The sternum, or breastbone, is the flat, dagger-shaped bone running down the center of the chest, protecting the heart and lungs. It is composed of three main parts: the manubrium at the top, the body in the middle, and the xiphoid process at the bottom. The xiphoid process is the smallest and most inferior segment of the sternum, often resembling a small, pointed tip. Its location is a crucial anatomical reference point due to its changing composition and clinical relevance.
Precise Anatomical Placement
The xiphoid process is situated at the end of the breastbone, projecting slightly downward and backward into the upper abdomen. It is located at the midline where the lower rib cage meets, forming the central point of the costal arch. In most adults, the structure measures between one and two inches in length, though its shape can vary, sometimes appearing pointed, rounded, or split.
Anatomically, the tip of the process aligns with the level of the tenth thoracic vertebra (T10) in the spinal column. This specific alignment makes it a reliable internal marker for locating other internal structures. A person can feel for this structure by tracing the center of the breastbone down to where the bone ends and the soft tissue of the abdomen begins. This firm projection marks the boundary between the chest and abdominal cavities.
Structural Composition and Maturation
The composition of the xiphoid process changes dramatically over a person’s lifetime. In infants and children, the process is composed entirely of hyaline cartilage, giving it a soft, flexible texture. This cartilaginous state means it is pliable and not yet a solid, bony structure.
As an individual ages, the process undergoes ossification, the natural process of cartilage turning into bone. This transition begins in late adolescence and progresses through adulthood, gradually hardening the structure. Fusion with the main body of the sternum, known as the xiphisternal joint, usually completes around the age of 40. This process explains why the structure feels firm in older adults.
Functional Role as a Skeletal Anchor
Despite its small size, the xiphoid process provides an anchor point for several muscle groups. It serves as a superior attachment site for the diaphragm, the dome-shaped muscle that drives breathing. The diaphragm’s movement is directly influenced by its connection here, making the process integral to the mechanics of respiration.
The xiphoid process also provides an origin point for the rectus abdominis muscle, commonly known as the “abs.” It helps anchor the aponeuroses, or flat sheet-like tendons, of other abdominal wall muscles. By connecting these large muscles of the trunk, the xiphoid process helps stabilize the rib cage and contributes to core strength and posture.
Clinical Relevance and Potential Pain
The xiphoid process is a significant landmark in emergency medicine, particularly during Cardiopulmonary Resuscitation (CPR). Healthcare providers use its position to identify the correct area on the sternum for chest compressions, which must be applied slightly above the process. Applying force directly to the xiphoid process during CPR is dangerous because its pointed shape makes it susceptible to fracture.
A fractured or forcefully depressed xiphoid process can cause internal injury, potentially lacerating the underlying liver tissue. Pain localized to this area is called Xiphodynia, which results from direct trauma, heavy lifting, or excessive coughing. This pain is sometimes mistaken for symptoms of other conditions, such as acid reflux or heart issues, due to its central chest location.