III. Development anomalies of individual vertebrae:
1. Assimilation of the atlas:
– atlanto-occipital assimilation (occipitalization) – partial or complete fusion of the I cervical vertebra with the occipital bone: two-sided (symmetric) or one-sided (asymmetric);
– atlantoaxial assimilation – partial or complete fusion of the I and II vertebrae.
2. Manifestation of the atlas (formation of the occipital vertebra – proatlas) –inclusion of the atlas particles into the occipital bone which is manifested in the presence of anomalous bony prominences in the circle of the great (occipital) foramen.
3. Kimmerle`s anomaly – transformation of the vertebral artery groove on the atlas into the canal as a result of formation of a bony outgrowth above this groove.
4. Development anomalies of the II cervical vertebra:
– agenesia (absence) of the dens;
– the dens and the body of the II cervical vertebra are not fused together.
5. Thoracolisation of the cervical vertebrae – formation of cervical ribs (most often from the VII cervical vertebra).
6. Sacralisation – fusion of the V lumbar vertebra with the I sacral vertebra: there are 4 vertebrae in the lumbar part of the vertebral column; the sacrum consists of 6 vertebrae.
7. Lumbarisation – the I sacral vertebra and the II sacral vertebra are not fused together: there are 6 vertebrae in the lumbar part of the vertebral column; the sacrum consists of 4 vertebrae.