径均为3.5 mm。 2.3.3 组装方法见图3。首先带融合器的寰枢椎后路内固定器装入适量自体骨(取髂骨)，然后将内固定器置于寰枢椎后侧，沿锁定孔方向钻孔，拧入2枚锁定螺钉，后将4个寰椎后弓钩抱紧后弓，选择枢椎椎弓根螺钉或枢椎椎板螺钉固定枢椎，构成带融合器的寰枢椎后路内固定系统。"

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