The Optimal Entry Point and Trajectory for Pedicle Screws to Avoid Superior Facet Joint Violation and Pedicle Penetration.

Background Accuracy is crucial in surgeries involving pedicle screws. This study aimed to determine the optimal screw entry points and trajectory angles for the pedicle screw technique used in the surgical treatment of lumbar instability. Methods To achieve this goal, a comparison was made between the screw entry points and trajectories determined using the commonly used intersection technique and those created in a three-dimensional (3D) simulation environment. Thirty-two cases of lumbar degenerative spondylolisthesis, selected from surgeries between 2018 and 2023, were included. Preoperative lumbar computed tomography (CT) images were converted into 3D models, and simulations for pedicle screw placement were conducted. Results Using the intersection technique, upper facet damage was noted in 31.3% of L1, 37.5% of L2, 6.3% of L3, and 31.3% of L5 segments. Adjustments to entry points and angles in the 3D environment were made to determine optimal trajectories. The revised screw angles showed statistically significant improvements at L1, L2, and L5 segments compared to the intersection technique. Conclusions The intersection technique does not appear safe in preserving the superior facet joint. A more lateral and caudal pedicle entry should be preferred in the upper segments, and at L5, a more lateral pedicle entry should be used. Consequently, the screw angles should be adjusted accordingly.