The Thoracic Cage: Sternum

The sternum consists of three fused bones: the manubrium, body, and xiphoid process. The manubrium is the broader superior portion where the first rib pair attaches. The body is the elongated central section articulating with ribs 3–7. The xiphoid process is the inferior cartilaginous tip that gradually ossifies with age after forty.

The sternum connects to the thoracic cage through multiple articulation points. The manubrium attaches to the first two rib pairs at the clavicular notch and sternal angle. The body articulates with costal cartilages of ribs 2–7 along its notched sides. The xiphoid process fuses with the body at the xiphisternal joint, located at the ninth thoracic vertebrae level.

The sternal angle is the slightly bent junction where the manubrium and body meet. The second rib attaches at this landmark. Since the first rib is hidden behind the clavicle, the sternal angle and second rib serve as essential palpable landmarks for identifying and counting the lower ribs during physical examination.

The sternum protects vital thoracic organs including the heart and lungs as part of the thoracic cage structure. It forms the anterior midline of the thoracic wall and connects to muscles including the diaphragm and rectus abdominis. The heart lies directly below the xiphisternal joint, making proper sternum anatomy critical during medical procedures like CPR.

During cardiopulmonary resuscitation, hands are placed mid-sternum to avoid fracturing the xiphoid process. If broken, the xiphoid process can be thrust into the heart or liver, causing severe internal bleeding. Proper hand placement prevents this injury while allowing effective chest compression to circulate blood during cardiac emergencies.

The xiphoid process is primarily cartilaginous early in life, making it flexible and vulnerable to injury. Gradually with age, it undergoes ossification, becoming bone. This process is typically complete after age forty, transforming the xiphoid process from a soft cartilaginous structure into a rigid bony landmark.

The jugular notch is a shallow U-shaped depression at the top of the manubrium, easily felt at the anterior base of the neck between the medial clavicle ends. The clavicular notches are shallow depressions on the manubrium's superior-lateral margins marking the sternoclavicular joints. These landmarks allow clinicians to locate and palpate the sternum accurately during examination.