In fall 2012, New York City Ballet associate artistic director Wendy Whelan, then a company principal, was taking morning class when her foot slid out from under her, causing her to pull the very top of what felt like her right hamstring muscle. "It shocked me from the inside out," she notes.

Whelan spent three months nursing her hamstring. But once she got back to performing, her right hip flexor began flaring up. "By the end of Nutcracker season, I could no longer bear standing in fifth position. I could not lift my right leg without severe pain," she says. "I couldn't imagine why or how this was suddenly becoming so debilitating." A sonogram revealed a complex labral tear in Whelan's hip.