CT value of bone in bone-screw interface: comparison between cortical screws and traditional pedicle screws

English Keywords:Pedicle cortical bone trajectory  Traditional pedicle trajectory  CT value  Trajectories

English Abstract:

  【Abstract】 Objectives: To compare the CT value of bone in bone-screw interface between cortical screws and traditional pedicle screws, and to provide theoretical basis for the application of cortical screws. Methods: The thin CT scan data were collected from lower lumbar spine of 300 patients, who were stratified by gender and age(at the interval of 10 years). The data of each group were imported into mimics 18.0 software to establish the three dimensional reconstruction models, and cylinders with different diameters were drawn to simulate the different trajectories. The region of interest(ROI) which was in bone-screw interface, was segmented and measured by CT value. Results: There was no statistically significant difference of CT value in ROI of both trajectories between L4 and L5 vertebral bodies in male or female of the same age. The mean CT values in ROI of cortical screws and traditional pedicle screws: 21-30 years group, in male were 547.4±48.2Hu and 311.1±20.3Hu, in female were 517.3±56.0Hu and 279.1±41.7Hu respectively; 21-30 years group, in male were 547.4±48.2Hu and 311.1±20.3Hu, in female were 517.3±56.0Hu and 279.1±41.7Hu respectively; 31-40 years group, in male were 519.6±48.9Hu and 258.7±26.5Hu, in female were 521.5±58.8Hu and 287.8±33.2Hu respectively; 41-50 years group, in male were 490.9±69.8Hu and 249.7±37.5Hu, in female were 500.7±81.0 and 262.0±72.1Hu respectively; 51-60 years group, in male were 436.5±65.7Hu and 217.4±20.8Hu, in female were 438.8±45.8Hu and 222.1±22.6Hu respectively; 61-70 years group, in male were 396.1±40.0Hu and 204.0±36.4Hu, in female were 364.5±73.6Hu and 153.5±27.1Hu respectively. The CT values for two different screw types in same age and gender were significantly different（P<0.05）, and the mean CT values for cortical screws were 1.7-2.3 times higher than those for traditional pedicle screws. The mean CT values within ROI for pedicle cortical bone trajectory between male and female patients were significantly different in the age groups of 21-30 and 61-70(P<0.05), and the differences for traditional pedicle trajectory in 21-30, 31-40 and 61-70 years group also were significant(P<0.05). Conclusions: The mean CT value of bone in bone-screw interface for cortical screws is significantly higher than that of traditional pedicle screws, which shows the higher bone-screw interface strength of cortical screws.