Os odontoideum eMedicine Orthopedics

Description: Os odontoideum describes a condition in which the dens is separated from the axis body. Os odontoideum initially was thought to be a congenital failure of fusion of the dens to the remainder of the axis. As such, it usually is grouped with other craniocervical junction abnormalities, such as dental aplasia and hypoplasia. These lesions are clinically important because the mobile or insufficient dens renders the transverse atlantal ligament (TAL) incompetent. Without a functional dens-TAL complex, translation of the atlas on the axis is not effectively restrained. With increased motion, upper cervical cord or vertebral artery impingement may occur.
Author: Eeric Truumees, MD 2005