Abstract
Introduction: Total hip arthroplasty (THA) is a commonly performed and highly successful surgical procedure. Metal-on-metal (MoM) THA implants were introduced two decades ago and subsequently recalled due to high early revision rates. Acetabular cup erosion and fragmentation secondary to chronic edge loading causing delayed instability are rare but devastating complications of MoM THA warranting expeditious revision surgery. Case Presentation: We report a 70-year-old male with a history of bilateral MoM THA who presented with left hip instability. In addition to the radiographic and clinical features of hip instability, macroscopic examination at revision surgery revealed extensive erosion and fragmentation of the antero-superior margin of the implanted cup, osteolysis, and widespread metallosis of the periarticular soft tissues. Discussion: This case highlights a significant adverse complication of MoM THA. Despite the industry's wide discontinuation and recall of these implants, MoM hip arthroplasty implants are present in many patients, who are all at risk of developing similar complications. Guidelines for the surveillance and treatment of both symptomatic and asymptomatic MoM THAs have been reported, although ambiguity remains in the optimal approach for managing patients with existing MoM THA. Conclusion: Failure of MoM hip arthroplasty is most commonly the result of adverse reaction to metal debris. We present a novel mechanism of failure in a patient presenting with late instability due to asymmetric wear of the MoM bearing surface.. While it is uncertain whether early intervention in this patient may have prevented this complication, arthroplasty surgeons should be aware of the various modes of failure for MoM hip implants, as expeditious revision surgery is often required.