The sternum, commonly known as the breastbone, is a vital component of your skeletal system, playing a crucial role in protecting your internal organs and supporting your body’s structure. Understanding where the sternum is located and its functions is key to appreciating its importance in overall health. This article delves into the anatomy, location, and significance of the sternum.
Sternum Location and Basic Anatomy
The sternum is situated at the center of your chest, in the anterior midline of the thorax. It’s a long, flat bone that runs vertically down the middle of your chest, right in front of your heart and lungs. Imagine a tie lying straight down the center of your shirt – that’s roughly where your sternum is located.
This bone is not a single piece but is comprised of three main sections that fuse together as you age:
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Manubrium: This is the uppermost part of the sternum. It’s a somewhat broad, quadrilateral shape and forms the top of the breastbone. You can feel the top of your manubrium as the slight curve at the base of your neck, between your collarbones. The very top of the manubrium features the suprasternal notch, a palpable dip easily felt at the base of the neck. On either side of the manubrium are clavicular notches, where your collarbones (clavicles) attach, forming the sternoclavicular joints, which are part of your shoulder complex. The manubrium also connects to the first and second ribs.
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Body (Corpus Sterni): Below the manubrium is the main, elongated part of the sternum, known as the body. This is the largest section, flat and blade-shaped. The sternal angle, a ridge-like horizontal prominence, marks the junction between the manubrium and the body. This angle is a crucial anatomical landmark, as it’s where the second ribs attach, and it helps in counting ribs during physical examinations. The sides of the sternal body have depressions where the cartilage of ribs three through seven connect.
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Xiphoid Process: The xiphoid process is the smallest and most inferior part of the sternum, located at the very bottom. It’s typically triangular in shape, but its size and form can vary significantly from person to person. In younger individuals, the xiphoid process is primarily cartilage, gradually ossifying (turning to bone) with age, usually completing by around age 40. Even in older adults, the degree of ossification can differ.
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Detailed Anatomy of the Sternum
To further understand where the sternum is located and how it functions, let’s delve deeper into each of its parts:
Manubrium
As the superior segment of the sternum, the manubrium is not just about location; it’s about connection. Its broad shape provides a strong anchor point for the collarbones and the first pair of ribs. The suprasternal notch at its top is a clinically significant landmark used in various medical procedures and examinations. The sternoclavicular joints, formed by the manubrium and clavicles, are the only bony attachments of the shoulder girdle to the axial skeleton, highlighting the manubrium’s role in upper body stability.
Sternal Body
The body of the sternum is the workhorse of the structure, providing the majority of the surface area for rib attachment. The costal cartilages of ribs three to seven articulate directly with the lateral borders of the sternal body, creating a flexible yet protective rib cage. The flat nature of the body contributes to its protective function over the underlying organs. The sternal angle, where the manubrium meets the body, is not just a point of articulation for the second rib; it also marks the approximate level of the second thoracic vertebra and the aortic arch, making it a vital landmark in thoracic anatomy.
Xiphoid Process
Despite being the smallest part, the xiphoid process is significant due to its inferior location and muscle attachments. It serves as an attachment point for several important muscles, including the diaphragm, which is crucial for breathing, and abdominal muscles. Its cartilaginous nature in younger years provides some flexibility to the lower rib cage. The xiphoid process’s variability in shape and ossification is clinically relevant, especially in procedures like CPR, where understanding its location and potential fragility is important to avoid injury.
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What Does the Sternum Do?
The sternum’s location at the front of the chest is strategically important for its functions:
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Protection of Vital Organs: The primary role of the sternum is to shield the thoracic mediastinum. This crucial cavity houses vital organs including the heart, lungs, thymus gland, major blood vessels like the aorta, trachea (windpipe), esophagus, and important nerves. The sternum acts as a bony shield, protecting these delicate organs from external impacts and trauma.
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Muscle Attachment and Support: The sternum is a key site for muscle attachments. Major muscles of the chest, neck, and abdomen anchor to the sternum, contributing to posture, movement, and breathing. For example, the pectoralis major, the large chest muscle, attaches to the sternum, as do muscles in the neck and abdominal wall. Crucially, the diaphragm, the primary muscle for respiration, attaches to the xiphoid process.
