Anatomy of the Subaxial Cervical Spine

Fig. 2.1

Axial view of the subaxial cervical spine

This chapter describes the essential anatomy of subaxial cervical spine (C3-C7).

2.1 Bony Anatomy

2.1.1 C3-C6

Vertebrae are composed by a vertebral body, anteriorly, and a neural arch, composed by pedicles and laminae, posteriorly (Fig. 2.2).

Fig. 2.2

Subaxial cervical vertebra: (a) superior, (b) anteroposterior, (c) lateral views

The typical lower cervical vertebra presents a small square vertebral body. A hook-shaped uncinate process, on each side of the superior endplate of vertebral bodies from third cervical to first thoracic, articulates with the corresponding uncus surface, on the inferior endplate of the vertebral body above, forming the uncovertebral joints (Luschka’s joints).

The neural arch is formed by two pedicles and two laminae and forms the posterior border of the vertebral foramen which is triangular in shape, with apex directed posteriorly [1].

Extending posteriorly from where the two laminae meet is the spinous process which is bifid.

The transverse process extends laterally from the junction of the pedicle and the lamina on each side. Cervical transverse processes have anterior and posterior bars, which delimitate the foramen transversarium, and terminate laterally as corresponding tubercles (connected by a costal – or intertubercular – lamella).

The attachment of the dorsal bar to the pediculolaminar junction represents the morphological transverse process, while the attachment of the ventral bar to the vertebral body represents remnants of ancient coastal elements.

It is important to consider that the anterior tubercle of the transverse process of the 6th cervical vertebra is bulky, and it is an important surgical landmark; moreover, it has a close relationship with the common carotid artery, and so is also called the carotid tubercle (Chassaignac tubercle) [2].

The junction between lamina and pedicle bulges laterally between the superior and inferior articular processes to form lateral masses on each side.

The superior articular facets, flat and ovoid, are directed superoposteriorly, whereas the corresponding inferior facets are directed mainly anteriorly, and lie nearer the coronal plane than the superior facets [3].

2.1.2 C7: Vertebra Prominens

C7 has some peculiar features that make it different from the other cervical vertebrae. Some of its characteristics are that of a transitional vertebra between the cervical and thoracic spine (Fig. 2.3).

Fig. 2.3

C7 peculiar features: (a) superior and (b) lateral views

The spinous process is not bifid; it is directed dorsally and downwards ending in a prominent tubercle for the attachment of the ligamentum nuchae.

The posterior tubercle of the transverse process is thicker than that in the other cervical vertebrae, and sometimes particularly prominent (cervical rib).

Articular surfaces are more vertical but still the superior, oriented dorsally, and the inferior, ventrally.

Another important consideration concerns the content and the shape of the foramen transversarium. In fact, it only contains the vertebral vein, and not the correspondent artery, as all other lower cervical vertebrae do. Moreover, it is often divided by a bony spicule, and its ventral burden is relatively thin and may be underdeveloped or partly deficient.

2.2 Joints and Ligamentous Anatomy

Joints within each motion segment are both anteriorly and posteriorly, between vertebral bodies and lateral masses, respectively.

Two adjacent vertebral bodies articulate within each other by means of three articulations: the two uncovertebral joints and a discosomatic joint. This latter is a synarthrosis since there is no joint cavity and the motion is obtained through the intervertebral disc located in between them. The intervertebral disc is a structure is formed by a central nucleus pulposus enclosed by the fibers of the annulus fibrosus in the peripheral part.

The uncovertebral joints are synovial joints formed by the uncinate process of the 3rd cervical to the 1st thoracic vertebra which articulates with the correspondent surface on the inferior part of the vertebral body above. These joints allow flexion-extension limiting lateral flexion.

Dorsally, two plain synovial joints formed by the inferior articular facet of a vertebra and the superior articular facet of the vertebra below. The orientation of the facet varies within the different regions of the spine and dictates the plane of motion at each relative level. In the cervical spine, superior articular facets are directed upwards and dorsally, whereas the corresponding inferior facets, downwards and ventrally. The capsules of these joints strongly contribute to segmental stability.

There is a system of ligaments (Fig. 2.4) connecting adjacent vertebrae, thus allowing segmental motion:

1.

Anterior longitudinal ligament (ALL)
2.

Posterior longitudinal ligament (PLL)
3.

Ligamentum flavum
4.

Interspinous ligaments
5.

Ligamentum nuchae

Fig. 2.4

(a) Posterior and (b) lateral views of a functional spinal unit with its posterior capsular and ligamentous structures (posterior ligamentous complex)

2.2.1 Anterior Longitudinal Ligament

This fibrous structure extends on the ventral surface of the vertebral bodies from the base of the skull to the sacrum. It resists hyperextension.

2.2.2 Posterior Longitudinal Ligament

This ligament lies within the spinal canal on the dorsal surface of the vertebral bodies extending from the occiput to the sacrum. Caution is advised during dissection of the anterior epidural space, since this ligament might be in close relationship with the dural sac.

2.2.3 Ligamentum Flavum

This structure owes its name (lat. flavus, yellow) to the great prevalence of elastic fibers which determine its color. Ligamenta flava are coupled, one at each lamina (right and left) of the vertebra and might be separated by a central fissure. They extend from half the ventral surface of the lamina of a vertebra to the superior margin of the lamina of the vertebra below. Caution is advised during opening of the canal, since this ligament might be in close relationship with the dural sac.

2.2.4 Interspinous Ligaments

These ligaments connect two contiguous spinous processes and extend anteriorly up to reach the ligamentum flavum.

2.2.5 Ligamentum Nuchae

This structure is stretched from the external occipital protuberance to the spinous process of C7 (Fig. 2.5). It represents the homologous of the supraspinous ligament in the thoracolumbar spine. Its fibers deepen to reach the spinous processes of each cervical vertebra contributing to separate the right and left paravertebral muscle compartments [4].