are u still doing squats? what exc. are u doing?
my advice would be to stick to heavy isolation exc. for a while.
u can merely just maintain w/ them more than u can w/ compounds IMO. perhaps using leg ext. if they are really disproportionate, then just lay off on total max weight and even though u might lose some muscle in the left, but u would have a better chance at sizing them up better.
i dunno, when i started lifting, my left arms was almost a whole inch smaller than my right. I tried to even them out as much as possible. and still to this day, they are still like this. not as much, but still the same.
btw, what did u have done on ur knee? I might have to be getting something done as well. I have a "floater" or rather piece of dead cartilage swimming around in my knee cap. every once in a while it will get lodged in funny and i wont be able to straighten my leg, or bend it. its not to pleasant.
--good luck..........