Five years ago, Lindsey Vonn retired from ski racing, largely because her aching right knee, damaged by high speed crashes and multiple surgeries, could no longer take the stress of the sport.

My career ended with no intention of coming back,” Vonn, the winner of three Winter Olympic medals and 82 World Cup races, said in an interview last week. But seven months ago, Vonn had right-knee replacement surgery. Ten weeks later, she resumed skiing and was startled to be pain-free. Read More