Sternum Anatomy Vector

Sternum: Overview, Anatomy, and Function (2024)

by | Updated: Feb 5, 2024

The sternum, commonly known as the breastbone, is a central figure in the human skeletal system, anchoring the rib cage and serving as a pivotal point for various muscular and cartilaginous attachments.

This flat, elongated bone plays a crucial role not only in providing structural integrity to the thoracic region but also in protecting vital organs such as the heart and lungs.

Understanding the sternum’s anatomy, functions, and its involvement in health and disease is essential for comprehending the complexities of the human thoracic structure and its role in overall bodily mechanics.

What is the Sternum?

The sternum, or breastbone, is a long, flat bone in the center of the chest. It connects to the ribs via cartilage, forming the front part of the rib cage, thereby protecting vital organs like the heart and lungs and supporting upper body structures.

Sternum and Thoracic Cage Illustration Vector

Parts

The sternum consists of the following parts:

  • Manubrium: The upper portion of the sternum. It articulates with the clavicles (collar bones) and the first two ribs, forming the major joints of the shoulders and the front of the rib cage.
  • Body (Gladiolus): This is the longest part of the sternum. It connects to the manubrium above and the xiphoid process below. The body provides attachment points for most of the ribs through costal cartilage.
  • Xiphoid Process: The smallest and most variable part, the xiphoid process is a thin, elongated structure that projects downward. It is made of cartilage in young individuals but gradually ossifies (turns into bone) with age. It serves as an attachment site for various muscles and ligaments.

Function

The sternum serves several key functions:

  • Protection of Vital Organs: It forms a protective shield for the heart, lungs, and major blood vessels, guarding them against physical impacts.
  • Support and Structure: As a central part of the rib cage, the sternum provides structural support for the upper body and aids in maintaining the shape and integrity of the chest cavity.
  • Muscle Attachment: Various muscles, including those used in breathing (like the diaphragm) and major upper body muscles, attach to the sternum, facilitating movement and respiratory functions.
  • Assisting in Respiration: By being a part of the rib cage, it helps in the expansion and contraction of the chest during breathing.

Development of the Sternum

The development of the sternum begins in the embryonic stage as bilateral strips of cartilaginous tissue in the thoracic region. These strips, known as sternal bars, gradually fuse together down the midline to form a single cartilaginous model of the sternum.

This fusion typically occurs during the sixth to ninth weeks of embryonic development. As the fetus grows, the cartilaginous model begins to ossify from several ossification centers.

The process starts in the manubrium and the body (gladiolus) of the sternum during late fetal development or soon after birth. The xiphoid process, being the last to ossify, may remain cartilaginous well into adulthood.

This ossification process is usually complete by the age of 25, resulting in a fully developed and hardened sternum, essential for its protective and structural roles in the human body.

Causes of Sternum Pain

Sternum pain, often perceived as chest pain, can arise from various causes:

  • Musculoskeletal Issues: Costochondritis (inflammation of the cartilage connecting the ribs to the sternum), strains or sprains in the chest muscles, or trauma to the chest area can cause sternum pain.
  • Cardiac Conditions: Conditions such as angina, heart attack, or pericarditis (inflammation of the lining around the heart) can manifest as pain in the sternum area.
  • Gastrointestinal Problems: Acid reflux or gastroesophageal reflux disease (GERD), where stomach acids back up into the esophagus, can cause burning pain near the sternum.
  • Respiratory Issues: Lung infections like bronchitis or pneumonia, or inflammation of the lining of the lungs (pleurisy), can lead to sternum pain, especially when coughing or breathing deeply.
  • Bone Diseases: Osteoporosis or other conditions affecting bone health can make the sternum more susceptible to fractures, causing pain.
  • Psychological Factors: Stress and anxiety can sometimes manifest as chest pain, including in the sternum area.

Note: It’s important to seek medical advice for sternum pain, especially if it’s severe, persistent, or accompanied by symptoms like shortness of breath, dizziness, or nausea, as it could indicate a serious condition.

Pectus Excavatum vs. Pectus Carinatum

Pectus excavatum and pectus carinatum are two different types of congenital deformities of the chest wall, involving the sternum and the ribs.

  • Pectus Excavatum: Often referred to as “funnel chest,” pectus excavatum is characterized by a sunken appearance of the chest. In this condition, the sternum and adjacent cartilages are depressed inward towards the spine, creating a concave shape in the chest. This can be mild or severe and may cause issues with the heart and lungs in more pronounced cases, as well as psychological distress due to the chest’s appearance.
  • Pectus Carinatum: Commonly known as “pigeon chest,” pectus carinatum is the opposite of pectus excavatum. It features a protrusion of the sternum and the ribs outward, giving the chest a convex or bulging appearance. This condition is less likely to cause physical complications compared to pectus excavatum, but it can still lead to self-consciousness about body image.

Both conditions are generally present at birth, but they often become more noticeable during the adolescent growth spurt.

While the exact cause of these deformities is not completely understood, they are believed to result from abnormal growth of the cartilage that connects the ribs to the sternum.

Treatment options vary based on severity and can range from physical therapy and braces to surgical correction.

FAQs About the Sternum

Why is the Sternum Called the Breastbone?

The sternum is commonly called the breastbone due to its location at the front of the chest (breast) area.

Its prominent position in the center of the chest, aligned with the breasts, makes it a central component of the thoracic structure, hence the name breastbone.

What is the Body of the Sternum?

