Analysis of a failed alumina THR ball head.

The favourable properties, on which is based the successful history of the use of alumina in orthopaedic surgery, are due to the tough control made by manufacturers on the whole process from raw materials purity to the quality controls. The minimum requirements of a medical grade alumina are stated from 1981 in ISO 6474 standard. Nevertheless, due to the voluntary character of standards, and lack of national and international laws, it was possible in the past to introduce into the market materials with characteristics not in compliance with the standard ISO 6474. A THR implanted on a fifty years old patient was revised three years after implantation, due to the failure of the alumina ball head. To understand the causes of such an early failure, the fragments of the retrieved ball head were submitted to a series of non destructive and destructive controls. The results show that the poor quality of the design and manufacture of the implant was the origin of the failure.