[Experimental results of stepped titanium shafts for hip endoprostheses]

Among the materials which can be used for hip prostheses to be implanted without bone cement, ceramics and titanium possess the best overall properties for insuring long-term stability in the light of present knowledge. However, considered separately, the two materials are most suitable for different special requirements. Results of long-term animal experiments conducted by different working groups on functionally stressed hip and tooth-root implants made of bio-inert Al2O3 ceramic and titanium have furnished knowledge of the possibilities and limitations of the adaptation reaction of the bone tissue. The present authors investigated whether, by combining Al2O3 ceramic and titanium, a cement-free total hip replacement can be adapted to specific local stresses, taking biomechanical rules and anatomical factors into account. In recent experimental series it proved possible to limit the problems which had occurred in previous series, reported elsewhere. Positive results in dogs led to a human implant which has so far been used 15 times, with Al2O3 (FRIALIT) acetabula and heads, which have been implanted successfully for a number of years, in combination with the new stepped titanium shaft. In addition to a short review of follow-up findings thus far, the results of the experimental investigations are presented.