What Causes Bump On Knee And Wrist?

Hi I have a random bump on my knee about the size of half a marble (but a little more elongated.) Anyway, this doesn't seem like a regular swelling or blister: it is hard and bone like, almost as if there was a build-up of calcium over my kneecap. I have never broken any bones, however I am a very active person. I have also noticed a similar, bone-like bump (a lot smaller: the size of a pimple) over my wrist. The bumps do not hurt, I just don't know where they came from.