I have damage to both knees. I had surgery in 2008 to fix an ACL partial rupture and cartilage shave in the right knee, and have a partial tear in my MCL in the left (all down to rugby), which cannot be operated on. I do find my knees can get tight and painful, however gentle stretching helps, as does trying to keep the weight down (not much luck with that). I wouldn't say it stops me doing much, apart from running hard/fast (don't do a lot of that anyway), and as stated before, a positive mental attitude goes a long way to combating it