• Qinguo Huang, Xiaoyu Yang, Dongying Zheng, Qiang Zhou, Hong Li, Lin Peng, Junhua Ye, Songtao Qi, and Yuntao Lu.
• Department of Neurosurgery, Nanfang Hospital, Southern Medical University, Guangzhou, China.
• Neurosurgery. 2023 Apr 1; 92 (4): 837853837-853.

BackgroundOur previous study suggested that atlanto-occipital instability (AOI) is common in patients with type II basilar invagination (II-BI).ObjectiveTo further understand the pathogenesis of AOI in Chiari malformations (CM) and CM + II-BI through systematic measurements of the bone structure surrounding the craniocervical junction.MethodsComputed tomography data from 185 adults (80 controls, 63 CM, and 42 CM + II-BI) were collected, and geometric models were established for parameter measurement. Canonical correlation analysis was used to evaluate the morphological and positional relationships of the atlanto-occipital joint (AOJ).ResultsAmong the 3 groups, the length and height of the condyle and superior portion of the lateral masses of the atlas (C1-LM) were smallest in CM + II-BI cases; the AOJ had the shallowest depth and the lowest curvature in the same group. AOJs were divided into 3 morphological types: type I, the typical ball-and-socket joint, mainly in the control group (100%); type II, the shallower joint, mainly in the CM group (92.9%); and type III, the abnormal flat-tilt joint, mainly in the CM + II-BI group (89.3%). Kinematic computed tomography revealed AOI in all III-AOJs (100%) and some II-AOJs (1.5%) but not in type I-AOJs (0%). Morphological parameters of the superior portion of C1-LM positively correlated with those of C0 and the clivus and significantly correlated with AOI.ConclusionDysplasia of the condyle and superior portion of C1-LM exists in both CM and II-BI cases yet is more obvious in type II-BI. Unstable movement caused by AOJ deformation is another pathogenic factor in patients with CM + II-BI.Copyright © 2022 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the Congress of Neurological Surgeons.

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