How to heal a few callus that my husband has in his knees?

We know that they sell some stuff to use in your toes, but what about the knees?How to heal a few callus that my husband has in his knees?
As long as there are no open sores or cuts on the knees, it is fine to use the same medication on your toes and knees. If they are thoroughly callused, a file may be useful in getting rid of the dead skin. Beware that the knees will be more tender after using the file and medication, though.