Case Report
Copyright ©The Author(s) 2018. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Orthop. May 18, 2018; 9(5): 72-77
Published online May 18, 2018. doi: 10.5312/wjo.v9.i5.72
Periosteal pseudotumor in complex total knee arthroplasty resembling a neoplastic process
Madhav Chowdhry, Matthew V Dipane, Edward J McPherson
Madhav Chowdhry, Matthew V Dipane, Edward J McPherson, LA Orthopedic Institute, Los Angeles, CA 90057, United States
Author contributions: All authors contributed equally to this paper in regards to conception and structure of this case report, data collection, literature review, drafting, critical revisions, and final approval of the final version.
Informed consent statement: A written informed consent was taken by the participant before the beginning of the study.
Conflict-of-interest statement: The authors of the study have no potential conflict of interest to declare.
Open-Access: This article is an open-access article which was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See:
Correspondence to: Edward J McPherson, MD, FACS, Director, LA Orthopedic Institute, 2200 West Third Street, Suite 400, Los Angeles, CA 90057, United States.
Telephone: +1-213-2075660
Received: January 5, 2018
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

This case report describes in detail an erosive distal diaphyseal pseudotumor that occurred 6 years after a complex endoprosthetic hinge total knee arthroplasty (TKA). A female patient had conversion of a knee fusion to an endoprosthetic hinge TKA at the age of 62. At her scheduled 6-year follow-up, she presented with mild distal thigh pain and radiographs showing a 6-7 cm erosive lytic diaphyseal lesion that looked very suspicious for a neoplastic process. An en bloc resection of the distal femur and femoral endoprosthesis was performed. Histologic review showed the mass to be a pseudotumor with the wear debris emanating from within the femoral canal due to distal stem loosening. We deduce that mechanized stem abrasion created microscopic titanium alloy particles that escaped via a small diaphyseal crack and stimulated an inflammatory response resulting in a periosteal erosive pseudotumor. The main lesson of this report is that, in the face of a joint replacement surgery of the knee, pseudotumor formation is a more likely diagnosis than a neoplastic process when encountering an expanding bony mass. Thus, a biopsy prior to en bloc resection, would be our recommended course of action any time a suspicious mass is encountered close to a TKA.

Keywords: Pseudotumor, Total knee arthroplasty, Metallic wear debris, Loose implant

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.