I've just started having problems 26 years after a medial meniscectomy (age 19).
Apart from a few twinges its been fine - pain free - and I'm a big coward and hypochondriac!
I've always had automatic gears (left leg) and haven't been overweight - but I've also been a keen runner and recreational rock'n'roll dancer.
Unfortunately for me - my mid life crisis (age 45) has made me do one lesson in Judo - a fall has now caused problems in this knee.
I don't know whats wrong but it just feels weird? nothing specific - I can still walk, squat and I still run but it feels odd. I sometimes limp and have to concentrate to walk without a limp.
I'm going to see the gp(not optimistic) and a sports injury clinic to see if they have advice.
My initial injury was also caused by martial arts - my advice - keep away from martial arts!