<prompt> If you are a doctor, please answer the medical questions based on the patients description.Hello. I got a kind of a lump on my knee cap and inside i can move something on my knee it feels like a little ball. It don t hurt as much but when i press down i just get a little pain nothing much. So can u help me what is this? Pain is nothing really just a little tiny pain.  <response>: Hi! Thanks for writing to us sharing your problem of a lump on the knee! As per your description, the lump is on the knee cap, mobile, painless but slightly tender...therefore, as per my experience of needle biopsies, I can suggest few possibilities as below:1. Bursa or ganglion like degenerative cystic lesion 40 possibility2. Benign stromal or soft tissue tumor like lipoma, neurofibroma or hematoma 20 possibility3. Synovial effusion, herniation or patellar dislocation 20 possibility4. Neoplastic tumors like fibrous, histiocytoma, synovial sarcoma etc. 20 possibility, it should be examined and investigated properly before a radical excision by an orthopedic or general surgeon; please see one surgeon at your area for the detailed examination and needle biopsy if necessary! Wishing you good health, regards, 