Case Report: Pseudotumor due to Trunnionosis in Ceramic‐on‐Ceramic THA Monoblock Acetabular Cup Disengagement

Adverse local tissue reaction (ALTR) and pseudotumor formation, representing inflammatory responses to wear debris that lead to osteolytic lesions, remain major long‐term complications of total hip replacement. Hard‐bearing total hip prostheses with improved tribological properties—particularly large‐diameter head (LDH) ceramic‐on‐ceramic (CoC) bearings and preassembled cup designs—have been introduced into clinical practice to minimize wear, increase the range of motion (ROM), and reduce dislocation rates. We describe the case of a young asymptomatic patient with a CoC total hip arthroplasty (THA) featuring a monoblock acetabular component, in whom a pseudotumor was incidentally detected. The lesion was associated with trunnionosis following spontaneous liner disassembly, which occurred without any clinical symptoms or audible signs such as the typical hip “clunk.” This case highlights the diagnostic challenges in identifying periprosthetic adverse reactions in asymptomatic patients and emphasizes the importance of timely recognition to prevent technically demanding revision procedures in catastrophic implant failures.