There is provided an orthopaedic joint prosthesis assembly which comprises a head part (500) of an orthopaedic joint prosthesis component and an alignment guide (510). The head part has a spherical bearing surface (504) for articulation with a corresponding joint surface, and an assembly surface (508) having a bore (506) formed in it for receiving a spigot on another part of the orthopaedic joint prosthesis. The bore has a first axis that extends perpendicular to the assembly surface. There is a discontinuity at an interface between the bearing surface and the assembly surface. The assembly surface is 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. The alignment guide comprises an axial portion (511) defining a 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. The axial portion comprises a plain bore sleeve (518) and a pair of arms (512, 514) that extend from a distal portion of the sleeve such that a space is formed between each arm. Each arm comprises a proximal end (516), a distal end (520) and an inner surface that has a contact surface shaped to substantially correspond to the bearing surface of the head part of the orthopaedic joint prosthesis, such that when the head part is mounted within the guide a nesting fit is formed between the bearing surface of the head part and the contact surface of each arm. The distal end of each arm joins to form a U-shaped bracket (522) which carries a U-shaped assembly surface seating member configured to engage the assembly surface of the head part of the orthopaedic joint prosthesis when the head part is mounted within the guide.La présente invention concerne un ensemble prothèse d'articulation orthopédique comprenant une partie tête d'un composant de prothèse d'articulation orthopédique et u
