Orthopedic implant allergies: a review of current knowledge on metal hypersensitivity and prosthesis failure

Metal hypersensitivity is an increasingly recognized factor in orthopedic implant failure, particularly in patients undergoing total joint arthroplasty (TJA), and may contribute to persistent pain, aseptic loosening, or early revision. This review synthesizes current evidence on the underlying immune mechanisms of metal hypersensitivity and explores their potential role in implant-related complications such as chronic inflammation, pain, and aseptic loosening. A systematic literature search was conducted using Embase.com and complementary databases; relevant studies involving patients with suspected or confirmed allergic responses to metallic orthopedic implants were identified and integrated into a narrative review of clinical presentations, diagnostic strategies, and outcomes. Diagnostic approaches remain variable and include clinical evaluation, dermatological patch testing, in vitro assays such as the lymphocyte transformation test (LTT), and histopathological examination of periprosthetic tissues, with no current consensus on a gold-standard method. Although metal hypersensitivity is associated with a subset of implant failures, the strength of evidence is limited by heterogeneous study designs, variable diagnostic criteria, and inconsistent reporting of outcomes. Future efforts should focus on standardizing diagnostic protocols, validating predictive tests, and developing patient-specific management algorithms - particularly regarding implant material selection - to improve care for patients with suspected metal allergies in orthopedic surgery.