Eosinophilic Metallosis: A Newly Described Entity in Failed Metal-on-Metal Arthroplasty

In recent years, metal-on-metal (MoM) orthopaedic implants have been associated with significant adverse tissue reactions, prompting revision surgeries and recalls by manufacturers. Adverse tissue reactions consist of a wide range of pathologic findings but are generally characterized by a histiocytic reaction to metal debris, with or without an inflammatory response. Inflammation is generally that of a lymphocytic infiltration that prompts concern of an immune reaction. Only occasionally have eosinophils been documented-never as a marked infiltrate. In this article, we present the first histologic description of a dominant eosinophilic infiltrate associated with MoM arthroplasty. In our case report, the patient is a 53-year-old woman who presented with recurrent fluid collections surrounding the hip after a MoM total hip arthroplasty. At the time of surgical revision, tissue samples were taken and found to consist of lymphocytes and a prominent infiltrating eosinophilia. To our knowledge, no factors predictive of this type of tissue response have been identified, and its significance remains unclear despite ongoing research about the nature of the immune response to metal. Future work may help to elucidate whether the type and significance of this response can be predicted preoperatively and modulated, if necessary, postoperatively.