Particulate gold as an anti-inflammatory mediator in bone allograft---an animal study.

Morselized allograft is widely used when increased bone stock is needed in implant surgery. Gold ions liberated from metallic gold surfaces act in an anti-inflammatory manner by inhibiting cellular NF-κB-DNA binding and suppressing I-κ B-kinase activation. This study investigated the effect of 45-63 μm sized gold particles mixed in morselized allograft. It was hypothesized that bio-released gold ions would influence allograft reabsorption, increase mechanical stability, and further stimulate osseointegration. A pair of 10 mm long implants surrounded by a 2.5-mm gap was inserted in proximal part of each humerus in 10 sheep. Each gap was filled with morselized allograft with 1.29 mg gold particles or nothing. Observation time was 12 weeks. The gold ion liberation was visualized by autometallographic tracing and showed liberation of gold ions. Biomechanical push-out tests and stereological histomorphometric analyses showed no statistically significant differences in the two groups. Although particulate gold was primarily observed surrounded by bone marrow tissue, no obvious clinically relevant short-term effects could be measured using gold as an anti-inflammatory mediator. These findings show that the released gold ions have only influenced cells adjacent to the particles without influencing the fixation and illustrates gold ions' limited field of effect. We suggest a new design for orthopedic implants by introducing gold dots on the prosthesis surface. This aims at suppressing the inflammatory foci along the implant-bone zone and reduces the risk of chronic inflammation before aseptic loosening without affecting bone remodeling. This implant model will be investigated in further studies.