Costovertebral Articulations

5e. Costovertebral Articulations

FIG. 312– Costovertebral articulations. Anterior view.

(Articulationes Costovertebrales)

The articulations of the ribs with the vertebral column may be divided into two sets, one connecting the heads of the ribs with the bodies of the vertebræ, another uniting the necks and tubercles of the ribs with the transverse processes.

1. Articulations of the Heads of the Ribs (articulationes capitulorum; costocentral articulations) (Fig. 312).—These constitute a series of gliding or arthrodial joints, and are formed by the articulation of the heads of the typical ribs with the facets on the contiguous margins of the bodies of the thoracic vertebræ and with the intervertebral fibrocartilages between them; the first, tenth, eleventh, and twelfth ribs each articulate with a single vertebra. The ligaments of the joints are:

The Articular Capsule.

The Radiate.

The Interarticular.

The Articular Capsule (capsula articularis; capsular ligament).—The articular capsule surrounds the joint, being composed of short, strong fibers, connecting the head of the rib with the circumference of the articular cavity formed by the intervertebral fibrocartilage and the adjacent vertebræ. It is most distinct at the upper and lower parts of the articulation; some of its upper fibers pass through the intervertebral foramen to the back of the intervertebral fibrocartilage, while its posterior fibers are continuous with the ligament of the neck of the rib.

The Radiate Ligament (ligamentum capituli costæ radiatum; anterior costovertebral or stellate ligament).—The radiate ligament connects the anterior part of the head of each rib with the side of the bodies of two vertebræ, and the intervertebral fibrocartilage between them. It consists of three flat fasciculi, which are attached to the anterior part of the head of the rib, just beyond the articular surface. The superior fasciculus ascends and is connected with the body of the vertebra above; the inferior one descends to the body of the vertebra below; the middle one, the smallest and least distinct, is horizontal and is attached to the intervertebral fibrocartilage. The radiate ligament is in relation, in front, with the thoracic ganglia of the sympathetic trunk, the pleura, and, on the right side, with the azygos vein; behind, with the interarticular ligament and synovial membranes.

In the case of the first rib, this ligament is not divided into three fasciculi, but its fibers are attached to the body of the last cervical vertebra, as well as to that of the first thoracic. In the articulations of the heads of the tenth, eleventh, and twelfth ribs, each of which articulates with a single vertebra, the triradiate arrangement does not exist; but the fibers of the ligament in each case are connected to the vertebra above, as well as to that with which the rib articulates.

The Interarticular Ligament (ligamentum capituli costæ interarticulare).—The interarticular ligament is situated in the interior of the joint. It consists of a short band of fibers, flattened from above downward, attached by one extremity to the crest separating the two articular facets on the head of the rib, and by the other to the intervertebral fibrocartilage; it divides the joint into two cavities. In the joints of the first, tenth, eleventh, and twelfth ribs, the interarticular ligament does not exist; consequently, there is but one cavity in each of these articulations. This ligament is the homologue of the ligamentum conjugale present in some mammals, and uniting the heads of opposite ribs, across the back of the intervertebral fibrocartilage.

Synovial Membranes.—There are two synovial membranes in each of the articulations where an interarticular ligament exists, one above and one below this structure; but only one in those joints where there are single cavities.

2. Costotransverse Articulations (articulationes costotransversariæ) (Fig. 313).—The articular portion of the tubercle of the rib forms with the articular surface on the adjacent transverse process an arthrodial joint.

In the eleventh and twelfth ribs this articulation is wanting.

The ligaments of the joint are:

The Articular Capsule.		The Posterior Costotransverse.
The Anterior Costotransverse.		The Ligament of the Neck of the Rib.
The Ligament of the Tubercle of the Rib.

The Articular Capsule (capsula articularis; capsular ligament).—The articular capsule is a thin membrane attached to the circumferences of the articular surfaces, and lined by a synovial membrane.

FIG. 313– Costotransverse articulation. Seen from above.

The Anterior Costotransverse Ligament (ligamentum costotransversarium anterius; anterior superior ligament).—The anterior costotransverse ligament is attached below to the sharp crest on the upper border of the neck of the rib, and passes obliquely upward and lateralward to the lower border of the transverse process immediately above. It is in relation, in front, with the intercostal vessels and nerves; its medial border is thickened and free, and bounds an aperture which transmits the posterior branches of the intercostal vessels and nerves; its lateral border is continuous with a thin aponeurosis, which covers the Intercostalis externus.

The first rib has no anterior costotransverse ligament. A band of fibers, the lumbocostal ligament, in series with the anterior costotransverse ligaments, connects the neck of the twelfth rib to the base of the transverse process of the first lumbar vertebra; it is merely a thickened portion of the posterior layer of the lumbodorsal fascia.

FIG. 314– Section of the costotransverse joints from the third to the ninth inclusive. Constrast the concave facets on the upper with the flattened facets on the lower transverse processes.

The Posterior Costotransverse Ligament (ligamentum costotransversarium posterius).—The posterior costotransverse ligament is a feeble band which is attached below to the neck of the rib and passes upward and medialward to the base of the transverse process and lateral border of the inferior articular process of the vertebra above.

The Ligament of the Neck of the Rib (ligamentum colli costæ middle costotransverse or interosseous ligament).—The ligament of the neck of the rib consists of short but strong fibers, connecting the rough surface on the back of the neck of the rib with the anterior surface of the adjacent transverse process. A rudimentary ligament may be present in the case of the eleventh and twelfth ribs.

The Ligament of the Tubercle of the Rib (ligamentum tuberculi costæ posterior costotransverse ligament).—The ligament of the tubercle of the rib is a short but thick and strong fasciculus, which passes obliquely from the apex of the transverse process to the rough non-articular portion of the tubercle of the rib. The ligaments attached to the upper ribs ascend from the transverse processes; they are shorter and more oblique than those attached to the inferior ribs, which descend slightly.

Movements.—The heads of the ribs are so closely connected to the bodies of the vertebræ by the radiate and interarticular ligaments that only slight gliding movements of the articular surfaces on one another can take place. Similarly, the strong ligaments binding the necks and tubercles of the ribs to the transverse processes limit the movements of the costotransverse joints to slight gliding, the nature of which is determined by the shape and direction of the articular surfaces (Fig. 314). In the upper six ribs the articular surfaces on the tubercles are oval in shape and convex from above downward; they fit into corresponding concavities on the anterior surfaces of the transverse processes, so that upward and downward movements of the tubercles are associated with rotation of the rib neck on its long axis. In the seventh, eighth, ninth, and tenth ribs the articular surfaces on the tubercles are flat, and are directed obliquely downward, medialward, and backward. The surfaces with which they articulate are placed on the upper margins of the transverse processes; when, therefore, the tubercles are drawn up they are at the same time carried backward and medialward. The two joints, costocentral and costotransverse, move simultaneously and in the same directions, the total effect being that the neck of the rib moves as if on a single joint, of which the costocentral and costotransverse articulations form the ends. In the upper six ribs the neck of the rib moves but slightly upward and downward; its chief movement is one of rotation around its own long axis, rotation backward being associated with depression, rotation forward with elevation. In the seventh, eighth, ninth, and tenth ribs the neck of the rib moves upward, backward, and medialward, or downward, forward, and lateralward; very slight rotation accompanies these movements.