[Results of experimental testing of a screw-in in polyethylene acetabulum in sheep]

In 12 sheep 21 total hip endoprosthesis were implanted, using a polyethylene acetabulum, which was provided with a continuous conique thread for implantation without cement. Out of 14 non luxated hips only 2 acetabula were loosened. After an implantation between 1 week and 18 months the remaining 12 sockets were macroscopically stable and were examined radiologically and histologically. After 3 months of increased osteogenesis a layer of collagenous tissue developed between implant and bone. In the loadbearing area this layer is from 50-80 microns thick and often the ridges of the thread are stabilised by a thin layer of fiber-cartilage, expanding around the implant with longer implantation. Bore-holes in the thread are filled with partially lamellous bone after 6 months. Though sometimes a considerable amount of polyethylene wear particles caused by the disadvantageous and small shape of the sheeparthroplasty was observed, none of the examined acetabula showed any signs of loosening.