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Clinical & Anatomical Features and Pathological Conditions of Surgically Treated Adult Patients with Occipitalization of the Atlas

Yasunori Tatara, MD,1 Takachika Shimizu, MD,2 Keisuke Fueki, MD,2 Masatake Ino, MD,2 Naofumi Toda, MD,2 Tetsu Tanouchi, MD,2 Nodoka Manabe, MD2

1Yokohama Minami Kyosai Hospital, Yokohama, Kanagawa, Japan 2Gunma Spine Center, Harunaso Hospital, Takasaki, Japan



This paper intends to clarify clinical and anatomical features as well as pathological conditions of surgically treated adult patients with occipitalization of the atlas.


The authors reviewed 12 consecutive adult patients with occipitalization of the atlas who un-derwent surgery for myleopathy in our hospital. Mainly using preoperative computed tomography and three-dimensional computed tomography angiography, we investigated their anomalies of the osseous structures and vertebral artery at the cervical spine including the craniovertebral junction (CVJ). We also developed a new classification system for occipitalization of the atlas.


Atlantoaxial subluxation (AAS) was detected in 9 patients (75%). The condition of AAS was irreducible in 7 patients. Among these 7 patients, deformity at the lateral at-lantoaxial joints was detected in 2 patients. C2-3 fusion was detected in 6 patients (67%) among 9 patients with AAS. Anomalies of the VA were detected in 11 patients (92%). Occipitalization of the atlas was classified into three types according to their pathological conditions. In type 1 (2 patients) the medial atlantoaxial joint is semi-dislocated and the lateral atlantoaxial joints are severely deformed. Type 2 (7 patients) exhibits AAS but the lateral atlantoaxial joints are not deformed. Type 3 (3 patients) is not associated with AAS and therefore does not exhibit osseous stenosis at the CVJ. In type 3 the myelopathy was caused by another coexisting condition.


Occipitalization of the atlas is classified into three types. The main pathological condi-tion in both types 1 and 2 is AAS. Reduction of AAS is essential in both; however, reduction of AAS in type 1 is more technically demanding than in type 2. The pathological conditions of type 3 are completely different from those of the others, so an accurate diagnosis must be made. The new classification system is a useful guide for surgeons when planning surgical strategies.

occipitalization of the atlas, atlantoaxial subluxation, craniovertebral junction, vertebral artery
Volume 9 Article 5