Hard coatings for orthopedic implants

Abstract

Total hip replacement (THR) surgery is currently a common and successful procedure, but THR implants sometimes fail because of aseptic loosening after relatively short periods of time. Observations from retrieved femoral and acetabular TH R components have shown that scoring of both bearing surfaces occurs; scoring of the metallic femoral head components is a result of abrasion by bone cement debris embedded in the ultrahigh molecular weight polyethylene (UHMWPE) acetabular cups. To reduce wear of these bearing surfaces the feasibility of applying titanium nitride (TiN) coatings to Ti–6Al–4 V femoral heads is being investigated. In vitro wear tests of TiN coated Ti–6Al–4V against UHMWPE and TiN coated Ti–6Al–4 V have been performed using a pin on disc wear testing device. Early results showed that the wear is different for each wear couple. The UHMWPE has been found to wear initially by removal of residual machining marks and then by removal of thin layers of polymer. Pins consisting of TiN coated Ti–6Al–4V run against UHMWPE discs had a thin polymer transfer film and were lightly scored. Untreated Ti–6Al–4 V pins under the same conditions also had a thin polymer transfer film, but were scored more severely and caused slightly more polymer wear than the TiN coated pins. When TiN coated Ti–6Al–4 V pins were tested against TiN coated Ti–6Al–4 V discs the character of wear differed. The predominant wear mechanism involved oxidation.