MIGRATION ANALYSIS OF SCREWED ACETABULAR COMPONENTS AFTER REVISION ARTHROPLASTIES IN THE HIP - RESULTS OF THE EINBILDRONTGENANALYSE (EBRA)

Out of 57 revised acetabular components, which were regularly checked, 47 had been replaced by a cemented Muller's acetabular reinforcement ring resp. a cementless Muller's Sl-shell with flange. Both types of c ups are anchored in the acetabular roof with cancellous bone screws (t ab. 1). 42 cases with radiograph series permitted a detailed analysis with the EBRA-method, a computer aided method for the evaluation of ac etabular spatial migration based on standard radiographs of the pelvis . The clinical results were very satisfying (tab. 6.). The screwed ace tabular components migrated little, although, some essential displacem ents of the center of rotation (in relation to the anatomical position ) had to be accepted. As was recognizable with today's inaccurate meth ods of measuring the center of the head, the displacement too far towa rds cranial influenced the migration tendency less than an excessive l ateralisation. Especially satisfying is the fact, that no increased mi gration was observed after reconstructional bone grafting of severe ac etabular defects, provided that at least a partly direct contact betwe en the acetabular component and the original bonestock was obtained. F or the first time EBRA shall be introduced here as a method which show s the migration and the spatial inclination of the acetabular cup in a vectoral chart.