A trial instrument assembly for use in a surgical procedure to replace an orthopaedic joint includes a trial implant having a stem portion for fitting within a prepared cavity in the patients bone. The stem portion defines a stem axis. A neck portion is connected to the stem portion to protrude from the cavity when the stem portion is within the cavity. The assembly includes a plane guide that extends from the neck portion in a plane that is selected from (i) a plane perpendicular to the stem axis, and (ii) a plane parallel to the stem axis, for use in determining the location of the trial implant relative to an anatomical feature in a direction measured along the stem axis or perpendicular to the stem axis, respectively.
