Metal hypersensitivity in total knee arthroplasty

Metals used in total knee arthroplasty cause hypersensitivity reactions in some patients. These reactions are known to be immune-mediated and are more likely to affect individuals with pre-existing metal sensitivity, but their mechanism is not fully known. It is difficult to predict pre-operatively whether a patient will be affected and there is no reliable investigation to guide implant choice. There appears to be little value in screening all patients for metal sensitivity before implantation as various studies have shown no significant difference in outcomes or failure rates post TKA in patients with history of metal sensitivity. However, the existing assessment tools are not specific enough to identify subtle problems with potential metal sensitivity association.

Symptoms of hypersensitivity reactions following total knee arthroplasty are often non-specific and difficult to differentiate from other acute presentations following total knee arthroplasty, for example infection. Metal hypersensitivity reactions are often a diagnosis of exclusion, and for this reason they are most likely under-diagnosed and under-reported. Management is controversial but periprosthetic hypersensitivity reactions will often ultimately require revision if no other cause is found. Metal debris are a concern in total hip arthroplasty and could represent another cause of metal-related pathology in total knee arthroplasty. Non-metallic materials are currently in development which may represent a preventative solution for metal hypersensitivity reactions in total knee arthroplasty, potentially also addressing additional concerns around the use of metallic implants such as the high density and thermal conductivity of the material in comparison with the replaced tissue.