What Is The Best Treatment For Pain In The Feet?

i am recovering from a bad break on my right ankle which required surgery and a metal plate being inserted. it is still sore to walk on my right foot. problem at the moment is that my left knee is sore now if i kneel on the lower left hand side of my knee cap. it is not sore to touch or move just when i kneel. it feels like i've knelt on a stone. what is wrong with my knee?