My character is an ex-sailor in his early twenties who in the past has suffered a (non-combat) knee injury that forced him to leave the Navy. For the purpose of the plot, he has to be able to walk around and run for short distances, but he suffers from at least some pain and has some sort of limit on his activity (like he probably can’t ever take up long-distance running or be a snowboarding champion). Maybe he has to wear a brace, or he walks with a slight limp. The main thing is that I need the problems from this injury to be permanent. The character is meant to be depressed, is out of work and has a drinking problem, and part of the depression is that he feels like he's already "ruined" and will never quite be the same again, so there should be no hope of it being 100% fixed by surgery or whatever means. I'd also prefer if the injury is something that can be caused by something relatively "normal," like sport or running or lifting, rather than anything dramatic like an explosion. Apart from that, the details are flexible.
I have googled "knee injury permanent damage" "knee injury chronic pain" and the like, with no luck. I can find plenty of examples of bad knee injuries, but they all seem to have a limited recovery time after treatment, or at the very worst, they’re fixed by surgery and then can cause problems 10 or 20 years down the line, and my guy is too young for that. This is great for those of us here in the real world, but it's making it very hard for me to torture my character.
Any ideas about what kind of injury could do this, and the extent of the problems it would cause? Thanks in advance!