Ribs 11 and 12 are the floating ribs. These are also known as vertebral ribs or free ribs. They are called "floating" because, unlike the other ribs, they do not attach to the sternum (breastbone) anteriorly. Instead, they terminate in the posterior abdominal wall musculature.
Understanding Rib Classification
The human rib cage is composed of 12 pairs of ribs, categorized into three types based on their connection to the sternum:
- True Ribs (1-7): These ribs attach directly to the sternum via their own costal cartilage.
- False Ribs (8-10): These ribs indirectly attach to the sternum; their costal cartilages connect to the cartilage of the rib above them.
- Floating Ribs (11-12): These ribs are the only ones that don't attach to the sternum at all. They are free-floating and connected only to the vertebrae in the back.
Function of Floating Ribs
Although not directly connected to the sternum, floating ribs still serve important functions:
- Protection: They offer some protection to organs in the lower thoracic cavity and upper abdomen, such as the kidneys.
- Flexibility: Their lack of anterior attachment provides greater flexibility in the lower rib cage. This is analogous to the difference between a rigid bridge and a flexible diving board.
Clinical Significance
While generally less likely to be broken than other ribs due to their location and flexibility, injuries to the floating ribs can still cause pain and discomfort.
