[Experimental study of primary fixation of screw-ring acetabular components. Role of initial screw-cutting]

Three types of screw-ring acetabular components were implanted to determine the characteristics of their holding power and to study the influence of screw-cutting. The acetabular components were screwed into vinyl polychloride foam. Their resistance was measured. The optimal value of the locking screw couple and the value of the couple beyond the one at which the acetabular component loosened were determined. One of acetabular components was screwed in with and also without preliminary screw-cutting. Its resistance to wrenching was measured in both situations. The resistance curve at wrenching was characteristic of each screw-ring acetabular component. The resistance to wrenching was significantly higher (p < 0.01) for a given acetabular component if it was screwed into a largely open block of foam at its bottom. The screw-cutting allowed for a significantly higher resistance to wrenching (p > 0.05). It allowed for the screwing in with the least effort and for a better perception of the tightening. Knowledge of the comportment of screw-ring acetabular components once installed, usage of preliminary screw-cutting and recourse to a dynametric key are the means of improving the installation of screw-ring acetabular components.