Clinical experience with Mueller total hip endoprostheses of different design and material.

Patients of the Orthopaedic University Hospital in Frankfurt operated between 1970 and 1977 were examined to control the success of implantations of total hip endoprostheses. Ninety-three percent of totally 1497 implanted hip prostheses are Müller standard type, additionally there have been implanted 44 Weber-Huggler prostheses and 54 special long stem prostheses. During the follow-up period of 10 years 7.4% of the primarily implanted prostheses had to be revised. The reasons for revision were loosening of the stem and/or socket in 56% of the cases, 20% infections, 14% technical errors and in 11% of the cases fractures of the stem occured. Fifty-two percent of the implanted Weber-Huggler prostheses with rotational ball heads made of polyester had to be revised in the meantime, 78% of the cases because of loosening of the prosthetic components. It could be shown that the number of infected cases could be diminished after introduction of an ultraclean air operating box. The change of the cross section of the Müller-type-stem from a round medial wedge to a flat one and the introduction of CoNiCrMo wrought alloy Protasul-10 instead of CoCrMo cast alloy Protasul-2 as stem material in 1973 resulted in a much smaller rate of loosened prostheses without fractures of the forged Protasul-10 stems. During the 6 examined years there has been no fracture of a prosthetic stem made of Protasul-10.