A trial implant component for use in a surgical procedure for replacement of a joint between a long bone and another bone, comprises a metaphyseal part which can be located so that it extends into a cavity at the resected face of the long bone in contact with the internal wall of the cavity in the metaphyseal region, and a disk which has an essentially flat shape and which can be fitted to the metaphyseal part to provide a gauge as to the appropriate size of a head part which is to be selected according to the location of the axis of the bone relative to the edge of the resected bone.
