An improved endoprosthetic device includes a modular rotational component affixed along the stem of a humeral prosthesis or a femoral prosthesis. The rotational component axis of rotation is coaxial with the stem, and its axis of rotation is located in close proximity to the intramedullary stem of the prosthesis or in close proximity to the distal articulation of the prosthesis. The rotational component includes a lobe ring adapted to limit the axis of rotation of the component. The lobe ring further includes ramp features that gradually limit the rotation of the rotational component shaft, thereby reducing the felt impulse when rotated to a stop, or no ramp feature to allow maximum rotation as allowed by the patient's soft tissue.
