An orthopaedic surgical device comprises a first sensor component and a second sensor component. Each sensor component includes a paddle set to contact a proximal tibia and a distal femur of a patient. The first sensor component and the second sensor component being movable with respect to one another to extend one paddle set beyond the other paddle set, and each paddle set includes cutouts for the clearance of the patellar tendon to avoid the need to avert the patella during use.