<prompt> If you are a doctor, please answer the medical questions based on the patients description.I have very acute pain in my knees,the left knee,had meniscus surgery 16 months ago,it swells behind the knee it s a lunp the size of ,ones thumb,the right knee has severe painburning and swelling and pops really loud ,like a rubber band been snapped against a paper bag??  <response>: Hi! There is kind of nagging chronic inflammation infection there, and it needs orthopedic opinion! Well, your problem is very common especially in young individuals and in such cases we generally do x-rayUSG or a fine needle aspiration biopsy for confirmation of the diagnosis. The possibilities come as follows:1. A chronic abscess or synovitis: 60 of cases2. An inflamed bursa 30 of cases3. Loose bodies like fragments of patella or tendons 5 cases4. Arthritis like erosive arthritis 5 casesTherefore, you need rest of the joint, investigations and must see an orthopedic surgeon for possible line of management. Wishing you good health! 