Pedicle screw placement in patients with variant atlas pedicle

OBJECTIVE: To investigate how the anatomy of variant atlas vertebra impacts on the strategy used to place pedicle screws used to treat atlantoaxial instability. METHODS: The study enrolled patients with cervical instability who had a posterior arch pedicle height <3.5 mm at the anchor point, a vertebral artery groove height <3.5 mm, or both. Pedicle screws were fitted according to the anatomy of the variant atlas vertebra. Patients were followed-up to evaluate accuracy of the screw placement and maintenance of cervical stability. RESULTS: A total of 28 patients were enrolled. The mean height of the atlas pedicle proximal section was >5.0 mm. For the vertebral artery groove, the height of the lateral region was significantly greater than that of the medial region. Approximately 60% of atlas vertebrae had lateral heights >3.5 mm (34 of 56). The majority of the posterior arch heights were <3.0 mm. There were no perioperative or postoperative complications observed. CONCLUSIONS: Pedicle screw placement in the lateral pedicle region is the safest and most reliable strategy to treat variant atlas pedicles.