Radiographic feasibility of novel cervical pedicle inlet screw placement during posterior cervical fusion

Cervical pedicle inlet screws represent a novel fixation technique similar to traditional pedicle screws but terminate before the pedicle isthmus, thus limiting risk of neurovascular injury. Cadaveric studies have demonstrated greater pullout strength in comparison to traditional lateral mass screws, but clinical feasibility data is limited. This study provides a radiographic assessment of the feasibility of cervical pedicle inlet screw placement.

Patients undergoing posterior cervical fusion for cervical myelopathy were analyzed. Using a 3D spine navigation workstation, trajectories for cervical pedicle inlet and traditional pedicle screws were planned on postoperative computed tomography scans from C3 to C6. Planned screw dimensions were compared among cervical pedicle inlet, traditional pedicle, and intraoperatively placed lateral mass screws.

Thirty patients were included, comprising 234 planned screws (117 bilateral levels). Pedicle inlet trajectories were feasible in all cases. Traditional pedicle screw trajectories were not feasible in 69 (29.5%) instances due to pedicle size or vertebral artery proximity. Pedicle inlet screws ranged from 4.0 mm × 14 mm to 4.5 mm × 24 mm. All pedicle inlet screws were larger in diameter than lateral mass screws, and 66% were longer (P=0.011). Linear regression analysis demonstrated the more caudal level was a modest but significant predictor of pedicle inlet screw length [R2=0.11, F(1, 232) =28.83, β=0.33, standard error (SE) =0.13, P<0.001].

Cervical pedicle inlet screws were universally feasible and consistently accommodated larger diameters and lengths compared with lateral mass fixation. Combined with prior biomechanical evidence, these findings support pedicle inlet screws as a promising alternative for subaxial cervical fixation.