The body of the sternum, or gladiolus, is the longest and largest part of the sternum. It lies between the manubrium, the upper part of the sternum, and the xiphoid process, the lower, small tip.

The body forms the bulk of the sternum and provides attachment points for several ribs via costal cartilages.

What is a Sternal Fracture?

A sternal fracture refers to a break or crack in the sternum. These fractures are typically caused by direct trauma to the chest, such as from a car accident or a severe blow during contact sports.

Symptoms can include pain, swelling, and bruising in the chest area. Sternal fractures are significant as they may indicate underlying injuries to internal organs.

What is the Sternoclavicular Joint?

The sternoclavicular joint is a pivotal articulation where the clavicle (collarbone) meets the sternum at the base of the neck. This joint is important for allowing a wide range of motions for the upper limbs and shoulders.

It’s one of the few bony joints that connect the appendicular skeleton (limbs and appendages) to the axial skeleton (main body frame).

When Does the Sternum Stop Growing?

The sternum stops growing and completes its development typically by the age of 25. The bone ossifies from several centers that appear from puberty and gradually fuse together.

The last part to ossify and fuse is the xiphoid process, which solidifies into bone from its original cartilaginous form, marking the end of the sternum’s growth.

What Does it Mean When Your Sternum Hurts?

Pain in the sternum can be indicative of various conditions

It often points to musculoskeletal issues like costochondritis (inflammation of the cartilage connecting the ribs to the sternum), but it can also signal more serious problems such as cardiac issues (like angina or heart attack), respiratory infections, or gastrointestinal disorders (such as acid reflux).

Persistent or severe sternum pain should be evaluated by a healthcare professional.

What is the Knob at the Bottom of the Sternum?

The knob at the bottom of the sternum is called the xiphoid process. It’s a small, cartilaginous extension of the sternum that eventually ossifies (turns into bone) typically by middle age.

The xiphoid process serves as an attachment point for various muscles and ligaments involved in the respiratory and abdominal functions.

What Organ is Closest to the Sternum?

The heart is the organ that is closest to the sternum. The sternum serves as a protective shield for the heart, lying just anterior to it.

Its proximity to the heart is why chest pain involving the sternum area is often taken seriously as a potential cardiac symptom. The lungs and major blood vessels are also located near the sternum.

What Happens if You Press the Xiphoid Process?

Pressing the xiphoid process can be uncomfortable or painful, as it’s a sensitive area. Excessive pressure on it, especially during CPR or other forceful actions, can lead to injury, including fracturing or dislocating the xiphoid process.

Such injuries may cause pain and swelling and could potentially harm internal organs due to their proximity to the liver and diaphragm.

Does the Sternum Have Cartilage?

Yes, the sternum is connected to the ribs by cartilage, specifically costal cartilage. This cartilage is crucial as it allows the rib cage to be flexible enough for breathing while still protecting vital organs.

The upper part of the sternum, the manubrium, also articulates with the clavicles through cartilaginous joints.

Does the Sternum Have Blood Vessels?

The sternum does contain blood vessels, which are essential for providing blood supply to the bone and surrounding tissue. These vessels are part of the systemic circulation and play a key role in the nourishment and health of the sternum.

The presence of these vessels is particularly important in the context of healing, such as after surgery or injury.

How Does the Sternum Heal After Open Heart Surgery?

After open heart surgery, where the sternum is split (sternotomy) to access the heart, the healing process involves several stages. Initially, the sternum is typically wired back together to ensure proper alignment and stability.

Bone healing then proceeds over the following weeks to months, similar to other bone healing processes, involving the formation of new bone tissue.

Adequate rest, nutrition, and following post-operative care instructions are crucial for effective healing. Pain management and avoiding strenuous activities are also important during the recovery period.

Can the Sternum Cause Shortness of Breath?

Yes, conditions affecting the sternum can lead to shortness of breath. For instance, deformities like pectus excavatum (sunken chest) can compress the lungs and reduce lung capacity, causing difficulty in breathing.

Injuries or inflammation of the sternum, such as from trauma or conditions like costochondritis, can also make breathing painful, leading to shallow breaths and a feeling of shortness of breath.

Can Sternum Pain Be Serious?

Sternum pain can be serious, depending on its cause. While it may often be due to benign issues like muscular strain or costochondritis, it can also indicate more serious conditions such as a heart attack, especially if accompanied by symptoms like sweating, nausea, or pain spreading to the arms.

Any persistent or severe chest pain, including sternum pain, should be evaluated by a healthcare professional promptly to rule out life-threatening conditions.

Final Thoughts

The sternum is a key component in the human skeletal framework, offering more than just structural support. It safeguards critical organs, assists in respiratory mechanics, and serves as an attachment site for important muscles.

Its significance extends beyond its physical attributes, impacting various medical conditions and surgical procedures.

The sternum’s multifaceted role in human anatomy underscores the complexity and sophistication of the skeletal system, highlighting the intricate interplay between different bodily structures necessary for optimal physiological functioning.

Written by:

John Landry, BS, RRT

John Landry is a registered respiratory therapist from Memphis, TN, and has a bachelor's degree in kinesiology. He enjoys using evidence-based research to help others breathe easier and live a healthier life.

References

  • Faarc, Kacmarek Robert PhD Rrt, et al. Egan’s Fundamentals of Respiratory Care. 12th ed., Mosby, 2020.
  • Altalib AA, Miao KH, Menezes RG. Anatomy, Thorax, Sternum. 2023 Jul 24. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023.

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