The xiphoid process is a small triangular protrusion in the skeleton of most vertebrates that extends down from the sternum in the center of the ribcage. In babies and young children it is typically made of flexible cartilage, but typically calcifies into bone by early adulthood. Almost all animals have this anatomical feature, which is sometimes also known as the xiphisternum, the ensiform process, the ensiform cartilage, or the xiphoid cartilage. Its primary job is to help join the sternum and the ribcage, and its early flexibility can help protect growing organs, too.
Even though this bone starts out made of flexible cartilage, it is usually considered an “immobile joint,” which means that it can’t move or bend with the body. Its flexibility is important where growth and development are concerned, though. The process is the both the lowest bone on the sternum and the smallest, and it helps the body anchor the diaphragm, the transverse thoracic, and the rectus abdominis. In humans it is located at the level of the 9th thoracic vertebra and the T6 dermatome. Many medical experts believe that the softer beginnings of this bone allow the ribcage and sternum the ability to grow, expand, and adjust without putting too much tension on each other.
Appearance at Birth
Some parents are alarmed to actually see this triangular piece protruding from the skin of their newborn babies and small infants, but in most cases this is completely normal. At birth the process often sits slightly above the base of the sternum, but usually descends into position within a few months. Even still, its triangular tip can sometimes be felt by pressing around the skin of the lower ribcage, particularly in slender children.
Sometime between late childhood and early adulthood — typically between the ages of 15 and 29 — the cartilage turns to bone in humans. This process is known as “ossification.” It usually happens slowly over months or years, but by the end the xiphoid process is typically completely fused to the sternum and is indistinguishable in terms of bone density and formation.
This bone is normally triangular in shape, which is partly where it gets its name: “xiphoid” comes from the Greek word xiphos, which means “straight sword or blade.” The cartilage edges are frequently likened to blades extending out of the sternum. Some people have processes that are slightly different shapes, however, and in most cases these are considered perfectly normal, too. Bifurcation, where the main body has been split into two separate parts, is relatively common, for instance; perforation, where there is a hole or slit in the surface, also happens. Most of the time these variations are due to genetics and heredity, and there isn’t usually any sort of health risk.
In Other Vertebrates
Most animals with ribcages have a xiphoid process, though the shape and precise function can vary from species to species. It’s usually the case that the bone starts as cartilage and hardens with age, as it does in people, but not always. The primary function and location is usually consistent, though.
When giving any type of cardio-pulmonary resuscitation (CPR), care should be taken to avoid pressure on the xiphoid process due to possible damage and even breakage. If this bone breaks, it can sometimes actually dislodge from the sternum and be pushed into the diaphragm or even up into the heart muscle. Even if it doesn’t go anywhere, a loose shard of bone floating in the body can lead to trouble later on. As a result, breakages are usually considered very serious and often require immediate surgery to repair.
The xiphoid region can also sustain damage in any type of collision or impact, and can sometimes even be dislodged or cracked by broken ribs. A breakage or injury can take months to heal and may result in a bony lump. Most experts recommend that anyone who has suffered a chest injury or who feels pressure in their ribs or lungs after an accident get checked out by an expert to rule out any serious consequences.