Alignment guide

An orthopaedic joint prosthesis assembly which comprises:

• a. a head part of an orthopaedic joint prosthesis component, which has a spherical bearing surface for articulation with a corresponding joint surface, and an assembly surface having a first bore formed in it for receiving a spigot on another part of the orthopaedic joint prosthesis, said bore having a first axis that extends perpendicular to the assembly surface, and in which there is a discontinuity at an interface between the bearing surface and the assembly surface, the said assembly surface being arranged on a plane which is parallel to, or contains, a plane which is defined by the opening to the bore in the head part when the head part is viewed from one side in cross-section, and
• b. an alignment guide comprising an axial portion and an arm extending from the axial portion, the arm including a distal portion and a proximal portion, the distal portion being configured to engage the assembly surface of the head part, the axial portion defining a second axis and being arranged to engage the bearing surface of the head part, directly or indirectly, when the head part is mounted within the guide, with the second axis coincident with the first axis, such when an impaction force is applied along the second axis the force is directed along the first axis.