Thank you very much everybody for your support and advice.
I consulted a nerve specialist and it is official now: my peroneal nerve is damaged. The nerve is examined (measured with some electrical tools). When the doctor used a taser-like tool and stimulated the nerve just above the damaged part, my foot lifted. Something I wasn’t able to do for several weeks. This means the axons of the nerve are not damaged, but the sheath of the axons are. This reduces the ability to conduct the normal impulse of a nerve cell. Electrical impulses will pass through the nerve, but not enough and therefore I cannot lift my foot. In another test a tiny needle measured some electrical activity in the muscle that should move my foot or toes, when I tried to move them as hard as I could. This also proves that impulses reach the muscle, but not enough.
The damage is not caused when I fractured my knee. I could move my foot an toes when I was examined at the first aid the evening I broke my knee. The nerve damage is probably caused during the week I had to wait for my surgery and my leg was fixed in a plaster cast. Because of the fracture my lower leg was displaced a bit outwards and backwards, so the peroneal nerve was more exposed than normal and got stuck between head of the calf bone and the cast.
It will probably recover completely but this will take several months to maybe more than a year.
No big deal at the moment. I still have seven weeks to wait until full weight bearing :-).