Trunnion Corrosion as a Cause of Recurrent Pseudotumor

With the introduction of second generation metal-on-metal (MM) hip implants in the mid-1990s, increased interest has arisen regarding the local biological effects of metal wear particles and ions on soft tissues, which have been grouped under the term adverse reactions to metal debris (ARMD). When these reactions constitute a soft tissue mass, they are usually referred to as a pseudotumor [15]. Histological studies of these masses have shown the presence of features characteristic of a non-specific inflammatory reaction (macrophages and wear particles) but also the presence of perivascular infiltrates of lymphocytes that are suggestive of a hypersensitivity reaction [3, 7, 13]. The first description of a hip implant-related pseudotumor was made in 1988 with a metal-on-polyethylene (MPE) bearing. The mass was attributed to a local response to metal ion release from corrosion at the Morse taper head-neck junction [16]. In 2008, a report of a multisurgeon experience with MM hip resurfacing arthroplasties (HRA) estimated that pseudotumors occurred in approximately 1% of patients within 5 years, but acknowledged that with time, the incidence of these pseudotumors may increase [15]. A year later, the same group reported on 16 cases of pseudotumors that went to revision surgery [6]. Five cases required re-revision for instability and loosening, and three of these cases had evidence of pseudotumor recurrence at the time of revision. We report on a patient who, after a hip resurfacing, presented with a pseudotumor that recurred after conversion to a conventional MPE total hip replacement (THR). Our hypothesis is that the recurrence was caused by ongoing corrosion at the Morse taper junction between the titanium stem and the cobalt-chromium-molybdenum (CoCrMo) head. The patient consented for the publication of this case.