Anatomy of Cervical Spine

The human vertebral column has five distinct regions, including cervical, thoracic, lumbar, sacral, and coccygeal. The cervical spine is crucial due to its proximity to the head and contains seven vertebrae, ligaments, and muscles that allow for a wide range of head and neck movements.

Additionally, cervical vertebrae have intervertebral disks for shock absorption and flexibility. The cervical region also has a wider spinal canal to accommodate the spinal cord, nerve roots, blood vessels, and meninges.

Structure

Typically, each vertebra of the spinal column consists of a body, spinous process, vertebral foramen, paired transverse processes, as well as superior and inferior articular facets on either side. The cervical vertebrae are anatomically unique compared to other areas of the spine.

Bifid spinous processes in the cervical vertebrae provide attachment space for the nuchal ligament, while triangular vertebral foramina accommodate the thicker cervical spinal cord. The cervical vertebrae possess transverse foramina on either side of the spine that transmit the vertebral arteries, which is a unique characteristic of this region.

Upper Cervical Spine (C1-C2)

The first two cervical vertebrae, atlas (C1) and axis (C2), are individually named because of their unique anatomical characteristics. Located at the junction between the base of the skull and the spinal column, they are part of the craniovertebral junction in the spine.

The atlas, which has a ring-like shape, does not have a body or spinous process, and therefore may not contribute to supporting the weight of the head. By working in unison, the atlas and axis enable rotational, flexion, and extension movements of the spine, rendering them the most pliable section of the entire vertebral column.

The atlas vertebra stands out for its unique structure, which takes the form of a ring without a vertebral body. It connects to the occiput above and the axis below via lateral masses that have corresponding condyles.

The odontoid process, also known as the dens, is a feature of the axis vertebra that emerged as a result of the fusion between the C1 body and the axis body, giving C2 its distinct identity. The median atlantoaxial joint enables the head to rotate freely without any need for the trunk to move.

Lower Cervical Spine (C3-C7)

The spinal column’s vertebral joints merge vertebral foramina to form the spinal canal, while intervertebral foramina are formed on each side of every vertebra pair. These foramina act as exit pathways for spinal nerve rootlets. C1-C7 rootlets exit the spinal canal through the superior notch of their corresponding cervical vertebrae, while C8 rootlets exit through the inferior notch of the C7 vertebra.

The spinal column’s vertebral joints merge vertebral foramina into a single canal referred to as the spinal canal, while intervertebral foramina are formed on each side of every vertebra pair. The neuroforamen or intervertebral foramen is formed by the superior and inferior notches of the corresponding vertebrae and serves as an exit pathway for the rootlets of spinal nerves.

The rootlets of the first seven pairs of cervical spinal nerves (C1-C7) exit the spinal canal through the superior notch of their corresponding cervical vertebrae, while the rootlets of the eighth pair (C8) exit through the inferior notch of the C7 vertebra.

Ligaments

The spinal column has several ligaments throughout its length, but the cervical spine has unique ligaments not found in other regions. Ligaments such as anterior and posterior longitudinal, ligamentum flavum, and interspinous are present at every vertebral level, while the nuchal ligament and transverse ligament of the atlas are exclusive to the cervical spine.

These cervical spine ligaments can be grouped as internal or external. Examples of external ligaments are the anterior atlantooccipital, atlanto-occipital, and anterior longitudinal ligaments. The internal ligaments include the transverse ligaments, accessory ligaments, alar ligaments, accessory atlantoaxial ligament, and tectorial membrane.

Intervertebral Discs

The intervertebral discs in the cervical spine enable spinal movement, support the weight transmission, and offer spinal stability. They consist of four components, namely the central nucleus pulposus, which is enclosed by the annulus fibrosus, and two end plates that are attached to the vertebrae’s body.

Movements of the Cervical Spine

50% of all cervical rotation occurs at the atlantoaxial joint. Additionally, the atlantoaxial occipital joint plays a role in 50% of neck flexion and extension. The cervical spine’s wide range of motion includes movements such as:

• Flexion: The cervical spine undergoes forward bending, which occurs when the head is directed downward.
• Extension: movement of the cervical spine where it bends backwards or straightens. For example, reaching upwards with the arms.
• Rotation: One side rotation of the head and cervical spine, as when turning the head to the side to look at the shoulder.
• Lateral flexion: bending the neck to the right or left side.

Functions of Cervical Spine

The cervical spine serves various functions in the head-neck region, such as:

• Safeguarding the spinal cord: The cervical spine safeguards the spinal cord which extends from the brain stem and passes through the spinal canal in the vertebral column. It protects the spinal cord from external compression.
• Supports the weight of the head: The weight of the head is supported by the cervical spine, which also maintains its position.
• Supports the blood supply to the brain: The vertebral artery passes through the transverse foramen of the cervical spine and is supported in sending blood to the brain.
• Supports Head-Neck movements: The neck muscles and cervical spine enable a broad range of motion in the neck region.

Blood Supply

The cervical region has both vertebral and carotid arteries, but only the vertebral arteries supply the spine through the cervical radicular arteries. The vertebral artery originates from the subclavian artery and passes through the foramen of the transverse process of C6 to enter the cervical region.

It then traverses through the cervical spine to reach the base of the skull. The basilar artery, which supplies the brainstem, is formed by the convergence of the vertebral arteries from both sides.

