My friend swears by lemons for her knees and elbows. She cuts them in half and rubs them in like you are making lemonade....she leans on a desk with her elbows in the lemons. I think she does it for around 10 minutes--she has great looking skin so it must be working for her. Would a foot pumice stone work with some type of scrub???? Also heavy lotion to keep your sking soft.
That stuff on the above post to rub and scrape the dirty skin sounds like a foot cream that would take the dead skin off your feet. Any beauty store or even drug store sells these products. I never thought of using them on my knees but I have one by Sally Hansen to use on my hands, that might work.