Abstract: A modular prosthetic acetabular cup for use in restorative hip replacement has an augment which can be attached to an acetabular cup outer shell to provide an acetabular cup with a cross section of a desired configuration. The augment can be attached to the acetabular cup by a coupling element having an outer dovetail portion which slidably engages a groove formed within the augment preferably open to at least a first end thereof. The inner end of the coupling element can engage screw holes of the acetabular cup. The groove of the augment further includes a second end having a gradually increasing distance from the outer surface of the shell and the inner surface of the augment on moving towards the second end of the augment.