An acetabular component prosthesis adapted for affixation in a recess in a pelvis, comprising: a cup shell having a generally convex outer surface adapted to be in contact with the bone in use, a generally concave inner surface and a rim; at least one pair of substantially adjacent flanges extending from the outer surface of the cup at a point proximal to the rim of the cup and angled at angle .theta. downwardly thereto; one flange of the pair being at an equal but opposite angle .alpha. to a plane extending across the apex of each of the flanges to the other of the pair; and at least one aperture in each of the pair of flanges through which in use fixation means may be passed to fix the cup into the recess in the pelvis.