The breastbone, formally known as the sternum, is a long, flat bone in the center of the chest. This structure provides a strong, central anchor for the anterior portion of the rib cage, forming a shield for the organs within the thoracic cavity. It is one of the largest flat bones in the body. Understanding the sternum’s location and composition is necessary to appreciate its function and how it relates to common experiences of chest pain or injury.
Defining the Sternum and Its Location
The sternum runs vertically down the midline of the upper chest, positioned just beneath the skin and muscles. This bone is easily palpable, meaning a person can physically feel it by tracing a line from the base of the neck down to the upper abdomen. The sternum connects to the ribs not directly by bone, but through flexible strips of hyaline cartilage known as costal cartilages. These cartilages link the first seven pairs of ribs to the breastbone, creating a joint that allows for the slight movement required during breathing.
The Three Distinct Segments
The sternum is composed of three distinct sections that fuse together over a person’s lifetime. The uppermost portion is the manubrium, a broad, somewhat quadrangular segment that articulates with the clavicles, or collarbones, at the top of the chest.
Just below the manubrium is the body of the sternum, which is the longest and flattest section. This central segment connects to the costal cartilages of the second through the seventh pairs of ribs. The manubrium and the body meet at a slight angle called the sternal angle.
The final, smallest segment is the xiphoid process, a pointed, cartilaginous projection at the bottom. The xiphoid process is largely made of cartilage in youth and typically ossifies, or turns into bone, later in adulthood.
Primary Roles of the Breastbone
The dual functions of the breastbone are to provide protection and to serve as a central point of skeletal attachment. Its position directly in front of the mediastinum makes it an effective shield for the internal organs. The sternum acts as a bony barrier safeguarding the heart, the lungs, and the major blood vessels from blunt force trauma.
The sternum’s second function is to act as a central anchor for the entire rib cage and several muscles. The connection to the ribs helps maintain the integrity of the thoracic cage, allowing it to expand and contract during respiration. Muscles involved in arm movement and breathing, including the pectoralis major and the diaphragm, have attachment points on the sternum.
Common Conditions and Pain Points
Pain felt in the area of the breastbone can arise from various sources, ranging from inflammation to injury. One of the most common causes is costochondritis, which is inflammation of the cartilage where the ribs join the sternum. This condition causes sharp, localized pain that often worsens with deep breathing or coughing, but it does not involve any visible swelling.
A similar but less common condition, Tietze syndrome, is distinguished by the presence of visible, tender swelling at the junction of one or two of the upper ribs. More severe sternal pain often results from a sternal fracture, typically caused by significant blunt trauma. These fractures can be painful and may signal potential injury to the underlying heart or lungs.
The sternum is also involved in medical procedures, notably during cardiopulmonary resuscitation (CPR), where chest compressions are applied. In open-heart surgery, a procedure called a sternotomy is performed, which involves vertically cutting the breastbone to access the thoracic cavity. Pain in the sternum area can also be referred pain from gastrointestinal conditions like acid reflux, which irritates the esophagus located behind the bone.