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Anterior Cruciate Ligament (ACL) Injury or Tear


A torn ACL is an injury or tear to the anterior cruciate ligament. The ACL is one of the four main stabilizing ligaments of the knee,

ACL tears may be due to contact or non-contact injuries. A blow to the side of the knee, which can occur during a football tackle, may result in an ACL tear.
Alternatively, coming to a quick stop, combined with a direction change while running, pivoting, landing from a jump, or overextending the knee joint (called hyperextended knee), can cause injury to the ACL.

Basketball, football, soccer, and skiing are common causes of ACL tears.
Your ACL can be injured if your knee joint is bent backward, twisted, or bent side to side. The chance of injury is higher if more than one of these movements occurs at the same time. Contact (being hit by another person or object) also can cause an ACL injury.
An ACL injury often occurs during sports. The injury can happen when your foot is firmly planted on the ground and a sudden force hits your knee while your leg is straight or slightly bent. This can happen when you are changing direction rapidly, slowing down when running, or landing from a jump. This type of injury is common in soccer, skiing, football, and other sports with lots of stop-and-go movements, jumping, or weaving. Falling off a ladder or missing a step on a staircase are other likely causes.


  • There may be an audible pop or crack at the time of injury
  • A feeling of initial instability, may be masked later by extensive swelling.
  • This injury is extremely painful, in particular immediately after sustaining the injury.
  • Swelling of the knee, usually immediate and extensive, but can be minimal or delayed (video).
  • Restricted movement, especially an inability to fully straighten the leg
  • Possible widespread mild tenderness

Early symptoms

  • A "popping" sound at the time of injury
  • Severe pain
  • Knee swelling within 6 hours of injury

Late symptoms

  • Knee joint instability
  • Arthritis
  • Feeling or hearing a pop in the knee at the time of injury.
  • Pain on the outside and back of the knee.
  • The knee swelling within the first few hours of the injury. This may be a sign of bleeding inside the knee joint. Swelling that occurs suddenly is usually a sign of a serious knee injury.
  • Limited knee movement because of pain or swelling or both.
  • The knee feeling unstable, buckling, or giving out.

ACL injury should be treated with a splint, ice, elevation of the joint (above the level of the heart), and pain relievers such as non-steroidal anti-inflammatory drugs (like ibuprofen). The patient should not continue to play until evaluation and treatment has taken place.

Some people may need crutches to walk until the swelling and pain has improved. Physical therapy may help regain joint motion and leg strength.

If instability continues even after leg strength and knee motion has returned, most orthopedists will recommend a reconstruction of the ACL. The old ligament cannot be fixed, so a new one needs to be constructed. Usually a piece of the patellar tendon (the tendon connecting the kneecap to the tibia) is used, although the hamstrings can also be effective. Cadaveric grafts may also be used to reconstruct the ACL.

There are two ways to treat the injury:

  • Exercises and training, also called rehab. It takes several months of rehab for your knee to get better.
  • Surgery: You and your doctor can decide if rehab is enough or if surgery is right for you.

If you have surgery, you will also have several months of rehab afterward.
Your treatment will depend on how much of the ACL is torn, whether other parts of the knee are injured, how active you are, your age, your overall health, and how long ago the injury occurred.

Use proper techniques when playing sports or exercising. Several women's collegiate sports programs have reduced ACL tears through a training program that teaches athletes how to minimize the stress they place on their ACL.


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