The term “floating rib” is used to refer to a specific anatomical structure and to a disorder which could better be termed a “slipped rib.” Both, as one might imagine from the name, involve the ribs, curved bones found in vertebrates. The ribs are attached to the spine and a structure called the sternum, creating the rib cage, a protective casing for vital organs such as the heart and lungs.
In the case of an anatomical structure, a floating rib is a rib which is attached to the spine, but not the sternum. Most people have floating ribs, with the 11th and 12th pairs of ribs being floating ribs. In some people, there are three pairs instead of two, and other individuals only develop one set of floating ribs. Floating ribs are entirely normal and nothing to be concerned about, and although they are not attached to the sternum, they aren't exactly floating around in the body cavity; numerous attachments usually keep the floating ribs more or less in place.
The function of the floating ribs is not fully understood. A floating rib could theoretically provide some protection to the contents of the abdominal cavity, but it isn't as necessary as the ribs which are attached to the sternum. The “false ribs,” as they are known, may be vestigial leavings of an earlier stage in human evolution. Evidence suggests that people have also been able to train their floating ribs into new positions, as seen in women who wear corsets for a prolonged period of time.
In some cases, a floating rib can cause problems for its owner. These ribs can slip out of position, putting pressure on internal organs, and they can also be broken as a result of trauma, causing considerable pain and putting the patient at risk for infection.
The disorder sometimes referred to as floating rib syndrome and better known as slipped rib syndrome occurs when a rib becomes dislocated, slipping out of its socket. Patients tend to experience considerable pain with this condition, which is usually a result of trauma, and it can be readily identified with a physical examination or medical imaging study of the area of interest. As with other rib injuries, the best treatment is usually partial immobilization, achieved by wrapping the ribcage tightly so that the rib cannot drift while it heals, but not so tightly that it cannot expand as the patient breathes.