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Effects of gold coating on experimental implant fixation

In their introduction, the authors refer to endoprostheses as being “a common end-stage treatment for degenerative joint diseases” and to the trend “that more and more younger patients receive” it. Up to 20% of all total hip replacements are said to be revisions, and “revision implants have an even shorter longevity and poorer functional outcome”. The authors’ study is therefore targeted at increased early implant fixation and increased implant longevity and investigates the gold coating of endoprostheses.

In the abstract they highlight that “insertions of orthopedic implants are traumatic procedures that trigger an inflammatory response. Macrophages have been shown to liberate gold ions from metallic gold. Gold ions are known to act in an anti-inflammatory manner by inhibiting cellular NF- B-DNA binding and suppressing I- B-kinase activation. The present study investigated whether gilding implant surfaces augmented early implant osseointegration and implant fixation by its modulatory effect on the local inflammatory response.”

Cylindrical porous Ti6Al4V implants were coated with gold and “inserted press-fit in the proximal part of tibiae in nine canines and control implants without gold inserted contralaterally. Observation time was 4 weeks. Biomechanical push-out tests showed that implants with gold coating had” a ~40% decrease in shear strength and ~50% decrease in shear stiffness. “Histomorphometrical analyses showed gold-coated implants had a decrease in overall total bone-to-implant contact of 35%.”

“Ion release was traced by autometallographic [AMG] silver enhancement.” “AMG revealed a release and uptake of gold ions in a small number of scattered cells” close to the gilded implant surface “most likely to be macrophages. AMG shows that some gold ions were released into the peri-implant space, where they were taken up most likely by macrophages”. Also the gold-coating may have “reduced growth of the osteoblasts responsible for bone remodelling, resulting in a reduced total bone-to-implant contact”.

The findings demonstrate that gilding of implants negatively affects mechanical strength and osseointegration because of a significant effect of the released gold ions on the local inflammatory process around the implant. The possibility that a partial metallic gold coating could prolong the period of satisfactory mechanical strength, however, cannot be excluded.” The authors therefore recommend that a “dosage-response study is needed in order to establish the exact amount of gold dotted on the implant surface that will have no influence on the fixation, but endow the implant with a permanent inflammatory-suppressing quality”.