Lateral collateral ligament injury of the left knee has typical symptoms such as obvious pressure pain, limitation of movement and swelling at the injury site, which varies according to the severity of the injury, and needs to be diagnosed at the clinic. The lateral collateral ligament is a rounded ligament located on the outside of the knee joint, and its main function is to prevent the knee joint from turning inward, which plays an extremely important role in maintaining the stability of the knee joint. When the lateral collateral ligament of the left knee is injured due to trauma, the typical symptom is pain on the lateral side of the left knee, where there are obvious pressure points. In addition, when the left knee lateral collateral ligament injury, the local tissue fluid leakage will cause swelling of the lateral knee joint, damage to blood vessels and other serious cases will appear obvious bruises. It may also cause limitation of movement, affect walking, and cause pain and other discomfort when flexing and extending the left knee joint. Specific symptoms and the presence of other accompanying symptoms depend on the severity of the injury. When the lateral collateral ligament of the left knee is injured, it is recommended to consult a doctor for a clear diagnosis through medical examination and imaging tests such as MRI to rule out the presence of meniscus and cruciate ligament injuries.