Find out the cause of the itchy dry knees. Generally, itching on the knee is likely caused by the presence of tinea corporis infecting the dry skin of the knee.
Wash with hydrogen peroxide and scrub the knee with a rough brush to get rid of the layer of dry skin and dead cells.
If itching occurs on the back side of the knee where the bend is, for example, on an obese person who cannot straighten the legs and the bend of the knee is always in a fold, then the itch may be due to the presence of tinea cruris. It really does not matter. Wash with a lot of hydrogen peroxide again and again until the skin is bleached and the itching stops.