My left knee started swelling at the beginning of Feb. After two weeks of constant swelling, and no injury that I can recall, I saw my PCP. She ordered and X-Ray (normal results) and put me on an anti inflammatory. After two more weeks with no change, she sent me to an Orthopedic specialist. I was diagnosed with Patellofemoral syndrome and treated with PT. After still only minor improvement in the six weeks since seeing the specialist, my PT sent me back to the Dr, The specialist still stands by his original diagnosis and decided to give me a cortisone injection today. After his exam, he said that if it were something more major, I would have pain in certain movements which I do not. I should also mention that I have had very slight pain since this started and as the swelling continues it only gets more bothersome. First, any thoughts on a cause? And second, I never received an MRI. Should I have?