Nousiainen T, Palosaari S, Peraniemi S, et al. - A prospective cohort study was conducted to evaluate how cup orientation and type of pseudotumour ascertained by the Hart classification affect the distribution of metals in blood, synovial fluid and tissues surrounding the metal-on-metal hip prosthesis in revision surgery patients. Researchers screened 1,029 metal-on-metal hip patients and of those, 60 patients that had revision surgery due to adverse metal reaction were included. They examined whole blood, synovial fluid and synovial/pseudotumour tissue samples for metal ion concentrations (Co, Cr, Mo and Ti). The results demonstrate that implant orientation alone does not explain the metal concentrations found in tissues or distribution of metals between different tissues. In periprosthetic soft tissues, the accumulation of metals increase the total metal load, and in the presence of a pseudotumour, this is reflected in the transfer ratio of Co from synovial fluid to the blood. The total metal load of the pseudotumour tissue should be characterized in further trials to ascertain whether this will serve new insights for clinical practice.