It began with a loud pop. Though Austin Sell had suffered from severe back pain since childhood, on a clear autumn morning in 2011, not long after his twenty-first birthday, the pain became something much more frightening. He was chasing his younger brother through their mother’s yard in Great Falls, Montana, and his left foot landed in a crevice. His upper body buckled backward; there was a sound like “a bungee cord being snapped in two.” He could tell that it was bad, a kind of bad he had not experienced before. A few hours later, having tried heat…