An anterior cruciate ligament, or ACL, injury is a tear in one of the knee ligaments that joins the upper leg bone with the lower leg bone. The ACL keeps the knee stable.
Injuries range from mild, such as a small tear, to severe, such as when the ligament tears completely or when the ligament and part of the bone separate from the rest of the bone.
Without treatment, the injured ACL is less able to control knee movement, and the bones are more likely to rub against each other. This is called chronic ACL deficiency. The abnormal bone movement can also damage the tissue (cartilage) that covers the ends of the bones. And it can trap and tear the pads (menisci) that cushion the knee joints. This damage can lead to osteoarthritis.
Symptoms of a severe and sudden (acute) ACL injury include:
After an acute injury, you will probably have to stop whatever you are doing because of the pain. But you may be able to walk.
To diagnose an ACL injury, your doctor will ask you to describe how you injured your knee and what you felt. The doctor will check your knee for swelling or tenderness. They may gently push and pull on your leg to see if the knee joint moves in an abnormal way. The exam is usually done on both legs so the doctor can compare one leg to the other to see what's normal for you.
You may have an X-ray to help make sure there isn't a different injury, like a broken bone. Ligaments can't be seen on an X-ray. An MRI is an imaging test that can help show the ACL. It can help your doctor see if you have an ACL tear. Often an injury that causes an ACL tear also injures other ligaments or the cartilage called the meniscus. An MRI can help your doctor diagnose these other injuries.
An ACL tear in children is often treated with surgery. This helps make your child's knee stable. And it may help them get back to being as active as they were before the injury. Surgery may also prevent other injuries to the knee. But with surgery, there is a small risk of an injury to your child's growing bone.
Sometimes, especially if your child is almost done growing, it may be better to wait. Waiting for the bones to mature may reduce the risk of an injury to the growing bone. Treatment without surgery includes rehabilitation, bracing, and a limit to activities.
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