The sternum, commonly known as the breastbone, is a flat, vertical bone situated in the center of the chest. It runs down the front of the torso, acting as a central plate for the chest wall. It is a fundamental component of the rib cage, providing structural integrity and connecting the ribs to complete the bony framework of the chest cavity.
Locating the Sternum: The Three Key Sections
The sternum is composed of three distinct segments that develop and often fuse together in adulthood. You can locate the sternum by feeling the hard, flat bone running vertically from the base of the neck down toward the upper abdomen. It is shaped somewhat like a short, broad sword, which helps visualize its three parts.
The uppermost section is the manubrium, a broad, quadrangular segment resembling the handle of the sword. Below the manubrium is the sternal body, also called the gladiolus. This is the longest and most central part of the bone, forming the main blade of the sternum.
The final, lowest portion is the xiphoid process, a small, triangular piece that points downward. This part is largely composed of cartilage in younger individuals and typically hardens into bone around age 40. The size and shape of the xiphoid process can vary significantly.
What is the Sternum’s Job?
The main function of the sternum is to provide a shield for the organs within the thoracic cavity. Working with the ribs, it forms a protective bony cage around the heart, lungs, and major blood vessels. This structure is designed to absorb and deflect physical trauma, helping to prevent injuries to these internal structures.
The sternum also serves as an anchor point, providing support for the entire upper torso. It acts as the central anterior attachment for the rib cage, stabilizing the structure. This attachment maintains the integrity of the chest wall during movement and breathing.
The connections between the sternum and the ribs allow for the expansion and contraction necessary for respiration. When inhaling, the rib cage, anchored by the sternum, expands slightly to increase the volume of the chest cavity. This movement helps the lungs draw in air efficiently.
Connected Bones and Clinical Relevance
The sternum forms joints with several other bones, creating a stable but flexible framework. At the top, the manubrium connects with the clavicles (collarbones), forming the sternoclavicular joints. These are the only direct joints connecting the upper limbs to the axial skeleton.
The ribs do not connect directly to the sternum; instead, they are joined by flexible strips of tissue called costal cartilage. The first seven pairs of ribs connect this way, with the cartilage providing elasticity to the rib cage. This connection allows the chest to move and expand during the breathing cycle.
Due to its central location, the sternum is an important landmark in several medical procedures. During Cardiopulmonary Resuscitation (CPR), guidelines recommend placing the heel of the hand over the lower half of the sternum to deliver effective chest compressions. This positioning helps target the heart while avoiding the xiphoid process.
The sternum also contains a significant amount of red bone marrow, which remains active in adults. Because of this, the sternum is sometimes used as a site for a bone marrow biopsy or aspiration. A needle is inserted into the sternal body to collect a sample, which is analyzed to diagnose various blood disorders.