The typical thoracic vertebrae are seven in number and atypical thoracic vertebra are five in number.
Vertebra T2 to T8 are typical and rest of them are atypical.
Both typical and atypical thoracic vertebrae are discussed.
Typical Thoracic Vertebra
The body of a typical thoracic vertebrae is heart shaped with roughly the same measurements from side to side and anteroposteriorly. On each side it bears 2 costal facets (demifacets). The superior costal facets are larger and placed on the upper border of the body near the pedicle. They articulate with the head of the numerically corresponding rib. The inferior costal facets are smaller and placed on the lower border in front of the inferior vertebral notch. They articulate with the next lower rib.
The vertebral foramen is comparatively small and circular.
The vertebral Arch
- The pedicles are directed straight backwards. The superior vertebral notch is shallow, while the inferior vertebral notch is deep and conspicuous.
- The laminae overlap each other from above.
- The superior articular processes project upwards from the junction of the pedicles and laminae. The articular facets are flat and are directed backwards and a little laterally and upwards. This direction permits rotatory movements of the spine.
- The inferior articular processes are fused to the laminae. Their articular facets are directed forwards and slightly downwards and medially.
- The transverse processes are large, and are directed laterally and backwards from the junction of the pedicles and laminae. The anterior surface of each process bears a facet near its tip, for articulation with the tubercile of the corresponding rib. In the upper 6 vertebrae, the costal facets on the transverse processes are concave and face forwards and laterally. In others the facets are flat and face upwards, laterally and slightly forwards.
- The spine is long, and is directed downwards and backwards. The 5th to 9th spines are the longest, more vertical and overlap each other. The upper and lower spines are less oblique in direction.
Attachments on a Typical Thoracic Spine Vertebra
- The upper and lower borders of the body give attachment, in front and behind respectively, to the anterior and posterior longitudinal ligaments.
- The upper borders and lower parts of the anterior surfaces of the laminae provide attachment to the ligamenta flava.
- The transverse process gives attachment to (i) the lateral costotransverse ligament (at the tip); (ii) the superior costotransverse ligament (lower border); the inferior costotransverse ligament (anterior surface); (iv) the intertransverse muscles (to upper and lower borders); (v) the levator costae (posterior surface).
- The spines give attachment to the supraspinous and interspinous ligaments. They also give attachment to several muscles including the trapezius, the rhomboids, the latissimus dorsi, the serrate posterior superior and inferior, and many deep muscles of the back.
Atypical Thoracic Vertebrae
First Thoracic Vertebra
- The body resembles that of a cervical vertebra. It is broad and not heart shaped. Its upper surface is lipped laterally and beveled anteriorly. The superior costal facet on the body is complete. It articulates with the head of the first rib. The inferior costal facet is a “demifacet” for the second rib.
- The spine is thick, long and nearly horizontal.
- The superior vertebral notches are well marked, as in cervical vertebrae.
Ninth Thoracic Vertebra
It resembles a typical thoracic vertebra except that the body has only the superior costal facets (demifacets). The inferior costal facets are absent.
Tenth Thoracic Vertebra
It resembles a typical thoracic vertebra except that the body has a single complete superior costal facet on each side, extending on to the root of the pedicle.
Eleventh Thoracic Vertebrae
- The body has a single large costal facet on each side, extending on to the upper part of the pedicle.
- The transverse process is small and has no articular facet. Sometimes it is difficult to differentiate between vertebrae T10 and T11.
Twelfth Thoracic Vertebra
- The shape of the body, pedicles, transverse processes and spine are similar to those of a lumbar vertebra. However, the body bears a single costal facet on each side, which lies more on the lower part of the pedicle than on the body.
- The transverse process is small and has no facet, but has superior, inferior and lateral tubercles.
- The inferior articular facets are lumbar in type and are directed laterally (everted), but the superior articular facets are thoracic in type.