Skiing and Your ACL

The down-low on the knee-ligament injury that’s all-too-common among skiers.
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Lindsey Vonn, Knee Strengthening Exercises

Lindsey Vonn, strengthening her legs muscles to protect her knee from the forces of downhill skiing. 

I should have known better. It had been warm overnight, the snow hadn’t frozen all the way through, the untracked piste—though groomed to delectable corduroy—was soft. Too soft for high performance carving. But I was giddy at the prospect of being able to lay deep trenches on skis actually designed to carve (I don’t get out on true carvers much these days). 

So even though it was the first run of the day—and conventional wisdom told me I should take it easy, make a few low-key turns to test out these unfamiliar skis and the snow conditions—I went for it. I unloaded the chair, made exactly three deep, exhilarating carving turns, and then I exploded.

The next sequence of events occurred in the blink of an eye and in slow motion: I’m rocketing down the slope on my left side, skis still attached, not slowing down until my left ski edge hooks up on the snow, left knee twists, "pop", and finally I begin to slow. 

You see, this isn’t my first rodeo. I’ve torn my ACL twice before (on my left and right knee)—both times while skiing. As a result, I’ve learned to recognize the tell-tale signs of the season-ending injury, and when I get up from my fall, I go through the checklist: Did I hear an audible pop in the knee during the crash? Check. A brief but acute moment of pain behind the affected knee? Check. Instability and weakness in the knee after standing and putting weight on that leg? Check. Numbness and the early signs of swelling around the knee? Unfortunately, yes.

Sure enough, my ski season ended on March 19, when an orthopedic doc confirmed that I had torn my left ACL, again. The news that I was now facing ACL-reconstruction surgery number three  was a blow, followed by moments of devastation and whines of “Why me?” Eventually—after more time than I would like to admit here—I left my own private pity party, came to my senses, and realized that it wasn’t just me. In fact, I was joining a VIP list of skiers sidelined by a similar injury in the final months of this season alone:

March 6: Caroline Gleich, professional ski mountaineer and Instagram influencer extraordinaire, announced that she had torn her ACL during a skiing crash, just six weeks before she was scheduled to climb Mount Everest for the first time. (But she’s not letting a little old ACL tear get in the way of those plans—she’s climbing Everest without it. Follow her epic ACL-less journey here.)

March 18: Pro skier John Collinson announced that he tore his ACL while filming with TGR in Canada. This is his second ACL tear. 

April 2: Lindsey Vonn, queen of knee injuries, undergoes yet another knee surgery to repair a torn LCL (lateral collateral ligament) and meniscus—injuries sustained in her October training crash at Copper Mountain that worsened over the course of her racing season.

April 20: Angel Collinson, John Collinson’s sister and fellow pro big mountain skier, announced in good humor that she had also torn her ACL, MCL, and meniscus after tomahawking down a line in Alaska. This is also her second ACL tear. 

Bottom line: Knee-ligament injuries—and torn ACLs in particular—are a common occupational hazard of skiing. According to the Steadman Clinic, a world-renowned orthopedic surgery and research center in Vail, Colo., ACL tears are one of the most common knee injuries, with approximately 200,000 cases diagnosed annually in the U.S. alone. It seems—at least to me, given my bad luck—an unfair share of those are sustained while skiing. What is it about our sport that taxes our ACL so heavily?

To answer that and related questions, I turned to my knee doc—Dr. Matthew Provencher, shoulder, knee and sports surgery specialist at the Steadman Clinic and former Chief of Sports Medicine Service at Massachusetts General Hospital.

What is the ACL, and what is its role in skiing?

ACL Tear

Left: The anatomy of a healthy knee and anterior cruciate ligament (ACL). Right: Anatomy of a torn ACL. 

"The anterior cruciate ligament (ACL) is one of the primary ligaments and stabilizers of the knee and is one of the four major ligaments that keeps your knee stable," explains Dr. Provencher. "The others are the PCL (posterior cruciate), MCL (medial cruciate), and LCL (Lateral cruciate) ligaments. The ACL helps stabilize the knee and prevents the tibia (shin bone) from slipping forward, but also helps prevent excessive rotation of the knee when fully extended. In skiing, the ACL stabilizes the knee through each turn and allows the knee to deal with varied and uneven terrain, from chopped up snow to powder."

What are the symptoms of an ACL tear?

"An ACL tear of the knee is usually an acute event that is often caused by a twisting, non-contact hyperextension injury—the knee is fully straight and sustains a twisting rotational force,” says Dr. Provencher. “Often, one experiences a ‘pop’ or event in the knee that produces immediate pain and then swelling. You can also feel that that knee just doesn’t feel ‘right’ after the event, and then progressive swelling sets in. The swelling can continue to increase for 36-48 hours and can cause loss of motion, pain, and discomfort. If the knee injury happens on the hill, it is often hard to ski down and complete the run due to the pain, swelling, and resulting instability in the knee caused by the ACL tear.”

Why are ACL injuries so common in skiing?

"Although they are still not very common as an overall injury relative to the number of skiers that participate in the sport—and considering the overall number of skier-days—they are more common than we would like," says Dr. Provencher.

"Your skis present an issue in that they act as a large lever (think about the physics involved in the playground see-saw) that provides torque on the knee joint—especially in rotation and extension," he explains. "If the lever (the ski), which is rigidly affixed to your foot and ankle, twists too aggressively without quadriceps and hamstring activation, the ACL is left to take a huge load across the ligament, and may tear due to the large forces placed on it. Your skis essentially increase the force behind that lever arm that externally rotates the knee to extremes it shouldn't be, especially if your quads and hamstrings aren't engaged properly. This is why we see an increase in injuries at the end of the day (think tired and fatigued quads and hamstrings), as the muscles are unable to counter this torque through the skis. So, there is validity and importance to a pre-season ACL injury prevention program that focuses on strengthening and conditioning your muscles around the knee."

Learn more: Ski Injury Prevention Exercises 

What should a skier do after sustaining a suspected knee injury on the hill?

“If this happens to your knee—you usually know that something is just not right,” says Dr. Provencher. “It’s important to make sure that the rest of you is OK, as we often see knee injuries in higher speed crashes that occur with other injuries, such as concussions, injuries to the tibia, etc. The best advice is to see how the knee feels after the event, and when in doubt, call for help. The ski patrol at resorts are extremely adept at dealing with on-hill knee injuries and it’ better to be safe and call ski patrol, who can then provide on-hill evaluation and assistance.”

Can you live without an ACL?

“Although the ACL is a very important ligament in the knee, not everyone needs an ACL,” explains Dr. Provencher. “The ACL is important for sports that require pivoting and cutting motions, and for activities in unstable environments—think hiking, skiing in powder and crud, activities on uneven terrain. However, linear sports—meaning straight-in-line activities like running, biking, rowing—don’t usually stress the ACL, so people who primarily engage in those activities may not need to have a functioning ACL. After an ACL injury, some people may opt out of reconstruction surgery and decide to change their activities and/or stick to linear sports. However, most skiers and snowboarders need an ACL to get back on the hill and perform.”

Read more: Breaking the shackles of a knee injury

Originally published as a SKImag.com original in April, 2019. For more great ski content delivered directly to your inbox, sign up for SKI's weekly e-newsletter.

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