Metal-on-Metal Total Hip Arthroplasties: Why Do They Fail?

Background: Metal sensitivity reaction is a major concern in painful failed metal-on-metal (MoM) total hip arthroplasty (THA), but it may not be the dominant failure mode. We investigated revised MoM THAs for failure etiologies, operative indications, and clinical outcomes. Methods: Ninety consecutive revised MoM THAs were reviewed. Preoperative evaluation included inflammatory markers, metal ion levels, radiographs, metal artifact reduction sequence magnetic resonance imaging, synovial fluid analysis, and operative histopathology. Outcome measures included advanced imaging and laboratory findings, revision etiology, and clinical outcomes. Results: Metal sensitivity reactions (MSRs) accounted for 36% of MoM failures, with 64% of MoM THA being revised for non-MSR-related etiologies. Failure etiologies not related to MoM bearing articulation included prosthetic joint infection (14%), aseptic loosening (13%), isolated abductor failure (7%), periprosthetic fracture (3%), recurrent dislocation (3%), symptomatic heterotopic ossification (3%), mechanical failure (1%), and angiosarcoma (1%). Additionally, 18% of patients had painful MoM THA with no identifiable failure etiology; of these patients, 69% had continued pain following revision. Patients with large periarticular fluid collections had an odds ratio of 19.2 (P =< 0.0001) of having MSR. Cobalt (Co) levels were statistically higher in patients with MSR compared to non-MSR-related failures ( Conclusions: The majority of revised MoM THAs did not have MSR. Large periarticular fluid collections and elevated Co levels were highly predictive of MSR. Painful MoM THA without an identifiable failure etiology resulted in a high incidence of persistent pain following revision.