The arches of the axis and the atlas, and the edges of the foramen magnum are held together by these loose and flexible sleeves of fibrous tissue, the atlanto-occipital and atlanto-axial ligaments. The arches of the regular cervical vertebrae are held together by strips of yellow fibrocartilage, known collectively as the ligamentum flavum. This article will discuss the anatomy and function of the axis. as for typical vertebrae but has two extra primary ossification centers for the dens (odontoid process) The primary ossification centers first appear at. one for each side of the posterior arch (two in total) C2 (axis): five primary ossification centers in total. The dens axis plays an important function for the movement of the head, acting as a stable pivot around which the atlas and head rotate. C1 (atlas): three primary ossification centers in total. 1 In the elderly population, this fracture type represents the most common cervical spine fracture and in the population older than 80 years, the most common spine fracture of all. The C3-L5 vertebrae typically have three primary ossification centers that start appearing at 9 weeks in utero and finish primary ossification by one year 1-4. Odontoid fractures are widely common and reported to account for up to 15 of all cervical spine injuries. Lastly, we’ll look at the ligaments that connect the vertebral arches. Its most characteristic feature is the prominent superior projection known as the dens axis, or odontoid process. Ossification of the vertebral column is complex but an overview of primary and secondary ossification centers is given below. Here’s the tectorial membrane, here in front of it is the divided transverse ligament of the atlas. The alar ligaments limit rotation of the head, specially in lateral flexion. They pass from here on the odontoid process, to here on the inside of the occipital condyles. We’ll remove all of the cruciform ligament to see the odontoid process and the alar ligaments. These, along with the transverse ligament of the atlas, are referred to collectively as the cruciform ligament. The transverse ligament prevents the odontoid process from being displaced backwards.Ī slender ligament, the superior band, runs upward from the transverse ligament to the base of the occiput, another one, the inferior band runs downward to the body of the axis. The transverse ligament is attached on each side to these two tubercles on the atlas. To see them, we’ll go back to the previous rear view, and remove the tectorial membrane.ĭirectlly beneath the tectorial membrane is this strong and important ligament, the transverse ligament of the atlas. We’ll see the transverse ligament of the atlas, the cruciform ligament (which the transverse ligament is part of), and the alar ligaments. Now we’ll look at the ligaments which hold the odontoid process in place, making it the stable pivot round which rotation of the head occurs.
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