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Facilitating Breathing: The sternum, along with the ribs and costal cartilage, forms the rib cage. The costal cartilage, which connects the ribs to the sternum, is flexible, allowing the rib cage to expand and contract during breathing. This movement is essential for the lungs to inflate and deflate, enabling respiration.
Conditions Associated with the Sternum
Given its prominent location and vital functions, the sternum can be affected by various conditions:
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Sternal Fractures: Trauma to the chest, such as from car accidents, falls, or direct blows, can cause sternal fractures. These fractures are serious because of the risk of injury to the underlying heart and lungs. Even forceful chest compressions during CPR can, in rare cases, lead to sternal fractures.
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Costochondritis: Inflammation of the costal cartilage, known as costochondritis, is a common cause of chest pain. While the exact cause is often unknown, it can be triggered by injury, heavy lifting, viral infections, or certain types of arthritis. The pain is typically felt in the chest and can be tender to the touch, sometimes worsened by breathing.
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Paget’s Disease of Bone (PDB): This condition disrupts the normal bone remodeling process, leading to weakened and deformed bones. While it can affect any bone, it can involve the sternum. Symptoms may include bone pain and fractures.
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Cancer: Cancer originating in the sternum is rare. More commonly, cancer in the sternum is metastatic, meaning it has spread from another site in the body. Chondrosarcoma, a cancer of cartilage, is the most frequent type of primary sternal cancer.
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Anatomical Variations: As mentioned earlier, variations like bifid xiphoid, sternal cleft, sternal foramen, pectus excavatum (sunken chest), and pectus carinatum (pigeon chest) can occur. These variations, while not always pathological, can sometimes cause complications or be mistaken for injuries on imaging.
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Diagnosing Sternum Issues
Diagnosing sternum-related problems typically begins with a physical examination and a review of symptoms. Healthcare providers may utilize several diagnostic tests:
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X-rays: Often the first-line imaging for suspected sternal fractures. While good for fractures, they may be less effective for detecting tumors due to overlapping organs.
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CT Scans: Computed tomography (CT) scans are excellent for detailed imaging of the sternum, making them the preferred method for detecting tumors and assessing fracture severity, as well as any damage to surrounding tissues.
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MRI Scans: Magnetic Resonance Imaging (MRI) provides even more detailed soft tissue imaging and can be better for detecting cancer spread and diagnosing sternal issues when other methods are inconclusive.
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Ultrasound: Ultrasound can be used to detect sternal fractures, though it can be operator-dependent and may take longer for a definitive diagnosis.
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Cardiac Monitoring (ECG): Electrocardiograms (ECGs) are essential for assessing heart function, particularly if sternal injury is suspected, to detect arrhythmias or cardiac contusions.
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Blood Tests: Blood tests, such as cardiac enzyme levels, can help assess for heart injury. Alkaline phosphatase (ALP) blood tests can aid in diagnosing bone disorders like Paget’s disease.
Maintaining Sternum Health
Just like any bone in your body, keeping your sternum healthy is important. General bone health tips apply:
- Consume a Calcium-Rich Diet: Calcium is crucial for bone strength. Include dairy products, leafy green vegetables, and fortified foods in your diet.
- Ensure Adequate Vitamin D Intake: Vitamin D helps your body absorb calcium. Sunlight exposure and vitamin D-rich foods or supplements are important.
- Regular Exercise: Weight-bearing exercises help strengthen bones, including the sternum.
- Avoid Smoking and Excessive Alcohol: These habits can negatively impact bone health.
- Protect Yourself from Injury: Wear appropriate safety gear during activities that could lead to chest trauma.
In Conclusion
Understanding where the sternum is located and its intricate anatomy reveals its critical role in protecting your vital organs, supporting your body’s structure, and facilitating breathing. Maintaining its health is an integral part of overall well-being. By adopting a bone-healthy lifestyle and being mindful of potential injuries, you can ensure your sternum continues to serve its essential functions effectively.
