Introduction: The articulating surfaces of a new metal-on-metal (MoM) hip prosthesis system were engineered with the ceramic Titanium-Niobium-Nitride (TiNbN) by Physical Vapor Deposition (PVD). The value of PVD technology rests in its ability to modify the surface properties of a device without changing the underlying material properties and biomechanical functionality. In addition to enhancing wear resistance, PVD coatings reduce friction and improve corrosion resistance and thus minimize metal ion release.

Purpose of the study: to investigate whether the elevation of the ion levels of chromium and cobalt, which is normally seen in the blood of patients after MoM hip arthroplasty, could be prevented by the use of the new MoM hip prosthesis with ceramic engineered articulating surfaces.

Materials and Methods: The ACCIS components are manufactured from casted hi-carbon Co-Cr-Mo alloy. Heat treatment reduces the block-carbides in number and size. The surfaces are polished and are micro-finished. Then the surfaces undergo TiNbN-ceramic surface engineering by PVD. The ACCIS prostheses for total hip- and resurfacing arthroplasty are manufactured by implantcast, Buxtehude, Germany.

200 ACCIS resurfacing hip prostheses were implanted in three centers: Morriston Hospital, Swansea, UK, Neville Hall Hospital, Abergavenny, UK and Arthro Clinic, Hamburg, Germany. Blood samples of 60 randomly selected patients were analyzed before surgery and at intervals of 3, 6, 12 and 24 months after surgery. Independent trace metal measurements were performed at the Universitätsklinikum Carl Gustav Carus Dresden, Germany.

Results: The Chromium concentrations were median 0,8215 (0,25–4,6) and the cobalt concentrations were median 1,34 (0,72–4,24)μ gr/L. None of the patients at any moment after operation showed significant increase of Cr and Co ions in the blood and ion levels above the normal limits as described in the Hand book for environmental medicine (1) were exceptional.

Discussion: The median concentrations of chromium and cobalt are significantly lower than levels published in the literature for other MoM metal prostheses. Because the ion level is believed to be a diagnostic tool to identify problems, the absence of an increase of the metal ion levels most probably demonstrates that wear of the metal surfaces can be only minimal (2).

Conclusion:

Surface engineering of metal articular surfaces effectively minimizes corrosion and metal ion release.