Knee injuries, what exercises can I do?

I have knee injuries do to a very bad fall and I find even walking can be painful after awhile. Is there anything I can do to strengthen them? Serious advice please!

I also injured my knee, it was a long time ago..let me see if I can remember what I did...um you can sit in a chair and straighten out your leg and flex it, kinda with your heel down and the toe straight up, um..I think I also did squats, lunges...really any exercises that you use the leg muscle. I would talk to your doctor and have them give you physical therapy exercises. Just remember because it is injured you don't want to push it or you'll injure it further.

One way to strenghen the muscles around the knees is to cycle or spin. The key is to spin the pedals at about 80 rpm the fast spin will make your knees, and legs stronger. This is no impact and less prone to more damage that can occur if you use your legs to lift weights.

Ride a stationary bike. It help me strenghthen my back and legs from injuries.