The cervical spine is the most superior portion of the vertebral column, located between the cranium and the thoracic vertebrae. It is composed of seven individual vertebrae, two of which are given distinctive names; the first cervix vertebrae (C1) is named the atlas, and the second cervical vertebrae (C2) is known as the axis. In this article, we will explore the anatomical elements of the cervical vertebrae, including their identifying features, articulations, and clinical relevance.
The cervical vertebrae have three main attributes that differentiate them from other vertebrae:
The atlas and axis possess additional features that separate them from the other cervical vertebrae.
Atlas: The atlas is the first cervical vertebra and articulates with both the occiput of the head, and the axis (C2). It does not have a vertebral body or a spinous process, but instead it has lateral masses which are linked by an anterior and posterior arch. Each lateral mass is equipped with superior and inferior articular facets; the superior articular facets are for articulation with the occipital condyles, and the inferior articular facets are for articulation with the axis (C2). The anterior arch of the atlas includes a facet for articulation with the dens of the axis, which is secured by the transverse ligament of the atlas, which is connected to the lateral masses. The posterior arch of the atlas has a groove for the vertebral artery and C1 spinal nerve.
Axis: The axis (C2) is easy to spot due to its dens (odontoid process) which extends superiorly from the anterior part of the vertebra. The dens articulates with the anterior arch of the atlas, creating the medial atlanto-axial joint, which allows for the rotation of the head independently of the torso. The axis also consists of superior articular facets, which articulate with the inferior articular facets of the atlas to form two lateral atlanto-axial joints.
The joints of the cervical spine can be divided into two categories: those that are located throughout the entire vertebral column, and those which are located exclusively in the cervical spine.
There are two different joints that are present throughout the entire length of the vertebral column:
There are two joints which are found exclusively in the cervical spine: the atlanto-axial (x3) and the atlanto-occipital joints (x2).
Atlanto-axial joints: These joints form the articulation between the atlas and the axis. There are three different types of atlanto-axial joints:
Atlanto-occipital joints: These joints occur between the superior facets of the lateral masses of the atlas and the occipital condyles at the base of the cranium. These are condyloid type synovial joints, and they permit flexion of the head, as in the nodding of the head.
There are six major ligaments to consider in the cervical spine. The majority of these ligaments are located throughout the entire vertebral column.
The anatomy of the cervical spine is complex, and its understanding is essential for successful diagnosis and treatment. The vertebrae of the cervical spine are distinctive in their features, particularly the atlas and axis. There are a variety of joints present in the cervical spine, including those unique to this area of the vertebrae, as well as ligaments that support and secure them in place. Through knowledge of these elements, a greater understanding of the entire cervical spine can be attained.
The cervical spine is the most superior portion of the vertebral column. Spanning between the cranium and the thoracic vertebrae, it is composed of seven distinct vertebrae, two of which are given unique names: the atlas (C1) and the axis (C2). The cervical spine is related to several neurovascular structures, particularly the vertebral artery, vein, sympathetic nerves, and spinal nerves. These structures pass through the transverse foramina and the intervertebral foramina, respectively, with the exception of C7, where the vertebral artery passes around the vertebra, instead of through. As C7 has a set of spatial nerves extending from above (C7) and below (C8) the vertebra, there are eight spinal nerves associated with seven cervical vertebrae.
Injuries to the cervical spine are fairly common and vary in severity. The most notable cases include Jefferson Fracture of the Atlas, Hyperextension (whiplash) Injury, Hangman’s Fracture, and Fracture of the Dens. Jefferson Fracture of the Atlas is caused by a vertical fall onto an extended neck, causing fracture of the lateral masses of the atlas. Hyperextension Injury is the result of rapid deceleration, causing fractures of any of the cervical vertebrae. Hangman’s Fractures occur due to high velocity hyperextension and distraction of the head, causing fractures of the pars interarticularis of the axis. Finally, Fracture of the Dens occurs due to fractures of the odontoid process, which is often unstable and at high risk of avascular necrosis.
The cervical vertebrae are differentiated from other vertebrae by three main features: the triangular vertebral foramen, the bifid spinous process (where the spinous process splits into two distally), and the transverse foramina (holes in the transverse processes which give passage to the vertebral artery, vein and sympathetic nerves).
In addition to the general features, the atlas and axis have specific characteristics which set them apart. The atlas is the first cervical vertebra and articulates with the occiput of the head and the axis (C2). Unlike the other cervical vertebrae, it has no vertebral body and no spinous process; instead, the atlas has lateral masses which are connected by an anterior and posterior arch. Each lateral mass contains a superior articular facet for articulation with occipital condyles, and an inferior articular facet for articulation with C2. The anterior arch contains a facet for articulation with the dens of the axis, which is secured by the transverse ligament of the atlas. The posterior arch has a groove for the vertebral artery and C1 spinal nerve.
The axis (C2) is easily identifiable due to its dens (odontoid process), which extends superiorly from the anterior portion of the vertebra. The dens articulates with the anterior arch of the atlas, in turn creating the medial atlanto-axial joint which allows for rotation of the head independent of the torso. The axis also contains superior articular facets, which articulate with the inferior articular facets of the atlas to form the two lateral atlanto-axial joints.
The joints of the cervical spine can be divided into two distinct groups; those which are present throughout the vertebral column, and those which are unique to the cervical spine. Present throughout the vertebral column, there are two different joints; the intervertebral disc which is made of fibrocartilage and connects adjacent vertebral bodies (a symphysis type cartilaginous joint) and the articulation of superior and inferior articular processes from adjacent vertebrae, which is a synovial type joint.
Unique to the cervical spine, there are two joints; the atlanto-axial (x3) and atlanto-occipital joints (x2). The atlanto-axial joints are formed by the articulation between the atlas and axis. The lateral atlanto-axial joints (x2) are formed by the articulation between the inferior facets of the lateral masses of C1 and the superior facets of C2.
