The external intercostal muscles fill each intercostal space from the rib tubercles back near the spine to the costochondral junctions in front, where they are replaced by the external intercostal membrane. Their fibres run downward and forward, like the external oblique in the abdominal wall. They raise the ribs during inspiration, increasing the transverse (bucket-handle) and anteroposterior (pump-handle) diameters of the chest, and their activity increases with breathing effort.
| Origin | Inferior border of each rib from the tubercle to the costochondral junction |
|---|---|
| Insertion | Superior border of the rib below |
| Nerve Supply | Intercostal nerves (T1 through T11) |
| Blood Supply | Posterior intercostal arteries |
| Actions |
|
|---|
During exercise and forced inspiration they contract to actively pull the upper ribs superiorly, increasing the anteroposterior and transverse diameters of the thorax and driving the respiratory airflow needed for high-intensity activity.
Intercostal nerve blocks targeting the intercostal nerves that supply the external intercostals are performed for post-thoracotomy pain management, rib fracture analgesia, and zoster neuralgia. Intercostal muscle strain from forceful coughing produces sharp well-localised rib cage pain reproduced by deep breathing and trunk rotation that must be distinguished from pneumothorax, pleuritis, and rib fracture.
The external intercostals are palpable in the intercostal spaces between the ribs, their fibres running downward and forward. Tenderness on intercostal palpation with reproduction on deep breathing localises intercostal muscle strain.
Muscle or nerve injury from forceful coughing, trunk rotation, or rib impact producing sharp intercostal pain reproduced by breathing and trunk movement, managed conservatively with analgesics and breathing support.
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