My son has a small, about the size of a pea, under the skin on his knee.  It moves around when you push on it.  His doctor sent him to get an xray because she thought it may have been a foreign object, because it didnt feel like a cyst.  Xray indicated it was not a foreign object and wants to do surgery to remove it and biospy it.  Im very worried.  What could it possibly be?
Welcome to Chat Doctor. 1. Its ganglia / cystic structure which arises from the ligament, tendon, bursar, joint space.2. There will not be pain, soreness, tenderness. In this case all you need to do is monitoring, if causing any discomfort excision is treatment of choice.3. Before excision I would recommend getting an ultrasound examination of the lump.4. Ultrasound examination will give a clear picture about the nature of the lump, its source and extensions. And a guided FNAC - fine needle aspiration cytology can be done to know the nature of cells.5. Excision / incision and Chat Doctor. 6. If you have no issues with MRI - that will be an excellent tool for joint spaces - however ultrasound solve the issue. Good luck. Hope I have answered your query.Anything to ask do not hesitate. Thank you.