"Do not implant!"--long-term follow-up of a patient who received a trial hip stem.

We describe the case of a patient who had undergone a total hip arthroplasty for primary osteoarthritis 17 years previously. Clinical and radiologic signs of aseptic loosening compelled a revision arthroplasty. Surprisingly, the removed femoral stem turned out to be a trial stem. Retrospective examination of the operative report revealed that at initial surgery the trial stem had become so tightly fixed that it could not be removed. The rectangular-shaped trial stem consisted of the same titanium alloy as the implantable stem, but had been coated with titanium nitride and polished. This coating prevented osseous integration but is also extremely wear resistant and chemically inert in the body environment. Consequently, a long-term "stable" painless anchorage of the prosthesis by mechanical interlocking alone was achieved.