Cervical Pedicle Inlet Screws: Clinical Results of a Novel Trajectory for Navigated Screw Placement in the Sub-axial...

IntroductionLateral mass screws are widely used in the sub-axial cervical spine but have poor pullout strength and result in a screw tulip that is medial, which limits both rod passage to nearby pedicle screws and the ability to centrally decompress the canal after screw placement. True pedicle screws have the highest pullout strength, but carry neurovascular risk. The cervical pedicle inlet (CPI) trajectory is a novel technique that involves a lateral starting point similar to a true pedicle screw, but the tip of the screw stops in the dense bone at the pedicle inlet, thus limiting neurovascular risk. Prior biomechanical studies have demonstrated increased pullout strength relative to lateral mass (LM) screws, but no clinical series have been published. The purpose of this study is to provide a preliminary clinical report on the radiographic and safety profile of this novel screw trajectory.MethodsWe retrospectively reviewed 388 screws placed from C3-7 from 64 consecutive cases of cervico-thoracic fusion from a single surgeon at a single center. All patients were ≥18 years and underwent posterior cervico-thoracic fusion with navigated CPI screw placement in the sub-axial cervical spine between 2020 and 2025. Intra-operative CT scans were available on all patients and were used to classify breaches with a modified Gertzbein-Robbins scale. Screws that were completely in bone were graded as "0," those with a 1-2 mm breach were graded as "1," and screws with > 2 mm breach and that were removed or repositioned intra-operatively were graded as "2."ResultsA total of 388 screws were placed. (292 CPI, 47 LM, 49 pedicle). For the CPI screws, 79% (232/292) were grade 0 (completely in bone), 18% (54/292) were grade 1 (1-2 mm breach), and 2% (6/292) were grade 2 (removed or repositioned intra-operatively). For the LM screws, 72% (34/47) were grade 0, 28% (13/47) were grade 1, and 0% (0/47) were grade 2. For pedicle screws, 61% (30/49) were grade 0, 29% (14/49) were grade 1, and 10% (5/49) were grade 2. CPI screws were more likely than LM or pedicle screws to be grade 0 (P < 0.01). Ten patients experienced some type of early post-operative complication, including delayed C5 palsy (6%, n = 4), superficial infection (3% n = 2), dysphagia (3%, n = 2), or other (3%, n = 2). There were no cases of return to OR for screw malposition or neurovascular injury related to screw placement, and no cases of CPI screw pullout or loosening within 6 months of surgery.ConclusionThe use of navigation allows for safe screw placement along the CPI trajectory, with no recorded screw related complications. For patients with cervical pedicles that are too small to accept a true pedicle screw, the CPI trajectory is a reasonable alternative.