[Iatrogenic "metalloma" (titanoma) caused by implant failure in "metal-backed" patellar joint surface replacement]

Patellofemoral problems frequently provide the cause for revisions after total knee replacements (TKR). Problems with metal-backed patellae, in particular, have been reported on in the past, with a failure rate of 33%. As a result of implant failure, there is an increase of polyethylene and metallic wear, which eventually leads to a synovialitis and metallosis. We report a case of a iatrogenic induced metallosis of the knee joint resulting from failure of a metal-backed patella component with the formation of a substantial pseudotumor within the popliteal fossa. Intraoperatively, a browny-grey, knotted and hard structure was to be seen, which histologically imposed as a hyalinated scar tissue with black particular deposits. Energy dispersive X-ray microanalysis showed a high level of titanium within the intra- and extracellular deposits. In differential diagnosis these findings were postulated as "metalloma" (titanoma). In cases of periprosthetic pseudotumors, particular those with implant failure, a iatrogenic-induced metalloma should be considered.