Thank you both a lot, Becky and Matt.
You're right, Becky, horrible Vets can be found everywhere. The problem is, the not negligent and responsible ones are very difficult to find here.
Well, I have to be just. One of our Pits was walking constantly on three legs , we took her rapidly to a Vet(another one of course) who made an x-ray, gave her antibiotica, anti-inflamatorias and a med against pain. It didn't change anything.
We then brought her in a clinic in another town. There they gladly discovered immediately, that the x-ray wasn't interpreted correctly. They also moved the knee stronger and said, that the space for the main bone was too big. This obviously since birth but within the years of moving it must have increased. Yesterday she had surgery and they implanted a larger "bone". Now of course she still limps and we can only hope, it will be ok after the surgery wounds are healed. At least the stitches seem to be done very thoroughly and on the whole she is doing almost too well! Just have to give her meds and keep her in the kennel for about two days. She tends to be very jaunty once she feels well.