The metal cotyloid cup (1), designed to receive an insert, has a T-shaped slot (5, 7) extending longitudinally from its equator (3) to cover an angle of some 70 degrees, and transversely over 20 - 95 degrees. <；??>；The metal cotyloid cup (1), designed to receive an insert, has a T-shaped slot (5, 7) extending longitudinally from its equator (3) to cover an angle of some 70 degrees, and transversely over 20 - 95 degrees. The transverse portion of the slot has a hole (8) of less than 4 mm diameter at each end. The two sections of the slot are less than 5 mm wide, with the longitudinal slot able to reduce by 0.5 mm under compression. The outer surface of the cup has non-metallic coating (9) less than 200 microns thick to promote bone growth, e.g. containing hydroxyapatite.
