ACL Tear

The Anterior Cruciate Ligament (ACL) is one of four major ligaments (ligaments connect bone to bone) of the knee joint that coordinate function and promote stability of the knee joint. It runs in a notch at the end of the femur (intercondylar notch) and originates at the back part of the femur (postero-medial aspect of the lateral femoral condyle) and attaches to the front part of the tibia (tibial eminence). In the knee, the ACL prevents forward movement of the tibia. It also provides roughly 90 percent of stability in the knee joint.

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The classic ACL injury occurs during a non-contact event usually when decelerating, stopping suddenly, twisting, cutting, or jumping. Often the patient will hear or feel a "pop" at the time of injury and sometimes they may report brief a hyperextension of the knee joint. Just after the injury some patients may be able to continue activity; however, most patients are unable to continue regular activity. A few hours after injury, the knee will swell considerably.

When the ACL is injured as a result of direct contact, football is often the associated sport. Most often, the knee is subjected to a direct blow to the lateral side and other ligaments are injured in addition to the ACL. The most common multi-ligament injury is the "unhappy triad" that includes the ACL, medial collateral ligament (MCL), and the medial meniscus.

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Symptoms include:

  • An audible pop at a moment of injury.
  • Knee tends to slip out of joint, feels unstable, and swelling and pain hinder movement.
  • Knee often feels as though it will give way or is unstable.

Your doctor may conduct physical tests and take X-rays to determine the extent of damage to your ACL. Most of the time you will need reconstruction surgery.

Only about a third of people with a completely torn ACL are able to build their muscle strength enough to resume normal activities without surgery. Still, the non-operative option exists, and having surgery or forgoing it is partly a personal choice.

Those who are not very active may choose a strengthening program instead of surgery, since the injury is not likely to interfere with their daily activities. Such a program takes about six to 10 months to complete. However, about 65 percent of all patients with a torn ACL will eventually develop a torn meniscus — a protective cartilage that reduces friction between the knee bones — which may predispose them to early onset arthritis.

Active, athletic people are more likely to opt for surgery, so that the knee can be repaired and rehabilitated and they can return to their activities.

The surgery is called an endoscopic ACL reconstruction and is done using small instruments through a Band-Aid size incision. It is done either on an outpatient basis or you may have to spend the night in the hospital. After four to six months, you should be able to return to unrestricted activity and competitive sports.

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Reviewed by health care specialists at UCSF Medical Center.

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