Sternum

The sternum, commonly known as the breastbone, is a flat bone located in the anterior midline of the thorax. It plays a crucial role in protecting vital thoracic organs and providing attachment points for several muscles. Understanding its anatomy and development is essential for clinical assessment and surgical interventions.

Anatomy of the Sternum

Gross Anatomy

The sternum is a flat bone that lies in the central anterior portion of the thoracic cage and consists of three main parts:

• Manubrium: The superior portion, articulating with the clavicles and first pair of ribs.
• Body (Gladiolus): The elongated central portion, articulating with the second to seventh ribs.
• Xiphoid Process: The small, inferior portion, which may ossify later in life and serves as an attachment for muscles such as the diaphragm and rectus abdominis.

The sternum forms articulations with the costal cartilages of the ribs and the clavicles, contributing to the stability of the thoracic cage.

Surface Features

• Sternal Angle (Angle of Louis): The junction between the manubrium and body, serving as a landmark for the second rib and mediastinal structures.
• Jugular Notch: A superior concavity of the manubrium, palpable at the root of the neck.
• Costal Notches: Lateral indentations where the costal cartilages articulate with the sternum.

Histology

• The sternum is composed of compact bone surrounding cancellous bone containing red bone marrow.
• It is a major site of hematopoiesis in adults, contributing to red blood cell and immune cell production.

Development and Ossification

The sternum develops from paired mesenchymal bars in the embryo that fuse in the midline, a process completed during childhood and adolescence.

• Ossification begins in the manubrium and body with multiple primary centers appearing during fetal life.
• Secondary ossification centers appear in the xiphoid process and the sternal body during adolescence.
• Variants and anomalies can occur, including sternal clefts, bifid xiphoid processes, or delayed fusion, which may have clinical significance.

Functions of the Sternum

The sternum serves multiple vital roles in the human body, contributing to both structural support and physiological function.

• Structural Support: Provides a central anchor for the anterior thoracic cage, contributing to stability and protection of the heart, lungs, and major vessels.
• Muscle Attachment: Serves as an attachment site for important muscles including the pectoralis major, sternocleidomastoid, and diaphragm.
• Respiratory Mechanics: Assists in thoracic expansion during respiration by providing leverage for rib movement.
• Hematopoietic Function: The red bone marrow within the sternum participates in blood cell production.

Clinical Significance

Common Disorders

• Sternal Fractures: Often result from blunt chest trauma or motor vehicle accidents, presenting with pain, swelling, and tenderness.
• Sternocostal Joint Dysfunction: Pain or inflammation at the costosternal junction, sometimes mimicking cardiac conditions.
• Sternal Tumors: Both primary and secondary malignancies can affect the sternum, presenting as swelling, pain, or pathological fractures.
• Sternal Infections: Osteomyelitis or mediastinitis may occur post-surgery or secondary to systemic infections.

Congenital Anomalies

• Sternal Cleft: Partial or complete failure of sternal fusion, occasionally associated with other midline defects.
• Pectus Excavatum: Posterior depression of the sternum, leading to cosmetic and sometimes cardiopulmonary compromise.
• Pectus Carinatum: Anterior protrusion of the sternum, which may require surgical correction in severe cases.

Diagnostic Evaluation

Assessment of the sternum involves both clinical examination and imaging to identify structural, traumatic, or pathological conditions.

• Clinical Examination: Inspection and palpation to detect tenderness, swelling, deformities, or abnormal movement.
• Radiography: Standard chest X-rays to evaluate fractures, dislocations, or gross structural anomalies.
• Computed Tomography (CT): High-resolution imaging for detailed assessment of bony architecture, fractures, tumors, and complex deformities.
• Magnetic Resonance Imaging (MRI): Evaluation of bone marrow, soft tissue, and sternal infections or neoplasms.
• Bone Scintigraphy: Useful in detecting metabolic activity, osteomyelitis, or metastatic disease.

Management and Treatment

Trauma and Fractures

• Conservative Management: Pain control, rest, and immobilization are usually sufficient for uncomplicated sternal fractures.
• Surgical Repair: Indicated in severe displacement, open fractures, or non-union cases, using fixation plates or wires.

Infections

• Prompt antibiotic therapy tailored to causative organisms.
• Surgical debridement may be required for osteomyelitis or mediastinitis unresponsive to medical therapy.

Congenital Deformities

• Surgical correction for pectus excavatum or carinatum using techniques such as the Nuss or Ravitch procedures.
• Non-surgical management may include physiotherapy and bracing in mild deformities.

Tumors

• Surgical excision and reconstruction for primary sternal tumors or metastases.
• Adjuvant therapy such as radiation or chemotherapy depending on tumor type.

Complications

Complications related to the sternum arise from trauma, surgical interventions, infections, or congenital anomalies and may affect both function and quality of life.

• Respiratory Compromise: Severe sternal fractures or deformities can impair chest wall mechanics and breathing.
• Chronic Pain: Persistent discomfort may occur after fractures, surgery, or sternal joint dysfunction.
• Infection: Osteomyelitis or mediastinitis following trauma or surgery can lead to severe morbidity.
• Non-union or Malunion: Inadequate healing after fractures or surgical correction may cause structural instability or deformity.

Prognosis

The prognosis of sternum-related conditions depends on the underlying pathology, timely intervention, and adequacy of treatment.

• Trauma and Fractures: Most patients recover fully with conservative management; surgical repair generally results in good functional outcomes.
• Congenital Deformities: Surgical correction typically improves cosmetic appearance and cardiopulmonary function, though long-term follow-up may be necessary.
• Infections and Tumors: Prognosis varies depending on severity, promptness of treatment, and presence of systemic disease.
• Long-Term Outcomes: With appropriate care, most individuals maintain normal chest wall function and quality of life.

References

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2. Drake RL, Vogl W, Mitchell AW. Gray’s Atlas of Anatomy. 2nd ed. Philadelphia: Elsevier; 2019.
3. Netter FH. Atlas of Human Anatomy. 8th ed. Philadelphia: Elsevier; 2019.
4. Thompson JF, O’Neill AC. Sternum and Sternocostal Joint Disorders. In: Rockwood and Green’s Fractures in Adults. 9th ed. Philadelphia: Wolters Kluwer; 2020.
5. Ravitch MM. The Correction of Pectus Excavatum and Carinatum. J Thorac Cardiovasc Surg. 1949;18(2):251-265.
6. American Academy of Orthopaedic Surgeons. Sternal Fractures. [Internet]. 2021 [cited 2025 Oct 7]. Available from: https://www.aaos.org/patients
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8. Schwarz JM, et al. Sternal Tumors and Surgical Management. Ann Thorac Surg. 2017;104(1):210-217.