From the interview:
It was really just a completely sudden thing. I'd been in New Zealand for almost a week and suddenly I squatted down, and when I got back up, my hip was completely locked up. That is something that has happened to me in the last five years, every two or three months. And on this particular occasion, I wasn't able to stretch it out. It was a matter of "okay, what is the diagnosis?" We went through all of the doctors, and eventually, the top hip specialist in the States, Dr. Marc Philippon, based out of the Steadman Hawkins Clinic in Vail, Colorado - he's also the guy who operated on Alex Rodriguez (of the New York Yankees) - said "yep, you've got labral tear, and you've got an impingement, and let's get you into surgery and get you fixed."