Although ACL (Anterior Cruciate Ligament) injuries overall are actually a small percentage of all snow sports injuries (10-15%) – it is very easy to rupture in the beginner and intermediate skier.
The most common 2 mechanisms are ‘The Phantom Foot’ and the ‘Boot Induced’ Mechanisms
“The Phantom Foot Mechanism”
- Uphill Arm is back
- Skier is off balanced to the rear
- Hips are below the knees
- Weight on the inside edge of the downhill ski tail
- Upper body facing downhill ski
This typically happens when the skier is either:
- Attempting to get up whilst still moving after a fall
- Attempting a recovery from an off-balance position
- Attempting to sit down after losing control
When the knee is in deep flexion (>130º) this causes the tibia to rotate internally and move forward, placing severe shear strain on the ACL. When the knee then moves inward this increases the rotary torque and simply is too much for the ligament. Usually the ligament ruptures very quickly as the load is so high and so fast. Skiers will complain of a loud pop and immediate pain in their knee.
“The Boot Induced Mechanism”
This occurs when a skier becomes off-balance to the rear whilst attempting a jump. Instinctively, the skier’s leg fully extends.
As a result the skier lands on the tails of the ski which force the back of the ski boot against the calf, driving the tibia out from under the femur and the ACL tears.
This can also happen simply from disembarking the chairlift too late and having to jump off at the end!
PREVENTION
To help prevent ACL injuries we advise the skier to:
- Always aim to keep arms forward, feet close together and hands over the skis.
- Don’t straighten your legs when you fall, keep your knees flexed
- Don’t land on your hand. Keep arms up and forward
- Don’t jump unless you know where and how to land. Land on both skis and keep your knees flexed.
