Learning Objective: By the end of this lesson, the learner should be able to describe the anatomy, parts, articulations, and clinical relevance of the sternum, and identify its landmarks on imaging and surface anatomy.
The sternum (breastbone) is a flat, elongated bone located in the anterior midline of the thorax.
It forms part of the bony thoracic cage, helping to protect vital organs such as the heart, lungs, and oesophagus.
The sternum also serves as an important attachment site for several muscles and articulates with the ribs and clavicles.
Parts of the Sternum
- Manubrium
- Body
- Xiphoid Process
In children, these parts are joined by cartilage, which ossifies with age to form a single bone in adults.
Manubrium
- The most superior portion, trapezoid in shape.
- The jugular notch is a visible depression at the superior border.
- Clavicular notches on either side articulate with the medial ends of the clavicles to form the sternoclavicular joints.
- Lateral edges articulate with the first costal cartilage and part of the second costal cartilage.
- Inferiorly joins the body at the sternal angle (Angle of Louis), a palpable landmark corresponding to the second costal cartilage.
Body
- The longest and largest portion.
- Articulates with the manubrium (manubriosternal joint) and xiphoid process (xiphisternal joint).
- Lateral margins show articular facets for the costal cartilages of ribs 3–6, and demifacets for ribs 2 and 7.
Xiphoid Process
- The smallest and most inferior part.
- Cartilaginous in youth and ossifies by age 40.
- Located at the level of the T10 vertebra.
- May articulate with the 7th costal cartilage.
- Serves as an attachment for the diaphragm and rectus abdominis.
Articulations
- Sternoclavicular joints – with the clavicles.
- Costal cartilages – of ribs 1–7.
- Manubriosternal and xiphisternal joints – between sternum parts.
Clinical Relevance
Sternal Fractures often occur after blunt chest trauma, such as car accidents.
- Most common site: manubriosternal joint.
- Usually comminuted (broken into several pieces).
- Rarely displaced due to pectoralis muscle attachments.
- It may be associated with cardiac or pulmonary injury.
- Diagnosis: X-ray, CT, or ultrasound.
- Mortality is due to associated visceral injury (25–45%), not the fracture itself.
