Preventing Anterior Cruciate Ligament Injuries in Alpine Skiing

After three days of continuous snow, the clouds finally parted and the resort glistened under acres of sparkling snow. For the first time in your lives, you and your friends were going to get to experience the thrill of deep powder on your winter vacation.
The group hooted and hollered as you glided your way down the untracked slopes. And then suddenly, it happened. Your wife took what appeared to be a simple fall. But she wasn't getting up. Complaining of excruciating knee pain, the ski patrol guessed that she injured her anterior cruciate ligament, or ACL. In an instant, your vacation was ruined.
Few of us like to dwell on getting injured when we head out for a day of skiing. That would be a bit morbid. However, with the declining states of fitness in adults and recent evolutions in ski equipment, you may be at more risk for injury than you'd care to admit.
It's estimated that there are more than 525,000 ski injuries per year. As many as 85,000 to 100,000 of these incidents represent injuries to the ACL. Since one third of all ACL patients require surgery at a national average of $17,000 per reconstruction, the estimated annual cost is more than $1.5 billion¹. And that doesn't include the costs of the initial evaluation, non-surgical care or future medical treatment for those who develop post-traumatic arthritis. But it's not all bad news. Fortunately, there are ways that you can significantly reduce your potential for serious knee injury.
Modern ski binding mechanisms have helped to protect the lower leg against injury. But it is not necessarily a result of improved release capabilities. One study showed that 95% of all the bindings tested had at least one fault and 50% of the bindings had release levels that were more than 20% above the recommended standards for the individual². One somewhat discouraging factor is the widely held belief that binding settings are made based on the ability of the mechanism to resist fracture to the tibia, not injury to the knee³.
The most effective methods for reducing equipment related, lower extremity injuries are good ski instruction that helps the beginning skier move out of the beginner ranks as quickly as possible, appropriately adjusted bindings and frequent self-testing of binding mechanisms⁴.
Most people that injure their ACL complain of one or more of the following: an audible "popping" sound, they feel their knee "give way," experience so much pain that they must stop activity or they sustain swelling within a few hours of injury⁵.
There are a number of causes of injury to the ACL; some predictable, some not. They include anatomical problems of the knee joint, neuromuscular elements, hormonal changes and poor skiing technique.
Anatomical Considerations of the Knee Joint
While relatively rare, some skiers suffer from an impingement, or "pinching" of the ACL against the notch at the end of the bones of the leg; either the tibia or femur⁶. Instead of having a smooth, U-shaped notch, a small percentage of skiers have a narrow, A-shaped notch, which is responsible for the shearing forces of the ACL against bone.
Neuromuscular Elements
The balance between the quadriceps (front of thigh) and hamstring (back of thigh) power and function is crucial to knee stability. "The typical quadriceps/hamstring strength ratio is somewhere around 60/40, whether you're a recreational skier or a world-class athlete," says Michael Torry, Ph.D., Director of Biomechanics at the Steadman-Hawkins Sports Medicine Foundation in Vail, Colorado. "Interestingly, as athletes become stronger through training, the ratio remains the same, but the power and endurance of the muscle groups increase." Other investigators have reported that strong quadriceps contraction between 10° to 30°of knee flexion significantly increases ACL strain while hamstring contraction helps to shield against it⁷.
Women and ACL Injury Rates
According to Carl F. Ettlinger, MS, Director of Vermont Safety Research in Underhill Center, Vermont, "Given equal skill levels, women are 2.5 times more likely to injure their ACL's, whereas men are more likely to sustain fractures and other blunt-impact injuries."
Research has found that female athletes rely more on their quadriceps muscles and take significantly longer to generate maximum hamstring muscle force than their male counterparts. Other studies have shown that women have more knee and muscle laxity than their male counterparts⁸. Therefore, in female athletes with above average hamstring flexibility, the protective ability of this muscle group may be diminished and the forces required to stabilize the knee are transferred directly to the ligaments. Though these elements may not be the primary cause of ACL injury in women, they may predispose female athletes to ACL disruption⁹.
Hormonal Changes in Women
As stated earlier, non-contact anterior cruciate ligament injuries are believed to be two to six times more common in women than in men, particularly in basketball, alpine skiing, volleyball and apparatus gymnastics¹⁰. One hypothesis is that any rise in the hormone estrogen, which can relax soft tissue, may predispose female athletes to ACL tears. Estrogen, a hormone with receptors in the human ACL, reduces the tensile strength of the ACL during mid-cycle of the menstrual period. In addition, estrogen has been reported to decrease fine motor skills by acting on the central and peripheral nervous systems¹¹.
