Abstract
Ceramic-on-ceramic was shown to have advantageous tribologic properties (low wear and friction). For medical applications two ceramics, alumina and zircona, are available. This case study shows that the combination of different ceramics for hard-hard pairings can be critical.
A 57 year old patient received a total hip prosthesis (cementless stem with a ceramic head and a monolithic ceramic cup). Thirty-five months postoperatively the patient complained about squeaking noises during walking and stair climbing. Clinical diagnoses showed a good range of motion and no signs of loosening. Conventional rehabilitation did not improve the situation and 43 months after primary surgery the cup and the head had to be revised on the patients request. Intraoperatively no loosening indications were found. The explanted components were analysed using a 3D co-ordinate measuring machine.
The head and the cup were made of different ceramics. The zirconia (ZrO2) head occurred rather white whereas the alumina (Al2O3) cup was yellow-reddish. The inner articulating surface of the cup showed no decoloration or wear. The surface of the head contained mated areas with surface defects in equatorial regions (maximum wear depth 9μm).
The head and the cup were combined from different manufacturers. The distinct surface changes and wear marks of the zirconia head probably caused the squeaking noise after 3 years in situ. Zirconia for medical applications is generally Y-TZP ceramic. Pressure, heating, and water can cause severe surface embrittlement. Pre-damaging due to the manufacturing process or friction in the joint might be the mechanism leading to pre-mature wear and failure. Joint components from different manufacturers should only be implanted with proper official authorisation.
