Skiers sustain over 20,000 anterior cruciate ligament tears each year, reports Dr. Carl Ettlinger, developer of the Vermont Ski Safety project. Ettlinger gained recognition in the ski industry by coining the phrase "Phantom Foot ACL'" which describes a series of interrelated technique problems that make skiers susceptible to ACL tears.
The Phantom Foot
Your skis have a tip and a tail. Your tips control the direction of your ski turns. Safe, efficient and effective ski technique requires the skier to keep her weight forward, with her shins pressed against her ski boot tongues. If she shifts her weight backward, so that her calves press against the hard plastic rear of the boot, she shifts her control to the ski tails, which were not designed for directional control. Tasked with responsibilities that normally belong to the ski tips, the ski tails become a phantom foot.
Tips vs. Tails
The tips of skis curve upward, whereas the tails are flat. The upward curve facilitates easy carving, which is the most efficient way to turn. The flat tails create skidding or twisting movements. Twisting or rotational movement is not always a bad thing. Powder skiing, for example, uses less carving and more rotation. Problems arise when the skier shifts his weight backward in conjunction with a twisting movement. The backward weight shift fights against gravity. It may causes you to fall backward while twisting your leg, which can lead to you tearing your ACL.
Phantom Foot Profile
In addition to shifting your weight toward your tails, Ettlinger identified other factors that contribute to the phantom foot profile, including uphill arm behind your body, hips lower than your knees, unweighted uphill ski, and weight on the inside edge of the downhill ski. Tears of the ACL usually happen to skiers demonstrating all or most of these technique problems. The poles behind the body issue, common in many skiers, shifts your weight backward toward the ski tails. Dropping your hips below your knees overstretches your knee ligaments, making them susceptible to tears.
Dangerous Scenarios
A ligament tear results from a combination of forces, including your skis, gravity, and your body weight, acting on your knee ligaments. Three potentially dangerous scenarios, when combined with a phantom foot profile, make ACL tears more likely. These include attempting to get up from a fall while still moving, attempting recovery from an off-balance position and attempting to sit down after losing control. Relaxing your body and allowing yourself to fall is the safest, albeit most counter-intuitive solution.
Prevention
Ski lessons with a certified instructor and equipment analysis and alignment with a certified boot-fitter may help you correct your technique problems and phantom foot. Many ACL tears result from a hamstring quadriceps muscle imbalance. Safe falling involves flexing your knees, but if your quadriceps have significantly more strength than your hamstrings, your knees will hyperextend and you can tear your ligaments. This is a particular problem for female athletes, who often have strong quadriceps and weak hamstrings. Performing additional hamstring strengthening exercises may make you less susceptible to growing a phantom foot.
