IMO, there are no exersises that will give you the results of squats for legs. i know from personal experience. you'll hear people say you can build monser legs without squats but i disagree.
take a good month off form squats or anything where you're using your tendons.
take extra stregth glucosamine and when you get back into lifiting, don't go heavy. use good form, do slow negatives and slow on the way up (to protect the tendons) and don't use your back. that way only your leg muscles will be doing the work. also, do a good 6 sets of leg extensions at 15 reps as your first exersise before squats without swinging to pre-exhaust the quads. that way, you won't have to go so heavy and you'll avoid injury.
don't wait long in between sets. this will further decrease the weight that you have to use to get a good workout.
if you're going heavier than 6 reps to faliure, WEAR KNEE PROTECTION. and if you're doing hack squats, wear knee protection AT ALL TIMES. even for warmups.
remember, slow negitve and slow on the way up is how you're gonna nurse and baby your knees. that and using FULL range of motion are most important. going all the way down without boucing and all the way up is better than putting more weight to compensate for the decreased range of motion. this will put MORE stress on the tendons. they act like breaks on a car when you only go half way down to come back up. they wear out eventually. full range of motion is the key but you CAN'T dive down on the negative or explode up.
and don't ever do what you were doing to get your knees so messed up in the first place. keep working out like this forever.
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"When you got love for something, there isn't really much you wouldn't do to do it." - Ronnie Coleman | 
