Utility of Laminar Fiducials for Registration to Maximize Safety of C2 Pedicle Screw Placement for Atlantoaxial Instability due to Os Odontoideum in Down Syndrome: A Technical Note

Atlantoaxial instability secondary to os odontoideum is a possible complication in Down syndrome. Common surgical treatment strategies include C1-2 fusion or occipitocervical fusion. The primary advantage of C1-2 fusion is motion preservation at the C0C1 joint, however, various anatomic abnormalities can preclude safe pedicle screw placement at C2. 5 mm and smaller C2 pedicles create a challenge in one-third of os odontoideum cases, thus appropriate utilities or alternative surgical strategies must be considered. Here we detail the utility of a real-time intraoperative navigation setup that allows for multiple in situ re-registrations for precise localization. We present a patient with Down syndrome with progressive myelopathy secondary to atlantoaxial instability from os odontoideum where in situ C2 and C3 laminar bone fiducials allowed for precise intraoperative navigation and successful cannulation of sub-5 mm C2 pedicles. Real-time feedback for operative navigation can provide immense value in similar high-risk cases.