A Guide on How to Locate the 5th Intercostal Space for Health Assessment

September 30, 2025 •

4 min read

The Angle of Louis, or sternal angle, is a crucial anatomical landmark that aligns with the second rib and is used as the starting point for counting ribs. Accurately knowing how to locate the 5th intercostal space is essential for healthcare professionals and students performing heart and lung assessments and other critical medical procedures.

Quick Summary

This guide provides a detailed method for finding the 5th intercostal space by palpating key landmarks, beginning with the Angle of Louis. Accurate identification of this area is critical for auscultating heart sounds, placing ECG leads, and safely performing procedures like chest drain insertion.

Key Points

Start at the Angle of Louis: This horizontal ridge on the sternum is the most reliable landmark and is continuous with the second rib.
Count Down from the Second Rib: After locating the second rib via the Angle of Louis, carefully palpate and count downward to identify the space below the fifth rib.
Use the Midclavicular Line: The intersection of the fifth intercostal space and the left midclavicular line indicates the heart's apex for assessing the apical pulse.
Consider Axillary Landmarks: For procedures like chest drain insertion, the 5th intercostal space is often identified in the mid-axillary line, within the "triangle of safety".
Adjust for Patient Variation: Remember that landmarks can vary with body size, age (e.g., in children), and conditions like emphysema.
Avoid the Neurovascular Bundle: To minimize risk during invasive procedures, healthcare providers should insert needles and tubes just above the superior border of the rib below to avoid the neurovascular bundle.

Understanding the Thoracic Cage

Before learning how to locate the 5th intercostal space, it is important to understand the basic anatomy of the chest wall. The intercostal spaces are the anatomical areas that lie between adjacent ribs. An adult typically has 12 pairs of ribs, resulting in 11 intercostal spaces on each side. The first seven pairs of ribs are known as "true ribs" because they connect directly to the sternum (breastbone) via costal cartilage. The eighth, ninth, and tenth pairs are "false ribs" as their cartilage connects indirectly via the cartilage of the seventh rib. The last two pairs, the eleventh and twelfth, are "floating ribs" because they do not attach to the sternum at all.

The accurate identification of intercostal spaces is a fundamental skill in medical practice. It is used to guide stethoscope placement for listening to heart and lung sounds, to correctly position electrocardiogram (ECG) leads, and for safe needle insertion during procedures such as thoracentesis.

The Role of the Angle of Louis

The Angle of Louis, or sternal angle, is arguably the most reliable starting point for counting ribs and locating the fifth intercostal space. This prominent horizontal ridge is formed at the junction of the manubrium (the upper part of the sternum) and the body of the sternum. Not only is it easy to palpate, but it also corresponds with the location of the second rib.

Step-by-Step Guide to Locate the 5th Intercostal Space

To find the 5th intercostal space, follow these steps with the patient in a supine or seated position:

Locate the Sternal Notch: Begin by finding the suprasternal or jugular notch, the U-shaped depression at the very top of the sternum.
Find the Angle of Louis: Slide your fingers downward along the midline of the sternum from the jugular notch until you feel a distinct horizontal ridge or bump. This is the Angle of Louis.
Identify the Second Rib and Space: Move your fingers laterally (to the side) from the Angle of Louis. The bony structure you encounter at this level is the second rib. Just below the second rib is the second intercostal space.
Count Down to the 5th Intercostal Space: Continue to slide your fingers down the chest wall, moving over the next palpable rib and then into the space below it. The order proceeds as follows:
- Over the second rib, into the second intercostal space.
- Over the third rib, into the third intercostal space.
- Over the fourth rib, into the fourth intercostal space.
- Over the fifth rib, into the fifth intercostal space.

Important Reference Lines for Pinpointing the Location

Once the correct intercostal space is located, imaginary reference lines on the chest are used to provide more precise anatomical coordinates. The two most common lines used in conjunction with the 5th intercostal space are:

Midclavicular Line (MCL): This imaginary line runs vertically down from the midpoint of the clavicle (collarbone). The intersection of the left 5th intercostal space and the midclavicular line marks the position of the apex of the heart, where the apical pulse is felt and the mitral valve is best heard.
Midaxillary Line (MAL): This line runs vertically down from the center of the armpit (axilla). In some procedures like thoracentesis or chest drain insertion, a specific point in the 5th intercostal space near the midaxillary line is used, sometimes within the "triangle of safety".

