Um... if the ligaments and the muscles around the knee are "fine", why would you need an operation?
Definitely get the MRI to see if there is anything crazy knocking around in there, but please don't go jumping into an op, once you take something out of the knee, you generally can't replace it...

is it in agony as you sit still, as you move it a bit, as someone else moves it, or what? if the doctor and physio can't help, find someone who can.