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
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.
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.
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.
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.
For this case, we utilized mutliplanar radiographs and a CT scan of the femur and knee.
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.
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.
Pseudotumor: a non-neoplastic, sterile, cystic lesion that develops as a result of an inflammatory reaction to small particulate metal debris.
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.