Posterior C1-2 Fusion Using Large-Diameter C2 Pars and Intralaminar Screws in the Setting of a High-Riding Vertebral Artery: A Case Report

A high-riding vertebral artery (HRVA) narrows the C2 pedicle corridor and increases the risk of vertebral artery injury during C2 pedicle or transarticular screw placement. Selecting an anchor that preserves safety without compromising stability remains challenging in such cases. A 32-year-old man with Down syndrome presented with neck and left-sided limb pain, left-hand clumsiness, and gait disturbance. Imaging showed atlantoaxial subluxation (AAS) with left HRVA. We performed posterior C1-2 fusion using a large-diameter C2 pars screw together with a C2 intralaminar screw on the HRVA side, plus a C1 lateral mass screw and a contralateral C2 pedicle screw. Postoperatively, symptoms improved, and no implant-related complications were observed at one-year follow-up. In AAS complicated by HRVA, a large-diameter C2 pars plus intralaminar screw construct can secure a safe trajectory while achieving satisfactory initial stability and clinical improvement. This hybrid strategy may serve as a practical alternative when a C2 pedicle trajectory is unsafe.