An orthopaedic surgical instrument system for use during a surgical procedure to implant an orthopaedic knee prosthesis includes a tibial base trial component (14) adapted to be positioned on a surgically-prepared proximal end of a patient's tibia and an insert component (16) shaped to be received in an opening (40) defined in the tibial base trial component. The insert component has a base plate (78) and a central post (94) extending upwardly from a superior surface (96) of the base plate. A superior surface (106) of the central post has a ramp surface (102) defined therein, with the ramp surface inclining superiorly in the anterior-to-posterior direction.