Clinical Significance of the 5th Intercostal Space

The precise location of this intercostal space is critical for several medical assessments and procedures. The following table compares its significance in adults and children.


Application	Adult Landmark	Pediatric Landmark	Clinical Rationale
Apical Pulse	5th intercostal space, left midclavicular line	4th intercostal space, left midclavicular line	Assesses the rate and rhythm at the heart's apex; position varies due to chest size and heart positioning.
ECG V4 Lead	5th intercostal space, left midclavicular line	V4 is typically placed in a similar anatomical position, adjusted for smaller chest size.	Correct lead placement is necessary for accurate cardiac rhythm and potential ischemia interpretation.
Chest Tube Placement	Mid-axillary line at 5th intercostal space (within "safe triangle")	Similar to adult placement but adjusted for anatomy and size.	The 5th intercostal space is a standard location for chest tube insertion to drain air or fluid.

Practical Considerations and Tips

Palpation is Key: While visual landmarks like the nipple line can be useful for initial approximation, they are unreliable and can shift based on body type, age, and sex. Always confirm with manual palpation.
Feel the Ribs: When counting, remember you are palpating the rib first, and the space is directly below it. Run your fingers along the rib to confirm its position before dropping into the space below.
Positioning the Patient: For optimal palpation, have the patient sit or lie down comfortably. Abducting the patient's arm can help with locating axillary landmarks.
Mind the Neurovascular Bundle: A crucial anatomical safety note is that the intercostal vein, artery, and nerve run along the inferior border of the rib within the intercostal groove. Therefore, when inserting a needle, it is safest to go just above the superior margin of the rib below to avoid damaging these structures.
Use Visual Aids: Medical students and professionals often use anatomical charts or apps to visualize the relationship between landmarks and internal organs. An authoritative source like the NCBI provides detailed diagrams of thoracic anatomy.

Conclusion

Mastering how to locate the 5th intercostal space is a foundational skill for accurate health assessment. The step-by-step method, beginning with the Angle of Louis and counting downward, provides a reliable and consistent approach. By combining palpation of the rib cage with the use of imaginary reference lines, healthcare providers can precisely identify this space for critical procedures and assessments, ensuring patient safety and diagnostic accuracy. This anatomical knowledge is vital for understanding cardiac and pulmonary physiology and serves as a cornerstone of competent clinical practice.

Outbound link (for optional inclusion): Anatomy, Angle of Louis - StatPearls - NCBI Bookshelf

Frequently Asked Questions

The Angle of Louis, also known as the sternal angle, is a palpable horizontal ridge where the manubrium and sternum body join. It is an important anatomical landmark because it corresponds to the level of the second rib, making it the starting point for counting intercostal spaces.

You can count ribs by first locating the Angle of Louis. From there, move your fingers laterally to find the second rib. The space immediately below the second rib is the second intercostal space. Continue counting down, feeling for the ribs and the spaces beneath them, until you reach the desired intercostal space.

A rib is one of the twelve pairs of bones forming the bony framework of the chest wall. An intercostal space is the anatomical space or gap located between two adjacent ribs.

Accurately locating the 5th intercostal space is essential for health assessment because it is where the apex of the heart is best auscultated and palpated (the apical pulse). It is also a key landmark for placing ECG leads and for various medical procedures.

The apex of the heart is located at the intersection of the left 5th intercostal space and the midclavicular line (a vertical line drawn down from the midpoint of the clavicle).

Yes, other methods include locating it in the mid-axillary line, often used for chest drain insertion, or using ultrasound guidance for more complex procedures. However, the Angle of Louis remains the most common and reliable method for a basic physical exam.

No, the anatomical position of the heart differs slightly in children due to their smaller and differently shaped chests. In young children, the apical pulse is typically auscultated at the 4th intercostal space.