A 19-year-old man is brought to the emergency department. His name is Christopher, and his chief complaint is: “Doc, I can’t walk.” He says that for the past two days, his legs have been hurting very badly, and it’s getting worse. The pain is mostly in his calves. As long as he doesn’t try to move much, it’s okay, but if he stands or stretches out his legs or feet, the pain becomes much worse.