Abstract: A prosthetic acetabular cup comprising a dome-shaped expandable shell having an annular rim portion (2) and an apex portion and a concave inner cavity extending therebetween for receiving a bearing liner; the shell further comprising an apex aperture (21) centrally disposed in the apex portion relative to a shell axis of rotation and a plurality of radially spaced slots (9) extending from proximal the rim portion to the apex aperture to define a plurality of shell segments expandable outwardly relative to the shell axis about a hinge portion connecting the segments together when an expanding force is applied at the aperture. The present invention provides a simple, correctable and mechanically stable means of inserting and securing a prosthetic acetabular cup in an acetabular bone cavity in a non-intrusive and precisely aligned manner.