An instrument for use in a joint replacement procedure. The instrument comprises a trial head (162) which corresponds to the head of an orthopaedic joint component having an upper surface defined by a curved surface and a bore formed in a lower surface. The instrument further comprises a trial connector (164) for connecting the trial head (162) to a stem part (12) of the orthopaedic joint component which is intended for location in the intramedullary cavity of a bone. The trial connector (164) can be fitted into the bore in the trial head (162) at a variable angular orientation. The instrument further comprises a rotating indicator (174) pivo tally coupled about a polar axis of the trial head (162) which is defined by the curved upper surface, the rotating indicator (174) being coupled to the trial connector (164) such that the rotational position of the rotating indicator (174) about the polar axis is indicative of the rotational position of the trial connector (164) within the bore in the trial head (162). The bore in the lower surface of the trial head (162) is eccentric of the polar axis and the connection between the trial connector (164) and the stem part (12) of the orthopaedic joint component is eccentric of the centre of the trial connector (164). A predetermined point on the rotating indicator (174) is indicative of the direction of maximum eccentricity of the trial head (162) relative to the connection between the trial connector (164) and the stem (12) of the orthopaedic component. Also disclosed is an assembly which comprises the instrument and an orthopaedic joint component which comprises a head part (20), a stem part (12) and a connector sleeve part (30).
