The invention relates to an acetabulum (1), in particular for the articulation of the hip or the shoulder, which comprises: a hard cup (2) with a convex outer surface (20) to be inserted and attached in the acetabular cavity of the bone； a shell (3) made of an implantable material that can be inserted into said cup (2) and is intended for receiving the head of an articular prosthesis, the shell having an opening with a low-taper frusto-conical outer wall (32), flaring towards the outside； a ring (4) that can be removably mounted at the opening of the cup (2) and having a frusto-conical inner wall (41) having a shape complementary to that of said outer wall (32) so that it is possible to fit said shell (3) therein via a link of the Morse taper type. The acetabulum is characterised in that the ring (4) includes a portion with an outer wall (40) having a surface that has a shape complementary to that of the opening (6) of the cup (2), and in that the ring (4) can be removed from said cup (2) by a rotational action of one of the parts defining the acetabulum about a longitudinal axis parallel to said central axis (X-X') or inclined thereto.
