Femoral prosthesis with an offset head

A femoral prosthesis comprising a stem part and a head part, in which the stem part comprises a body section for location in the femur of a patient and a neck section comprising a spigot, in which the head part comprises a bearing surface formed as part of a sphere and a reverse side, in which the bearing surface comprises a polar axis extending through a center of the sphere, in which a bore is provided in said reverse side adapted to receive said spigot, in which said bore comprise a bore axis, and in which said bore axis is oblique to said polar axis, in which an outer surface of the spigot or an inner surface of the bore is provided with a protrusion, in which the other of said outer surface or said inner surface is provided with a co-operating indent, in which the protrusion is disposed in the indent when the head part is fitted onto the spigot, and in which at least part of the protrusion is radially distorted from the bore axis such that rotation of the head part about the bore axis is prevented, in which the protrusion is symmetrical about the bore axis, in which the bore comprises a base surface at an inner end thereof, in which the spigot comprises a free end face, and in which said protrusion is formed on said base surface and said indent on said free end face, in which said protrusion comprises a central portion and one or more arm portions extending therefrom, and in which said indent comprises a co-operating shape, in which said protrusion comprises four arm portions arranged at 90 degree intervals, and in which said indent comprises a co-operating shape.