Observations at the articular surface of hip prostheses: an analytical electron microscopy study on wear and corrosion.

We used scanning electron microscopy in combination with X-ray microanalysis to evaluate Co-, Cr-, and Mo-based human femoral hip prostheses. In total, 23 retrieved implants and four new implants were included in this study. Scanning electron microscopy of the polished surface of all arthroplasties showed, in addition to the polishing marks, small round and angular holes or pits. Other types of surface irregularities were interpreted as wear or corrosion of the metal compound. In all cases studied, corrosion propagated from holes at the surface of the polished prosthesis heads, in some cases also along phase boundaries. X-ray microanalysis of the intact prosthetic surface showed a relative composition of the elements Co, Cr, and Mo, which was in agreement with the manufacturer's information (63:33:4%). However, X-ray microanalysis spot analysis of the surface holes showed deviation in the relative composition of the elements Co, Cr, and Mo and also the presence of Si, Ti, and Al. Furthermore, Ti and Al could be traced back at an artificially made fracture plane of a new prosthesis. Therefore, Ti and Al have to be present during the manufacturing process. These impurities in the metal prosthesis alloy may create a galvanic element with the Co, Cr, Mo alloy of the implant. If this is the case, such a galvanic element in combination with the electrolyte environment formed by body fluids, can induce galvanic corrosion with release of metal particles.