About two weeks ago I got my first real injury from hammering. My wrist began to feel weak and a little numb. It would also "click" when I moved it around. I suppose I gave myself some accute arthritus. It was caused from a modification I did to my main hammer when the head was coming loose. I hammered a steel wedge in through the top which caused the handle to rattle everytime I struck it against my work. This rattled my wrist pretty badly, and in a few days I think I destroyed a good amount of cartilage in my wrist.
I took a break after that, kept my wrist still, and waited for it to feel right again. I also put a new handle on my hammer so it wouldn't rattle my wrist again.
