Earlier this year, a Syrian American orthopedic surgeon was shopping with his two toddlers at a Walmart in Grand Rapids, Michigan, when he heard the familiar ping of a notification from WhatsApp, the encrypted messaging service: A teenager had been shot in the leg and the bullet had passed straight through his tibia. The fractured bone punctured his skin like a spear. Although it was the surgeon’s day off, he took the call—as an expert in complex bone operations, this was his specialty.

But this was no ordinary case. His patient was over 6,000 miles away, awaiting care in a makeshift medical clinic in Madaya, a town in Syria some 28 miles from Damascus. The clinic is only a 45-minute drive from Damascus Hospital, but it might as well be on the other side of the world. Madaya, a rebel-held town controlled by the Islamist group Ahrar al-Sham, has been held under siege by Hezbollah, which is fighting on behalf of the Syrian government, since last July. Hezbollah won’t let anything in or out of the town; it was a Hezbollah fighter, locals say, who shot the teenager in the leg.