I am dealing with the same issue. At my 1 year follow up the x-ray showed fluid in the joint. He aspirated it and it was bloody. Had a MRI and CT scan. No infection and everything looks good with the alignment. Sent me to PT and having me do strengthening exercises. It is swollen and stiff. I have lost the mobility I gained in PT after surgery. Everything went well until now. They are thinking tendinitis in the knee. My surgeon said this happens to 3% of patients. Not happy about this.