Introduction
Ribs are the cartilaginous and bony structure that covers the thoracic cavity. They run posteroanteriorly from the thoracic vertebrae posteriorly to the sternum anteriorly. There are 12 pairs of ribs, each attached posteriorly to the thoracic vertebrae.
Classification
Ribs can be classified in two ways:
- Based on their relation to the sternum:
- True ribs
- False ribs
- Floating ribs
- Based on features:
- Typical ribs
- Atypical ribs
True Ribs
- Also called vertebrosternal ribs.
- There are 7 true ribs – ribs 1-7.
- They are called true ribs because they are directly attached to the sternum by their own costal cartilages.
False Ribs
- Also called vertebrochondral ribs.
- Ribs 8, 9, and usually 10.
- False ribs because these ribs are not connected to the sternum directly, but their costal cartilages are connected to the cartilage of the rib above them (the 7th rib).
Floating Ribs
- Vertebral/free ribs.
- Ribs 11 & 12.
- Floating ribs are not connected to any costal cartilages, for the rudimentary cartilages of these ribs do not even indirectly connect to the sternum. Instead, they end in the posterior abdominal musculature.
Typical Ribs
These ribs are similar in that they all have:
- Head
- Neck
- Tubercle
- Angle
- Shaft (body)
Head
- Wedge-shaped and has two articulatory facets separated by the crest of the head.
- One facet for articulation to the numerical corresponding vertebra.
- The other facet for articulation to the vertebra superior to it.
Neck
- Located between the head and the tubercle.
- Connects the head of the ribs with the body at the level of the tubercle.
Tubercle
- Located at the junction of the neck and body.
- It has two parts:
- A smooth articular part articulates with the corresponding transverse process of the vertebra.
- A rough non-articular part which provides attachment for the costotransverse ligament.
Shaft
- The shaft is thin, flat, and curved.
- The point of greatest curvature is called the angle of the ribs.
- The angle also demarcates the lateral limit of attachment of the deep back muscle to the ribs.
- The concave internal surface of the body has a costal groove paralleling the interior border of the ribs which provides some protection for the intercostal nerves and vessels.
Atypical Ribs
These include the 1st, 2nd, 10th, 11th, and 12th ribs. These ribs are also referred to as dissimilar ribs. They are not similar to one another and also have some specific features which separate them from the typical ribs.
1st Rib
- It is the broadest, shortest, and most sharply curved of the ribs.
- It is nearly horizontal.
- It has a single facet on its head for articulation with the T1 vertebra only and has a tubercle for articulation with the transverse process of the T1 vertebra.
- It has only two transversely directed grooves crossing its superior surface for subclavian vessels. The grooves are separated by a scalene tubercle and ridge to which the anterior scalene is attached.
2nd Rib
- It is thinner, less curved, and substantially longer than the 1st rib.
- Its head has two facets for articulation to the T1 and T2 vertebrae.
- Its main atypical feature is a rough area on its upper surface which is a tuberosity for serratus anterior.
10th, 11th, and 12th Ribs
- Like the 1st ribs, they have only one facet on their heads and articulate with a single vertebra.
- The 11th and 12th are short and have no neck or tubercle.
Superior views
Clinical Correlates
- Fracture of rib
- Flail chest (stove-in-chest) – several adjacent ribs fracture producing a piece of chest wall that moves in the opposite direction during respiration.
- Cervical rib – congenital; the lowest cervical vertebra (C7) overdevelops to form an extra rib.
- Lumbar rib (gorilla rib) – L1 vertebra overdevelops to form an extra rib.
