Metallosis is the infiltration of periprosthetic soft tissues and bone by metallic debris. The debris is most commonly from wear of metallic prosthesis (usually of the metal-backed polyethylene patellar prosthesis), but metallic debris can also be generated from hinged prostheses and, as in the case shown above, repetitive contact of fractured prosthesis components.
The particles can lead to metal-induced synovitis, and the release of cytokines by histiocytes stimulated by the metallic debris can lead to significant osteolysis.
Patients often present with pain and a joint effusion, usually 1-2 years after surgery.
Radiographs reveal periprosthetic metallic debris, and sometimes a dense joint effusion is seen. In more than half of patients, a thin opaque line outlines the periprosthetic pseudocapsule: The so-called metal-line sign or bubble sign. (The metal-line sign can also be seen after intraarticular injection of gold salts and dissolution of migrated lead bullets into the joint). Osteolysis may complicate the picture, and a high index of suspicion is appropriate.