A visualization study of anterior transpedicular cortical screw placement in the lower cervicalspine

The anterior transpedicular cortical screw technique for the subaxial cervical spine represents a novel surgical fixation method for treating cervical spondylosis. Due to the complex anatomical structure of the cervical spine, screw placement presents certain technical challenges. Research on screw placement-related parameters will facilitate the widespread clinical application of this technique.

This study aimed to visualize and determine the optimal trajectory for placing cortical bone screws in the lower cervical spine (C3-C7) via an anterior approach, providing anatomical data for clinical application.

Select 100 healthy adult volunteers (50 males and 50 females)and perform continuous CT scans of their cervical spine with a layer thickness of 0.625 mm and a spacing of 0 mm. Use MIMICS21.0 software to establish a three-dimensional digital model of the lower cervical spine, and create a hollow screw model with an outer diameter of 2.8 mm and an inner diameter of 0.5 mm. Visualize the placement of screws at different segments from anterior to posterior through the vertebral body and pedicle. Screw position was adjusted to maximize cortical purchase within the pedicle without breach. Parameters including the distances to the midline and superior endplate of entry points, and lateral/cephalad angles of the screws were measured. All measurements were conducted in MIMICS21.0 software, and the same data was measured by two people and averaged to compare the differences between male and female, left and right sides of the same indicator data.

The entry points of all four segments of the lower cervical spine are located on the same side of the pedicle. The distance between the entry points and the mid sagittal line, as well as the vertical distance to the upper endplate of the same vertebra, are between 1.96 mm-2.62 mm and 1.30 mm-1.93 mm, respectively, showing a gradual increase from C3 to C5 and a gradual decrease from C5 to C7. There is no statistically significant difference between the left and right sides of each segment or between males and females; All screws of the four segments of the lower cervical spine need to be tilted outward and upward, with tilt angles between 24.27°-39.42° and 16.60°-18.57°, respectively. The tilt angles also show a gradual increase from C3 to C5 and a gradual decrease from C5 to C7, with no statistically significant differences between the left and right sides of each segment or between males and females.

It is feasible to insert cortical pedicle screws via the anterior cervical approach, maximizing screw purchase on cortical bone. Compared to conventional screws, this method may facilitate easier insertion and better plate conformity.