Poor Skiing Technique
Poor skiing technique refers to any lapse in balance or alignment that predisposes a joint to injury. This includes "bad luck." According to Ettlinger, ACL injuries on the ski slope often result not from falling but from an attempt to recover from a loss of balance. "People get off balance, they get injured, then they fall," says Ettlinger¹²." As opposed to running, jumping or soccer, most ACL injuries in alpine skiing result from internal rotation of the tibia with the knee flexed beyond 90 degrees, a position that results when a skier, falling backward, catches the inside edge of the tail of the downhill ski. Ettlinger states that there are two major types of falls that contribute to ACL injuries.
Common Types of Falls
There are a number of mechanisms of injury, or types of falls that can result in ACL ruptures. The two types that are best documented are the boot-induced landing and the phantom-foot phenomenon¹.
The BOOT-INDUCED LANDING is probably the easiest injury to avoid. It typically occurs when the skier begins a jump off balance with their weight to the rear. When the skier lands, the tail of the uphill ski hits first. As the center of pressure against the bottom of the ski moves forward, the pressure of the boot against the back of the leg increases. At the same time, the muscles of the skier's leg automatically contract to hold the leg in a fully extended position. By the time the portion of the ski under the boot heel hits the snow, there is no laxity left in the skier's legs to absorb the jarring impact and the back of the boot drives the tibia out from under the femur, tearing the ACL.
The PHANTOM FOOT SYNDROME is the most common type of fall leading to ACL injury. It is called the Phantom Foot Syndrome because the tail of the downhill ski acts like a lever that points in a direction opposite that of the human foot.
In the phantom foot syndrome, the skier falls backward between the skis, catching the inside edge of the downhill ski, driving the leg into forced internal rotation. There are three types of situations that can lead to the Phantom Foot Syndrome:
1) Attempting to get up while still moving after a fall.
2) Attempting a recovery from an off-balance position.
3) Attempting to sit down after losing control.
Prevention of ACL Injuries
Now that you've heard the bad news, its time for the good. There are a number of steps that you can take to help minimize your risk for injuring your ACL. These include proper conditioning, better skiing mechanics and reducing unsubstantiated risk-taking behavior.
One popular myth is that pre-season conditioning will make you immune to injury. "Preseason conditioning programs don't reduce knee injuries in alpine skiing," says Robert Johnson, MD, an orthopedic surgeon at the University of Vermont who has published several studies on ski injuries. "Many claims have been made but none have ever been proven. World-class skiers have the highest ACL injury rates and they're the best trained and the strongest."
Pre-season conditioning will, however, help balance the quadriceps/hamstrings strength ratio, and strengthen small muscles groups, resulting in more stability of the knee. "While it's impossible to completely prevent injuries to the ACL, there are a number of sound conditioning exercises that you can use to help minimize your risk for getting hurt," says Steve Stalzer, Director of Therapy at the Howard Head Sports Medicine Center in Vail, Colorado. The Howard Head Center is the physical therapy group for Vail Valley Medical Center and is a provider for the U.S. Ski team. "Skiers should focus on "closed-chain" exercises. Closed-chain exercises involve both ends of the joints being connected to immovable objects. For instance, a squat or leg press anchors the foot when standing on the ground, while the femur is anchored at the hip joint. Closed-chain exercises increase joint compressive forces and cause more hamstring contraction when compared to open-chain exercises. The effect is increased knee stability and decreased ACL strain." An example of an "open-chain" exercise is the seated knee extension. For more information regarding pre-season conditioning programs, please check with a licensed physical therapist or your local fitness facility.
Minimizing Phantom Foot Syndrome Injuries
The most effective way to reverse the trend is to immediately employ the following maneuvers:
1) Push your arms forward.
2) Move your feet together.
3) Keep your hands over your skis.
In Summary… No one wants to think about getting injured. But skiing, by nature, carries a number of inherent risks; risks that can be minimized through proper preseason conditioning and practicing the described response strategies.
"Some of the most valuable instruction that skiers can receive, is how to correctly fall," says Dr. Torry. "It's important for skiers at all levels to acknowledge that occasionally, they're going to go down. There's nothing wrong with that."

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