Technique of C2 Subfacetal Screw in Patients with High-Riding Vertebral Artery.

Abstract

A C2 pedicle screw provides robust construct for fixation in atlantoaxial dislocation.^1-5 However, inserting a C2 pedicle screw with the standard technique in cases with narrow pedicle and high-riding vertebral artery (VA) may endanger the artery.⁶ A pars screw is also risky and biomechanically inferior.^3-5 This video demonstrates the technique of safe insertion of subfacetal screws, directly into the C2 body while safeguarding the VA in a patient with atlantoaxial dislocation/basilar-invagination with cervicomedullary compression (Video 1). Computed tomography angiography showed a high-riding VA with a thin pedicle. The patient underwent posterior C1-C2 joint manipulation and fixation.¹^,² After the joints were exposed, the VA was dissected from the medial border of the C2 transverse foramen and a subfacetal screw was inserted directly into the C2-body, safeguarding the artery.⁷ The screw trajectory is similar to that described by Goel et al⁸ (15-20 degrees cranial and 30-40 degrees medial). The entry point in the Goel technique is 2 mm below the medial portion of C2 superior articular surface. However, with a high-riding VA, the entry point needs to be shifted medially. C1 lateral mass screws were inserted according to the standard technique and fixed to C2 screws with rods. Postoperatively, the patient improved and radiology showed satisfactory reduction with good flow across the VA on angiography. There is a minimal risk of arterial injury/spasm due to its handling. Nevertheless, the benefit of a strong construct clearly outweighs this risk. Alternatively, one may insert a C2 laminar screw. However, the biomechanical considerations are better with the C2 pedicle screws and the overall construct may be not ideal as the fixation is away from the C1-C2 joint.^3-5^,⁹.