A knee prosthetic system includes a femoral component, a fixed tibial bearing component, a mobile tibial bearing component and an integrated or common tibial base component. The same tibial base component can be used with either the fixed tibial bearing component or the mobile tibial bearing component. The fixed bearing component and tibial base component have mating anti-rotation features. One embodiment of the mobile bearing component does not engage the anti-rotation feature of the tibial base component. Another embodiment engages the anti-rotation feature to allow for limited rotation.