The anterior cruciate ligament connects the femur and tibia and is an important structure that maintains the stability of the knee joint. Injury to the ACL can result in degenerative knee osteoarthritis due to abnormal dynamic changes in the joint. The images below show the arthroscopic and MRI shapes of the ACL. ACL injuries often occur during low velocity, deceleration sports where the knee is in rotation rather than in contact. The mechanism of ACL injury is the force of valgus, external rotation, and hyperextension of the knee. The patient often hears or hears a “pop” during exercise and is then unable to continue. The knee joint then swells and an acute knee hematoma occurs. Even after the hematoma subsides, the patient is often left with knee instability and weak legs, typically afraid to run fast or at variable speeds. The first thing that needs to be determined in patients with anterior cruciate ligament injuries is whether there is joint instability and the degree of motion in which the joint instability occurs. In patients with ACL injuries caused by contact injuries, bone contusions are commonly seen on MRI. In the moment of ACL injury, there may be a combination of subluxation or almost total dislocation of the knee. Approximately 60-75% of patients will have a concomitant meniscal rupture. The O’Donoghue triad, a diagnosis of simultaneous ACL, medial collateral ligament, and medial meniscus injuries, is often diagnosed clinically, but is actually less likely to occur than simultaneous ACL, medial collateral ligament, and lateral meniscus injuries. The Lachmann test (Lachmann test) is a commonly used test for ACL injuries, with a soft endpoint sensation on physical examination. Instruments are used to detect instability most commonly with the KT-1000 or KT-2000; it is generally accepted that a difference of 3mm between the maximum hand pull test and the normal side, or a direct reading of more than 11mm in the test, indicates significance. This method is now also used as one of the assessment methods for the results of treatment. Plain x-rays are necessary, and MRI provides insight into the presence of lesions throughout the knee joint and surrounding tissues to facilitate treatment selection.