<p>The prosthesis has a tibial part comprising an anchoring portion to be inserted in a tibia, and a tibial plateau arranged at an end of the portion. An anchoring portion of a femoral part is inserted in a femur. A pivot (28) articulates the femoral part with the tibial part, and is rotatably mounted in a bearing of one of the parts. The bearing has a cylindrical opening with elliptical surface to receive the pivot. The elliptical surface is directed such that a major axis of elliptical section is perpendicular to a direction of extension of the anchoring portion of the tibial part.</p>
