An Injury to the Anterior Cruciate Ligament (ACL) in the Knee

An ACL tear is an injury that occurs when the anterior cruciate ligament in your knee is stretched too far or torn. Located in the middle of the knee, the ACL is one of the four main ligaments (strong but flexible connective tissues) in the knee that connects the femur (thighbone) to the tibia (shinbone). Its job is to keep the tibia from moving out in front of the femur and help the knee stay stable when you turn.

Skiers and athletes who play soccer, football and basketball are especially vulnerable to ACL tears. You may experience an ACL tear during a sport or other activity if you:

  • Stop moving abruptly
  • Change direction too quickly
  • Land incorrectly from a jump
  • Get hit in the knee

Symptoms, Diagnosis and Outlook

Symptoms of an ACL tear include pain and swelling of the knee. Your knee may have made a popping sound and “given out” at the time of injury. The pain and swelling may go away when you rest but then return when you’re active. You may also notice a loss in range of motion and an unstable feeling in the knee.

ACL tears should be quickly evaluated by an orthopaedic and sports medicine specialist – even if the pain and swelling go away with rest. Without proper evaluation, your knee may become further damaged. To diagnose your injury, your doctor will perform a physical exam. He or she may also complete an MRI test to see the inside of your knee.

Athletes and active individuals will often elect to have surgery (surgery is elective and depends on what activities the patient wishes to participate in) after an ACL injury in order to return to their sports and activities. Recovery from surgery can take six months or longer. If you’re not an athlete and your injury is mild, you may be able to return to your normal daily routine without surgery – though your doctor may recommend using a brace and/or crutches and doing physical therapy to protect and strengthen your knee.

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