intercostal

Intercostal is an adjective meaning “between the ribs.” In anatomy it refers to structures and spaces located between adjacent ribs, typically within the intercostal spaces. Each intercostal space contains important components of respiration and chest wall mechanics, including muscles, nerves, and vessels that run in a defined pattern along the inferior border of a rib.

Intercostal muscles include the external intercostal muscles, internal intercostal muscles, and innermost intercostal muscles, with subcostal and transversus thoracis sometimes described as part of the same regional system. The external intercostals run obliquely downward and forward and elevate the ribs during inspiration; the internal and innermost intercostals run in the opposite direction and depress the ribs during forced expiration. These muscle layers are arranged in opposing sheets to aid ventilation and rib movement.

Nerves and vessels: The intercostal nerves are the anterior rami of the thoracic spinal nerves T1 through T11, providing motor innervation to the intercostal muscles and sensory innervation to the overlying skin and pleura. The intercostal arteries comprise posterior intercostal arteries branching from the thoracic aorta and anterior intercostal arteries from the internal thoracic arteries; veins accompany these vessels and drain to the azygos system and internal thoracic veins. The neurovascular bundle typically lies along the inferior border of a rib (the VAN arrangement).

Intercostal spaces: There are 11 intercostal spaces, numbered 1 through 11, each containing the intercostal muscles, nerves, and vessels. Clinically important concepts include intercostal nerve blocks for pain control, thoracostomy or chest tube placement, and careful avoidance of injury to the pleura to prevent pneumothorax. Injury to intercostal nerves or vessels can occur with rib fractures or thoracic procedures.