WHAT ARE THE IMPORTANT LIGAMENTS OF THE CRANIOCERVICAL JUNCTION?
MAIN STABILIZERS OF THE CRANIOCERVICAL JUNCTION
Tectorial Membrane
The tectorial membrane, a superior extension of the posterior longitudinal ligament, extends to the anterior margin of the foramen magnum and covers the caudal portion of the clivus. It is a strong, wide band of fibrous tissue that runs from the occipital bone of the skull down to the axis (C2). The tectorial membrane is the major craniocervical stabilizer. It helps to stabilize the craniocervical junction by limiting excessive flexion and extension of the head and neck.
Alar Ligaments
The pair of alar ligaments that attach the axis (C2) to the base of the skull. Their work is to hold your head onto your neck. Alar ligaments are short, thick bands of tissue that run from the side of the dens to the occipital bone. They are important in limiting rotation of the head and neck. Together with the transverse ligament, these ligaments are primary stabilizers of the craniocervical junction.
Transverse Ligament of the Atlas (TAL)
This transverse ligament of the atlas is arguably the most important ligament in your body. It is the thickest and the strongest of the craniocervical junction ligaments.
It is a primary stabilizer and one of the most important stabilizers of the craniocervical junction. It limits anterior subluxation / dislocation of the atlas and provides stability to the craniocervical junction. It holds the odontoid process (the bony projection of the axis that sits in the right of the atlas) in place and prevents it from compressing the spinal cord.
Cruciate / Cruciform Ligament
This ligament consists of two bands: the transverse ligament of the atlas and the longitudinal band that form the shape of a cross. It is an important ligament that holds the posterior dens of C2 in articulation at the atlanto-axial joint. It provides additional support to the odontoid process and helps prevent excessive motion of the craniocervical junction. Ultimately, the cruciate ligament of the atlas prevents abnormal movements of the atlanto-axial joint. The longitudinal bands prevent hyperflexion and hyperextension of the occipital bone, and hold the transverse ligament of the atlas in a normal position.
LIGAMENTS THAT PLAY A ROLE IN LIMITING FLEXION OR EXTENSION
Nuchal Ligament
This is an upward continuation of the supraspinous ligament and extends from the bony projection off every vertebra called the spinous process (of the C7 vertebra) attaching to the back of the occipital bone. It limits too much bending of the neck.
Anterior Atlanto-Occipital Membrane (AAOM)
The anterior atlanto-occipital membrane is a slim structure attaches the front side of the atlas bone (C1) to the foramen magnum (the big hole in the base of your skull). It serves to provide stability to the craniocervical junction in a number of ways including: restricts excessive forward movement (anterior translation), limits atlanto-occipital extension, it provides support to the atlanto-occipital joint, it assists in load-sharing between the anterior column of the spine and it protects vital structures that lie posterior to the atlas (C1) including the spinal cord and brain stem.
VERY LITTLE INVOLVEMENT, IF ANY PART, IN CRANIOCERVICAL INSTABILITY:
Posterior Atlanto-Occipital Membrane (PAOM)
It is believed that this membrane plays very little part in the stability of the atlanto-occipital joint. The main function is to separate the suboccipital muscles from the cervical spinal cord and the contents of the posterior cranial fossa, allowing for the movement of the head and neck.
Apical Ligament of the Dens
This ligament extends from the tip of the odontoid process to the basion. It probably offers little significant contribution to craniocervical junction stability.
Important Note:
With the exception of the alar ligaments and transverse ligament of the atlas, there is quite a bit of contradicting medical studies on the biomechanics and ligament’s roles in stability; and so take this information with a grain of salt!
To help diagnose some conditions of the craniocervical junction, there are a number of measurements that are used by doctors, specifically radiologists, on images of different modalities to help to decide whether you have craniocervical instability or not. Dynamic images such as the head and neck in flexion, extension, side bending and rotation, are better for ruling out craniocervical instability over neutral images
MEASUREMENTS USED TO HELP DIAGNOSE CRANIOCERVICAL INSTABILITY