Costal cartilage normally allows forward movement of the ribs, providing flexibility to the chest wall. There are usually 12 pairs of cartilage associated with the rib cage. Seven of these typically connect the ribs with the sternum, or breast bone, while the three below are mostly located in between the associated rib bones. The last two connect the lower ribs with the abdominal wall. These are a type of hyaline cartilage, which is made partly of flexible collagen fibers and generally supports and protects bones from the forces of motion.
Composed of the same material as cartilage in the nose, joints, and respiratory tract, this kind of connective tissue is usually found throughout the rib cage. There are normally two surfaces to each costal cartilage. The front surface is usually positioned forward, passing upward from the ribs; in the case of the first one, it attaches to a major ligament and muscle. A link between the sternum and a major chest muscle is often provided by the first six or seven cartilages, while the rest connect the ribs to other abdominal muscles.
The rear surface of costal cartilage, on the interior of the chest wall, usually connects to various internal muscles, including the diaphragm which helps expand and contract the lungs. Cartilage tissue of this type also typically has two different shaped borders. There are also extremities that can connect with the bone tissue of the ribs, sternum, and in some cases, the cartilage above another.
Depending on the costal cartilage, it can be different lengths and widths. The first typically passes forward and downward, the second goes in the same direction as the rib, while the third one travels upward. For most of the other ribs, the cartilage follows the ribs and angles upward toward the sternum or the cartilage on top of it. It also supports the ribcage by its shape. Some of it stays the same width across the entire length, like the first two, while some costal cartilage is wider at the attachment to the rib than at the sternum.
The shape and position of costal cartilage is significant in that it enables normal movement between the ribs, chest wall, and muscles. Deformities can alter the position of the cartilage and affect nerves, arteries, and other structures, sometimes causing paralysis or lack of blood flow to the arm. In rickets, for example, the ribs are often enlarged where they connect to the costal cartilage, creating structural and mechanical abnormalities that can affect motion and breathing.
