Thoracic spine is also called dorsal spine and is constituted by next 12 vertebrae after cervical spine.
If you palpate back of neck from above downwards in mid line, you would come across a sudden projection or bump in the lower part of neck. This projection is posterior spinous process of C7 vertebra and projects out due to its large size. C7 connects on top of T1.
Similarly, the lowest vertebra of the thoracic spine, T12, connects with L1 or first vertebra in lumbar spine. Between these two are ten other thoracic vertebra connected to each other.
Identification of Thoracic Vertebra
The thoracic vertebrae are identified by the presence of costal facets on the sides of the vertebral bodies. Costal facets of each vertebra articulate with corresponding rib. The costal facets may be two or only one on each side.There are twelve thoracic vertebrae, out of which the 2nd to 8th are typical and the remaining 5 i.e.1st, 9th, 10th, 11th and 12th are atypical.
Typical Thoracic Vertebra
- The body is heart shaped with roughly the same measurements from side to side and anteroposteiroly. 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 gives 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.
The 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.
The 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.
The 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.
The 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.
The 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.
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