Introduction:
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.
Methods:
This study was a retrospective clinical evaluation of prospectively enrolled patients. One hundred consecutive patients who underwent posterior lumbar spinal fusion using the guide system performed by three experienced spine surgeons, which were not familiar with CBT screw insertion before using the guides. First, three-dimensional planning of the CBT screw placement was performed using preoperative CT data and a simulation software. Screw guides for each vertebra was created preoperatively. A total of 412 screws were inserted using this guide. Postoperative computed tomography was used to evaluate pedicle perforation and measure screw deviations between the planned and actual screw positions.
Results:
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.
Discussion:
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. The results showed that 92.7% of the screws were placed accurately inside the pedicle. In a previous study, the screw perforation incidence rate using CBT was reported as 20% with the freehand technique (1). Although the perforation rate was 7.3% in this study, no neurovascular injuries were observed, and all deviated screws had Grade A (<2 mm) inferomedial deviation. Moreover, this study used 185 screws (44.9%) with a 7 mm diameter, which is thicker than in previous studies. The cutoff value of the CBT screw insertion depth in the vertebral body for achieving bone fusion was reported to be 39.2% (2), and the % depth in this study was 60.9 ± 8.1%, which was a much higher. This patient-specific template guide may be a promising solution for achieving accurate long screw insertion and reducing the number of complications, even for surgeons who are not experienced in the CBT technique.