Internal intercostal membrane

At a glance

English

Internal intercostal membrane

Latin (TA2)

Membrana intercostalis interna

System

Ligament

Region

Thorax

Side

Paired, left and right

About the internal intercostal membrane

The internal intercostal muscles fill the middle layer of each intercostal space. They begin at the sternum in front and run back around the chest wall, but near the angles of the ribs their fleshy fibres stop. From there to the vertebral column the layer continues as a thin fibrous sheet, the internal intercostal membrane, also termed posterior. It is the mirror image of the external intercostal membrane, which replaces the outer muscle layer at the front of the space.

The membrane stretches between the lower border of one rib and the upper border of the rib below, from the rib angles medially to the region of the costotransverse joints, where it blends with the superior costotransverse ligament. Its fibres follow the line of the internal intercostal muscle, running downwards and backwards. Outside it the external intercostal muscle remains fleshy, since at the back of the chest the external layer is muscular all the way to the rib tubercles. Inside it, between the membrane and the pleura, run the posterior intercostal vessels and the intercostal nerve on their way forwards from the spine.

Its role is to complete the middle layer of the chest wall where the muscle is absent, keeping the space firm and helping the wall resist the pressure changes of breathing. It transmits some of the tension of the internal intercostal muscles towards the vertebral column.

The membrane is a useful landmark in regional anaesthesia. In a paravertebral block the needle is passed beside the spine; the internal intercostal membrane and the superior costotransverse ligament lie just behind the paravertebral space, so feeling the needle pass through them, or seeing them on ultrasound, indicates that local anaesthetic will spread around the spinal nerves as they leave the intervertebral foramina.

Attachments and function

Attaches from

The angle of the rib, where the fleshy internal intercostal muscle ends.

Attaches to

The region of the costotransverse joints near the vertebral column, blending with the superior costotransverse ligament.

Function

Completes the middle layer of the posterior intercostal space and continues the line of the internal intercostal muscle to the spine.

Nerve supply

In the territory of the intercostal nerves, which run just deep to it.

Blood supply

The posterior intercostal arteries running beside it.