Analysis of the migration of the cemented Muller hip cup versus the cementless Zweymuller hip cup.

Objective: Is the cementless Zweymuller hip cup superior to the cemented Mu ller cup? Method: This article presents a radiographic analysis of 25 cemen ted Muller acetabular cups versus 22 cementless Zweymuller cups using the E inbildrontgenanalyse (EBRA), a software tool for radiographic measurement o f acetabular cup migration. In addition, we determined the effects of the c up anteversion and inclination, the polyethylene wear, the lateral bone cov erage of the acetabular cup, the position of the center of rotation, and in dividual factors on the incidence of cup migration. Results: The incidence of cup migration was 64% in the cementless group and 48% in the cemented gr oup after a mean follow-up of 6 years. The average migration rate was 0.33 mm/a for cementless Zweymuller cups and 0.38 mm/a for cemented Muller cups. Cup anteversion and inclination showed no effect on the incidence of cup m igration. The combination metal-polyethylene (0.17 mm per year) demonstrate d a significantly higher wear rate in comparison to the ceramic-polyethylen e combination (0.11 mm per year). Incompletely lateral covered cups demonst rated a significantly higher incidence of cup migration. Cranial or medial deviations of the center of rotation up to 5 mm are tolerable, in contrast to caudal or lateral deviations that lead to a significantly higher inciden ce of cup migration. Conclusion: The superiority of the cementless Zweymull er cup was not observed. We recommend a complete lateral bone coverage of t he hip cup. Cranial and medial deviations of the center of rotation up to 5 mm are tolerable. In the present study the polyethylene wear of the cerami c-polyethylene combination was significantly less as compared with the meta lpolyethylene combination.