The human torso contains a series of spaces between the ribs, known as intercostal spaces. These eleven paired spaces are numbered according to the rib positioned above them. Each intercostal space houses muscles, nerves, and blood vessels that contribute to the function and integrity of the chest wall. Understanding the location of these spaces is important for various medical assessments and procedures, as they serve as consistent anatomical landmarks on the body’s surface. The fourth intercostal space is particularly relevant due to its consistent position relative to key internal structures.
Locating the 4th Intercostal Space
Finding the fourth intercostal space on the human body involves a systematic palpation technique, starting with easily identifiable bony landmarks on the sternum, or breastbone. Begin by locating the suprasternal notch, the soft depression at the top of the sternum where the collarbones meet.
Moving downwards from this notch, a distinct horizontal ridge can be felt on the sternum, approximately 1.5 inches below. This ridge is called the sternal angle (Angle of Louis), and it marks the junction between the manubrium and the body of the sternum.
The sternal angle is a significant landmark because the second costal cartilage, connecting the second rib to the sternum, attaches at this level. Once identified, move your fingers laterally to either side of the sternum to feel the second rib. The space immediately below this second rib is the second intercostal space.
From this point, continue to palpate downwards, counting each rib and the space below it. Slide your fingers over the third rib, then into the third intercostal space. Next, move over the fourth rib; the space directly below it is the fourth intercostal space.
This method of counting down from the sternal angle provides a reliable way to locate specific intercostal spaces. Consistent palpation along the sternal border helps ensure accuracy, even with individual anatomical variations.
Clinical Significance
Knowledge of the fourth intercostal space is important in several medical contexts, particularly for diagnostic procedures and interventional treatments. One common application involves the placement of electrodes for an electrocardiogram (ECG), which records the heart’s electrical activity. Leads V1 and V2 are positioned in the fourth intercostal space, immediately to the right and left of the sternum, respectively. Precise placement ensures accurate readings.
The fourth intercostal space also serves as a general anatomical reference for auscultation, the medical practice of listening to internal body sounds. While specific heart valve sounds are best heard at slightly different locations, the fourth and fifth intercostal spaces near the sternal border are relevant for assessing the tricuspid valve area.
Medical procedures like chest tube insertion target the fourth or fifth intercostal space, often along the mid-axillary line. This location is considered a “safe zone” for inserting a tube into the pleural space to drain air, blood, or fluid from around the lungs.
While needle decompression for tension pneumothorax is performed in the second intercostal space, some guidelines consider the fourth or fifth intercostal space laterally as an alternative. The exact placement depends on the clinical situation and patient anatomy.
Internal Anatomy at the 4th Intercostal Space
Beneath the surface at the level of the fourth intercostal space lie several important internal structures. The space itself contains layers of intercostal muscles, which are important for breathing mechanics. These muscles are supplied by intercostal nerves, arteries, and veins, which run within the intercostal groove along the inferior border of the rib above.
The fourth intercostal space is situated in close proximity to the heart, particularly the right side, including portions of the right atrium and right ventricle, which lie behind the sternum at this level. The lungs, encased by their pleural membranes, also extend to this level. Major blood vessels, such as the aorta and pulmonary artery, are also located within the general vicinity of this space.