We observed the surface structure of alumina ceramic prosthesis after clinical use to elucidate it's wear mechanism. The knee prosthesis (Kyocera co., Ltd.) had been used in 4 patients suffering from osteosarcoma of the distal femur, and those were retrieved at autopsy. The joints consisted of alumina ceramics in the femoral component and high density polyethylene (HDP) in the tibial component. All patients had been fully weight-bearing. The periods from limb sparing surgery to removal ranged from 13 months to 4 years. The surface of the weight bearing and non-weight bearing areas of the retrieved joints were observed under a scanning electron microscope.
The surface of the alumina ceramics showed a polygonal crystal structure scattered with small holes. The density of the holes tended to increase in the weight bearing areas more than in the non-weight bearing areas. With regard to the HDP, a large number of linear scars were found to run in the direction of the joint movement. These results suggest that wear of the HDP in alumina ceramics joints in vivo occurs as a result of the tearing off of alumina ceramics crystals and the interposition of these crystals between the femoral and tibial components.
