[He blanket answer of 'an accident' won't cut it here.] Caught in a grenade blast.

[It says enough. Years later, the traumatic event still replays itself in his dreams although not as often as before. He looks to his hand contemplatively, metal fingers smoothly flexing and curling.]

It works as you would expect any other prosthetic - - but because it's military grade tech, it has added versatility to get a soldier out of a pinch.