Knee ligament injuries are graded based on the severity of injury. In grade I the ligament is mildly damaged and slightly stretched, but the knee joint is stable. In grade II there is a partial tear of the ligament. In grade III there is a complete tear of the ligament and the ligament is divided into two halves making the knee joint unstable. The surgical repair of the completely torn ligament involves reconstruction of the torn ligament using a tissue graft taken from another part of the body, or from a donor. The damaged ligament is replaced by the graft and fixed to the femur and tibia using metallic screws. Gradually, over a period of a few months, the graft heals.