C1 Lateral Mass Screw Insertion Caudally From the C2 Nerve Root to Avoid Craniocervical Fusion in a Patient With Atlantoaxial Subluxation Associated With Ponticulus Posticus: A Case Report.

This report describes the case of a 78-year-old female patient with a rare complex upper cervical spine disorder combined with atlantoaxial subluxation (AAS), ponticulus posticus (PP), and high-riding vertebral artery (HRVA), treated with posterior C1-C3 screw fixation. To avoid vertebral artery injury during screw insertion, a C1 lateral mass screw (LMS) on the PP side was inserted from the caudal side of the C2 nerve root. Preoperative three-dimensional CT angiography is important for selecting the optimal posterior screw entry point and trajectory among several screw options. C1 LMS insertion from the caudal side of the C2 nerve root may be an alternative screw trajectory in the PP with vertebral artery running variation.