[Hydroxyapatite ceramic coatings for anchoring components of hip joint prostheses (technical aspects)]

Following the positive clinical results obtained with pure hydroxyapatite ceramic in the form of granules, the development of coatings of this material for anchoring components of artificial joints was initiated 6 years ago with the aim of improving implant bone bonding. Among the various coating procedures available, the plasma spraying process alone would appear capable of producing coatings which meet the requirements of a bioactive and osteotropic layer between bone and implant, in particular with respect to coating thickness and bond strength. However, the plasma spraying process at first seemed to be out of the question because of the high process temperature involved. After studying the factors affecting the transformation mechanism, it proved possible to suppress the phase transformation by a suitable preparation of the hydroxyapatite ceramic powder, and a combination of particular process parameters. The coating process and the quality checks are described in detail, and the properties of the coating compared with the requirements it has to fulfill.