I crushed my left leg in '72 in a head on collision on Interstate 80. Confused old guy came down an exit thinking it was an entrance and kept barreling down the road. Didn't walk for a couple of years. I have had constant pain since, but you get used to it. Tore the meniscus in the right leg 7 or 8 years ago. High pain threshold meant I didn't do anything about it until it was too late. Now both knees are bone on bone. However, a good therapist gave me a combination yoga/stretch/exercise routine that has kept me mobile. I am not running or jumping, but I can kickstart my bikes and otherwise do what I need to. Only downside is that between my routine, a hot shower, ablutions, and breakfast, it takes me an hour and a half just to start my day.
Ed from NJ