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Your anterior cruciate ligament (ACL) is one of the four main ligaments, or bands of tissue, that keeps the bones of your knee joint together. It also stabilizes it and allows you to control movement of the knee in different directions.

The ACL connects your thigh bone (femur) with your shinbone (tibia) and works in tandem with your posterior cruciate ligament (PCL) to allow you to move your knee back and forth.

People who play certain kinds of sports are at an increased risk for sustaining an ACL sprain or tear. Specifically, sports that require you to make a lot of sudden changes of direction, like soccer, basketball or football, increase your risk of tearing your ACL. You can also experience an ACL injury through direct contact to your knee.

Let’s cover the symptoms of an ACL injury.

If you’ve ever had an ACL tear, you probably remember the sensations all too well. The most common symptoms of an ACL tear include:

  • Popping sound. If you hear a pop coming from your knee at the time of the injury, it may be a tear.
  • Pain. Severe pain is one of the most common signs of an ACL tear, and it will worsen if you try to stand up.
  • Swelling. The knee joint will begin to swell, and the swelling is usually immediate.
  • Instability. Your knee might buckle or give out underneath you.
  • Inability to walk. You may not be able to walk or even put weight on the affected leg.

These symptoms can vary based on the severity of the injury and your tolerance for pain.

ACL tear pain location

If you tear your ACL, it’s probably going to hurt. Some people only feel mild pain. But in many cases, an ACL tear is going to hurt a lot. You’ll typically feel the pain coming from the center of your knee.

Not every ACL tear is a full or complete tear.

ACL injuries fall into three categories, with the mildest injuries being Grade 1. A Grade 2 tear describes a situation when the ACL has been overstretched, gotten loose, and is partially torn. Grade 3 describes complete ligament tears.

Some people do experience a partial ACL tear, which falls into the middle category. Research suggests that between 10 and 27 percent of ACL injuries are partial tears. What this means is that the person stretches or loosens the ACL, or that one of the two bundles that make up the ACL is torn. It’s still likely to be painful, and you’ll still experience some swelling. The instability of the knee joint can vary with this kind of injury.

An ACL strain is the least serious of the ACL injuries. It’s a Grade 1 injury. With an ACL strain, the anterior cruciate ligament is stretched, even overstretched, but not actually torn. It can still be painful. Your knee joint should still remain reasonably stable.

After you experience an injury to your ACL, a doctor will first examine your knee and take note of the swelling. They will also check your knee’s range of motion.

This may entail the use of a diagnostic test called a Lachman test, during which you lie on your back. Then the doctor will bend your knee and rotate it to assess its ability to move. This test can help the doctor determine what grade of injury you’ve probably sustained.

Another test that a doctor might use during the physical exam is the anterior drawer test. While lying on your back, you’ll bend your knee and keep your foot on the exam table. Then your doctor will apply pressure behind the knee and see if your leg moves out of place, which would signal an injury to your ACL.

Next up is an X-ray to see if any bones have been fractured. If there’s no evidence of any breaks, a magnetic resonance imaging (MRI) test may follow to assess the damage to your ACL.

A doctor may also choose to perform arthroscopy to check out the damage to your ACL and treat it. This is a type of surgical procedure that entails the insertion of a tiny camera into your knee through a small incision.

If you think you’ve torn your ACL, it’s a good idea to seek medical care right away. Research suggests that a partial tear can progress to a complete tear, which may involve more intensive treatment, so you’ll want to get it checked out.

Once a doctor has assessed the extent of the damage, it’s time to consider the next step.

For a mild injury, you’ll probably be instructed to rest, elevate your leg, and apply ice packs to your knee to help with the pain and swelling. You might need to wear a brace on your knee for a while to stabilize it.

However, more serious injuries may require more intensive treatment, especially because about half of all ACL injuries involve damage to other structures in the knee joint like other ligaments or the meniscus, which is cartilage in the knee joint.

Surgery is often necessary for ACL tears to restore stability and function to your knee. A surgeon may be able to do arthroscopic surgery, which is less invasive and could get you on the road to healing. Afterward, you may need some physical therapy to rebuild your strength and regain full range of motion.

If you notice that something doesn’t feel quite right with your knee, don’t ignore it, especially after an injury.