Initial stability of press-fit acetabular components: an in vitro biomechanical study.

Component shape, surface finish, and presence of holes for adjuvant screw fixation should all affect initial stability and hence long-term fixation of total hip acetabular components. We conducted a study to determine stability against edge loading and torsion in commercial implants that differed in these design variables. Components were seated into synthetic cancellous bone blocks, and loads and insertion energies necessary to seat the components were measured. Components were then edge-loaded or twisted to failure. Compared with several hemispherical components, an elliptical component without holes and sintered beads had significantly more stability under both loading conditions. The presence of more holes in hemispherical components significantly improved stability in edge loading but not in torsion. Finally, plasma-spray and small-bead coatings showed improved stability compared with fiber-mesh and large-bead coatings.