THE ABILITY OF VARIOUS ACETABULAR COMPONENTS TO RESIST PROTRUSIO MIGRATION

A foam model of a protrusio acetabulum with cylindrical voids of varyi ng diameters was used to test acetabular components for their ability to resist migration within the defect. A bipolar component, a hemisphe rical cup, and a hemispherical cup with peripheral rim augmentation we re tested in defects with diameters ranging from 1 to 3 mm less than t he major diameter of the component. The cup with peripheral rim augmen tation demonstrated 20% to 40% greater resistance to migration than th e hemispherical cup, depending on the extent of under-reaming, with th e bipolar component consistently demonstrating the lowest load to fail ure. The results of this study confirm the less-than-satisfactory clin ical results seen with bipolar reconstruction of protrusio acetabuli, and support the use of ''fixed'' cups in these settings.