Tears or ruptures of the anterior cruciate ligament (ACL) are a common type of knee injury, with approximately 250,000 reported annually in the United States. This type of injury occurs frequently in sports. ACL injuries commonly occur in the following instances:

  • As a result of cutting, pivoting or single-leg landing, and without any external trauma
  • Through a twisting force applied to the knee while the foot is planted on the ground, or upon landing on one foot


  • From a direct trauma to the knee, usually the outside of the knee, as may occur in many contact sports
Knee Cortisone InjectionACL tears and/or ruptures are very common knee injuries.
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ACL Injury: Causes and Risk Factors

Women and girls are most susceptible to ACL injury.

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Injury to the ACL is painful and most individuals report a “pop” in their knee, followed by a feeling of instability that hinders many athletic activities, as well as simple daily activities such as walking down stairs. Surgery is often recommended to restore knee function, but is not always necessary.

Description of an ACL Tear

The ACL is one of the main ligaments that help stabilize the knee by preventing the tibia (shin-bone) from sliding forward in relation to the femur (thigh-bone). It attaches to the knee at the bottom back of the femur (thigh bone) and crosses diagonally through the knee joint to attach at the upper part of the tibia (shin bone).

The posterior cruciate ligament crosses the knee joint in the opposite direction, making an X shape (cruciate is from the Latin word for cross). The ACL and PCL work together to provide important stability for the knee joint, especially during movement that involves sudden change of motion or impact.

An ACL injury may be diagnosed when the ligament is overstretched or torn. The tear may be partial or complete; a complete tear of the ACL is also known as an ACL rupture.

Several ACL prevention programs have been suggested and proven successful.

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