Abstract: An orthopaedic surgical instrument assembly is disclosed. The orthopaedic surgical assembly includes a guide tower, an offset tool attached to the guide tower, and a stem trial. A guide tower includes a base surface adapted to be positioned on a proximal end of a patient's tibia and defining a first axis extending through the base surface. The offset tool is configured to rotate about the first axis. The offset tool includes a tool body that is positioned in the guide tower and is integrally formed with a shaft extending through an opening defined in the base surface of the guide tower. The stem trial is removably coupled to a lower end of the shaft.

Abstract: Methods of surgically preparing a patient's tibia are disclosed. Some methods include positioning a guide tower on a surgically-prepared proximal surface above an opening of a medullary canal of the patient's tibia, attaching a stem trial to a lower end of an offset tool that is sized to be received in the guide tower, and advancing the stem trial through the guide tower and the surgically-prepared proximal surface into the medullary canal. The method may include moving the guide tower to a desired offset orientation on the surgically-prepared proximal surface and advancing a reamer through the guide tower into the medullary canal. The method may also include positioning a tibial base trial on the surgically-prepared proximal surface based on the desired offset orientation.