Anterior cruciate ligament (ACL) injury

The anterior cruciate ligament (ACL) can be injured if the knee is straightened beyond its normal limits (hyperextended), twisted, or bent side to side. ACL injuries may include tears of the ligament, a complete rupture of the ligament, or a separation of the ligament from the upper or lower leg bone (avulsion). Injuries to the bone, other knee ligaments, or a cartilage (meniscus) often occur at the same time as ACL injuries.

Symptoms of a severe and sudden (acute) ACL injury include:

  • Feeling or hearing a pop in the knee at the time of injury.
  • Pain that may be mild or severe.
  • A sudden feeling of instability in the knee after a jump, change in direction, or after a direct blow to the side of the knee.
  • Knee swelling within 1 to 2 hours of an injury.
  • Swelling that is severe enough to limit movement.

Symptoms of a chronic ACL injury include a feeling of instability and sometimes pain and swelling.

Treatment for ACL injuries will depend on the severity of the knee injury and your activity level. The goal of treatment is to stabilize the knee and prevent further damage to the knee. Treatment includes rehabilitation exercises and possibly surgery.

Last Updated: September 24, 2009

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