MoM vs. PJI: That is the Question

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Authors: Aggarwal V, Parvizi J, Tischler E, Gordon P, Austin, M.
The Rothman Institute at Thomas Jefferson University Hospital, Philadelphia, PA

Title: MoM vs. PJI: That is the Question

Background: Metal-on-metal (MoM) bearings gained recent popularity in total hip arthroplasty (THA).  However, reports of adverse local tissue reactions (ALTR) have led to increased focus surrounding the failures of this bearing surface. 

Hypothesis/Purpose: The purpose of this study is to review major clinical findings from cases of failed MoM THA, to recognize the difficulty in differentiating these cases from periprosthetic joint infection (PJI), and to present an algorithm for diagnosing patients with ALTR vs. PJI.

Methods: We identified 9 patients out of 1054 revisions done at our institution (2005-2012) who underwent revision THA for ALTR due to MoM bearing surface.  In addition, a PubMed literature search using selected MeSH keyword terms yielded 14 relevant articles presenting a total of 54 patients from 2005-2012 who experienced ALTR in THA.  For all 63 patients, the corresponding clinical presentation, laboratory and imaging results, and intraoperative gross and histopathologic findings were identified.

Results: Groin pain aggravated by weight bearing was the most common presentation occurring in 68.2% of patients with reported symptoms. ESR was normal in 60.7% of cases and CRP was normal in 54.9% of cases. Synovial white blood cell count and differential showed a widely varying range of mean values.  Intraoperatively, “creamy” fluid was present in 59.4% of aseptic cases with intraoperative data.  In addition, metallosis was noted in 43.8% of aseptic cases with intraoperative data. Histopathologic results varied widely with only 58.8% of patients displaying perivascular inflammation and lymphocytic infiltrate suggestive of metal hypersensitivity.

Discussion: Overall, the literature demonstrates few diagnostic differences between ALTR and PJI. 

Conclusion: We propose a diagnostic algorithm to approach this challenging issue, yet further methods need to be developed to differentiate ALTR from PJI in MoM bearings.