External Intercostal Tendinous Membrane

membrana intercostalis externa

The external intercostal muscles transition anteriorly to an aponeurotic membrane, the external intercostal membrane, in the anterior intercostal spaces where the cartilaginous ribs do not have the same bony contour. This membranous sheet completes the chest wall between the cartilaginous ribs and sternum.

Anatomical Data

Boundaries & Contents

Location	Front of the chest wall, in the anterior part of each intercostal space
Boundaries	Begins where the external intercostal muscle fibres end, near the costochondral junctions Extends forward to the sternum Lies between the adjacent ribs and costal cartilages, superficial to the internal intercostal muscle
Contents	Internal intercostal muscle visible through it

Biomechanics

Function & Actions

Replaces the external intercostal muscle in the front of the space and completes the outer layer of the chest wall.

Clinical Relevance

Clinical Notes

The external intercostal membrane is the structure traversed in anterior chest wall procedures and in intercostal nerve blocks performed near the costal cartilages. Its aponeurotic nature means it provides less mechanical protection anteriorly than the muscular lateral intercostal wall. It is the layer lifted in the subcostal approach to the upper abdomen.

Pathology

Common Injuries & Conditions

Anterior Chest Wall Weakness from Intercostal Membrane Disruption

Loss of anterior chest wall support from external intercostal membrane disruption in multiple rib fractures or surgical approaches, contributing to paradoxical chest wall movement in flail chest.

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