In many hospitals the femoral component of a hip arthroplasty is cemented but the acetabular component is used cement free [hybrid total hip reconstruction (THR)], mostly according to the press-fit principle; it is, however, pathohistologically verified, from surface replacement of the femoral head and the knee joint, that forces are transmitted through the rim of the cup, and that behind the cup a severe bony atrophy develops as time goes on (Draenert and Draenert 1992). Not all knowledge from studies on femoral components has been applied to the cementation technique of the acetabulum. Cementing the acetabulum must take into consideration that cement never should remain unconstrained, and should if ever possible be reinforced by bony structures, therefore the compact bone of the roof must be opened till the cancellous structure is freed.