A novel technique of lower cervical pedicle screw placement controlled by virtual safe core of pedicle screw trajectory based on CT data / 中华骨科杂志

ABSTRACT

Objective:To introduce a novel method of the virtual construction for pedicle screw trajectory (PST) of subaxial cervical spine based on CT data and to investigate its effects on improving the accuracy rate of subaxial cervical pedicle screw technique.Methods:The CT data of cervical spine (C 3, 4) of 60 subjects, including 30 males and 30 females, were collected for analysis. The data were imported into Mimics 20.0. Further, the virtual safe core (G-zone) of the PST was constructed using the method designed by authors. The following data was collected: 1) the efficiency rate of the method for virtual constructed of PST and G-zone; 2) the spatial position of the virtual safe core, including the distance between G-zone and the tangent line of upper and lower outer edge of Luschka's joint on the coronal plane, and the distance between the G-zone and the posterior edge of the vertebral body on sagittal plane; 3) the length, width and height of G-zone; 4) the abduction angle of pedicle screw on axial plane, and the cranial and caudad inclination angle on the sagittal plan of the pedicle; 5) the mean distance between the cortex of lateral mass and the G-zone; 6) the positive projection area of the trajectory on the coronal plan. Results:The efficiency rate of the method for virtual constructed of PST and safe core were C 3 95% (57/60) and C 4 100% with 97.5% (117/120) the total efficiency rate. The mean height of safe core was C 3 4.99±1.04 mm (left) and 4.95±0.88 mm (right), C 4 5.41±0.93 mm (left) and 5.16±1.39 mm (right). The mean width of safe core was C 3 3.79±0.87 mm (left) and 3.44±0.88 mm (right), C 4 3.99±0.68 mm (left) and 3.60±0.92 mm (right). The mean length of safe core was 3.5 mm. The distance between the G-zone and the tangent line of upper and lower outer edge of Luschka's joint on the coronal plane was C 3 0.66±0.54 mm (left) and 0.69±0.67 mm (right), C 4 0.62±0.59 mm (left) and 0.65±0.64 mm (right). The distance between the G-zone and the posterior edge of the vertebral body on sagittal plane was C 3 2.08±0.41 mm and C 4 2.34±0.60 mm, C 4>C 3 ( P<0.05). The interval of abduction angle on the axial plane of C 3 were 28.16°±7.82° to 67.46°±7.54° (left) and 29.46°±7.5° to 64.08°±9.79° (right), C 4 27.64°±4.56° to 69.95°±6.66° (left) and 29.17°±5.92° to 71.14°±5.07° (right). The range of cranial and caudad inclination angle of pedicle screw on sagittal plane were C 3 24.12°±5.35° (left) and 24.40°±4.86° (right), C 4 24.87°±5.7° (left) and 25.65°±5.62° (right). The mean distance between the entering cortex and the center of G-zone was C 3 11.93±0.76 mm (left) and 12.12±0.83 mm (right), C 4 11.24±0.71 mm (left) and 11.34±1.01 mm (right). The positive projection area of the PST on the coronal plan was C 3 41.38±15.68 mm 2 (left) and 37.66±13.77 mm 2 (right), C 4 44.54±12.96 mm 2 (left) and 40.33±15.54 mm 2 (right), C 4 left>C 4 right ( P<0.05). Conclusion:The efficiency rate of the virtual construction method for PST and safe core of the subaxial cervical spine was 97.5%. The length, width, and height of the virtual safe core were suitable for the implantation of the commonly used cervical pedicle screw with a diameter of 3.5 mm. The virtual G-zone was morphologically stable and easy to recognize on the anteroposterior and lateral cervical fluoroscopy view, which can provide a reliable landmark for the implementation of the pedicle screw of the subaxial cervical spine.