A Complete Guide to Your Sternum
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Medically reviewed by Oluseun Olufade, MD
The sternum is a long, flat bone at the center of your chest. It is sometimes referred to as the breastbone. The sternum's main function is to protect the vital organs that sit behind it, including the heart.
The sternum also supports surrounding bones and muscles. The ribs connect to the sternum by cartilage, and the sternum anchors major muscles of the neck, thorax, and abdominal wall.
Some people may have variations in the shape and characteristics of their sternum. Associated conditions of the sternum, like fractures, can be dangerous because of its position over vital organs. That's one of the reasons why keeping your sternum healthy—like any other bone—is important.
Anatomy of the Sternum
The sternum is a vertical T-shaped bone located toward the front of the chest. It comprises three segments: the manubrium, body, and xiphoid process.
The top portion of the sternum is called the manubrium. It is broad-shaped with four sides. The top of the manubrium is known as the suprasternal notch. On the sides of the manubrium are the left and right clavicular notches. These notches meet with the collarbones (clavicles) to form one of four joints in the shoulder (sternoclavicular joints) as well as the first pair of ribs.
The manubrium meets the next part of the sternum at a point called the sternal angle; this is also where the second rib's cartilage attaches. This second part of the sternum, the middle portion, is the body of the sternum. It is the longest portion of the bone. The body of the sternum is flat and has sunken ridges on its sides, where the third through seventh pairs of ribs join the sternum via cartilage.
The final portion of the sternum is a triangular-shaped bone called the xiphoid process. The size and shape of the xiphoid process vary person to person. It is usually made mostly of cartilage until the age of 40. Age-related changes in the xiphoid process also differ. By 60, the xiphoid process will typically start to harden and calcify.
Location
The sides of the sternum attach to the ribs by costal cartilage. Costal cartilage allows for chest movement when you breathe. The cartilage also acts as a shock absorber when there is any trauma to the chest wall.
Important muscles, like those in the neck, thorax, and abdominal wall, attach to the sternum. Connecting to the body of the sternum is the pectoralis major muscle, the largest muscle of the chest wall. Another major and essential attachment site is where the xiphoid process attaches to the diaphragm, which is a critical muscle for breathing.
Anatomical Variations
People assigned female at birth typically have a thinner body of the sternum. Any other variations of the sternum are usually present in the lower portion. The most common sternal variation is bifid xiphoid, where the xiphoid process has two endings rather than a triangular-shaped one. Other possible variations of the sternum include:
Sternal angle: Misplacement of the sternal angle could cause an incorrect count of ribs during physical exams, affecting chest procedures.
Sternal cleft: When the sternum fails to fuse or grow together, there could be an area of separation. A sternal cleft can make it so the heart and great vessels (arteries and veins directly connected to the heart) have no protection.
Sternal foramen: This is another potential complication due to the failure of the sternum to fuse and can create an oval-shaped hole in the sternum.
Pectus excavatum: This is when the sternum and costal cartilage become pressed inward. When this happens, the chest wall appears to be sunken in.
Pectus carinatum: This happens when the sternum and costal cartilage have an abnormal outward placement, causing the chest to appear to protrude out.
The sternum can have many other variations that can affect healthcare providers' decisions when performing certain procedures on the chest. Sometimes, these variations can also be mistaken for fractures on radiology pictures taken of the chest.
What Does the Sternum Do?
The sternum's main function is to act as a protective barrier to the thoracic mediastinum from trauma. The thoracic mediastinum is an important body cavity in the chest that holds the heart, lungs, thymus, lymph nodes, parts of the aorta, trachea, esophagus, and some nerves.
The sternum also allows for the attachment of muscles such as the diaphragm. The costal cartilage that runs alongside the bone allows for movement of the chest wall to expand when you breathe in and out.
Associated Conditions
The sternum is subject to injuries and diseases, just like any other part of the body. Some associated conditions of the sternum can be hazardous since the sternum surrounds and protects vital organs like the heart and lungs. Conditions and injuries that can affect the sternum include:
Sternal fractures: Fractures of the sternum are usually from traffic accidents or physical assaults. When there is a fracture to the sternum, there is risk of damage to internal organs and soft tissue. Another cause of sternal fracture is from chest compressions during cardiopulmonary resuscitation (CPR).
Costochondritis: The costal cartilage can become inflamed and cause pain. The inflammation is known as costochondritis. There is usually no known cause for the inflammation, but injuries, heavy lifting, viral infections, and some types of arthritis can cause it. The most common symptom of costochondritis is sternum chest pain and tenderness of the chest when touched. There might also be discomfort when breathing.
Paget's disease of bone (PDB): There is a normal process of bone breakdown and rebuilding. But with Paget's disease of the bone, the normal process is malfunctioned, resulting in bones that are not as strong as they should be. Most people do not have symptoms, but some may experience bone pain and fractures.
Cancer: The sternum is typically not a common place for cancers to develop. When cancer does develop there, it is usually metastatic from another area—meaning cancer from another part of the body has spread to the sternum. Chondrosarcoma is the most common cancer to affect the sternum, specifically the cartilage. People with this condition typically have a slow-growing, large, painless mass at the chest wall.
Diagnostic Testing
When diagnosing sternum problems, healthcare providers usually start with a review of symptoms followed by a physical exam. Some standard tests that a healthcare provider may order might include:
X-rays: This is what is usually used as an initial test when healthcare providers suspect sternal injuries. While chest X-rays are accurate for determining fractures, they aren't as precise for diagnosing sternum tumors because other organs, like the lungs, may block the lesions.
Computed tomography (CT) scan: A CT scan is the testing method of choice for detecting lesions of the sternum, such as tumors. They help surgeons by giving them enhanced details of the tumor before an operation and can detect any further cancer growth. A CT scan can also help determine injury to other organs or tissues after a sternal fracture.
Magnetic resonance imaging (MRI): An MRI is better at detecting cancer growth to other areas than a CT scan and can be beneficial when another testing method cannot diagnose sternal problems.
Ultrasound: Although it may take longer to get a final diagnosis and is dependent on the skill of the technician, an ultrasound can help detect sternal fractures.
Cardiac monitoring: Done with an electrocardiogram, or an ECG, cardiac monitoring is essential to detect any abnormal heart rhythms or heart bruising when there is an injury to the sternum.
Blood tests: Lab work, such as for determining levels of cardiac enzymes, can help detect heart injury. Another blood test, alkaline phosphatase (ALP), can detect bone disorders like PDB.
Tips for Keeping Your Sternum Healthy
The 200-plus bones in your body serve many important functions—the sternum is no exception. It offers structural support, protects of vital organs, helps you breathe, and more. Keeping your bones, including your sternum, healthy is key to allowing them to serve you properly.
Try these tips for maintaining a healthy sternum:
Make sure you are taking in an adequate amount of vitamin D and calcium to reduce your risk of fractures.
Practice weight-bearing exercises and resistance training to strengthen your bones.
Prevent falls by keeping rooms well-lit and clutter-free, wearing appropriate footwear, and completing balance exercises.
Maintain proper posture.
A Quick Review
The sternum is a long, flat bone at the front of your chest that protects vital organs like the heart and lungs. The sternum also helps in other ways, such as with the breathing process and with anchoring nearby organs. There might be some variations in how the sternum forms or looks, which can sometimes be a risk to your health because the organs behind the sternum aren't getting the protection they need. Injuries to your sternum can also be a health risk because the broken sternum can damage surrounding organs or tissue. Keeping your sternum healthy by increasing bone strength and minimizing trauma is key.
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