Knee prosthesis with four degrees freedom

1. A knee prosthesis for implanting in a knee joint including a femur and a tibia, the tibia having a longitudinal axis, the prosthesis comprising:

a femoral component defining a fixed axis of rotation;

a tibial component defining a hole and having a proximal-distal axis substantially parallel to the longitudinal axis of the tibia; and

a hinge assembly including a hinge rod and a pin connecting the femoral component and the tibial component, the hinge rod having a circular opening adapted to allow the pin to pass therethrough, the hinge rod adapted to slide in the hole of the tibial component, the hinge assembly defining a hinge axis that is transverse to the proximal-distal axis of the tibial component,

wherein the femoral component rotates about the hinge axis, and the hinge axis moves substantially along an axis substantially parallel to the proximal-distal axis of the tibial component upon flexion of the knee joint.

2. The knee prosthesis of claim 1 , further comprising:

a box having opposing walls formed on the femoral component;

the opposing walls each defining a circular aperture; and

at least one bushing adapted to fit in the circular aperture.

3. The knee prosthesis of claim 2 , wherein the hinge rod is capable of translating and rotating in the hole while the pin rotates in the circular apertures of the opposing walls.

4. The knee prosthesis of claim 1 , wherein, when compared to a known posterior stabilized knee prosthesis of a post-cam design having a femoral component with a constant radius cam, the fixed axis of rotation of the femoral component is located along an axis corresponding to the center of curvature of the constant radius cam.

5. A knee prosthesis for implanting in a knee joint including a femur and a tibia, the tibia having a longitudinal axis, the prosthesis comprising:

a tibial component defining a hole and having a proximal-distal axis substantially parallel to the longitudinal axis of the tibia;

a pin;

a hinge rod adapted to slide in the hole of the tibial component, the hinge rod having a circular opening adapted to allow the pin to pass therethrough; and

a femoral component being hinged to the tibial component and defining a fixed axis of rotation,

wherein the femoral component is adapted to rotate with respect to the tibial component about the proximal-distal axis of the tibial component, the femoral component is adapted to rotate with respect to the tibial component about a hinge axis transverse to the proximal-distal axis, the femoral component is adapted to translate with respect to the tibial component in a medial-lateral direction, and the femoral component is adapted to translate along the proximal-distal axis with respect to the tibial component, and

wherein the fixed axis of rotation of the femoral component is adapted to translate substantially along an axis substantially parallel to the proximal-distal axis of the tibia component.

6. The knee prosthesis of claim 5 , further comprising:

a box having opposing walls formed on the femoral component;

the opposing walls each defining a circular aperture; and

at least one bushing adapted to fit in the circular aperture.

7. The knee prosthesis of claim 6 , wherein the hinge rod is capable of translating and rotating in the hole while the pin rotates in the circular apertures of the opposing walls.

8. The knee prosthesis of claim 7 , wherein, when compared to a known posterior stabilized knee prosthesis of a post-cam design having a femoral component with a constant radius cam, the fixed axis of rotation of the femoral component is located along an axis corresponding to the center of curvature of the constant radius.