atlanto-axial instability

atlanto-axial instability

Abnormal mobility of the articulation of the ATLAS BONE with the AXIS BONE. This is demonstrable on X-ray by a separation of more than 3 mm, at the front, between the body of the atlas and the odontoid process of the axis. People with this abnormality should avoid activities that could bring about dislocation (subluxation) of the bones and serious risk to the spinal cord. Atlanto-axial instability is found in about 20 per cent of people with Down's syndrome because of laxity in the ligaments between the skull and the spine.

Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005