@knirky: I ruptured my meniscus (left knee internal) in 1984 I was 22 then, I was playing football and I just heard it snap, I thought my knee was broken.
I was really worried but a Dr told me it was the meniscus and all I could do was have it removed. I didn't like the idea so once the pain ceased I just didn't think about it, but apparently the tear was big because every now and then when I made a sudden move my knee would just lock up and I couldn't pass a certain level with it, I would have to give it a sudden jerk (which was very painful, (if you saw Lethal Weapon 2 were Gibson gets out of a straight jacket by disjointing his shoulder you get an idea of what it was like) sometimes I'd take 6 or 8 shots of whiskey just to get the courage to make the move.
But eventually I decided I wanted it removed and had all the tests done, but a friend of mine who had one removed told me you didn't quite end up the same, he said it felt like one leg was longer than the other one. So I didn't remove, and continued having my knee lock every once in a while, but the last time it was so severe it really hurt when I fixed it and I think I tore right through the meniscus because that was about 11 years ago and it hasn't locked anymore even though it does feel kind of weird but no pain.
You have to decide if you want it fixed, remember I live in a third world country, medicine isn't up to the standards you have in Germany so maybe your experience could be much better than what I could expect here, I don't know what modern options you have.
I do know that I was told the recuperation time would be about 6 weeks.