Can you post a picture of your chicken's ankle? Does it eel puffy like a small abscess? If you think it is bumblefoot, you can try soaking the foot for several days in epsom salts or betadine and water to see if it "comes to a head." Sometimes cleaning the feet also help you to see the classic dark spot on the bottom of the foot. There is a product called TriCideNeo, that is for fish, but can be used to soak feet that have bumblefoot. I would rather do the surgery myself, but I never do it unless the chicken is limping or the bumblefoot looks very red, swollen, and painful. Everyone has their own method to knowing when to do surgery or not.