Imaging study of tri-cortical screw oblique fixation in thoracic spine

English Keywords:Tricortical screws  Oblique fixation  CT measurement  Thoracic vertebrae

English Abstract:

  【Abstract】 Objectives: To simulate tricortical screws oblique fixation in the thoracic vertebras of normal adults to determine the radiographic trajectory parameter and to evaluate its feasibility and safety. Methods: The imaging data of patients who underwent plain CT scan and three-dimensional reconstruction of thoracic spine in our hospital from January 2019 to October 2021 were analyzed retrospectively. 100 patients without thoracic anatomical abnormalities were selected, including 50 males and 50 females, aged from 25 to 68 years old, with an average of 40.0±11.6 years. The trajectories of thoracic tricortical screws which were oblique fixed on the light speed imaging workstation were simulated: taking the intersection of the lower third connecting line of the pedicle and the connecting line of the lateral edge of the superior articular process as the entry point of the tricortical oblique screw, reconstructing its three-dimensional image, and taking it as the center for rotary cutting to obtain the longest and widest ideal screw path. The sagittal angle, transverse angle and length of the screw trajectories were measured. The normal distribution was verified between the same-sex parameters. The paired design t-test was used to verify the difference between the three cortical oblique screw channel parameters of different genders. One-way ANOVA was used to test for different vertebral parameters. Results: The length of screws′ trajectories increased from top to bottom, and the length of males′ trajectories were significantly longer than that of females at each vertebral level(P<0.05). The shortest average trajectories were in T2 level. On this segment, the longest average trajectory was 48.8±3.1mm for man, 45.5±2.3mm for woman, the shortest average trajectory was 40.2±1.8mm for men and 37.4±1.7mm for women. The longest average trajectory was in T12. On this segment, the longest was 65.4±2.9mm and the shortest was 54.5±2.1mm for man, 61.6±2.2mm and 51.4±1.6mm for woman. For screw placement angle, there was no statistical difference between genders, but there were certain statistical differences between thoracic vertebrae. The sagittal angle decreased from T2 to T6 or T7 and increased from T6 or T7 toT12. The maximum value of the maximum average sagittal angle and the minimum average sagittal angle were located at the T12 level, which were 46.1°±2.2° and 25.4°±1.5° respectively. The minimum values of the maximum and minimum average sagittal angles were located at T6, which were 39.3°±2.5° and 19.6°±2.1° respectively. The maximum value of the optimum average sagittal angle was located at T2, which was 44.2°±2.5°; The minimum value of the average optimum sagittal angle was located at T7, which was 36.7°±2.4°. Except for the minimum transverse angle, the maximum average transverse angle and the optimal average transverse angle decreased first and then increased from T2-T12. Each maximum value was located in T2 segment, with the maximum average transverse angle of 38.5°±4.0°, the minimum average transverse angle of 22.6°±2.6°, and the optimum average transverse angle of 30.0°±2.4°. The minimum value of the maximum average transverse angle was located at T7, which was 25.2°±2.4°; The minimum value of the optimum average transverse angle was located at T8, which was 19.0°±1.4°, and the minimum average transverse angle was located in T12, which was 12.9°±2.3°. Conclusions: This study successfully simulated the oblique fixation of adult tricortical screws in thoracic spine, which confirms the safety and feasibility of the screw, and also provides anatomical parameters for the clinical application of the screw.