Comparison of flanged and unflanged acetabular cup design

BACKGROUND AND PURPOSE Adequate depth of cement penetration and cement mantle thickness is important for the durability of cemented cups. A flanged cup, as opposed to unflanged, has been suggested to give a more uniform cement mantle and superior cement pressurization, thus improving the depth of cement penetration. This hypothesis was tested experimentally. MATERIALS AND METHODS The same cup design with and without flange (both without cement spacers) was investigated regarding intraacetabular pressure, cement mantle thickness, and depth of cement penetration. With machine control, the cups were inserted into open-pore ceramic acetabular models (10 flanged, 10 unflanged) and into paired cadaver acetabuli (10 flanged, 10 unflanged) with prior pressurization of the cement. RESULTS No differences in intraacetabular pressures during cup insertion were found, but unflanged cups tended to migrate more towards the acetabular pole. Flanged cups resulted in thicker cement mantles because of less bottoming out, whereas no differences in cement penetration into the bone were observed. INTERPRETATION Flanged cups do not generate higher cementation pressure or better cement penetration than unflanged cups. A possible advantage of the flange, however, may be to protect the cup from bottoming out, and there is possibly better closure of the periphery around the cup, sealing off the cement-bone interface.