The sacral vertebrae fuse to form the sacrum and the coccygeal vertebrae fuse to form the coccyx. Thus, the sacral and coccygeal vertebrae are false vertebrae, while the others are true vertebrae.

Cervical Vertebrae (A-G)

Of the seven vertebrae comprising the cervical spine, three can be readily distinguished: the first, or atlas, the second, or axis, and the seventh, the vertebra prominens. Only small differences characterize the third, fourth, fifth, and sixth cervical vertebrae. The vertebral body (1) is continuous posteriorly with the vertebral arches (2), each of which consists of an anterior pedicle (3) and a posterior lamina (4). At the junction of these two parts, a superior articular process (5) projects cranially and an inferior articular process (6) extends caudally. A recess, the superior vertebral notch (7), is present between the superior articular process and the vertebral body, whereas a larger inferior vertebral notch (8) is found between the inferior articular process and the body. The articular processes bear articular surfaces or facets (9); the superior articular facet is directed backward, the inferior articular facet forward. The vertebral arches terminate in a spinous process (10), which is directed posteriorly and which, in the third to sixth cervical vertebrae, is bifid at its tip. The cervical vertebral body and its arches enclose a relatively large vertebral foramen (11). The transverse process (12) extends laterally and includes a vertebral and costal element (see p. 52) that incompletely fuse during development so that a transverse foramen (13) is preserved. The transverse process also has an anterior tubercle (14) and a posterior tubercle (15), between which runs the groove for a spinal nerve (16).

In the third cervical vertebra, the articular facets on the superior articular processes form an angle of 142° to each other open posteriorly (aperture angle, Putz), whereas in the fourth to seventh cervical vertebrae, this angle is approximately 180°.

The anterior tubercle of the sixth cervical vertebra may be especially prominent and is called the carotid tubercle (17). The upper end plates of the bodies of the third to seventh cervical vertebrae have raised lateral margins, the uncal processes or unci (18; see p. 58).

The seventh cervical vertebra has a large spinous process that is significant as the highest palpable spinous process of the vertebral column. It is therefore called the vertebra prominens. Its transverse process usually lacks an anterior tubercle (E).

Variants: The transverse process of C7 (G) is incompletely developed and the costal element has incompletely fused (19) so that the part arising from this anlage can be distinctly differentiated from the vertebra. If the costal element is preserved independently, a cervical rib develops (20). Cervical ribs are usually present bilaterally. When they are present only on one side, they are more frequently found on the left side than on the right. The transverse foramen may be bipartite in different vertebrae.

Clinical tip: The presence of a cervical rib may cause a triad of disorders, known also as Naffziger syndrome:

Vascular complaints

Complaints arising from the brachial plexus (sensory disturbances, especially of the ulnar nerve)

Palpable mass in the greater supraclavicular fossa

Fig. 2.1 Cervical vertebrae.

First Cervical Vertebra (A-C)

The atlas differs basically from the other vertebrae in that it lacks a vertebral body. It consists of a smaller anterior arch (1) and a larger posterior arch (2). Both arches have small protuberances in the median plane, the anterior (3) and posterior (4) tubercles. The posterior tubercle may sometimes be very poorly developed. Lateral to the large vertebral foramen (5) of the atlas are the lateral masses (6), each of which has a superior (7) and an inferior (8) articular facet. The superior articular facet is concave and its medial margin is often indrawn. A bipartite superior articular facet is sometimes present. The inferior articular facet is flat or may be very slightly deepened and almost circular. On the inner side of the anterior arch is the articular facet for the dens, the fovea dentis (9). From the transverse foramen (11), which is located in the transverse process (10), the groove for the vertebral artery (12), runs across the posterior arch.

Variants: The groove for the vertebral artery may be replaced by a canal (13). Rarely, the atlas is divided into two halves joined by cartilage. Equally rarely, unilateral or bilateral assimilation of the atlas, that is, bony fusion with the skull, may be observed.

Second Cervical Vertebra (D-F)

The axis differs from C3 to C6 by the presence of the dens (14). The dens forms a toothlike process on the upper surface of the body of the axis and terminates in a rounded point called the apex (15). The anterior surface of the dens has a definite articular surface-the anterior articular facet (16). Its posterior surface may have a smaller articular facet-the posterior articular facet (17).

The lateral articular facets slope laterally. The poorly developed transverse process (18) contains the transverse foramen.

The shape of the lateral articular facets is somewhat complex. Although they may appear almost flat in a bony (macerated) preparation, they are more ridged when their cartilaginous covering is present. This covering is important in the joint between the atlas and the axis (see p. 60). The spinous process (19) is large and often, although not always, has a bifurcated tip. It develops from the joined parts of the vertebral arch (20), which in common with the vertebral body (21) encompass the vertebral foramen (22).

Clinical note: Isolated fractures of the arch of the atlas may occur, especially after motor vehicle accidents, and require differentiation from congenital variants of the atlas (see p. 44). A fracture of the dens is the typical axis fracture. Care is required because free proatlas segments (see p. 52) may rarely be found within the atlantooccipital membrane.

The position of the dens axis relative to the body of C2 depends on the curvature of the cervical spine. In the absence of lordosis (see p. 62) it faces slightly backward. Its longitudinal axis then makes an angle with the vertical through the body of the second cervical vertebra.

Fig. 2.2 Cervical vertebrae, continued.

Thoracic Vertebrae (A-D)

The 12 thoracic vertebrae each have a vertebral body (1), which has incompletely ossified upper and lower end plates of compact bone and posterior openings for emergence of the basivertebral veins. Laterally the vertebral body usually has two costal facets (2), each of which forms half of an articular facet (D) for articulation with the head of a rib. The first, 10th, 11th, and 12th thoracic vertebrae are exceptions.

The first thoracic vertebra (D) has a complete articular facet (3) at the superior border of its body and a demifacet (4) at the inferior border. The 10th vertebra (D) has only a demifacet (5), while the 11th (D) has a complete articular facet (6) at its superior border. The 12th thoracic vertebra (D) bears the articular facet for the head of the rib in the midlateral surface of the vertebral body (7).

From the posterior surface of the body arises the vertebral arch with its pedicles (8), which are continued on each side into the laminae of the vertebral arch (9). The two laminae unite to form the spinous process (10). The spinous processes of the first through ninth thoracic vertebrae overlap each other like roof tiles, so that their tips lie one to one-and-a-half vertebrae lower than the corresponding vertebral bodies. They are triangular in cross section, in contrast to the spinous processes of the last three thoracic vertebrae, which are vertically oriented plates. These plates are not angled...

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