Selection Of The Ideal Trajectory Of Atlas Pedicle Screws

Objective:Three-dimensional reconstruction of cancellous bone and shape of Atlas,On the basis of design the ideal screw trajectory of atlas pedicle screw,and reduce the resistance and screw penetrating complications.Methods:3D reconstruction of atlas inte rnal spongy bone and shape using Mimics10.01 software was conducted by collecting the image data of Atlas TLC scanning(scanning conditions: voltage 220 V,thickness 0.75 mm,interval 0.8mm)of 60 volunteers(30 males and 30 females).The center point C(Atlas pedicle without spongy bone with pedicle center instead)was determined based on the 3D images and the original image data of atlas pedicle spongy bone.C point was taken as the center point of ideal screw trajectory,the head inclination angle of atlas pedicle screw as that of screw and the angle bisector of largest medial and lateral angle of inclination as ideal screw trajectory to explore the motion range of screw in the lateral mass of spongy bone and observe whether screw was through the pedicle.Ideal trajectory with the posterior arch of the intersection as the entry point,the entry point and the measuring parameters of anatomical landmarks.Results:The distance of male and female ideal screw point to pedicle medial wall L1 were(7.89 ±1.39)mm,(7.30 ± 0.98)mm,respectively;the distance to the median sagittal plane L2 were(22.86 ±2.30)mm,(21.23 ± 1.64)mm;the distance to pedicle upper and lower edge ratio L3/L4 were(1±0.10),(1.01±0.11).The ideal screws included angle alpha of male and female were(11.70±5.68)°,(11.70±5.48),respectively;the maximum included angle alpha 1 were(32.51±5.79)°,(30.52 ± 6.40)°;maximum camber angle alpha 2 were(9.10±7.80)°,(7.04 ±7.13)°;the pedicle width of D were(9.70±1.57),(8.70 ±1.24)mm;height of H were(5.24 ±1.15),(4.38±0.81)mm.60 volunteers simulation of image data are put into a 3.5mm diameter screws,a total of 120 medals.The screw through the pedicle occurred in 10 cases(1 male and 9 females)for smaller pedicle height or anatomical variation,incidence of 8.33%.Conclusion: The ideal entry point of screw is 7-8mm adjacent to the medial wall of pedicle,the center of upper and lower edge of posterior arch,with screw introversion of(11-12)degrees and same axis with the pedicle.