For all the grueling training hours Nicole Chapko has spent in the pool, it was the most mundane of movements that threatened her swimming career.

In June 2011, Chapko was riding a coach bus to a swim meet in Nashville, Tenn., with her St. Charles Swimming Club teammates. She was heading toward the front of the bus to hand one of her coaches a DVD. Chapko isn’t sure what caused her to lose her balance, but she lurched awkwardly, and her kneecap popped out of socket.

“I tell people, and they laugh and say ‘Sorry I’m laughing’ because it seems like such a weird way to dislocate your knee,” Chapko said. “But I guess it happens.”