An orthopaedic surgical system includes a sensor module for determining the joint force of a patient's knee joint and an adaptor for coupling various tibial trialing components to the sensor module. The sensor module includes a tibial paddle to which the adaptor is configured to couple. The adaptor and tibial paddle include structures that control the orientation at which the adaptor is attachable to the tibial paddle. Some tibial trialing components may be positioned over the adaptor in a mobile orientation that facilities rotation of the tibial trialing component relative to the tibial paddle or a fixed orientation that restricts the rotation of the tibial trialing component.