I know someone who's just had surgery for something very similar...though I don't know if they had the blackened fingers. I don't know the name of the condition
(sorry!),but apparently its hereditary,and causes the fingers to curl in on themselves.. I recognised it because of the strange lumps/bumps on the palm of your hand.
This person is a volunteer I work with...her husband gave me most of the info,and apparently he has it too...not so advanced though...and he showed me the palms of his hands with the same tell tale bumps.
Wish I could give more info,and I don't expect to see either of these people until next week at the earliest.