The present invention provides a prosthetic trialing system for use in preparing a patient for an implant, and particularly, a tibial trialing system, as well as methods of using the trialing system to install the implant prostheses. Tibial trials according to the present invention employ intermediate stems or adapters (32) which connect to the plate trial (10). They therefore permit connection of the intermediate stem trial (32) to the trial plate (10) without interference to the proximal surface (12) of the plate trial (10) and without interference to the range of motion of a mobile bearing (62) on the plate trial (10). Additionally, a range of intermediate stem trials (32) and stems (52) may be offered to fit a range of plates (10) for various geometries and modularity.