Sex-specific differences in ossification patterns of the atlas and axis: a computed tomography study.

Background: We investigated the sex-specific differences in ossification patterns of the first two cervical vertebrae in Chinese children.
Methods: A retrospective computed tomography (CT) study was performed between June 2016 and December 2020. Patients younger than 16 years with cervical CT images acquired ≤ 1.5 mm slice thickness were included. All eligible patients were stratified into 2 sex groups and 16 age groups based on 1-year intervals. The ossification status of each synchondrosis and ossification variants were evaluated.
Results: A total of 910 subjects (518 males and 392 females) were included in the study. For the C1 vertebra, the neurocentral synchondroses closed at a median age of 8 years in males and 6.3 years in females, and the posterior synchondrosis fused at 5.4 years in males and at 4.4 years in females. Multifocal anterior arch ossification centers were present in 74 of 411 (18%) subjects, whereas posterior arch variants were observed in 18 of 258 (7%) subjects. For the C2 vertebra, the sequence of complete fusion was as follows: posterior synchondrosis, neurocentral synchondroses, and dentoneural synchondrosis. Uniquely, a fusion line was observed in the dentocentral synchondrosis through adolescence. Anterior arch variants of the C2 vertebra occurred in 17 of 248 (6.9%) subjects. There was no significant difference between the sexes in ossification variants.
Conclusions: All synchondroses of the first two cervical vertebrae fuse slightly earlier in females. The sequence of fusion follows a posterior-to-anterior and caudal-to-cephalad pattern in both sexes. Congenital variants are not rare and should not be confused with trauma.
(© 2022. Children's Hospital, Zhejiang University School of Medicine.)