Femoral ball heads for total hip replacement are made of various mater
ials, e.g. cobalt chrome alloy, coated metal, or various ceramics. Sta
ndard sockets are made of polyethylene, alumina ceramics, or CFRP. Due
to tribological reasons some of the combinations of head and socket t
hat seem possible are prohibited. The approved and prohibited combinat
ions are reviewed and reasons for not approving are discussed.