The tubercle of a rib articulates with the transverse process of a vertebra.

Thoracic

Thoracic vertebrae (T1 to T12) can be identified by the presence of facets on the lateral aspects of the bodies for articulation with the heads (posterior ends) of the ribs (see Figure 3.11B). The spines of the thoracic vertebrae are fairly long and tend to closely overlap each other, especially in the middle of the region (see Figure 3.7A). The transverse processes of the thoracic vertebrae are also fairly long; they gradually decrease in length from T1 to T12. The superior and inferior articular facets articulate in a plane that slopes sharply downward posteriorly. The overlapping spines, relatively thin intervertebral discs and splinting effect of the ribs result in a smaller overall range of movement in the thoracic region than in the cervical region.

Thoracic Vertebrae

The thoracic vertebrae possess slightly triangular bodies with flat superior and inferior end plates and longer pedicles than the cervical vertebrae that cover the intervertebral foraminae. The thoracic transverse processes project posteroinferolaterally. Each thoracic vertebra articulates with a pair of ribs. Each rib end articulates with demifacets above and below the discs to form synovial costovertebral joints as well as the thoracic transverse processes to form costotransverse joints. The thoracic vertebrae possess longer laminae than the cervical vertebrae to form a wider spinal canal. They meet posteriorly to form long, inferiorly projecting spinous processes.

Thoracic Vertebrae

Thoracic vertebrae are somewhat heart shaped and are intermediate in size between the lumbar and cervical vertebrae. The anatomy of a typical thoracic vertebra is shown in Figure 7.4A. They exhibit costal facets on each side at the junction of the vertebral body and the pedicle and on the transverse processes. These facets are unique to the thoracic vertebrae (Figure 7.4B). These costal facets are also observed on the thoracic transverse processes (except for the T10-12 vertebrae). The vertebrae at the rostral and caudal regions have some transitional morphological features; that is, the T1-4 vertebrae have some cervical features, and T9-12 vertebrae have some lumbar features. The surface area gradually increases from T1-12. The middle four thoracic vertebrae have almost equal lateral and AP dimensions. Lateral dimensions increase toward the cervical and lumbar extremes of the thoracic region. The spinous processes of the first, second, eleventh, and twelfth thoracic vertebrae are horizontal; third, fourth, ninth, and tenth are oblique; and the fifth to eighth spinous processes overlap, and are long and vertical. The size of the transverse processes increases progressively from T1-12. The cervical features of T1 include the superior vertebral notch and the lumbar features of T12 include the lateral direction of the inferior articular processes. The laminae are broad and sloping and overlap one another similar to shingles on a roof. The thoracic facets are oriented along the coronal plane. At the thoracolumbar junction, they assume a more oblique, sagittal orientation.

Thoracic vertebrae in humans

The thoracic vertebrae lie in the posterior wall of the thorax with twelve pairs of ribs attached to them. Thoracic vertebrae have bodies of intermediate size. They are distinguished by their long, slender spines and by the presence of facets on the sides of the bodies articulating with the heads of the ribs and by facets on the transverse processes articulating with the tubercles of ribs. (Fig 3.4) The thoracic spine has three distinct regions: upper, middle and lower. Those of the upper region have some features similar to cervical vertebrae and those in the lower region have some features similar to lumbar vertebrae.

6.4.2 Special Thoracic Vertebrae (Figure 6.9)

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The first thoracic vertebra (T-1) has a whole costal facet superiorly and a half costal facet inferiorly. It retains more cervical-like characteristics of its spine and body than any other thoracic vertebra.

The tenth thoracic vertebra (T-10) usually has a complete, superiorly placed costal facet on each side of the vertebral body and costal articulations on the transverse processes.

The eleventh thoracic vertebra (T-11) has an intact, superiorly placed costal facet on each side of the vertebral body, but no costal articulation on the transverse processes.

The twelfth thoracic vertebra (T-12) resembles T-11, but the inferior articular facets assume the lumbar pattern.

Thoracic Vertebrae

The thoracic vertebrae are heart-shaped and have dual articulations for both ribs as well as for the superior and inferior vertebrae. The transverse diameter of the pedicles is smallest from T3 to T6. At T1, the transverse diameter is larger, with an average of 7.3 mm in men and 6.4 mm in women.5 The first thoracic vertebra has a complete facet on the side of the body for the first rib head and an inferior demifacet for the second rib head. The ninth to twelfth vertebrae have costal articulations with their respective ribs. The last two ribs are smaller and do not attach to the sternum. The thoracic facets are rotated 20 degrees forward on the coronal plane and 60 degrees superiorly on the sagittal plane (Figure 2-3).

