I had an accident at work and injured my knee. I had surgery nd some other treatments,the pain is still there?

My doctor was sugesting a second surgery and I was sent to an IME and FCE but I do not have the results yet. In the mean time, I went to another doctor, had an MRI and looked for a second opinion. This doctor says that the surgery will not do anything for me, suggested some physical therapy (which I had waaay to many), and another exploratory surgery. But he says that my condition pretty much is irreversible. So I guess I just will have to live with the pain. How do I know if I have reached maximum medical improvement(MMI) ? Or how is the permanent partial disability(PPD) or permanent total disability(PTD) been set ?