Posterior C1-C2 fixation for atlantoaxial instability due to a dysplastic C1 arch, complicated by an accidental vertebral artery injury managed with intravascular intervention and salvage contralateral unilateral fusion.

Posterior fixation with fusion is recommended in symptomatic congenital anomalies of the upper cervical spine. Altered vertebral anatomy in such cases increases the likelihood of intraoperative complications, where injury to the vertebral artery (VA) may result in cerebellar and dorsolateral medulla oblongata ischemia. Prompt and appropriate intervention is paramount if complications arise. We present a patient with a dysplastic C1 arch, leading to atlantodental arthrosis and anterior C1 subluxation with resultant compressive myelopathy of the spinal cord. During elective surgery, a VA injury occurred, which was managed with intravascular intervention and salvage contralateral posterior unilateral C1-C2 fusion. Postoperatively, the patient developed partial Wallenberg syndrome. Imaging revealed two ischemic changes in the cerebellar hemisphere. One year after surgery, the patient showed substantial improvement following comprehensive rehabilitation, able to ambulate without support and maintain a significant level of independence in everyday activities.