Surgical Strategy Analysis of Chiari Malformation With or Without Type II Basilar Invagination According to the Morphological Types of the Atlanto-Occipital Joint: A Retrospective Study of 212 Patients.

Objective: Our previous study categorized atlas occipital joint (AOJ) morphology into three types, with types II and III-AOJ associated with Chiari malformation (CM) with and without Type II basilar invagination (II-BI), respectively. This study aimed to assess the feasibility of tailoring surgical strategies for patients with CM based on AOJ morphological types.

Methods: We retrospectively studied 212 CM patients who underwent foramen magnum decompression (FMD) or combined occipitocervical fusion (OCF). Patients were divided into four groups: (1) pure CM with II-AOJ who underwent FMD (CM-II-FMD); (2) pure CM with III-AOJ who underwent FMD + OCF (CM-III-OCF); (3) CM-III-FMD; and (4) CM + II-BI with III-AOJ who underwent FMD + OCF (BI-III-OCF). Clinical data, including manifestations, imaging findings, surgical details, and neurological assessments, were analyzed at the final follow-up to assess surgical efficacy.

Results: Patients in the BI-III-OCF, CM-III-OCF, and CM-II-FMD groups exhibited a significant improvement in clinical symptoms (pain, sensory disturbances, motor weakness, gait ataxia, and bladder and bowel dysfunction) compared to preoperative levels (p < 0.05). Results from the Japanese Orthopedic Association scale and Neck Disability Index indicated a significant reduction in the degree of neurological impairment within these groups (p < 0.05). Furthermore, the Chicago Chiari Outcome Scale scores indicated superior surgical outcomes for patients in these groups. Imaging analyses demonstrated significant reductions in the syringomyelic segment, syringomyelia width, and tonsillar herniation distance among these patients (p < 0.05). However, the CM-III-FMD group did not significantly improve in these areas (p > 0.05). Postoperative complications occurred in 4.3% of FMD + OCF patients and 3.3% of FMD-only patients.

Conclusion: AOJ morphological types can guide surgical treatment strategies for CM with or without II-BI. FMD alone is suitable for II-AOJ cases, whereas III-AOJ cases should be treated with FMD combined with OCF.