Titanium lines: a manifestation of metallosis and tissue response to titanium alloy megaprostheses at the knee.

Titanium alloy, in its Ti-318 (Ti-A16-V4) format, is a widely used material for orthopaedic implants. However, it has frequently been reported as causing black staining of the periprosthetic tissues as a result of debris from metallic wear. This process of metallosis has been implicated in implant failure. We report three cases in which titanium alloy prostheses for primary bone tumours at the knee have caused the formation of fluid-filled cysts containing metallic debris. The cysts result in radiological appearances which may mimic soft tissue tumour recurrence and also contribute to post-operative failure of the extensor mechanism of the knee.