寰枕融合畸形患者寰枢侧块关节形态变化与寰枢椎脱位的三维特征

Morphological changes of the atlantoaxial facet joint and three-dimensional characteristics of atlantoaxial dislocation in patients with atlanto-occipital assimilation

目的分析寰枕融合畸形伴寰枢椎脱位时侧块关节的形态学变化与脱位的三维特征。方法寰枕融合畸形伴寰枢椎脱位患者36例行螺旋CT扫描后，数据以DICOM格式传送至三维可视化工作站，重建颅颈交界区三维模型，按照骨性畸形、寰齿关节、侧块关节的次序观察骨性畸形及寰枢椎脱位的三维特征。结果寰枢侧块关节呈关节滑脱者57侧（79％）、关节整体变形前倾者61侧（85％）和关节面分离者11侧（15％）。对照两侧对称或不对称侧块关节的形态变化与脱位时寰椎与枢椎的三维位置关系，本组寰枢椎脱位的三维分型可归纳为三种：对称型（14／36例，39％），为两侧寰枢椎侧块关节呈大致对称的关节滑脱和关节整体变形前倾；旋转型（13／36例，36％），为两侧寰枢侧块关节呈显著不对称的关节滑脱和关节整体变形前倾；分离型（9／36例，25％），为至少一侧侧块关节出现关节面的完全分离。结论寰枕融合畸形时先天性的关节发育异常、继发的关节变形以及韧带的疲劳拉伸等多种因素及其相互作用是寰枢椎脱位发生的根本原因。采用三维可视化方法直观地观察和分析寰枢椎脱位及寰枢侧块关节形态．对于手术决策和内固定方案选择等具有重要价值。

Objective To explore the morphological changes of the atlantoaxial facet joint and the three-dimensional characteristics of joint dislocation in patients with atlanto-occipital assimilation accompanied by atlantoaxial dislocation. Methods Thirty-six patients with atlanto-occipital assimilation and concurrent atlantoaxial dislocation underwent spiral CT scanning of the craniovertebral junction, and the imaging data in DICOM format were transferred to the three-dimensional visualization workstation to construct the three-dimensional model of the craniovertebral junction. The characteristics of atlantoaxial dislocation in association with the bony malformation were studied in the reconstructed model. Results Multiple anomalies of the atlantoaxial facet joint were found in these patients, including joint dislocation involving 57 sides in the 36 patients, skeletal deformity in 61 sides, and facet separation in 11 sides. Three-dimensional classification identified 3 types of atlantoaxial dislocation in these patients, namely symmetrical type （14 cases, 39%） representing the approximately symmetrical joint dislocation and/or skeletal distortion, rotational type （13 cases, 36% ） representing apparently asymmetrical joint dislocation and/or skeletal deformity, and separate type （9 cases, 25%） with separation of the joint facets. Conclusion In patients with atlanto-occipital assimilation, multiple factors including developmental anomaly, secondary skeletal deformity and ligament extension and fatigue interact as the fundamental causes ofatlantoaxial dislocation. The CT-based three-dimensional model of the craniovertebral junction allows visualization of the atlantoaxial facet joint and atlantoaxial dislocation to provide important evidence for surgical planning and decision on the internal fixation approaches.