An implantable prosthesis comprises a polyethylene prosthetic member that is substantially transparent to x-rays and a radiographic marker that is substantially opaque to x-rays. The radiographic marker is configured as a tension spring arranged as a continuous ring encircling the prosthetic member....http://www.google.de/patents/US5405402?utm_source=gb-gplus-sharePatent US5405402 - Implantable prosthesis with radiographic marker
