In the 1970Ős famous sport stars like Joe Namath, Gale Sayers, and Tony Dorsett had to give up the thing they loved because of three letters, ACL. Then, it was rare for a skier to have this kind of injury, more likely were the fractures of the ankle and lower leg. However, the stiffer and higher-cut boots and anti-friction ski bindings led to the extinction of tibia fractures and sent the ACL statistics into the mountains. all of the stress is places on the knee. And that could be bad news if the knee is hyperextended, hyperflexed, or torqued. There are differences of opinion when it comes to the direction that the knee is in for this injury, however these are the likely scenarios in which the ACL is injured.
The first type of mechanism is called the Phantom Foot. This is when the tail of the downhill ski acts as a lever, which applies bending and twisting loads to the knee. Carl Ettlinger, who is the head of the Vermont Safety Research, believes that a high percentage of ACL injuries occur this way. In watching videotaped footage, he has found the same sequence of events leading to a tear: The uphill arm goes back as the skier leans backwards, the hips fall below the knees and the uphill ski becomes unweighted, thus, weight is placed on the inside edge of the downhill ski and the upper body faces the downhill ski.
The second type of mechanism is called the Boot-Induced, hence the name is the action. When a skier hyperextends the legs trying to recover from a jump, the skier hits the ground with his weight to the rear. The tail hits first and the muscles of the leg contract, thus, the hyperextension as the back of the boot drives the tibia out from under the femur.
Third is the Forward fall. This is opposite of the boot-induced tear. The skier is thrown to the front of his/her boots. With this kind of pressure, the ski presses the downhill leg to the rear. At the same time, the forward momentum pushes the skier forward, driving the thigh to the front. These opposing forces puts the knee in a bad position.
The final mechanism of the injury only happens during high speeds. The skier makes a turn with the knees close together, However, if the ski skids out of a turn because of certain environmental conditions, the downhill knee can be jarred into a side-to-side motion, thus, ripping the ACL.