My experience with musk ox is that it WILL eventually shrink. I have a Treeman knife with a nice piece of musk ox and it has shrunk over the past couple years. Sent it back and they filled in the gap with 2-ton epoxy......other than re-handling and using a different material, I think it's the best fix available.

Unfortunately, if you have a musk ox handled knife.....be prepared to be a little disappointed.....I think it's inevitable.