The science of how Olympian Lindsey Vonn can ski on injured knees

Lindsey Vonn’s knees reveal the toll of elite skiing—and the body’s resilience

By Tanya Lewis edited by Andrea Thompson

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Lindsey Vonn is a physiological marvel. The 41-year-old Olympic gold medalist skier has, quite literally, risen to the top of her sport and stayed there, despite numerous injuries that could have been career-ending.

In 2018 she announced she was retiring the following year, citing concerns about her physical condition as she got older. But in 2024 she returned to competition after a remarkably successful partial knee replacement surgery on her right knee. She was all set to compete in the Milano Cortina Winter Olympics this week when she crashed in a race in Crans-Montana on January 30 and ruptured the anterior cruciate ligament (ACL) on her other knee. Nevertheless, the world class skier says she plans to still compete in the Games.

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“My Olympic dream is not over,” she wrote on Instagram last week.

Downhill skiing is a punishing sport. Elite skiers can reach speeds above 80 miles per hour, and because kinetic energy goes up with the square of the velocity it exerts considerable force on the body. And the knees bear a lot of the brunt. If your weight is centered over your skis and you’re in control, that’s not a problem. But if you end up, say, too far back on your skis, or you land wrong, it creates shearing forces on the knee that can cause injuries.

Vonn has suffered repeated damage to her ligaments over the years, and that can cause the joint to loosen and cause problems. Sam Ward, co-director of the Wu Tsai Human Performance Alliance at the University of California, San Diego, compared this to the wear and tear on a tire. “First of all, it hurts,” he says. “Second of all, as you lose tread on your tire, you can imagine things get a little sloppier as you’re driving around,” says Ward, who is an orthopedic surgeon but has not treated Vonn. If the joint is painful and swells up, it changes the way your brain controls the knee, he says. Vonn couldn’t walk without pain or limping and was unable to straighten her knee, according to the New York Times.

In 2024 Vonn underwent robotic surgery to partially replace her right knee with a titanium one—effectively retreading the tire. The knee consists of three key components: the lower end of the femur (thighbone), the upper end of the tibia (shinbone) and the patella (kneecap), all of which are covered in cartilage. In contrast to a total knee replacement, in which portions of all three bones and cartilage are removed and replaced with artificial ones, a partial knee replacement only replaces one of these parts, leaving the healthy ligaments intact. Using a surgical robot made by MAKO Surgical Corp., Martin Roche, an orthopedic surgeon at the Hospital for Special Surgery in West Palm Beach, Fla., created a scan of her knee, removed the damaged cartilage and bone in a minimally invasive surgery and installed the titanium implant.

The surgery was a success: Vonn was able to straighten her knee again, and after two months, she was wakeboarding on it, the Times reported. She returned to ski competition soon afterward.

Vonn was gearing up for a comeback at the Milano-Cortina Olympics when she tore her ACL last week. She announced that she also had bone bruising and damage to her meniscus‚ a thin, crescent-shaped piece of cartilage in the knee that acts as a shock absorber.

The ACL is a ligament that connects the shin bone to the thigh bone. It provides rotational stability for the knee. ACL tears are one of the most common injuries not just in skiing but in many sports. And they’re more common in female athletes, because women have looser joints and less muscle mass than men and land differently from jumps.

In her latest injury Vonn appears to have absorbed a lot of shock, possibly because of the terrain and her stiff boots, and had what’s known in skiing as a “recovery”—basically, when you get off-balance and have to go into an unusual position, but you don’t fall—as her skis “grabbed,” says Christopher Brown, a former All-American ski racer and ski coach, as well as a professor of mechanical and materials engineering at Worcester Polytechnic Institute. Skis have very sharp edges that are designed to grab on to ice to help change direction. And if the ski turns underneath you, and you have stiff boots that limit motion, you can be applying a shear load to the top of the tibia, or shinbone, creating what’s called a “valgus load”—a force toward the body’s midline—and inward rotation. This is “the most common injury mechanism for the ACL in skiing,” Brown says.

ACL tears sometimes require surgery to reconstruct the ligament, although not always. You can ski with a torn ACL, but the knee has less stability. Vonn has said she plans to ski with a brace at the Olympics.

As impressive as Vonn’s physical ability is, Ward says, a lot of it comes down to mental fortitude. “The mental part of the game is giant here,” he says. Whether Vonn will end up winning a gold medal at this Olympics remains to be seen. “I’m not a betting person,” Ward says, “but if I was a betting person, I would not bet against this person.”

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