Radiological studies for the best position and trajectory of the anterior cervical pedicle screw in the lower cervical spine in normal populations.

Background: Anterior cervical transpedicular screw (ACTPS) surgery has gained popularity due to its strong biomechanical fixation via a single anterior approach, especially in cases like osteoporosis requiring three-column stabilization. However, precise entry point and trajectory are essential, as malpositioning can cause serious complications such as spinal cord or vertebral artery injury. This study aims to evaluate a novel preoperative planning program designed to improve accuracy in locating the optimal entry point and trajectory for ACTPS. Methods: This study included normal patients who underwent cervical spine computed tomography (CT) scans. All pedicles of the lower cervical spine were measured in length, diameter, angle of trajectory in the sagittal, coronal, and axial planes after finding the best position for the placement of the pedicle screw. The entry point was identified and classified into grid zones (zones 1 to 4) on the anterior surface of the vertebral body. Results: In the axial plane, the safe zones for the inserted pedicle screw were in zone 2 and zone 3. The entry points screws started with the mean lengths of the distance from the midline axis being 1.7±0.5 mm and the mean angulations of the entry points of the screws were 46.2°±2.6°. The screw lengths were longer in men (32.9±1.8 mm) than in women (30.7±1.6 mm) all cervical levels and the screw lengths at C6-C7 levels were gradually longer than the levels of C3-C5. In the sagittal plane, the best entry points of all ACTPS trajectories started from the upper half of the vertebral body. The trajectory of the screws was nearly parallel (sagittal angulation mean 1.4°±0.6°) to the anterior boarder of the upper vertebral endplate, incline from the caudal (C3) to the cephalad (C7). In the coronal plane, the average diameters of the pedicle gradually increased from C3 to C7. The larger pedicle diameter was found in men (3.3±0.3 mm) than in women (3.1±0.2 mm) at all cervical levels with statistical significance. Conclusions: The optimal entry points for ACTPS in the lower cervical spine are located on the midline axis and near the superior vertebral border of the vertebral body, with trajectory angulations in the axial plane of 46.2°±2.6° and nearly parallel to the superior vertebral border in the sagittal plane, at 1.4°±0.6°. The pedicle screw lengths range from around 31.8±1.7 mm. ACTPS is a feasible option for lower cervical spine fixation. Our CT-based measurements, which include essential anatomical parameters of the cervical spine, will assist surgeons in performing this procedure.