The right common carotid artery arises from the brachiocephalic artery, while the left common carotid artery originates from the aortic arch. At the level of the C3 vertebrae, the common carotid arteries bifurcate into the internal and external carotid arteries.

Nerves

The cervical spine houses the spinal cord as it exits the skull and has two nerve roots on each side, the ventral root for motor signals and the dorsal root for sensory signals. There are eight cervical spinal nerves despite the presence of only seven cervical vertebrae, and each nerve exits adjacent to its corresponding vertebra except for C8, which exits caudally to the C7 vertebra.

Muscles

The muscles that support and enable head and neck movements have their origin and insertion points on the cervical vertebrae. The erector spinae muscles, located in the deep back, run the entire length of the spine and attach to the spinous and transverse processes of the cervical and upper thoracic vertebrae on the posterior side.

These muscles aid in maintaining proper posture and contribute to the movements of the vertebral column, including flexion and extension. The muscles located in the posterior neck and suboccipital triangle are linked to the cervical vertebrae, allowing for neck extension, rotation, and lateral bending. These muscles comprise:

• Suboccipital muscles:
  • Rectus capitis posterior major
  • Rectus capitis posterior minor
  • Oblique capitus supoerior
  • Oblique capitis inferior
• Longissimus capitis
• Semispinalis capitis
• Semispinalis cervicus
• Splenius capitis
• Splenius cervicus

The muscles located in the front of the neck also have their origin at different points on the cervical vertebrae, and then attach to the skull or the first and second ribs. These muscles facilitate various movements of the neck, such as flexion, rotation, and lateral bending, and they also stabilize the skull:

• Sternocleidomastoid (SCM)
• Scalenes
• Platysma

Physiological Variants

The presence of a bifid spinous process is not universal in all cervical vertebrae across individuals. Literature has indicated that only the cervical vertebrae C2-C4 consistently have a bifid spinous process.

The growth plate development is contributed by the secondary ossification centers present in the superior and inferior surfaces of the vertebral body. An interruption in this process can result in a significant developmental anomaly in the cervical vertebrae.

Surgical Considerations

Surgery for cervical spine problems needs careful consideration as important structures, including the trachea, esophagus, nerves, and blood vessels, surround the area.

Anterior and posterior approaches are two options for surgical interventions on the cervical spine. The anterior approach is appropriate for situations that require access to the vertebral body, as well as for addressing fractures, infections, tumor resection, and other conditions.

It is crucial to exercise proper hemostasis and retraction techniques during surgical interventions to avoid harm to the surrounding structures. Common complications include infections, hematoma formation, and abscesses.

Neurovascular or adjacent organ injuries are potential complications of cervical spine surgery that can cause dysphagia, dysphonia, or difficulty swallowing. Damage to the stellate ganglion located at the C6 level can lead to the presentation of Horner syndrome, which includes symptoms such as ptosis, anhidrosis, and miosis.

It is necessary to evaluate postoperative complications, and a lateral X-ray is typically performed to assess the presence and size of soft tissue swelling. To indicate a healthy inflammatory response, the size of swelling should not exceed specific limits at various spinal levels.

The cervical spine’s posterior elements can be accessed through the posterior approach, which is commonly used for standard procedures such as instrumentation, removal, and repair of the laminae. Fixation of pedicle screws through a posterior approach for C3 to C6 can be difficult because of the small size of the pedicles.

While a lateral approach is a more suitable choice, there is a risk of injuring the vertebral artery during the procedure, and when inserting a screw at C1, it should be angled medially to avoid this. Patients should be informed about the risk of restricted movement of the atlantoaxial joint resulting from any operative procedure that may involve or cause fusion of C1 and C2.

Clinical Significance

Neck pain is a prevalent disability, particularly among the elderly, with an annual prevalence rate exceeding 30%. Classification of neck pain can be based on the etiology (mechanical, neuropathic, or referred) or duration (acute, subacute, or chronic).

Neck pain is often linked to several rheumatologic conditions, including chronic rheumatoid arthritis. Prompt evaluation and treatment of the underlying cause of neck pain is crucial to prevent long-term disabilities.

Differentiation between neuropathic and mechanical neck pain can be done through proper history, examination, and investigations. X-ray is the initial imaging modality, but CT is superior, while MRI is useful for visualizing soft tissue injuries.

Traumatic or sports injuries often present as acute neck pain, which requires immediate stabilization to prevent long-term complications. Atlas fractures are a common type of fracture in the upper cervical spine, comprising around 2% of all vertebral fractures.

Fractures known as Jefferson fractures commonly occur at the anterior and posterior arches, which are the weakest points of the atlas. Treatment involves immobilization and cranial traction. They can also lead to injury to the transverse ligament and spinal cord, emphasizing the need for immediate treatment via occipital-cervical arthrodesis.

Fractures in the odontoid process may result from hyperflexion or extension, and spondylolisthesis may occur due to the displacement of one vertebra over another, leading to acute pain and neurological symptoms. A fracture called a hangman’s fracture may occur due to high-intensity. This kind of fracture is a severe injury that can lead to either death or complete paralysis of the body.

Chronic rheumatoid arthritis can cause atlantoaxial joint instability, while subacute or chronic neck pain in individuals over 40 years of age is often associated with degeneration, which may lead to compression of nerve roots and cervical radiculopathy.

Other causes of neuropathic pain include disc herniation and stenosis. Additionally, hyperextension during intubation can result in atlantoaxial subluxation, which can be followed by spinal shock.