Phase transformation of a new generation yttria-stabilized zirconia femoral head after total hip arthroplasty.

We examined a new-generation yttria-stabilized zirconia head manufactured by NGK 1 year after total hip arthroplasty. Monoclinic content of the retrieved head was twice that of the unused head at the pole and equator. A fourfold increase in monoclinic content was observed at 5 mm below the equator. Transformation from the tetragonal phase to the monoclinic phase occurred in the new generation zirconia with alumina doping within a relatively short period in vivo.