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HealthInfo Canterbury

What is an ACL injury?

Front view of the knee, showing femur, articular cartilage, lateral collateral ligament, anterior cruciate ligament, lateral meniscus, medial meniscus, medial collateral ligament, fibula, and tibiaYour anterior cruciate ligament is one of two ligaments inside your knee joint. The other one is called the posterior cruciate ligament. (Anterior means front, posterior means back.)

The ACL stabilises your knee when you twist or pivot it. An ACL injury can be just to the ligament, or it might involve other parts of your knee as well. It is more common in women and teenage girls than in men. A tendency to injure your ACL can run in families.

Usually, an ACL injury is caused by a direct blow to your knee, or after twisting or landing awkwardly. So it's more common among people who play sports like rugby, netball and soccer, which involve a lot of pivoting and twisting.

When you tear or rupture your ACL, your knee will completely give way, and it's common to hear a popping sound. Your knee will immediately swell, and you'll feel some pain. You should see a doctor or a physiotherapist if you have these symptoms. They will examine your knee. You may also need an X-ray.

Straight after an ACL injury you should try to reduce swelling by using RICE treatment (rest, ice, compression, elevation). Usually the swelling will go down over a few days, but if you can't bend your knee past 45 degrees (halfway), you may need to have fluid drained from your knee through a needle.

It may be difficult to put weight on your leg, in which case you will need crutches for a short time. Wearing a Tubigrip bandage can also help to reduce swelling, but if you wear one, take it off when you go to bed at night.

On the next page: How is an ACL injury treated?

Written by a Christchurch physiotherapist. Adapted by HealthInfo clinical advisers. March 2016.

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