A robotic surgery system for preparing a humerus to receive a stemless shoulder implant based on a possible future location of a stemmed shoulder implant to be placed in the humerus during a subsequent possible revision surgery, the robotic surgery system comprising: a robotic manipulator; a cutting tool to be coupled to said robotic manipulator; a localizer configured to track movement of said cutting tool and the humerus; and a controller (26, 54) coupled to said robotic manipulator and said localizer, said controller (26, 54) configured to operate said robotic manipulator to control movement of said cutting tool relative to the humerus based on a virtual object that defines a volume of material to be removed from the humerus to receive the stemless shoulder implant, characterized in that said controller (26, 54) is further configured to: define a virtual intramedullary axis of the humerus in a coordinate system prior to resecting a humeral head of the humerus; determine positions of a plurality of landmarks on the humerus; plan a resection of the humeral head based on a location of the virtual intramedullary axis and the positions of the plurality of landmarks, wherein the planned resection of the humeral head corresponds to a possible future location of a stemmed shoulder implant defined in the coordinate system prior to resecting a humeral head of the humerus, wherein, when the controller (26, 54) plans the resection, it is further configured to define a virtual resection plane; and define said virtual object in the coordinate system based on the planned resection and, thus, based on the possible future location of the stemmed shoulder implant with respect to the coordinate system. a robotic manipulator; a cutting tool to be coupled to said robotic manipulator; a localizer configured to track movement of said cutting tool and the humerus; and a controller (26, 54) coupled to said robotic manipulator and said localizer, said controller (26, 54) configured to operate said robotic manipulator to control movement of said cutting tool relative to the humerus based on a virtual object that defines a volume of material to be removed from the humerus to receive the stemless shoulder implant, characterized in that said controller (26, 54) is further configured to: define a virtual intramedullary axis of the humerus in a coordinate system prior to resecting a humeral head of the humerus; determine positions of a plurality of landmarks on the humerus; plan a resection of the humeral head based on a location of the virtual intramedullary axis and the positions of the plurality of landmarks, wherein the planned resection of the humeral head corresponds to a possible future location of a stemmed shoulder implant defined in the coordinate system prior to resecting a humeral head of the humerus, wherein, when the controller (26, 54) plans the resection, it is further configured to define a virtual resection plane; and define said virtual object in the coordinate system based on the planned resection and, thus, based on the possible future location of the stemmed shoulder implant with respect to the coordinate system. define a virtual intramedullary axis of the humerus in a coordinate system prior to resecting a humeral head of the humerus; determine positions of a plurality of landmarks on the humerus; plan a resection of the humeral head based on a location of the virtual intramedullary axis and the positions of the plurality of landmarks, wherein the planned resection of the humeral head corresponds to a possible future location of a stemmed shoulder implant defined in the coordinate system prior to resecting a humeral head of the humerus, wherein, when the controller (26, 54) plans the resection, it is further configured to define a virtual resection plane; and define said virtual object in the coordinate system based on the planned resection and, thus, based on the possible future location of the stemmed shoulder implant with respect to the coordinate system.