Modified high-entry C1 screw placement for bilateral persistent first intersegmental artery in atlantoaxial instability: a case report

초록

Background – Atlantoaxial instability (AAI) is a recognized cervical manifestation of rheumatoid arthritis (RA) and may require posterior C1-C2 fixation. Conventional C1 lateral mass screw placement can be hazardous when anomalous vertebral artery (VA) anatomy is present, particularly in patients with persistent first intersegmental artery (PFIA). Case description – A 70-year-old woman with long-standing RA presented with a 6-month history of nuchal pain, rotational neck pain, and occipital neuralgia. Plain radiographs demonstrated AAI with an atlantodental interval of 7.5 mm, and magnetic resonance imaging revealed widening of the C1–C2 interspinous space without spinal cord compression. Computed tomography (CT) angiography revealed bilateral PFIA, with both VAs ascending directly into the foramen magnum without traversing the transverse foramen of C1. Because this anatomy directly intersected the conventional C1 lateral mass screw trajectory, a modified high-entry point was selected at the junction of the posterior arch and lateral mass. C1 lateral mass-C2 pedicle screw fixation was performed without intraoperative vascular or neural complication, and postoperative CT confirmed satisfactory implant placement. Early postoperative neck pain and occipital neuralgia improved. Conclusion – In patients with RA-associated AAI and bilateral PFIA, the standard C1 lateral mass trajectory may be unsafe. This case illustrates that a modified high-entry C1 screw placement can be a feasible alternative when guided by careful preoperative vascular imaging and individualized surgical planning.

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