The ribs are the series of long, flat, curved bones that form the protective cage of the thorax (chest). The human rib cage is made up of 12 paired rib bones, each of which articulates with the vertebral column posteriorly and terminates anteriorly as cartilage. The small joints between the ribs and the vertebrae permit a gliding motion of the ribs on the vertebrae during breathing. They partially enclose and protect the chest cavity where many vital organs including the heart and lungs are located.
Anatomy of the ribs
The ribs usually have the following anatomical components:
- Head: It is shaped like a wedge. It has two articular facets separated by a wedge of the bone. One facet articulates with the numerically corresponding vertebrae, and the other articulates with the vertebrae above.
- Neck: It contains no bony prominences but simply connects the head with the body. The place where the neck meets the body has a roughed tubercle with a facet that articulates with the transverse process of the corresponding vertebrae.
- Body: The body or shaft of the rib is flat and curved. The internal surface of the shaft has a groove for a bundle of nerves and blood vessels that supply the thorax, protecting the vessels and nerves from damage.
Most of the ribs that possess these components are typical ribs. The atypical ribs that do not have all these features are
- First rib (wide and short, has two costal grooves and one articular facet)
- Second rib (thin, long and has a tuberosity on its superior surface for the attachment of the serratus anterior muscle)
- Rib 10 (only one articular facet)
- Rib 11 and 12 (one articular facet with no neck)
According to their attachment to the sternum, the ribs are classified into three groups:
- True ribs: These directly articulate with the sternum with their costal cartilages from the first to the seventh rib. They articulate with the sternum by the sternocostal joints. The first rib is an exception because it could uniquely articulate with the clavicle by the costoclavicular joint.
- False ribs (8, 9 and 10): These indirectly articulate with the sternum because their costal cartilages connect with the seventh costal cartilage by the costochondral joint.
- Floating ribs (11 and 12): These do not articulate with the sternum at all (distal two ribs).
What are the functions of the ribs?
The important functions of ribs include
- Protecting the contents of the thoracic cavity and mediastinum.
- Moving superiorly (up), inferiorly (down), anteriorly(front) and posteriorly (back) to facilitate breathing. The unique position of ribs increases or decreases the size of the thoracic cavity as ribs move, assisting the lungs in respiration. Control of these movements happens via muscles called the diaphragm, external intercostals and the intercartilaginous portion of the internal intercostals.
- Providing a place where some muscles originate or attach.
- Playing a role in erythropoiesis (red blood cell formation) during development when the child is still inside the uterus.
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Graeber GM, Nazim M. The Anatomy of the Ribs and the Sternum and Their Relationship to Chest Wall Structure and Function. Thorac Surg Clin. November 2007; 17(4): 473-489. https://www.sciencedirect.com/science/article/abs/pii/S154741270600106X