Metallosis Following Non-Metal-on-Metal Hip Arthroplasty: A Case Report and Review.

Introduction: Metallosis which is traditionally associated with Metal-on-Metal (MoM) hip arthroplasty can occur with other bearing surfaces too, posing diagnostic challenges. They can be asymptomatic or present with local and systemic symptoms. This article reports a case of metallosis in a total hip replacement (THR) with metal on polyethylene (PE) articulation who presented with dislocation. It also reviews the pathology and various presentations of metallosis following hip arthroplasty. Case Report: A 35-year-old female patient presented 4 years after a left THR with recurrent dislocation. It was an uncemented prosthesis with metal on PE articulation. Serology and radiological investigations were done to evaluate for infection, implant loosening, implant malposition, etc. The femoral stem appeared to be in varus malposition. She was posted for revision surgery with a pre-operative plan to change the femoral stem and head if necessary. Intraoperative signs of local metallosis were noticed. Debridement was done along with the change of the femoral stem and bearing surface to ceramic on PE. Metallosis was also later confirmed by the histopathological report. The patient has been symptom-free during the 2-year follow-up period. Conclusion: Metallosis can occur even in non-MoM articulations and a high degree of clinical suspicion is required to detect the same preoperatively. Classical signs of metallosis can often be absent in the early disease and subtle signs of instability must be looked out for even in the absence of obvious misalignment in radiographic assessment. Metallosis when combined with malposition or malalignment can be more detrimental. If detected early before osteolysis and periarticular soft tissue damage sets in, a complete revision of all the implant components and abductor damage can be avoided. In suspected cases, a lower threshold should be adopted for sending blood and joint aspirates for cobalt-chromium levels.