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
Case characteristics

A 68-year-old female, six years after a complex revision total knee arthroplasty (TKA) with an endoprosthetic hinge device, presents with distal thigh pain and an eccentric periosteal mass adjacent to the medial diaphyseal cortex.

Clinical diagnosis

The radiographic characteristics of the periosteal mass suggested a neoplastic process, but the histologic review of the lesion at the time of wide marginal excision showed the lesion to be a pseudotumor.

Differential diagnosis

Preoperatively, based on radiographic review and CT scan of the lesion, we strongly suspected the mass to be a neoplasia; we did not suspect this lesion to be a pseudotumor.

Laboratory diagnosis

As with any abnormal presentation involving a TKA, infection must always be ruled out first. Our laboratory tests included CBC with differential, ESR, and quantitative CRP. We also performed a knee aspiration, sending the fluid for cultures, Alpha-defensin, Synovasure® and cell count analysis.

Imaging diagnosis

For this case, we utilized mutliplanar radiographs and a CT scan of the femur and knee.

Pathological diagnosis

Visual review of the tumor showed the mass to be cystic with a dark grey inner complexion and a cavity filled with sero-sanguinous fluid. Histologic examination of the mass showed characteristic cells and structures consistent with a metal debris induced pseudotumor.


The tumor mass was thought to be neoplastic; therefore, we performed an en bloc removal of the distal native femur, femoral endoprosthetic construct, and tumor mass.

Related reports

In the entire Medline literature, there are only 5 case reports describing a pseudotumor about a TKA; of these 5 reports, only one was, in our opinion, a true metal-induced pseudotumor.

Term explanation

Pseudotumor: a non-neoplastic, sterile, cystic lesion that develops as a result of an inflammatory reaction to small particulate metal debris.

Experiences and lessons

In the face of a recent joint replacement surgery of the knee, pseudotumor formation is a more likely diagnosis than a neoplastic process when an expanding mass is encountered.