Applied anatomy of the cervical spine

Chapter contents

The anatomy of the cervical spine is complex and unique. To understand the diagnosis and treatment of the multiple disorders affecting this vital region, a thorough knowledge of the anatomy is necessary.

Bones

The cervical spine has seven vertebrae, which may be divided into two groups that are distinct both anatomically and functionally: the upper pair (C1 and C2, the atlas and axis) and the lower five (C3–C7) (Fig. 1).

Fig 1 Anterior view of the cervical spine. From Standring, Gray’s Anatomy, 40th edn. Churchill Livingstone/Elsevier, Philadelphia, 2009 with permission.

Upper cervical spine

The upper cervical spine has the first and second vertebrae – the atlas and axis – and forms a unit with the occiput.

The atlas (Fig. 2) does not have a vertebral body – this has been absorbed into the axis vertebra, to form the odontoid process (Fig. 3). A thick anterior arch remains, extending into and joining the two lateral masses, on which are the superior atlantal joint facets, which articulate with the occipital condyles; and the inferior joint facets of the axis. The posterior arch is thinner than the anterior arch and forms the posterior junction of the lateral masses. The large vertebral foramen thus formed has a larger diameter in the transverse than in the sagittal plane.

Fig 2 The atlas, superior view. 1, Anterior tubercle; 2, anterior arch; 3, outline of the dens; 4, superior articular facet; 5, outline of transverse ligament; 6, groove for cervical artery and C1; 7, posterior arch; 8, transverse process; 9, foramen transversum; 10, vertebral foramen; 11, posterior tubercle. From Standring, Gray’s Anatomy, 40th edn. Churchill Livingstone/Elsevier, Philadelphia, 2009 with permission.

Fig 3 (A) Axis, superior view. 1, Dens – attachment of apical ligaments; 2, superior articular facet; 3, dens – attachment of alar ligaments; 4, foramen transversum; 5, pedicle; 6, spinous process; 7, body; 8, transverse process; 9, vertebral foramen; 10, inferior articular process; 11, lamina. (B) Axis, lateral aspect. 1, Dens – attachment of alar ligaments; 2, dens – facet for the anterior arch of the atlas; 3, groove for transverse ligament of atlas; 4, superior articular facet; 5, lateral mass; 6, divergent foramen transversum; 7, body; 8, ventral lip of body; 9, lamina; 10, spinous process; 11, inferior articular facet; 12, transverse process. From Standring, Gray’s Anatomy, 40th edn. Churchill Livingstone/Elsevier, Philadelphia, 2009 with permission.

The transverse processes contain a transverse foramen through which the vertebral artery passes before it loops back above the upper surface of the posterior arch, which sometimes contains an arterial groove, although anatomical anomalies are frequently encountered.

The posterior aspect of the anterior arch has a facet for articulation with the odontoid process of the axis, which is held in place by the transverse ligament, spanned between two tubercles, which project from the inner sides of the lateral masses.

The axis

The second cervical vertebra is the axis (Fig. 3). Its vertebral body is formed by fusion with the vertebral body of the atlas to form the odontoid process (or dens), which is completely separate from the atlas. The laminae of the axis are very well developed and blend into a bifid spinous process.

Both transverse processes have a transverse foramen for the vertebral arteries. The superior articular facets of the axis articulate with the inferior articular facets of the atlas. The inferior articular facets of the axis articulate with the superior articular facets of the third vertebra.

Lower cervical spine

The lower cervical spine is composed of the third to the seventh vertebrae which are all very similar. Each vertebral body is quite small (Fig. 4). Its height is greater posteriorly than anteriorly and it is concave on its upper aspect and convex on its lower. On its upper margin it is lipped by a raised edge of bone. The anteroinferior border of the vertebral body projects over the anterosuperior border of the lower vertebra.

Fig 4 Seventh cervical vertebra, superior view. 1, Body; 2, superior articular process; 3, inferior articular process; 4, spinous process; 5, uncinate process; 6, foramen transversum; 7, transverse process; 8, pedicle; 9, vertebral foramen; 10, lamina. From Standring, Gray’s Anatomy, 40th edn. Churchill Livingstone/Elsevier, Philadelphia, 2009 with permission.

Anterolateral (in the upper vertebrae) to posterolateral (in the lower vertebrae) on the upper surface of the body, two uncinate processes project upwards and articulate with the lower notches (or anvils) of the upper vertebra to form the joints of von Luschka or uncovertebral joints.

Laterally, the transverse processes have an anterior and a posterior tubercle, which are respectively the remnants of an embryonic rib and transverse process. The spinal nerve lies in the groove between the two tubercles. The transverse process also has a transverse foramen for the vertebral artery and vein. This is not so at C7, where the foramen encloses only the accessory vertebral vein.

The intervertebral foramina are between the superior and inferior pedicles. The articular processes for the articulation with the other vertebrae are more posterior. The two laminae blend together in a bifid spinous process (at C3, C4 and C5).

The spinous processes of C6 and C7 are longer and taper off towards the ends. C7 has a large spinous process and is, therefore, called the vertebra prominens.

Intervertebral discs

There are six cervical discs, because there is no disc between the upper two joints. The first disc is between the axis (C2) and C3. From this level downwards to the C7–T1 joint they link together and separate the vertebral bodies. Each is named after the vertebra that lies above: e.g. the C4 disc is the disc between the C4 and C5 vertebrae (Fig. 5).

Fig 5 The intervertebral discs.

The disc, comprised of an annulus fibrosus, a nucleus pulposus and two cartilaginous endplates, has the same functions as the lumbar disc, and so will not be discussed in detail (see Ch. 31, Applied Anatomy of the Lumbar Spine). There are, however, some differences (Table 1). At the cervical spine the discs are more effectively within the spine than they are at the thoracic or lumbar levels because of the superior concavity and inferior convexity of each vertebral body. They are also about one-third thicker anteriorly than posteriorly, which gives the cervical spine a lordotic curve that is not related to the shape of the vertebral bodies. The annulus fibrosus is also thicker in its posterior part than it is in the lumbar spine. The further down the spine, the more the nucleus pulposus lies anteriorly in the disc, and it disappears earlier in life than it does in the lumbar spine. For both these reasons, nuclear disc prolapses are uncommon after the age of 30.

Table 1

Differences between the cervical and lumbar discs

Cervical	Lumbar
Contained by vertebral bodies	Not contained by vertebral bodies
Thicker anteriorly than posteriorly	Equal height
Annulus thicker posteriorly	Annulus weaker posteriorly
Nucleus in anterior part of disc	Nucleus in posterior part of disc