Injured Left Knee - MRI Showed Tear - Bad Swelling

Injured left knee - MRI showed tear - bad swelling and pain. Dr drained it once and gave cortisone shot. Felt good for a day or two. Swelling and pain came back with a vengeance. Had arthroscopic surgery. Was told there was no tear but there were crystals. Dr believed it was gout - performed synovectomy. He said it was very inflamed. Pathology came back - no crystals. What?? Now I’m confused. I’m 5 days post surgery and I assume the pain and swelling now is from the surgery. What is wrong with my knee? Any ideas?