There are several types of plane type synovial joints that occur at different locations in the human body. One of these is the medial atlanto-axial joint, formed by the articulation of the dens of C2 with the articular facet of C1. This is a pivot type synovial joint that provides a relatively small range of movement.
The atlanto-occipital joints are also considered plane type synovial joints. These joints occur between the superior facets of the lateral masses of the atlas and the occipital condyles at the base of the cranium. This is a condyloid type synovial joint, permitting flexion of the head – such as in the act of nodding.
When examining the cervical spine, there are six major ligaments to consider. Out of these six, the majority are present throughout the entire vertebral column. These typically include the anterior and posterior longitudinal ligaments – long ligaments which run the length of the vertebral column, covering the vertebral bodies and intervertebral discs. Additionally, there is the ligamentum flavum which connects the laminae of adjacent vertebrae, as well as the interspinous ligament which connects the spinous processes of adjacent vertebrae.
The unique ligaments to the cervical spine include the nuchal ligament, a continuation of the supraspinous ligament which attaches to the tips of the spinous processes from C1-C7. The nuchal ligament provides the proximal attachment for the rhomboids and trapsetus muscles which help to stabilize the neck muscles. Finally, there is the transverse ligament of the atlas which connects the lateral masses of the atlas, and in doing so helps to anchor the dens in place.
The cervical spine has a close relationship with several neurovascular structures in the neck. The transverse foramina of the cervical vertebrae provide a passageway by which the vertebral artery, vein, and sympathetic nerves can pass. Here, C7 is an exception in which the vertebral artery passes around the vertebra instead of through it. The spinal nerves are also intimately related to the cervical vertebrae, extending from above its respective vertebrae, through the intervertebral foramen created by the articulation of the articular processes. Again, C7 is an exception in that it has a set of spinal nerves extending from both above (C7) and below (C8) the vertebra.
Injuries to the cervical spine may occur in a variety of ways, though some of the most common injuries occur as a result of a car accident, a poorly executed rugby tackle, or a fall onto an extended neck. These events may lead to several different types of cervical spine injuries.
Jefferson Fracture of the Atlas – a vertical fall onto an extended neck, such as in the act of diving into excessively shallow water, can compress the lateral masses of the atlas between the occipital condyles and the axis. This can cause the masses to be driven apart, potentially resulting in the fracture of one or both anterior/posterior arches. In extreme cases, the transverse ligament of the atlas may also be ruptured. Though the vertebral foramen is large, it is still possible that damage may occur to the vertebral column further down.
Hyperextension (Whiplash) Injury – this type of injury, often occurring as the result of a rear-end traffic collision or a poorly performed rugby tackle, involves the head being whipped back on the shoulders. In minor cases, this causes the anterior longitudinal ligament of the spine to become damaged, resulting in acute pain for the patient. More severe cases can result in fractures to any of the cervical vertebrae, potentially leading to subluxation or dislocation – especially at the C2 level where the body of C2 may move anteriorly with respect to C3. In the worst cases, spinal cord involvement can occur, potentially leading to quadriplegia or even death.
Hangman’s Fracture – this type of fracture, which involves a fracture of the pars interarticularis (bony column between the superior and inferior articular facets of the axis), typically occurs due to a rapid hyperextension and distraction of the head. This is a very dangerous injury as the force involved is often severe enough to rupture of the spinal cord, resulting in deep unconsciousness, respiratory failure, and cardiac failure.
Fracture of the Dens – fractures of the odontoid process may account for up to 40% of C2 fractures, many of which are highly unstable and at high risk of avascular necrosis. As with any fracture to the vertebral column, there is always a risk of spinal cord involvement.
The cervical spine is a complex structure composed of seven vertebrae. It provides support and protection for the spinal cord, and has a number of unique features that set it apart from the other vertebrae. The atlas and axis are the vertebrae that form the joint at the uppermost level of the spine, and the vertebral foramens of the cervical vertebrae are wider than those of the thoracic vertebrae. Ligaments are found between the vertebrae, providing stability and helping to protect the spine from movements that could cause damage to the vertebrae or spinal cord. The anatomical relationships between the vertebrae, muscles, tendons, and ligaments are also of great clinical relevance, as any injury to the cervical spine can involve them.
One such injury is a Jefferson fracture of the atlas, which can occur when there is a front-to-back force placed on the cervical vertebrae. This can cause the vertebrae to be pushed beyond its normal range of motion, resulting in a fracture of the atlas vertebrae. Hyperextension, also known as whiplash, is another type of injury to the cervical spine that results from a rapid back-and-forth motion of the neck. It can cause stretched or torn ligaments and muscles, as well as displaced vertebrae. Lastly, the hangman's fracture is a fracture of the second vertebrae in the cervical spine, caused by a sudden, forced hyperextension of the neck. It is usually due to a sudden acceleration-deceleration motion, such as in a car crash.
The anatomy of the cervical spine is a complex matter, and any injury to the spine can occur as a result of a variety of different causes, ranging from a simple slip and fall to a more serious car accident. It is important for individuals to understand how and why certain injuries to the neck and spine can occur, as well as to know what can be done to prevent them.
In order to properly treat any injury to the cervical spine, it is essential for medical professionals to have an understanding of the anatomy of the cervical spine, as well as the relationships between the vertebrae and the muscles, tendons, and ligaments. Knowing the anatomy of the cervical spine can help doctors diagnose and treat any injuries effectively. It is also important for individuals to be aware of the common injuries that can occur to the cervical spine, such as the Jefferson fracture, hyperextension injury, and the hangman's fracture, so that they can take proper precautions to prevent them.
