A Program To Help Reduce The Risk Of Serious Knee Injuries Among Alpine Skiers.
The development of this pamphlet and the companion DVD, A Guide To KNEE- FRIENDLY Skiing, was made possible through generous contributions from the National Ski Areas Association and the major equipment suppliers.
The information that follows is based in part on a forty-five year study conducted by: Dr. Robert Johnson – University of Vermont, Department of Orthopedics; Dr. Jasper Shealy – Rochester Institute of Technology, and Carl Ettlinger – Vermont Safety Research. However, the opinions and recommendations expressed are solely those of Vermont Safety Research.
WARNING: No claim is made that adherence to the principles set forth in this pamphlet will prevent injury. This pamphlet does not cover all the ways in which skiers can be injured, nor does it cover how to fall, when to fall, or how to stop after a fall.
Knee injuries are a fact of life in any sport, but over the past 30-35 years serious knee sprains, usually involving the anterior cruciate ligament (ACL), have become an inherent risk of modern Alpine skiing, with more than 20,000 sustained each year by skiers in the U. S. alone. The ACL, located near the center of the knee, helps to maintain proper alignment of the load-bearing surfaces. Injury to the ACL can result in an unstable knee, which may lead to expensive surgery or a lengthy period of rehabilitation if the injured skier is to resume an active lifestyle.
One bright spot in this picture is a video-based training program developed to help reduce the risk of certain types of knee injury among ski area employees. Ski areas using this program have cut ACL sprains among instructors and patrollers by more than half. This success has led to the development of programs for the skiing public.
Events leading up to ACL injury are subtle, giving the skier little or no warning of impending injury. ACL Awareness programs provide three independent strategies for dealing with this lack of warning:
- Avoid altogether high risk behavior
- Routinely correct poor skiing technique
- Recognize and respond quickly and effectively to potentially dangerous situations
Although there are many ways in which knee injuries can occur in skiing, this pamphlet concentrates on the two most common scenarios, the Phantom Foot and the Boot Induced.
THE PHANTOM FOOT ACL
One common ACL injury scenario has been termed the Phantom Foot because it involves the tail of the ski, a lever which points in a direction opposite that of the human foot. Phantom Foot injuries can occur when the tail of the downhill ski, in combination with the stiff back of the ski boot, acts as a lever to apply a unique combination of twisting and bending loads to the knee.
RECOGNIZING POTENTIALLY DANGEROUS SITUATIONS
Three types of situations can lead to the Phantom Foot syndrome:
- Attempting to get up while still moving after a fall.
- Attempting a recovery from an off-balance position.
- Attempting to sit down after losing control.
To help reduce the risk of Phantom Foot injury, skiers must first learn to recognize potentially dangerous situations while there is still time to respond.The list that follows represents a profile of the Phantom Foot ACL.
Six elements define the profile:
- Uphill arm back.
- Skier off-balance to the rear.
- Hips below the knees.
- Uphill ski unweighted.
- Weight on the inside edge of downhill ski tail.
- Upper body generally facing downhill ski.
Although these elements may fall into place in almost any order during a sudden loss of balance or control, the order shown here is characteristic of the chain of events which can often put the average skier at risk.
Result:
When all six elements of the Phantom Foot profile are present, at the same time, injury to the downhill leg is imminent.
If the risk of Phantom Foot injury is to be reduced, skiers must respond quickly and effectively to eliminate one or more elements of the profile.
RESPONDING TO POTENTIALLY DANGEROUS SITUATIONS
When elements of the Phantom Foot begin to fall into place, the ideal initial response is one that addresses as many elements as practical without limiting the skier’s ability to take other appropriate measures, including any actions necessary to avoid collision with obstacles or other skiers.
The following actions are a good example of an appropriate initial response:
- Arms forward.
- Feet together
- Hands over skis.
Phantom Foot injuries occur when the tail of the downhill ski, in combination with the stiff back of the Alpine boot, apply a combination of twisting and bending loads to the knee.
The plan above was developed to:
- Reposition the downhill thigh in line with the downhill ski in order to reduce twisting loads on the knee
- Reposition the uphill ski so that it is available for weight transfer
- Put the skier in a good position for either a recovery or a controlled fall (bail-out)
However, this plan is only one example of the type of response that may help reduce the risk of injury. With time you can develop your own plan and with practice your response can be quick and effective.
