Complex Atlantoaxial Dislocation with Basilar Invagination and an Anomalous Dominant Right Vertebral Artery: C1 Lateral Mass Screw Placement Above the Vertebral Artery

Complex atlantoaxial dislocation (AAD) with basilar invagination (BI) is a craniovertebral junction anomaly that can cause progressive myelopathy, and anomalous vertebral artery (VA) anatomy makes C1-C2 instrumentation hazardous. We report an 18-year-old male with quadriparesis for 2 years, with loss of fine touch and joint position sense, and no history of trauma. Imaging showed complex AAD with BI, atlanto-occipital assimilation, a rotated C1-C2 joint, C2-C3 block vertebra, chronic cervical cord injury at C1 and a dominant, abnormally coursing right VA. Posterior fixation was done with a C2 pedicle screw and a right C1 screw placed above the vertebral artery. There was no blood loss, the post-operative course was uneventful and the post-operative X-ray was satisfactory. Careful pre-operative assessment of VA anatomy allows safe, individualised C1 screw placement.