Make a small hole in a titanium screw, either ingrave the privkey inside that cavity, or insert something durable with the privkey engraved on it within the cavity. Seal it. Now, go and break your arm, insert a few screws to fix it. The screw with the privkey goes along with the other screw. If somebody ever asks, just say you were in a horrible ice skating accident when you tried to qualify for the nationals. Privkey secured. Retrieval might be another matter, but you're in this for the long term, no?
This is a bad idea. Not only should you not hurt yourself to keep your money safe, but you would also need to further hurt yourself to be able to spend your money. In order for cold storage to be effective it not only needs to be safe from attackers but also allow you to be able to spend your money with semi ease.
You would also risk that the doctor would put in the incorrect screw in your arm (you would not be able to put them in yourself)