Knee arthoplasty: recently developed ceramics offer new solutions.

Knee arthroplasty has reached a high degree of reliability. Many of the remaining long-term loosening cases are due to the polyethylene wear debris. The introduction of the alumina ceramic to polyethylene bearing couple had been a promising means for its reduction. The discussion of its applications in total knee replacements shows the possibilities and limitations of this bearing couple. The complete avoidance of the polyethylene debris can be expected from the articulation of alumina ceramic against itself, as long-term follow-up studies of total hip replacements clearly indicate. However, this combination can only be considered with a design of the prostheses in which any incongruity of the articulating surfaces can be excluded. As this necessitates the introduction of an additional component into the relatively narrow space between the femoral condyle and the tibia replacement, a further condition is the availability of a material which, whilst maintaining the tribological advantages of the alumina ceramic, has a much higher mechanical strength than the medical grade alumina ceramic available before. As the specifications of a recently developed modification of an alumina ceramic are in the desired range, with an improvement by a factor of two for nearly all relevant properties, a total knee replacement in which all articulating surfaces are in complete congruity and consist of this extremely wear resistant modified alumina ceramic could be designed, manufactured, and tentatively implanted in a human cadaver knee.