Angular Reduction and Therapeutic Efficacy Analysis of Type B Basilar Invagination

Objective: To investigate the angular reduction technique for type B basilar invagination and to analyze the clinical efficacy of this method.Methods: A retrospective study was conducted on 45 patients diagnosed with Type B basilar invagination at the Neurosurgery Department of the First Affiliated Hospital of Chongqing Medical University between June 2016 and September 2022.The cohort consisted of 7 males and 38 females, with a mean age of 52.6 ± 11.4 years (range: 25-72 years). Patients were categorized into two groups according to the surgical method employed: the angular reduction group and the simple decompression group. The angular reduction group received interarticular fusion cage implantation combined with occipital-cervical fixation using the cantilever technique and posterior atlanto-occipital decompression. In contrast, the simple decompression group underwent only posterior atlanto-occipital decompression and dural expansion plasty. Surgical outcomes were assessed through comparative analysis of pre-and post-operative CT three-dimensional reconstructions and MRI scans, evaluation of Japanese Orthopaedic Association (JOA) scores, and monitoring of post-operative complications. Results: At the one-year postoperative follow-up: (1) In the angular reduction group, both the clivus axis angle (CAA) and cervicomedullary angle (CMA) significantly increased post-surgery, whereas no significant changes were observed in the simple decompression group. (2) Among the 27 patients with syringomyelia, a reduction in syrinx diameter was observed postoperatively in both groups, with no statistically significant difference between the groups (P>0.05). (3) The postoperative Japanese Orthopaedic Association scores and JOA improvement rates were significantly higher in the angular reduction group compared to the simple decompression group (P<0.05). (4) In the angular reduction group, a single case of incision infection was observed, with no reported instances of intracranial infection or cerebrospinal fluid leakage. The incidence of postoperative complications was significantly lower in the angular reduction group compared to the simple decompression group. Conclusion: For patients with type B basilar invagination, the combination of interarticular fusion cage implantation, occipital-cervical fixation using the cantilever technique, and posterior atlanto-occipital decompression can effectively increase CAA and CMA. Without necessitating dural opening, the reduction in syrinx diameter achieved was comparable to that of the simple decompression group. Moreover, the postoperative clinical symptom improvement rate was superior to that of the simple decompression group, with a lower incidence of postoperative complications and better prognosis.