I'm starting doing push up at home, leverage for an easy start. When I place my hands on the edge of a sharp edge, like bed edge, my wrists are hurt. When I gripping a round bar, the hurt disappears. I know I shouldn't push up with the sharp edge anymore, but I would like to learn the mechanism behind that, for education purpose.
Compare the angle of your hand to your forearm when gripping a sharp edge vs gripping a bar. I think you'll find you are bending your wrist farther backward (maybe even "bottoming out" the joint) when gripping a sharp edge and increasing the strain there.