Materials & Methods

Based on clinical computed tomography data and a method previously published [1], volume and shape information of a representative defect, chosen in consultation with four senior hip revision surgeons, was derived. Volume and shape of the representative defect was approximated by nine reaming procedures with hemispherical acetabular reamers, resulting in a simplified defect with comparable volume (18.9 ml original vs. 18.8 ml simplified) and shape. From this simplified defect (Defect D), three additional defect models (Defect A, B, C) were derived by excluding certain reaming procedures, resulting in four defect models to step-wise test different acetabular revision components. A surrogate acetabular model made of 20 PCF polyurethane foam with the main support structures was developed [2]. For the exemplary test, three series for Defect A were defined: Native (acetabulum without defect), Empty (defect acetabulum without filling), Filled (defect acetabulum with BGS filling). All series were treated with a pressfit-cup and subjected to dynamic axial load in direction of maximum resultant force during level walking. Minimum load was 300 N and maximum load was increased step-wise from 600 N to 3000 N. Total relative motion between cup and foam, consisting of inducible displacement and migration, was assessed with the optical measurement system gom Aramis (gom GmbH, Braunschweig, DE).