Failed Metal-on-Metal: Full of Puss, is it Infected?

While metal-on-metal (MoM) surface bearings have regained popularity in total hip arthroplasty (THA), recent publicity regarding adverse local tissue reactions (ALTR) and systemic ion production has led to increased focus surrounding the failures of this bearing surface. The purpose of this review is to highlight the literature regarding clinical presentation of failed MoM THA, and the difficulty in differentiating these cases from periprosthetic joint infection (PJI). A PubMed literature search using MeSH terms “metal on metal” AND “hip” AND (“replacement” OR “arthroplasty”) AND (“reaction” OR “infection”) yielded 19 relevant articles from 2008–2012 regarding ALTR in THA. Included in these were 7 studies discussing MoM reactions and PJI. The most common symptoms in patients with adverse response to MoM bearings were groin pain aggravated by weight bearing; fever and elevated inflammatory markers were not uncommon in this population. Presence of “creamy milk-stained fluid” under high pressure was frequently encountered intraoperatively. Three studies found perivascular lymphocyte infiltration (PVLI) as suggestive of metal hypersensitivity reaction; however, two studies reported PVLI to be nonspecific for MoM prostheses failures. Serum metal ion levels were not adequate indicators of ALTR. Eight cases of PJI presenting concomitantly with ALTR were reported and suggested metal reaction may predispose to bacterial infection. Studies concurred that negative bacterial cultures were the only reliable characteristic distinguishing MoM reaction from PJI. Overall, the literature showed few conclusive diagnostic differences between the two conditions. Further studies will be required to definitively diagnose ALTR in MoM bearings preoperatively.