Please advise me what type of knee injury causes foot numbness?

A few can...: The posterior knee injury with resulting fluid collection, formation of a large cyst may cause impingement on the tibial nerve supplying the foot. Also, while injuring the knee, one can have a back injury affecting the sciatic nerve supplying the entire leg.

Swelling: Swelling of the knee especially in the back of the knee can put pressure on the nerve and create numbness down the leg and foot. This is often seen with a bakers cyst of the knee.