Atlas lateral mass screw insertion under virtual surgical system

English Keywords:Atlas  Lateral mass screw  Fixation  Virtual surgery system

English Abstract:

  【Abstract】 Objectives: To establish a standard system and a standard operational process of atlas lateral mass screw insertion assisted by virtual surgical system and to investigate its feasibility and accuracy. Methods: CT scan were performed on eight specimens(bilateral) of atlas(C1) without damage or bony malformation, then the data were transferred into the virtual surgery system for three-dimensional reconstruction and multiple planar reformation(MPR) so as to measure the C1 lateral mass, the junctional zone of lateral mass and underside of posterior arch pedical and midpoint of inner border of transverse foramen and inner wall of the posterior arch of atlas was selected as screw insertion point. The following parameters were measured: the distance between the inner border of transverse foramen and the inner wall of posterior arch of atlas(L1), the distance between screw insertion point and the highest point of front border of lateral mass(L2), the vertical distance between screw insertion point and the highest point of front border of lateral mass(L3), the angle between perpendicular of screw insertion point and tangent of up border of lateral mass(α), the angle between perpendicular of screw insertion point and tangent of inner border of transverse foramen(β), the angle between perpendicular of screw insertion point(γ) and tangent of inner border of lateral mass[δ：（β+γ）／2－β]. The measurements were performed on left and right sides and the mean values were taken for statistical analysis. Based on the measurements, the procedure of atlas lateral mass screw insertion was simulated on specimens, the virtual surgical system reconstructed, and the accuracy of insertion finally evaluated. Results: A virtual surgical system for operational process was established. The relative parameters of atlas lateral mass were as follows, L1: the left side was 9.82±0.76mm, the right side was 9.16±0.85mm; L2: the left side was 21.76±1.36mm, the right side was 21.50±1.02mm; L3: the left side was 17.78±1.67mm, the right side was 18.22±1.60mm; α: the left side was 36.78°±1.23°, the right side was 35.78°±2.40°; β: the left side was 18.84°±1.80°, the right side was 18.40°±1.71°; γ: the left side was 31.49°±0.60°, the right side was 30.46°±1.56°; δ: the left side was 6.32°±1.08°, the right side was 6.25°±1.11°. All data from left and right side by virtual surgery system showed no statistical difference(P>0.05). All sixteen screws located in lateral mass accurately, with no penetration into surrounding structure. Conclusions: Atlantoaxial lateral mass screw insertion assisted by the virtual surgical system is feasible and accurate.