Allergic reactions as differential diagnosis for periprosthetic infection

Metallic orthopedic devices are composed of elements known to be skin sensitizers in the general population and metal-on-metal hip prostheses in particular have the theoretical advantage of producing less abrasive wear than metal-on-polyethylene prostheses. However, there is concern about the possibility of hypersensitivity reactions with typical elicitors, such as nickel, chromium or cobalt. These materials are also used for total knee arthroplasty (TKA) and may elicit an immune response the role of which is still unclear in the outcome of arthroplasty. The immune response is dominated by perivascular T and B lymphocyte tissue infiltration around the hip replacement. The infiltrates are mostly surrounded by so-called high endothelial venules. This reaction is associated with periprosthetic osteolysis and aseptic loosening of the prostheses. The differentiation of hypersensitivity and low-grade infection is initially a diagnosis by exclusion using aspiration cultures. The final diagnosis is only resolved by histological investigation of synovial tissue. A close cooperation between orthopedic surgeons, pathologists and microbiologists is necessary to diagnose specific cellular differences in hypersensitivity and infection in tissue investigations.