When a purple bruise appears on the knee, the following treatment measures can be taken: 1. Apply a cold compress to the area as soon as possible to prevent secondary subcutaneous bleeding. It is recommended that ice be applied for 10 minutes and that a towel be used to wrap the ice to prevent frostbite from direct contact with the skin. 2. After the medicine is finished, you can use an elastic bandage or knee brace to protect and fix the area. In addition, the patient must pay attention to strengthen the protection of this area during daily activities to prevent it from being rubbed and squeezed. After the above mentioned treatment measures, most of the purple skin and bruises will gradually be relieved. If there is no relief, or if there is a subcutaneous hematoma, it is important to go to an orthopedic clinic to identify the cause and ask for medical help.