Science & nature · Evidence-backed
Sternum (Breastbone): Key Facts
Located at the midline of the chest, the sternum—or breastbone—forms the anterior component of the rib cage. Though often overlooked, it plays a crucial role in safeguarding the heart and lungs, facilitating respiration, and providing anchor points for muscles of the upper body. Understanding its structure and associated pathologies is essential for both students of anatomy and clinicians.
The sternum is a central flat bone of the thoracic cage that protects vital organs, articulates with ribs and clavicles, and serves as an attachment site for numerous muscles. This overview covers its anatomy, functions, common conditions and clinical relevance, drawing exclusively from authoritative medical sources.
Definition and anatomical location
The sternum, commonly known as the breastbone, is a long, flat bone situated in the midline of the anterior thoracic wall. It lies superficially beneath the skin and can be palpated easily at the centre of the chest. Anatomically, it forms the front component of the rib cage, extending from the base of the neck down to the upper abdomen. This positioning allows it to shield vital thoracic organs while providing a rigid anchor for adjacent skeletal structures.
Three main parts: manubrium, body and xiphoid process
The sternum is divided into three distinct regions: the manubrium at the superior end, the elongated body (or gladiolus) in the middle, and the small xiphoid process at the inferior tip. The manubrium is quadrangular or trapezoidal and bears the jugular notch; the body is the longest segment and connects to ribs three through seven via costal cartilage; the xiphoid process is initially cartilaginous and gradually ossifies with age.
Articulation with the ribs via costal cartilage
Each side of the sternum receives the anterior ends of the ribs through hyaline cartilage. The first pair of ribs attaches to the manubrium, while ribs two through seven connect to the sternal body; the eighth, ninth and tenth ribs indirectly articulate via the costal cartilages of the ribs above. This cartilaginous linkage creates a flexible yet sturdy framework that permits thoracic expansion during breathing.
Protection of the heart and lungs
By forming the anterior wall of the thoracic cage, the sternum shields the heart, lungs and major blood vessels from direct mechanical trauma. Its flat, rigid structure absorbs and distributes forces that might otherwise compress these vital organs, thereby reducing the risk of contusion or laceration during impacts such as falls or collisions.
Role in completing the rib cage
Together with the twelve pairs of ribs and the thoracic vertebrae, the sternum completes the bony rib cage that encloses the thoracic cavity. This closed cage maintains the negative intrathoracic pressure essential for lung inflation and provides a stable base for the attachment of upper limb muscles and the shoulder girdle.
Sternoclavicular joint and shoulder girdle stability
The superior lateral borders of the manubrium articulate with the clavicles to form the sternoclavicular joints, the only bony connections between the axial skeleton and the upper limbs. These plane synovial joints allow elevation, depression, protraction and retraction of the shoulders, contributing to a wide range of arm movements while transmitting forces from the arms to the trunk.
Muscle attachments on the sternum
Numerous muscles of the chest, neck and upper abdomen originate or insert on the sternum. The pectoralis major and sternocleidomastoid attach to the manubrium, while the rectus abdominis and transversus thoracis insert on the body and xiphoid process. These attachments enable movements such as arm flexion, head rotation and abdominal tension, integrating the sternum into both respiratory and postural mechanics.
Contribution to respiratory mechanics
During inhalation, the sternum moves slightly upward and outward as the ribs elevate, increasing the anteroposterior diameter of the thoracic cavity. Conversely, during exhalation it descends, helping to decrease thoracic volume. This subtle motion, facilitated by the costal cartilages, works in concert with the diaphragm to drive pulmonary ventilation.
Causes and types of sternal fractures
Sternal fractures most commonly result from blunt force trauma to the anterior chest, such as that sustained in motor‑vehicle collisions, high‑impact sports injuries or falls from height. The fracture may be direct, where the impact site corresponds to the break, or indirect, where force transmitted through the sternum produces a fracture closer to the front or back of the bone.
Costochondritis: inflammation of rib‑sternum cartilage
Costochondritis is an inflammatory condition affecting the cartilage that joins the ribs to the sternum, most often involving the second to fifth costal joints. It presents with localized sharp pain and tenderness that can worsen with movement, deep breathing or pressure on the affected area. Although the exact trigger is frequently unknown, infection, repetitive strain or arthritis may precipitate the inflammation.
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