Back To Basics at The Craniovertebral Junction: Occipito-Cervical Fusion for Basilar Invagination with Atlantoaxial Instability.

INTRODUCTION: Basilar invagination (BI) with atlantoaxial instability is a complex craniovertebral junction disorder that causes progressive cervicomedullary compression and disabling myelopathy. Although reduction-based techniques such as distraction-compression-extension-reduction (DCER) have expanded surgical options, conventional occipitocervical fusion remains an important stabilization strategy in selected patients with rigid deformity, advanced neurological compromise, or infective craniovertebral junction pathology. MATERIALS AND METHODS: This retrospective case series included three patients with BI and atlantoaxial instability, including one with infective C1-C2 spondylodiscitis, who underwent posterior occipitocervical fusion with foramen magnum decompression between 2024 and 2025. Clinical outcomes were assessed using the Nurick grade, Visual Analog Scale (VAS), and Oswestry Disability Index (ODI). Radiographic evaluation included the atlantodental interval (ADI), clivo-axial angle (CXA), Chamberlain's line, and McRae's line. Perioperative complications and neurological outcomes were recorded. All patients completed 12 months of follow-up. RESULTS: All patients presented with advanced myelopathy (Nurick Grade III-V) and marked craniovertebral instability (ADI, 6.2-9.0 mm; CXA, 125°-132°). Posterior occipitocervical fusion with foramen magnum decompression was successfully completed in all patients without intraoperative neurological deterioration, implant-related complications, or revision surgery. Neurological status remained stable or improved throughout follow-up. The patient with infective spondylodiscitis demonstrated improvement in VAS (8 to 3) and ODI (64% to 38%), while all patients achieved radiographic construct stability at final follow-up. CONCLUSIONS: Occipitocervical fusion with foramen magnum decompression provided satisfactory neurological stabilization, radiographic stability, and functional improvement in this small series of patients with complex BI and atlantoaxial instability. It remains a valuable stabilization strategy for selected patients when reduction-based techniques are not feasible.