[munificent]

A fistula from a piercing connects two surface exits to each other, like a wormhole through your body. Once complete, the piercing touches nothing internal to you, just skin.

But in this case, the prosthetic must penetrate through the skin to connect to bone.

[failrate]

Then transdermals as popularized by Steve Haworth. They go through skin and are mounted to flesh and bone.

[roarcher]

I'd have the same question about them. I'm not disputing that it works, I just don't understand how the body isn't constantly fighting it. Or leaking.

[failrate]

In the case of the Metal Mohawk, it actually was difficult for the owner to maintain. He kept bumping the spikes on things and eventually had them removed. Granted, his was a cosmetic change and not a functional one. I would be willing to put up with extra care to effectively replace a hand. Additionally, consider that people who receive donor transplants will use immune suppressants for the remainder of their life. That said, material selection is also important.