Intercostal spaces

The intercostal spaces are the areas betweenspace between the ribs. There are 11 spaces on each side and they are numbered according to the rib which makes the superior border of the space.

Contents

The intercostal spaces contain 3 layers of muscle;  the external, internal and innermost layers with the neurovascular bundle found between the internal and innermost layers.

Muscle Layers

• The Externalexternal intercostal muscle is the outer mostoutermost muscle of the intercostal space. This muscle has fibres which run in a downwards, forwards and medial direction from the lowerinferior border of the superior rib to insert into the outer lip of the inferior rib.
• The Internalinternal intercostal muscle is the middle layer of the intercostal space. This muscle has fibres which run in a downwards, backwards and lateral direction from the costal grooveinferior border of the superior superior rib to insert into the superior border of the inferior rib.
• The deepest layer of muscle in the intercostal space is made up of three muscles which are collectively known as  the the tranversus thoracis group. This group includes the subcostal muscles (posteriorly)posteriorly, the innermost intercostals (laterally) laterally, and the tranversus thoracis/ sternocostalis muscle (anteriorly)muscles anteriorly.

Neurovascular bundle

The neurovascular bundles are found between the middle and innermost layers in the subcostal, protected by the costal groove of the superior rib of each intercostal space. They are ordered vein, artery, nerve from superior to inferior. The collateral neurovascular bundle runs at the lower edge of the space, just above the inferior rib and the order is reversed, nerve, artery, vein from superior to inferior.

Venous drainage:

Posterior veins drain into azygos or hemiazygos veins. Anterior veins drain into internal thoracic or musculophrenic veins.

Arterial supply:

The structures in each intercostal space are supplied by a single large posterior artery and 2 smaller anterior arteries.

Large posterior artery in the first and second intercostal spaces 1 & 2 branch arise from the superior intercostal artery (a branch from the costocervical artery). Those in the remaining spaces 3-11 branch branch directly from the descending thoracic aorta.

The two smaller anterior arteries in spaces 1-6 branch fromthe first 6 spaces arise from the internal thoracic artery and in spaces 7-11 branch fromthe remaining spaces from the musculophrenic artery.

Nerve supply:

Each intercostal space is supplied segmentally by muscular branches of anterior rami of spinal nerves T1-T11.

Branches The branches of anterior rami of spinal nerves are:

• rami communicantes
• lateral cutaneous branch
• muscular branches
• Parietal pleura branches
• Parietal peritoneal sensory branches (from T7-11 only)
• Collateral branch
• terminal anterior cutaneous branch