In this article, the individual bones of the cervical spine, the major internal and external ligaments that hold the bones in place and the various vertebral fractures will be reviewed.
The cervical vertebrae are the smallest vertebrae in the spinal column. There are seven individual bones and the first, second and seventh are uniquely shaped, whereas the third to the sixth are similarly shaped. Firstly, the third to sixth vertebrae will be discussed, followed by the first, second and seventh. Once the bones have been examined, the external cervical ligaments and the superficial and deep internal ligaments will also be duly noted.
C3 to C6 have small bodies with posterior and lateral pedicles. The short spinous processes are bifid in shape whereas the vertebral foramina are shaped like large triangles. Within each transverse process there is a foramen transversarium and at the level of C6 the vertebral artery enters the corresponding foramen. The anterior tubercle and the posterior tubercle are the anterior and posterior portions of the transverse processes.
C1, otherwise known as the atlas, is the first cervical vertebrae as well as the first vertebrae in the spinal column. It supports the skull which sits directly above it and it only has an anterior arch and a posterior arch, with no body or spinous process. Laterally, large bone masses help to support the occipital condyles of the skull superiorly and balance the atlas upon the axis inferiorly. As with the other vertebrae, the foramen transversarium is located within a large transverse process.
The axis or C2 as it is clinically called, has its odontoid process (dens) located on its superior surface. It has a large bifid spinous process and in contrast to C1, a small transverse process which houses its foramen transversarium.
Lastly, C7 which is also called the vertebra prominens is the only cervical vertebra whose spinous process is not bifid. It is called the most prominent vertebra because its long spinous process protrudes from under the skin and is visible to the naked eye. It has a large transverse process like the atlas, which also holds the foramen transversarium that encapsulates the vertebral veins and occasionally the vertebral arteries.
The External Ligaments
The yellow ligaments, otherwise known as the ligamenta flava attach themselves to the anterior aspects of the lamina inside the vertebral foramen and they extend from the axis up until the first sacral vertebrae, surpassing the adjacent cervical vertebrae and thoracic vertebrae.
The anterior longitudinal ligament is anterior to the axis and is continuous with the anterior atlantoaxial ligament. It attaches to the anterior surfaces of the vertebral bodies and it runs from the axis to the sacrum.
The anterior atlanto-occipital membrane is continuous with the atlanto-occipital joint for a lateral viewpoint and stretches between the foramen magnum on its posterior margin cranially to the anterior arch of the atlas caudally.
The posterior atlanto-occipital membrane extends between the same two anatomical structures as the superior atlanto-occipital membrane; however their primary difference is that this membrane allows the vertebral artery to pass through it on its lateral margin.
Lastly, the ligamentum nuchae runs between two bony areas known as the occipital protuberance of the medial nuchal line on the occipital bone of the skull cranially and the spinous process of the cervical vertebrae C7 caudally. When running between these two bony extensions, the ligament attaches to the posterior tubercle of the atlas, as well as the spinous processes of the axis below it and the cervical vertebrae C3 to C6.
The Internal Ligaments
The internal ligaments are categorized according to their placement into deep and superficial ligaments. The superficial ligaments include the tectorial membrane and the posterior longitudinal ligament.
The posterior longitudinal ligament sits superiorly to the axis and continues with the fibers of the tectorial membrane. It attaches to the posterior surfaces of the vertebral bodies and splays out between the axis and the sacrum, within the vertebral foramen.
The tectorial membrane starts superior to the posterior longitudinal ligament, before it continues caudally to meet it. Its origin is on the occipital bone of the cranium, in the basilar region, where it becomes one with the Dura mater and inserts onto the posterior part of the axial body.
The deep ligaments include the alar ligament, the apical ligament of the dens, the superior longitudinal band of the cruciate ligament, the transverse ligament of the atlas and the inferior longitudinal band.
The superior longitudinal band of the cruciate ligament is part of the transverse ligament of the atlas, so these two ligaments will be discussed simultaneously, as will the inferior longitudinal band, which makes up the third and final component of the cruciate ligament. The superior band extends cranially and is attached to the basilar portion of the occipital bone of the skull, just as the inferior band opposes it and attaches caudally on the posterior aspect of the axial body. The thickest part of this entire arrangement is the transverse ligament which holds the dens and the anterior arch together by running in the anterior arch of the atlas from side to side.
The alar ligament, which is also called the ‘check ligament’ limits the rotational axis of the skull, by extending from the dens to the occipital condyle on its mesial side.
Lastly, the apical ligament of the dens extends from the anterior margin of the foramen magnum to the dens.
In this section, three of the most common vertebral fractures will be mentioned, including odontoid fractures, the hangman’s fracture and the Jefferson fracture:
- Odontoid fractures have three types of fracture because the axis can fracture in three different places or levels. If only the tip of the odontoid process is fractured, then it is a type I fracture. Type II fractures include the tip, as well as the base or the neck of the odontoid process. Lastly, the type III fracture can be seen when the tip, the neck and part of the body of the axis fractured.
- The Hangman’s fracture is a transversal fracture at the level of C2 (Cervical vertebra number two) between the superior and inferior articulating facets of the vertebral arch. This occurs most frequently in car accidents, where the neck extends and the axis is compressed, causing traumatic spodylolisthesis. Historically, this also occurred during executions, where prisoners were hung by the neck until death by a hangman, hence the name.
- The Jefferson fracture occurs upon the atlas at the level of C1 (Cervical vertebra number one) due to its compression by the skull. Because of this extra pressure the axis is overloaded and bursts, compromising the vertebral artery. The majority of patients do not have any neurological implications, but those who do, suffer from neck pain. This type of fracture has two subtypes:
- Stable: when the transverse ligament of the atlas is intact and it can be resolved by giving the patient a soft collar to wear known as an orthosis.
- Unstable: when the transverse ligament of the atlas is not intact and this subtype creates many more problems for both the patient and the physician. The patient often needs cranial traction through a halo, as well as cervical fusion.
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