Comprehensive Osteopathic Medical Licensing Examination (COMLEX USA) Practice

Floating ribs lack which type of articulation?

1. Anterior articulation

2. Posterior articulation

3. Both anterior and posterior articulation

4. Articulation with cartilage

The correct answer is: Anterior articulation

Floating ribs are characterized by their unique structural features compared to other ribs in the ribcage. Specifically, they have no anterior articulation, meaning they do not connect to the sternum or cartilage that attaches to the sternum. These ribs are typically the 11th and 12th pairs of ribs and are termed "floating" because they are only attached to the vertebrae at the back. Their posterior articulation with the thoracic vertebrae is intact, which is why they can still be considered part of the ribcage even though they do not extend all the way to the front. This lack of anterior articulation allows for greater flexibility in the lower part of the ribcage, which is favorable for expansion during respiration, but also limits the overall rigidity and protective structure usually offered by the sternum and cartilage connections. In summary, floating ribs lack anterior articulation distinctly, which differentiates them from other ribs that typically articulate both anteriorly with the sternum or costal cartilage and posteriorly with the vertebrae.