Sternum

The sternum consists of three parts: the manubrium (upper portion), the body (middle, largest portion), and the xiphoid process (inferior, cartilaginous tip). The junction between the manubrium and body creates the sternal angle (angle of Louis), a palpable landmark at the T4-T5 level that marks the bifurcation of the trachea, the level of the second costal cartilage, and the aortic arch.

The sternum contains red bone marrow throughout adulthood, making it an active site of hematopoiesis—the production of blood cells including red blood cells, white blood cells, and platelets. Because it is accessible through the overlying skin, the sternum is used for bone marrow aspiration and biopsy procedures to diagnose blood disorders such as leukemia, lymphoma, anemia, and multiple myeloma.

Median sternotomy is the surgical procedure of longitudinally splitting the sternum from the sternal notch to the xiphoid process to gain wide exposure of the mediastinal contents. It is the standard approach for open-heart surgery, including coronary artery bypass grafting, valve repair or replacement, and cardiac transplantation. The sternum is subsequently wired together with stainless steel wires for closure and heals over several months.

Sternal fractures are most commonly caused by high-energy direct anterior chest trauma, classically from the steering wheel in motor vehicle collisions without airbag protection. Because the sternum lies directly anterior to the heart and great vessels, sternal fractures raise concern for associated injuries including myocardial contusion (bruising of the heart muscle), aortic injury, and pericardial effusion. An ECG and cardiac monitoring are typically performed after sternal fracture.

The xiphoid process is the small, cartilaginous inferior tip of the sternum that may partially ossify in adulthood. It serves as an attachment point for the rectus abdominis muscle and the diaphragm, and is the landmark for the lower border of the heart. It is important to identify the xiphoid process during cardiopulmonary resuscitation (CPR) to ensure chest compressions are applied to the lower sternum, not to the xiphoid, which could fracture and lacerate abdominal organs.