Metal Release in Total Knee Arthroplasty: A Review of Mechanisms, Adverse Local Tissue Reactions, and Biological Effects.

Compared to the hip, where investigators associate metal release with adverse local tissue reactions (ALTRs), metal-related complications in total knee arthroplasty (TKA) remain controversial and underexplored. Primary TKA systems use monobloc components, limiting corrosion and subsequent concerns. However, like the joints they replace, metal components degrade in vivo. In this narrative review, we aimed to summarize clinically relevant knowledge on metal release within the context of TKA for practicing orthopaedic surgeons. We asked: do ALTRs associated with metal release occur in the knee, and if so, to what extent? To answer this research question, we identified in vivo degradation mechanisms, including wear, mechanically assisted crevice corrosion, and electrocautery damage. Next, we synthesized case reports and retrospective clinical studies documenting ALTRs in primary and revision TKAs. Then, we reviewed the biological response to cobalt chrome debris, focusing on genotoxicity, immune responses, and hypersensitivity. While clinical evidence suggests that patients rarely experience severe biological reactions like pseudotumors, ALTRs associated with metal release can and do occur following TKA. To overcome knowledge gaps related to the prevalence of ALTR in TKA, prospective clinical trials are needed.