I have had a third knee for about 5 years. I had it drained several times and it just comes back. I had an MRI done and it did not show anything so I went to an ortho-pod and was told the same thing as you , that he could remove the bursa. Then he told me that it could grow back again. He said sometimes the slightest irritation can cause this as a small part of the meniscus being pushed out. My knee actually looked ok and for my age the padding in my knee was very good. The surgery would probably reveal the cause, but in the likelihood of an infection I would be down for 12 weeks. He also told me that infection in knee surgery is way more common than other types of surgery. I think I will wait until I retire. The knee does not bother me at all. , I did almost 40 miles yesterday with some steep uphills and no problem. The worst part of this is the ugly “third knee” look and people asking if it is cancer or something! Joe