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ACL sprains account for about 15% of skiing injuries. They are one of the more serious knee injuries, partly because a full ACL rupture produces a very unstable knee that requires surgical repair (a “knee reconstruction”), and also because a fall that is bad enough to produce an ACL injury will often also injure other ligaments, bone or cartilage.

ACL injuries mainly occur when the tibia (shin bone) is sheared forwards on the femur (thigh bone), or when the knee is hyperextended (instead of bending backwards the shin bone is rotated forwards).

Because of the angle of the ski boot and the fact that the ankle is in a fixed position, if the back of the ski catches or hits first then the back of the ski boot drives the upper calf forwards, shearing the tibia forwards on the end of the thigh bone and damaging the ACL. The ACL also plays a role in controlling rotation of the knee so if this forward shearing is also associated by a rotation force then the ACL is very prone to injury. Hyperextension may occur if you catch an edge and the ski slows and changes direction and you effectively go forwards over towards the front of the ski.

There are 2 classic things that people report with ACL injuries. The first is hearing a “pop” during the fall (this may sometimes also be loud enough to be heard by other people nearby), and the second is a large swelling that appears rapidly (within 1-2 hours). This aggressive swelling is called a haemarthrosis, which means bleeding directly into the joint.

Other common things that people report after an ACL injury are moderate to severe pain (interestingly, sometimes complete ACL ruptures are not very painful because the 2 torn ends have no tension through them), inability to put weight through the knee, instability and feeling like the knee may just give way underneath them, and loss of range of movement.

Assessment in the clinic includes a thorough history and then several specific tests to check for the integrity of the ACL. If an ACL injury is suspected then you will be referred for orthopaedic assessment and usually an MRI. The earlier this is done the better especially as associated cartilage injury is relatively common, however some current schools of thought advocate delaying surgical ACL repair until the acute inflammation have resolved. Either way, early physio to reduce swelling, restore range and maintain/improve quads muscle function are extremely beneficial.

Partial tears of the ACL are treated in similar ways to partial tears of other ligaments, however complete tears routinely require surgical repair, especially if you plan to continue skiing and most other sports. Following surgical ACL repair physio is vital for progressing back to full function and minimizing the risk of future problems. Depending on the surgery performed, any associated injuries, and your individual recovery pattern, return to full sporting activity is usually from 9 to 12 months and you may require a brace to help support your knee when skiing.

So, now you have a little background on the common ligament injuries encountered when skiing. Basically, if you have a knee injury that limits your weight-bearing or movement, produces some swelling or any feelings of instability then you should be assessed by a physio as early as possible. This is important not just for a speedy recovery from this injury but is also vital for preventing secondary problems and potentially more injuries in the future due to incomplete recovery. Enjoy your time on the slopes.

If you have any questions, please reach out to Dr. Kelly Cunningham at Austin Ortho + Bio at 512.410.0767.


Dr. Kelly Cunningham Physician

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