BACKGROUND : Based on standard computed tomography (CT) and micro-CT scan axis images, our study aims to analyse the incidence of variation of non-fusion ossification centre in the base of the odontoid and its anatomical structure characteristics, to compare ossification centre images and analyse the possible features of the ossification centre that can influence adult odontoid fractures. METHODS : Fifty cases were selected for standard cervical CT of the normal axis bone (second cervical) anatomy to calculate the incidence of variation of the non-fusion ossification centre in the base of the odontoid and the indexes of associated anatomical structure. In addition, five dry bone samples with the odontoid were chosen for micro-CT to analyse the clear anatomic structure of the trabecular bone in the ossification centre. RESULTS : Incidence of variation of non-fusion ossification centre in the base of the odontoid was 28%. In the non-ossification group, the mean sagittal diameter of the base of odontoid (SDBO, mm) was 7.64 ± 1.29 mm, the mean transverse diameter of the base of odontoid (TDBO, mm) was 7.14 ± 1.55 mm, and the SDBO:TDBO ratio was 1.1 ± 0.22. In the ossification group, the mean SDBO was 7.7 ± 1.15 mm, the mean TDBO was 7.38 ± 1.32 mm, and the SDBO:TDBO ratio was 1.07 ± 0.21. There was no significant difference in the associated indexes between the ossification and non-ossification groups (p > 0.05). Micro-CT revealed the micro-structure of trabecular bone in the ossification centre and the close relationship between the trabecular bone and the odontoid. One existing non-ossification centre in the base of the odontoid was found in the five odontoid images. The trabecular bone indexes chosen in the target area of the ossification centre were weaker than those in other areas. CONCLUSIONS : The variation rate of the non-fusion ossification centre in the base of the odontoid is relatively high and may be an important factor in the aetiology of type II and III odontoid fractures.