Study on the best entry region and trajectory of anterior transpedicular root screws

Objective: To evaluate the best entry region and trajectory of anterior transpedicular root screws (ATPRS). Methods: From January 2018 to May 2019, 50 cervical CT date integral of healthy people were selected from Ningbo No. 6 Hospital and were confirmed no obvious defect. Of these, 24 cases were males and 26 were females, aged 20-49 (32±5) years. The CT data was imported into Mimics by DICOM format, then 3D reconstruction was performed. In the coronal plane, the area from the centreline of the anterior of C(3-7) to the left Z-line(marked a line through the intersection of the anterior of the luschak joint and upper endplates, parallel to the centralline of the anterior of the vertebral body) was divided into nine areas. Then virtual screw with diameter of 3.5 mm was inserted. Record the length of screw of each area (L), the angle between screw and the posterior of the vertebral body in horizontal plane(α), the angle between screw and the anterior of the vertebral body in sagittal plane (β), individually. The data between groups were compared by independent sample t test. Results: The best regions were zone 9 of C(3), C(4); zone 8, 9 of C(5); zone 2-3, 5-9 of C(6); zone 1-9 of C(7) in men. And these were zone 9 of C(3); zone 3, 6, 8 and 9 of C(4), C(5); zone 2-3, 5-9 of C(6); zone 1-9 of C(7) in women. The distribution of best region was almost the same in men and women, zone 9 of each segment was the best region, and the screw length was the longest. It increased gradually from C(3) to C(7). C(3) had the least region, C(4) and C(5) had less, while C(6) and C(7) had the most. The horizontal angle of C(3-7) in men and women were 44.0°-47.2°, 40.2°-45.3° in zone 1, 4 and 7, respectively; 35.1°-41.4°, 34.6°-38.7° in zone 2, 5 and 8, respectively; 30.0°-37.2°, 30.2°-34.5° in zone 3, 6 and 9, respectively; and it demonstrated a gradually decreased trend. The sagittal angle of C(3-7) in men and women was 85.3°-97.4°, 80.5°-88.9° in zone 1-3, respectively; 101.2°-113.7°, 101.0°-109.3° in zone 4-6, respectively; 116.6°-128.8°, 119.9°-125.3° in zone 7-9, respectively; and it demonstrated a gradually increased trend. There was no significant difference in the horizontal and sagittal angle between men and women (both P>0.05). Conclusions: Anterior transpedicular root screw is a feasible internal fixation technique. It has wide region and the Z-line can be used as a reference for screw placement.