1, Diagnosis: Medial collateral ligament laxity of the knee is mostly due to clinical misdiagnosis or the use of inappropriate treatment methods, which requires careful history taking, comprehensive physical examination and relevant ancillary examinations in our clinical work with patients with knee trauma. 2. Among the stable structures of the knee joint, the medial collateral ligament is weak. When the knee is subjected to direct or indirect violence in flexion that can cause severe abduction and external rotation of the knee, it can lead to injury to the medial collateral ligament of the knee. The anterior cruciate ligament, medial femoral condyle, tibial plateau, joint capsule and medial meniscus can be injured at the same time when the violence is high. Direct violence is often applied to the lateral aspect of the knee. Indirect violence from car accidents, skiing falls, etc. can cause the knee to be strained in the valgus position and injured. Understanding the history of the injury is helpful in making a clear diagnosis. 3. During physical examination, attention should be paid to the valgus stress test of the knee joint. A positive valgus stress test in knee extension indicates an injury to the anterior longitudinal bundle of the medial collateral ligament. A positive valgus stress test at 30° of knee flexion indicates damage to the oblique bundle. In patients with medial collateral ligament injuries, the drawer test and the Lachman test should be examined to determine if there is a combined cruciate ligament injury. Severe instability of the knee joint due to medial collateral ligament injury and a significant increase in the medial gap opening should be highly suspected in combination with other knee ligament injuries. Arthroscopy should be performed in such patients to clarify the diagnosis. 4. Among the auxiliary examinations, stress radiographs of the knee joint are the most common method of examination. 5. Acute medial collateral ligament injury should be diagnosed early. Surgical treatment is the most effective way to ensure joint stability. After ligament injury, improper treatment can lead to loss of the ligament’s restraining and limiting effect on the tibia, which can be followed by ligamentous laxity knee instability and osteoarthritis. There are many treatment options for old medial collateral ligament laxity, but they can be fundamentally divided into static and dynamic repair methods.