Anterior cruciate ligament injury

The anterior cruciate ligament ("ACL") is an important, internal, stabilizer of the knee joint, restraining hyperextension. It is injured when its biomechanical limits are exceeded (over stretched), often with a hyperextension mechanism.

Formerly, ACL injuries occurred most often in a sports contact injury, when other structures were frequently involved. A particularly severe form of the contact injury is called the "unhappy triad" or "O'Donaghue's triad", and involves the anterior cruciate ligament, the medial collateral ligament, and the medial meniscus. Presently, ACL injury is more commonly a non-contact injury, such as a dismount from a layup in basketball. Both forms occur more frequently in athletes than in the general population and are prevalent in alpine skiing, association football, American football, Australian rules football, basketball, rugby, professional wrestling, martial arts, and artistic gymnastics. It is also known to be about three times more common in women than men.