In any design or method of cup fixation the one limiting factor is the space available within the variable quality of the acetabular bone stock. With the acrylic cement, having ensured the quality of bone-cement interface, the cup position/orientation can be adjusted within the polymerising cement mass.

With “cementless” techniques the room for manoeuvre is limited. The aim is to prepare the cavity to accept a press-fit symmetric cup into a predetermined position and orientation. This becomes more complex with increasing dimensions of hard on hard articulations and even more so when the need to preserve the femoral bone stock becomes the guiding principle.

Attempts to establish the “safe zone” for cup position and orientation gained priority [1].

With the Charnley technique the operative details were stated [2] and the long term results published [3].