Final answer:
The signs described are indicative of flail chest, a serious condition resulting from trauma to the rib cage, which leads to paradoxical movement of a segment of the chest wall during respiration.
Step-by-step explanation:
Paradoxical chest wall movement, bony crepitus, rib segment depressed with inhalation and elevated with exhalation are signs of a condition known as flail chest. Flail chest occurs when a segment of the rib cage breaks due to trauma and becomes detached from the rest of the chest wall. This condition leads to paradoxical movements because the detached segment moves in the opposite direction to the rest of the chest wall during breathing. This can cause severe pain and impair breathing. The effective treatment often requires stabilization of the chest wall and may need surgical intervention in severe cases.