Design, construction and modularity of pressfit acetabular cups

To enable a comparison of different pressfit acetabular cups objective criteria are essential. The aim of this study is to describe the design features of this type of cup and to analyse currently available cups. 30 implants were systematically measured and analysed. The mean surface roughness (R-a) was determined and configurations established with the light section technique. For further evaluation the cups were transversely sectioned. The cups are made of pure titanium, titanium alloy or polyethylene coated with titanium. Five implants take the form of monoblocks. The configuration is predominately (n = 25) flattened spherical. The size of eight cups corresponds to the outer diameter, 19 cups have a larger outer diameter (overdimensioning), 3 cups have a smaller outer diameter (underdimensioning). The magnitude of overdimensioning is, on average, 1.9%. 9 cups are provided with plugs, hollow cylinders, fins or rings as outer stabilizers. Surface roughness achieved with corundum blasting is 6.8 mum. Titanium porous-coated implants have a surface roughness of 21-32 mum. 24 cups have polyethylene inserts, most of which are snap-fixed with equatorial lips. For 16 cups, full-ceramic inserts are available. 4 cups have a metal insert. Titanium implants with structured or HAC-coated surfaces have become the accepted standard for cementless acetabular cup implantation. Together with ceramic, metal, or modified polyethylene inserts they meet the requirement for permanent osteo-integrative stability.