Angulation Error Assessment for the Trajectory in the Anteroposterior and Lateral Fluoroscopic Views During Percutaneous Endoscopic Transforaminal Discectomy: Which One is More Reliable?

Background Anteroposterior (AP) and lateral fluoroscopies are often used to evaluate the intraoperative location and angulation of the trajectory in percutaneous endoscopic transforaminal discectomy (PETD). Although the location of the trajectory shown in the fluoroscopy is absolutely accurate, the angulation is not always reliable. This study aimed to evaluate the accuracy of the angle shown in the AP and the lateral fluoroscopic view. Methods A technical study was performed to assess the angulation errors of PETD trajectories shown in AP and lateral fluoroscopic views. After reconstructing a lumbar CT image, a virtual trajectory was placed into the intervertebral foramen with gradient-changing coronal angulations of the cephalad angle plane (CACAP). For each angulation, virtual AP and lateral fluoroscopies were taken and the cephalad angles (CA) of the trajectory shown in the AP and the lateral fluoroscopic views, which indicated the coronal CA and the sagittal CA respectively, were measured. The angular relations among the real CA, the CACAP, the coronal CA, and the sagittal CA were further demonstrated with formulae. Results In PETD, the coronal CA was nearly consistent with the real CA, whereas the sagittal CA decreased dramatically with the increment of the CACAP. The angle differences between CA and sagittal CA were much greater than the angle differences between CA and coronal CA. Conclusion The AP view is more reliable than the lateral view in determining the CA of the PETD trajectory.