For theraputic excercises, you are going to want to go high rep, low weight. The muscles in the knees are very small and respond better to high rep excercises. If you are looking to bulk up your legs, then go for lower rep, heavy weight exercises. Stationary lunges are good. Try this: Do 15 stationary lunges forward, 15 to the side, and 15 to the back. Its a little funky at first, but you will get used to it within the first few reps. Do that for each leg at least once per day. Also do pistol squats. For those, balance on 1 leg and life the other leg about 6 inches off the ground. Squad down using your one leg and barely tough the raised leg to the ground. Do this 15 times to the front, side, and back just like the lunges. The third and final exercise for therapy (as well as losing weight) is stand on the bottom step of a set of stairs in your home. Keeping 1 leg on the very top, lower your other leg down until it touches the lower step. Do 20 per leg.
This is a great cardio exercise too. Try not to rest too much between sets. That will keep your heart rate up. DON NOT FORGET TO STRETCH!!! Stretch your legs at least once (its better if you do it twice) per day. Take 10 minutes and do a full lower body stretch. Your knee muscles/legaments/tendons are very sensitive and if you are having knee pain, you may just need to stretch it to recover from the injury. Im pretty well versed in the area of therapy, diet, and excercise, so if you have any more questions, feel free and PM me.