Occipitocervical fusion restores vertebral artery hemodynamics and relieves posterior circulation symptoms in basilar invagination: a patient-specific computational fluid dynamics study.

OBJECTIVE: To investigate vertebral artery (VA) hemodynamic changes after occipitocervical fusion in patients with basilar invagination (BI) using image-based computational fluid dynamics (CFD), and to evaluate correlations among sagittal alignment, hemodynamic alterations, and symptom improvement. METHODS: Thirty-nine Goel type I BI patients who underwent preoperative traction followed by posterior occipitocervical fusion between January 2020 and June 2024 were retrospectively analyzed. Cervical sagittal parameters, including the occipitocervical angle (O-C2A), C2-C7 sagittal vertical axis (SVA), C2-C7 Cobb angle, and T1 slope (T1S), were measured from lateral radiographs. CTA-based CFD models of vertebral artery segments V3-V4 were reconstructed to derive diameter (D), mean flow velocity (MV), peak systolic velocity (PSV), wall pressure (WP), wall shear stress (WSS), and blood flow quantity (Q). Clinical outcomes were assessed using Japanese Orthopaedic Association (JOA), Neck Disability Index (NDI), and Dizziness Handicap Inventory (DHI) scores. RESULTS: Postoperative O-C2A increased significantly (17.14 ± 7.79° vs. 8.36 ± 7.59°, P < 0.05), while C2-C7 SVA, Cobb, and T1S remained stable (P > 0.05). Hemodynamically, postoperative MV (0.37 ± 0.06 m/s vs. 0.33 ± 0.06 m/s, P < 0.001), PSV (1.24 ± 0.18 m/s vs. 1.10 ± 0.15 m/s, P < 0.001), and Q (0.24 ± 0.07 L/min vs. 0.21 ± 0.06 L/min, P < 0.001) were significantly elevated. WP and WSS showed nonsignificant reductions. Clinical scores improved markedly from baseline to the final follow-up: NDI (from 35.3 ± 22.1% to 18.4 ± 16.4%, P < 0.001), JOA score (from 7.6 ± 3.6 to 9.7 ± 3.6, P < 0.001), and DHI (from 40.2 ± 16.9 to 28.6 ± 12.8, P < 0.001). ΔO-C2A correlated positively with ΔD (r = 0.387, P < 0.05) and ΔQ (r = 0.327, P < 0.05). ΔQ was negatively correlated with ΔDHI (r = -0.440, P < 0.01). CONCLUSIONS: Posterior occipitocervical fusion effectively restores craniovertebral alignment, improves VA hemodynamics, and alleviates posterior circulation ischemic symptoms. Changes in O-C2A, C2-C7 SVA, and T1S closely correlate with VA diameter and flow, highlighting the key role of cervical sagittal alignment in regulating VA perfusion. Therefore, achieving optimal sagittal alignment is crucial. These results demonstrate both the mechanical and neurovascular benefits of the procedure, supporting its clinical efficacy in BI.