Your anterior cruciate ligament, or ACL, is one of four ligaments that connect your thigh bone to your shin bone. Charged with limiting excessive movement of your shin bone and excessive rotation of your knee joint, your ACL may be vulnerable during Alpine skiing. Preexisting muscle imbalances, along with faulty skiing or falling technique, can make you susceptible to ACL tears.
The Phantom Foot
The ski industry credits Carl Ettlinger and his Vermont Safety team of researchers for identifying a phenomenon called the "phantom foot," which makes skiers susceptible to ACL tears. If your instructor tells you that you have a "backseat" alignment, meaning that you keep most of your weight on your ski tails, you may fit the phantom foot profile. Other facets include keeping your poles behind your body and dropping your hips below your knees. When you shift control from your skis tips to your ski tails, your tails act as powerful levers, which twist your skis in the opposite direction of your feet. The resulting twisting movement may tear your ACL.
Falling
Falling is inevitable during skiing, but not all falls cause ACL tears. Locking your knees during a fall, trying to stop a fall by locking your knees, or attempting to get up from a fall while still moving puts excess pressure on your ACL and may cause a tear. In some cases, the fall itself will not tear your ACL, but the manner in which you attempt to get up will. If you fall backward with your skis facing directly downhill, you need to turn your body so that your skis face across the slope. Otherwise, your skis may slide out from under you as you attempt to get up, causing you to fall again. The second fall may be more serious than the first.
Binding Release Settings
Your binding or DIN settings may make the difference between a minor injury and a complete tear. The ski shop technician calculates your DIN setting according to your height, weight, boot sole length, age, proficiency and skiing style. Ski instructors use the term "DIN sin" to describe people who give false information to the shop technicians, in order to get a higher binding release setting. Using a higher release setting will prevent your skis from releasing during the fall, but the force of your skis may twist your leg and tear your ACL.
Muscle Imbalance
In order to prevent athletic injuries, your hamstrings must be at least 80 percent as strong as your quadriceps, warns athletic coach Brian Mackenzie of SportsCoach.com. Your hamstrings bend your knees, whereas your quadriceps straighten them. A muscular imbalance between your hamstrings and quadriceps increases the possibility that you will ski with your weight on your ski tails or lock your knees during a fall. Hamstring/quadriceps muscle imbalances are common among women, says orthopedist Dr. Thomas J. Haverbush, who are thus more likely to suffer ACL injuries.
Boot Induced ACL Tears
The boot-induced ACL injury, also called the boot induced anterior drawer, occurs among ski jumpers. It usually begins with the skier in an unbalanced position with his weight on his ski tails. When he lands on his ski tails, the force of his heavy, stiff boot, combined with that of his skis, pushes against his calf, in turn pushing his shinbone so that it moves forward in front of the thigh bone, tearing the ACL.
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