Unilateral versus bilateral posterior C1 lateral mass-C2 pedicle screw fixation for traumatic odontoid fractures: a retrospective comparative cohort study.

OBJECTIVE: Bilateral posterior C1 lateral mass-C2 pedicle screw fixation is the standard surgical treatment for unstable traumatic odontoid fractures. However, unilateral fixation may be required when bilateral instrumentation cannot be safely completed because of anatomical constraints or intraoperative complications. This study compared the clinical and radiological outcomes of unilateral and bilateral posterior C1-C2 fixation in patients with traumatic odontoid fractures. METHODS: This retrospective comparative cohort study included 43 adult patients who underwent posterior C1 lateral mass-C2 pedicle screw fixation for traumatic odontoid fractures between 2016 and 2024. Fourteen patients underwent unilateral fixation and 29 underwent bilateral fixation. The primary outcome was CT-confirmed fusion. Secondary outcomes included pain, neurological function, radiological parameters, operative variables, complications, and reoperation. Longitudinal radiological outcomes were evaluated using baseline-adjusted linear mixed-effects models where appropriate. RESULTS: CT-confirmed fusion was achieved in 92.9% of patients in the unilateral group and 93.1% in the bilateral group (p = 1.000). Time to fusion, nonunion, screw loosening, and reoperation rates were comparable between groups. Both groups demonstrated significant improvement in neck pain, with no significant between-group differences in pain reduction or neurological recovery. High-riding vertebral artery anatomy was more frequently associated with unilateral fixation, although the difference did not reach statistical significance (p = 0.057). Intraoperative vascular or venous events were more common in the unilateral group (35.7% vs. 6.9%, p = 0.028), reflecting the anatomical and technical factors leading to unilateral completion. Longitudinal analyses demonstrated no significant between-group differences in postoperative ADI or PADI behavior, while baseline-adjusted analysis showed no significant difference in postoperative C1-C2 angle. CONCLUSION: In patients with traumatic odontoid fractures, unilateral posterior C1-C2 fixation achieved CT-confirmed fusion, radiological stability, and clinical outcomes comparable to bilateral fixation. Although bilateral fixation remains the preferred strategy, unilateral fixation represents a reasonable salvage or anatomy-driven alternative when safe bilateral instrumentation cannot be achieved.