An acetabular socket (1) for a hip endoprosthesis comprises a socket shell (7) and a socket insert (8). The socket shell (7) is configured for implantation in a pelvic bone (2) of a patient and has an inner surface (12) that defines an accommodating space (10) extending about an axis of rotation (11). The socket insert (8) is coupleable with the socket shell (7) and is configured to provide a bearing for a joint head (6) of a prosthesis stem (3). The socket insert (8) has an outer surface (14) configured to be seated in the accommodating space (10) of the socket shell (7). A moveable anti-lock means (17) is provided between the socket shell (7) and the socket insert (8). In a first position the anti-lock means (17) restrains the socket insert (8) from seating within die accommodating space (10) of the socket shell (7) but the anti-lock means (17) is moveable into a second position wherein the socket insert (7) is capable of seating within the socket shell (7) and of coupling therewith. The anti-lock means (17) preventing the socket insert (8) from prematurely locking into an undesirable position in the socket shell (7) prior to correct positioning and orientation by a surgeon during implantation.
