Intercostal Spaces

INTERCOSTAL  SPACES

• Spaces between the ribs are called as intercostal spaces.
• They are 11 pairs within the thoracic wall.
• Anteriorly only 9 pairs are present as the last 2 pairs of spaces are open in front.
• Spaces intervening between the typical ribs, traversed by vessels and nerves confined to the thoracic wall, are known as typical intercostal spaces.
• 3^rd, 4^th, 5^th & 6^th intercostal spaces are called as typical intercostal spaces.

Boundaries :- 

Above - Sharp lower margin of upper rib & cartilage

Below - Blunt upper margin of lower rib and its cartilage

In front - Lateral border of sternum between the costal notches

Behind - Body of corresponding thoracic vertebra

Characteristic  Features :-

• Each space is directed downward and forward.
• Widest part being at the costo-chondral junction.
• Each space shows 2 parts – inter-osseous & inter-cartilaginous parts.

Contents :-

• Intercostal Muscles
• Intercostal Vessels
• Intercostal Nerves

 

INTERCOSTAL  MUSCLES

(Find the Video Tutorial Here

👇

https://www.youtube.com/watch?v=36CI2H5reZA&t=4s)

• Muscles are arranged in 3 sheets.
• From outside to inside they are – intercostalis externus, intercostalis internus & intercostalis intimus.

Intercostalis  Externus :-

• It extends from the sternum up to the tubercles of ribs.
• In the inter-cartilaginous part, it is replaced by aponeurosis known as anterior intercostal membrane.
• It arises from the lower border of upper rib.
• Inserts into the outer lip of upper border of lower rib.
• In the anterior part of the space, fibres are directed downwards forwards and medially.
• In the posterior part of the space, fibres are directed downwards and laterally.

Intercostalis  Internus :-

• It extends from sternum to the posterior angles of ribs.
• Posteriorly it is replaced by posterior intercostal membrane.
• It arises from the costal groove of upper rib.
• Inserts into the intermediate part of upper border of the lower rib.
• The fibres are directed at right angles to those of the externus muscle.

Intercostalis  Intimus :-

• It is a part of transversus thoracis muscle.
• It occupies middle 2/4^th of a typical intercostal space.
• Intercostal vessels and nerves run between intercostalis internus and intimus muscles.
• Intercostalis intimus is absent in upper two spaces.
• It arises from the upper lip of costal groove of upper rib.
• Inserts into the inner lip of upper border of rib below.
• The fibres are directed same as intercostalis internus.

Nerve Supply

• All intercostal muscles are supplied by corresponding intercostal nerve.

Actions

• Eternal intercostal muscles elevate the ribs and help in inspiration.
• Internal intercostal muscles depress the ribs and help in expiration.
• The prevent blowing out or sucking in of the intercostal spaces during respiration.

INTERCOSTAL  ARTERIES

• In each space the arteries are arranged into 2 groups – anterior & posterior.

Anterior Intercostal Arteries

• They are present in all 9 spaces anteriorly.
• In each space they are 2 in number - one follows the lower margin of upper rib and the other follows the upper margin of lower rib.
• They anastomose with posterior intercostal arteries at the junction of anterior 1/3^rd & posterior 2/3^rd of the space.
• In upper 6 spaces they are branches of internal thoracic artery.
• In succeeding 3 spaces they are derived from musculo-phrenic artery.

Posterior Intercostal Arteries

• They are present in all 11 spaces posteriorly.
• In each space 1 posterior intercostal artery is present.
• In upper 2 spaces they are derived from superior intercostal artery.
•  In lower 9 spaces they are derived from descending thoracic aorta.

Right posterior intercostal arteries -

• They are longer than that of left side.

Pass backwards and laterally in front of the vertebral column

Run behind the oesophagus, thoracic duct, azygos vein & sympathetic trunk.

Left posterior intercostal arteries -

They pass backward and laterally by the side of vertebrae

Run behind the hemiazygos vein and sympathetic trunk.

Further each artery..

Passes upwards and laterally towards the angle of upper rib

Runs between the costal pleura and posterior intercostal membrane

Then passes forward along the costal groove of upper rib in the same space

Runs between the internus and intimus muscles intervening between the vein above and nerve below

Anastomoses with the upper anterior intercostal artery

Near the angle of the rib gives off a collateral branch which runs forwards close to the upper margin of lower rib and anastomoses with lower anterior intercostal artery. 

