Anterior cruciate ligament rupture of the knee is a common knee injury associated with sports and exercise. The injury typically arises when the foot is tightly locked against the floor or ground, whereby a sudden change of direction combined with the slowed motion causes a rotary motion of the upper part of the tibia and a force rupturing the cruciate ligament. Approximately 30% of the injuries take place during a situation of direct contact. The instability of the knee due to the rupture may be strongly invalidizing. In such case surgical therapy is required, if appropriate conservative treatment does not lead to a good result.