Ross is right in that if you keep doing what you are doing you will start numb yourself to pain in that area which is what Muay Thai boxers do with shins.
Back in the day we had Makiwara boards, what Kane was talking about.
http://www.ctr.usf.edu/shotokan/makiwara.html
Also if you strengthen you hands and grip you will be able to clench a fist tighter which in some cases will aid in preventing bone movement when hitting, but you have to make sure that you close your fist tight and not leave it loose like a boxer. (all of which has been said.)
Also you could have the tightest and most dense fist ever but you are going to break your wrist if you don't know proper alignment for punching.