An orthopaedic surgical instrument assembly comprises a cutting block having a base plate, and a pair of curved arms extending posteriorly from the base plate, each curved arm including a posterior surface and a cutting guide defined in the posterior surface. A stem trial is positioned proximal to the base plate of the cutting block. An offset tool has a proximal end coupled to the stem trial and a distal end coupled to the cutting block. The proximal end defines a first axis and the distal end defines a second axis extending parallel to the first axis. The proximal end is configured to pivot relative to the distal end.
