The manubrium is the uppermost section of the sternum, or breastbone, located at the upper front of the chest. It serves as a key component of the rib cage, forming a protective structure. It also helps anchor several important structures within the chest.
Its Place in the Chest
The manubrium is situated superiorly within the sternum, directly below the neck and nestled between the clavicles, or collarbones. It is the broadest part of the sternum, quadrangular or trapezoidal in shape, narrowing slightly towards its lower border. A noticeable depression at its superior border, visible and palpable, is known as the jugular or suprasternal notch. On either side of this notch are the clavicular notches.
What Connects To It
The manubrium forms specific connections with several bones and cartilages in the upper chest. At its upper lateral corners, it articulates with the clavicles at the sternoclavicular joints, facilitating movement of the shoulders. The cartilages of the first pair of ribs connect directly to the manubrium. The upper part of the cartilages from the second pair of ribs articulates with a partial facet on the manubrium.
Inferiorly, the manubrium joins with the main body of the sternum at a distinct ridge known as the sternal angle, also called the manubriosternal joint. While allowing only a small degree of movement, this articulation is a significant anatomical landmark.
Why It Matters
The manubrium’s position and connections contribute to its important functions. It provides a protective shield for vital organs in the upper chest, including the heart, lungs, and major blood vessels. The bone also serves as an anchor point for several muscles of the neck and chest. These muscles, such as the sternocleidomastoid and pectoralis major, influence breathing mechanics and upper limb movement.
The movement at the manubriosternal joint, also known as the sternal angle, assists in the expansion of the thoracic cage during inhalation. This angle is a clinically significant landmark for healthcare professionals. It allows for the identification of the second rib, which helps in accurately counting the remaining ribs during physical examinations. The sternal angle is also used to locate specific organs and perform various medical procedures, such as listening to heart sounds or identifying the level of the tracheal bifurcation.