My dad was a pilot, who happened to start his career flying in Vietnam. His first tour he was shot down over water and picked up about an hour later. He said his knee hurt like hell. Dr gave him a shot of something and sent him on his way.
22 years later, he found out his ACL was partially severed in that knee. 22 years. Good times.
Did he end up having the surgery once he found out?
Nope. He was on the road to knee replacement, but doing a lot of self-imposed PT to strengthen his quads, and losing weight on WW, has gotten things back to almost normal.