The thoracic wall is segmental in design and composed of skeletal elements and muscles. It extends between: the superior thoracic aperture, bordered by vertebra TI, rib I, and the manubrium of the sternum; and the inferior thoracic aperture, bordered by vertebra TXII, rib XII, the end of rib XI, the costal margin, and the xiphoid process of the sternum.
The skeletal elements of the thoracic wall consist of the thoracic vertebrae, intervertebral discs, ribs, and sternum.
There are twelve thoracic vertebrae, each of which is characterized by articulations with ribs.
A typical thoracic vertebra has a heart-shaped vertebral body, with roughly equal dimensions in the transverse and anteroposterior directions, and a long spinous process (Fig. 3.18). The vertebral foramen is generally circular and the laminae are broad and overlap with those of the vertebra below. The superior articular processes are flat, with their articular surfaces facing almost directly posteriorly, while the inferior articular processes project from the laminae and their articular facets face anteriorly. The transverse processes are club shaped and project posterolaterally.
Articulation with ribs
A typical thoracic vertebra has three sites on each side for articulation with ribs.
Two demifacets (i.e., partial facets) are located on the superior and inferior aspects of the body for articulation with corresponding sites on the heads of adjacent ribs. The superior costal facet articulates with part of the head of its own rib, and the inferior costal facet articulates with part of the head of the rib below.
An oval facet (transverse costal facet) at the end of the transverse process articulates with the tubercle of its own rib.
Not all vertebrae articulate with ribs in the same fashion (Fig. 3.19):
The superior costal facets on the body of vertebra TI are complete and articulate with a single facet on the head of its own rib—in other words, the head of rib I does not articulate with vertebra CVII.
Similarly, vertebra TX (and often TIX) articulates only with its own ribs and therefore lacks inferior demifacets on the body.
Vertebrae TXI and TXII articulate only with the heads of their own ribs—they lack transverse costal facets and have only a single complete facet on each side of their bodies.
There are twelve pairs of ribs, each terminating anteriorly in a costal cartilage (Fig. 3.20).
Although all ribs articulate with the vertebral column, only the costal cartilages of the upper seven ribs, known as true ribs, articulate directly with the sternum. The remaining five pairs of ribs are false ribs:
The costal cartilages of ribs VIII to X articulate anteriorly with the costal cartilages of the ribs above.
Ribs XI and XII have no anterior connection with other ribs or with the sternum and are often called floating ribs.
A typical rib consists of a curved shaft with anterior and posterior ends (Fig. 3.21). The anterior end is continuous with its costal cartilage. The posterior end articulates with the vertebral column and is characterized by a head, neck, and tubercle.
The head is somewhat expanded and typically presents two articular surfaces separated by a crest. The smaller superior surface articulates with the inferior costal facet on the body of the vertebra above, whereas the larger inferior facet articulates with the superior costal facet of its own vertebra.
The neck is a short flat region of bone that separates the head from the tubercle.
The tubercle projects posteriorly from the junction of the neck with the shaft and consists of two regions, an articular part and a nonarticular part:
The articular part is medial and has an oval facet for articulation with a corresponding facet on the transverse process of the associated vertebra.
The raised nonarticular part is roughened by ligament attachments.
The shaft is generally thin and flat with internal and external surfaces.