The Ribs

The ribs are a vital component of the human skeletal system, forming the rib cage that protects the organs in the thoracic cavity, primarily the heart and lungs. The rib cage also plays a crucial role in respiration, as it expands and contracts with the movement of the diaphragm during breathing.

1.0Introduction

• The average person is born with 24 ribs—12 on each side. The ribs are located in the thoracic cage and thorax, along with their costal cartilages and the sternum. Each rib is made up of a few different components: the head, the neck, the tubercle, the angle, and the body.
• Their length increases from 1st to 7th rib and then diminishes from above downwards.
• The ribs lie one above the other and the spaces between them are known as 'Intercostal spaces'.
• The ribs are obliquely placed so that intercostal spaces are deeper in front than behind.

2.0Classification

• True Ribs 1st to 7th - They are connected in front through costal cartilages with the sternum.
• False Ribs 8th to 12th - Vertebro-chondral Ribs: The cartilages of 8th. 9th and 10th ribs are joined each to the cartilage of the rib just above.
• Floating Ribs: 11th and 12th. They are free at their anterior ends.
• Typical: The ribs which present common features.
• Atypical: The ribs which present special features. They are 1st, 2nd, 10th, 11th and 12th ribs.

3.0Typical Ribs

(i) Curved

(ii) Angulated: The angle lies about 2.5 inches from the tubercle.

(iii) Twisted: Such that the two ends will not touch a horizontal surface.

Parts of Rib

• Anterior end
• Posterior end
• Shaft

Anterior End - Recognised by the presence of a small cup-shaped depression which articulates with the lateral end of the corresponding costal cartilage.

Posterior End - It consists of (1) Head (2) Neck (3) Tubercle

Head

• Bears 2 small facets separated by a transverse ridge called ‘Crest’.
• Larger lower facet articulates with the body of numerically corresponding vertebrae. Upper facet articulates with the vertebra above.
• The crest lies opposite the intervertebral disc.

Neck 

• Flat portion adjoining the head; about 1 inch long.
• Lies in front of the transverse process of numerically corresponding vertebra.
• It possesses: 2 surfaces: Anterior and Posterior.

2 borders: Upper and lower.

Tubercle 

• Situated on the posterior surface of the rib, at the junction of neck and shaft.
• Consists of 2 parts 

1. Medial articular part: bears an oval facet to articulate with the transverse process of numerically corresponding vertebra.
2. Lateral non-articular part: rough; 

Shaft 

• Thin and flat. 
• It is curved, bent and twisted on itself.
• It possesses : 2 surfaces : External and Internal.

2 borders : Superior and Inferior.

External surface

• Convex and smooth
• A rough ridge crosses this surface at some distance from the tubercle, indicating the posting of angle.

Internal surface 

• Smooth
• Has a groove (costal groove) along its lower border, limited, above by a ridge.

Superior border 

• Rounded
• It has got an inner and an outer lip behind.

Inferior border 

• Sharp border
• Forms lower margin of costal groove.
• Gives origin to External intercostal muscle.

4.0Atypical Ribs

1. First Rib

Distinguishing features 

• No twist.
• No angle as it is merged with the tubercle.
• No costal groove.
• Most curved.
• Shortest of all ribs.
• Broad and flat from above downwards.
• Single facet on the head

Head 

• Small and circular.
• Bears one nearly rounded facet for articulation with the upper part of the side of the body of 1st thoracic vertebra.

Neck 

• Rounded; faces upwards, backwards and laterally.

Tubercle 

• Thick and prominent.
• Faces upwards and backwards.
• Coincides with the angle.
• Has an oval facet for articulation with the transverse process of 1st thoracic vertebra.

Shaft 

• It possesses: 2 surface : (i) Superior, (ii) Inferior.

2 borders: (iii) Outer, (iv) Inner.

Superior surface:

• (i) Rough and irregular.
• (ii) Crossed by 2 oblique shallow grooves separated from each other by an ill-defined ridge. This ridge ends at the inner border of the rib in a small projection called ‘scalene tubercle’.

Interior surface : 

• (i) Smooth surface.
• (ii) Does not bear a costal groove.
• (iii) Related to pleura.

Outer border : 

• (i) Convex.

Inner border : 

• (i) Concave.
• (ii) Bears the scalene tubercle near its center.

Anterior end 

• Largest and thickest of all ribs.
• Articulates with 1st costal cartilage through which it is connected to sternum.

2. Second Rib

Distinguishing features 

• It has no twist-so both ends of this rib touch any plane surface upon which it is kept.
• It has a slight angle which lies close to the tubercle.
• It is about twice as long as the 1st rib.
• Head is small and bears 2 facets.
• Neck is small.
• Tubercle is divided into articular and nonarticular parts; the non articular part is smaller.
• Surfaces are External and Internal.

i. External surface : 

(i) faces upwards and slightly outwards.

(ii) It is convex.

(iii) Has a rough impression behind its middle.

ii. Internal surface : 

(i) Smooth and concave.

(ii) Faces downwards and slightly inwards.

(iii) There is a short costal groove at its posterior part.

3. Tenth Rib

• The head bears a single articular facet which articulates with the facet near the upper border of the body of the 10th thoracic vertebra .
• Other features are the same as in typical ribs.

4. Eleventh Rib

• The head bears only one large articular facet which articulates with the 11th  thoracic vertebra .
• It doesn’t possess a neck or tubercle.
• No articulation with the transverse process of 11th  thoracic vertebra .
• The Coastal groove on the internal surface is faint and shallow.
• It has a slight angle.
• Anterior end is pointed.

5. Twelfth Rib

• It has no angle.
• It has no twist.
• It has no neck, no tubercle and no coastal groove.
• It has a single large articular facet on the head which articulates with the 12th  thoracic vertebra ; no articulation with the transverse process.
• Anterior end is pointed.
• Shaft possesses: 2 surfaces : (i) External (ii) Internal

2 borders : (iii) Upper (iv) Lower

5.0Ribcage/Thoracic cage

Ribs form a large part of the thoracic wall and are connected behind to the vertebral column; in front the upper 7 pairs articulate through costal cartilages with the sternum; they form the anterior, posterior and lateral walls creating  a bony cage for protection of lungs and heart known as thoracic cage or rib cage.

6.0Functions of Ribs

• Protection: They protect vital organs in the thoracic cavity, including the heart and lungs, from injury.
• Support: Ribs provide structural support to the chest wall, helping to maintain the shape of the thoracic cavity.
• Respiration: Ribs play a crucial role in the mechanics of breathing. When the diaphragm contracts, the ribs move outward and upward, allowing the lungs to expand and fill with air.
• Attachment: They serve as attachment points for muscles involved in respiration and movements of the upper body.
• Blood Cell Production: The bone marrow inside the ribs can produce red and white blood cells, contributing to the body’s hematopoietic system.