Typical Ribs & First Rib

Ribs

There are a total of 12 pairs of ribs.

Classification of ribs

1. According to features

• Typical ribs: 3^rd -9^th
• Atypical ribs: 1^st, 2^nd,10^th,11^th, and 12^th

Note:

• Typical ribs have the same general features.
• Atypical ribs have special features.

2. According to relation with the sternum

• True ribs: 1^st – 7^th i.e upper 7 ribs
• False ribs: 8^th -12^th i.e lower 5 ribs

Note:

• True ribs =articulate with sternum anteriorly
• False ribs=Do not articulate with sternum anteriorly

3. According to articulation

• Vertebrosternal ribs= 1^st -7^th
• Vertebrochondral ribs: 8^th -10^th
• Floating ribs: 11^th and 12^th

Note:

• Vertebrosternal ribs: articulate posteriorly with vertebrae and anteriorly with sternum
• Vertebrochondral ribs: articulate posteriorly with vertebrae and anteriorly with costal cartilage of higher rib
• Floating ribs: articulate posteriorly with vertebrae and anteriorly free.

Typical ribs

Why it is called typical?

• It is curved
• It is angulated
• It is twisted
• A costal groove is present.

 

Anatomical point

1. The posterior end consists of the head, neck, and tubercle which lies at the midline.
2. Anterior end bears cup-shaped depression which lies anteriorly slightly below then the posterior end.
3. Costal groove present in the lower margin of the inner surface.

Parts

1. Anterior end
2. Posterior end
3. Shaft

1. Anterior end

• It bears a cup-shaped depression.
• It forms a costochondral joint which is the primary cartilaginous type of joint.

2. Posterior end

• It presents a head, neck, and tubercle.

Head

• It bears two articular facets,
• Lower facet is larger and articulates with the body of the corresponding vertebra.
• Upper facet is smaller and articulates with the body of the upper higher vertebra.
• Two facets are separated by a crest.
• Crest articulate with an intervertebral disc which is a fibrocartilage type of joint.

Tubercle

It has two-part

1.  The medial articular part articulates with the transverse process and forms a costotransverse joint which is the plane type of synovial joint.
2. Lateral non-articular.

Shaft

1. Two surface=outer surface and  inner surface
2. Two border=upper and lower border

Attachment

1. Internal intercostal muscle
2. External intercostal muscle
3. Intercostalis intimus

Muscle	Origin	Insertion	Direction of fiber	Actions
External intercostal	Lower border of the rib above	Outer lip of upper border of rib below	Downward, forward, and medially	Elevates the rib during inspiration
Internal intercostal	Floor of the costal groove of the rib above	Inner lip of the upper border of the rib below	downward, backward, and laterally	Elevates the rib during expiration
Intercostalis Intimus	Inner surface of the rib above	Inner surface of the rib below	Downward, backward and laterally	Elevates the rib during expiration

Costal groove

Contents

From above to downward

• Intercostal vein
• Intercostal artery
• Intercostal nerve

Note:

All together they are called neurovascular boundle.

Intercostal space

• It is the space between two adjacent ribs.
• Anterior intercostal space=9 in number
• Posterior intercostal space=11 in number

Contents

• Intercostal vain
• Intercostal artery
• Intercostal nerve
• Intercostal membrane
• Intercostal muscles

Movement of ribs

1. Palm handle movement

• It increases the anterior and posterior diameter

2. Bucket handle movement

• It increases the transverse diameter

Note:

When the diaphragm contracts, it increases the vertical diameter.

Ossification

• The process of formation of bone is called ossification.
• Intra cartilaginous ossification

Note

• All the flat bones except the vault and clavicle have Intra cartilaginous ossification.
• Whereas the vault and clavicle have intramembranous ossification.
• Morphologically it is a flat type of bone.

 

First rib

Side determination

• Its larger end is directed anteriorly and its smaller end is directed posteriorly.
• The surface of its shaft having two grooves separated by a ridge is directed superiorly
• Its concave border is directed inward and its convex border is directed outward.

The trick for side determination

• Put the ribs on the table.
• If both ends touch the table then be sure that the first ribs belong to that particular side.

Distinguishing Features

• Shortest, broadest, and most curved rib
• No costal groove
• It is not twisted.
• It has a single facet in the head.

Anatomical point

• This is the first rib of the left/right side.
• Posterior end bears a single facet.
• Anterior end bears a cup-shaped depression
• The superior surface is marked by two shallow grooves.

Features

End

1. Anterior end

• It articulates with the First costal cartilage.
• It forms a costochondral joint which is the primary cartilaginous joint.

2. Posterior end

• It articulates with the body of 1^st vertebrae.
• It forms a costovertebral joint which is a plane type of synovial joint.

Surface

1. Superior surface

• It has two grooves which are separated by a slight ridge called a scalene tubercle.
• The Anterior groove lodges the subclavian vein.
• The posterior groove lodges the subclavian artery and lower trunk of brachial plexus.
• In front of the anterior groove it provides attachment to subclavius muscle and costoclavicular ligament.
• The area behind the posterior groove gives insertion to the scalenus medius.
• Serratus anterior inserted at the scalenus tubercle.

2. Inferior surface

• It is related to costal pleura.

Border

1. Outer border

• Serratus anterior originates from the 1^st to 8^th ribs.
• The serratus anterior is supplied by the long thoracic nerve.
• Injury of the long thoracic nerve leads to winging of the scapula.

2. Inner border

• The base of the supra pleural membrane is attached to the inner border of 1^st rib.
• Whereas the apex of the supra pleural membrane is attached at the tip of the transverse process of C7

Anterior relation of neck

From medial to lateral

1. Sympathetic chain
2. First posterior intercostal vein
3. Superior intercostal artery
4. The ventral ramus of T1 spinal nerve