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In Klippel-Feil patients with atlantoaxial dislocation, narrow C2 pedicles are often encountered preventing pedicle screw placement. Alternative techniques, including translaminar screws, pars screws, and inferior process screws could not achieve 3-column rigid fixation, and have shown inferior biomechanical stability. The present study aimed to evaluate the feasibility, safety, and efficacy of C3 pedicle screws (C3PSs) as an option for atlantoaxial stabilization in Klippel-Feil patients, and to introduce a freehand technique, the "medial sliding technique," for safe and accurate C3PS insertion. Thirty-seven Klippel-Feil patients with congenital C2–3 fusion who have received atlantoaxial fixation were reviewed. Preoperative CT and CT angiography were acquired to evaluate the feasibility of C3PS placement. C1 lateral mass and C3PS constructs were used for atlantoaxial stabilization. The "medial sliding technique" was introduced to facilitate C3PS insertion. Clinical outcomes and complications were evaluated, and screw accuracy was graded on postoperative CT scans. Morphological measurements showed that more than 80% C3 pedicles could accommodate a 3.5-mm screw. Fifty-eight C3PSs were placed in 33/37 patients using the medial sliding technique. Overall, 96.7% screws were considered safe and there was no related neurovascular complications; 27/33 patients exhibited neurological improvement and 30/33 patients had a solid bone fusion at an average 19.3-month follow-up. Therefore, the C3PS was a feasible option for atlantoaxial fixation in Klippel-Feil patients. The clinically efficiency of C3PS was satisfied with high fusion rates and low complications. The medial sliding technique we used could facilitate safe and accurate placement of C3PSs in Klippel-Feil patients with fused C2–3 vertebra. [ABSTRACT FROM AUTHOR]

Purpose: To introduce a novel surgical protocol for safe and accurate placement of C1 lateral mass screws in patients with atlas assimilation, basilar invagination and atlantoaxial instability, and to categorize the screw accuracy and perioperative complications regarding this technique in a large case series. Methods: Between January 2015 and January 2020, patients who had atlas assimilation, basilar invagination and atlantoaxial instability, and underwent atlantoaxial fixation using C1 lateral mass screws were reviewed. C1 lateral mass screws were placed with a novel surgical protocol following a series key steps, including posterior para-odontoid ligament release, panoramic exposure of the invaginated lateral mass, and diligent protection of the abnormal VA. Screw accuracy and related complications were specifically evaluated. Results: A total of 434 C1 lateral mass screws were placed. Fifteen screws (3.5%) were classified as unacceptable, 54 screws (12.4%) were classified as acceptable, and 365 screws (84.1%) were classified as ideal. Overall, 96.5% of screws were deemed safe. There were no cases of vascular injury or permanent neurological defects. One patient with an unacceptable screw presented with hypoglossal nerve paralysis and recovered after an immediate revision surgery. Thirty-seven patients complained about occipital neuralgia and were successfully managed with medication. Conclusion: Placement of C1 lateral mass screws in patients with atlas assimilation, basilar invagination and atlantoaxial instability following this surgical protocol is safe and accurate. Thorough para-odontoid ligamental release, wide exposure of the invaginated lateral mass, and diligent protection of the vertebral artery are critical to maximize the chances of successful screw placement. [ABSTRACT FROM AUTHOR]