Abstract: Knee prosthesis with mobile congruent insert, presenting four well differenciated parts: a tibial part (1), a femoral, patellar part (2) and another part which replaces the meniscus of a human knee. The femoral and tibial parts are metal parts whereas the part which is called insert and substitutes the patella and the meniscus is made of plastic material more particularly polyethylene of ultra high molecular weight, and reproduces in its upper portion the geometry of the femoral condyles and in its lower planar portion has a bore (8) wherein is housed a pivot (4, 18) provided on the tibial tray (5, 19). The tibial part (1, 17) is comprised of a platen (5, 19) and an cross-shaped pin which prevents the rotation of the prosthesis once implanted.