Published online May 18, 2018. doi: 10.5312/wjo.v9.i5.72
Peer-review started: January 6, 2018
First decision: January 23, 2018
Revised: January 30, 2018
Accepted: February 28, 2018
Article in press: February 28, 2018
Published online: May 18, 2018
Core tip: Pseudotumor formation is a biologic response to microscopic metal particulate debris observed in metal-to-metal total hip bearings. It is considered non-existent in total knee arthroplasty (TKA), where the bearing surface articulates metal-to-ultrahigh molecular weight polyethylene. This report describes a rare case of pseudotumor formation in an endoprosthetic hinge TKA, as a result of femoral stem loosening with metallic debris exiting through a small crack in the distal femoral diaphysis. This case reveals that pseudotumor formation should always be considered when evaluating an expanding mass around a TKA.