The anterior cruciate ligament (ACL) is one of four main ligaments that stabilize the human knee. The ACL, located in the middle of the knee, keeps the tibia (shin bone) from sliding in front of the femur (thigh bone).

The ACL can be injured by a hard impact on the side of the knee (as from a football tackle), hyperextension of the knee, or a sudden stop and change in direction while running, turning, or landing from a jump. People with a suspected ACL injury should ice the knee, take nonsteroidal antiinflammatory drugs (NSAIDs) such as ibuprofen, and see their health-care providers. Magnetic resonance imaging (MRI) is often used to confirm an ACL injury.

A mild to moderate ACL injury may heal on its own over time. During recovery, patients are generally advised to rest the knee, in some cases by using crutches. Other measures include taking NSAIDs, icing the knee, wearing a knee brace, and stretching and performing strength exercises as recommended by the patient’s health-care team.

In some cases, ACL reconstruction is required. In ACL reconstruction, tendons are taken from elsewhere in the leg (a procedure known as an autograft) or from a cadaver or live donor (an allograft) and used to replace the injured ligament.

This column is written by Robert S. Dinsmoor, a medical writer and editor based in Massachusetts.

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