QUO VADIS? THE RISKS AND BENEFITS INHERENT IN USE OF CERAMIC IMPLANTS FOR JOINT REPLACEMENTS?

Abstract

Alumina has been the dominant ceramic used in orthopaedics since 1970. It is near diamond hardness is superior to all other biomaterials and its wettability has been a great benefit for tribological reasons. Over the past 30 years, this ceramic has gradually been optimized with superior processing, higher purity, greater density, and somewhat higher strength. Also serial numbers have been added to uniquely identify implant components and proof-testing now ensures that every implant is pre-clinically tested, compared to prior methods of sampling only 2–3% for destructive tests. The clinical downside remaining has been the small but troublesome fracture incidence of alumina implants. Historically, this has averaged 0.015% (15 per 100,000 cases) overall but varied from 0.08% up to 13% in those clinical series experiencing fractures (Heros, Sem. Arthrop-98). As well as creating patient hardships, fracture of any implant in the USA frequently leads to major lawsuits. Thus ceramic implants must be treated w While there has as yet been no FDA-approval given to market ceramic cups in the USA, there are a number of ceramic candidates being developed for both THR and TKR. These include zir-conia-alumina composites as well as new zironia/zirconia or zirconia/alumina combinations for THR. In addition, there are new combinations of toughened aluminas and also other choices such as silicone nitrides proposed for use with either metal CoCr heads or CoCr cups. Finally an alternate approach has been to provide a metal zirconium knee joint with a ceramic zirconia coating for improved bearing performance. Thus, the state of the art of alumina implants will be reviewed and put into perspective with the “new and improved” ceramics currently on the horizon. This survey will put into perspective the physical and mechanical attributes as well as the clinical performance of ceramic implants.