Comparison of in vivo cementless acetabular fixation

Cementless fixation in total hip arthroplasty is increasingly popular because of the failure rates of cemented components, particularly in younger patients. The reported European studies with cementless acetabular implants and the relatively short-term American studies suggest that loosening is not a problem with any of the designs in clinical use. This point of view is reminiscent of that regarding cemented acetabular components prior to the realization that cemented acetabular failure was a delayed long-term phenomenon. Cementless acetabular components are principally of two types, threaded and porous coated. Prior to this study, there was little clinical or experimental evidence to indicate which design gains superior fixation and which is most likely to maintain long-term fixation and durability. Fixation of threaded and porous-coated components was evaluated mechanically and histologically in dogs after weight-bearing periods of two and six months. The threaded specimens were significantly looser than the porous-coated specimens at both two and six months. There was a trend toward loosening of both types of components with time. Fibrous tissue alone appeared to invest all of the threaded components, whereas bone and fibrous-tissue ingrowth appeared to incorporate the porous components. The mineral apposition rate for the components was not significantly different between the two components or between different regions in the specimens.