Imaging measurement and biomechanical study of cortical screws of cervical pedicle

English Keywords:Cortical bone screws  Pedicle screw  Withdrawal force  Biomechanics

English Abstract:

  【Abstract】 Objectives： To investigate the feasibility of cervical pedicle cortical bone screw in clinical use, the selection of screw insertion points, the parameters of screw insertion direction, and the biomechanical analysis after screw insertion. Methods: Randomly select the CT data of 30 patients hospitalized in our hospital from January 2014 to June 2018 who have undergone cervical CT three-dimensional reconstruction. There are 16 males and 14 females, aged 30-60 years (48.0±5.6 years). The data of cervical vertebrae (C4-C6) CT continuous scans were collected, and the morphological data of the height and width of each pedicle were measured. The angle range of cortical screw placement in each vertebral body was calculated by simulating the cortical screw roll angle and head inclination angle on the image processing system. Measure each The lateral inclination angle and head inclination angle of the screw are calculated and the angle range of each vertebral cortical bone screw placement is calculated. Select 18 complete adult fresh cervical spine specimens (select C4-C6), use the left and right pedicles of each cervical spine specimen as a test unit for random placement of screws, and place traditional pedicle screws as group A. The screws placed in the cortical bone channel belong to group B. Then, all cervical spine specimens with traditional cervical pedicle screws and pedicle cortical bone screws were scanned by CT, and the levels of nail placements were evaluated according to the Grade standard. Fix the cervical spine specimens with traditional pedicle screws and pedicle cortical screws on a special fixture. Before the biomechanics test, adjust the angle between the screw and the fixture by rotating the fixture base, and detect the maximum vertical axis of the screw. To pull out force, compare the results of the two groups. Results: The heights and widths of C4, C5 and C6 were respectively 7.3±0.8mm and 5.5±0.3mm, 7.4±0.6mm and 5.9±0.2mm, and 7.6±0.6mm and 6.2±0.3mm. In the cortical screw group, C4 roll angle was 39.5°±2.3°, head inclination angle was 10.3°±0.4°; C5 roll angle was 39.3°±1.3°, head inclination angle was 10.9°±0.5°; C6 roll angle was 37.7°±0.9°, head inclination angle was 11.7°±0.3°. In group A, 52 cases of traditional pedicle screw placements were performed in level 1 and 2 in level 2; while in group B, 51 cases of pedicle cortical screwplacements were in level 1 and 3 in level 2. The difference was not statistically significant(P>0.05). The average fixed length C4 of group A was 34.2±1.8mm, C5 was 34.3±2.3mm, and C6 was 34.6±1.9mm; the average fixed length of group B was 23.3±1.4mm, C5 was 24.3±2.1mm, and C6 was 25.7±1.3mm, the difference was not statistically significant(P>0.05). The maximum extraction force of the traditional cervical pedicle screw group was 521.2±15.58N, and that of the pedicle cortical screw group was 527.41±18.93N, with no significant difference between the two groups(P>0.05). Conclusions: CT scan shows that cervical cortical screw technique is safe and feasible; the extraction force of cervical cortical screw is equivalent to that of traditional pedicle screw. Cortical screw can be clinically used as a new and safe cervical pedicle screw.