The sternum, or breastbone, is the flat bone running down the center of your chest. It serves as the structural anchor of your rib cage, protects your heart and lungs from impact, plays a role in breathing, and produces blood cells throughout your life. For a single bone, it does a surprising amount of work.
Three Parts, One Bone
The sternum is made up of three distinct segments. The manubrium is the wide, handle-shaped piece at the top where your collarbones and first pair of ribs connect. Below that sits the body, the longest section, where most of your ribs attach. At the very bottom is the xiphoid process, a small pointed piece that starts out as cartilage in childhood and gradually hardens into bone. All three segments begin ossifying (turning from cartilage into solid bone) between the fifth month of fetal development and shortly after birth, though the xiphoid process can remain partially cartilaginous well into adulthood.
Anchoring the Rib Cage
Your first seven pairs of ribs, called true ribs, connect directly to the sternum through strips of flexible cartilage known as costal cartilage. This creates a rigid but slightly elastic cage around your chest. The sternum acts as the front wall’s keystone: without it, your ribs would have no central attachment point and the entire structure would lose its shape and strength. That costal cartilage is important too. It gives the rib cage just enough flex to expand when you breathe and absorb minor impacts without cracking.
Protecting the Heart and Lungs
The sternum sits directly in front of the heart, major blood vessels, and a large portion of both lungs. It functions as a bony shield against blunt force to the chest. This protection is critical: the organs behind it are soft, pressurized, and vital. A strong enough blow can still fracture the sternum, but the bone absorbs and distributes much of the force that would otherwise reach the heart directly.
That said, the sternum’s protective role has limits. Motor vehicle collisions account for 60 to 90 percent of sternal fractures, typically from deceleration forces or impact with a steering wheel. When the sternum does break, the real danger comes from injuries to what’s behind it, including bruising of the heart muscle, lung damage, or disruption of the aorta. The bone itself usually heals; it’s the associated injuries that carry serious risk.
Helping You Breathe
Every breath you take involves the sternum. When you inhale, the muscles between your ribs (intercostals) contract and lift the rib cage upward and outward, pulling the sternum forward. This expands the chest cavity, creating negative pressure that draws air into the lungs. When you exhale, the sternum drops back as those muscles relax and the rib cage compresses.
The diaphragm, your primary breathing muscle, also has a direct connection to the sternum. It originates partly from the back surface of the xiphoid process at the bottom of the bone. So the sternum isn’t just passively moving during respiration. It’s a structural attachment point for the very muscles driving the process.
Producing Blood Cells
This is the function most people don’t expect from a chest bone. The sternum contains red bone marrow, the spongy tissue responsible for manufacturing blood cells. Flat bones like the sternum, hip bones, ribs, skull, and shoulder blades are the primary sites where this production happens in adults. The marrow inside the sternum continuously generates red blood cells (which carry oxygen), white blood cells (which fight infection), and platelets (which help blood clot).
This is why doctors sometimes use the sternum as a site for bone marrow aspiration, a procedure where a needle is inserted into the bone to collect a marrow sample. The sternum’s position close to the skin surface and its reliable marrow content make it a practical choice when clinicians need to evaluate blood cell production or diagnose blood disorders.
Sternum Pain and Costochondritis
If you’ve felt pain or tenderness right at your breastbone, you’re not alone. One of the most common causes is costochondritis, an inflammation of the cartilage connecting your ribs to the sternum. The pain is typically sharp or pressure-like, worst where the cartilage meets the bone, and it often affects the upper ribs on the left side. It can radiate into the arms and shoulders, which is why many people initially worry they’re having a heart problem.
Costochondritis pain tends to worsen with deep breathing, coughing, sneezing, or any twisting motion of the chest wall. It usually resolves on its own over weeks, though it can be stubborn. The sternum itself isn’t damaged in costochondritis. The inflammation is in the cartilage junction, but because that junction is right at the bone’s surface, the pain feels like it’s coming from the sternum itself.
The Sternum in Heart Surgery
For open-heart procedures, surgeons need direct access to the chest cavity, and the sternum is what stands in the way. In a median sternotomy, the surgeon cuts vertically through the breastbone from the top (between the collarbones) to the bottom, then spreads the two halves apart to expose the heart. It’s one of the most common surgical approaches in cardiac medicine.
Recovery takes about eight weeks for the bone to heal, during which you’d need to avoid heavy lifting, pushing, or pulling that could stress the healing halves. The sternum is wired back together at the end of surgery, and the bone gradually fuses. Because of this lengthy healing timeline, sternotomy is considered major surgery, and the recovery period often shapes a patient’s return to normal activity more than the heart procedure itself.