August 2012 Van Der Straeten C1, Grammatopoulos G, Gill HS, Calistri A, Campbell P, De Smet KA. Read Complete Study Here: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3549185/pdf/11999_2012_Article_2526.pdf The interpretation of metal ion concentrations and their role in clinical management of patients with metal-on-metal implants is still controversial. We questioned whether patients undergoing hip resurfacing with no clinical problems could be differentiated from those with clinical (pain, loss of function) and/or radiographic (component malpositioning, migration, bone loss), problems based on metal ion levels, and if there was a threshold metal level that predicted the need for clinical intervention… We retrospectively identified 453 unilateral and 139 bilateral patients with ion measurements at minimum follow-up of 12 months (mean, 4.3 years; range, 1 – 12.9 years)… Well-functioning group ions were lower than the poorly functioning group ion levels. The acceptable upper levels were: chromium (Cr) 4.6 μg/L, cobalt (Co) 4.0 μg/L unilateral and Cr 7.4 μg/L, Co 5.0 μg/L bilateral. The specificity of these levels in predicting poor function was high (95%) and sensitivity was low (25%). There were more males in the well-functioning group and more females and smaller femoral components in the poorly functioning group. Metal levels higher than these proposed safe upper limits can predict problems with metal-on-metal resurfacings and are important parameters in the management of at-risk patients.