The “angle of Louis,” also known as the sternal angle, is a bony projection on the front of the chest. It forms where the top part of the breastbone, the manubrium, connects with the main body of the sternum. This junction creates a slight angle or ridge that can be felt on the chest surface. The angle of Louis serves as a reliable reference point for various structures within the chest.
Locating the Angle
To locate the angle of Louis, begin by finding the jugular notch, the indentation at the very top of your sternum, between your collarbones. From this notch, gently slide your fingers downwards along the center of your breastbone. You will feel the flat, wider upper part of the sternum, known as the manubrium.
Continue moving your fingers down until you encounter a distinct ridge. This elevation marks the junction where the manubrium meets the main body of the sternum, forming the angle of Louis.
Anatomical Connections
The angle of Louis is positioned at the level of the second pair of costal cartilages, which connect the second ribs to the sternum. This anatomical correspondence also aligns with the intervertebral disc between the fourth and fifth thoracic vertebrae in the spine. An imaginary horizontal plane extending from the sternal angle backward to this intervertebral disc divides the mediastinum, the central compartment of the chest, into upper and lower sections.
Several internal structures are found at this same transverse level. The trachea, or windpipe, divides into its two main bronchi at the level of the sternal angle. The aortic arch, the curved portion of the body’s largest artery, begins and ends at this level. The upper border of the pericardium, the sac surrounding the heart, also corresponds to the sternal angle.
Clinical Importance
Healthcare professionals use the angle of Louis as a starting point for counting ribs during physical examinations. Since the second rib attaches directly at the sternal angle, it provides a consistent and easily identifiable landmark, making it simpler to count the ribs below it. This method is helpful because the first rib is often difficult to feel as it is located beneath the clavicle.
The angle’s location also guides the placement of stethoscopes for listening to heart and lung sounds. It helps pinpoint the correct intercostal spaces for assessing specific heart valve sounds. Medical procedures like needle insertions, chest tube placements, and central venous catheter insertions rely on the angle of Louis as a reliable anatomical guide. Accurate identification of this landmark is important for precise incision placement and anatomical orientation during thoracic surgeries.