I got hit had on by an 85 mph drunk back about '74 or 5, I was about 26. Crushed a knee cap and cut the tendons in two. Killed the drunk. He was in a big old Lincoln. I was pulling a gooseneck loaded with a tractor and such, probably what saved me. It took a year before it would bend half way.
Now at 74, my joints are good, but that leg will sometimes just fold. You should have seen me the last time on a ladder and it folded!!