Any suggestions?

I have glass knees...had osgood slaughters disease as a teen (one part of the knee grows too fast for the other part)...I outgrew that for the most part, but developed all kinds of complications in my knees from it...

whenever i try to add size and strength to my knees i get counterproductive results...when i try to move up to heavy weights in squatting, my knees eventually start hurting when i walk...I feel like my lower body is not as strong as it should be, and i experience alot of pain in my legs when playing basketball...

I was told that leg extensions are not good for someone with my condition...I squat with light weights, do leg pressed with light weights, but it seems like even then my knees feel a little stiff afterwards...

So what the hell else can I do to strenghten my knees and strengthen my legs as a whole without hurting my knees?