Rib Characteristics And Costovertebral Articulations
A typical rib has a head, a neck, and a body. The head articulates with one or two vertebral bodies (see below). A tubercle at the lateral end of the relatively short neck articulates with the transverse process of the lower of the two vertebrae with which the head of the rib articulates. As the body is followed anteriorly, the “angle” of the rib is formed. At the inferior border of the body is the costal or subcostal groove, partially housing the intercostal artery, vein, and nerve. Each rib is continued anteriorly by a costal cartilage by which it is attached either directly or indirectly to the sternum, except for the eleventh and twelfth ribs, which have no sternal attachment.
The ﬁrst and second ribs differ from the typical rib and therefore need special description. The ﬁrst rib— the shortest and most curved of all the ribs—is quite ﬂat, and its almost horizontal surfaces face roughly superiorly and inferiorly. On its superior surface are grooves for the subclavian artery and subclavian vein, separated by a tubercle for the attachment of the scalenus anterior muscle.
The second rib is a good deal longer than the ﬁrst, but its curvature is very similar to the curvature of the ﬁrst rib. The angle of the second rib, which is close to the tubercle, is not at all marked. Its external surface faces to some extent superiorly but a bit more outward than that of the ﬁrst rib.
The typical articulation of a rib with the vertebral column involves both the head and tubercle of the rib. The head has two articular facets—the superior facet making contact with the vertebral body above and the inferior one with the vertebral body below. Between these, the head of the rib is bound to the intervertebral disc by the intraarticular ligament. The articular facet on the tubercle of the rib contacts the transverse process of the lower of the two vertebrae. These are true or synovial joints, with articular cartilages, joint capsules, and synovial cavities. The articulations of the ﬁrst, tenth, eleventh, and twelfth ribs are each with only one vertebra, the vertebra of the same number.
The ligaments related to the typical articulation of a rib with the vertebral column are as follows: for articulation of the head of the rib, the intraarticular ligament and the capsular ligament, with a thickening of its anterior part forming the radiate ligament; and for the costotransverse joint, the thin capsular ligament, the lateral costotransverse ligament between the lateral part of the tubercle of the rib and the tip of the transverse process, and the superior costotransverse ligament attached to the transverse process of the rib above.
The ﬁrst and the last two (or three) ribs each has a single articular facet that makes contact with an impression on the side of the thoracic vertebra of the same number. No intraarticular ligament is present, so there is just a single synovial cavity, in contrast to the two synovial cavities present for the, typical rib. The lowest ribs do not have synovial joints between their tubercles and the transverse processes of the related vertebrae.