Final answer:
The most appropriate next step in the management of this patient is Abdominal and pelvic CT. This will help evaluate for any potential injuries and guide further management.
Step-by-step explanation:
The most appropriate next step in the management of this patient is E. Abdominal and pelvic CT. Given the mechanism of injury and the presence of bilateral ecchymoses and tenderness at the upper thigh, there is concern for possible damage to the internal organs, such as the abdomen and pelvis. An abdominal and pelvic CT scan will help to evaluate for any potential injuries, such as fractures, internal bleeding, or organ damage, and guide further management.