The ribs are the bony framework of the thoracic cavity.
- The ribs form the main structure of the thoracic cage protecting the thoracic organs, however their main function is to aid respiration.
- 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 3 groups: true, false, and floating ribs.
- The true ribs are the ribs that directly articulate with the sternum with their costal cartilages - ribs 1-7. They articulate with the sternum by the sternocostal joints. The first rib is an exception to that rule; it is a synarthrosis and the first rib could uniquely articulate with the clavicle by the costoclavicular joint
- The false ribs (8,9,10) are the ribs that indirectly articulate with the sternum, as their costal cartilages connect with the seventh costal cartilag by the costochondral joint.
- The floating ribs (11,12) do not articulate with the sternum at all (distal two ribs).
Structure and Function
Typically, the ribs have the following anatomical components:
- Head with two articular facets
- Costal groove
Most of the ribs are typical ribs ie they have all these features. The atypical ribs which 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)
- Tenth rib (only one articular facet)
- Eleventh rib, Twelfth rib (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 (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).
- provide a place where some muscles originate or attach
- play a role in erythropoiesis during development (at birth, the erythropoiesis sites change, it recedes in long bones and persists in flat bones, like ribs)
There are a number of muscles related to ribs.
- intercostal muscles: situated in the intercostal spaces.
- diaphragm: arises from the inner surfaces of the costal cartilages on the sixth rib
- serratus anterior: originates anterolaterally from the 1st to 8th ribs
- pectoralis major and minor muscles arise from superior anterior ribs
- latissimus dorsi: originates from the 9th to 12th ribs
- scalenus anterior, posterior and medius muscles have attachments on the first and second ribs
- rectus abdominis: inserts at the xiphisternum and the 5th to 7th costal cartilages
Ribs fractures are prevalent, as they comprise 12% of total fractures in patients. (The risk notably increases with age).
- Rib fractures - traumatic or atraumatic (most due to direct penetrating or blunt trauma to the chest).
- Ribs 1 through 3 are the hardest to break and signify a significant degree of trauma if fractured.
- Ribs 4 through 10 are typically the most vulnerable
- Ribs 11 through 12 are more mobile and therefore more difficult to break.
- In the elderly, falls are a common etiology of rib fractures and are associated with higher mortality and morbidity than younger patients.
- Rib fractures may be pathologic as a result of cancer metastasis from other organs.
- Through repetitive stress and microtrauma, athletes can develop rib fractures with chronic use.
- Spontaneous rib fractures can also occur due to severe cough and are more likely to occur in those with osteoporosis or underlying lung disease.
- Children tend to have more elastic ribs than adults do, children are less likely to sustain rib fractures (children with rib fractures is a sign of significant trauma and should warrant an investigation of possible child abuse)
Other common abnormalities are:
- Rib dislocation
- Tumors. These tumors may be primary or secondary lesions.
- Radiopedia Ribs Available from:https://radiopaedia.org/articles/ribs (last accessed 14.4.2020)
- Safarini OA, Bordoni B. Anatomy, Thorax, Ribs. InStatPearls [Internet] 2019 Feb 19. StatPearls Publishing.Available from:https://www.ncbi.nlm.nih.gov/books/NBK538328/ (last accessed 14.4.2020)
- Kuo K, Kim AM. Rib Fracture.Available from:https://www.ncbi.nlm.nih.gov/books/NBK541020/ (last accessed 14.4.2020)