The anterior cruciate ligament is an important ligament in the knee joint that prevents the tibia from moving forward and stabilizes the knee joint during knee extension. If the anterior cruciate ligament is hit in a traffic accident or if a knee sprain occurs during exercise, the ligament can often be damaged. After a ligament rupture, a diagnosis of ligament damage should be made by performing two tests: 1. The anterior drawer test can be done by fixing the foot, flexing the knee 90°, and pulling the tibia forward. If there is significant laxity compared to the contralateral side, an ACL injury is suspected. 2. The Lachmann test is performed by fixing the distal femur at 30° of knee flexion, while allowing the tibia to be pulled forward in a drawer-like motion. If there is significant laxity compared to the contralateral side, an ACL injury should also be suspected. Related ancillary tests, such as MRI, should also be performed. MRI is very helpful in the diagnosis of ACL rupture, with an accuracy rate of more than 95%.