The sternum, commonly known as the breastbone, is a flat bone positioned in the central part of the chest. It forms the front of the rib cage. This bone serves as a connecting point for the ribs via cartilage, contributing to the overall structure of the thoracic cavity. It plays a role in protecting internal organs.
Anatomy and Structure
The sternum is a T-shaped bone, approximately 6 inches long in adults. It consists of three distinct parts: the manubrium, the body (also known as the gladiolus), and the xiphoid process. These parts are connected by cartilage in children, which typically ossifies during adulthood.
The manubrium is the uppermost and widest portion of the sternum, resembling the handle of a sword. It articulates with the clavicles (collarbones) at the sternoclavicular joints and with the first pair of ribs. The body, or gladiolus, is the longest and flat central part of the sternum, akin to the blade of a sword. It provides attachment points for the costal cartilages of the second through seventh ribs along its lateral borders.
The xiphoid process is the smallest and most inferior part of the sternum, and resembles the tip of a sword. It is primarily cartilaginous in younger individuals, gradually ossifying with age. This process serves as an attachment site for certain abdominal muscles and a portion of the diaphragm. The junction between the manubrium and the body forms a palpable ridge known as the sternal angle, or angle of Louis, which is a useful anatomical landmark for locating the second rib.
Role and Importance
The sternum protects vital internal organs such as the heart, lungs, and major blood vessels from external trauma. It works in conjunction with the ribs and vertebral column to create a strong, bony enclosure.
Beyond protection, the sternum contributes to the structural integrity of the thoracic cage. It provides a stable anterior attachment point for the ribs, which allows for the maintenance of chest cavity shape and volume. This stability is essential for the mechanics of breathing, as the rib cage, connected to the sternum, can expand and contract to facilitate lung inflation and deflation. The sternum also serves as an attachment site for several muscles, including parts of the pectoralis major and certain abdominal muscles.
Common Issues and Clinical Relevance
The sternum can be affected by various conditions, leading to pain or requiring medical attention. One common cause of sternum pain is costochondritis, an inflammation of the cartilage that connects the ribs to the sternum. This condition can cause sharp chest pain that worsens with movement, deep breaths, coughing, or pressure on the chest, but usually resolves on its own. Tietze syndrome is similar but involves visible swelling near the affected joints, often higher on the rib cage.
Sternal fractures, breaks in the breastbone, usually result from blunt force trauma, such as motor vehicle collisions or direct impacts to the chest. These fractures can cause severe localized pain, especially with breathing or movement, and may be accompanied by bruising or swelling. While isolated sternal fractures often heal well, their presence may indicate other serious internal injuries to the heart or lungs, necessitating careful medical evaluation.
The sternum is also a site for medical procedures, notably bone marrow aspiration. This procedure involves inserting a needle into the sternum to collect a sample of bone marrow for diagnostic purposes, such as identifying blood disorders like leukemia or anemia. The sternum is chosen for this procedure due to its accessibility and the presence of active bone marrow, and a local anesthetic is used to minimize discomfort.