The Thoracic Vertebrae

The 13 thoracic vertebrae (T1–T13) Fig. 4.4, are defined by their articulations with ribs. T2 is unusual as it bears a long dorsal spine that is further extended by a pointed cartilage, which may ossify in adulthood (Johnson et al., 1999). The majority of the thoracic vertebrae articulate with both the head (capitulum) and tubercle of a rib. The head articulates with a pair of demi-facets: one at the antero-lateral part of the body of the vertebra with the same number as the rib, and one at the postero-lateral part of the body of the vertebra immediately anterior. Thus rib 3 articulates with T3 and T2; rib 1 articulates with T1 and C7 and so forth, but towards the posterior end of the thoracic vertebrae, the facets may be single and appear only on the vertebra with the same number as the rib in question. As mentioned above, the articulation of the head is with the parapophysis of Owen’s terminology. The tubercles of the ribs articulate with transverse processes, that is, with the diapophyses. Spinal nerves emerge via the intervertebral foramina formed by the notches of the pedicles, emerging ventral to the articular processes. The posterior thoracic vertebrae may bear further ‘pophyses’: the accessory and mamillary processes (see below).

Thoracic Spinal Anatomy

The thoracic vertebrae are distinguished from their lumbar and cervical counterparts by their articulation with the ribs. There are two points of connection of the ribs with the thoracic vertebral column. One is at the vertebrae, and the second is at the transverse process. On the second through ninth thoracic vertebrae, these articulations are shared by adjacent vertebrae by a demifacet. The rib head articulation thereby covers the intervening intravertebral disc. The 1st, 10th, 11th, and 12th rib heads articulate with a single vertebra. The articular capsule surrounds the joint and becomes continuous with the intervertebral fibrocartilage of the annulus. A radiate ligament connects the rib head with the side of the vertebral bodies spanning the adjacent vertebrae and the annulus. Anterior to this ligament are the ganglia of the thoracic sympathetic trunk and the pleura. Contained by the radiate ligaments are the synovial membranes of the demifacets and the intra-articular ligament connecting the rib head to the annular fibers belonging to the demifacets. The second point of attachment of the rib to the vertebrae is by the costotransverse articulation. This is a synovial articulation connecting the tubercle of the rib with the transverse process of that vertebral segment.

The thoracic vertebrae increase in size as one moves caudal in the spine, and they form a nearly circular vertebral canal whose anteroposterior dimensions are equal to the transverse dimensions. The demifacets articulate with the vertebral bodies. At the vertebrae above the articulation, this articulation is lateral and at the root of the pedicle. The articulation with the vertebrae below is near the inferior vertebral notch covering the pedicle and is in close proximity to the transverse process and the superior facet. The facet joints of the vertebrae are oriented in a coronal plane, with the inferior facet of the superior vertebrae overlapping the superior facet of the inferior vertebrae as do shingles on a roof. The 1st cervical as well as the 9th, 10th, 11th, and 12th vertebrae have no demifacets. The synovial joints with the rib are contained over the vertebrae and lateral pedicle of that single vertebra. The ribs of the 11th and 12th vertebrae have no articulations with transverse processes.

Thoracic Spine

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The thoracic vertebrae are intermediate in size between the cervical and lumbar vertebrae (Fig. 1-7). Their size increases as one moves down the spinal column.

The defining characteristic of thoracic vertebrae is their intimate relationship with the ribs (Vollmer et al. 1997). A rib articulates at the junction of the vertebral body and pedicle (superior costal facet) of its named vertebra and the vertebra above (inferior costal facet). The rib also articulates with the transverse costal facet of the transverse process of its named vertebra. These relations of the rib and the vertebrae are supported by accessory ligaments that make the thoracic spine mechanically stiffer than the cervical and lumbar spine.

Anteriorly, the thoracic vertebral bodies are relatively heart shaped. Sometimes, the left side of the vertebrae has a depression secondary to the descending aorta.

The pedicles of the thoracic vertebrae are oval in cross section. These have been reported to be 10 mm in height and 4.5 mm in width at T4 and 14 mm height and 7.8 mm in width at T12 (Vaccaro et al. 1995). As with the pedicles of the lumbar spine, the walls are thicker medially than laterally.

The spinal canal has less free space for the spinal cord than the cervical and lumbar regions.

Posteriorly, the thoracic vertebrae have long, slender spinous processes that point downward and overlap the vertebral arches of the inferior vertebra.

The transverse processes are posteriorly angulated, leaving room for the ribs to pass anterior to them.

9.4.2 Special Thoracic Vertebrae (Figures 9.16–9.19)

The first thoracic vertebra (T-1) has a whole costal facet superiorly and a half costal facet inferiorly. It retains more cervical-like characteristics of its spine and body than any other thoracic vertebra.

The tenth thoracic vertebra (T-10) usually has a complete, superiorly placed costal facet on each side of the vertebral body and costal articulations on the transverse processes.

The eleventh thoracic vertebra (T-11) has an intact, superiorly placed costal facet on each side of the vertebral body but no costal articulation on the transverse processes.

The twelfth thoracic vertebra (T-12) resembles T-11, but the inferior articular facets assume the lumbar pattern.

The long axis of the spinous process is posterior and is angled sharply inferiorly, particularly in the mid-thoracic region.

The superior articular facet faces posteriorly, and the inferior one faces anteriorly.

The costal articulation on the transverse processes faces anterolaterally.

In lateral aspect the inferior articular facets are separated from the rear half of the vertebral body by a considerable gap.

The inferior dimensions of the body are greater than its superior dimensions.