An orthopaedic surgical instrument system includes a hinged tibial insert trial and a tibial base trial. A post adapter is sized to be positioned over a post of the tibial base trial and to be positioned in a central opening defined in the hinged tibial insert trial. The hinged tibial insert trial includes a housing configured to be received in a femoral component and a button mechanism to selectively secure the hinged tibial insert trial to the femoral component. The system may include a shim trial sized to be attached to an inferior surface of the hinged tibial insert trial.