CORRECTING POOR TECHNIQUE
It may also be possible to help reduce the risk of serious knee sprains by paying closer attention to skiing technique. Several elements of the Phantom Foot profile can be considered bad habits. Uphill arm back, off-balance to the rear, and hips below the knees, are not part of normal skiing technique.
If the following corrective actions are routinely taken whenever any one of these errors in technique is encountered, it could help prevent the chain of events leading to ACL injury from ever getting started:
- Maintain balance and control.
- Keep hips above knees.
- Keep arms forward.
However, when several elements of the Phantom Foot syndrome fall into place rapidly a practiced response, such as 1) arms forward, 2) skis together, 3) hands over skis, must be implemented quickly.
AVOIDING HIGH RISK BEHAVIOR
Many injuries might be prevented by learning a few simple rules and avoiding altogether certain types of high risk behavior.
Don’t (fully) straighten your legs when you fall. If your ultimate intent is to bail out by means of a controlled fall, knees should remain flexed until you have stopped sliding. Although you should routinely correct your stance whenever your hips fall below your knees, attempting to straighten your legs as part of an initial response to the full-blown threat of an ACL injury puts the already vulnerable downhill knee at even greater risk. Return to a normal skiing stance only as part of a maneuver to recover balance and control after you have addressed other elements of the profile.
Don’t try to get up until you’ve stopped sliding. Unless you are trying to avoid an obstacle or another skier, when you’re down–stay down.
Don’t land on your hand. Keep your arms up and forward in any kind of fall. Pushing off or breaking your fall with your uphill arm greatly increases the chance of injury. Whether you’re trying to get up or sit down, if your skis are still moving, you’re at risk.
THE BOOT INDUCED ACL
The knee injury scenario that is probably the simplest to avoid altogether has been termed the Boot Induced ACL. The injury is sustained during hard landings by off-balance skiers. Typically, the skier begins a jump off-balance to the rear, and rotates the downhill arm up and rearward in an attempt to regain balance before landing. This motion is instinctively coordinated with the extension of the skier’s uphill leg.
When the skier lands, the tail of the uphill ski hits first. As the center of pressure of the snow against the bottom of the ski moves forward, the pressure of the boot against the back of the leg increases, while 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 system to absorb the jarring impact and the back of the boot is able to drive the tibia out from under the femur, thereby tearing the ACL. To avoid this type of injury, skiers should avoid any type of aerial maneuver which could leave them off-balance on landing.
Don’t jump unless you know where and how to land. Land on both skis, if possible, and keep your knees flexed.
Avoiding high risk behavior, routinely correcting technique, and recognizing and responding effectively to potentially dangerous situations are as important to injury reduction in Alpine skiing as having your bindings checked, keeping your equipment in good shape, and following Your Responsibility Code.
Although the message conveyed by this pamphlet may be simple, developing a true appreciation of its meaning can be more difficult. The greatest benefit of this program is derived from a clear mental image and an inner awareness of the events leading up to the most common types of ACL injury. Careful viewing of the companion video, A GUIDE TO KNEE-FRIENDLY SKIING, can be a valuable part of the overall learning process (see below for more information).—CFE
For more information on what you need to know… From renting gear to sliding on snow: gearingtogo.com
REMEMBER
Avoid High Risk Behavior:
- Don’t fully straighten your legs when you fall. Keep your knees flexed.
- Don’t try to get up until you’ve stopped sliding. When you’re down–stay down.
- Don’t land on your hand. Keep your arms up and forward.
- Don’t jump unless you know where and how to land. Land on both skis and keep your knees flexed.
Routinely Correct Skiing Technique:
- Maintain balance and control.
- Keep hips above knees.
- Keep arms forward.
Recognize Potentially Dangerous Situations:
- Uphill arm back.
- Off-balance to the rear.
- Hips below the knees.
- Uphill ski unweighted.
- Weight on inside edge of downhill ski tail.
- Upper body generally facing downhill ski.
Response:
1.) Arms forward.
2.) Feet together.
3.) Hands over skis.
ACL Awareness Video
For more information on obtaining the most recent edition of the companion DVD, A Guide To Knee-Friendly Skiing, for home viewing please visit ACL Awareness Training.
Training kits are also available for skiing professionals at: nsaa.org
