Kyle O'Flaherty used to be stoked by his weekly workout routine, a heavy rotation of cycling, boxing, jiu-jitsu, and running. But even at age 20, his hips started to ache, and not just during exercise. He's not unusual. "I've seen a tremendous spike in young, active men with hip pain in my practice in the past five to 10 years," says orthopedic surgeon Benjamin Domb, M.D. In fact, more 45- to 54-year-olds are opting for hip replacement, according to a National Hospital Discharge Survey. Follow our guide to stay out of the OR and keep your hips pain-free.