Final answer:
Flail chest occurs when multiple ribs are fractured in several places, leading to independent movement of a section of the thoracic cage, often causing a spontaneous pneumothorax and requiring urgent medical care.
Step-by-step explanation:
The condition associated with a fracture of several ribs causing a section of the chest to move independently from the rest of the chest wall is called flail chest. This occurs when multiple ribs are broken in more than one place, allowing for a segment of the chest wall to move in a paradoxical motion. The rib cage typically includes 12 pairs of ribs attached to the thoracic vertebrae, with the top seven pairs known as true ribs, the next three pairs as false ribs, and the bottom two pairs as floating ribs. The true ribs attach directly to the sternum via costal cartilage, while the false ribs attach indirectly or not at all, and the floating ribs do not attach to the sternum or to another rib, but rather to muscles in the abdominal wall.
During normal respiration, the chest wall moves outward and expands. However, with flail chest, the affected segment moves inward during inhalation and outward during exhalation, creating an inefficient and potentially life-threatening situation. This can lead to a spontaneous pneumothorax, or collapsed lung, and requires immediate medical attention.