A computer assisted surgery system for conducting orthopedic surgery on a knee joint includes a condyle digitizer having a posterior condyle abutment surface defining a first plane and a distal condyle abutment surface defining a second plane perpendicular to the first plane, and a trackable member which is locatable and trackable in three dimensional space by the computer assisted surgery system to define at least orientation of the condyle digitizer in real time. A computer determines a most remote reference point of the femur of the knee joint lying within at least one of the first and second planes when the condyle digitizer is abutted against condyles of the femur such that the posterior condyle abutment surface abuts a posterior side of the condyles and the distal condyle abutment surface abuts a distal side of the condyles.