INTERCOSTAL  VEINS

• They correspond to the arteries.
• Arranged into 2 groups – anterior & posterior.

Anterior Intercostal Veins

• Each space presents 2 anterior intercostal veins.
• In upper 6 spaces they drain into internal thoracic vein.
• In succeeding 3 spaces they drain into musculo-phrenic vein.

Posterior Intercostal Veins

• Each space presents 1 posterior intercostal vein.
• Each vein receives tributaries from vertebral venous plexus.

Termination on right side –

• 1^st posterior vein drains into right brachio-cephalic vein.
• 2^nd 3^rd & 4^th posterior veins unite to form right superior intercostal vein which drains into the arch of azygos vein.
• 5^th – 11^th posterior veins open into azygos vein.

Termination on left side –

• 1^st posterior vein drains into left brachio-cephalic vein.
• 2^nd 3^rd & 4^th posterior veins unite to form left superior intercostal vein which drains into the left brachio-cephalic vein.
• 5^th – 7^th posterior veins open into superior hemi-azygos vein, which terminates into azygos vein.
• 8^th – 11^th posterior veins open into inferior hemi-azygos vein, which terminates into azygos vein.

INTERCOSTAL  NERVES

• Intercostal nerves are 11 pairs.
• Each nerve is a continuation of ventral ramus of corresponding thoracic spinal nerve.
• 3^rd - 6^th intercostal nerves are typical, as they are confined to the thoracic wall.

Typical  Intercostal  Nerve :-

Course & Relations 

Each typical intercostal nerve passes out through the intervertebral foramen

Appears in the posterior part of intercostal space

Lies medial to the superior costo-transverse ligament

Passes upwards & laterally behind the sympathetic trunk

Runs within the endothoracic fascia

Intervenes between the costal pleura & posterior intercostal membrane

Reaches the angle of upper rib in the corresponding intercostal space

 

Gives off collateral & lateral cutaneous branches at the angle

Then enters the costal groove along the lower border of upper rib, lying below the intercostal vein & artery, whereas the collateral branch runs along the upper border of lower rib lying above the collateral vessels

Runs forward in the costal groove, between intercostalis internus & intimus muscles

On reaching the anterior part of the space, nerve passes in front of sterno-costalis muscle & internal thoracic artery

Near the sternum, pierces the intercostalis internus, anterior intercostal membrane & pectoralis major muscles

 

Become cutaneous as anterior cutaneous nerve 

Terminates by dividing into medial & lateral cutaneous branches.

 

Branches

Communicating Branches -

Ganglionic branches to-

• Corresponding sympathetic ganglion by grey & white rami communicantes.
• White ramus conveys pre-ganglionic sympathetic fibres to the ganglion.
• Grey ramus conveys post-ganglionic sympathetic fibres from the ganglion.

Branches to- adjacent intercostal nerves.

Distributing Branches -

Muscular branches-

• Supply- Intercostal muscles & transversus thoracis muscle.

Collateral branch-

• Arises near the angle of rib
• Anteriorly it may unite with the trunk of intercostal nerve or terminates as additional anterior cutaneous nerve.
• Supplies- Parietal pleura & periosteum of ribs.

Lateral cutaneous branch-

• Arises near the angle of rib
• Pierces the intercostalis internus & externus muscles at the mid-axillary line & become cutaneous.
• Terminates by dividing into anterior & posterior cutaneous branches.
• Anterior cutaneous branch unites with the lateral cutaneous branch anteriorly.
• Posterior cutaneous branch unites with the cutaneous branch from dorsal ramus of corresponding thoracic spinal nerve.
• Supplies- Skin over the corresponding intercostal space.

Anterior cutaneous nerve-

• It is the terminal part of intercostal nerve near the sternum.
• Supplies- Overlying skin on the anterior part of the space, through its medial & lateral branches. 

 

APPLIED  ASPECTS

Intercostal Neuralgia

• Sharp burning pain in the area of skin supplied by intercostal nerves.
• Cause- Irritation of intercostal nerve by rib fractures or Herpes zoster (viral disease).

Pleural Tap / Thoracocentesis / Paracentesis 

• In pleural tap, to collect the fluid from pleural cavity, the needle should be introduced at mid-axillary line, midway between the ribs of an intercostal space.
• That avoids the injury to trunk of intercostal nerve & its collateral branch.