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Lehigh Valley Children's Hospital

ACL Injuries

Learn about Anterior Cruciate Ligament (ACL) injuries, knee injury, causes, symptoms, diagnosis, treatment, follow-up care at Lehigh Valley Health Network.

The knee is a vulnerable joint that bears a great deal of stress from everyday movements, such as lifting and kneeling, and from high-impact activities, such as jogging or Zumba®. The knee is where three main bones join: the femur (thighbone), the tibia (shinbone) and the patella (kneecap). Several ligaments attach to the femur and tibia and give the joint strength and stability. One of these, the anterior cruciate ligament (ACL), is in the center of the knee and limits rotation and the forward movement of the tibia.

The ACL is most often stretched or torn by a sudden twisting motion – when, for example, your feet are planted one way and your knees are turned another. You also can injure your ACL by quickly changing the direction in which you’re moving, by putting the brakes on too quickly when running or when landing from a jump.

Recent studies estimate that nearly 250,000 ACL injuries occur annually in the United States. Active women are at least twice as likely to suffer serious knee injuries as men due to differences in hormones and anatomy. Children and teens of both genders have a greater risk for ACL injuries than adults because their bones, muscles, tendons and ligaments aren’t fully developed.

Common symptoms of an ACL injury are:

  • Feeling and hearing a pop at the time of injury
  • Pain in the back and outside of the knee (you may not feel pain immediately)
  • Swelling at the knee
  • Limited movement
  • Instability and the feeling that the knee will give out

If you think you have an ACL injury, it’s important to keep weight off the knee until you can see your health care provider, or you may damage the knee cartilage. If you must walk, use crutches, and be sure to see a doctor right away to have your knee evaluated.

Treatment for an ACL injury may include:

  • Medication such as ibuprofen
  • Muscle-strengthening exercises
  • Protective knee brace for use during exercise
  • Ice pack to reduce swelling
  • Surgery

The RICE method (rest, ice, compression, elevation) generally is recommended for any ACL injury and may be the best form of treatment for a mild injury.