Real-world clinical accuracy of long cortical bone trajectory screw placement using a patient-specific template guide

Cortical bone trajectory (CBT) screws can be very reliable anchors if inserted precisely anterior to the vertebral body; however, their trajectory is narrow, and malpositioning of the screw is not rare, especially for surgeons who are not familiar with the CBT screw. Patient-specific template guides are a solution to this problem; however, their accuracy and usefulness in clinical settings remain unclear. The aim of the present study was to evaluate the accuracy of long CBT placement using a patient-specific screw-guide system.

This research involved a retrospective clinical evaluation of patients who had been enrolled prospectively. One hundred consecutive patients who underwent posterior lumbar spinal fusion using the guide system performed by three experienced spine surgeons were included. Initially, the placement of the CBT screws was mapped out in three dimensions utilizing simulation software. Prior to the surgery, a specific screw guide was designed for each vertebra. Using these guides, a total of 412 screws were placed. To assess any perforation of the pedicle and to compare the discrepancies between the intended and the actual positions of the screws, postoperative computed tomography (CT) scans were utilized.

Overall, 382 screws (92.7%) were fully inside the pedicle (L2-5) and there was no incidence of neurovascular injuries. The mean depth of the screw in the vertebral body (% depth) was 60.9%±8.1% and the mean % depth deviation between planned screws and actual screw was 9.6%±7.1% in total. In all vertebrae, the mean % depth was approximately 10% smaller for the actual screws than the planned screws. The mean sagittal and transverse angular deviations between the planned screws and actual screws were 2.30±1.87° and 1.89±1.26°, respectively. Overall, deviation in the sagittal angle tended to be cranial.

We demonstrated that a patient-specific screw guide is useful for supporting precise long CBT screw insertion into the lumbar spine in a clinical setting. This patient-specific template guide could be a potential solution to accurately insert long CBT screws and reduce complications, even for surgeons who are not experienced in the CBT technique.