A false rib is one of the five lower pairs that do not connect directly to the sternum. There are 12 pairs of ribs which are attached to the vertebrae of the spine. Of these, seven attach to the breast bone, or sternum, in the front of the body by cartilage called costal cartilage. These are known as true ribs. The eighth, ninth and tenth pairs connect to the cartilage of the seventh pair and are called the vertebro-chondral ribs. The remaining two pairs, which are the lowest, have no cartilaginous attachment to the sternum. They have no anchor at all in the front of the body and are referred to as floating, vertebral or fluctuating ribs.
The twelve pairs of ribs constitute the ribcage which protects the internal organs and supports the upper body. Ribs are curved flat bones with ligaments and muscles between them. These support the ribcage and allow the expansion and contraction necessary for breathing. The floating ribs give additional protection to the stomach, spleen and kidneys as well as give structure to the thorax.
This type of rib, especially if it is floating, is relatively small and more delicate than true ribs and it has a cartilaginous tip. Some people have more or fewer false ribs than others and in some population groups such as the Japanese, the tenth rib can be a floating rib as it lacks the cartilaginous connection the to the seventh rib. The use of a corset can modify the position of the floating ribs in a form of body modification. In Victorian times when tight corsets were worn by the more fashionable ladies, a false rib could turn inward, overlap the sternum and fracture. This in turn affected the lungs which could atrophy and collapse, with a danger of puncturing the lung.
A false rib can be susceptible to conditions such as fracture, osteomyelitis and infection. They are vulnerable to breakages and many heal by themselves with no further problem but others can heal badly and cause chronic pain and even disability. Despite the false rib having more elasticity than the other bones in the body, sometimes even a violent cough is enough to cause rib trauma. It can take up to eight weeks for a fracture to heal with the muscle underneath the ribcage usually providing enough support for the rib to heal well.
Flemish anatomist Vesalius was the first to note there were 12 pairs of ribs in both sexes in 1543. The finding caused a lot of controversy as, until then, it was assumed that men would have one less rib than women because of the belief that Adam had to give one of his to form Eve. There are people who have one pair of ribs more or fewer than others but this does not depend on gender.