Manubrium

The manubrium is the broad, upper portion of the sternum (breastbone) that forms the anterior part of the thoracic cage. It serves as an important structural element for rib and clavicle articulation and acts as a protective shield for underlying thoracic organs. The manubrium also serves as an attachment point for several muscles of the neck and thorax.

Location

The manubrium is located in the midline of the upper anterior thoracic wall, just below the neck. It lies anterior to the upper mediastinum and superior to the body of the sternum. It connects laterally with the clavicles and first pair of ribs and is continuous inferiorly with the sternal body at the manubriosternal joint.

Structure

The manubrium is trapezoid-shaped and measures approximately 4–5 cm in length. It is broader and thicker than the sternal body and consists of compact cortical bone externally and cancellous bone internally.

Key Features

• Jugular (suprasternal) notch: A concave notch on the superior border, visible as a surface landmark at the base of the neck
• Clavicular notches: Articulate with the medial ends of the clavicles at the sternoclavicular joints
• Costal notches: On the lateral borders for articulation with the first ribs and part of the second ribs
• Manubriosternal joint: A symphysis between the manubrium and body of sternum; forms the palpable sternal angle (angle of Louis)

Articulations

• Clavicle: Sternoclavicular joint via clavicular notches
• First rib: Costal cartilage articulates directly with the manubrium
• Second rib: Articulates at the manubriosternal joint (shared with sternal body)
• Sternal body: Forms the manubriosternal joint at the sternal angle

Muscle Attachments

• Sternocleidomastoid: Attaches to the superior margin (medial head)
• Pectoralis major: Attaches to the anterior surface
• Sternohyoid: Attaches to the posterior superior aspect
• Sternothyroid: Also attaches posteriorly near the midline

Function

• Supports clavicular and upper rib articulation
• Forms the anterior wall of the upper thoracic cavity
• Protects major thoracic structures including the trachea, esophagus, and great vessels
• Provides muscle attachment points for head and chest movement

Blood Supply

• Arterial: Internal thoracic artery and anterior intercostal branches
• Venous: Drains into internal thoracic and brachiocephalic veins

Innervation

• Sensory innervation to overlying skin is provided by anterior cutaneous branches of intercostal nerves (T1–T2)

Clinical Relevance

• Sternal angle (Angle of Louis): Anatomical landmark for the second rib and level of bifurcation of the trachea (T4–T5)
• Fractures: Rare but can result from blunt trauma; may injure underlying mediastinal structures
• Sternal puncture: Occasionally used to access bone marrow in hematological procedures
• Palpation: The jugular notch and sternal angle are commonly used as surface landmarks during physical examination