The Anatomy of a Normal Sternum
The sternum, commonly called the breastbone, is a critical component of the rib cage, offering vital protection to the heart and lungs. Located in the center of the chest, it is a flat, vertical bone composed of three main segments that, in adults, have fused into a single bone. Understanding these parts helps paint a clearer picture of what a normal sternum should look like.
The Manubrium: The 'Handle'
The uppermost part of the sternum is the manubrium, a broad, handle-like section. It is roughly trapezoid-shaped and is where the clavicles (collarbones) and the first pair of ribs attach. A notable feature is the jugular notch, a shallow indentation at the very top of the manubrium. The manubrium joins with the body of the sternum at a prominent ridge known as the sternal angle or Angle of Louis.
The Body: The 'Blade'
The central and longest part of the sternum is the body, or gladiolus. This section is flat and runs vertically down the chest. Along its lateral borders, the cartilage of the ribs—from the second to the seventh pair—connects to the sternal body. In some individuals, faint horizontal ridges can be seen across the body, representing the fusion lines of the original four bone segments, or sternebrae, during development.
The Xiphoid Process: The 'Tip'
The xiphoid process is the smallest, most inferior portion of the sternum. This pointed end piece is made of mostly cartilage in childhood, gradually ossifying (turning into bone) as a person ages. The shape and size of the xiphoid process are highly variable among individuals. Given its position, care must be taken during chest compressions, such as in CPR, to avoid injuring this part of the sternum.
What a Normal Sternum Looks Like: Key Features
A normal sternum is a relatively straight, flat bone with a slight anterior convexity (outward curve). However, several factors contribute to its specific appearance, including gender, age, and individual variations.
Variations in Shape and Size
- Overall Length: An average sternum measures about 6 to 8 inches in length, but this can vary. The sternum is typically longer in males than in females.
- Gender Differences: Studies have shown that females tend to have shorter and thinner sterna compared to males. Differences in manubrium and body length have been shown to be useful in differentiating genders in forensic anthropology.
- Developmental Factors: The sternum develops from cartilage that gradually fuses. The fusion of the xiphoid process is particularly variable and can result in different shapes, such as a bifid (split) or perforate (with a hole) xiphoid. These are considered normal anatomical variations and not abnormalities.
How to Examine Your Sternum
To perform a simple self-examination of your sternum, follow these steps:
- Stand upright: Place your fingers at the center of your chest, just below your collarbones.
- Locate the manubrium: Feel the wide, handle-like top part of the bone.
- Find the sternal angle: Slide your fingers down until you feel a noticeable ridge or angle where the manubrium and body meet. This is a key anatomical landmark.
- Palpate the body: Continue tracing the flat surface of the sternum downwards.
- Identify the xiphoid process: At the bottom, you may be able to feel the small, pointed tip of the xiphoid process.
While performing this check, note any unusual bumps, indentations, or tenderness. Remember that slight variations in shape are common.
Common Chest Wall Deformities and Variations
While a normal sternum is relatively straight and flat, some people have more noticeable structural variations, often stemming from abnormal cartilage growth during development. The two most common are pectus excavatum and pectus carinatum.
Comparing Pectus Excavatum and Pectus Carinatum
| Feature | Pectus Excavatum (Funnel Chest) | Pectus Carinatum (Pigeon Chest) |
|---|---|---|
| Appearance | Inward displacement or sunken appearance of the sternum and ribs. | Outward protrusion of the sternum and costal cartilages. |
| Frequency | More common, affecting about 1 in 400 births. | Less common, affecting about 1 in 1,000 to 1,500 children. |
| Primary Cause | Overgrowth of costal cartilages that push the sternum inward. | Overgrowth of costal cartilages that push the sternum outward. |
| Symptoms | In severe cases, can compress the heart and lungs, causing shortness of breath, chest pain, and reduced exercise tolerance. | Most cases are asymptomatic, though some may experience chest pain or shortness of breath with exercise. |
| Psychological Impact | Can cause self-consciousness and emotional distress, especially during puberty. | Can cause self-consciousness and impact body image. |
Other Congenital Variations
Besides the main pectus deformities, other less common variations exist, such as a cleft sternum, where the sternum fails to fuse completely in the midline. These conditions are typically identified at birth or early childhood.
When to Be Concerned About Your Sternum
While slight variations are normal, certain signs may indicate an underlying issue, ranging from minor inflammation to more serious conditions. It is important to consult a healthcare professional if you experience:
- Persistent Pain: Any ongoing tenderness, swelling, or pain, particularly if it worsens with deep breathing, coughing, or physical activity. This could indicate conditions like costochondritis, an inflammation of the cartilage connecting the ribs to the sternum.
- Visible Deformity: If you notice a new or worsening indentation or protrusion, it is worth seeking a medical evaluation, especially if it coincides with a period of rapid growth.
- Clicking or Grinding: A clicking, popping, or grinding sensation in the chest area, especially near the collarbone, can indicate a joint issue, such as in the sternoclavicular joint.
- Associated Symptoms: Seek emergency treatment if chest pain is accompanied by jaw or neck pain, dizziness, excessive sweating, or rapid breathing, as these can be signs of a serious heart condition.
Conclusion
In summary, a normal sternum has a relatively flat, vertical structure composed of three distinct segments: the manubrium, body, and xiphoid process. Its specific appearance can vary based on individual factors, gender, and age, and minor variations, like the shape of the xiphoid process, are common and typically harmless. However, more pronounced deformities, such as pectus excavatum and carinatum, exist and may require medical assessment. By understanding the key features of what a normal sternum should look like, you can better monitor your own health and recognize when professional medical advice may be necessary for any persistent pain or significant changes in your chest's structure. For further information on chest wall deformities, you can visit the Cleveland Clinic website.
