The ribs are the bony framework of the thoracic cavity. Generally, there are twelve pairs of ribs. Each rib articulates posteriorly with two thoracic vertebrae; by the costovertebral joint. An exception to this rule is that the first rib articulates with the first thoracic vertebra only. According to their attachment to the sternum, the ribs are classified into three groups: true, false, and floating ribs. The true ribs are the ribs that directly articulate with the sternum with their costal cartilages; they are the first seven ribs. The false ribs are the ribs that indirectly articulate with the sternum, as their costal cartilages connect with the seventh costal cartilage; by the costochondral joint; They are the eighth, ninth, and tenth ribs. However, the floating ribs are the ribs that do not articulate with the sternum at all; they are the distal two ribs. The true ribs articulate with the sternum by the sternocostal joints. The first rib is an exception to that rule; it is a synarthrosis. Another thing that is good to know is that the first rib could uniquely articulate with the clavicle by the costoclavicular joint.
Typically, the ribs have the following anatomical components:
Most of the ribs are typical ribs; which means that they have all these features. The atypical ribs which do not have all these features are:
The first rib is atypical because it is wide and short, has two costal grooves, and one articular facet.
The second rib is thin, long, and has a tuberosity on its superior surface for the attachment of the serratus anterior muscle.
The tenth rib has only one articular facet.
The eleventh and twelfth ribs have only one articular facet with no neck.
The functions of the ribs are critical, as they protect the contents of the thoracic cavity and mediastinum, move superiorly, inferiorly, anteriorly and posteriorly to facilitate breathing, provide a place where some muscles originate or attach, and play a role in erythropoiesis during development.
The ribs are critical in breathing since their flexibility in their movement increases/decreases the size of the thoracic cavity; assisting the lungs in respiration. Control of these movements is via the diaphragm, external intercostals, and the intercartilaginous portion of the internal intercostals. At birth, the erythropoiesis sites change, it recedes in long bones and persists in flat bones, like ribs.
The ribs form embryologically by the differentiation of somites. Somite formation starts when the paraxial mesoderm begins to spiral and form a somitomere. Subsequently, somitomeres aggregate and form somites.
The ribs receive their blood supply anteriorly; by the anterior intercostal arteries. However, they are supplied posteriorly; by the posterior intercostal arteries. Good to know, that the anterior intercostal arteries of the first seven ribs are branches of the internal thoracic artery. By contrast, the anterior intercostal arteries of the eighth, ninth, and tenth ribs are branches from the musculophrenic artery. All ten of these ribs are supplied posteriorly by the posterior intercostal arteries. Good to mention, that the first two posterior intercostal arteries are branches of the superior intercostal artery, a subsidiary of the costocervical trunk that arises from the left subclavian artery. Anyhow, the lower nine arteries are branches of the descending thoracic aorta. The floating ribs receive vascular supply differently since they are short and have no sternal articulation, only receiving supply posteriorly by the posterior intercostal arteries. The eleventh rib receives vascular supply by the posterior intercostal artery and the twelfth rib by the subcostal artery.
The nomenclature of the costal veins is the same as the arteries; they differ as to where they drain blood. The anterior intercostal veins drain blood into the internal thoracic and musculophrenic veins. The posterior intercostal veins drain blood into the azygos and hemiazygos system. The subcostal vein drains the blood of the twelfth rib.
Note: all arteries and veins run in the costal groove of each rib.
The intercostal nerves supply the ribs by sensory and motor branches. They run between the innermost and internal intercostal muscles; inferior to the blood vessels in the costal groove. They exit the groove when they branch. Their branches are:
Many muscles act on or affect the movement of the ribs. These muscles are:
The rib cage’s volume is 10% smaller in females than males. Nevertheless, the cranio-caudal inclination of the ribs is greater in females. A general rule is that the females’ ribs grow longer relative to the axial skeleton than in males.
Other variants in the ribs between individuals are developmental deformities and cervical/short rib that mimics true rib diseases.
The ribs are very important, and healthcare workers should know of the anatomical structures that lie deep to the ribs. The ribs can be counted by palpation to determine the site of thoracentesis or a thoracostomy tube. The rib count is also done before surgery to ensure that one opens the thoracic cavity in the proper location.
Tumors may also develop in the ribs. These tumors may be primary or secondary lesions. According to one study, the cure rate of benign and malignant cancers in the ribs through resection was 100% successful without recurrence.
Pectus excavatum and pectus carinatum are the most common chest deformities in young patients. These lesions affect the patient psychosocially and physiologically; chiefly because the deformity is cosmetic. Besides, some of these patients may also experience difficulty with respiration. Surgical correction is done when necessary; to avoid complications affecting the heart and lungs.
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