If the injury is relatively mild, only subcutaneous bleeding or tissue fluid exudation caused by the mass, the impact is not significant, you can immediately use ice or cold towels on the surface of the cold compress, in order to stop the mass further expansion as well as stop bleeding. After a day, you need to use hot towels on the surface for hot compresses, the purpose is to accelerate local blood circulation, so that the mass subsides faster or bruising subsides more quickly. If the injury is severe, not only is there a subcutaneous mass, but there may also be a patellar fracture or internal knee injury, which can be further clarified by a knee radiograph or knee MRI if necessary. If there is a patella fracture, surgery may be performed if necessary; or if there is ligament damage inside the joint, treatment with a cast or external brace may be necessary.