The sternum, often called the breastbone, is a flat, dagger-shaped bone positioned in the center of the chest. It serves as a central component of the rib cage, connecting to the ribs via cartilage and providing an anterior shield for vital organs like the heart and lungs from external trauma. This bone also offers attachment points for various muscles, contributing to the structural integrity of the chest.
The Manubrium
The manubrium is the broad, superior part of the sternum, resembling a quadrangular or trapezoidal shape. At the vertebral level of T3-T4, this section features a concave depression on its superior aspect known as the jugular notch, or suprasternal notch, which is visible at the base of the neck. Lateral to the jugular notch, the manubrium has clavicular notches that articulate with the medial ends of the clavicles, or collarbones, forming the sternoclavicular joints. The manubrium also articulates with the costal cartilages of the first pair of ribs and a portion of the second pair of ribs, fitting into facets on its lateral borders. The lower border of the manubrium connects with the sternal body.
The Sternal Body
The sternal body, also known as the gladiolus, is the longest and central segment of the sternum. It has a flat, rectangular structure and is situated between the manubrium above and the xiphoid process below. This part of the sternum articulates with the costal cartilages of ribs 2 through 7. The junction where the manubrium and the sternal body meet forms a slight anterior protrusion called the sternal angle, or Angle of Louis. This angle is a significant anatomical landmark because the costal cartilage of the second pair of ribs attaches precisely at this point. Healthcare professionals use the sternal angle to help locate and count ribs, which is particularly useful for identifying intercostal spaces during medical assessments.
The Xiphoid Process
The xiphoid process is the smallest and most inferior part of the sternum. Its shape and size can vary considerably among individuals, sometimes appearing pointed, bifid (forked), or even perforated. Initially, this structure is cartilaginous, particularly in infants and young children. Ossification, the process of turning into bone, typically begins in early childhood and continues into adulthood, often completing by the age of 40, though some individuals may not have a fully ossified xiphoid process until age 60. The xiphoid process serves as an attachment point for several muscles, including the diaphragm, which is essential for breathing, and abdominal muscles like the rectus abdominis. Its position makes it a relevant landmark for procedures like cardiopulmonary resuscitation (CPR), where proper hand placement avoids injury to underlying organs like the liver.