As the number of arthroplasties increase, so do the number of hypersensitivity reactions to protheses. Although immunological reactions are infrequent, when they do occur they may be life-altering. There is growing evidence that metal hypersensitive patients experience poorer outcomes after surgery. Despite this, it is not known whether implant failure is caused by metal allergy or whether metal allergy results from sensitisation due to metal ion release from failing devices. However “it is a generally thought that hypersensitivity testing should be performed using validated methods in patients with a documented or suspected medical history of metal allergy, especially in those undergoing MoM joint replacement and when the causes of any loosening are doubtful.” Granchi et al 2012
Additionally: “MELISA test could help the surgeon in selecting the most appropriate and tolerated implant material for the patients and may benefit the performance of the implantation by decreasing postoperative complications or revision surgeries.” Podzimek et al 2021
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Orthopaedic implants release metal debris through different types of corrosion. Metal ions bind to enzymes and cell proteins in the body and may be responsible for adverse immunological events as they may act as haptens. Delayed-type hypersensitivity (type IV) mediated by T lymphocytes is the most common type of hypersensitivity
MELISA (MEmory Lymphocyte Immuno Stimulation Assay) is a clinically validated blood test which measures the antigen-specific T cell response to a suspected metal allergen. Used to detect Delayed-type hypersensitivity (type IV) which is mediated by antigen specific T-cells. The test can identify individuals who may suffer side effects from metal exposure and pinpoint which metals to avoid.
Lymphocytes are isolated from whole blood. The suspected allergens to be tested are added in 2-3 dilutions and incubated for 5 days. A positive control (Pokeweed) and 3 negative controls are also established. 3H thymidine is added and its uptake from allergen specific dividing lymphocytes is measured. Lymphocyte proliferation is reported as a Stimulation Index (SI). An SI above 3 represents a positive reaction to an antigen. The presence of lymphoblasts and dividing lymphocytes is also confirmed by morphology.
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