for example, going on a hike with one bum knee means for every big step up and big step down you probably relied on your good knee to carry the load. And knees/ankles/quads/Achilles/shins are designed to share the load...

When I got my first severe ankle injury I tried getting back too early. Leading to a catastrophic knee injury (Patellar grade 2, MCL grade 2, ACL grade 1 and shredded knee cap), leading to more back problems and soreness on my good knee. Years of PT and rehab and I am just now getting back to being physical beyond what a 6th grader can do...