Metallosis is a late uncommon complication of knee arthroplasties due to prosthetic loosening or component displacement. Oxinium prosthesis used to have components that attempted and proved to decrease prosthetic wear and consequent metallosis in the past. However, new studies showed that a combination of a shallow anterior tab snap-fit locking mechanism and thin dovetail lips make it susceptible to polyethylene dislocation and prosthesis loosening. The following case report show metallosis development in a 69-year-old female patient with a 20-year history of stage IV left gonarthrosis (Kellgren and Lawrence classification) who underwent a total knee arthroplasty (TKA) with a high-flex PS Genesis II prosthesis (Smith & Nephew, Hertfordshire, UK). We discuss the role of the material and her rheumatoid arthritis background in orthopedic mechanical failure. It is crucial that designers focus on the improvement of locking mechanisms and polyethylene properties.