Re: Metal on Metal warning The latest from the US of A on this subject - also gives some information on the sensitivity of metal ions: Surgeon discusses rate, presentation of metal allergy in joint replacement Although metal allergy with total joint replacement exists, the prevalence of this condition is unknown, according to Joshua J. Jacobs, MD. “Metal allergy [with] orthopaedic implants has been well documented in isolated cases,” Jacobs said during his presentation at the American Academy of Orthopaedic Surgeons 2012 Annual Meeting/Orthopaedics Research Society symposium. “The true prevalence is unknown. Clinically significant symptomatologies seem to be rare in total knee replacements and metal-on-polyethylene total hip replacements, but much more common in metal- on-metal total hips. Based on case reports and device literature, Jacobs said that metal allergy exists and has been seen as a temporal association. It can have different presentations and many involve a rash. In some examples, patients suffer skin reactions after implantation of total joint replacement devices. In other cases, the reaction goes away after the implant is removed for nonunion or refracture, only to return after re-implantation. “In my mind, those sorts of cases prove to me that this is a real clinical entity,” Jacobs said. Using patch testing, 14% of the general population would be sensitive to nickel and 10% would be sensitive to cobalt and chromium. However, Jacob said that patch testing may be flawed because it may have no bearing on what is occurring happening in deep tissues. “Metal-on-metal allergy is the cause of clinical symptomatology, such as pain and swelling,” Jacobs said. These allergies present as skin reactions such as dermatitis, or patients may have a history of allergy to jewelry. The responses to these allergies can present as stiff knees, pseudotumors, necrosis or unexplained pain, Jacobs said. “In patients with metal-on-metal surface replacements, there is a direct correlation between serum metal levels and metal sensitivity determined by [lymphocyte transformation testing] LTT,” Jacobs said. “Current diagnostic methods, both patch testing and in vitro, do require more robust clinical validation, but it can be useful in preop screening for patients with in vitro metal allergies when there is a history of reaction to jewellery.” Reference: Jacobs JJ. Clinical manifestations of metal allergy. Adverse reactions to byproducts of joint replacements (AAOS/ORSI). Presented at the American Academy of Orthopaedic Surgery 2012 Annual Meeting. Feb. 7-11. San Francisco.