I'm responding to an old post but what are you gonna when things are still this quiet. This seems like the busiest Sonic community here in the fediverse at least?

But I actually looked this up a little while back. Turns out Echidnas can actually grow some serious claws, which they use mostly to dig.

So I can see what they're going for / where they got the idea for Knuckles' design. They're probably legit claws.

And I seem to remember him chipping them in Sonic X, but it's not treated as an amputation or anything and later they're fine, so presumably they grow like claws / nails too.