A receptacle for receiving a mating member in an orthopedic joint, wherein the receptacle comprises: a first portion shaped so as to contact with the mating member, in normal use； a second portion shaped so as to not contact with the mating member, in normal use, wherein the first portion comprises a non-spherical surface. A mating member for being received by a receptacle, wherein the mating member comprises: a first portion shaped so as to contact with the receptacle, in normal use； a second portion shaped so as to not contact with the receptacle, in normal use, wherein the first portion comprises a non-spherical surface. Also disclosed are receptacles and heads of generally elliptical shape.
