The second intercostal space is the equivalent of the gap between the second and third ribs of the anterior thorax, usually the intercostal space between the flat pairs of sternal angles, and an important anatomical landmark. The second intercostal space is equivalent to the level of the flat-to-tracheal bifurcation and the fourth or fifth vertebra of the thoracic spine, and is also an anatomical landmark for clinical localization, puncture, and drainage, especially in patients with spontaneous pneumothorax, where the second intercostal space is usually chosen to select the incision and puncture point at the site off the midclavicular line The surgical operation is performed. It is also possible to count the ribs, especially in thoracic trauma with rib fractures, and the second rib space is usually used as the basic reference for selecting the incision for thoracic surgery.