Design and radiological confirmation of three-column cortical bone trajectory in the lower thoracic vertebrae

This study aims to design novel cortical bone trajectories for the lower thoracic vertebrae that traverse the anterior, middle, and posterior columns. We seek to establish novel theoretical guidelines and placement strategies to optimize the trajectory of CBT screws in osteoporotic patients.

Five different diameters of CBT screws, ranging from 3.5 mm to 5.5 mm, were designed. The tip of the simulated screw was aimed at the anterior half of the vertebral body, with appropriate cephalad and lateral angles. Screw placement was simulated using Mimics software, and key parameters-maximum screw length, cephalad angle, lateral angle, and bone density along the screw path-were measured. We then compared screw placement parameters across different spinal segments and screw specifications, analyzing factors influencing the success of three-column CBT screw placement.

Successful simulation of three-column CBT screw placement in the lower thoracic spine (T9-12) was achieved with a high success rate. As screw diameter increased, the maximum screw length decreased, while cephalad and lateral angles increased. The HU values along the trajectories of the three-column CBT screws were significantly higher than those of traditional thoracic pedicle screw trajectories (p < 0.05). Key factors affecting the success of three-column CBT screw placement were pedicle width and screw diameter.

By adjusting the entry point and modifying the cephalad and lateral angles, the concept of three-column CBT screw fixation can be effectively applied to the lower thoracic vertebrae.