what happened then
I think expecting checkin agents to be familiar with all the modern medical apparatus is a bit much. So as a first pass the check in agent says please can you remove it.
Hopefully at that point your friend and his surgeon friend and his paperwork explained the detail, and the agent gracefully backed down or sought a supervisor? This is kinda normal in customer services where the front line person knows the rules, but isn't familiar enough with all the infinite variations and goes and gracefully gets help when something they'll encounter every ten years occurs?
G