<s>[INST] I was walking outside in the pasture and started feeling a stinging feeling behind my knee. As soon as I reached down I could feel a lump the size of a quarter. I took my pants off to let my daughter look at it and she could see the lump was turning purple already. I walked into the house and showed my husband. By this time, less than five minutes the lump had hardened and ran along the vein creating a long hardened purple bruise about one inch long. I put Benadryl cream on the area, but it continued to stay swolen and purple. Any suggestions? [/INST] Hello!Thank you for the query.The color of it indicates that hematoma is the most probable reason. Due to some kind of vein rupture the blood has appeared in the soft tissues. This causes local inflammation and gives pain and hardness. Other possibility is vein thrombosis. Symptoms can be similar to those caused by hematoma. I suggest you to consult general surgeon with this issue. Dopplers veins ultrasound should be done in case of any doubts.Hope this will help.Regards. </s>