The intercostal space (ICS) is the anatomical region between two adjacent ribs. Since there are twelve ribs on each side, there are eleven such spaces, numbered according to the rib immediately superior to them. Locating these spaces is a fundamental skill in anatomy and medicine, as they provide reliable access points to internal structures. The second intercostal space is particularly important because it serves as the initial reference point for counting all other ribs and spaces on the anterior chest wall.
Locating the Sternal Angle Landmark
The process of finding the second intercostal space begins with locating the Sternal Angle, also known as the Angle of Louis or the manubriosternal junction. This junction is a slight, horizontal ridge where the upper portion of the sternum (manubrium) meets the main body of the sternum. Palpating this landmark is the most reliable method for accurately identifying the second rib.
To locate this angle, place fingers in the suprasternal notch, the soft dip at the very top of the breastbone. Slowly slide the fingers downward along the sternum until a distinct, subtle transverse ridge is felt approximately two inches below the notch. This bony prominence is the Sternal Angle.
The Sternal Angle is significant because the costal cartilage of the second rib articulates directly at this point on both sides of the sternum. Since the first rib is difficult to feel as it is largely obscured by the clavicle, the second rib provides the first readily identifiable bony structure for counting. Once this fixed point is confirmed, the second intercostal space is found immediately below the second rib.
Counting Down to the Second Space
After identifying the Sternal Angle, maintain gentle but firm pressure to feel the second rib extending laterally from the angle. This bony structure is solid and unyielding under the fingertips. The second intercostal space is the soft depression located immediately inferior to this palpable second rib.
To confirm the position, the finger should drop into the slight groove beneath the hard ridge of the second rib. This soft area contrasts clearly with the surrounding bone, as it is filled with muscle, nerves, and blood vessels. Move the fingers a short distance away from the sternal border onto the chest wall to ensure the space is fully felt.
This technique should be practiced on both the right and left sides of the sternum, as the second intercostal space extends horizontally around the chest wall. For individuals with greater body mass, palpation may require slightly firmer pressure and focused use of the fingertips to feel past the subcutaneous layers. Once the second space is found, subsequent ribs and spaces can be counted down one by one.
Why This Location Matters
The second intercostal space is a consistently used anatomical reference point due to its stable relationship with the Sternal Angle, making it a foundation for clinical assessment. This location is important for auscultation, the medical practice of listening to internal body sounds, primarily those of the heart and lungs. The heart’s aortic valve is best heard in the right second intercostal space, just lateral to the sternum.
The pulmonic valve is assessed in the left second intercostal space, also immediately next to the sternal border. These two points, often called the “base” of the heart, are where the sounds of blood entering the major arteries can be clearly evaluated. The reliable nature of this landmark ensures healthcare providers can consistently locate the correct spot for diagnostic assessment.
The second intercostal space also acts as the starting point for reliably counting the remaining ribs and spaces, guiding other medical procedures. For instance, the apex of the heart is typically found near the fifth intercostal space, and counting down from the second ICS ensures accurate localization. Its consistent position establishes it as a dependable anatomical reference for mapping the underlying structures of the thoracic cavity.