The medial collateral ligament of the knee is an important ligament of the knee joint and plays a vital role in maintaining the stability of the knee joint. 3. bruising and petechiae or pressure pain, due to bleeding, bruising and petechiae can be seen under the skin, and there is significant pressure pain at the injury site. 4. joint instability and limited movement, the knee joint is often limited in internal and external rotation, especially when the external rotation, there is significant instability of the joint, and one side of the collateral ligament is injured. It is important to have an early MRI and choose a treatment according to the degree of ligament damage.