Applied Anatomy – Sternum
1. Definition Table
| Category | Explanation |
|---|---|
| What is it? | – Flat, elongated bone in the midline of the anterior thoracic wall – Forms the central component of the thoracic cage |
| Most unique feature | – Direct articulation with the clavicles and first seven costal cartilages – Landmark for CPR, sternal puncture, and thoracic surgery |
| Structurally characterized by | – Composed of three parts: manubrium, body, and xiphoid process – Articulates with ribs and clavicles – Contains red marrow in adults |
| Functionally characterized by | – Protects mediastinal organs (heart, great vessels, thymus) – Serves as an anchor point for ribs and muscles – Assists in thoracic stability and respiration |
| Composed of | – Manubrium: Superior segment – Body (gladiolus): Middle and largest segment – Xiphoid process: Inferior and smallest segment |
| Common diseases | – Sternal fractures (usually from trauma or CPR) – Osteomyelitis – Sternal dehiscence (post-surgery) – Sternal tumors (e.g., metastases) |
| Diagnosis – Clinical | – Anterior chest pain – Swelling or tenderness over the sternum – Clicking or instability post-surgery |
| Diagnosis – Imaging | – X-ray: May detect fractures – CT: Best for visualizing bony details – MRI: Evaluates marrow and soft tissues (e.g., tumors or infection) |
| Diagnosis – Labs | – Blood cultures for suspected osteomyelitis – CRP/ESR to assess inflammation – Biopsy if neoplasm suspected |
| Treatment (Rx) | – Conservative care for minor fractures – Surgical repair or wiring for unstable fractures or dehiscence – Antibiotics for infection – Resection or radiation for malignancies |
2. Parts Table
| Part | Description |
|---|---|
| Manubrium | – Superior portion – Articulates with clavicles and first two ribs – Contains the jugular notch and sternoclavicular joints |
| Body (Gladiolus) | – Middle and largest portion – Articulates with costal cartilages of ribs 2–7 – Forms most of the sternal surface |
| Xiphoid Process | – Small, inferior segment – Cartilaginous in youth, ossifies with age – Can be palpated just above the epigastrium |
3. Historical Note
| Era | Highlights |
|---|---|
| Ancient Times | – Recognized by Egyptian and Greek anatomists – Associated with the “breastbone” in battle injuries |
| Classical Era | – Galen described sternal segments and their clinical importance – Used as an anatomical reference in early dissections |
| Modern Era | – Key landmark in CPR and sternal puncture – Integral to thoracic surgery (e.g., median sternotomy) – Evolving focus on sternal preservation and reconstruction post-cardiac surgery |
4. MCQs
🧠 Basic Science
Q1: Which structure articulates directly with the manubrium of the sternum?
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A. 3rd costal cartilage
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B. 5th rib
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C. Clavicle
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D. Sternocleidomastoid muscle
Answer: C. Clavicle
Explanation:
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Clavicle (Correct): Articulates at the sternoclavicular joint on the manubrium.
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3rd costal cartilage (Incorrect): Articulates with the body of the sternum.
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5th rib (Incorrect): Articulates with the lower part of the body.
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Sternocleidomastoid (Incorrect): Attaches near the manubrium but does not articulate.
Q2: Which part of the sternum is often used for bone marrow biopsy in adults?
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A. Xiphoid process
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B. Manubrium
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C. Sternoclavicular joint
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D. Costal cartilage
Answer: B. Manubrium
Explanation:
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Manubrium (Correct): Contains hematopoietically active marrow and is accessible for biopsy.
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Xiphoid process (Incorrect): Small, avascular, and not used for biopsy.
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Sternoclavicular joint (Incorrect): Joint space, not a marrow-containing site.
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Costal cartilage (Incorrect): Cartilaginous, not suitable for biopsy.
🩺 Clinical
Q3: A patient suffers blunt chest trauma during a car crash. What is the most likely complication if the sternum is fractured?
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A. Tension pneumothorax
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B. Flail chest
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C. Cardiac contusion
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D. Diaphragmatic rupture
Answer: C. Cardiac contusion
Explanation:
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Cardiac contusion (Correct): The heart lies directly behind the sternum and can be bruised in trauma.
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Tension pneumothorax (Incorrect): Related to lung trauma, not specifically sternum.
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Flail chest (Incorrect): Involves multiple rib fractures, not the sternum.
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Diaphragmatic rupture (Incorrect): Usually occurs with abdominal trauma.
Q4: What is the clinical significance of the xiphoid process in CPR?
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A. Landmark to compress directly over
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B. Contains pacemaker cells
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C. Should be avoided during compressions
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D. Attachment site for internal jugular vein
Answer: C. Should be avoided during compressions
Explanation:
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Avoided (Correct): Compressing over xiphoid risks injury to liver or diaphragm.
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Landmark to compress directly over (Incorrect): Chest compressions are done over the mid-sternum, not the xiphoid.
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Pacemaker cells (Incorrect): Found in the sinoatrial node of the heart.
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Internal jugular vein (Incorrect): Not related to the xiphoid attachment.
🖼️ Imaging
Q5: Which modality best demonstrates a sternal fracture after CPR?
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A. MRI
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B. X-ray
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C. CT
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D. Bone scan
Answer: C. CT
Explanation:
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CT (Correct): Best at identifying sternal fractures with fine detail.
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MRI (Incorrect): Good for soft tissue and marrow but not first-line for fracture.
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X-ray (Incorrect): May miss subtle or posterior fractures.
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Bone scan (Incorrect): Detects metabolic activity, not used for acute fracture.
Q6: A sternal lesion on imaging that shows cortical destruction and soft tissue extension most likely suggests:
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A. Sternal foramen
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B. Bone island
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C. Metastasis
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D. Osteophyte
Answer: C. Metastasis
Explanation:
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Metastasis (Correct): Aggressive bone lesion with cortical breakthrough and soft tissue mass.
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Sternal foramen (Incorrect): Congenital benign variant, not aggressive.
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Bone island (Incorrect): Incidental sclerotic focus with no cortical destruction.
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Osteophyte (Incorrect): Bone spur, not typically seen in sternum.
5. Memory Image Idea 💡
| Concept | Components |
|---|---|
| The Shield of the Heart | – Imagine the sternum as a vertical shield over a glowing heart beneath it – Three segments: • Top = Manubrium, like the helmet crest • Middle = Body, like the broad chestplate • Bottom = Xiphoid, like the tapered point – Each rib arches like a protective rib cage enclosing the heart and lungs – Transparent overlay of vessels and thymus beneath the shield – Title: “The Shield of the Heart – TheCommonVein.com“ |