<s>[INST] My daughter (3 years old) has a hard knot behind her knee, in the bend of her leg. I have felt of it, pushed on it, however, she says it is not painful and she doesn t limp on it or shows any signs of discomfort. It is bigger than a golf ball in size. Is this something I need to be concerned about? Thanks, Angie [/INST] Hi,Dear,Welcome with your query to HCM.Studied your query in full depth of its details.Reviewed it in context of your health concerns.Based On the facts, You mostly seem to suffer from-Bakers Cyst in Popliteal bursa -most common possibility ?or it could be Myxoma  of the Knee.Other causes like Osteogenic Sarcoma of the lower end of the thigh with secondary Cyst in Popliteal Bursa needs to be ruled out.CT Knee study would fix other causes also.Treatment -To fix the primary causes like Tb knee arthritis  and others.Treat it by Arthroscopic MB Cyst Excision by posterior approach.Hope that ,This reply would help you to plan further treatment soon with your treating doctors.Best of Luck and early recovery.Welcome any further query in this regard,which would be replied in next session.Good Day!!Dr.Savaskar M.N.Senior Surgical Specialist </s>