interkostal

Interkostal, commonly written intercostal in English, refers to structures situated between the ribs. There are eleven intercostal spaces on each side of the thorax, extending from the superior border of the first rib to the inferior border of the eleventh rib. These spaces contain intercostal muscles, neurovascular structures, and connective tissue that together support respiration and chest wall integrity.

Within each intercostal space, the intercostal muscles form overlapping layers. The external intercostal muscles run obliquely downward and forward and assist in elevating the ribs during inspiration. The internal and innermost intercostal muscles lie deeper and act mainly to depress the ribs during forced expiration. The intercostal neurovascular bundle travels along the inferior border of the rib above, within the costal groove, and is classically described in the order vein, artery, nerve from superior to inferior (the VAN arrangement).

The intercostal nerves are the ventral rami of thoracic spinal nerves T1 through T11, with T12 contributed by the subcostal nerve. They provide motor innervation to the intercostal muscles and sensory innervation to the overlying skin, parietal pleura, and chest wall. Blood supply to the intercostal spaces is supplied by posterior intercostal arteries (branches of the thoracic aorta) and anterior intercostal arteries (branches of the internal thoracic arteries), with corresponding venous drainage.

Clinical relevance includes intercostal nerve blocks for analgesia, management of rib fractures or herpes zoster–related neuralgia, and considerations in procedures near the thoracic cage due to the risk of pneumothorax. The term derives from Latin, meaning between ribs, and spelling variants exist across languages.