What can we do to prevent swelling in the leg, and constant cramps and strains in the knee area?

Wear. Compression hose to prevent the selling but i would be more concerened with the cause. Get checked by your doctor.
Leg swelling. This depends completely on what is causing the leg swelling etc. As there are many possibilities. It is important to report this to your doctor so you can be examined for the cause of the problem. Then proper treatment of the cause will help you.