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.

The dimensional changes of hip sockets of total endoprosthesis of the Müller Type are subject of this article. Regular-anterior/posterior radiographs of the pelvis were taken to determine the orientation of the center of the prosthetic head in relation to the wire marker of the poly(ethylene) cup. Further measurements were done using casts of worn acetabular cups gained at revisional surgery. The possible errors of measurements of both methods are discussed. Both, creep and wear contribute to the dimensional changes of the hip sockets, the proportional amount of each mechanism is not known. Data from laboratory examinations suggest a relatively high rate of creep in the early time of function. With longer periods the dimensional changes are predominantly caused by wear. In the beginning of joint function our measurements show a high rate of the yearly dimensional change. The shift of the head amounted 0.5 mm per year and diminished after five years to rates of 0.15 to 0.2 mm. All dimensional changes that exceed a shift to the head of 0.2 mm per year are considered to be unfavourable and to contribute to loosening.