A 28-year-old female is the restrained driver in a high-speed, head-on MVC with severe deceleration. She is awake and oriented but complains of chest pain radiating to her back. Vitals: BP 92/54, HR 118, RR 26, SpO₂ 94% on high-flow O₂. Physical exam reveals diminished pulses in the lower extremities compared to the upper extremities. Breath sounds are equal bilaterally, and there are no signs of JVD, tracheal deviation, or muffled heart tones. Which of the following is the MOST likely cause of her presentation?