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Overview of an ACL injury

Tirohanga whānui ki tētahi wharanga ACL

Your anterior cruciate ligament (ACL) 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 just be to the ligament, or it might involve other parts of your knee as well. It's 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 twisting or landing awkwardly or by a direct blow to your knee. So, it's more common among people who play sports like rugby, netball and soccer that involve a lot of pivoting and twisting.

Diagnosing an ACL tear

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'll examine your knee. You may also need an X-ray to make sure there are no injuries to the bones. You're likely to need an MRI scan to confirm the diagnosis of a ruptured ACL.

Treating an ACL tear

Straight after an ACL injury you should try to reduce swelling by using RICE treatment (Rest, Ice, Compression, Elevation). The swelling will usually 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'll 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.

People who injure their ACL may need surgery to stabilise their knee. Surgery may also be offered to athletes or workers who do a lot of pivoting or twisting.

But people who have a fully functional knee that doesn't give way are unlikely to need surgery. Strengthening exercises that help to keep their knee stable are the best treatment.

In the first few weeks after an injury, it's difficult to tell which people will need surgery, so it's best to try strengthening rehabilitation first.

On the next page: Treating an ACL injury

Written by a Christchurch physiotherapist. Adapted by HealthInfo clinical advisers. Last reviewed July 2022.

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