I am by no means an expert on this subject, but I think I have a useful thing to add. I think about these things a bit differently now that I'm bordering on middle-aged.
I assume that you guys talk this stuff over with your doctors before doing something like this, right? I know several people who have joint damage in their hands from various sources. It is impossible to adequately describe the debilitating nature of serious joint damage and the damage might not be reversible. Also, it might seem like you're adapting now and getting tougher and better, but I don't think that means that you're not causing permanent long-term damage. Not being a doctor, I can't be sure of this assertion. I sure as heck can't be sure of the opposite statement -- can you? If you're not a doctor then you can't.
If there's any kind of serious risk of long-term problems, then you should steer clear of this kind of stuff. You only get one set of hands and will be borderline handicapped if you mess them up. Also, you'll be a lot better fighter when you're older if your hands actually work.
There's no way I would consider doing anything like this without a doctor's advice. A martial arts instructor (with all due respect) might focus on turning you into a better fighter NOW, more than whether you are able to write, type, etc when you're older.
That's my two cents worth. I emphasize again that I'm not claiming to be an expert on this subject.