<p>US baby boomers are fueling a wave of joint replacement surgeries, hoping to use new artificial knees and hips to stay active as they get older.</p><p>The 45-64 age group accounted for more than 40 percent of the more than 906,000 total knee or total hip replacement surgeries in 2009, the last year for which figures were available from the American Academy of Orthopedic Surgeons.</p><p>Boomers will account for a majority of these joint replacements in 2011, according to projections by Drexel University specialist Steven Kurtz.</p>