Correct answer:

In the context of rib fractures a bony spicule may penetrate the lung, which results in air escaping into the pleural cavity to cause a pneumothorax. A tension pneumothorax results if the pleural tear is valvular, allowing air to be sucked into the pleural cavity at each inspiration but preventing air returning to the bronchi on expiration. A tension pneumothorax produces rapidly increasing dyspnoea; the trachea and the apex beat are displaced away from the side of the pneumothorax and, on the left side, cardiac dullness may be absent. The chest on the affected side gives a tympanitic percussion note with bulging of the intercostal spaces.