This may be a partial or complete union. Assimilation of the atlas is the most common anomaly found at the craniocervical junction. Other terms describing this abnormality are atlantooccipital fusion and/or occipitalization of the atlas. Of importance, is not that the diagnostician be aware of the varied terms given to this osseous anomaly - but that such anomaly may exist without any typical symptom presentation, and thus, serious consequences of upper cervical spinal manipulative therapy may arise without a complete and adequate clinical assessment.
Occipitalization of the atlas is the most common malformation of the craniovertebral junction. It can be diagnosed on lateral teleradiography and its finding imposes screening for associated atlantoaxial instability. In case of instability, brisk movements of the cervical spine during surgery may result in compression and distortion of the spinal chord and vertebro-basilar vascular system.
Its diagnosis imposes screening for other spinal malformations (spinal fusion, hemivertebra, spina bifida occulta). The major risk is compression and distortion of the spinal chord and vertebro-basilar vascular system, during surgery or anesthesia 1)