I feel your pain, had surgery on my left knee in which all of my quad muscles were detached from my knee and reattached in the proper place to hold my knee from dislocating. Now 16 months later my right quad is still bigger than my left but it's getting much stronger through excercise and training. Haven't done any isolation on just my left but since it was considerably smaller it had the capacity to grow fast and has almost caught up with my right quad. I'd say just work out squats and stuff and if it is still lagging badly isolate it until it catches up