Pseudotumor in total knee revision arthroplasty resembling heterotopic ossification: A case report

Pseudotumors are well-known complications following total hip arthroplasty (THA), usually attributed to debris-induced inflammation from direct metal-on-metal contact between implants. In total knee arthroplasty (TKA), the traditional use of polyethylene as a bearing surface prevents direct metal articulation. Thus, pseudotumor formation in TKA usually suggests atypical metal interaction between the prosthetic components. We presented the case of a 65-year-old male who developed a progressively growing mass in the left posterior knee after revision TKA, debuting as heterotopic ossification (HO) based on the radiographic assessment. Subsequent histopathological examination establishes the diagnosis of a pseudotumor. Pseudotumors impose a diagnostic challenge in TKA due to their non-specific presentation and imaging, which may overlap with other etiologies. Currently, there are no standardized guidelines for pseudotumor assessment in TKA, and each case should be approached individually without relying on a simple diagnostic tool. Physicians should consider a comprehensive approach supported by a high index of suspicion to include pseudotumors within the differential diagnosis of knee periprosthetic masses. •Pseudotumors occur due to debris-induced inflammation from metal-on-metal contact between implants.•Pseudotumors are common complications following total hip arthroplasty yet are very unusual in total knee replacement.•We describe a pseudotumor following revision total knee arthroplasty, initially diagnosed as heterotopic ossification.•This report highlights the need for a comprehensive approach when assessing knee periprosthetic masses.