Hip joint prosthesis having a zirconia head and a ceramic cup

An acetabular cup having a monolithic socket for receiving a ceramic femoral head having a surface roughness Ra of no more than 50 nm, wherein the improvement comprises the monolithic socket consists essentially of YTZP and has a surface roughness of no more than 50 nm.

A knee joint prosthesis comprising:

• a) a femoral component having a base and a plurality of tynes extending therefrom in the same direction, and
• b) a tibial plate having a surface shaped for receiving the tynes,
• wherein the tynes have an outer surface comprising zirconia partially stabilized by between 2 mol % and 5 mol % rare earth oxide and a surface roughness of no more than 100 nm, and wherein the surface of the tibial plate receiving the tynes is a ceramic having a surface roughness of no more than 100 nm.