Lindsey Vonn’s attempt to compete in the Milano Cortina Olympics after rupturing her ACL is extraordinary but not impossible, according to U.S. musculoskeletal scientist Douglas Van Citters. He explained that elite athletes can sometimes function without an ACL if surrounding muscles and ligaments are strong enough to stabilize the knee. Vonn, who also suffered bone bruising and meniscal damage, plans to ski with a brace and begin training soon, though the risk of further injury remains.