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