Where is the fourth intercostal space located?

Fourth Intercostal Space Location

The fourth intercostal space is located in the area between the fourth and fifth ribs, and can be found at approximately 77% of the sternal length when the sternum measures 15 cm 1.

Anatomical Definition

The intercostal space is defined as the area bounded by a superior rib margin and an inferior rib margin 1. The fourth intercostal space specifically lies between the fourth rib above and the fifth rib below.

Clinical Landmarks for Locating the Fourth Intercostal Space

Sternal Length Method

• The fourth intercostal space correlates with sternal length: it is located at 77% of the distance from the sternal notch to the xiphoid process when the sternum measures 15 cm 2
• As sternal length increases to 26 cm, this percentage decreases to approximately 57% 2
• This method is particularly useful in obese patients where palpation of ribs is difficult 2, 3

Traditional Palpation Method

• The fourth intercostal space can be located by palpating the ribs along various anatomical lines:
  • Midclavicular line: an imaginary vertical line originating from the midpoint of the clavicle 1
  • Anterior axillary line: an imaginary vertical line descending along the lateral chest wall from the armpit 1

Clinical Applications

Surgical Access

The fourth intercostal space serves as a key surgical landmark:

• Robotic cardiac surgery: the camera port is placed in the medial aspect of a minithoracotomy incision in the fourth intercostal space 4
• Robotic retractor port: placed through the fourth or fifth intercostal space between the midclavicular line and right lateral sternal border 4

Chest Tube Placement

While the fourth or fifth intercostal space in the mid- or anterior-axillary line is the most appropriate site for chest tube placement 5, the fourth intercostal space specifically is used for certain procedures requiring more superior access.

Important Clinical Caveats

• Pediatric considerations: In children, the nipple can serve as an alternative landmark, with the fourth intercostal space typically found at or near the nipple level at the midaxillary line in the majority of cases 6
• Individual variation: The exact location varies with body habitus and sternal length, making measurement-based approaches more reliable than fixed anatomical assumptions 2, 3
• Avoid internal mammary vessels: When accessing the fourth intercostal space anteriorly near the sternum, care must be taken to avoid injury to the internal mammary artery and vein 4