An anterior cruciate ligament (ACL) tear is an injury to the ligament in your knee that keeps your shinbone from sliding forward.

The ACL stabilizes your knee, so tearing it either partially or completely can cause pain and swelling. It’s a common injury among athletes. Ignoring a torn ACL can potentially lead to further injury.

ACL injuries are commonly seen in basketball, football, and soccer players, who often jump or pivot in reaction to other athletes. Ignoring a torn ACL can potentially lead to further knee injury.

ACL tears typically occur in highly active people. Certain movements tend to cause ACL injuries:

  • landing flat-footed from a jump
  • overextending your knee joint
  • changing direction fast
  • changing speed while running

You can also injure your ACL if the side of your knee is hit. This might happen in a car accident or a football tackle.

ACL tears are typical sports injuries. Basketball, skiing, football, and soccer are a few of the sports that make athletes vulnerable to knee injuries, because these activities involve jumping or pivoting. According to the American Academy of Orthopedic Surgeons, ACL injuries are two to 10 times more likely to occur in female athletes than in male athletes.

People who hurt their ACLs usually hear a popping sound as soon as the tear occurs. Swelling of the knee generally happens within six hours of injury and may be quite severe. The condition can be painful, especially when walking, twisting, or turning on your injured leg. You’ll also generally feel that your knee is unstable, as if it’s going to give out from underneath you.

An ACL tear needs to be examined by an orthopedic surgeon or knee specialist. The doctor will review your medical history and ask how you injured yourself. The physical exam typically includes observing your knee’s stability and range of movement. Your doctor may also order the following tests:

  • An X-ray will help determine whether there are any broken bones.
  • An MRI helps to specifically diagnose an ACL tear and look at the other ligaments and structures in your knee.
  • If there are concerns about small bone fractures, you might need a CT scan of your knee.

Treatment for an ACL tear depends on the extent of your injury and your specific goals and needs. Some people can continue their normal lives with an ACL injury but may later suffer from other knee injuries. For an athlete, surgery and physical therapy may be the best answers for resuming athletics as quickly as possible.

In all cases, it’s important to see a healthcare provider immediately to ensure that there are no broken bones or damage to other ligaments. If your knee is blue, seek medical help immediately, as your blood vessels may be injured.

Sometimes this type of injury requires a complete surgical reconstruction using a tendon from the patella (kneecap) or hamstring. Using donor tissue is also an option.

When you first injure yourself, your doctor may recommend an over-the-counter pain reliever (like ibuprofen). If you’re having surgery, ask your doctor about the required medications for both before and after your surgery. Prior to surgery, you may be told to stop taking medicines that interfere with your blood’s ability to clot, like aspirin.

Following surgery, you may need up to six months of physical therapy to regain your full range of motion and leg strength.

Reconstructive surgeries usually have good outcomes, allowing you to have less pain and more leg strength and knee stability. With proper treatment, you should have a good recovery, but arthritis is a potential risk to the knee. However, it may be worse if surgery is not performed, depending on whether the person returns to active sports.

A strong and agile body reduces your risk for an ACL tear. If you’re an athlete, learn and practice preventive techniques for reducing the pressure on your knees. Landing on the balls of your feet rather than flat-footed, for example, allows your calf muscles to support your body. This decreases unnecessary pressure on your knees.